Catalysts

13 pages, 3855 KiB

Open AccessEditor’s ChoiceArticle

by Diana Nelli, Cesare Roncaglia, Samuel Ahearn, Marcel Di Vece, Riccardo Ferrando and Chloé Minnai

Catalysts 2021, 11(6), 718; https://doi.org/10.3390/catal11060718 - 9 Jun 2021

Cited by 14 | Viewed by 3216

Abstract

PtPd nanoparticles are among the most widely studied nanoscale systems, mainly because of their applications as catalysts in chemical reactions. In this work, a combined experimental-theoretical study is presented about the dependence of growth shape of PtPd alloy nanocrystals on their composition. The [...] Read more.

PtPd nanoparticles are among the most widely studied nanoscale systems, mainly because of their applications as catalysts in chemical reactions. In this work, a combined experimental-theoretical study is presented about the dependence of growth shape of PtPd alloy nanocrystals on their composition. The particles are grown in the gas phase and characterized by STEM-HRTEM. PtPd nanoalloys present a bimodal size distribution. The size of the larger population can be tuned between 3.8 ± 0.4 and 14.1 ± 2.0 nm by controlling the deposition parameters. A strong dependence of the particle shape on the composition is found: Pd-rich nanocrystals present more rounded shapes whereas Pt-rich ones exhibit sharp tips. Molecular dynamics simulations and excess energy calculations show that the growth structures are out of equilibrium. The growth simulations are able to follow the growth shape evolution and growth pathways at the atomic level, reproducing the structures in good agreement with the experimental results. Finally the optical absorption properties are calculated for PtPd nanoalloys of the same shapes and sizes grown in our experiments. Full article

(This article belongs to the Special Issue Heterogeneous Catalysts Optimization: From Material Design to Properties)

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30 pages, 33501 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Aftertreatment Technologies for Diesel Engines: An Overview of the Combined Systems

by Ferenc Martinovic, Lidia Castoldi and Fabio Alessandro Deorsola

Catalysts 2021, 11(6), 653; https://doi.org/10.3390/catal11060653 - 21 May 2021

Cited by 40 | Viewed by 11035

Abstract

The abatement of the pollutants deriving from diesel engines in the vehicle sector still represents an interesting scientific and technological challenge due to increasingly limiting regulations. Meeting the stringent limits of NO_x and soot emissions requires a catalytic system with great complexity, [...] Read more.

The abatement of the pollutants deriving from diesel engines in the vehicle sector still represents an interesting scientific and technological challenge due to increasingly limiting regulations. Meeting the stringent limits of NO_x and soot emissions requires a catalytic system with great complexity, size of units, and number of units, as well as increased fuel consumption. Thus, an after-treatment device for a diesel vehicle requires the use of an integrated catalyst technology for a reduction in the individual emissions of exhaust gas. The representative technologies devoted to the reduction of NO_x under lean-burn operation conditions are selective catalytic reduction (SCR) and the lean NO_x trap (LNT), while soot removal is mainly performed by filters (DPF). These devices are normally used in sequence, or a combination of them has been proposed to overcome the drawbacks of the individual devices. This review summarizes the current state of NO_x and soot abatement strategies. The main focus of this review is on combined technologies for NO_x removal (i.e., LNT–SCR) and for the simultaneous removal of NO_x and soot, like SCR-on-Filter (SCRoF), in series LNT/DPF and SCR/DPF, and LNT/DPF and SCR/DPF hybrid systems. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NOx by NH3)

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29 pages, 8877 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Lipase Immobilization in Mesoporous Silica Nanoparticles for Biofuel Production

by Aniello Costantini and Valeria Califano

Catalysts 2021, 11(5), 629; https://doi.org/10.3390/catal11050629 - 13 May 2021

Cited by 54 | Viewed by 7191

Abstract

Lipases are ubiquitous enzymes whose physiological role is the hydrolysis of triacylglycerol into fatty acids. They are the most studied and industrially interesting enzymes, thanks to their versatility to promote a plethora of reactions on a wide range of substrates. In fact, depending [...] Read more.

Lipases are ubiquitous enzymes whose physiological role is the hydrolysis of triacylglycerol into fatty acids. They are the most studied and industrially interesting enzymes, thanks to their versatility to promote a plethora of reactions on a wide range of substrates. In fact, depending on the reaction conditions, they can also catalyze synthesis reactions, such as esterification, acidolysis and transesterification. The latter is particularly important for biodiesel production. Biodiesel can be produced from animal fats or vegetable oils and is considered as a biodegradable, non-toxic and renewable energy source. The use of lipases as industrial catalysts is subordinated to their immobilization on insoluble supports, to allow multiple uses and use in continuous processes, but also to stabilize the enzyme, intrinsically prone to denaturation with consequent loss of activity. Among the materials that can be used for lipase immobilization, mesoporous silica nanoparticles represent a good choice due to the combination of thermal and mechanical stability with controlled textural characteristics. Moreover, the presence of abundant surface hydroxyl groups allows for easy chemical surface functionalization. This latter aspect has the main importance since lipases have a high affinity with hydrophobic supports. The objective of this work is to provide an overview of the recent progress of lipase immobilization in mesoporous silica nanoparticles with a focus on biodiesel production. Full article

(This article belongs to the Special Issue Enzyme Immobilization and Biocatalysis)

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15 pages, 1792 KiB

Open AccessEditor’s ChoiceReview

Waste Animal Bones as Catalysts for Biodiesel Production; A Mini Review

by Fayaz Hussain, Saad Alshahrani, Muhammad Mujtaba Abbas, Haris Mahmood Khan, Asif Jamil, Haseeb Yaqoob, Manzoore Elahi M. Soudagar, Muhammad Imran, Mushtaq Ahmad and Mamoona Munir

Catalysts 2021, 11(5), 630; https://doi.org/10.3390/catal11050630 - 13 May 2021

Cited by 55 | Viewed by 10765

Abstract

Slaughterhouse waste is considered to be an emerging issue because of its disposal cost. As an alternative, it would be a great prospect for the bioeconomy society to explore new usages of these leftover materials. As per food safety rules mentioned by EU [...] Read more.

Slaughterhouse waste is considered to be an emerging issue because of its disposal cost. As an alternative, it would be a great prospect for the bioeconomy society to explore new usages of these leftover materials. As per food safety rules mentioned by EU legislation, all bone waste generated by slaughterhouses ought to be disposed of by rendering. The huge quantity of worldwide bone waste generation (130 billion kilograms per annum) is an environmental burden if not properly managed. The waste animal bones can be efficiently employed as a heterogeneous catalyst to produce biodiesel. This mini review summarized the recent literature reported for biodiesel generation using waste animal bones derived heterogeneous catalyst. It discusses the sources of bone waste, catalyst preparation methods, particularly calcination and its effects, and important characteristics of bones derived catalyst. It suggests that catalysts extracted from waste animal bones have suitable catalytic activity in transesterification of different oil sources to generate a good quality biodiesel. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis in Green Chemistry)

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14 pages, 1424 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Photocatalytic Degradation of Sulfolane Using a LED-Based Photocatalytic Treatment System

by Sripriya Dharwadkar, Linlong Yu and Gopal Achari

Catalysts 2021, 11(5), 624; https://doi.org/10.3390/catal11050624 - 12 May 2021

Cited by 15 | Viewed by 4296

Abstract

Sulfolane is an emerging industrial pollutant detected in the environments near many oil and gas plants in North America. So far, numerous advanced oxidation processes have been investigated to treat sulfolane in aqueous media. However, there is only a few papers that discuss [...] Read more.

Sulfolane is an emerging industrial pollutant detected in the environments near many oil and gas plants in North America. So far, numerous advanced oxidation processes have been investigated to treat sulfolane in aqueous media. However, there is only a few papers that discuss the degradation of sulfolane using photocatalysis. In this study, photocatalytic degradation of sulfolane using titanium dioxide (TiO₂) and reduced graphene oxide TiO₂ composite (RGO-TiO₂) in a light-emitting diode (LED) photoreactor was investigated. The impact of different waters (ultrapure water, tap water, and groundwater) and type of irradiation (UVA-LED and mercury lamp) on photocatalytic degradation of sulfolane were also studied. In addition, a reusability test was conducted for the photocatalyst to examine the degradation of sulfolane in three consecutive cycles with new batches of sulfolane-contaminated water. The results show that LED-based photocatalysis was effective in degrading sulfolane in waters even after three photocatalytic cycles. UVA-LEDs displayed more efficient use of photon energy when compared with the mercury lamps as they have a narrow emission spectrum coinciding with the absorption of TiO₂. The combination of UVA-LED and TiO₂ yielded better performance than UVA-LED and RGO-TiO₂ for the degradation of sulfolane. Much lower sulfolane degradation rates were observed in tap water and groundwater than ultrapure water. Full article

(This article belongs to the Special Issue Photo(electro)catalytic Reactions Combined with Ozone Oxidation Technique)

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14 pages, 4201 KiB

Open AccessEditor’s ChoiceArticle

Atmospheric Pressure Tornado Plasma Jet of Polydopamine Coating on Graphite Felt for Improving Electrochemical Performance in Vanadium Redox Flow Batteries

by Song-Yu Chen, Yu-Lin Kuo, Yao-Ming Wang, Wei-Mau Hsu, Tzu-Hsuan Chien, Chiu-Feng Lin, Cheng-Hsien Kuo, Akitoshi Okino and Tai-Chin Chiang

Catalysts 2021, 11(5), 627; https://doi.org/10.3390/catal11050627 - 12 May 2021

Cited by 6 | Viewed by 4072

Abstract

The intrinsic hydrophobicity of graphite felt (GF) is typically altered for the purpose of the surface wettability and providing active sites for the enhancement of electrochemical performance. In this work, commercial GF is used as the electrodes. The GF electrode with a coated-polydopamine [...] Read more.

The intrinsic hydrophobicity of graphite felt (GF) is typically altered for the purpose of the surface wettability and providing active sites for the enhancement of electrochemical performance. In this work, commercial GF is used as the electrodes. The GF electrode with a coated-polydopamine catalyst is achieved to enhance the electrocatalytic activity of GF for the redox reaction of vanadium ions in vanadium redox flow battery (VRFB). Materials characteristics proved that a facile coating via atmospheric pressure plasma jet (APPJ) to alter the surface superhydrophilicity and to deposit polydopamine on GF for providing the more active sites is feasibly achieved. Due to the synergistic effects of the presence of more active sites on the superhydrophilic surface of modified electrodes, the electrochemical performance toward VO²⁺/VO₂⁺ reaction was evidently improved. We believed that using the APPJ technique as a coating method for electrocatalyst preparation offers the oxygen-containing functional groups on the substrate surface on giving a hydrogen bonding with the grafted functional polymeric materials. Full article

(This article belongs to the Special Issue Catalysts and Electrode Functionalization for Redox Flow Battery)

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19 pages, 5187 KiB

Open AccessEditor’s ChoiceArticle

Particle Number Emissions of a Euro 6d-Temp Gasoline Vehicle under Extreme Temperatures and Driving Conditions

by Barouch Giechaskiel, Victor Valverde, Anastasios Kontses, Anastasios Melas, Giorgio Martini, Andreas Balazs, Jon Andersson, Zisis Samaras and Panagiota Dilara

Catalysts 2021, 11(5), 607; https://doi.org/10.3390/catal11050607 - 10 May 2021

Cited by 22 | Viewed by 4506

Abstract

With the introduction of gasoline particulate filters (GPFs), the particle number (PN) emissions of gasoline direct-injection (GDI) vehicles are below the European regulatory limit of 6 × 10¹¹ p/km under certification conditions. Nevertheless, concerns have been raised regarding emission levels at the [...] Read more.

With the introduction of gasoline particulate filters (GPFs), the particle number (PN) emissions of gasoline direct-injection (GDI) vehicles are below the European regulatory limit of 6 × 10¹¹ p/km under certification conditions. Nevertheless, concerns have been raised regarding emission levels at the boundaries of ambient and driving conditions of the real-driving emissions (RDE) regulation. A Euro 6d-Temp GDI vehicle with a GPF was tested on the road and in the laboratory with cycles simulating congested urban traffic, dynamic driving, and towing a trailer uphill at 85% of maximum payload. The ambient temperatures covered a range from −30 to 50 °C. The solid PN emissions were 10 times lower than the PN limit under most conditions and temperatures. Only dynamic driving that regenerated the filter passively, and for the next cycle resulted in relatively high emissions although they were still below the limit. The results of this study confirmed the effectiveness of GPFs in controlling PN emissions under a wide range of conditions. Full article

(This article belongs to the Special Issue Present Challenges in Catalytic Emission Control for Internal Combustion Engines)

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18 pages, 3470 KiB

Open AccessFeature PaperEditor’s ChoiceReview

A Brief Review of Catalytic Cathode Materials for Na-CO₂ Batteries

by Dong Sui, Meijia Chang, Haiyu Wang, Hang Qian, Yanliang Yang, Shan Li, Yongsheng Zhang and Yingze Song

Catalysts 2021, 11(5), 603; https://doi.org/10.3390/catal11050603 - 7 May 2021

Cited by 43 | Viewed by 5897

Abstract

As an emerging energy storage technology, Na-CO₂ batteries with high energy density are drawing tremendous attention because of their advantages of combining cost-effective energy conversion and storage with CO₂ clean recycle and utilization. Nevertheless, their commercial applications are impeded by unsatisfactory [...] Read more.

As an emerging energy storage technology, Na-CO₂ batteries with high energy density are drawing tremendous attention because of their advantages of combining cost-effective energy conversion and storage with CO₂ clean recycle and utilization. Nevertheless, their commercial applications are impeded by unsatisfactory electrochemical performance including large overpotentials, poor rate capability, fast capacity deterioration, and inferior durability, which mainly results from the inefficient electrocatalysts of cathode materials. Therefore, novel structured cathode materials with efficient catalytic activity are highly desired. In this review, the latest advances of catalytic cathode materials for Na-CO₂ batteries are summarized, with a special emphasis on the electrocatalysts for CO₂ reduction and evolution, the formation and decomposition of discharge product, as well as their catalytic mechanism. Finally, an outlook is also proposed for the future development of Na-CO₂ batteries. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts: Achievements in Electrocatalysis for Sustainable Energy Technologies)

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16 pages, 4367 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

CpCo(III) Precatalysts for [2+2+2] Cycloadditions

by Fabian Fischer, Michael Eder and Marko Hapke

Catalysts 2021, 11(5), 596; https://doi.org/10.3390/catal11050596 - 4 May 2021

Cited by 2 | Viewed by 3966

Abstract

Catalysts applied in cobalt-catalyzed cyclotrimerizations reactions in general rely on the use of Co(I) precatalysts or the in situ generation of Co(I) catalysts from Co(II) sources by reduction in the presence of steering ligands, often by addition of less noble metals. In this [...] Read more.

Catalysts applied in cobalt-catalyzed cyclotrimerizations reactions in general rely on the use of Co(I) precatalysts or the in situ generation of Co(I) catalysts from Co(II) sources by reduction in the presence of steering ligands, often by addition of less noble metals. In this paper, we report the synthesis and properties of novel stable CpCo(III) complexes as precatalysts and their exemplary evaluation for application in catalytic [2+2+2] cycloadditions. The role of phosphite neutral ligands, as well as iodide and cyanide as anionic ligands, on the reactivity of the complexes was evaluated. A modified one-pot approach to the synthesis of Cp ring-functionalized Cp’Co(III) complexes was developed. The investigations demonstrated that CpCo(III) complexes can be directly applied as catalysts in catalytic cyclotrimerizations of triynes without reducing agents as additives. Full article

(This article belongs to the Special Issue Cobalt Catalysis: Recent Progress and Developments)

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23 pages, 7555 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Toward Scaling-Up Photocatalytic Process for Multiphase Environmental Applications

by Mohamed Gar Alalm, Ridha Djellabi, Daniela Meroni, Carlo Pirola, Claudia Letizia Bianchi and Daria Camilla Boffito

Catalysts 2021, 11(5), 562; https://doi.org/10.3390/catal11050562 - 28 Apr 2021

Cited by 78 | Viewed by 7289

Abstract

Recently, we have witnessed a booming development of composites and multi-dopant metal oxides to be employed as novel photocatalysts. Yet the practical application of photocatalysis for environmental purposes is still elusive. Concerns about the unknown fate and toxicity of nanoparticles, unsatisfactory performance in [...] Read more.

Recently, we have witnessed a booming development of composites and multi-dopant metal oxides to be employed as novel photocatalysts. Yet the practical application of photocatalysis for environmental purposes is still elusive. Concerns about the unknown fate and toxicity of nanoparticles, unsatisfactory performance in real conditions, mass transfer limitations and durability issues have so far discouraged investments in full-scale applications of photocatalysis. Herein, we provide a critical overview of the main challenges that are limiting large-scale application of photocatalysis in air and water/wastewater purification. We then discuss the main approaches reported in the literature to tackle these shortcomings, such as the design of photocatalytic reactors that retain the photocatalyst, the study of degradation of micropollutants in different water matrices, and the development of gas-phase reactors with optimized contact time and irradiation. Furthermore, we provide a critical analysis of research–practice gaps such as treatment of real water and air samples, degradation of pollutants with actual environmental concentrations, photocatalyst deactivation, and cost and environmental life-cycle assessment. Full article

(This article belongs to the Special Issue Air and Water Purification Processes through Photocatalysis: Scale Up Perspectives)

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19 pages, 5354 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Effect of Co Incorporation on the CO Oxidation Activity of LaFe_1−xCo_xO₃ Perovskites

by Maik Dreyer, Moritz Krebs, Sharif Najafishirtari, Anna Rabe, Klaus Friedel Ortega and Malte Behrens

Catalysts 2021, 11(5), 550; https://doi.org/10.3390/catal11050550 - 27 Apr 2021

Cited by 19 | Viewed by 4016

Abstract

Perovskite oxides are versatile materials due to their wide variety of compositions offering promising catalytic properties, especially in oxidation reactions. In the presented study, LaFe_1−xCo_xO₃ perovskites were synthesized by hydroxycarbonate precursor co-precipitation and thermal decomposition thereof. Precursor and [...] Read more.

Perovskite oxides are versatile materials due to their wide variety of compositions offering promising catalytic properties, especially in oxidation reactions. In the presented study, LaFe_1−xCo_xO₃ perovskites were synthesized by hydroxycarbonate precursor co-precipitation and thermal decomposition thereof. Precursor and calcined materials were studied by scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TG), and X-ray powder diffraction (XRD). The calcined catalysts were in addition studied by transmission electron microscopy (TEM) and N₂ physisorption. The obtained perovskites were applied as catalysts in transient CO oxidation, and in operando studies of CO oxidation in diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). A pronounced increase in activity was already observed by incorporating 5% cobalt into the structure, which continued, though not linearly, at higher loadings. This could be most likely due to the enhanced redox properties as inferred by H₂-temperature programmed reduction (H₂-TPR). Catalysts with higher Co contents showing higher activities suffered less from surface deactivation related to carbonate poisoning. Despite the similarity in the crystalline structures upon Co incorporation, we observed a different promotion or suppression of various carbonate-related bands, which could indicate different surface properties of the catalysts, subsequently resulting in the observed non-linear CO oxidation activity trend at higher Co contents. Full article

(This article belongs to the Special Issue Surface Design of Metal Oxide Catalysts)

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31 pages, 3760 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Main Hydrogen Production Processes: An Overview

by Marco Martino, Concetta Ruocco, Eugenio Meloni, Pluton Pullumbi and Vincenzo Palma

Catalysts 2021, 11(5), 547; https://doi.org/10.3390/catal11050547 - 25 Apr 2021

Cited by 131 | Viewed by 16900

Abstract

Due to its characteristics, hydrogen is considered the energy carrier of the future. Its use as a fuel generates reduced pollution, as if burned it almost exclusively produces water vapor. Hydrogen can be produced from numerous sources, both of fossil and renewable origin, [...] Read more.

Due to its characteristics, hydrogen is considered the energy carrier of the future. Its use as a fuel generates reduced pollution, as if burned it almost exclusively produces water vapor. Hydrogen can be produced from numerous sources, both of fossil and renewable origin, and with as many production processes, which can use renewable or non-renewable energy sources. To achieve carbon neutrality, the sources must necessarily be renewable, and the production processes themselves must use renewable energy sources. In this review article the main characteristics of the most used hydrogen production methods are summarized, mainly focusing on renewable feedstocks, furthermore a series of relevant articles published in the last year, are reviewed. The production methods are grouped according to the type of energy they use; and at the end of each section the strengths and limitations of the processes are highlighted. The conclusions compare the main characteristics of the production processes studied and contextualize their possible use. Full article

(This article belongs to the Special Issue Catalysts for Sustainable Hydrogen Production: Preparation, Applications and Process Integration)

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22 pages, 4501 KiB

Open AccessEditor’s ChoiceReview

Research Progress on Catalytic Water Splitting Based on Polyoxometalate/Semiconductor Composites

by Yue Wu and Lihua Bi

Catalysts 2021, 11(4), 524; https://doi.org/10.3390/catal11040524 - 20 Apr 2021

Cited by 25 | Viewed by 6226

Abstract

In recent years, due to the impact of global warming, environmental pollution, and the energy crisis, international attention and demand for clean energy are increasing. Hydrogen energy is recognized as one of the clean energy sources. Water is considered as the largest potential [...] Read more.

In recent years, due to the impact of global warming, environmental pollution, and the energy crisis, international attention and demand for clean energy are increasing. Hydrogen energy is recognized as one of the clean energy sources. Water is considered as the largest potential supplier of hydrogen energy. However, artificial catalytic water splitting for hydrogen and oxygen evolution has not been widely used due to its high energy consumption and high cost during catalytic cracking. Therefore, the exploitation of photocatalysts, electrocatalysts, and photo-electrocatalysts for rapid, cost effective, and reliable water splitting is essentially needed. Polyoxometalates (POMs) are regarded as the potential candidates for water splitting catalysis. In addition to their excellent catalytic properties and reversibly redox activities, POMs can also modify semiconductors to overcome their shortcomings, and improve photoelectric conversion efficiency and photocatalytic activity, which has attracted more and more attention in the field of photoelectric water splitting catalysis. In this review, we summarize the latest applications of POMs and semiconductor composites in the field of photo-electrocatalysis (PEC) for hydrogen and oxygen evolution by catalytic water splitting in recent years and take the latest applications of POMs and semiconductor composites in photocatalysis for water splitting. In the conclusion section, the challenges and strategies of photocatalytic and PEC water-splitting by POMs and semiconductor composites are discussed. Full article

(This article belongs to the Section Photocatalysis)

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15 pages, 1589 KiB

Open AccessEditor’s ChoiceArticle

Microbial Removal of Pb(II) Using an Upflow Anaerobic Sludge Blanket (UASB) Reactor

by Jeremiah Chimhundi, Carla Hörstmann, Evans M. N. Chirwa and Hendrik G. Brink

Catalysts 2021, 11(4), 512; https://doi.org/10.3390/catal11040512 - 19 Apr 2021

Cited by 12 | Viewed by 3135

Abstract

The main objective of this study was to achieve the continuous biorecovery and bioreduction of Pb(II) using an industrially obtained consortia as a biocatalyst. An upflow anaerobic sludge blanket reactor was used in the treatment process. The bioremediation technique that was applied made [...] Read more.

The main objective of this study was to achieve the continuous biorecovery and bioreduction of Pb(II) using an industrially obtained consortia as a biocatalyst. An upflow anaerobic sludge blanket reactor was used in the treatment process. The bioremediation technique that was applied made use of a yeast extract as the microbial substrate and Pb(NO₃)₂ as the source of Pb(II). The UASB reactor exhibited removal efficiencies of between 90 and 100% for the inlet Pb concentrations from 80 to 2000 ppm and a maximum removal rate of 1948.4 mg/(L·d) was measured. XRD and XPS analyses of the precipitate revealed the presence of Pb⁰, PbO, PbS and PbSO₄. Supporting experimental work carried out included growth measurements, pH, oxidation–reduction potentials and nitrate levels. Full article

(This article belongs to the Special Issue Biocatalysis for Green Chemistry)

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23 pages, 14979 KiB

Open AccessEditor’s ChoiceArticle

A Thermally Conductive Pt/AAO Catalyst for Hydrogen Passive Autocatalytic Recombination

by Alina E. Kozhukhova, Stephanus P. du Preez, Aleksander A. Malakhov and Dmitri G. Bessarabov

Catalysts 2021, 11(4), 491; https://doi.org/10.3390/catal11040491 - 12 Apr 2021

Cited by 34 | Viewed by 4362

Abstract

In this study, a Pt/anodized aluminum oxide (AAO) catalyst was prepared by the anodization of an Al alloy (Al6082, 97.5% Al), followed by the incorporation of Pt via an incipient wet impregnation method. Then, the Pt/AAO catalyst was evaluated for autocatalytic hydrogen recombination. [...] Read more.

In this study, a Pt/anodized aluminum oxide (AAO) catalyst was prepared by the anodization of an Al alloy (Al6082, 97.5% Al), followed by the incorporation of Pt via an incipient wet impregnation method. Then, the Pt/AAO catalyst was evaluated for autocatalytic hydrogen recombination. The Pt/AAO catalyst’s morphological characteristics were determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The average Pt particle size was determined to be 3.0 ± 0.6 nm. This Pt/AAO catalyst was tested for the combustion of lean hydrogen (0.5–4 vol% H₂ in the air) in a recombiner section testing station. The thermal distribution throughout the catalytic surface was investigated at 3 vol% hydrogen (H₂) using an infrared camera. The Al/AAO system had a high thermal conductivity, which prevents the formation of hotspots (areas where localized surface temperature is higher than an average temperature across the entire catalyst surface). In turn, the Pt stability was enhanced during catalytic hydrogen combustion (CHC). A temperature gradient over 70 mm of the Pt/AAO catalyst was 23 °C and 42 °C for catalysts with uniform and nonuniform (worst-case scenario) Pt distributions. The commercial computational fluid dynamics (CFD) code STAR-CCM+ was used to compare the experimentally observed and numerically simulated thermal distribution of the Pt/AAO catalyst. The effect of the initial H₂ volume fraction on the combustion temperature and conversion of H₂ was investigated. The activation energy for CHC on the Pt/AAO catalyst was 19.2 kJ/mol. Prolonged CHC was performed to assess the durability (reactive metal stability and catalytic activity) of the Pt/AAO catalyst. A stable combustion temperature of 162.8 ± 8.0 °C was maintained over 530 h of CHC. To confirm that Pt aggregation was avoided, the Pt particle size and distribution were determined by TEM before and after prolonged CHC. Full article

(This article belongs to the Section Catalytic Materials)

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17 pages, 3576 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Enantioselective Catalytic C-H Amidations: An Highlight

by Eleonora Tosi, Renata Marcia de Figueiredo and Jean-Marc Campagne

Catalysts 2021, 11(4), 471; https://doi.org/10.3390/catal11040471 - 6 Apr 2021

Cited by 14 | Viewed by 4359

Abstract

The crucial role played by compounds bearing amide functions, not only in biological processes but also in several fields of chemistry, life polymers and material sciences, has brought about many significant discoveries and innovative approaches for their chemical synthesis. Indeed, a plethora of [...] Read more.

The crucial role played by compounds bearing amide functions, not only in biological processes but also in several fields of chemistry, life polymers and material sciences, has brought about many significant discoveries and innovative approaches for their chemical synthesis. Indeed, a plethora of strategies has been developed to reach such moieties. Amides within chiral molecules are often associated with biological activity especially in life sciences and medicinal chemistry. In most of these cases, their synthesis requires extensive rethinking methodologies. In the very last years (2019–2020), enantioselective C-H functionalization has appeared as a straightforward alternative to reach chiral amides. Therein, an overview on these transformations within this timeframe is going to be given. Full article

(This article belongs to the Special Issue Catalytic Approaches for Amide Synthesis)

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21 pages, 3341 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Developments in Dielectric Barrier Discharge Plasma-Assisted Catalytic Dry Reforming of Methane over Ni-Based Catalysts

by Xingyuan Gao, Ziting Lin, Tingting Li, Liuting Huang, Jinmiao Zhang, Saeed Askari, Nikita Dewangan, Ashok Jangam and Sibudjing Kawi

Catalysts 2021, 11(4), 455; https://doi.org/10.3390/catal11040455 - 1 Apr 2021

Cited by 69 | Viewed by 8631

Abstract

The greenhouse effect is leading to global warming and destruction of the ecological environment. The conversion of carbon dioxide and methane greenhouse gases into valuable substances has attracted scientists’ attentions. Dry reforming of methane (DRM) alleviates environmental problems and converts CO₂ and [...] Read more.

The greenhouse effect is leading to global warming and destruction of the ecological environment. The conversion of carbon dioxide and methane greenhouse gases into valuable substances has attracted scientists’ attentions. Dry reforming of methane (DRM) alleviates environmental problems and converts CO₂ and CH₄ into valuable chemical substances; however, due to the high energy input to break the strong chemical bonds in CO₂ and CH₄, non-thermal plasma (NTP) catalyzed DRM has been promising in activating CO₂ at ambient conditions, thus greatly lowering the energy input; moreover, the synergistic effect of the catalyst and plasma improves the reaction efficiency. In this review, the recent developments of catalytic DRM in a dielectric barrier discharge (DBD) plasma reactor on Ni-based catalysts are summarized, including the concept, characteristics, generation, and types of NTP used for catalytic DRM and corresponding mechanisms, the synergy and performance of Ni-based catalysts with DBD plasma, the design of DBD reactor and process parameter optimization, and finally current challenges and future prospects are provided. Full article

(This article belongs to the Special Issue Plasma-Catalysis for Environmental and Energy-Related Applications)

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13 pages, 2297 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Multi-Scale Biosurfactant Production by Bacillus subtilis Using Tuna Fish Waste as Substrate

by Jiheng Hu, Jie Luo, Zhiwen Zhu, Bing Chen, Xudong Ye, Peng Zhu and Baiyu Zhang

Catalysts 2021, 11(4), 456; https://doi.org/10.3390/catal11040456 - 1 Apr 2021

Cited by 27 | Viewed by 5165

Abstract

As one of the most effective biosurfactants reported to date, lipopeptides exhibit attractive surface and biological activities and have the great potential to serve as biocatalysts. Low yield, high cost of production, and purification hinder the large-scale applications of lipopeptides. Utilization of waste [...] Read more.

As one of the most effective biosurfactants reported to date, lipopeptides exhibit attractive surface and biological activities and have the great potential to serve as biocatalysts. Low yield, high cost of production, and purification hinder the large-scale applications of lipopeptides. Utilization of waste materials as low-cost substrates for the growth of biosurfactant producers has emerged as a feasible solution for economical biosurfactant production. In this study, fish peptone was generated through enzyme hydrolyzation of smashed tuna (Katsuwonus pelamis). Biosurfactant (mainly surfactin) production by Bacillus subtilis ATCC 21332 was further evaluated and optimized using the generated fish peptone as a comprehensive substrate. The optimized production conduction was continuously assessed in a 7 L batch-scale and 100 L pilot-scale fermenter, exploring the possibility for a large-scale surfactin production. The results showed that Bacillus subtilis ATCC 21332 could effectively use the fish waste peptones for surfactin production. The highest surfactin productivity achieved in the pilot-scale experiments was 274 mg/L. The experimental results shed light on the further production of surfactins at scales using fish wastes as an economical substrate. Full article

(This article belongs to the Special Issue Biocatalysts and Their Environmental Applications)

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25 pages, 2924 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Facet-Dependent Reactivity of Ceria Nanoparticles Exemplified by CeO₂-Based Transition Metal Catalysts: A Critical Review

by Michalis Konsolakis and Maria Lykaki

Catalysts 2021, 11(4), 452; https://doi.org/10.3390/catal11040452 - 31 Mar 2021

Cited by 47 | Viewed by 6268

Abstract

The rational design and fabrication of highly-active and cost-efficient catalytic materials constitutes the main research pillar in catalysis field. In this context, the fine-tuning of size and shape at the nanometer scale can exert an intense impact not only on the inherent reactivity [...] Read more.

The rational design and fabrication of highly-active and cost-efficient catalytic materials constitutes the main research pillar in catalysis field. In this context, the fine-tuning of size and shape at the nanometer scale can exert an intense impact not only on the inherent reactivity of catalyst’s counterparts but also on their interfacial interactions; it can also opening up new horizons for the development of highly active and robust materials. The present critical review, focusing mainly on our recent advances on the topic, aims to highlight the pivotal role of shape engineering in catalysis, exemplified by noble metal-free, CeO₂-based transition metal catalysts (TMs/CeO₂). The underlying mechanism of facet-dependent reactivity is initially discussed. The main implications of ceria nanoparticles’ shape engineering (rods, cubes, and polyhedra) in catalysis are next discussed, on the ground of some of the most pertinent heterogeneous reactions, such as CO₂ hydrogenation, CO oxidation, and N₂O decomposition. It is clearly revealed that shape functionalization can remarkably affect the intrinsic features and in turn the reactivity of ceria nanoparticles. More importantly, by combining ceria nanoparticles (CeO₂ NPs) of specific architecture with various transition metals (e.g., Cu, Fe, Co, and Ni) remarkably active multifunctional composites can be obtained due mainly to the synergistic metalceria interactions. From the practical point of view, novel catalyst formulations with similar or even superior reactivity to that of noble metals can be obtained by co-adjusting the shape and composition of mixed oxides, such as Cu/ceria nanorods for CO oxidation and Ni/ceria nanorods for CO₂ hydrogenation. The conclusions derived could provide the design principles of earth-abundant metal oxide catalysts for various real-life environmental and energy applications. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Gerhard Ertl on the Occasion of His 85th Birthday)

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26 pages, 5868 KiB

Open AccessEditor’s ChoiceReview

Review on the Visible Light Photocatalysis for the Decomposition of Ciprofloxacin, Norfloxacin, Tetracyclines, and Sulfonamides Antibiotics in Wastewater

by Samar Shurbaji, Pham Thi Huong and Talal Mohammed Altahtamouni

Catalysts 2021, 11(4), 437; https://doi.org/10.3390/catal11040437 - 29 Mar 2021

Cited by 103 | Viewed by 8770

Abstract

Antibiotics are chemical compounds that are used to kill or prevent bacterial growth. They are used in different fields, such as the medical field, agriculture, and veterinary. Antibiotics end up in wastewater, which causes the threat of developing antibacterial resistance; therefore, antibiotics must [...] Read more.

Antibiotics are chemical compounds that are used to kill or prevent bacterial growth. They are used in different fields, such as the medical field, agriculture, and veterinary. Antibiotics end up in wastewater, which causes the threat of developing antibacterial resistance; therefore, antibiotics must be eliminated from wastewater. Different conventional elimination methods are limited due to their high cost and effort, or incomplete elimination. Semiconductor-assisted photocatalysis arises as an effective elimination method for different organic wastes including antibiotics. A variety of semiconducting materials were tested to eliminate antibiotics from wastewater; nevertheless, research is still ongoing due to some limitations. This review summarizes the recent studies regarding semiconducting material modifications for antibiotic degradation using visible light irradiation. Full article

(This article belongs to the Special Issue Photocatalytic Oxidation/Ozonation Processes)

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53 pages, 6120 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Advanced Two-Dimensional Heterojunction Photocatalysts of Stoichiometric and Non-Stoichiometric Bismuth Oxyhalides with Graphitic Carbon Nitride for Sustainable Energy and Environmental Applications

by Kishore Sridharan, Sulakshana Shenoy, S. Girish Kumar, Chiaki Terashima, Akira Fujishima and Sudhagar Pitchaimuthu

Catalysts 2021, 11(4), 426; https://doi.org/10.3390/catal11040426 - 26 Mar 2021

Cited by 72 | Viewed by 8059

Abstract

Semiconductor-based photocatalysis has been identified as an encouraging approach for solving the two main challenging problems, viz., remedying our polluted environment and the generation of sustainable chemical energy. Stoichiometric and non-stoichiometric bismuth oxyhalides (BiOX and Bi_xO_yX_z where X [...] Read more.

Semiconductor-based photocatalysis has been identified as an encouraging approach for solving the two main challenging problems, viz., remedying our polluted environment and the generation of sustainable chemical energy. Stoichiometric and non-stoichiometric bismuth oxyhalides (BiOX and Bi_xO_yX_z where X = Cl, Br, and I) are a relatively new class of semiconductors that have attracted considerable interest for photocatalysis applications due to attributes, viz., high stability, suitable band structure, modifiable energy bandgap and two-dimensional layered structure capable of generating an internal electric field. Recently, the construction of heterojunction photocatalysts, especially 2D/2D systems, has convincingly drawn momentous attention practicably owing to the productive influence of having two dissimilar layered semiconductors in face-to-face contact with each other. This review has systematically summarized the recent progress on the 2D/2D heterojunction constructed between BiOX/Bi_xO_yX_z with graphitic carbon nitride (g-C₃N₄). The band structure of individual components, various fabrication methods, different strategies developed for improving the photocatalytic performance and their applications in the degradation of various organic contaminants, hydrogen (H₂) evolution, carbon dioxide (CO₂) reduction, nitrogen (N₂) fixation and the organic synthesis of clean chemicals are summarized. The perspectives and plausible opportunities for developing high performance BiOX/Bi_xO_yX_z-g-C₃N₄ heterojunction photocatalysts are also discussed. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)

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34 pages, 6186 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Direct Synthesis of Dimethyl Ether from CO₂: Recent Advances in Bifunctional/Hybrid Catalytic Systems

by Noelia Mota, Elena Millán Ordoñez, Bárbara Pawelec, José Luis G. Fierro and Rufino M. Navarro

Catalysts 2021, 11(4), 411; https://doi.org/10.3390/catal11040411 - 24 Mar 2021

Cited by 80 | Viewed by 14227

Abstract

Dimethyl ether (DME) is a versatile raw material and an interesting alternative fuel that can be produced by the catalytic direct hydrogenation of CO₂. Recently, this process has attracted the attention of the industry due to the environmental benefits of CO [...] Read more.

Dimethyl ether (DME) is a versatile raw material and an interesting alternative fuel that can be produced by the catalytic direct hydrogenation of CO₂. Recently, this process has attracted the attention of the industry due to the environmental benefits of CO₂ elimination from the atmosphere and its lower operating costs with respect to the classical, two-step synthesis of DME from syngas (CO + H₂). However, due to kinetics and thermodynamic limits, the direct use of CO₂ as raw material for DME production requires the development of more effective catalysts. In this context, the objective of this review is to present the latest progress achieved in the synthesis of bifunctional/hybrid catalytic systems for the CO₂-to-DME process. For catalyst design, this process is challenging because it should combine metal and acid functionalities in the same catalyst, in a correct ratio and with controlled interaction. The metal catalyst is needed for the activation and transformation of the stable CO₂ molecules into methanol, whereas the acid catalyst is needed to dehydrate the methanol into DME. Recent developments in the catalyst design have been discussed and analyzed in this review, presenting the different strategies employed for the preparation of novel bifunctional catalysts (physical/mechanical mixing) and hybrid catalysts (co-precipitation, impregnation, etc.) with improved efficiency toward DME formation. Finally, an outline of future prospects for the research and development of efficient bi-functional/hybrid catalytic systems will be presented. Full article

(This article belongs to the Special Issue Catalysts for Production and Conversion of Syngas)

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36 pages, 2112 KiB

Open AccessEditor’s ChoiceReview

An Overview of Lean Exhaust deNOx Aftertreatment Technologies and NOx Emission Regulations in the European Union

by Tommaso Selleri, Anastasios D. Melas, Ameya Joshi, Dario Manara, Adolfo Perujo and Ricardo Suarez-Bertoa

Catalysts 2021, 11(3), 404; https://doi.org/10.3390/catal11030404 - 23 Mar 2021

Cited by 88 | Viewed by 12597

Abstract

This paper reviews the recent advances in the management of nitrogen oxide (NOx) emissions from the internal combustion engine of light-duty and heavy-duty vehicles, addressing both technical and legal aspects. Particular focus is devoted to the often-virtuous interaction between new legislation imposing more [...] Read more.

This paper reviews the recent advances in the management of nitrogen oxide (NOx) emissions from the internal combustion engine of light-duty and heavy-duty vehicles, addressing both technical and legal aspects. Particular focus is devoted to the often-virtuous interaction between new legislation imposing more restrictions on the permitted pollutant emission levels and new technologies developed in order to meet these restrictions. The review begins first with the American and then European directives promulgated in the 1970s, aimed at limiting emissions of pollutants from road transport vehicles. Particular attention is paid to the introduction of the Euro standards in the European Union for light- and heavy-duty vehicles, used as a legal and time frame reference for the evolution of emission aftertreatment systems (ATSs). The paper also describes governmental approaches implemented for the control of pollutant emissions in circulating vehicles, such as market surveillance and in-service conformity. In parallel, it is explained how the gradual introduction of small-scale devices aimed at the NOx control, such as lean NOx traps (LNTs) systems, and, most of all, the selective catalytic reduction (SCR) of NOx, permitted the application to road-transport vehicles of this ATS, originally designed in larger sizes for industrial usage. The paper reviews chemical processes occurring in SCR systems and their advantages and drawbacks with respect to the pollutant emission limits imposed by the legislation. Their potential side effects are also addressed, such as the emission of extra, not-yet regulated pollutants such as, for example, NH₃ and N₂O. The NOx, N₂O, and NH₃ emission level evolution with the various Euro standards for both light- and heavy-duty vehicles are reported in the light of experimental data obtained at the European Commission’s Joint Research Centre. It is observed that the new technologies, boosted by increasingly stricter legal limits, have led in the last two decades to a clear decrease of over one order of magnitude of NOx emissions in Diesel light-duty vehicles, bringing them to the same level as Euro 6 gasoline vehicles (10 mg/km to 20 mg/km in average). On the other hand, an obvious increase in the emissions of both NH₃ and N₂O is observed in both Diesel and gasoline light-duty vehicles, whereby NH₃ emissions in spark-ignition vehicles are mainly linked to two-reaction mechanisms occurring in three-way catalysts after the catalyst light-off and during engine rich-operation. NH₃ emissions measured in recent Euro 6 light-duty vehicles amount to a few mg/km for both gasoline and Diesel engines, whereby N₂O emissions exceeding a dozen mg/km have been observed in Diesel vehicles only. The present paper can be regarded as part of a general assessment in view of the next EU emission standards, and a discussion on the role the SCR technology may serve as a NOx emission control strategy from lean-burn vehicles. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NOx by NH3)

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25 pages, 7449 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Hydrogen Production via Pd-TiO₂ Photocatalytic Water Splitting under Near-UV and Visible Light: Analysis of the Reaction Mechanism

by Bianca Rusinque, Salvador Escobedo and Hugo de Lasa

Catalysts 2021, 11(3), 405; https://doi.org/10.3390/catal11030405 - 23 Mar 2021

Cited by 56 | Viewed by 10537

Abstract

Photocatalytic hydrogen production via water splitting using a noble metal on a TiO₂ is a technology that has developed rapidly over the past few years. Specifically, palladium doped TiO₂ irradiated with near-UV or alternatively with visible light has shown promising results. [...] Read more.

Photocatalytic hydrogen production via water splitting using a noble metal on a TiO₂ is a technology that has developed rapidly over the past few years. Specifically, palladium doped TiO₂ irradiated with near-UV or alternatively with visible light has shown promising results. With this end in mind, strategically designed experiments were developed in the Photo-CREC Water-II (PCW-II) Reactor using a 0.25 wt.% Pd-TiO₂ under near-UV and visible light, and ethanol as an organic scavenger. Acetaldehyde, carbon monoxide, carbon dioxide, methane, ethane, ethylene, and hydrogen peroxide together with hydrogen were the main chemical species observed. A Langmuir adsorption isotherm was also established for hydrogen peroxide. On this basis, it is shown that pH variations, hydrogen peroxide formation/adsorption, and the production of various redox chemical species provide an excellent carbon element balance, as well as OH^• and H^• radicals balances. Under near-UV irradiation, 113 cm³ STP of H₂ is produced after 6 h, reaching an 99.8% elemental carbon balance and 99.2% OH^• and H^• and radical balance. It is also proven that a similar reaction network can be considered adequate for the photoreduced Pd-TiO₂ photocatalyst yielding 29 cm³ STP of H₂ with 95.4% carbon and the 97.5% OH^•–H^• radical balance closures. It is shown on this basis that a proposed “series-parallel” reaction network describes the water splitting reaction using the mesoporous Pd-TiO₂ and ethanol as organic scavenger. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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13 pages, 1735 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Optical Management of CQD/AgNP@SiNW Arrays with Highly Efficient Capability of Dye Degradation

by Po-Hsuan Hsiao, Sasimontra Timjan, Kuan-Yi Kuo, Joon-Ching Juan and Chia-Yun Chen

Catalysts 2021, 11(3), 399; https://doi.org/10.3390/catal11030399 - 22 Mar 2021

Cited by 12 | Viewed by 3438

Abstract

The facile synthetic method for the preparation of incorporated carbon quantum dots (CQDs)/Ag nanoparticles (AgNPs) with well-aligned silicon nanowire (SiNW) arrays is demonstrated, offering the superior photodegradation capabilities covering UV to visible wavelength regions. By examining the morphology, microstructure, crystallinity, chemical feature, surface [...] Read more.

The facile synthetic method for the preparation of incorporated carbon quantum dots (CQDs)/Ag nanoparticles (AgNPs) with well-aligned silicon nanowire (SiNW) arrays is demonstrated, offering the superior photodegradation capabilities covering UV to visible wavelength regions. By examining the morphology, microstructure, crystallinity, chemical feature, surface groups, light-emitting, and reflection characteristics, these hybrid heterostructures are systematically identified. Moreover, the involving degradation kinetics, band diagram, cycling capability, and underlying mechanism of photodegradation are investigated, validating their remarkable and reliable photocatalytic performances contributed from the strongly reduced light reflectivity, superior capability of charge separation, and sound wettability with dye solutions. Full article

(This article belongs to the Special Issue Photocatalytic Removal of Dyes)

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17 pages, 10272 KiB

Open AccessEditor’s ChoiceReview

A Review of Hydrogen Purification Technologies for Fuel Cell Vehicles

by Zhemin Du, Congmin Liu, Junxiang Zhai, Xiuying Guo, Yalin Xiong, Wei Su and Guangli He

Catalysts 2021, 11(3), 393; https://doi.org/10.3390/catal11030393 - 19 Mar 2021

Cited by 241 | Viewed by 27936

Abstract

Nowadays, we face a series of global challenges, including the growing depletion of fossil energy, environmental pollution, and global warming. The replacement of coal, petroleum, and natural gas by secondary energy resources is vital for sustainable development. Hydrogen (H₂) energy is [...] Read more.

Nowadays, we face a series of global challenges, including the growing depletion of fossil energy, environmental pollution, and global warming. The replacement of coal, petroleum, and natural gas by secondary energy resources is vital for sustainable development. Hydrogen (H₂) energy is considered the ultimate energy in the 21st century because of its diverse sources, cleanliness, low carbon emission, flexibility, and high efficiency. H₂ fuel cell vehicles are commonly the end-point application of H₂ energy. Owing to their zero carbon emission, they are gradually replacing traditional vehicles powered by fossil fuel. As the H₂ fuel cell vehicle industry rapidly develops, H₂ fuel supply, especially H₂ quality, attracts increasing attention. Compared with H₂ for industrial use, the H₂ purity requirements for fuel cells are not high. Still, the impurity content is strictly controlled since even a low amount of some impurities may irreversibly damage fuel cells’ performance and running life. This paper reviews different versions of current standards concerning H₂ for fuel cell vehicles in China and abroad. Furthermore, we analyze the causes and developing trends for the changes in these standards in detail. On the other hand, according to characteristics of H₂ for fuel cell vehicles, standard H₂ purification technologies, such as pressure swing adsorption (PSA), membrane separation and metal hydride separation, were analyzed, and the latest research progress was reviewed. Full article

(This article belongs to the Special Issue Catalysts for Sustainable Hydrogen Production: Preparation, Applications and Process Integration)

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17 pages, 8454 KiB

Open AccessEditor’s ChoiceArticle

Hexavalent Chromium Removal via Photoreduction by Sunlight on Titanium–Dioxide Nanotubes Formed by Anodization with a Fluorinated Glycerol–Water Electrolyte

by Siti Azlina Rosli, Nurhaswani Alias, Nurulhuda Bashirom, Syahriza Ismail, Wai Kian Tan, Go Kawamura, Atsunori Matsuda and Zainovia Lockman

Catalysts 2021, 11(3), 376; https://doi.org/10.3390/catal11030376 - 13 Mar 2021

Cited by 23 | Viewed by 3638

Abstract

In this paper, titanium–dioxide (TiO₂) nanotubes (TNTs) are formed by anodic oxidation with a fluorinated glycerol–water (85% and 15%, respectively) electrolyte to examine the effect of fluoride ion concentration, time, and applied voltage on TNT morphologies and dimensions. For fluoride ion [...] Read more.

In this paper, titanium–dioxide (TiO₂) nanotubes (TNTs) are formed by anodic oxidation with a fluorinated glycerol–water (85% and 15%, respectively) electrolyte to examine the effect of fluoride ion concentration, time, and applied voltage on TNT morphologies and dimensions. For fluoride ion concentration, the surface etching increases when the amount of ammonium fluoride added to the electrolyte solution increases, forming nanotube arrays with a clear pore structure. At a constant voltage of 20 V, TNTs with an average length of ~2 µm are obtained after anodization for 180 min. A prolonged anodization time only results in a marginal length increment. The TNT diameter is voltage dependent and increases from approximately 30 nm at 10 V to 310 nm at 60 V. At 80 V, the structure is destroyed. TNTs formed at 20 V for 180 min are annealed to induce the TiO₂ anatase phase in either air or nitrogen. When ethylenediaminetetraacetic acid is added as a hole scavenger, 100% hexavalent chromium removal is obtained after 120 min of sunlight exposure for nitrogen-annealed TNTs. Full article

(This article belongs to the Special Issue Advances in Photocatalytic Wastewater Purification)

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13 pages, 4810 KiB

Open AccessEditor’s ChoiceArticle

Green Synthesis of Silver and Gold Nanoparticles via Sargassum serratifolium Extract for Catalytic Reduction of Organic Dyes

by Beomjin Kim, Woo Chang Song, Sun Young Park and Geuntae Park

Catalysts 2021, 11(3), 347; https://doi.org/10.3390/catal11030347 - 8 Mar 2021

Cited by 62 | Viewed by 5191

Abstract

The green synthesis of inorganic nanoparticles (NPs) using bio-materials has attained enormous attention in recent years due to its simple, eco-friendly, low-cost and non-toxic nature. In this work, silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) were synthesized by the marine algae extract, Sargassum [...] Read more.

The green synthesis of inorganic nanoparticles (NPs) using bio-materials has attained enormous attention in recent years due to its simple, eco-friendly, low-cost and non-toxic nature. In this work, silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) were synthesized by the marine algae extract, Sargassum serratifolium (SS). The characteristic studies of bio-synthesized SS-AgNPs and SS-AuNPs were carried out by using ultraviolet–visible (UV–Vis) absorption spectroscopy, dynamic light scattering (DLS), high-resolution transmission electron microscope (HR-TEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Phytochemicals in the algae extract, such as meroterpenoids, acted as a capping agent for the NPs’ growth. The synthesized Ag and Au NPs were found to have important catalytic activity for the degradation of organic dyes, including methylene blue, rhodamine B and methyl orange. The reduction of dyes by SS-AgNPs and -AuNPs followed the pseudo-first order kinetics. Full article

(This article belongs to the Special Issue Innovative Catalytic and Photocatalytic Systems for Environmental Remediation)

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31 pages, 3219 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Kinetics and Selectivity Study of Fischer–Tropsch Synthesis to C₅₊ Hydrocarbons: A Review

by Zahra Teimouri, Nicolas Abatzoglou and Ajay K. Dalai

Catalysts 2021, 11(3), 330; https://doi.org/10.3390/catal11030330 - 5 Mar 2021

Cited by 78 | Viewed by 12620

Abstract

Fischer–Tropsch synthesis (FTS) is considered as one of the non-oil-based alternatives for liquid fuel production. This gas-to-liquid (GTL) technology converts syngas to a wide range of hydrocarbons using metal (Fe and Co) unsupported and supported catalysts. Effective design of the catalyst plays a [...] Read more.

Fischer–Tropsch synthesis (FTS) is considered as one of the non-oil-based alternatives for liquid fuel production. This gas-to-liquid (GTL) technology converts syngas to a wide range of hydrocarbons using metal (Fe and Co) unsupported and supported catalysts. Effective design of the catalyst plays a significant role in enhancing syngas conversion, selectivity towards C₅₊ hydrocarbons, and decreasing selectivity towards methane. This work presents a review on catalyst design and the most employed support materials in FTS to synthesize heavier hydrocarbons. Furthermore, in this report, the recent achievements on mechanisms of this reaction will be discussed. Catalyst deactivation is one of the most important challenges during FTS, which will be covered in this work. The selectivity of FTS can be tuned by operational conditions, nature of the catalyst, support, and reactor configuration. The effects of all these parameters will be analyzed within this report. Moreover, zeolites can be employed as a support material of an FTS-based catalyst to direct synthesis of liquid fuels, and the specific character of zeolites will be elaborated further. Furthermore, this paper also includes a review of some of the most employed characterization techniques for Fe- and Co-based FTS catalysts. Kinetic study plays an important role in optimization and simulation of this industrial process. In this review, the recent developed reaction rate models are critically discussed. Full article

(This article belongs to the Special Issue Application of Metal-Based Nanocatalysts for Addressing Environmental Issues and Energy Demand)

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44 pages, 16182 KiB

Open AccessFeature PaperEditor’s ChoiceReview

TiO₂ Photocatalysis for the Transformation of Aromatic Water Pollutants into Fuels

by Osama Al-Madanat, Yamen AlSalka, Wegdan Ramadan and Detlef W. Bahnemann

Catalysts 2021, 11(3), 317; https://doi.org/10.3390/catal11030317 - 28 Feb 2021

Cited by 52 | Viewed by 8176

Abstract

The growing world energy consumption, with reliance on conventional energy sources and the associated environmental pollution, are considered the most serious threats faced by mankind. Heterogeneous photocatalysis has become one of the most frequently investigated technologies, due to its dual functionality, i.e., environmental [...] Read more.

The growing world energy consumption, with reliance on conventional energy sources and the associated environmental pollution, are considered the most serious threats faced by mankind. Heterogeneous photocatalysis has become one of the most frequently investigated technologies, due to its dual functionality, i.e., environmental remediation and converting solar energy into chemical energy, especially molecular hydrogen. H₂ burns cleanly and has the highest gravimetric gross calorific value among all fuels. However, the use of a suitable electron donor, in what so-called “photocatalytic reforming”, is required to achieve acceptable efficiency. This oxidation half-reaction can be exploited to oxidize the dissolved organic pollutants, thus, simultaneously improving the water quality. Such pollutants would replace other potentially costly electron donors, achieving the dual-functionality purpose. Since the aromatic compounds are widely spread in the environment, they are considered attractive targets to apply this technology. In this review, different aspects are highlighted, including the employing of different polymorphs of pristine titanium dioxide as photocatalysts in the photocatalytic processes, also improving the photocatalytic activity of TiO₂ by loading different types of metal co-catalysts, especially platinum nanoparticles, and comparing the effect of various loading methods of such metal co-catalysts. Finally, the photocatalytic reforming of aromatic compounds employing TiO₂-based semiconductors is presented. Full article

(This article belongs to the Special Issue Multifunctional Materials for Photocatalytic and Photoactivated Processes)

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51 pages, 12744 KiB

Open AccessEditor’s ChoiceReview

TiO₂-Graphene Quantum Dots Nanocomposites for Photocatalysis in Energy and Biomedical Applications

by Anuja Bokare, Sowbaranigha Chinnusamy and Folarin Erogbogbo

Catalysts 2021, 11(3), 319; https://doi.org/10.3390/catal11030319 - 28 Feb 2021

Cited by 53 | Viewed by 10569

Abstract

The focus of current research in material science has shifted from “less efficient” single-component nanomaterials to the superior-performance, next-generation, multifunctional nanocomposites. TiO₂ is a widely used benchmark photocatalyst with unique physicochemical properties. However, the large bandgap and massive recombination of photogenerated charge [...] Read more.

The focus of current research in material science has shifted from “less efficient” single-component nanomaterials to the superior-performance, next-generation, multifunctional nanocomposites. TiO₂ is a widely used benchmark photocatalyst with unique physicochemical properties. However, the large bandgap and massive recombination of photogenerated charge carriers limit its overall photocatalytic efficiency. When TiO₂ nanoparticles are modified with graphene quantum dots (GQDs), some significant improvements can be achieved in terms of (i) broadening the light absorption wavelengths, (ii) design of active reaction sites, and (iii) control of the electron-hole (e⁻-h⁺) recombination. Accordingly, TiO₂-GQDs nanocomposites exhibit promising multifunctionalities in a wide range of fields including, but not limited to, energy, biomedical aids, electronics, and flexible wearable sensors. This review presents some important aspects of TiO₂-GQDs nanocomposites as photocatalysts in energy and biomedical applications. These include: (1) structural formulations and synthesis methods of TiO₂-GQDs nanocomposites; (2) discourse about the mechanism behind the overall higher photoactivities of these nanocomposites; (3) various characterization techniques which can be used to judge the photocatalytic performance of these nanocomposites, and (4) the application of these nanocomposites in biomedical and energy conversion devices. Although some objectives have been achieved, new challenges still exist and hinder the widespread application of these nanocomposites. These challenges are briefly discussed in the Future Scope section of this review. Full article

(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)

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26 pages, 1829 KiB

Open AccessEditor’s ChoiceReview

Advances in Valorization of Lignocellulosic Biomass towards Energy Generation

by Ikram ul Haq, Kinza Qaisar, Ali Nawaz, Fatima Akram, Hamid Mukhtar, Xin Zohu, Yong Xu, Muhammad Waseem Mumtaz, Umer Rashid, Wan Azlina Wan Ab Karim Ghani and Thomas Shean Yaw Choong

Catalysts 2021, 11(3), 309; https://doi.org/10.3390/catal11030309 - 26 Feb 2021

Cited by 117 | Viewed by 10785

Abstract

The booming demand for energy across the world, especially for petroleum-based fuels, has led to the search for a long-term solution as a perfect source of sustainable energy. Lignocellulosic biomass resolves this obstacle as it is a readily available, inexpensive, and renewable fuel [...] Read more.

The booming demand for energy across the world, especially for petroleum-based fuels, has led to the search for a long-term solution as a perfect source of sustainable energy. Lignocellulosic biomass resolves this obstacle as it is a readily available, inexpensive, and renewable fuel source that fulfills the criteria of sustainability. Valorization of lignocellulosic biomass and its components into value-added products maximizes the energy output and promotes the approach of lignocellulosic biorefinery. However, disruption of the recalcitrant structure of lignocellulosic biomass (LCB) via pretreatment technologies is costly and power-/heat-consuming. Therefore, devising an effective pretreatment method is a challenge. Likewise, the thermochemical and biological lignocellulosic conversion poses problems of efficiency, operational costs, and energy consumption. The advent of integrated technologies would probably resolve this problem. However, it is yet to be explored how to make it applicable at a commercial scale. This article will concisely review basic concepts of lignocellulosic composition and the routes opted by them to produce bioenergy. Moreover, it will also discuss the pros and cons of the pretreatment and conversion methods of lignocellulosic biomass. This critical analysis will bring to light the solutions for efficient and cost-effective conversion of lignocellulosic biomass that would pave the way for the development of sustainable energy systems. Full article

(This article belongs to the Special Issue New Trends in the Use of Catalysts for Biofuel and Bioproduct Generation)

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18 pages, 3448 KiB

Open AccessEditor’s ChoiceArticle

The Efficacy of Silver Nitrate (AgNO₃) as a Coating Agent to Protect Paper against High Deteriorating Microbes

by Amr Fouda, Gomaa Abdel-Maksoud, Hosam A. Saad, Adil A. Gobouri, Zuhair M. Mohammedsaleh and Mohamad Abdel-Haleem El-Sadany

Catalysts 2021, 11(3), 310; https://doi.org/10.3390/catal11030310 - 26 Feb 2021

Cited by 40 | Viewed by 7837

Abstract

This study focuses on the efficacy of silver nitrate (AgNO₃) as a coating agent used to preserve papers against microbial deterioration. To this end, the in vitro cytotoxicity of AgNO₃ was assessed against two normal cell lines, WI-38 and HFB-4, [...] Read more.

This study focuses on the efficacy of silver nitrate (AgNO₃) as a coating agent used to preserve papers against microbial deterioration. To this end, the in vitro cytotoxicity of AgNO₃ was assessed against two normal cell lines, WI-38 and HFB-4, to detect a safe dose that can be used as a coating agent, which was 80 µg mL⁻¹. Bacillus subtilis B3 and Penicillium chrysogenum F9 were selected as high deteriorating microbes, previously isolated from a historical manuscript dating back to 1677 A.-D. The microbial growth inhibition, color change, mechanical properties, and cellulosic fibers of untreated/treated papers were evaluated. The data showed the efficacy of AgNO₃ to inhibit the growth of B. subtilis with a percentage of 100% after 7 days, while it inhibits the growth of P. chrysogenum with a percentage of 85.9 ± 1.1% after 21 days. The color and mechanical properties of treated paper in the presence/absence of microbial inoculation were slightly changed, although they changed greatly due to microbial growth in the absence of AgNO₃. The EDX analysis confirmed the successful adsorption of Ag-ion on papers, with a weight percentage of 1.9%. The cellulosic fibers of untreated paper in the presence of microbial growth were highly deteriorated as compared with treated and standard filter paper (shown by FT-IR and SEM). Full article

(This article belongs to the Special Issue Gold, Silver and Copper Catalysis)

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25 pages, 2218 KiB

Open AccessEditor’s ChoiceReview

Effective Strategies, Mechanisms, and Photocatalytic Efficiency of Semiconductor Nanomaterials Incorporating rGO for Environmental Contaminant Degradation

by Noor Haida Mohd Kaus, Ahmad Fadhil Rithwan, Rohana Adnan, Mohd Lokman Ibrahim, Sirikanjana Thongmee and Siti Fairus Mohd Yusoff

Catalysts 2021, 11(3), 302; https://doi.org/10.3390/catal11030302 - 25 Feb 2021

Cited by 56 | Viewed by 6123

Abstract

The water pollution problems severely affect the natural water resources due to the large disposal of dyes, heavy metals, antibiotics, and pesticides. Advanced oxidation processes (AOP) have been developed using semiconductor nanomaterials as photocatalysts for water treatment as an essential strategy to minimize [...] Read more.

The water pollution problems severely affect the natural water resources due to the large disposal of dyes, heavy metals, antibiotics, and pesticides. Advanced oxidation processes (AOP) have been developed using semiconductor nanomaterials as photocatalysts for water treatment as an essential strategy to minimize environmental pollution. Significant research efforts have been dedicated over the past few years to enhancing the photocatalytic efficiencies of semiconductor nanomaterials. Graphene-based composites created by integrating reduced graphene oxide (rGO) into various semiconductor nanomaterials enable the unique characteristics of graphene, such as the extended range of light absorption, the separation of charges, and the high capacity of adsorption of pollutants. Therefore, rGO-based composites improve the overall visible-light photocatalytic efficiency and lead to a new pathway for high-performance photocatalysts’ potential applications. This brief review illustrates the strategies of combining rGO with various semiconductor nanomaterials and focuses primarily on modification and efficiency towards environmental contaminants. Full article

(This article belongs to the Special Issue Photocatalysis: Activity of Nanomaterials)

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23 pages, 5140 KiB

Open AccessFeature PaperEditor’s ChoicePerspective

Metal-Organic Frameworks in Oxidation Catalysis with Hydrogen Peroxide

by Oxana Kholdeeva and Nataliya Maksimchuk

Catalysts 2021, 11(2), 283; https://doi.org/10.3390/catal11020283 - 21 Feb 2021

Cited by 40 | Viewed by 7537

Abstract

In recent years, metal–organic frameworks (MOFs) have received increasing attention as selective oxidation catalysts and supports for their construction. In this short review paper, we survey recent findings concerning use of MOFs in heterogeneous liquid-phase selective oxidation catalysis with the green oxidant–aqueous hydrogen [...] Read more.

In recent years, metal–organic frameworks (MOFs) have received increasing attention as selective oxidation catalysts and supports for their construction. In this short review paper, we survey recent findings concerning use of MOFs in heterogeneous liquid-phase selective oxidation catalysis with the green oxidant–aqueous hydrogen peroxide. MOFs having outstanding thermal and chemical stability, such as Cr(III)-based MIL-101, Ti(IV)-based MIL-125, Zr(IV)-based UiO-66(67), Zn(II)-based ZIF-8, and some others, will be in the main focus of this work. The effects of the metal nature and MOF structure on catalytic activity and oxidation selectivity are analyzed and the mechanisms of hydrogen peroxide activation are discussed. In some cases, we also make an attempt to analyze relationships between liquid-phase adsorption properties of MOFs and peculiarities of their catalytic performance. Attempts of using MOFs as supports for construction of single-site catalysts through their modification with heterometals will be also addressed in relation to the use of such catalysts for activation of H₂O₂. Special attention is given to the critical issues of catalyst stability and reusability. The scope and limitations of MOF catalysts in H₂O₂-based selective oxidation are discussed. Full article

(This article belongs to the Special Issue Heterogeneous Selective and Total Catalytic Oxidation)

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22 pages, 7449 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Sonochemical and Sonoelectrochemical Production of Energy Materials

by Faranak Foroughi, Jacob J. Lamb, Odne S. Burheim and Bruno G. Pollet

Catalysts 2021, 11(2), 284; https://doi.org/10.3390/catal11020284 - 21 Feb 2021

Cited by 39 | Viewed by 7079

Abstract

Sonoelectrochemistry is the combination of ultrasound and electrochemistry which provides many advantages in electrochemistry, such as fast reaction rates, surface cleaning and activation, and increased mass transport at an electrode. Due to the advantages, some efforts have been made in order to benefit [...] Read more.

Sonoelectrochemistry is the combination of ultrasound and electrochemistry which provides many advantages in electrochemistry, such as fast reaction rates, surface cleaning and activation, and increased mass transport at an electrode. Due to the advantages, some efforts have been made in order to benefit sonoelectrochemistry in the field of energy and environmental engineering. This review paper highlights the developed progress of the application of sonoelectrochemistry in the production of hydrogen, electrocatalyst materials and electrodes for fuel cells and semiconductor photocatalyst materials. This review also provides the experimental methods that are utilized in several sonoelectrochemical techniques, such as different set-ups generally used for the synthesis of energy-related materials. Different key parameters in the operation of sonoelectrochemical synthesis including ultrasonication time, ultrasound frequency and operation current have been also discussed. There are not many research articles on the sonoelectrochemical production of materials for supercapacitors and water electrolyzers which play crucial roles in the renewable energy industry. Therefore, at the end of this review, some articles which have reported the use of ultrasound for the production of electrocatalysts for supercapacitors and electrolyzers have been reviewed. The current review might be helpful for scientists and engineers who are interested in and working on sonoelectrochemistry and electrocatalyst synthesis for energy storage and energy conversion. Full article

(This article belongs to the Special Issue Catalysis Under Ultrasonic Irradiation)

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30 pages, 5825 KiB

Open AccessEditor’s ChoiceReview

Towards the Large-Scale Electrochemical Reduction of Carbon Dioxide

by Subin Park, Devina Thasia Wijaya, Jonggeol Na and Chan Woo Lee

Catalysts 2021, 11(2), 253; https://doi.org/10.3390/catal11020253 - 13 Feb 2021

Cited by 58 | Viewed by 9972

Abstract

The severe increase in the CO₂ concentration is a causative factor of global warming, which accelerates the destruction of ecosystems. The massive utilization of CO₂ for value-added chemical production is a key to commercialization to guarantee both economic feasibility and negative [...] Read more.

The severe increase in the CO₂ concentration is a causative factor of global warming, which accelerates the destruction of ecosystems. The massive utilization of CO₂ for value-added chemical production is a key to commercialization to guarantee both economic feasibility and negative carbon emission. Although the electrochemical reduction of CO₂ is one of the most promising technologies, there are remaining challenges for large-scale production. Herein, an overview of these limitations is provided in terms of devices, processes, and catalysts. Further, the economic feasibility of the technology is described in terms of individual processes such as reactions and separation. Additionally, for the practical implementation of the electrochemical CO₂ conversion technology, stable electrocatalytic performances need to be addressed in terms of current density, Faradaic efficiency, and overpotential. Hence, the present review also covers the known degradation behaviors and mechanisms of electrocatalysts and electrodes during electrolysis. Furthermore, strategic approaches for overcoming the stability issues are introduced based on recent reports from various research areas involved in the electrocatalytic conversion. Full article

(This article belongs to the Special Issue Recent Advances in Catalytic CO₂ Conversion for Value-Added Chemical Production)

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15 pages, 21354 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Tailoring Properties of Metal-Free Catalysts for the Highly Efficient Desulfurization of Sour Gases under Harsh Conditions

by Cuong Duong-Viet, Jean-Mario Nhut, Tri Truong-Huu, Giulia Tuci, Lam Nguyen-Dinh, Charlotte Pham, Giuliano Giambastiani and Cuong Pham-Huu

Catalysts 2021, 11(2), 226; https://doi.org/10.3390/catal11020226 - 9 Feb 2021

Cited by 7 | Viewed by 3011

Abstract

Carbon-based nanomaterials, particularly in the form of N-doped networks, are receiving the attention of the catalysis community as effective metal-free systems for a relatively wide range of industrially relevant transformations. Among them, they have drawn attention as highly valuable and durable catalysts for [...] Read more.

Carbon-based nanomaterials, particularly in the form of N-doped networks, are receiving the attention of the catalysis community as effective metal-free systems for a relatively wide range of industrially relevant transformations. Among them, they have drawn attention as highly valuable and durable catalysts for the selective hydrogen sulfide oxidation to elemental sulfur in the treatment of natural gas. In this contribution, we report the outstanding performance of N-C/SiC based composites obtained by the surface coating of a non-oxide ceramic with a mesoporous N-doped carbon phase, starting from commercially available and cheap food-grade components. Our study points out on the importance of controlling the chemical and morphological properties of the N-C phase to get more effective and robust catalysts suitable to operate H₂S removal from sour (acid) gases under severe desulfurization conditions (high GHSVs and concentrations of aromatics as sour gas stream contaminants). We firstly discuss the optimization of the SiC impregnation/thermal treatment sequences for the N-C phase growth as well as on the role of aromatic contaminants in concentrations as high as 4 vol.% on the catalyst performance and its stability on run. A long-term desulfurization process (up to 720 h), in the presence of intermittent toluene rates (as aromatic contaminant) and variable operative temperatures, has been used to validate the excellent performance of our optimized N-C²/SiC catalyst as well as to rationalize its unique stability and coke-resistance on run. Full article

(This article belongs to the Special Issue Catalysts and Processes for H₂S Conversion to Sulfur)

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18 pages, 12744 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Stereoselective, Multicomponent Catalytic Carbonylative Approach to a New Class of α,β-Unsaturated γ-Lactam Derivatives

by Raffaella Mancuso, Ida Ziccarelli, Matteo Brindisi, Cosimo D. Altomare, Luca Frattaruolo, Aurelia Falcicchio, Nicola Della Ca’, Anna Rita Cappello and Bartolo Gabriele

Catalysts 2021, 11(2), 227; https://doi.org/10.3390/catal11020227 - 9 Feb 2021

Cited by 17 | Viewed by 3451

Abstract

We report a stereoselective, multicomponent catalytic carbonylative approach to a new class of α,β-unsaturated γ-lactam derivatives with potential biological activity, that are, alkyl (Z)-2-(2-oxopyrrolidin-3-ylidene)acetates. Our method is based on the catalytic assembly of readily available building blocks, namely, homopropargylic amines, carbon [...] Read more.

We report a stereoselective, multicomponent catalytic carbonylative approach to a new class of α,β-unsaturated γ-lactam derivatives with potential biological activity, that are, alkyl (Z)-2-(2-oxopyrrolidin-3-ylidene)acetates. Our method is based on the catalytic assembly of readily available building blocks, namely, homopropargylic amines, carbon monoxide, an alcohol, and oxygen (from air). These simple substrates are efficiently activated in ordered sequence under the action of a very simple catalytic system, consisting of PdI₂ in conjunction with KI to give the γ-lactam products in 47–85% yields. Carbonylation reactions are carried out at 100 °C for 2–5 h under 40 atm of a 4:1 mixture of CO‒air, with 0.5–5 mol% of PdI₂ and 5–50 mol% of KI. Full article

(This article belongs to the Special Issue Polycyclic Heterocycles by Catalyzed Processes)

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18 pages, 4169 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

W-Doped ZnO Photocatalyst for the Degradation of Glyphosate in Aqueous Solution

by Mariaconcetta Russo, Giuseppina Iervolino and Vincenzo Vaiano

Catalysts 2021, 11(2), 234; https://doi.org/10.3390/catal11020234 - 9 Feb 2021

Cited by 37 | Viewed by 4645

Abstract

In this paper, the photocatalytic degradation of glyphosate by zinc oxide (ZnO) photocatalysts doped with tungsten (W) was investigated under solar simulated light. The photocatalysts were successfully synthesized through a simple precipitation method and subsequently characterized by different techniques: Raman spectroscopy, UV–Vis, N [...] Read more.

In this paper, the photocatalytic degradation of glyphosate by zinc oxide (ZnO) photocatalysts doped with tungsten (W) was investigated under solar simulated light. The photocatalysts were successfully synthesized through a simple precipitation method and subsequently characterized by different techniques: Raman spectroscopy, UV–Vis, N₂ adsorption at −196 °C, X-ray diffraction, and SEM analysis. In particular, all the prepared catalysts were characterized by a crystallite size of about 28 nm and a hexagonal wurtzite structure. After the W doping, the bandgap energy decreased from 3.22 of pure ZnO to 3.19 for doped ZnO. This allowed us to obtain good results in terms of glyphosate degradation and simultaneous mineralization under solar simulated lamps, making the process environmentally friendly and with almost zero energy costs. In particular, the best photocatalytic performance was obtained with 100 W-ZnO (prepared with 1.5 mol% of W). With this catalyst, after 180 min of exposure to solar simulated light, the glyphosate degradation and mineralization was equal to 74% and 30%, respectively. Furthermore, it has been shown that the best catalyst dosage was equal to 1.5 g/L. The study on the influence of pH evidenced that the best photocatalytic performances are obtained at spontaneous (neutral) pH conditions. Finally, to determine the main reactive species in the glyphosate oxidation, the effects of different radical scavengers were tested. The results evidenced that the glyphosate oxidation mechanism seems to be related mainly to the O₂^•− generated under simulated solar light irradiation, but also in minor part to h⁺. Full article

(This article belongs to the Section Photocatalysis)

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11 pages, 1567 KiB

Open AccessEditor’s ChoiceArticle

Biocatalytic Transformation of 5-Hydroxymethylfurfural into 2,5-di(hydroxymethyl)furan by a Newly Isolated Fusarium striatum Strain

by Alberto Millán, Núria Sala, Mercè Torres and Ramon Canela-Garayoa

Catalysts 2021, 11(2), 216; https://doi.org/10.3390/catal11020216 - 6 Feb 2021

Cited by 16 | Viewed by 3621

Abstract

The compound 2,5-di(hydroxymethyl)furan (DHMF) is a high-value chemical block that can be synthesized from 5-hydroxymethylfurfural (HMF), a platform chemical that results from the dehydration of biomass-derived carbohydrates. In this work, the HMF biotransformation capability of different Fusarium species was evaluated, and F. striatum [...] Read more.

The compound 2,5-di(hydroxymethyl)furan (DHMF) is a high-value chemical block that can be synthesized from 5-hydroxymethylfurfural (HMF), a platform chemical that results from the dehydration of biomass-derived carbohydrates. In this work, the HMF biotransformation capability of different Fusarium species was evaluated, and F. striatum was selected to produce DHMF. The effects of the inoculum size, glucose concentration and pH of the media over DHMF production were evaluated by a 2³ factorial design. A substrate feeding approach was found suitable to overcome the toxicity effect of HMF towards the cells when added at high concentrations (>75 mM). The process was successfully scaled-up at bioreactor scale (1.3 L working volume) with excellent DHMF production yields (95%) and selectivity (98%). DHMF was purified from the reaction media with high recovery and purity by organic solvent extraction with ethyl acetate. Full article

(This article belongs to the Special Issue Biocatalysis and Whole-Cell Biotransformation in Biomanufacturing)

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43 pages, 6348 KiB

Open AccessEditor’s ChoiceReview

Electrocatalysis by Heme Enzymes—Applications in Biosensing

by Lidia Zuccarello, Catarina Barbosa, Smilja Todorovic and Célia M. Silveira

Catalysts 2021, 11(2), 218; https://doi.org/10.3390/catal11020218 - 6 Feb 2021

Cited by 35 | Viewed by 5393

Abstract

Heme proteins take part in a number of fundamental biological processes, including oxygen transport and storage, electron transfer, catalysis and signal transduction. The redox chemistry of the heme iron and the biochemical diversity of heme proteins have led to the development of a [...] Read more.

Heme proteins take part in a number of fundamental biological processes, including oxygen transport and storage, electron transfer, catalysis and signal transduction. The redox chemistry of the heme iron and the biochemical diversity of heme proteins have led to the development of a plethora of biotechnological applications. This work focuses on biosensing devices based on heme proteins, in which they are electronically coupled to an electrode and their activity is determined through the measurement of catalytic currents in the presence of substrate, i.e., the target analyte of the biosensor. After an overview of the main concepts of amperometric biosensors, we address transduction schemes, protein immobilization strategies, and the performance of devices that explore reactions of heme biocatalysts, including peroxidase, cytochrome P450, catalase, nitrite reductase, cytochrome c oxidase, cytochrome c and derived microperoxidases, hemoglobin, and myoglobin. We further discuss how structural information about immobilized heme proteins can lead to rational design of biosensing devices, ensuring insights into their efficiency and long-term stability. Full article

(This article belongs to the Special Issue Perspectives in Bioinorganic Catalysis)

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10 pages, 843 KiB

Open AccessEditor’s ChoicePerspective

The Current State of Research on PET Hydrolyzing Enzymes Available for Biorecycling

by Fusako Kawai

Catalysts 2021, 11(2), 206; https://doi.org/10.3390/catal11020206 - 3 Feb 2021

Cited by 75 | Viewed by 14205

Abstract

This short paper reviews two groups of enzymes designated as polyethylene terephthalate (PET) hydrolases: one consists of thermophilic cutinases from thermophilic microorganisms (actinomycetes and a fungus) and the other consists of mesophilic cutinases, the representative of which is IsPETase from a mesophilic [...] Read more.

This short paper reviews two groups of enzymes designated as polyethylene terephthalate (PET) hydrolases: one consists of thermophilic cutinases from thermophilic microorganisms (actinomycetes and a fungus) and the other consists of mesophilic cutinases, the representative of which is IsPETase from a mesophilic bacterium. From the viewpoint that PET hydrolysis requires a high temperature close to the glass transition temperature (65–70 °C in water) of PET, mesophilic cutinases are not suitable for use in the enzymatic recycling of PET since their degradation level is one to three orders of magnitude lower than that of thermophilic cutinases. Many studies have attempted to increase the thermostability of IsPETase by introducing mutations, but even with these modifications, the mesophilic cutinase does not reach the same level of degradation as thermophilic cutinases. In addition, this kind of trial contradicts the claim that IsPETase works at ambient temperature. As plastic pollution is an urgent environmental issue, scientists must focus on feasible thermophilic enzymes for the enzymatic processing of disposed PET, rather than on mesophilic cutinases. Thermophilic and mesophilic cutinases must be evaluated precisely and comparatively, based on their features that enable them to hydrolyze PET, with the aim of enzymatic PET disposal. The level of thermophilic cutinases has already reached their optimal level in PET biorecycling. The optimal level may be reached through the processing of PET waste, by amorphization and micronization into readily hydrolysable forms and the improvement of PET hydrolases by engineering higher degradation ability and low-cost production. Here I summarize the critical points in the evaluation of PET hydrolases and discuss the biorecycling of PET. Full article

(This article belongs to the Special Issue Biocatalysts and Their Environmental Applications)

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26 pages, 2161 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Progress on Modified Calcium Oxide Derived Waste-Shell Catalysts for Biodiesel Production

by Hui Khim Ooi, Xin Ning Koh, Hwai Chyuan Ong, Hwei Voon Lee, Mohd Sufri Mastuli, Yun Hin Taufiq-Yap, Fahad A. Alharthi, Abdulaziz Ali Alghamdi and Nurul Asikin Mijan

Catalysts 2021, 11(2), 194; https://doi.org/10.3390/catal11020194 - 2 Feb 2021

Cited by 41 | Viewed by 8707

Abstract

The dwindling of global petroleum deposits and worsening environmental issues have triggered researchers to find an alternative energy such as biodiesel. Biodiesel can be produced via transesterification of vegetable oil or animal fat with alcohol in the presence of a catalyst. A heterogeneous [...] Read more.

The dwindling of global petroleum deposits and worsening environmental issues have triggered researchers to find an alternative energy such as biodiesel. Biodiesel can be produced via transesterification of vegetable oil or animal fat with alcohol in the presence of a catalyst. A heterogeneous catalyst at an economical price has been studied widely for biodiesel production. It was noted that various types of natural waste shell are a potential calcium resource for generation of bio-based CaO, with comparable chemical characteristics, that greatly enhance the transesterification activity. However, CaO catalyzed transesterification is limited in its stability and studies have shown deterioration of catalytic reactivity when the catalyst is reused for several cycles. For this reason, different approaches are reviewed in the present study, which focuses on modification of waste-shell derived CaO based catalyst with the aim of better transesterification reactivity and high reusability of the catalyst for biodiesel production. The catalyst stability and leaching profile of the modified waste shell derived CaO is discussed. In addition, a critical discussion of the structure, composition of the waste shell, mechanism of CaO catalyzed reaction, recent progress in biodiesel reactor systems and challenges in the industrial sector are also included in this review. Full article

(This article belongs to the Special Issue Catalysts for Biofuel and Bioenergy Production)

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19 pages, 2708 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Mesoporous Methyl-Functionalized Titanosilicate Produced by Aerosol Process for the Catalytic Epoxidation of Olefins

by Lucia E. Manangon-Perugachi, Valentin Smeets, Alvise Vivian, Itika Kainthla, Pierre Eloy, Carmela Aprile, Damien P. Debecker and Eric M. Gaigneaux

Catalysts 2021, 11(2), 196; https://doi.org/10.3390/catal11020196 - 2 Feb 2021

Cited by 13 | Viewed by 3482

Abstract

Titanosilicates (Ti-SiO₂) are well-known catalysts for the epoxidation of olefins. Isolated Ti inserted in the silica framework in tetrahedral coordination are the active species. Recently, adjusting the hydrophobic/hydrophilic balance of such catalysts’ surfaces has appeared as a promising tool to further [...] Read more.

Titanosilicates (Ti-SiO₂) are well-known catalysts for the epoxidation of olefins. Isolated Ti inserted in the silica framework in tetrahedral coordination are the active species. Recently, adjusting the hydrophobic/hydrophilic balance of such catalysts’ surfaces has appeared as a promising tool to further boost their performance. However, adjusting the hydrophobic/hydrophilic balance via a one-pot classical sol-gel generally leads to a decrease in the Ti dispersion and/or collapse of the pore network. To overcome this limitation, hydrophobic mesoporous Ti-SiO₂ were here synthesized by aerosol-assisted one-pot sol–gel, which allowed the simultaneous control of their Ti loading, degree of methyl-functionalization, and textural properties. Methyl-functionalization was achieved by a partial substitution of tetraethoxy silane (TEOS) by methyltriethoxy silane (MTES) in different ratios. Solid-state ²⁹Si-NMR, FTIR, TGA, and vapor-phase water adsorption showed that methyl moieties were effectively incorporated, conferring a hydrophobic property to the Ti-SiO₂ catalysts. ICP-AES, DRUV, XPS, and N₂ physisorption demonstrated that Ti dispersion and textural properties were both successfully preserved upon the incorporation of the methyl moieties. In the epoxidation of cyclooctene with tert-butyl hydroperoxide as oxidant, the hydrophobic Ti-SiO₂ showed higher catalytic performance than pristine Ti-SiO₂ prepared without MTES. In addition to disentangling the positive effect of adjusting the hydrophobic/hydrophilic balance of epoxidation catalysts on their performance, this contribution highlights the advantages of the aerosol procedure to synthesize mesoporous functionalized catalysts with very high dispersion of active sites. Full article

(This article belongs to the Section Catalytic Materials)

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22 pages, 4202 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Extra-Heavy Oil Aquathermolysis Using Nickel-Based Catalyst: Some Aspects of In-Situ Transformation of Catalyst Precursor

by Alexey V. Vakhin, Firdavs A. Aliev, Irek I. Mukhamatdinov, Sergey A. Sitnov, Sergey I. Kudryashov, Igor S. Afanasiev, Oleg V. Petrashov and Danis K. Nurgaliev

Catalysts 2021, 11(2), 189; https://doi.org/10.3390/catal11020189 - 1 Feb 2021

Cited by 58 | Viewed by 4544

Abstract

In the present work, we studied the catalytic performance of an oil-soluble nickel-based catalyst during aquathermolysis of oil-saturated crushed cores from Boca de Jaruco extra-heavy oil field. The decomposition of nickel tallate and some aspects of in-situ transformation of the given catalyst precursor [...] Read more.

In the present work, we studied the catalytic performance of an oil-soluble nickel-based catalyst during aquathermolysis of oil-saturated crushed cores from Boca de Jaruco extra-heavy oil field. The decomposition of nickel tallate and some aspects of in-situ transformation of the given catalyst precursor under the steam injection conditions were investigated in a high-pressure batch reactor using XRD and SEM analysis methods. The changes in physical and chemical properties of core extracts after the catalytic aquathermolysis process with various duration were studied using gas chromatography for analyzing gas products, SARA analysis, GC-MS of saturated and aromatic fractions, FT-IR spectrometer, elemental analysis, and matrix-activated laser desorption/ionization (MALDI). The results showed that nickel tallate in the presence of oil-saturated crushed core under the injection of steam at 300 °C transforms mainly into nonstoichiometric forms of nickel sulfide. According to the SEM images, the size of nickel sulfide particles was in the range of 80–100 nm. The behavior of main catalytic aquathermolysis gas products such as CH₄, CO₂, H₂S, and H₂ depending on the duration of the process was analyzed. The catalytic upgrading at 300 °C provided decrease in the content of resins and asphaltenes, and increase in saturated hydrocarbon content. Moreover, the content of low-molecular alkanes, which were not detected before the catalytic aquathermolysis process, dramatically increased in saturates fraction after catalytic aquathermolysis reactions. In addition, the aromatics hydrocarbons saturated with high molecular weight polycyclic aromatic compounds—isomers of benzo(a)fluorine, which were initially concentrated in resins and asphaltenes. Nickel sulfide showed a good performance in desulfurization of high-molecular components of extra-heavy oil. The cracking of the weak C–S bonds, which mainly concentrated in resins and asphaltenes, ring-opening reactions, detachment of alkyl substitutes from asphaltenes and inhibition of polymerization reactions in the presence of catalytic complex reduced the average molecular mass of resins (from 871.7 to 523.3 a.m.u.) and asphaltenes (from 1572.7 to 1072.3 a.m.u.). Thus, nickel tallate is a promising catalyst to promote the in-situ upgrading of extra-heavy oil during steam injection techniques. Full article

(This article belongs to the Special Issue Heavy Oil In Situ Upgrading and Catalysis)

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27 pages, 4940 KiB

Open AccessEditor’s ChoiceReview

Recent Developments in the Use of Heterogeneous Semiconductor Photocatalyst Based Materials for a Visible-Light-Induced Water-Splitting System—A Brief Review

by Prabhakarn Arunachalam, Keiji Nagai, Mabrook S. Amer, Mohamed A. Ghanem, Rajabathar Jothi Ramalingam and Abdullah M. Al-Mayouf

Catalysts 2021, 11(2), 160; https://doi.org/10.3390/catal11020160 - 25 Jan 2021

Cited by 54 | Viewed by 7207

Abstract

Visible-light-driven photoelectrochemical (PEC) and photocatalytic water splitting systems featuring heterogeneous semiconductor photocatalysts (oxynitrides, oxysulfides, organophotocatalysts) signify an environmentally friendly and promising approach for the manufacturing of renewable hydrogen fuel. Semiconducting electrode materials as the main constituents in the PEC water splitting system have [...] Read more.

Visible-light-driven photoelectrochemical (PEC) and photocatalytic water splitting systems featuring heterogeneous semiconductor photocatalysts (oxynitrides, oxysulfides, organophotocatalysts) signify an environmentally friendly and promising approach for the manufacturing of renewable hydrogen fuel. Semiconducting electrode materials as the main constituents in the PEC water splitting system have substantial effects on the device’s solar-to-hydrogen (STH) conversion efficiency. Given the complication of the photocatalysis and photoelectrolysis methods, it is indispensable to include the different electrocatalytic materials for advancing visible-light-driven water splitting, considered a difficult challenge. Heterogeneous semiconductor-based materials with narrower bandgaps (2.5 to 1.9 eV), equivalent to the theoretical STH efficiencies ranging from 9.3% to 20.9%, are recognized as new types of photoabsorbents to engage as photoelectrodes for PEC water oxidation and have fascinated much consideration. Herein, we spotlight mainly on heterogenous semiconductor-based photoanode materials for PEC water splitting. Different heterogeneous photocatalysts based materials are emphasized in different groups, such as oxynitrides, oxysulfides, and organic solids. Lastly, the design approach and future developments regarding heterogeneous photocatalysts oxide electrodes for PEC applications and photocatalytic applications are also discussed. Full article

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19 pages, 4187 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Catalytic Advances in Hydrotreatment Processes of Pyrolysis Bio-Oil

by Giuseppe Bagnato, Aimaro Sanna, Emilia Paone and Enrico Catizzone

Catalysts 2021, 11(2), 157; https://doi.org/10.3390/catal11020157 - 23 Jan 2021

Cited by 41 | Viewed by 8503

Abstract

Catalytic hydrotreatment (HT) is one of the most important refining steps in the actual petroleum-based refineries for the production of fuels and chemicals, and it will play also a crucial role for the development of biomass-based refineries. In fact, the utilization of HT [...] Read more.

Catalytic hydrotreatment (HT) is one of the most important refining steps in the actual petroleum-based refineries for the production of fuels and chemicals, and it will play also a crucial role for the development of biomass-based refineries. In fact, the utilization of HT processes for the upgrading of biomass and/or lignocellulosic residues aimed to the production of synthetic fuels and chemical intermediates represents a reliable strategy to reduce both carbon dioxide emissions and fossil fuels dependence. At this regard, the catalytic hydrotreatment of oils obtained from either thermochemical (e.g., pyrolysis) or physical (e.g., vegetable seeds pressing) processes allows to convert biomass-derived oils into a biofuel with properties very similar to conventional ones (so-called drop-in biofuels). Similarly, catalytic hydro-processing also may have a key role in the valorization of other biorefinery streams, such as lignocellulose, for the production of high-added value chemicals. This review is focused on recent hydrotreatment developments aimed to stabilizing the pyrolytic oil from biomasses. A particular emphasis is devoted on the catalyst formulation, reaction pathways, and technologies. Full article

(This article belongs to the Special Issue Sustainable and Environmental Catalysis)

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30 pages, 2184 KiB

Open AccessEditor’s ChoiceReview

Catalytic Reaction of Carbon Dioxide with Methane on Supported Noble Metal Catalysts

by András Erdőhelyi

Catalysts 2021, 11(2), 159; https://doi.org/10.3390/catal11020159 - 23 Jan 2021

Cited by 30 | Viewed by 9145

Abstract

The conversion of CO₂ and CH₄, the main components of the greenhouse gases, into synthesis gas are in the focus of academic and industrial research. In this review, the activity and stability of different supported noble metal catalysts were compared [...] Read more.

The conversion of CO₂ and CH₄, the main components of the greenhouse gases, into synthesis gas are in the focus of academic and industrial research. In this review, the activity and stability of different supported noble metal catalysts were compared in the CO₂ + CH₄ reaction on. It was found that the efficiency of the catalysts depends not only on the metal and on the support but on the particle size, the metal support interface, the carbon deposition and the reactivity of carbon also influences the activity and stability of the catalysts. The possibility of the activation and dissociation of CO₂ and CH₄ on clean and on supported noble metals were discussed separately. CO₂ could dissociate on metal surfaces, this reaction could proceed via the formation of carbonate on the support, or on the metal–support interface but in the reaction the hydrogen assisted dissociation of CO₂ was also suggested. The decrease in the activity of the catalysts was generally attributed to carbon deposition, which can be formed from CH₄ while others suggest that the source of the surface carbon is CO₂. Carbon can occur in different forms on the surface, which can be transformed into each other depending on the temperature and the time elapsed since their formation. Basically, two reaction mechanisms was proposed, according to the mono-functional mechanism the activation of both CO₂ and CH₄ occurs on the metal sites, but in the bi-functional mechanism the CO₂ is activated on the support or on the metal–support interface and the CH₄ on the metal. Full article

(This article belongs to the Special Issue Catalysis for CO₂ Conversion)

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21 pages, 2645 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Abatement of 1,2,4-Trichlorobencene by Wet Peroxide Oxidation Catalysed by Goethite and Enhanced by Visible LED Light at Neutral pH

by David Lorenzo, Aurora Santos, Andrés Sánchez-Yepes, Leandro Óscar Conte and Carmen María Domínguez

Catalysts 2021, 11(1), 139; https://doi.org/10.3390/catal11010139 - 19 Jan 2021

Cited by 18 | Viewed by 3054

Abstract

There is significant environmental concern about chlorinated organic compounds (COCs) in wastewater, surface water, and groundwater due to their low biodegradability and high persistence. In this work, 1,2,4-trichlorobenzene (124-TCB) was selected as a model compound to study its abatement using wet peroxide oxidation [...] Read more.

There is significant environmental concern about chlorinated organic compounds (COCs) in wastewater, surface water, and groundwater due to their low biodegradability and high persistence. In this work, 1,2,4-trichlorobenzene (124-TCB) was selected as a model compound to study its abatement using wet peroxide oxidation at neutral pH with goethite as a heterogeneous catalyst, which was enhanced with visible monochromatic light-emitting diode (LED) light (470 nm). A systematic study of the main operating variables (oxidant and catalyst concentration and irradiance) was accomplished to investigate their influence in the abatement of 124-TCB in water. The reaction was carried out in a well-mixed reactor of glass irradiated by a visible LED light. The hydrogen peroxide concentration was tested from 0 to 18 mM, the goethite concentration within the range 0.1–1.0 g·L⁻¹ and the irradiance from 0.10 to 0.24 W·cm⁻² at neutral pH. It was found that this oxidation method is a very efficient technique to abate 124-TCB, reaching a pollutant conversion of 0.9 when using 0.1 g·L⁻¹ of goethite, 18 mM of H₂O₂, and 0.24 of W·cm⁻². Moreover, the system performance was evaluated using the photonic efficiency (ratio of the moles of 124-TCB abated and the moles of photons arriving at the reactor window). The maximum photonic efficiencies were obtained using the lowest lamp powers and moderate to high catalyst loads. Full article

(This article belongs to the Special Issue Green Catalysts: Application to Waste and Groundwater Treatment)

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