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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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56 pages, 6811 KiB  
Review
C-,N- and S-Doped TiO2 Photocatalysts: A Review
by Aleksandra Piątkowska, Magdalena Janus, Kacper Szymański and Sylwia Mozia
Catalysts 2021, 11(1), 144; https://doi.org/10.3390/catal11010144 - 19 Jan 2021
Cited by 248 | Viewed by 21606
Abstract
This article presents an overview of the reports on the doping of TiO2 with carbon, nitrogen, and sulfur, including single, co-, and tri-doping. A comparison of the properties of the photocatalysts synthesized from various precursors of TiO2 and C, N, or [...] Read more.
This article presents an overview of the reports on the doping of TiO2 with carbon, nitrogen, and sulfur, including single, co-, and tri-doping. A comparison of the properties of the photocatalysts synthesized from various precursors of TiO2 and C, N, or S dopants is summarized. Selected methods of synthesis of the non-metal doped TiO2 are also described. Furthermore, the influence of the preparation conditions on the doping mode (interstitial or substitutional) with reference to various types of the modified TiO2 is summarized. The mechanisms of photocatalysis for the different modes of the non-metal doping are also discussed. Moreover, selected applications of the non-metal doped TiO2 photocatalysts are shown, including the removal of organic compounds from water/wastewater, air purification, production of hydrogen, lithium storage, inactivation of bacteria, or carbon dioxide reduction. Full article
(This article belongs to the Special Issue State-of-the-Art Catalytic Materials in Europe)
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18 pages, 2892 KiB  
Article
CO Oxidation Efficiency and Hysteresis Behavior over Mesoporous Pd/SiO2 Catalyst
by Rola Mohammad Al Soubaihi, Khaled Mohammad Saoud, Myo Tay Zar Myint, Mats A. Göthelid and Joydeep Dutta
Catalysts 2021, 11(1), 131; https://doi.org/10.3390/catal11010131 - 16 Jan 2021
Cited by 20 | Viewed by 4685
Abstract
Carbon monoxide (CO) oxidation is considered an important reaction in heterogeneous industrial catalysis and has been extensively studied. Pd supported on SiO2 aerogel catalysts exhibit good catalytic activity toward this reaction owing to their CO bond activation capability and thermal stability. Pd/SiO [...] Read more.
Carbon monoxide (CO) oxidation is considered an important reaction in heterogeneous industrial catalysis and has been extensively studied. Pd supported on SiO2 aerogel catalysts exhibit good catalytic activity toward this reaction owing to their CO bond activation capability and thermal stability. Pd/SiO2 catalysts were investigated using carbon monoxide (CO) oxidation as a model reaction. The catalyst becomes active, and the conversion increases after the temperature reaches the ignition temperature (Tig). A normal hysteresis in carbon monoxide (CO) oxidation has been observed, where the catalysts continue to exhibit high catalytic activity (CO conversion remains at 100%) during the extinction even at temperatures lower than Tig. The catalyst was characterized using BET, TEM, XPS, TGA-DSC, and FTIR. In this work, the influence of pretreatment conditions and stability of the active sites on the catalytic activity and hysteresis is presented. The CO oxidation on the Pd/SiO2 catalyst has been attributed to the dissociative adsorption of molecular oxygen and the activation of the C-O bond, followed by diffusion of adsorbates at Tig to form CO2. Whereas, the hysteresis has been explained by the enhanced stability of the active site caused by thermal effects, pretreatment conditions, Pd-SiO2 support interaction, and PdO formation and decomposition. Full article
(This article belongs to the Special Issue Sustainable and Environmental Catalysis)
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13 pages, 4004 KiB  
Article
Synthesis of N-Doped TiO2 for Efficient Photocatalytic Degradation of Atmospheric NOx
by Tamal Tahsin Khan, Gazi A. K. M. Rafiqul Bari, Hui-Ju Kang, Tae-Gyu Lee, Jae-Woo Park, Hyun Jin Hwang, Sayed Mukit Hossain, Jong Seok Mun, Norihiro Suzuki, Akira Fujishima, Jong-Ho Kim, Ho Kyong Shon and Young-Si Jun
Catalysts 2021, 11(1), 109; https://doi.org/10.3390/catal11010109 - 14 Jan 2021
Cited by 67 | Viewed by 6845
Abstract
Titanium oxide (TiO2) is a potential photocatalyst for removing toxic NOx from the atmosphere. Its practical application is, however, significantly limited by its low absorption into visible light and a high degree of charge recombination. The overall photocatalytic activity of [...] Read more.
Titanium oxide (TiO2) is a potential photocatalyst for removing toxic NOx from the atmosphere. Its practical application is, however, significantly limited by its low absorption into visible light and a high degree of charge recombination. The overall photocatalytic activity of TiO2 remains too low since it can utilize only about 4–5% of solar energy. Nitrogen doping into the TiO2 lattice takes advantage of utilizing a wide range of solar radiation by increasing the absorption capability towards the visible light region. In this work, N-doped TiO2, referred to as TC, was synthesized by a simple co-precipitation of tri-thiocyanuric acid (TCA) with P25 followed by heat treatment at 550 degrees C. The resulting nitrogen doping increased the visible-light absorption and enhanced the separation/transfer of photo-excited charge carriers by capturing holes by reduced titanium ions. As a result, TC samples exhibited excellent photocatalytic activities of 59% and 51% in NO oxidation under UV and visible light irradiation, in which the optimum mass ratio of TCA to P25 was found to be 10. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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15 pages, 3382 KiB  
Article
Electrocatalytic Oxidation of Glucose on Boron and Nitrogen Codoped Graphene Quantum Dot Electrodes in Alkali Media
by Siyong Gu, Chien-Te Hsieh, Chih-Peng Kao, Chun-Chieh Fu, Yasser Ashraf Gandomi, Ruey-Shin Juang and Kenneth David Kihm
Catalysts 2021, 11(1), 101; https://doi.org/10.3390/catal11010101 - 13 Jan 2021
Cited by 17 | Viewed by 3836
Abstract
A novel solvothermal technique has been developed in the presence of C/N/B precursor for synthesizing B-N-coped graphene quantum dots (GQDs) as non-metal electrocatalysts towards the catalytic glucose oxidation reaction (GOR). Both N-doped GQD and B-N-codoped GQD particles (~4.0 nm) possess a similar oxidation [...] Read more.
A novel solvothermal technique has been developed in the presence of C/N/B precursor for synthesizing B-N-coped graphene quantum dots (GQDs) as non-metal electrocatalysts towards the catalytic glucose oxidation reaction (GOR). Both N-doped GQD and B-N-codoped GQD particles (~4.0 nm) possess a similar oxidation and amidation level. The B-N-codoped GQD contains a B/C ratio of 3.16 at.%, where the B dopants were formed through different bonding types (i.e., N‒B, C‒B, BC2O, and BCO2) inserted into or decorated on the GQDs. The cyclic voltammetry measurement revealed that the catalytic activity of B-N-codoped GQD catalyst is significantly higher compared to the N-doped GQDs (~20% increase). It was also shown that the GOR activity was substantially enhanced due to the synergistic effect of B and N dopants within the GQD catalysts. Based on the analysis of Tafel plots, the B-N-codoped-GQD catalyst electrode displays an ultra-high exchange current density along with a reduced Tafel slope. The application of B-N-codoped GQD electrodes significantly enhances the catalytic activity and results in facile reaction kinetics towards the glucose oxidation reaction. Accordingly, the novel design of GQD catalyst demonstrated in this work sets the stage for designing inexpensive GQD-based catalysts as an alternative for precious metal catalysts commonly used in bio-sensors, fuel cells, and other electrochemical devices. Full article
(This article belongs to the Special Issue Recent Advances in Biocatalysis and Metabolic Engineering)
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14 pages, 5298 KiB  
Article
ZIF-67 Derived MnO2 Doped Electrocatalyst for Oxygen Reduction Reaction
by Usman Salahuddin, Naseem Iqbal, Tayyaba Noor, Saadia Hanif, Haider Ejaz, Neelam Zaman and Safeer Ahmed
Catalysts 2021, 11(1), 92; https://doi.org/10.3390/catal11010092 - 12 Jan 2021
Cited by 22 | Viewed by 4933
Abstract
In this study, zeolitic imidazolate framework (ZIF-67) derived nano-porous carbon structures that were further hybridized with MnO2 were tested for oxygen reduction reaction (ORR) as cathode material for fuel cells. The prepared electrocatalyst was characterized by X-ray powder diffraction (XRD), scanning electron [...] Read more.
In this study, zeolitic imidazolate framework (ZIF-67) derived nano-porous carbon structures that were further hybridized with MnO2 were tested for oxygen reduction reaction (ORR) as cathode material for fuel cells. The prepared electrocatalyst was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Energy Dispersive X-ray Analysis (EDX). Cyclic voltammetry was performed on these materials at different scan rates under dissolved oxygen in basic media (0.1 M KOH), inert and oxygen rich conditions to obtain their I–V curves. Electrochemical impedance spectroscopy (EIS) and Chronoamperometry was also performed to observe the materials’ impedance and stability. We report improved performance of hybridized catalyst for ORR based on cyclic voltammetry and EIS results, which show that it can be a potential candidate for fuel cell applications. Full article
(This article belongs to the Special Issue MOFs for Advanced Applications)
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35 pages, 13158 KiB  
Review
Chronicle of Nanocelluloses (NCs) for Catalytic Applications: Key Advances
by Loredana Maiuolo, Vincenzo Algieri, Fabrizio Olivito, Matteo Antonio Tallarida, Paola Costanzo, Antonio Jiritano and Antonio De Nino
Catalysts 2021, 11(1), 96; https://doi.org/10.3390/catal11010096 - 12 Jan 2021
Cited by 20 | Viewed by 4794
Abstract
Nanocellulose (NC) is a biomaterial with growing interest in the field of nanocomposites and sustainable materials. NC has various applications including biodegradable materials, reinforcing agents, packaging films, transpiring membranes and medical devices. Among the many applications, the use of NC functionalized with organic [...] Read more.
Nanocellulose (NC) is a biomaterial with growing interest in the field of nanocomposites and sustainable materials. NC has various applications including biodegradable materials, reinforcing agents, packaging films, transpiring membranes and medical devices. Among the many applications, the use of NC functionalized with organic and inorganic groups has found wide use as a catalyst in chemical transformations. The goal of this review is to collect the current knowledge on its catalytic applications for chemical groups conversion. We have chosen to organize the manuscript according to subdivision of NC into Bacterial Nanocellulose (BNC), Cellulose Nanocrystals (CNCs), and Cellulose Nanofibers (CNFs) and their role as inorganic- and organic-functionalized NC-catalysts in organic synthesis. However, in consideration of the fact that the literature on this field is very extensive, we have decided to focus our attention on the scientific productions of the last five years. Full article
(This article belongs to the Section Catalytic Materials)
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18 pages, 3752 KiB  
Article
Morphology-Controlled Synthesis of ZnO Nanostructures for Caffeine Degradation and Escherichia coli Inactivation in Water
by Shaila Thakur, Sudarsan Neogi and Ajay K. Ray
Catalysts 2021, 11(1), 63; https://doi.org/10.3390/catal11010063 - 5 Jan 2021
Cited by 19 | Viewed by 3920
Abstract
Photocatalytic and antibacterial activity of nanoparticles are strongly governed by their morphology. By varying the type of solvent used, one can obtain different shapes of ZnO nanoparticles and tune the amount of reactive oxygen species (ROS) and metal ion (Zn2+) generation, [...] Read more.
Photocatalytic and antibacterial activity of nanoparticles are strongly governed by their morphology. By varying the type of solvent used, one can obtain different shapes of ZnO nanoparticles and tune the amount of reactive oxygen species (ROS) and metal ion (Zn2+) generation, which in turn dictates their activity. ZnO nanostructures were fabricated via facile wet chemical method by varying the type of solvents. Solar light assisted photocatalytic degradation of caffeine and antibacterial activity against E. coli were examined in presence ZnO nanostructures. In addition to an elaborate nanoparticle characterization, adsorption and kinetic experiments were performed to determine the ability of nanostructures to degrade caffeine. Zone of inhibition, time kill assay and electron microscopy imaging were carried out to assess the antibacterial activity. Experimental findings indicate that ZnO nanospheres generated maximum ROS and Zn2+ ions followed by ZnO nanopetals and ZnO nanorods. As a result, ZnO nanospheres exhibited highest degradation of caffeine as well as killing of E. coli. While ROS is mainly responsible for the photocatalytic activity of nanostructures, their antibacterial activity is mostly due to the combination of ROS, metal ion, physical attrition and cell internalization. Full article
(This article belongs to the Special Issue Sustainable and Environmental Catalysis)
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13 pages, 2587 KiB  
Article
Photocatalytic Pretreatment of Commercial Lignin Using TiO2-ZnO Nanocomposite-Derived Advanced Oxidation Processes for Methane Production Synergy in Lab Scale Continuous Reactors
by Yu-Ming Chu, Hafiz Muhammad Asif Javed, Muhammad Awais, Muhammad Ijaz Khan, Sana Shafqat, Falak Sher Khan, Muhammad Salman Mustafa, Dawood Ahmed, Sami Ullah Khan and Rana Muhammad Arif Khalil
Catalysts 2021, 11(1), 54; https://doi.org/10.3390/catal11010054 - 2 Jan 2021
Cited by 28 | Viewed by 4124
Abstract
The photocatalytic pretreatment of lignocellulosic biomass to oxidize lignin and increase biomass stability has gained attention during the last few years. Conventional pretreatment methods are limited by the fact that they are expensive, non-renewable and contaminate the anaerobic digestate later on. The present [...] Read more.
The photocatalytic pretreatment of lignocellulosic biomass to oxidize lignin and increase biomass stability has gained attention during the last few years. Conventional pretreatment methods are limited by the fact that they are expensive, non-renewable and contaminate the anaerobic digestate later on. The present study was focused to develop a metal-derived photocatalyst that can work with visible electromagnetic spectra light and oxidize commercial lignin liquor. During this project the advanced photocatalytic oxidation of lignin was achieved by using a quartz cube tungsten T3 Halogen 100 W lamp with a laboratory manufactured TiO2-ZnO nanoparticle (nanocomposite) in a self-designed apparatus. The products of lignin oxidation were confirmed to be vanillic acid (9.71 ± 0.23 mg/L), ferrulic acid (7.34 ± 0.16 mg/L), benzoic acid (6.12 ± 0.17 mg/L) and p-coumaric acid (3.80 ± 0.13 mg/L). These all products corresponded to 85% of the lignin oxidation products that were detectable, which is significantly more than any previously reported lignin pretreatment with even more intensity. Furthermore, all the pretreatment samples were supplemented in the form of feedstock diluent in uniformly operating continuously stirred tank reactors (CSTRs). The results of pretreatment revealed 85% lignin oxidation and later on these products did not hinder the CSTR performance at any stage. Moreover, the synergistic effects of pretreated lignin diluent were seen that resulted in 39% significant increase in the methane yield of the CSTR with constant operation. Finally, the visible light and nanoparticles alone could not pretreat lignin and when used as diluent, halted and reduced the methane yield by 37% during 4th HRT. Full article
(This article belongs to the Special Issue Catalytic Conversion of Lignins for Valuable Chemicals)
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15 pages, 3679 KiB  
Article
Novel Preparation of Cu and Fe Zirconia Supported Catalysts for Selective Catalytic Reduction of NO with NH3
by Katarzyna Świrk, Ye Wang, Changwei Hu, Li Li, Patrick Da Costa and Gérard Delahay
Catalysts 2021, 11(1), 55; https://doi.org/10.3390/catal11010055 - 2 Jan 2021
Cited by 10 | Viewed by 3176
Abstract
Copper and iron promoted ZrO2 catalysts were prepared by one-pot synthesis using urea. The studied catalysts were characterized by XRD, N2 physisorption, XPS, NH3-TPD, and tested in the selective catalytic reduction of NO with NH3 (NH3-SCR) [...] Read more.
Copper and iron promoted ZrO2 catalysts were prepared by one-pot synthesis using urea. The studied catalysts were characterized by XRD, N2 physisorption, XPS, NH3-TPD, and tested in the selective catalytic reduction of NO with NH3 (NH3-SCR) in the absence and presence of water vapor under the experimental conditions representative of exhaust gases from stationary sources. The influence of SO2 on catalytic performance was also investigated. Among the studied catalysts, the Fe-Zr sample showed the most promising results in NH3-SCR, being active and highly selective to N2. The addition of SO2 markedly improved NO and NH3 conversions during NH3-SCR in the presence of H2O. The improvement in acidic surface properties is believed to be the cause. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx by NH3)
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18 pages, 4596 KiB  
Article
Application of Mineral Iron-Based Natural Catalysts in Electro-Fenton Process: A Comparative Study
by Zahra Heidari, Rasool Pelalak, Reza Alizadeh, Nihal Oturan, Saeed Shirazian and Mehmet A. Oturan
Catalysts 2021, 11(1), 57; https://doi.org/10.3390/catal11010057 - 2 Jan 2021
Cited by 41 | Viewed by 4438
Abstract
The potential use of novel iron based mineral catalysts as an effective and available material for electrocatalytic oxidation of refractory contaminants by heterogeneous electro-Fenton (HEF) process was studied for the first time. For this purpose, four natural catalysts, namely ilmenite (FeTiO3), [...] Read more.
The potential use of novel iron based mineral catalysts as an effective and available material for electrocatalytic oxidation of refractory contaminants by heterogeneous electro-Fenton (HEF) process was studied for the first time. For this purpose, four natural catalysts, namely ilmenite (FeTiO3), pyrite (FeS2), chromite (FeCr2O4), and chalcopyrite (CuFeS2) were selected as the source of ferrous iron (Fe2+) ions. The catalyst samples were appropriately characterized by X-ray diffraction (XRD) and RAMAN analysis. The degradation kinetics and mineralization rate of 0.2 mM antibiotic cefazolin (CFZ), as a contaminant of emerging concern, were comparatively investigated by HEF using the catalysts mentioned above. The effect of important experimental parameters such as catalysts loading and current on the process efficiency was investigated. Moreover, the performance of these new mineral catalysts was compared in term of CFZ degradation kinetics, mineralization power, mineralization current efficiency and electrical energy consumption. A greater enhancement in degradation/mineralization of CFZ was obtained when using chalcopyrite as the catalyst in HEF. The stability and reusability experiments demonstrated negligible decrease in catalytic activity of chalcopyrite after five consecutive runs. Besides, the rate constant for CFZ oxidation by hydroxyl radicals was estimated according the pseudo-first-order reaction kinetics. The empirical assessment, in addition to economic evaluation, confirmed that iron based mineral catalysts and specifically chalcopyrite could be an appropriate and cost-effective alternative catalyst for HEF due to its high catalytic activity, availability, eco-friendly nature and low energy consumption compared to other synthesized catalysts. Full article
(This article belongs to the Special Issue Green Catalysts: Application to Waste and Groundwater Treatment)
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16 pages, 12086 KiB  
Article
Ordered Mesoporous Carbon as a Support for Palladium-Based Hydrodechlorination Catalysts
by Farzeen Sakina, Carlos Fernandez-Ruiz, Jorge Bedia, Luisa Gomez-Sainero and Richard T. Baker
Catalysts 2021, 11(1), 23; https://doi.org/10.3390/catal11010023 - 28 Dec 2020
Cited by 7 | Viewed by 2576
Abstract
Ordered mesoporous carbon (OMC) was employed as a support for palladium nanoparticles in catalysts for the gas phase hydrodechlorination (HDC) of trichloromethane (TCM). 1 wt% palladium was incorporated using three methods: incipient wetness (IW); a dilute solution (DS) method; and a solid-liquid (SL) [...] Read more.
Ordered mesoporous carbon (OMC) was employed as a support for palladium nanoparticles in catalysts for the gas phase hydrodechlorination (HDC) of trichloromethane (TCM). 1 wt% palladium was incorporated using three methods: incipient wetness (IW); a dilute solution (DS) method; and a solid-liquid (SL) method. The effect of the preparation method on catalyst structure and activity was investigated. Catalyst composition and nanostructure were studied using gas physisorption, high specification transmission electron microscopy and X-ray photoelectron spectroscopy. Catalytic conversion and product selectivities were determined in steady-state activity tests at temperatures between 70 and 300 °C. Two of the catalysts (IW and DS) showed excellent dispersion of fine Pd nanoparticles of average diameter ~2 nm. These materials showed excellent activity for HDC of TCM which compares favourably with the performance reported for Pd on amorphous carbon catalysts. In addition, they showed relatively high selectivities to the more valuable higher hydrocarbons. However, the SL method gave rise to catalysts with larger particles (~3 nm) and a less uniform palladium distribution. This resulted in lower conversion and lower selectivities to higher hydrocarbons and in more severe catalyst deactivation at the highest reaction temperatures. Full article
(This article belongs to the Special Issue Progress in Catalytic Hydrodechlorination)
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30 pages, 11068 KiB  
Review
Biocatalysis with Laccases: An Updated Overview
by Ivan Bassanini, Erica Elisa Ferrandi, Sergio Riva and Daniela Monti
Catalysts 2021, 11(1), 26; https://doi.org/10.3390/catal11010026 - 28 Dec 2020
Cited by 104 | Viewed by 11627
Abstract
Laccases are multicopper oxidases, which have been widely investigated in recent decades thanks to their ability to oxidize organic substrates to the corresponding radicals while producing water at the expense of molecular oxygen. Besides their successful (bio)technological applications, for example, in textile, petrochemical, [...] Read more.
Laccases are multicopper oxidases, which have been widely investigated in recent decades thanks to their ability to oxidize organic substrates to the corresponding radicals while producing water at the expense of molecular oxygen. Besides their successful (bio)technological applications, for example, in textile, petrochemical, and detoxifications/bioremediations industrial processes, their synthetic potentialities for the mild and green preparation or selective modification of fine chemicals are of outstanding value in biocatalyzed organic synthesis. Accordingly, this review is focused on reporting and rationalizing some of the most recent and interesting synthetic exploitations of laccases. Applications of the so-called laccase-mediator system (LMS) for alcohol oxidation are discussed with a focus on carbohydrate chemistry and natural products modification as well as on bio- and chemo-integrated processes. The laccase-catalyzed Csp2-H bonds activation via monoelectronic oxidation is also discussed by reporting examples of enzymatic C-C and C-O radical homo- and hetero-couplings, as well as of aromatic nucleophilic substitutions of hydroquinones or quinoids. Finally, the laccase-initiated domino/cascade synthesis of valuable aromatic (hetero)cycles, elegant strategies widely documented in the literature across more than three decades, is also presented. Full article
(This article belongs to the Special Issue Industrial Biocatalysis: Challenges and Opportunities)
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26 pages, 2793 KiB  
Review
Direct Electrochemical Enzyme Electron Transfer on Electrodes Modified by Self-Assembled Molecular Monolayers
by Xiaomei Yan, Jing Tang, David Tanner, Jens Ulstrup and Xinxin Xiao
Catalysts 2020, 10(12), 1458; https://doi.org/10.3390/catal10121458 - 14 Dec 2020
Cited by 35 | Viewed by 6743
Abstract
Self-assembled molecular monolayers (SAMs) have long been recognized as crucial “bridges” between redox enzymes and solid electrode surfaces, on which the enzymes undergo direct electron transfer (DET)—for example, in enzymatic biofuel cells (EBFCs) and biosensors. SAMs possess a wide range of terminal groups [...] Read more.
Self-assembled molecular monolayers (SAMs) have long been recognized as crucial “bridges” between redox enzymes and solid electrode surfaces, on which the enzymes undergo direct electron transfer (DET)—for example, in enzymatic biofuel cells (EBFCs) and biosensors. SAMs possess a wide range of terminal groups that enable productive enzyme adsorption and fine-tuning in favorable orientations on the electrode. The tunneling distance and SAM chain length, and the contacting terminal SAM groups, are the most significant controlling factors in DET-type bioelectrocatalysis. In particular, SAM-modified nanostructured electrode materials have recently been extensively explored to improve the catalytic activity and stability of redox proteins immobilized on electrochemical surfaces. In this report, we present an overview of recent investigations of electrochemical enzyme DET processes on SAMs with a focus on single-crystal and nanoporous gold electrodes. Specifically, we consider the preparation and characterization methods of SAMs, as well as SAM applications in promoting interfacial electrochemical electron transfer of redox proteins and enzymes. The strategic selection of SAMs to accord with the properties of the core redox protein/enzymes is also highlighted. Full article
(This article belongs to the Special Issue Enzymatic Bioelectrocatalysis)
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15 pages, 5918 KiB  
Article
Photocatalytic Degradation of Quinoline Yellow over Ag3PO4
by Asma Tab, Mohamed Dahmane, Belabed Chemseddin, Bachir Bellal, Mohamed Trari and Claire Richard
Catalysts 2020, 10(12), 1461; https://doi.org/10.3390/catal10121461 - 14 Dec 2020
Cited by 16 | Viewed by 3567
Abstract
In this study, the ability of Ag3PO4 to achieve the photocatalytic degradation of quinoline yellow (QY) a hazardous and recalcitrant dye, under UVA and visible light was investigated. The photocatalyst Ag3PO4 was synthesized through a precipitation method, [...] Read more.
In this study, the ability of Ag3PO4 to achieve the photocatalytic degradation of quinoline yellow (QY) a hazardous and recalcitrant dye, under UVA and visible light was investigated. The photocatalyst Ag3PO4 was synthesized through a precipitation method, and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), BET Brunauer–Emmett-Teller (BET) analysis, UV-Differential Reflectance Spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR). Ag3PO4 could successfully induce the photocatalytic degradation of QY under UVA and visible light. Optimal parameters were 0.5 g·L−1 of the catalyst, 20 ppm of QY and pH~7. Ag3PO4 was 1.6-times more efficient than TiO2 Degussa P25 under UVA light in degrading QY. Total organic carbon (TOC) analyses confirmed the almost complete QY mineralization. At least eight intermediate degradation products were identified by liquid chromatography coupled to high resolution mass spectrometry. The stability of Ag3PO4 was satisfactory as less than 5% Ag metal appeared in XRD analyses after 3 reuse cycles. These results show that under optimized conditions Ag3PO4 can efficiently achieve quinolone yellow mineralization. Full article
(This article belongs to the Special Issue Understanding the Molecular Mechanisms of Photocatalysis)
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21 pages, 2969 KiB  
Review
One-Step Catalytic or Photocatalytic Oxidation of Benzene to Phenol: Possible Alternative Routes for Phenol Synthesis?
by Antonietta Mancuso, Olga Sacco, Diana Sannino, Vincenzo Venditto and Vincenzo Vaiano
Catalysts 2020, 10(12), 1424; https://doi.org/10.3390/catal10121424 - 5 Dec 2020
Cited by 47 | Viewed by 15983
Abstract
Phenol is an important chemical compound since it is a precursor of the industrial production of many materials and useful compounds. Nowadays, phenol is industrially produced from benzene by the multi-step “cumene process”, which is energy consuming due to high temperature and high [...] Read more.
Phenol is an important chemical compound since it is a precursor of the industrial production of many materials and useful compounds. Nowadays, phenol is industrially produced from benzene by the multi-step “cumene process”, which is energy consuming due to high temperature and high pressure. Moreover, in the “cumene process”, the highly explosive cumene hydroperoxide is produced as an intermediate. To overcome these disadvantages, it would be useful to develop green alternatives for the synthesis of phenol that are more efficient and environmentally benign. In this regard, great interest is devoted to processes in which the one-step oxidation of benzene to phenol is achieved, thanks to the use of suitable catalysts and oxidant species. This review article discusses the direct oxidation of benzene to phenol in the liquid phase using different catalyst formulations, including homogeneous and heterogeneous catalysts and photocatalysts, and focuses on the reaction mechanisms involved in the selective conversion of benzene to phenol in the liquid phase. Full article
(This article belongs to the Section Photocatalysis)
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46 pages, 5156 KiB  
Review
Photocatalytic TiO2-Based Nanostructured Materials for Microbial Inactivation
by Ilaria De Pasquale, Chiara Lo Porto, Massimo Dell’Edera, Francesca Petronella, Angela Agostiano, Maria Lucia Curri and Roberto Comparelli
Catalysts 2020, 10(12), 1382; https://doi.org/10.3390/catal10121382 - 26 Nov 2020
Cited by 58 | Viewed by 8915
Abstract
Pathogenic microorganisms can spread throughout the world population, as the current COVID-19 pandemic has dramatically demonstrated. In this scenario, a protection against pathogens and other microorganisms can come from the use of photoactive materials as antimicrobial agents able to hinder, or at least [...] Read more.
Pathogenic microorganisms can spread throughout the world population, as the current COVID-19 pandemic has dramatically demonstrated. In this scenario, a protection against pathogens and other microorganisms can come from the use of photoactive materials as antimicrobial agents able to hinder, or at least limit, their spreading by means of photocatalytically assisted processes activated by light—possibly sunlight—promoting the formation of reactive oxygen species (ROS) that can kill microorganisms in different matrices such as water or different surfaces without affecting human health. In this review, we focus the attention on TiO2 nanoparticle-based antimicrobial materials, intending to provide an overview of the most promising synthetic techniques, toward possible large-scale production, critically review the capability of such materials to promote pathogen (i.e., bacteria, virus, and fungi) inactivation, and, finally, take a look at selected technological applications. Full article
(This article belongs to the Section Photocatalysis)
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14 pages, 3780 KiB  
Article
New Approach to Synthesis of Tetralin via Naphthalene Hydrogenation in Supercritical Conditions Using Polymer-Stabilized Pt Nanoparticles
by Alexey V. Bykov, Daria V. Alekseeva, Galina N. Demidenko, Alexandre L. Vasiliev, Linda Nikoshvili and Lioubov Kiwi-Minsker
Catalysts 2020, 10(11), 1362; https://doi.org/10.3390/catal10111362 - 23 Nov 2020
Cited by 19 | Viewed by 4132
Abstract
Supercritical (SC) fluid technologies are well-established methods in modern green chemical synthesis. Using SC fluids as solvents instead of traditional liquids gives benefits of higher diffusivity and lower viscosity, which allows mass transfer intensification and, thus, an increased production rate of chemical transformations. [...] Read more.
Supercritical (SC) fluid technologies are well-established methods in modern green chemical synthesis. Using SC fluids as solvents instead of traditional liquids gives benefits of higher diffusivity and lower viscosity, which allows mass transfer intensification and, thus, an increased production rate of chemical transformations. Therefore, a conjugation of heterogeneous catalysis with SC media is a large step toward a green chemistry. Tetralin (TL) is an important hydrogen donor solvent used for biomass liquefaction. In industry, TL is obtained via catalytic hydrogenation of naphthalene (NL). Herein, for the first time we have demonstrated the NL hydrogenation with close to 100% selectivity to TL at almost full conversion in the SC hexane. The observed transformation rates in SC hexane were much higher allowing process intensification. The downstream processes can be also facilitated since hexane after depressurisation can be easily separated from the reaction products via simple rectification. The TL synthesis was studied in a batch reactor at variation of reaction temperature and overall pressure. For the first time for this process, low Pt-loaded (1 wt.%) nanoparticles stabilized within hyper-cross-linked aromatic polymer (HAP) were applied. The Pt/HAP catalyst was stable under reaction conditions (250 °C, 6 MPa) allowing its recovery and reuse. Full article
(This article belongs to the Special Issue Heterogeneous Catalysis in Green Chemistry)
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13 pages, 4881 KiB  
Article
Efficient Photocatalytic CO2 Reduction with MIL-100(Fe)-CsPbBr3 Composites
by Ruolin Cheng, Elke Debroye, Johan Hofkens and Maarten B. J. Roeffaers
Catalysts 2020, 10(11), 1352; https://doi.org/10.3390/catal10111352 - 20 Nov 2020
Cited by 33 | Viewed by 5074
Abstract
Bromide-based metal halide perovskites (MHPs) are promising photocatalysts with strong blue-green light absorption. Composite photocatalysts of MHPs with MIL-100(Fe), as a powerful photocatalyst itself, have been investigated to extend the responsiveness towards red light. The composites, with a high specific surface area, display [...] Read more.
Bromide-based metal halide perovskites (MHPs) are promising photocatalysts with strong blue-green light absorption. Composite photocatalysts of MHPs with MIL-100(Fe), as a powerful photocatalyst itself, have been investigated to extend the responsiveness towards red light. The composites, with a high specific surface area, display an enhanced solar light response, and the improved charge carrier separation in the heterojunctions is employed to maximize the photocatalytic performance. Optimization of the relative composition, with the formation of a dual-phase CsPbBr3 to CsPb2Br5 perovskite composite, shows an excellent photocatalytic performance with 20.4 μmol CO produced per gram of photocatalyst during one hour of visible light irradiation. Full article
(This article belongs to the Special Issue MOFs for Advanced Applications)
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38 pages, 3393 KiB  
Review
Visible-Light Photocatalysts and Their Perspectives for Building Photocatalytic Membrane Reactors for Various Liquid Phase Chemical Conversions
by Raffaele Molinari, Cristina Lavorato and Pietro Argurio
Catalysts 2020, 10(11), 1334; https://doi.org/10.3390/catal10111334 - 17 Nov 2020
Cited by 83 | Viewed by 9348
Abstract
Photocatalytic organic synthesis/conversions and water treatment under visible light are a challenging task to use renewable energy in chemical transformations. In this review a brief overview on the mainly employed visible light photocatalysts and a discussion on the problems and advantages of Vis-light [...] Read more.
Photocatalytic organic synthesis/conversions and water treatment under visible light are a challenging task to use renewable energy in chemical transformations. In this review a brief overview on the mainly employed visible light photocatalysts and a discussion on the problems and advantages of Vis-light versus UV-light irradiation is reported. Visible light photocatalysts in the photocatalytic conversion of CO2, conversion of acetophenone to phenylethanol, hydrogenation of nitro compounds, oxidation of cyclohexane, synthesis of vanillin and phenol, as well as hydrogen production and water treatment are discussed. Some applications of these photocatalysts in photocatalytic membrane reactors (PMRs) for carrying out organic synthesis, conversion and/or degradation of organic pollutants are reported. The described cases show that PMRs represent a promising green technology that could shift on applications of industrial interest using visible light (from Sun) active photocatalysts. Full article
(This article belongs to the Special Issue Photocatalytic Synthesis)
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26 pages, 6334 KiB  
Review
Some Critical Insights into the Synthesis and Applications of Hydrophobic Solid Catalysts
by Denise Cavuoto, Federica Zaccheria and Nicoletta Ravasio
Catalysts 2020, 10(11), 1337; https://doi.org/10.3390/catal10111337 - 17 Nov 2020
Cited by 28 | Viewed by 5224
Abstract
The preparation methods of hydrophobic materials such as zeolites, modified silicas and polymers has been reviewed. Particular attention has been paid to the characterization methods classified according to the surface and bulk composition, on one hand, and to the measure of interactions with [...] Read more.
The preparation methods of hydrophobic materials such as zeolites, modified silicas and polymers has been reviewed. Particular attention has been paid to the characterization methods classified according to the surface and bulk composition, on one hand, and to the measure of interactions with water or organic solvents, on the other. Some selected applications are analyzed in order to understand the relevance of the reactants/products adsorption to address activity and selectivity of the reaction. Thus, absorption of a non-polar reactant or desorption of a hydrophilic product are much easier on a hydrophobic surface and can effectively boost the catalytic activity. Full article
(This article belongs to the Section Catalytic Materials)
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38 pages, 4628 KiB  
Review
Nanostructured Anodic Copper Oxides as Catalysts in Electrochemical and Photoelectrochemical Reactions
by Damian Giziński, Anna Brudzisz, Janaina S. Santos, Francisco Trivinho-Strixino, Wojciech J. Stępniowski and Tomasz Czujko
Catalysts 2020, 10(11), 1338; https://doi.org/10.3390/catal10111338 - 17 Nov 2020
Cited by 39 | Viewed by 7839
Abstract
Recently, nanostructured copper oxides formed via anodizing have been intensively researched due to their potential catalytic applications in emerging issues. The anodic Cu2O and CuO nanowires or nanoneedles are attractive photo- and electrocatalysts since they show wide array of desired electronic [...] Read more.
Recently, nanostructured copper oxides formed via anodizing have been intensively researched due to their potential catalytic applications in emerging issues. The anodic Cu2O and CuO nanowires or nanoneedles are attractive photo- and electrocatalysts since they show wide array of desired electronic and morphological features, such as highly-developed surface area. In CO2 electrochemical reduction reaction (CO2RR) copper and copper-based nanostructures indicate unique adsorption properties to crucial reaction intermediates. Furthermore, anodized copper-based materials enable formation of C2+ hydrocarbons and alcohols with enhanced selectivity. Moreover, anodic copper oxides provide outstanding turnover frequencies in electrochemical methanol oxidation at lowered overpotentials. Therefore, they can be considered as precious metals electrodes substituents in direct methanol fuel cells. Additionally, due to the presence of Cu(III)/Cu(II) redox couple, these materials find application as electrodes for non-enzymatic glucose sensors. In photoelectrochemistry, Cu2O-CuO heterostructures of anodic copper oxides with highly-developed surface area are attractive for water splitting. All the above-mentioned aspects of anodic copper oxides derived catalysts with state-of-the-art background have been reviewed within this paper. Full article
(This article belongs to the Special Issue Porous Materials for Photocatalysis and Energy)
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33 pages, 6659 KiB  
Review
Fe-Exchanged Small-Pore Zeolites as Ammonia Selective Catalytic Reduction (NH3-SCR) Catalysts
by Feng Gao
Catalysts 2020, 10(11), 1324; https://doi.org/10.3390/catal10111324 - 14 Nov 2020
Cited by 47 | Viewed by 5590
Abstract
Cu-exchanged small-pore zeolites have been extensively studied in the past decade as state-of-the-art selective catalytic reduction (SCR) catalysts for diesel engine exhaust NOx abatement for the transportation industry. During this time, Fe-exchanged small-pore zeolites, e.g., Fe/SSZ-13, Fe/SAPO-34, Fe/SSZ-39 and high-silica Fe/LTA, have also [...] Read more.
Cu-exchanged small-pore zeolites have been extensively studied in the past decade as state-of-the-art selective catalytic reduction (SCR) catalysts for diesel engine exhaust NOx abatement for the transportation industry. During this time, Fe-exchanged small-pore zeolites, e.g., Fe/SSZ-13, Fe/SAPO-34, Fe/SSZ-39 and high-silica Fe/LTA, have also been investigated but much less extensively. In comparison to their Cu-exchanged counterparts, such Fe/zeolite catalysts display inferior low-temperature activities, but improved stability and high-temperature SCR selectivities. Such characteristics entitle these catalysts to be considered as key components of highly efficient emission control systems to improve the overall catalyst performance. In this short review, recent studies on Fe-exchanged small-pore zeolite SCR catalysts are summarized, including (1) the synthesis of small-pore Fe/zeolites; (2) nature of the SCR active Fe species in these catalysts as determined by experimental and theoretical approaches, including Fe species transformation during hydrothermal aging; (3) SCR reactions and structure-function correlations; and (4) a few aspects on industrial applications. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction: From Basic Science to deNOx Applications)
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50 pages, 2428 KiB  
Review
Rhizopus oryzae Lipase, a Promising Industrial Enzyme: Biochemical Characteristics, Production and Biocatalytic Applications
by Josu López-Fernández, M. Dolors Benaiges and Francisco Valero
Catalysts 2020, 10(11), 1277; https://doi.org/10.3390/catal10111277 - 3 Nov 2020
Cited by 60 | Viewed by 11853
Abstract
Lipases are biocatalysts with a significant potential to enable a shift from current pollutant manufacturing processes to environmentally sustainable approaches. The main reason of this prospect is their catalytic versatility as they carry out several industrially relevant reactions as hydrolysis of fats in [...] Read more.
Lipases are biocatalysts with a significant potential to enable a shift from current pollutant manufacturing processes to environmentally sustainable approaches. The main reason of this prospect is their catalytic versatility as they carry out several industrially relevant reactions as hydrolysis of fats in water/lipid interface and synthesis reactions in solvent-free or non-aqueous media such as transesterification, interesterification and esterification. Because of the outstanding traits of Rhizopus oryzae lipase (ROL), 1,3-specificity, high enantioselectivity and stability in organic media, its application in energy, food and pharmaceutical industrial sector has been widely studied. Significant advances have been made in the biochemical characterisation of ROL particularly in how its activity and stability are affected by the presence of its prosequence. In addition, native and heterologous production of ROL, the latter in cell factories like Escherichia coli, Saccharomyces cerevisiae and Komagataella phaffii (Pichia pastoris), have been thoroughly described. Therefore, in this review, we summarise the current knowledge about R. oryzae lipase (i) biochemical characteristics, (ii) production strategies and (iii) potential industrial applications. Full article
(This article belongs to the Section Biocatalysis)
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41 pages, 3338 KiB  
Review
Recent Advances in Glycerol Catalytic Valorization: A Review
by Manuel Checa, Sergio Nogales-Delgado, Vicente Montes and José María Encinar
Catalysts 2020, 10(11), 1279; https://doi.org/10.3390/catal10111279 - 3 Nov 2020
Cited by 136 | Viewed by 11558
Abstract
Once a biorefinery is ready to operate, the main processed materials need to be completely evaluated in terms of many different factors, including disposal regulations, technological limitations of installation, the market, and other societal considerations. In biorefinery, glycerol is the main by-product, representing [...] Read more.
Once a biorefinery is ready to operate, the main processed materials need to be completely evaluated in terms of many different factors, including disposal regulations, technological limitations of installation, the market, and other societal considerations. In biorefinery, glycerol is the main by-product, representing around 10% of biodiesel production. In the last few decades, the large-scale production of biodiesel and glycerol has promoted research on a wide range of strategies in an attempt to valorize this by-product, with its transformation into added value chemicals being the strategy that exhibits the most promising route. Among them, C3 compounds obtained from routes such as hydrogenation, oxidation, esterification, etc. represent an alternative to petroleum-based routes for chemicals such as acrolein, propanediols, or carboxylic acids of interest for the polymer industry. Another widely studied and developed strategy includes processes such as reforming or pyrolysis for energy, clean fuels, and materials such as activated carbon. This review covers recent advances in catalysts used in the most promising strategies considering both chemicals and energy or fuel obtention. Due to the large variety in biorefinery industries, several potential emergent valorization routes are briefly summarized. Full article
(This article belongs to the Special Issue Catalytic Valorization of Glycerol: Strategies and Perspectives)
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19 pages, 4906 KiB  
Review
Recent Advances in Enzymatic and Chemoenzymatic Cascade Processes
by Noelia Losada-Garcia, Zaida Cabrera, Paulina Urrutia, Carla Garcia-Sanz, Alicia Andreu and Jose M. Palomo
Catalysts 2020, 10(11), 1258; https://doi.org/10.3390/catal10111258 - 30 Oct 2020
Cited by 40 | Viewed by 7004
Abstract
Cascade reactions have been described as efficient and universal tools, and are of substantial interest in synthetic organic chemistry. This review article provides an overview of the novel and recent achievements in enzyme cascade processes catalyzed by multi-enzymatic or chemoenzymatic systems. The examples [...] Read more.
Cascade reactions have been described as efficient and universal tools, and are of substantial interest in synthetic organic chemistry. This review article provides an overview of the novel and recent achievements in enzyme cascade processes catalyzed by multi-enzymatic or chemoenzymatic systems. The examples here selected collect the advances related to the application of the sequential use of enzymes in natural or genetically modified combination; second, the important combination of enzymes and metal complex systems, and finally we described the application of biocatalytic biohybrid systems on in situ catalytic solid-phase as a novel strategy. Examples of efficient and interesting enzymatic catalytic cascade processes in organic chemistry, in the production of important industrial products, such as the designing of novel biosensors or bio-chemocatalytic systems for medicinal chemistry application, are discussed Full article
(This article belongs to the Special Issue Enzymes in Sustainable Chemistry)
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11 pages, 1818 KiB  
Article
Carbon Nitride-Perovskite Composites: Evaluation and Optimization of Photocatalytic Hydrogen Evolution in Saccharides Aqueous Solution
by Andrea Speltini, Lidia Romani, Daniele Dondi, Lorenzo Malavasi and Antonella Profumo
Catalysts 2020, 10(11), 1259; https://doi.org/10.3390/catal10111259 - 30 Oct 2020
Cited by 30 | Viewed by 3508
Abstract
The application of hybrid photocatalysts made of carbon nitride and lead-free perovskites, namely DMASnBr3/g-C3N4 and PEA2SnBr4/g-C3N4, for the H2 evolution from saccharides aqueous solution is described. The novel composites [...] Read more.
The application of hybrid photocatalysts made of carbon nitride and lead-free perovskites, namely DMASnBr3/g-C3N4 and PEA2SnBr4/g-C3N4, for the H2 evolution from saccharides aqueous solution is described. The novel composites were tested and compared in terms of hydrogen evolution rate (HER) under simulated solar light, using Pt as a reference co-catalyst, and glucose as a representative sacrificial biomass. The conditions were optimized to maximize H2 generation by a design of experiments involving catalyst amount, glucose concentration and Pt loading. For both materials, such parameters affected significantly H2 photogeneration, with the best performance observed using 0.5 g L−1 catalyst, 0.2 M glucose and 0.5 wt% Pt. Under optimized conditions, DMASnBr3/g-C3N4 showed a 5-fold higher HER compared to PEA2SnBr4/g-C3N4, i.e., 925 µmoles g−1 h−1 and 190 µmoles g−1 h−1, respectively (RSD ≤ 11%, n = 4). The former composite, which affords an HER 15-fold higher in aqueous glucose than in neat water, provided H2 also with no metal co-catalyst (around 140 µmoles g−1 h−1), and it was reusable for at least three photoreactions. Encouraging results were also collected by explorative tests on raw starch solution (around 150 µmoles g−1 h−1). Full article
(This article belongs to the Special Issue Towards Green, Enhanced Photocatalysts for Hydrogen Evolution)
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20 pages, 1892 KiB  
Review
Heterogeneous Catalysis with the Participation of Ionic Liquids
by Olga Bartlewicz, Izabela Dąbek, Anna Szymańska and Hieronim Maciejewski
Catalysts 2020, 10(11), 1227; https://doi.org/10.3390/catal10111227 - 22 Oct 2020
Cited by 61 | Viewed by 6399
Abstract
This mini-review briefly describes the recent progress in the design and development of catalysts based on the presence of ionic liquids. In particular, the focus was on heterogeneous systems (supported ionic liquid (IL) phase catalysts (SILPC), solid catalysts with ILs (SCILL), porous liquids), [...] Read more.
This mini-review briefly describes the recent progress in the design and development of catalysts based on the presence of ionic liquids. In particular, the focus was on heterogeneous systems (supported ionic liquid (IL) phase catalysts (SILPC), solid catalysts with ILs (SCILL), porous liquids), which due to the low amounts of ionic liquids needed for their production, eliminate basic problems observed in the case of the employment of ionic liquids in homogeneous systems, such as high price, high viscosity, and efficient isolation from post-reaction mixtures. Full article
(This article belongs to the Special Issue Ionic Liquids in Catalysis)
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61 pages, 1805 KiB  
Review
Direct Alcoholysis of Carbohydrate Precursors and Real Cellulosic Biomasses to Alkyl Levulinates: A Critical Review
by Anna Maria Raspolli Galletti, Claudia Antonetti, Sara Fulignati and Domenico Licursi
Catalysts 2020, 10(10), 1221; https://doi.org/10.3390/catal10101221 - 21 Oct 2020
Cited by 47 | Viewed by 5324
Abstract
Alkyl levulinates (ALs) represent outstanding bio-fuels and strategic bio-products within the context of the marketing of levulinic acid derivatives. However, their synthesis by acid-catalyzed esterification of pure levulinic acid, or by acid-catalyzed alcoholysis of furfuryl alcohol, although relatively simple, is still economically disadvantageous, [...] Read more.
Alkyl levulinates (ALs) represent outstanding bio-fuels and strategic bio-products within the context of the marketing of levulinic acid derivatives. However, their synthesis by acid-catalyzed esterification of pure levulinic acid, or by acid-catalyzed alcoholysis of furfuryl alcohol, although relatively simple, is still economically disadvantageous, due to the high costs of the pure precursors. The direct one-pot alcoholysis of model C6 carbohydrates and raw biomass represents an alternative approach for the one-step synthesis of ALs. In order to promote the market for these bio-products and, concurrently, the immediate development of new applications, it is necessary to speed up the intensification of their production processes, and this important achievement is onlypossible by using low-cost or, even better, waste biomasses, as starting feedstocks. This review provides an overview of the most recent and promising advances on the one-pot production of ALs from model C6 carbohydrates and real biomasses, in the presence of homogeneous or heterogeneous acid catalysts. The use of model C6 carbohydrates allows for the identification of the best obtainable ALs yields, resulting in being strategic for the development of new smart catalysts, whose chemical properties must be properly tuned, taking into account the involved reaction mechanism. On the other hand, the transition to the real biomass now represents a necessary choice for allowing the next ALs production on a larger scale. The improvement of the available synthetic strategies, the use of raw materials and the development of new applications for ALs will contribute to develop more intensified, greener, and sustainable processes. Full article
(This article belongs to the Section Biomass Catalysis)
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35 pages, 4679 KiB  
Review
Gold-Catalyzed Intermolecular Alkyne Hydrofunctionalizations—Mechanistic Insights
by Chin Hin Leung, Marco Baron and Andrea Biffis
Catalysts 2020, 10(10), 1210; https://doi.org/10.3390/catal10101210 - 19 Oct 2020
Cited by 49 | Viewed by 7067
Abstract
An overview of the current state of mechanistic understanding of gold-catalyzed intermolecular alkyne hydrofunctionalization reactions is presented. Moving from the analysis of the main features of the by-now-generally accepted reaction mechanism, studies and evidences pointing out the mechanistic peculiarities of these reactions using [...] Read more.
An overview of the current state of mechanistic understanding of gold-catalyzed intermolecular alkyne hydrofunctionalization reactions is presented. Moving from the analysis of the main features of the by-now-generally accepted reaction mechanism, studies and evidences pointing out the mechanistic peculiarities of these reactions using different nucleophiles HNu that add to the alkyne triple bond are presented and discussed. The effects of the nature of the employed alkyne substrate and of the gold catalyst (employed ligands, counteranions, gold oxidation state), of additional additives and of the reaction conditions are also considered. Aim of this work is to provide the reader with a detailed mechanistic knowledge of this important reaction class, which will be invaluable for rapidly developing and optimizing synthetic protocols involving a gold-catalyzed alkyne hydrofunctionalization as a reaction step. Full article
(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)
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36 pages, 12381 KiB  
Review
Gold-Catalyzed Addition of Carboxylic Acids to Alkynes and Allenes: Valuable Tools for Organic Synthesis
by Victorio Cadierno
Catalysts 2020, 10(10), 1206; https://doi.org/10.3390/catal10101206 - 18 Oct 2020
Cited by 26 | Viewed by 6381
Abstract
In this contribution, the application of gold-based catalysts in the hydrofunctionalization reactions of alkynes and allenes with carboxylic acids is comprehensively reviewed. Both intra- and intermolecular processes, leading respectively to lactones and linear unsaturated esters, are covered. In addition, cascade transformations involving the [...] Read more.
In this contribution, the application of gold-based catalysts in the hydrofunctionalization reactions of alkynes and allenes with carboxylic acids is comprehensively reviewed. Both intra- and intermolecular processes, leading respectively to lactones and linear unsaturated esters, are covered. In addition, cascade transformations involving the initial cycloisomerization of an alkynoic acid are also discussed. Full article
(This article belongs to the Special Issue Recent Advances in Organometallic Chemistry and Catalysis)
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18 pages, 49862 KiB  
Article
Mono vs. Difunctional Coumarin as Photoinitiators in Photocomposite Synthesis and 3D Printing
by Mahmoud Rahal, Haifaa Mokbel, Bernadette Graff, Joumana Toufaily, Tayssir Hamieh, Frédéric Dumur and Jacques Lalevée
Catalysts 2020, 10(10), 1202; https://doi.org/10.3390/catal10101202 - 17 Oct 2020
Cited by 37 | Viewed by 3890
Abstract
This work is devoted to investigate three coumarin derivatives (Coum1, Coum2, and Coum3), proposed as new photoinitiators of polymerization when combined with an additive, i.e., an iodonium salt, and used for the free radical polymerization (FRP) of acrylate monomers under mild irradiation conditions. [...] Read more.
This work is devoted to investigate three coumarin derivatives (Coum1, Coum2, and Coum3), proposed as new photoinitiators of polymerization when combined with an additive, i.e., an iodonium salt, and used for the free radical polymerization (FRP) of acrylate monomers under mild irradiation conditions. The different coumarin derivatives can also be employed in three component photoinitiating systems with a Iod/amine (ethyl 4-dimethylaminobenzoate (EDB) or N-phenylglycine (NPG)) couple for FRP upon irradiation with an LED @ 405 nm. These compounds showed excellent photoinitiating abilities, and high polymerization rates and final conversions (FC) were obtained. The originality of this work relies on the comparison of the photoinitiating abilities of monofunctional (Coum1 and Coum2) vs. difunctional (Coum3) compounds. Coum3 is a combined structure of Coum1 and Coum2, leading to a sterically hindered chemical structure with a relatively high molecular weight. As a general rule, a high molecular weight should reduce the migration of initiating molecules and favor photochemical properties such as photobleaching of the final polymer. As attempted, from the efficiency point of view, Coum3 can initiate the FRP, but a low reactivity was observed compared to the monofunctional compound (Coum1 and Coum2). Indeed, to study the photochemical and photophysical properties of these compounds, different parameters were taken into account, e.g., the light absorption and emission properties, steady state photolysis, and fluorescence quenching. To examine these different points, several techniques were used including UV-visible spectroscopy, real-time Fourier Transform Infrared Spectroscopy (RT-FTIR), fluorescence spectroscopy, and cyclic voltammetry. The photochemical mechanism involved in the polymerization process is also detailed. The best coumarins investigated in this work were used for laser writing (3D printing) experiments and also for photocomposite synthesis containing glass fibers. Full article
(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)
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20 pages, 5718 KiB  
Article
Novel Push–Pull Dyes Derived from 1H-cyclopenta[b]naphthalene-1,3(2H)-dione as Versatile Photoinitiators for Photopolymerization and Their Related Applications: 3D Printing and Fabrication of Photocomposites
by Ke Sun, Shaohui Liu, Corentin Pigot, Damien Brunel, Bernadette Graff, Malek Nechab, Didier Gigmes, Fabrice Morlet-Savary, Yijun Zhang, Pu Xiao, Frédéric Dumur and Jacques Lalevée
Catalysts 2020, 10(10), 1196; https://doi.org/10.3390/catal10101196 - 15 Oct 2020
Cited by 41 | Viewed by 3552
Abstract
A series of eleven push–pull chromophores with specific structures have been designed for the free radical polymerization of acrylates, but also for the fabrication of photocomposites and 3D-printed structures. New photoinitiating systems comprising the different push–pull dyes showed excellent photochemical reactivities at 405 [...] Read more.
A series of eleven push–pull chromophores with specific structures have been designed for the free radical polymerization of acrylates, but also for the fabrication of photocomposites and 3D-printed structures. New photoinitiating systems comprising the different push–pull dyes showed excellent photochemical reactivities at 405 nm. Notably, polymerization reactions could be initiated with light-emitting diodes (LEDs) which constitute a unique opportunity to promote the free radical polymerization under mild conditions, i.e., low light intensity (e.g., sunlight) and under air. Photopolymerization is an active research field, and push–pull dyes have already been investigated for this purpose. Besides, it remains of crucial interest to investigate new reactive structures capable of efficiently initiating photopolymerization reactions. The plausible potential of these structures to act as efficient photoinitiators in vat photopolymerization (or 3D printing) and fabrication of photocomposites prompts us to select eleven new push–pull dyes to design multi-component photoinitiating systems activable with LEDs emitting at 405 nm. Precisely, a tertiary amine, i.e., ethyl dimethylaminobenzoate (EDB) used as an electron/hydrogen donor and an iodonium salt used as an electron acceptor were selected to behave as powerful co-initiators to construct three-component photoinitiating systems (PISs) with the different push–pull dyes. Among these new PISs, dye 8 and 9-based PISs could efficiently promote the free radical photopolymerization of acrylates upon exposure to a LED emitting at 405 nm also upon sunlight irradiation, highlighting their huge performance. Photoinitiating abilities could be explained on the basis of steady state photolysis experiments. Fluorescence measurements and electron spin resonance (ESR) spin-trapping experiments were also performed to obtain a deeper insight into the chemical mechanisms supporting the polymerization reaction and determine the way the initiating species, i.e., the radicals, are observed. Finally, two investigated dye-based PISs were applied to the fabrications of photocomposites. Three-dimensional patterns with excellent spatial resolutions were generated by the laser writing technique to identify the effects of photopolymerization of acrylates both in the absence and presence of fillers (silica). Interestingly, comparison between the 3D objects fabricated by the PISs/monomer systems and the PISs/monomer/filler photocomposites indicates that the newly designed photocomposites are suitable for practical applications. Full article
(This article belongs to the Special Issue Progression in Photocatalytic Materials for Efficient Performance)
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38 pages, 5124 KiB  
Review
Doping of Graphitic Carbon Nitride with Non-Metal Elements and Its Applications in Photocatalysis
by Halyna Starukh and Petr Praus
Catalysts 2020, 10(10), 1119; https://doi.org/10.3390/catal10101119 - 28 Sep 2020
Cited by 123 | Viewed by 14008
Abstract
This review outlines the latest research into the design of graphitic carbon nitride (g-C3N4) with non-metal elements. The emphasis is put on modulation of composition and morphology of g-C3N4 doped with oxygen, sulfur, phosphor, nitrogen, carbon [...] Read more.
This review outlines the latest research into the design of graphitic carbon nitride (g-C3N4) with non-metal elements. The emphasis is put on modulation of composition and morphology of g-C3N4 doped with oxygen, sulfur, phosphor, nitrogen, carbon as well as nitrogen and carbon vacancies. Typically, the various methods of non-metal elements introducing in g-C3N4 have been explored to simultaneously tune the textural and electronic properties of g-C3N4 for improving its response to the entire visible light range, facilitating a charge separation, and prolonging a charge carrier lifetime. The application fields of such doped graphitic carbon nitride are summarized into three categories: CO2 reduction, H2-evolution, and organic contaminants degradation. This review shows some main directions and affords to design the g-C3N4 doping with non-metal elements for real photocatalytic applications. Full article
(This article belongs to the Section Catalytic Materials)
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8 pages, 1101 KiB  
Perspective
Heterogeneous Photocatalysis Scalability for Environmental Remediation: Opportunities and Challenges
by Sherif A. Younis and Ki-Hyun Kim
Catalysts 2020, 10(10), 1109; https://doi.org/10.3390/catal10101109 - 25 Sep 2020
Cited by 70 | Viewed by 5358
Abstract
Heterogeneous photocatalysis is an ecofriendly technique for purifying organic pollutants in environmental systems. While pilot-scale photoreactors have explored photocatalytic system upscalibility, their practical implementation is restricted for various reasons. These include feed composition alteration, complicated photoreactor designs, high operation and synthesis costs, photocatalyst [...] Read more.
Heterogeneous photocatalysis is an ecofriendly technique for purifying organic pollutants in environmental systems. While pilot-scale photoreactors have explored photocatalytic system upscalibility, their practical implementation is restricted for various reasons. These include feed composition alteration, complicated photoreactor designs, high operation and synthesis costs, photocatalyst poisoning, low quantum yield under solar irradiation, fast exciton recombination, and low reuse or regeneration capabilities. In this paper, we highlight the photocatalyst scalability challenges for real-world applications. We also provide an in-depth discussion on photocatalyst opportunities for effective air and water pollution control. Lastly, we offer a contemporary perspective on photocatalysis scale-up for the real environmental treatment. Full article
(This article belongs to the Special Issue Innovative Catalytic and Photocatalytic Systems for Environmental Remediation)
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50 pages, 17506 KiB  
Review
Recent Advancements and Future Prospects in Ultrathin 2D Semiconductor-Based Photocatalysts for Water Splitting
by Xiaoyong Yang, Deobrat Singh and Rajeev Ahuja
Catalysts 2020, 10(10), 1111; https://doi.org/10.3390/catal10101111 - 25 Sep 2020
Cited by 55 | Viewed by 7841
Abstract
Ultrathin two-dimensional (2D) semiconductor-mediated photocatalysts have shown their compelling potential and have arguably received tremendous attention in photocatalysis because of their superior thickness-dependent physical, chemical, mechanical and optical properties. Although numerous comprehensions about 2D semiconductor photocatalysts have been amassed up to now, low [...] Read more.
Ultrathin two-dimensional (2D) semiconductor-mediated photocatalysts have shown their compelling potential and have arguably received tremendous attention in photocatalysis because of their superior thickness-dependent physical, chemical, mechanical and optical properties. Although numerous comprehensions about 2D semiconductor photocatalysts have been amassed up to now, low cost efficiency, degradation, kinetics of charge transfer along with recycling are still the big challenges to realize a wide application of 2D semiconductor-based photocatalysis. At present, most photocatalysts still need rare or expensive noble metals to improve the photocatalytic activity, which inhibits their commercial-scale application extremely. Thus, developing less costly, earth-abundant semiconductor-based photocatalysts with efficient conversion of sunlight energy remains the primary challenge. In this review, it begins with a brief description of the general mechanism of overall photocatalytic water splitting. Then a concise overview of different types of 2D semiconductor-mediated photocatalysts is given to figure out the advantages and disadvantages for mentioned semiconductor-based photocatalysis, including the structural property and stability, synthesize method, electrochemical property and optical properties for H2/O2 production half reaction along with overall water splitting. Finally, we conclude this review with a perspective, marked on some remaining challenges and new directions of 2D semiconductor-mediated photocatalysts. Full article
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23 pages, 2763 KiB  
Review
Towards the Green Synthesis of Furfuryl Alcohol in A One-Pot System from Xylose: A Review
by Gerardo Gómez Millán and Herbert Sixta
Catalysts 2020, 10(10), 1101; https://doi.org/10.3390/catal10101101 - 23 Sep 2020
Cited by 33 | Viewed by 7197
Abstract
In the pursuit of establishing a sustainable biobased economy, valorization of lignocellulosic biomass is increasing its value as a feedstock. Nevertheless, to achieve the integrated biorefinery paradigm, the selective fractionation of its complex matrix to its single constituents must be complete. This review [...] Read more.
In the pursuit of establishing a sustainable biobased economy, valorization of lignocellulosic biomass is increasing its value as a feedstock. Nevertheless, to achieve the integrated biorefinery paradigm, the selective fractionation of its complex matrix to its single constituents must be complete. This review presents and examines the novel catalytic pathways to form furfuryl alcohol (FuOH) from xylose in a one-pot system. This production concept takes on chemical, thermochemical and biochemical transformations or a combination of them. Still, the bulk of the research is targeted to develop heterogeneous catalytic systems to synthesize FuOH from furfural and xylose. The present review includes an overview of the economic aspects to produce this platform chemical in an industrial manner. In the last section of this review, an outlook and summary of catalytic processes to produce FuOH are highlighted. Full article
(This article belongs to the Special Issue Recent Advances in Catalytic Sustainable Processes in Biorefineries)
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19 pages, 6794 KiB  
Review
Antiviral Effect of Visible Light-Sensitive CuxO/TiO2 Photocatalyst
by Masahiro Miyauchi, Kayano Sunada and Kazuhito Hashimoto
Catalysts 2020, 10(9), 1093; https://doi.org/10.3390/catal10091093 - 21 Sep 2020
Cited by 68 | Viewed by 12252
Abstract
Photocatalysis is an effective technology for preventing the spread of pandemic-scale viruses. This review paper presents an overview of the recent progress in the development of an efficient visible light-sensitive photocatalyst, i.e., a copper oxide nanoclusters grafted titanium dioxide (CuxO/TiO2 [...] Read more.
Photocatalysis is an effective technology for preventing the spread of pandemic-scale viruses. This review paper presents an overview of the recent progress in the development of an efficient visible light-sensitive photocatalyst, i.e., a copper oxide nanoclusters grafted titanium dioxide (CuxO/TiO2). The antiviral CuxO/TiO2 photocatalyst is functionalised by a different mechanism in addition to the photocatalytic oxidation process. The CuxO nanocluster consists of the valence states of Cu(I) and Cu(II); herein, the Cu(I) species denaturalizes the protein of the virus, thereby resulting in significant antiviral properties even under dark conditions. Moreover, the Cu(II) species in the CuxO nanocluster serves as an electron acceptor through photo-induced interfacial charge transfer, which leads to the formation of an anti-virus Cu(I) species and holes with strong oxidation power in the valence band of TiO2 under visible-light irradiation. The antiviral function of the CuxO/TiO2 photocatalyst is maintained under indoor conditions, where light illumination is enabled during the day but not during the night; this is because the remaining active Cu(I) species works under dark conditions. The CuxO/TiO2 photocatalyst can thus be used to reduce the risk of virus infection by acting as an antiviral coating material. Full article
(This article belongs to the Special Issue Nanomaterials for Photocatalytic Degradation of Organic Pollutants and Inactivation of Microorganisms)
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19 pages, 3087 KiB  
Article
Biocatalysis at Extreme Temperatures: Enantioselective Synthesis of both Enantiomers of Mandelic Acid by Transesterification Catalyzed by a Thermophilic Lipase in Ionic Liquids at 120 °C
by Jesús Ramos-Martín, Oussama Khiari, Andrés R. Alcántara and Jose María Sánchez-Montero
Catalysts 2020, 10(9), 1055; https://doi.org/10.3390/catal10091055 - 14 Sep 2020
Cited by 19 | Viewed by 4142
Abstract
The use of biocatalysts in organic chemistry for catalyzing chemo-, regio- and stereoselective transformations has become an usual tool in the last years, both at lab and industrial scale. This is not only because of their exquisite precision, but also due to the [...] Read more.
The use of biocatalysts in organic chemistry for catalyzing chemo-, regio- and stereoselective transformations has become an usual tool in the last years, both at lab and industrial scale. This is not only because of their exquisite precision, but also due to the inherent increase in the process sustainability. Nevertheless, most of the interesting industrial reactions involve water-insoluble substrates, so the use of (generally not green) organic solvents is generally required. Although lipases are capable of maintaining their catalytic precision working in those solvents, reactions are usually very slow and consequently not very appropriate for industrial purposes. Increasing reaction temperature would accelerate the reaction rate, but this should require the use of lipases from thermophiles, which tend to be more enantioselective at lower temperatures, as they are more rigid than those from mesophiles. Therefore, the ideal scenario would require a thermophilic lipase capable of retaining high enantioselectivity at high temperatures. In this paper, we describe the use of lipase from Geobacillus thermocatenolatus as catalyst in the ethanolysis of racemic 2-(butyryloxy)-2-phenylacetic to furnish both enantiomers of mandelic acid, an useful intermediate in the synthesis of many drugs and active products. The catalytic performance at high temperature in a conventional organic solvent (isooctane) and four imidazolium-based ionic liquids was assessed. The best results were obtained using 1-ethyl-3-methyl imidazolium tetrafluoroborate (EMIMBF4) and 1-ethyl-3-methyl imidazolium hexafluorophosphate (EMIMPF6) at temperatures as high as 120 °C, observing in both cases very fast and enantioselective kinetic resolutions, respectively leading exclusively to the (S) or to the (R)-enantiomer of mandelic acid, depending on the anion component of the ionic liquid. Full article
(This article belongs to the Special Issue Applied Biocatalysis in Europe: A Sustainable Tool for Improving Life Quality)
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11 pages, 2680 KiB  
Review
Carbonic Anhydrases: Versatile and Useful Biocatalysts in Chemistry and Biochemistry
by Andrea Angeli, Fabrizio Carta and Claudiu T. Supuran
Catalysts 2020, 10(9), 1008; https://doi.org/10.3390/catal10091008 - 3 Sep 2020
Cited by 51 | Viewed by 10915
Abstract
Metalloenzymes such as the carbonic anhydrases (CAs, EC 4.2.1.1) possess highly specialized active sites that promote fast reaction rates and high substrate selectivity for the physiologic reaction that they catalyze, hydration of CO2 to bicarbonate and a proton. Among the eight genetic [...] Read more.
Metalloenzymes such as the carbonic anhydrases (CAs, EC 4.2.1.1) possess highly specialized active sites that promote fast reaction rates and high substrate selectivity for the physiologic reaction that they catalyze, hydration of CO2 to bicarbonate and a proton. Among the eight genetic CA macrofamilies, α-CAs possess rather spacious active sites and show catalytic promiscuity, being esterases with many types of esters, but also acting on diverse small molecules such as cyanamide, carbonyl sulfide (COS), CS2, etc. Although artificial CAs have been developed with the intent to efficiently catalyse non-biologically related chemical transformations with high control of stereoselectivity, the activities of these enzymes were much lower when compared to natural CAs. Here, we report an overview on the catalytic activities of α-CAs as well as of enzymes which were mutated or artificially designed by incorporation of transition metal ions. In particular, the distinct catalytic mechanisms of the reductase, oxidase and metatheses-ase such as de novo designed CAs are discussed. Full article
(This article belongs to the Special Issue Synthesis and Catalytic Applications of S-, Se- and Te-Containing Compounds: Recent Advances in Organic Synthesis)
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31 pages, 22767 KiB  
Review
From Alkynes to Heterocycles through Metal-Promoted Silylformylation and Silylcarbocyclization Reactions
by Gianluigi Albano and Laura Antonella Aronica
Catalysts 2020, 10(9), 1012; https://doi.org/10.3390/catal10091012 - 3 Sep 2020
Cited by 15 | Viewed by 4537
Abstract
Oxygen and nitrogen heterocyclic systems are present in a large number of natural and synthetic compounds. In particular, oxa- and aza-silacyclane, tetrahydrofuran, benzofuran, cycloheptadifuranone, cycloheptadipyrrolone, pyrrolidine, lactone, lactam, phthalan, isochromanone, tetrahydroisoquinolinone, benzoindolizidinone, indoline and indolizidine scaffolds are present in many classes of biologically [...] Read more.
Oxygen and nitrogen heterocyclic systems are present in a large number of natural and synthetic compounds. In particular, oxa- and aza-silacyclane, tetrahydrofuran, benzofuran, cycloheptadifuranone, cycloheptadipyrrolone, pyrrolidine, lactone, lactam, phthalan, isochromanone, tetrahydroisoquinolinone, benzoindolizidinone, indoline and indolizidine scaffolds are present in many classes of biologically active molecules. Most of these contain a C=O moiety which can be easily introduced using carbonylative reaction conditions. In this field, intramolecular silylformylation and silylcarbocyclization reactions may afford heterocyclic compounds containing a carbonyl functional group together with a vinylsilane moiety which can be further transformed. Considering these two aspects, in this review a detailed analysis of the literature data regarding the application of silylformylation and silylcarbocyclization reactions to the synthesis of several heterocyclic derivatives is reported. Full article
(This article belongs to the Special Issue Metal Promoted Cyclocarbonylation Reactions in the Synthesis of Heterocycles)
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73 pages, 15140 KiB  
Review
Electrode Materials for Supercapacitors: A Review of Recent Advances
by Parnia Forouzandeh, Vignesh Kumaravel and Suresh C. Pillai
Catalysts 2020, 10(9), 969; https://doi.org/10.3390/catal10090969 - 26 Aug 2020
Cited by 501 | Viewed by 53949
Abstract
The advanced electrochemical properties, such as high energy density, fast charge–discharge rates, excellent cyclic stability, and specific capacitance, make supercapacitor a fascinating electronic device. During recent decades, a significant amount of research has been dedicated to enhancing the electrochemical performance of the supercapacitors [...] Read more.
The advanced electrochemical properties, such as high energy density, fast charge–discharge rates, excellent cyclic stability, and specific capacitance, make supercapacitor a fascinating electronic device. During recent decades, a significant amount of research has been dedicated to enhancing the electrochemical performance of the supercapacitors through the development of novel electrode materials. In addition to highlighting the charge storage mechanism of the three main categories of supercapacitors, including the electric double-layer capacitors (EDLCs), pseudocapacitors, and the hybrid supercapacitors, this review describes the insights of the recent electrode materials (including, carbon-based materials, metal oxide/hydroxide-based materials, and conducting polymer-based materials, 2D materials). The nanocomposites offer larger SSA, shorter ion/electron diffusion paths, thus improving the specific capacitance of supercapacitors (SCs). Besides, the incorporation of the redox-active small molecules and bio-derived functional groups displayed a significant effect on the electrochemical properties of electrode materials. These advanced properties provide a vast range of potential for the electrode materials to be utilized in different applications such as in wearable/portable/electronic devices such as all-solid-state supercapacitors, transparent/flexible supercapacitors, and asymmetric hybrid supercapacitors. Full article
(This article belongs to the Special Issue Electrocatalysis and Electrode Materials for Energy Production)
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38 pages, 7405 KiB  
Review
Photocatalysis for Air Treatment Processes: Current Technologies and Future Applications for the Removal of Organic Pollutants and Viruses
by Salvador Escobedo and Hugo de Lasa
Catalysts 2020, 10(9), 966; https://doi.org/10.3390/catal10090966 - 24 Aug 2020
Cited by 38 | Viewed by 11424
Abstract
Photocatalysis for air treatment or photocatalytic oxidation (PCO) is a relatively new technology which requires titanium dioxide (TiO2) and a source of light (Visible or near-UV) to degrade pollutants contained in air streams. Present approaches for the photodegradation of indoor pollutants [...] Read more.
Photocatalysis for air treatment or photocatalytic oxidation (PCO) is a relatively new technology which requires titanium dioxide (TiO2) and a source of light (Visible or near-UV) to degrade pollutants contained in air streams. Present approaches for the photodegradation of indoor pollutants in air streams aim to eliminate volatile organic compounds (VOCs) and viruses, which are both toxic and harmful to human health. Photocatalysis for air treatment is an inexpensive and innovative green process. Additionally, it is a technology with a reduced environmental footprint when compared to other conventional air treatments which demand significant energy, require the disposal of used materials, and release CO2 and other greenhouse gases to the environment. This review discusses the most current and relevant information on photocatalysis for air treatment. This article also provides a critical review of (1) the most commonly used TiO2-based semiconductors, (2) the experimental syntheses and the various photocatalytic organic species degradation conversions, (3) the developed kinetics and computational fluid dynamics (CFD) and (4) the proposed Quantum Yields (QYs) and Photocatalytic Thermodynamic Efficiency Factors (PTEFs). Furthermore, this article contains important information on significant factors affecting the photocatalytic degradation of organic pollutants, such as reactor designs and type of photoreactor irradiation. Overall, this review describes state-of-the-art photocatalysis for air treatment to eliminate harmful indoor organic molecules, reviewing as well the potential applications for the inactivation of SARS-CoV2 (COVID-19) viruses. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)
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38 pages, 25382 KiB  
Review
Recent Advances on Copper Complexes as Visible Light Photoinitiators and (Photo) Redox Initiators of Polymerization
by Guillaume Noirbent and Frédéric Dumur
Catalysts 2020, 10(9), 953; https://doi.org/10.3390/catal10090953 - 20 Aug 2020
Cited by 39 | Viewed by 5866
Abstract
Metal complexes are used in numerous chemical and photochemical processes in organic chemistry. Metal complexes have not been excluded from the interest of polymerists to convert liquid resins into solid materials. If iridium complexes have demonstrated their remarkable photochemical reactivity in polymerization, their [...] Read more.
Metal complexes are used in numerous chemical and photochemical processes in organic chemistry. Metal complexes have not been excluded from the interest of polymerists to convert liquid resins into solid materials. If iridium complexes have demonstrated their remarkable photochemical reactivity in polymerization, their high costs and their attested toxicities have rapidly discarded these complexes for further developments. Conversely, copper complexes are a blooming field of research in (photo) polymerization due to their low cost, easy syntheses, long-living excited state lifetimes, and their remarkable chemical and photochemical stabilities. Copper complexes can also be synthesized in solution and by mechanochemistry, paving the way towards the synthesis of photoinitiators by Green synthetic approaches. In this review, an overview of the different copper complexes reported to date is presented. Copper complexes are versatile candidates for polymerization, as these complexes are now widely used not only in photopolymerization, but also in redox and photoassisted redox polymerization processes. Full article
(This article belongs to the Special Issue Recent Advances in Photoredox Catalysts)
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22 pages, 4034 KiB  
Article
Deciphering the Mechanism of Silver Catalysis of “Click” Chemistry in Water by Combining Experimental and MEDT Studies
by Hicham Ben El Ayouchia, Lahoucine Bahsis, Ismail Fichtali, Luis R. Domingo, Mar Ríos-Gutiérrez, Miguel Julve and Salah-Eddine Stiriba
Catalysts 2020, 10(9), 956; https://doi.org/10.3390/catal10090956 - 20 Aug 2020
Cited by 23 | Viewed by 4716
Abstract
A combined experimental study and molecular electron density theory (MEDT) analysis was carried out to investigate the click of 1,2,3-triazole derivatives by Ag(I)-catalyzed azide-alkyne cycloaddition (AgAAC) reaction as well as its corresponding mechanistic pathway. Such a synthetic protocol leads to the regioselective formation [...] Read more.
A combined experimental study and molecular electron density theory (MEDT) analysis was carried out to investigate the click of 1,2,3-triazole derivatives by Ag(I)-catalyzed azide-alkyne cycloaddition (AgAAC) reaction as well as its corresponding mechanistic pathway. Such a synthetic protocol leads to the regioselective formation of 1,4-disubstituted-1,2,3-triazoles in the presence of AgCl as catalyst and water as reaction solvent at room temperature and pressure. The MEDT was performed by applying Density Functional Theory (DFT) calculations at both B3LYP/6-31G(d,p) (LANL2DZ for Ag) and ωB97XD/6-311G(d,p) (LANL2DZ for Ag) levels with a view to decipher the observed regioselectivity in AgAAC reactions, and so to set out the number of silver(I) species and their roles in the formation of 1,4-disubstituted-1,2,3-triazoles. The comparison of the values of the energy barriers for the mono- and dinuclear Ag(I)-acetylide in the AgAAC reaction paths shows that the calculated energy barriers of dinuclear processes are smaller than those of the mononuclear one. The type of intramolecular interactions in the investigated AgAAC click chemistry reaction accounts for the regioselective formation of the 1,4-regiosisomeric triazole isomer. The ionic character of the starting compounds, namely Ag-acetylide, is revealed for the first time. This finding rules out any type of covalent interaction, involving the silver(I) complexes, along the reaction pathway. Electron localization function (ELF) topological analysis of the electronic structure of the stationary points reaffirmed the zw-type (zwitterionic-type) mechanism of the AgAAC reactions. Full article
(This article belongs to the Special Issue Computational Chemistry and Catalysis: Prediction and Design)
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22 pages, 5403 KiB  
Article
Magnesium Effect in K/Co-Mg-Mn-Al Mixed Oxide Catalyst for Direct NO Decomposition
by Kateřina Karásková, Kateřina Pacultová, Anna Klegova, Dagmar Fridrichová, Marta Valášková, Květuše Jirátová, Paweł Stelmachowski, Andrzej Kotarba and Lucie Obalová
Catalysts 2020, 10(8), 931; https://doi.org/10.3390/catal10080931 - 13 Aug 2020
Cited by 9 | Viewed by 3780
Abstract
Emission of nitric oxide represents a serious environmental problem since it contributes to the formation of acid rain and photochemical smog. Potassium-modified Co-Mn-Al mixed oxide is an effective catalyst for NO decomposition. However, there are problems related to the thermal instability of potassium [...] Read more.
Emission of nitric oxide represents a serious environmental problem since it contributes to the formation of acid rain and photochemical smog. Potassium-modified Co-Mn-Al mixed oxide is an effective catalyst for NO decomposition. However, there are problems related to the thermal instability of potassium species and a high content of toxic and expensive cobalt. The reported research aimed to determine whether these shortcomings can be overcome by replacing cobalt with magnesium. Therefore, a series of Co-Mg-Mn-Al mixed oxides with different Co/Mg molar ratio and promoted by various content of potassium was investigated. The catalysts were thoroughly characterized by atomic absorption spectroscopy (AAS), temperature-programmed reduction by hydrogen (TPR-H2), temperature-programmed desorption of CO2 (TPD-CO2), X-ray powder diffraction (XRD), N2 physisorption, species-resolved thermal alkali desorption (SR-TAD), and tested in direct NO decomposition with and without the addition of oxygen and water vapor. Partial substitution of magnesium for cobalt did not cause an activity decrease when the optimal molar ratio of K/Co on the normalized surface area was maintained; it means that the portion of expensive and toxic cobalt can be successfully replaced by magnesium without any decrease in catalytic activity. Full article
(This article belongs to the Special Issue Catalytic Decomposition of N2O and NO)
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18 pages, 671 KiB  
Review
Treatment of Produced Water with Photocatalysis: Recent Advances, Affecting Factors and Future Research Prospects
by Lu Lin, Wenbin Jiang, Lin Chen, Pei Xu and Huiyao Wang
Catalysts 2020, 10(8), 924; https://doi.org/10.3390/catal10080924 - 12 Aug 2020
Cited by 114 | Viewed by 8773
Abstract
Produced water is the largest byproduct of oil and gas production. Due to the complexity of produced water, especially dissolved petroleum hydrocarbons and high salinity, efficient water treatment technologies are required prior to beneficial use of such waste streams. Photocatalysis has been demonstrated [...] Read more.
Produced water is the largest byproduct of oil and gas production. Due to the complexity of produced water, especially dissolved petroleum hydrocarbons and high salinity, efficient water treatment technologies are required prior to beneficial use of such waste streams. Photocatalysis has been demonstrated to be effective at degrading recalcitrant organic contaminants, however, there is limited understanding about its application to treating produced water that has a complex and highly variable water composition. Therefore, the determination of the appropriate photocatalysis technique and the operating parameters are critical to achieve the maximum removal of recalcitrant compounds at the lowest cost. The objective of this review is to examine the feasibility of photocatalysis-involved treatment for the removal of contaminants in produced water. Recent studies revealed that photocatalysis was effective at decomposing recalcitrant organic compounds but not for mineralization. The factors affecting decontamination and strategies to improve photocatalysis efficiency are discussed. Further, recent developments and future research prospects on photocatalysis-derived systems for produced water treatment are addressed. Photocatalysis is proposed to be combined with other treatment processes, such as biological treatments, to partially reduce total organic carbon, break down macromolecular organic compounds, increase biodegradability, and reduce the toxicity of produced water. Full article
(This article belongs to the Special Issue Advances in Photocatalytic Wastewater Purification)
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22 pages, 6164 KiB  
Review
A Review on Catalysts Development for Steam Reforming of Biodiesel Derived Glycerol; Promoters and Supports
by Nasim Ghaffari Saeidabad, Young Su Noh, Ali Alizadeh Eslami, Hyun Tae Song, Hyun Dong Kim, Ali Fazeli and Dong Ju Moon
Catalysts 2020, 10(8), 910; https://doi.org/10.3390/catal10080910 - 10 Aug 2020
Cited by 42 | Viewed by 6120
Abstract
In the last decades, environmental crises and increasing energy demand have motivated researchers to investigate the practical techniques for the production of clean fuels through renewable energy resources. It is essential to develop technologies to utilize glycerol as a byproduct derived from biodiesel. [...] Read more.
In the last decades, environmental crises and increasing energy demand have motivated researchers to investigate the practical techniques for the production of clean fuels through renewable energy resources. It is essential to develop technologies to utilize glycerol as a byproduct derived from biodiesel. Glycerol is known as a sustainable and clean source of energy, which can be an alternative resource for the production of value-added chemicals and hydrogen. The hydrogen production via steam reforming (SR) of glycerol using Ni-based catalysts is one of the promising approaches for the entry of the hydrogen economy. The purpose of this review paper is to highlight the recent trends in hydrogen production over Ni-based catalysts using the SR of glycerol. The intrinsic ability of Ni to disperse easily over variable supports makes it a more viable active phase for the SR catalysts. The optimal reaction conditions have been indicated as 650–900 °C, 1 bar, and 15 wt% Ni in catalysts for high glycerol conversion. In this review paper, the effects of various supports, different promoters (K, Ca, Sr, Ce, La, Cr, Fe), and process conditions on the catalytic performance have been summarized and discussed to provide a better comparison for the future works. It was found that Ce, Mg, and La have a significant effect on catalytic performance as promoters. Moreover, SR of glycerol over hydrotalcite and perovskite-based catalysts have been reviewed as they suggest high catalytic performance in SR of glycerol with improved thermal stability and coke resistance. More specifically, the Ni/LaNi0.9Cu0.1O3 synthesized using perovskite-type supports has shown high glycerol conversion and sufficient hydrogen selectivity at low temperatures. On the other hand, hydrotalcite-like catalysts have shown higher catalytic stability due to high thermal stability and low coke formation. It is vital to notice that the primary concern is developing a high-performance catalyst to utilize crude glycerol efficiently. Full article
(This article belongs to the Special Issue Catalytic Steam Reforming)
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18 pages, 4444 KiB  
Article
Low Temperature Synthesis of Photocatalytic Mesoporous TiO2 Nanomaterials
by Massimo Dell’Edera, Francesca Petronella, Alessandra Truppi, Leonarda Francesca Liotta, Nunzio Gallì, Teresa Sibillano, Cinzia Giannini, Rosaria Brescia, Francesco Milano, Marinella Striccoli, Angela Agostiano, Maria Lucia Curri and Roberto Comparelli
Catalysts 2020, 10(8), 893; https://doi.org/10.3390/catal10080893 - 7 Aug 2020
Cited by 21 | Viewed by 5087
Abstract
We report the synthesis of mesoporous TiO2 nanostructures based on the decomposition of TiOSO4 in aqueous alkaline solution at room temperature, followed by mild thermal treatment (110 °C) in an oven and suitable to yield up to 40 g of product [...] Read more.
We report the synthesis of mesoporous TiO2 nanostructures based on the decomposition of TiOSO4 in aqueous alkaline solution at room temperature, followed by mild thermal treatment (110 °C) in an oven and suitable to yield up to 40 g of product per batch. The duration of the thermal treatment was found to be crucial to control crystalline phase composition, specific surface area, surface chemistry and, accordingly, the photocatalytic properties of the obtained TiO2 nanocrystals. The thorough investigation of the prepared samples allowed us to explain the relationship between the structure of the obtained nanoparticles and their photocatalytic behavior, that was tested in a model reaction. In addition, the advantage of the mild treatment against a harsher calcination at 450 °C was illustrated. The proposed approach represents a facile and sustainable route to promptly access an effective photocatalyst, thus holding a significant promise for the development of solutions suitable to real technological application in environmental depollution. Full article
(This article belongs to the Special Issue Nanomaterials in Photo(Electro)catalysis)
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25 pages, 2166 KiB  
Review
Value-Added Bio-Chemicals Commodities from Catalytic Conversion of Biomass Derived Furan-Compounds
by Aitziber Iriondo, Ion Agirre, Nerea Viar and Jesús Requies
Catalysts 2020, 10(8), 895; https://doi.org/10.3390/catal10080895 - 7 Aug 2020
Cited by 23 | Viewed by 5691
Abstract
The depletion of fossil resources in the near future and the need to decrease greenhouse gas emissions lead to the investigation of using alternative renewable resources as raw materials. One of the most promising options is the conversion of lignocellulosic biomass (like forestry [...] Read more.
The depletion of fossil resources in the near future and the need to decrease greenhouse gas emissions lead to the investigation of using alternative renewable resources as raw materials. One of the most promising options is the conversion of lignocellulosic biomass (like forestry residues) into bioenergy, biofuels and biochemicals. Among these products, the production of intermediate biochemicals has become an important goal since the petrochemical industry needs to find sustainable alternatives. In this way, the chemical industry competitiveness could be improved as bioproducts have a great potential market. Thus, the main objective of this review is to describe the production processes under study (reaction conditions, type of catalysts, solvents, etc.) of some promising intermediate biochemicals, such as; alcohols (1,2,6-hexanetriol, 1,6-hexanetriol and pentanediols (1,2 and 1,5-pentanediol)), maleic anhydride and 5-alkoxymethylfuran. These compounds can be produced using 5-hydroxymethylfurfural and/or furfural, which they both are considered one of the main biomass derived building blocks. Full article
(This article belongs to the Special Issue Heterogeneous Catalysis in Green Chemistry)
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27 pages, 5286 KiB  
Review
Enzyme-Coated Micro-Crystals: An Almost Forgotten but Very Simple and Elegant Immobilization Strategy
by Rodolpho R. C. Monteiro, José C. S. dos Santos, Andrés R. Alcántara and Roberto Fernandez-Lafuente
Catalysts 2020, 10(8), 891; https://doi.org/10.3390/catal10080891 - 6 Aug 2020
Cited by 47 | Viewed by 5789
Abstract
The immobilization of enzymes using protein coated micro-crystals (PCMCs) was reported for the first time in 2001 by Kreiner and coworkers. The strategy is very simple. First, an enzyme solution must be prepared in a concentrated solution of one compound (salt, sugar, amino [...] Read more.
The immobilization of enzymes using protein coated micro-crystals (PCMCs) was reported for the first time in 2001 by Kreiner and coworkers. The strategy is very simple. First, an enzyme solution must be prepared in a concentrated solution of one compound (salt, sugar, amino acid) very soluble in water and poorly soluble in a water-soluble solvent. Then, the enzyme solution is added dropwise to the water soluble solvent under rapid stirring. The components accompanying the enzyme are called the crystal growing agents, the solvent being the dehydrating agent. This strategy permits the rapid dehydration of the enzyme solution drops, resulting in a crystallization of the crystal formation agent, and the enzyme is deposited on this crystal surface. The reaction medium where these biocatalysts can be used is marked by the solubility of the PCMC components, and usually these biocatalysts may be employed in water soluble organic solvents with a maximum of 20% water. The evolution of these PCMC was to chemically crosslink them and further improve their stabilities. Moreover, the PCMC strategy has been used to coimmobilize enzymes or enzymes and cofactors. The immobilization may permit the use of buffers as crystal growth agents, enabling control of the reaction pH in the enzyme environments. Usually, the PCMC biocatalysts are very stable and more active than other biocatalysts of the same enzyme. However, this simple (at least at laboratory scale) immobilization strategy is underutilized even when the publications using it systematically presented a better performance of them in organic solvents than that of many other immobilized biocatalysts. In fact, many possibilities and studies using this technique are lacking. This review tried to outline the possibilities of this useful immobilization strategy. Full article
(This article belongs to the Special Issue Multienzymatic Catalysis and/or Enzyme Co-immobilization)
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