Catalysts

29 pages, 7264 KiB

Open AccessEditor’s ChoiceReview

Recent Advances of Oxygen Carriers for Hydrogen Production via Chemical Looping Water-Splitting

by Wenxi Chang, Yue Hu, Weibin Xu, Chuande Huang, Haonan Chen, Jiahui He, Yujia Han, Yanyan Zhu, Xiaoxun Ma and Xiaodong Wang

Catalysts 2023, 13(2), 279; https://doi.org/10.3390/catal13020279 - 26 Jan 2023

Cited by 23 | Viewed by 4623

Abstract

Hydrogen is an important green energy source and chemical raw material for various industrial processes. At present, the major technique of hydrogen production is steam methane reforming (SMR), which suffers from high energy penalties and enormous CO₂ emissions. As an alternative, chemical [...] Read more.

Hydrogen is an important green energy source and chemical raw material for various industrial processes. At present, the major technique of hydrogen production is steam methane reforming (SMR), which suffers from high energy penalties and enormous CO₂ emissions. As an alternative, chemical looping water-splitting (CLWS) technology represents an energy-efficient and environmentally friendly method for hydrogen production. The key to CLWS lies in the selection of suitable oxygen carriers (OCs) that hold outstanding sintering resistance, structural reversibility, and capability to release lattice oxygen and deoxygenate the steam for hydrogen generation. Described herein are the recent advances in designing OCs, including simple metal oxides (e.g., Fe, Zn, Ce, and Ti-based metal oxides) and composite metal oxides (e.g., perovskite, spinel, and garnets), for different CLWS processes with emphasis on the crucial parameters that determine their redox performance and future challenges. Full article

(This article belongs to the Special Issue Catalysts in Chemical Looping Technology for Energy Storage and Carbon Emission Reduction)

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9 pages, 2286 KiB

Open AccessEditor’s ChoiceCommunication

High-Temperature-Treated LTX Zeolites as Heterogeneous Catalysts for the Hock Cleavage

by Jan Drönner, Karim Bijerch, Peter Hausoul, Regina Palkovits and Matthias Eisenacher

Catalysts 2023, 13(1), 202; https://doi.org/10.3390/catal13010202 - 15 Jan 2023

Cited by 1 | Viewed by 2960

Abstract

Hydroxybenzene, commonly known as phenol, is one of the most important organic commodity chemicals. To produce phenol, the cumene process is the most used process worldwide. A crucial step in this process is the Hock rearrangement, which has a major impact on the [...] Read more.

Hydroxybenzene, commonly known as phenol, is one of the most important organic commodity chemicals. To produce phenol, the cumene process is the most used process worldwide. A crucial step in this process is the Hock rearrangement, which has a major impact on the overall cumene consumption rate and determines the safety level of the process. The most used catalyst for the cleavage of cumene hydroperoxide (CHP) is sulfuric acid. Besides its strong corrosive property, which increases plant investment costs, it also requires neutralization after the decomposition step to prevent side reactions. In this study, we show that high-temperature-treated Linde Type X (LTX) zeolites exhibit a high activity for the peroxide cleavage step. In addition, the structure–activity relationship responsible for this good performance in the reaction system of the HOCK rearrangement was investigated. XRPD analyses revealed the formation of a new phase after temperature treatment above 900 °C. The Si/Al ratio determined by EDX suggested the formation of extra-framework aluminum, which was confirmed by solid-state NMR analysis. The newly formed extra-framework aluminum was found to be responsible for the high catalytic activity. BET analyses showed that the surface area drops at higher calcination temperatures. This leads to a lower catalytic activity for most known reactions. However, for this study, no decrease in activity has been observed. The newfound material shows extraordinarily high activity as a catalyst in the HOCK cleavage and has the potential to be a heterogeneous alternative to sulfuric acid for this reaction. Full article

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

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10 pages, 5401 KiB

Open AccessEditor’s ChoiceCommunication

Bienzymatic Cascade Combining a Peroxygenase with an Oxidase for the Synthesis of Aromatic Aldehydes from Benzyl Alcohols

by Yunjian Ma, Zongquan Li, Hao Zhang, Vincent Kam Wai Wong, Frank Hollmann and Yonghua Wang

Catalysts 2023, 13(1), 145; https://doi.org/10.3390/catal13010145 - 8 Jan 2023

Cited by 4 | Viewed by 2833

Abstract

Aromatic aldehydes are important aromatic compounds for the flavour and fragrance industry. In this study, a parallel cascade combining aryl alcohol oxidase from Pleurotus eryngii (PeAAOx) and unspecific peroxygenase from the basidiomycete Agrocybe aegerita (AaeUPO) to convert aromatic primary [...] Read more.

Aromatic aldehydes are important aromatic compounds for the flavour and fragrance industry. In this study, a parallel cascade combining aryl alcohol oxidase from Pleurotus eryngii (PeAAOx) and unspecific peroxygenase from the basidiomycete Agrocybe aegerita (AaeUPO) to convert aromatic primary alcohols into high-value aromatic aldehydes is proposed. Key influencing factors in the process of enzyme cascade catalysis, such as enzyme dosage, pH and temperature, were investigated. The universality of PeAAOx coupled with AaeUPO cascade catalysis for the synthesis of aromatic aldehyde flavour compounds from aromatic primary alcohols was evaluated. In a partially optimised system (comprising 30 μM PeAAOx, 2 μM AaeUPO at pH 7 and 40 °C) up to 84% conversion of 50 mM veratryl alcohol into veratryl aldehyde was achieved in a self-sufficient aerobic reaction. Promising turnover numbers of 2800 and 21,000 for PeAAOx and AaeUPO, respectively, point towards practical applicability. Full article

(This article belongs to the Special Issue Enzymes in Biomedical, Cosmetic and Food Application)

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19 pages, 1029 KiB

Open AccessEditor’s ChoiceReview

Electrochemically Assisted Persulfate Oxidation of Organic Pollutants in Aqueous Solution: Influences, Mechanisms and Feasibility

by Jianting Sun, Wei Zheng, Gang Hu, Fan Liu, Siyuan Liu, Lie Yang and Zulin Zhang

Catalysts 2023, 13(1), 135; https://doi.org/10.3390/catal13010135 - 6 Jan 2023

Cited by 7 | Viewed by 3444

Abstract

Electrochemically (EC) assisted persulfate (PS) oxidation processes (EPOPs) have gained increasing attention in recent years. In this review, the current status and prospects of EC/PS degradation of organic pollutants are discussed and summarized. It was found that the oxidation of most organic contaminants [...] Read more.

Electrochemically (EC) assisted persulfate (PS) oxidation processes (EPOPs) have gained increasing attention in recent years. In this review, the current status and prospects of EC/PS degradation of organic pollutants are discussed and summarized. It was found that the oxidation of most organic contaminants could be significantly enhanced or accelerated using the combination of EC and PS compared to single treatments. Moreover, the effects of various operational variables on the removal of organic contaminants were investigated. Some variables are highly sensitive, and the optimal conditions are case-specific. Regarding the degradation mechanisms, radical-induced reactions and nonradical reactions both exist for the elimination of organic contaminants. Oxidants (including S₂O₈²⁻ and SO₄^•−) can be produced from SO₄²⁻ near the anode, which is a unique feature of EPOPs. In some studies, the electrical energy consumption of EPOPs has been controlled to a reasonably low level in lab-scale attempts. Although there are still a few drawbacks or difficulties (e.g., potential electrode fouling, dependency on batch mode) for large-scale applications, EPOPs offer a promising alternative to traditional advanced oxidation techniques. Full article

(This article belongs to the Special Issue Advanced Catalytic Material for Water Treatment)

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26 pages, 8885 KiB

Open AccessEditor’s ChoiceReview

Selectivity in the Aliphatic C–H Bonds Oxidation (Hydroxylation) Catalyzed by Heme- and Non-Heme Metal Complexes—Recent Advances

by Renata Siedlecka

Catalysts 2023, 13(1), 121; https://doi.org/10.3390/catal13010121 - 5 Jan 2023

Cited by 6 | Viewed by 3951

Abstract

The oxyfunctionalization of non-activated C-H bonds has attracted considerable attention for several years. Following the example of enzymatic systems, a multitude of catalytic systems capable of carrying out such a transformation efficiently and selectively have been described. The great discoveries in this area [...] Read more.

The oxyfunctionalization of non-activated C-H bonds has attracted considerable attention for several years. Following the example of enzymatic systems, a multitude of catalytic systems capable of carrying out such a transformation efficiently and selectively have been described. The great discoveries in this area were described at the beginning of the 21st century, but due to the growing demand for precise syntheses (e.g., for the needs of the pharmaceutical industry), new solutions or new applications for already known catalytic systems are constantly being sought. This review article summarizes the development of metal complex-catalyzed selective functionalization of saturated C-H bonds since 2010. However, brief references to previous studies are also made for clarity. There is a huge amount of literature reports in this area, so we intend to highlight only the most important findings in the selective hydroxylation of saturated C–H bonds. Their practical applications in synthesis will also be pointed out. Full article

(This article belongs to the Special Issue Heteroaromatic N-oxides in Synthesis and Asymmetric Catalysis)

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22 pages, 5652 KiB

Open AccessEditor’s ChoiceReview

In Situ Surface Reconstruction of Catalysts for Enhanced Hydrogen Evolution

by Yingbo Zhang, Junan Pan, Gu Gong, Renxuan Song, Ye Yuan, Mengzhu Li, Weifeng Hu, Pengcheng Fan, Lexing Yuan and Longlu Wang

Catalysts 2023, 13(1), 120; https://doi.org/10.3390/catal13010120 - 5 Jan 2023

Cited by 14 | Viewed by 3493

Abstract

The in situ surface reconstitution of a catalyst for hydrogen evolution refers to its structure evolution induced by strong interactions with reaction intermediates during the hydrogen evolution reaction (HER), which eventually leads to the self-optimization of active sites. In consideration of the superior [...] Read more.

The in situ surface reconstitution of a catalyst for hydrogen evolution refers to its structure evolution induced by strong interactions with reaction intermediates during the hydrogen evolution reaction (HER), which eventually leads to the self-optimization of active sites. In consideration of the superior performance that can be achieved by in situ surface reconstitution, more and more attention has been paid to the relationship between active site structure evolution and the self-optimization of HER activity. More and more in situ and/or operando techniques have been explored to track the dynamic structural evolution of HER catalysts in order to clarify the underlying mechanism. This review summarizes recent advances in various types of reconstruction such as the reconfiguration of crystallinity, morphological evolution, chemical composition evolution, phase transition refactoring, surface defects, and interface refactoring in the HER process. Finally, different perspectives and outlooks are offered to guide future investigations. This review is expected to provide some new clues for a deeper understanding of in situ surface reconfiguration in hydrogen evolution reactions and the targeted design of catalysts with desirable structures. Full article

(This article belongs to the Special Issue Recent Progress in Development of Hydrogenation and Dehydrogenation Catalysts)

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16 pages, 3569 KiB

Open AccessEditor’s ChoiceArticle

Redrawing HER Volcano with Interfacial Processes—The Role of Hydrogen Spillover in Boosting H₂ Evolution in Alkaline Media

by Sanjin J. Gutić, Dino Metarapi, Aleksandar Z. Jovanović, Goitom K. Gebremariam, Ana S. Dobrota, Bojana Nedić Vasiljević and Igor A. Pašti

Catalysts 2023, 13(1), 89; https://doi.org/10.3390/catal13010089 - 1 Jan 2023

Cited by 9 | Viewed by 3750

Abstract

The requirements for the efficient replacement of fossil fuel, combined with the growing energy crisis, places focus on hydrogen production. Efficient and cost-effective electrocatalysts are needed for H₂ production, and novel strategies for their discovery must be developed. Here, we utilized Kinetic [...] Read more.

The requirements for the efficient replacement of fossil fuel, combined with the growing energy crisis, places focus on hydrogen production. Efficient and cost-effective electrocatalysts are needed for H₂ production, and novel strategies for their discovery must be developed. Here, we utilized Kinetic Monte Carlo (KMC) simulations to demonstrate that hydrogen evolution reaction (HER) can be boosted via hydrogen spillover to the support when the catalyst surface is largely covered by adsorbed hydrogen under operating conditions. Based on the insights from KMC, we synthesized a series of reduced graphene-oxide-supported catalysts and compared their activities towards HER in alkaline media with that of corresponding pure metals. For Ag, Au, and Zn, the support effect is negative, but for Pt, Pd, Fe, Co, and Ni, the presence of the support enhances HER activity. The HER volcano, constructed using calculated hydrogen binding energies and measured HER activities, shows a positive shift of the strong binding branch. This work demonstrates the possibilities of metal–support interface engineering for producing effective HER catalysts and provides general guidelines for choosing novel catalyst–support combinations for electrocatalytic hydrogen production. Full article

(This article belongs to the Special Issue Advanced Nanomaterials for Electrocatalysis: Synthesis, Characterization and Application)

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9 pages, 1621 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Influence of Butanol Isomerization on Photothermal Hydrogen Production over Ti@TiO₂ Core-Shell Nanoparticles

by Sara El Hakim, Mathéo Bathias, Tony Chave and Sergey I. Nikitenko

Catalysts 2022, 12(12), 1662; https://doi.org/10.3390/catal12121662 - 17 Dec 2022

Cited by 1 | Viewed by 1996

Abstract

In this work, we reported for the first time the effect of butanol isomerization on the photothermal production of hydrogen in the presence of a noble, metal-free Ti@TiO₂ core-shell photocatalyst. The experiments were performed in aqueous solutions of 1-BuOH, 2-BuOH, and t-BuOH [...] Read more.

In this work, we reported for the first time the effect of butanol isomerization on the photothermal production of hydrogen in the presence of a noble, metal-free Ti@TiO₂ core-shell photocatalyst. The experiments were performed in aqueous solutions of 1-BuOH, 2-BuOH, and t-BuOH under Xe lamp irradiation (vis/NIR: 8.4 W, UV: 0.6 W) at 35–69 °C. The increase in temperature significantly enhanced H₂ formation, indicating a strong photothermal effect in the studied systems. However, in dark conditions, H₂ emission was not observed even at elevated temperatures, which clearly points out the photonic origin of H₂ photothermal formation. The rate of H₂ production followed the order of 1-BuOH >> 2-BuOH > t-BuOH in the entire range of studied temperatures. In the systems with 1-BuOH and 2-BuOH, hydrogen was the only gaseous product measured online in the outlet carrier argon using mass spectrometry. By contrast, a mixture of H₂, CH₄, and C₂H₆ was detected for t-BuOH, indicating a C–C bond scission with this isomer during photocatalytic degradation. The apparent activation energies, E_a, with 1-BuOH/2-BuOH isomers (20–21 kJ·mol⁻¹) was found to be larger than for t-BuOH (13 kJ·mol⁻¹). The significant difference in thermal response for 1-BuOH/2-BuOH and t-BuOH isomers was ascribed to the difference in the photocatalytic mechanisms of these species. The photothermal effect with 1-BuOH/2-BuOH isomers can be explained by the thermally induced transfer of photogenerated, shallowly trapped electron holes to highly reactive free holes at the surface of TiO₂ and the further hole-mediated cleavage of the O-H bond. In the system with t-BuOH, another mechanism could also contribute to the overall process through hydrogen abstraction from the C–H bond by an intermediate ^•OH radical, leading to CH₃^• group ejection. Formation of ^•OH radicals during light irradiation of Ti@TiO₂ nanoparticle suspension in water has been confirmed using terephthalate dosimetry. This analysis also revealed a positive temperature response of ^•OH radical formation. Full article

(This article belongs to the Special Issue Photocatalysis and Sonocatalysis for Environmental Applications: Synergy or Competition?)

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13 pages, 559 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Biotransformation of the Proteogenic Amino Acids Phenylalanine, Tyrosine and Tryptophan by Yarrowia Species: An Application to the Preparative Synthesis of Natural Phenylacetic Acid

by Stefano Serra, Antonio Castagna, Stefano Marzorati and Mattia Valentino

Catalysts 2022, 12(12), 1638; https://doi.org/10.3390/catal12121638 - 14 Dec 2022

Cited by 3 | Viewed by 3309

Abstract

The biotransformation of the aromatic amino acids phenylalanine, tyrosine and tryptophan originates a number of bioactive compounds. Yeasts are the most used microorganisms for the transformation of (L)-phenylalanine into the flavour phenylethanol. Here, we reported a study on the biotransformation of the proteogenic [...] Read more.

The biotransformation of the aromatic amino acids phenylalanine, tyrosine and tryptophan originates a number of bioactive compounds. Yeasts are the most used microorganisms for the transformation of (L)-phenylalanine into the flavour phenylethanol. Here, we reported a study on the biotransformation of the proteogenic aminoacids phenylalanine, tyrosine and tryptophan by yeast strains belonging to Yarrowia genus. We found that the latter microorganisms, in high aerobic conditions, metabolise the aromatic amino acids (L)-phenylalanine and (L)-tyrosine with the almost exclusive formation of phenylacetic acid and 4-hydroxyphenylacetic acid, respectively. Differently, the biotransformation of (L)-tryptophan with Y. lipolytica, gave anthranilic acid as the main product. As stated by the European and USA legislations concerning natural flavour production, phenylacetic acid obtained by microbial conversion of phenylalanine of natural origin can be commercialised as a natural flavour. Accordingly, our findings were exploited in a new process, based on the Yarrowia strains-mediated biotransformation of natural (L)-phenylalanine, that allows the large-scale preparation of the high-value, natural flavour, phenylacetic acid. Full article

(This article belongs to the Section Biocatalysis)

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16 pages, 2891 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fast and Complete Destruction of the Anti-Cancer Drug Cytarabine from Water by Electrocatalytic Oxidation Using Electro-Fenton Process

by Sule Camcioglu, Baran Özyurt, Nihal Oturan, Clément Trellu and Mehmet A. Oturan

Catalysts 2022, 12(12), 1598; https://doi.org/10.3390/catal12121598 - 7 Dec 2022

Cited by 10 | Viewed by 2299

Abstract

The fast and complete removal of the anti-cancer drug cytarabine (CYT) from water was studied, for the first time, by the electro-Fenton process using a BDD anode and carbon felt cathode. A catalytic amount (10⁻⁴ M) of ferrous iron was initially added [...] Read more.

The fast and complete removal of the anti-cancer drug cytarabine (CYT) from water was studied, for the first time, by the electro-Fenton process using a BDD anode and carbon felt cathode. A catalytic amount (10⁻⁴ M) of ferrous iron was initially added to the solution as catalyst and it was electrochemically regenerated in the process. Complete degradation of 0.1 mM (24.3 mg L⁻¹) CYT was achieved quickly in 15 min at 300 mA constant current electrolysis by hydroxyl radicals (^●OH) electrocatalytically generated in the system. Almost complete mineralization (91.14% TOC removal) of the solution was obtained after 4 h of treatment. The mineralization current efficiency (MCE) and energy consumption (EC) during the mineralization process were evaluated. The absolute (second order) rate constant for the hydroxylation reaction of CYT by hydroxyl radicals was assessed by applying the competition kinetics method and found to be 5.35 × 10⁹ M⁻¹ s⁻¹. The formation and evolution of oxidation reaction intermediates, short-chain carboxylic acids and inorganic ions were identified by gas chromatography-mass spectrometry, high performance liquid chromatography and ion chromatography analyses, respectively. Based on the identified intermediate and end-products, a plausible mineralization pathway for the oxidation of CYT by hydroxyl radicals is proposed. Full article

(This article belongs to the Special Issue Catalysts in Chemical Oxidation/Advanced Oxidation Processes (AOP) for Water Purification and Recovery)

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13 pages, 5079 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Heterostructured Photocatalysts Associating ZnO Nanorods and Ag-In-Zn-S Quantum Dots for the Visible Light-Driven Photocatalytic Degradation of the Acid Orange 7 Dye

by Maroua Mrad, Bilel Chouchene, Tahar Ben Chaabane, Thomas Gries, Ghouti Medjahdi, Lavinia Balan and Raphaël Schneider

Catalysts 2022, 12(12), 1585; https://doi.org/10.3390/catal12121585 - 6 Dec 2022

Cited by 7 | Viewed by 2525

Abstract

Heterostructured photocatalysts associating ZnO nanorods (NRs) sensitized by quaternary Ag-In-Zn-S (AIZS) quantum dots (QDs) were prepared by depositing AIZS QDs at the surface of ZnO NRs followed by thermal treatment at 300 °C. The ZnO/AIZS catalysts were characterized by X-ray diffraction, electron microscopy, [...] Read more.

Heterostructured photocatalysts associating ZnO nanorods (NRs) sensitized by quaternary Ag-In-Zn-S (AIZS) quantum dots (QDs) were prepared by depositing AIZS QDs at the surface of ZnO NRs followed by thermal treatment at 300 °C. The ZnO/AIZS catalysts were characterized by X-ray diffraction, electron microscopy, UV-vis diffuse spectroscopy and by photoelectrochemical measurements. Their photocatalytic activity was evaluated for the bleaching of the Acid Orange 7 (AO7) dye under visible light irradiation. Results show that the association of ZnO NRs with 10 wt% AIZS QDs affords the photocatalyst the highest activity due to the enhanced visible light absorption combined with the improved charge separation. The ZnO/AIZS(10) photocatalyst degrades 98% AO7 in 90 min under visible light illumination, while ZnO NRs can only decompose 11% of the dye. The ZnO/AIZS(10) photocatalyst was also found to be stable and can be reused up to eight times without significant alteration of its activity. This work demonstrates the high potential of AIZS QDs for the development of visible light active photocatalysts. Full article

(This article belongs to the Special Issue Advances in Solar- and Visible-Light Photocatalysis)

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14 pages, 2652 KiB

Open AccessEditor’s ChoiceArticle

Rh-Catalyzed Environmentally Benign Selective Hydrogenation of a Broad Variety of Functional Groups Using Al-Water as a Hydrogen Source

by Guoshu Xie and Béla Török

Catalysts 2022, 12(12), 1578; https://doi.org/10.3390/catal12121578 - 5 Dec 2022

Cited by 4 | Viewed by 3112

Abstract

Supported rhodium catalysts were screened to catalyze the one-step hydrogenation of a broad variety of functional groups. The results show that 5% Rh/Al₂O₃ and 5% Rh/C performed well in controlling selective hydrogenation under the desired amount of time and temperature. [...] Read more.

Supported rhodium catalysts were screened to catalyze the one-step hydrogenation of a broad variety of functional groups. The results show that 5% Rh/Al₂O₃ and 5% Rh/C performed well in controlling selective hydrogenation under the desired amount of time and temperature. In this regard, partial and full hydrogenation were achieved by controlling reaction time or temperature. In addition to aliphatic C–C, C–N, C–O, and N–O multiple bonds, the applicability of this method was demonstrated by the hydrogenation of C=C double bonds of arenes, which is considered challenging. Importantly, the Al-H₂O system producing hydrogen in situ and the high, controllable selectivity make this protocol environmentally benign and highly efficient. Full article

(This article belongs to the Special Issue Recent Developments in Rh Catalysts II)

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11 pages, 3801 KiB

Open AccessEditor’s ChoiceArticle

Deactivation and Regeneration of Palladium Catalysts for Hydrogenation Debenzylation of 2,4,6,8,10,12-Hexabenzyl-2,4,6,8,10,12-Hexaazaisowurtzitane (HBIW)

by Qunfeng Zhang, Mei Wang, Jiacheng Qian, Shuyuan Lou, Jianhong Jin, Bingcheng Li, Chunshan Lu, Feng Feng, Jinghui Lv, Qingtao Wang and Xiaonian Li

Catalysts 2022, 12(12), 1547; https://doi.org/10.3390/catal12121547 - 1 Dec 2022

Cited by 6 | Viewed by 4170

Abstract

2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW, also known as CL-20) is an important energetic compound. As one of the representatives of the third generation of energetic materials, it has an excellent performance, providing broad application prospects for the development of new weapons and equipment. The synthesis of [...] Read more.

2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW, also known as CL-20) is an important energetic compound. As one of the representatives of the third generation of energetic materials, it has an excellent performance, providing broad application prospects for the development of new weapons and equipment. The synthesis of CL-20 is usually obtained from 2,4,6,8,10,12-hexabenzyl-2,4,6,8,10,12-hexaazaisowurtzitane (HBIW) through two catalytic hydrogenolysis and debenzylation reactions, followed by nitration. The most critical step is the hydrogenolysis debenzyl-acetylation process of HBIW because this process requires a large amount of expensive palladium-based catalyst, and the catalyst is completely deactivated after one use. In response to this problem, there is no suitable solution at present, resulting in the high cost of the entire synthesis process. Therefore, reducing the production cost of CL-20 by increasing the catalyst stability is one of the current research priorities. By using AAS, XRD, XPS, TEM, BET, TG and other characterization techniques, the reasons for catalyst deactivation were explored. Studies have shown that the main reason for catalyst deactivation is that a large number of blockages accumulate in the pores of the catalyst after the reaction, which greatly weakens the transfer of the reactant HBIW, intermediate substances, and product 2,6,8,12-tetraacetyl-4,10-dibenzyl-2,4,6,8,10,12-hexaazaisowurtzitane (TADBIW) in the catalyst pores, and the blockage may block the active site of the catalyst. A regeneration treatment method for catalyst deactivation was developed. This method uses chloroform and glacial acetic acid as reagents, which, when combined with stirring and ultrasonic operation, finally restores the activity of the Pd(OH)₂/C catalyst. The BET and TG parameters of the regenerated catalyst indicate that catalyst textural and structural properties have greatly recovered, indicating that this treatment method can remove the blockages in the catalyst pores. Full article

(This article belongs to the Special Issue Advanced Catalysis for Green Fuel Synthesis and Energy Conversion)

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16 pages, 4820 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Tunable Production of Diesel Bio-Blendstock by Rhenium-Catalyzed Hydrogenation of Crude Hexanoic Acid from Grape Pomace Fermentation

by Domenico Licursi, Anna Maria Raspolli Galletti, Claudia Antonetti, Gonzalo A. Martinez, Emma Jones, Lorenzo Bertin, Nicola Di Fidio, Sara Fulignati, Gianluca Pasini and Stefano Frigo

Catalysts 2022, 12(12), 1550; https://doi.org/10.3390/catal12121550 - 1 Dec 2022

Cited by 9 | Viewed by 2456

Abstract

The transition from fossil resources to renewable ones represents a pressing need. The acidogenic fermentation of biomass-derived ethanol to carboxylic acids represents a novel and smart possibility, opening the way for the production of further value-added bio-products through cascade chemical approaches. In this [...] Read more.

The transition from fossil resources to renewable ones represents a pressing need. The acidogenic fermentation of biomass-derived ethanol to carboxylic acids represents a novel and smart possibility, opening the way for the production of further value-added bio-products through cascade chemical approaches. In this work, the hydrogenation of commercial hexanoic acid to give 1-hexanol/hexyl hexanoate mixtures was preliminary studied in the presence of commercial rhenium catalysts (Re₂O₇ and 5 wt% Re/C), which resulted as mainly active and selective towards 1-hexanol. On the other hand, the use of niobium phosphate as the acid co-catalyst markedly shifted the selectivity towards hexyl hexanoate. Moreover, 5 wt% Re/C and physical mixtures of (5 wt% Re/C + niobium phosphate) were further tested for the hydrogenation of crude hexanoic acid obtained through fermentation of white grape pomace, confirming the promising performance of these catalytic systems and their recyclability. For the first time, the employment of 1-hexanol/hexyl hexanoate mixtures as a diesel blendstock was evaluated, highlighting a significant reduction of soot and CO emissions, without any significant change in the engine performance. The promising properties of these oxygenated additives are favorable for the partial replacement of traditional fossil fuels, in accordance with the short-term goals of EU countries. Full article

(This article belongs to the Special Issue Recent Trends in Catalytic Functionalization of Platform Molecules Derived from Raw Materials)

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15 pages, 3917 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Water Photo-Oxidation over TiO₂—History and Reaction Mechanism

by Yoshio Nosaka

Catalysts 2022, 12(12), 1557; https://doi.org/10.3390/catal12121557 - 1 Dec 2022

Cited by 15 | Viewed by 4205

Abstract

Photocatalytic water oxidation over titanium dioxide (TiO₂) was overviewed by surveying briefly the history of water photo-oxidation, followed by profiling the research for the molecular mechanism of oxygen evolution reaction (OER) at the TiO₂ surface. As the experimental approach to [...] Read more.

Photocatalytic water oxidation over titanium dioxide (TiO₂) was overviewed by surveying briefly the history of water photo-oxidation, followed by profiling the research for the molecular mechanism of oxygen evolution reaction (OER) at the TiO₂ surface. As the experimental approach to investigate the reaction mechanism, ESR, NMR, and STM were described as well as FTIR spectroscopy. Detection of reactive oxygen species, which are the intermediate species in the OER, was also involved in discussing the mechanism. As the theoretical approach to the reaction mechanism, some research with density functional theory (DFT) for anatase (101) surface was illustrated. Since the OER activity of rutile TiO₂ is higher than that of anatase, and the rutile (011) surface has been assigned to the oxidation facet, we performed a DFT calculation for a (011) surface model molecule. The results were successfully discussed with the reported mechanism. The first oxidation step occurs at the bridging OH site, which faces a Ti_5C site. The water molecule which coordinates both sites is oxidized, and the resultant radical coordinates the Ti_5C site to form a trapped hole Ti-O•. In the second step, a coordinated water molecule is oxidized at the Ti-O• site to form a Ti-OOH structure. Full article

(This article belongs to the Special Issue 50 Years of Research in Photocatalysis: Scientific Advances, Discoveries and New Perspectives)

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10 pages, 2376 KiB

Open AccessEditor’s ChoiceCommunication

Hydrogen Evolution Volcano(es)—From Acidic to Neutral and Alkaline Solutions

by Goitom K. Gebremariam, Aleksandar Z. Jovanović, Ana S. Dobrota, Natalia V. Skorodumova and Igor A. Pašti

Catalysts 2022, 12(12), 1541; https://doi.org/10.3390/catal12121541 - 30 Nov 2022

Cited by 10 | Viewed by 6506

Abstract

As the global energy crisis continues, efficient hydrogen production is one of the hottest topics these days. In this sense, establishing catalytic trends for hydrogen production is essential for choosing proper H₂ generation technology and catalytic material. Volcano plots for hydrogen evolution [...] Read more.

As the global energy crisis continues, efficient hydrogen production is one of the hottest topics these days. In this sense, establishing catalytic trends for hydrogen production is essential for choosing proper H₂ generation technology and catalytic material. Volcano plots for hydrogen evolution in acidic media are well-known, while a volcano plot in alkaline media was constructed ten years ago using theoretically calculated hydrogen binding energies. Here, for the first time, we show that the volcano-type relationships are largely maintained in a wide range of pH values, from acidic to neutral and alkaline solutions. We do this using theoretically calculated hydrogen binding energies on clean metallic surfaces and experimentally measured hydrogen evolution overpotentials. When metallic surfaces are exposed to high anodic potentials, hydrogen evolution can be boosted or significantly impeded, depending on the type of metal and the electrolyte in which the reaction occurs. Such effects are discussed here and can be used to properly tailor catalytic materials for hydrogen production via different water electrolysis technologies. Full article

(This article belongs to the Special Issue Advanced Nanomaterials for Electrocatalysis: Synthesis, Characterization and Application)

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18 pages, 1796 KiB

Open AccessEditor’s ChoiceArticle

Synthesis of Polysubstituted 1,2-Dihydro-3H-pyrrolo[1,2-a]indol-3-ones through Domino Palladium-Catalyzed Reactions of Indol-2-ylmethyl Acetates with 1,3-Dicarbonyl Derivatives

by Antonia Iazzetti, Antonio Arcadi, Stefano Dessalvi, Giancarlo Fabrizi, Antonella Goggiamani, Federico Marrone, Andrea Serraiocco, Alessio Sferrazza and Karim Ullah

Catalysts 2022, 12(12), 1516; https://doi.org/10.3390/catal12121516 - 25 Nov 2022

Cited by 8 | Viewed by 2701

Abstract

A straightforward assembly of polysubstituted 1,2-dihydro-3H-pyrrolo[1,2-a]indol-3-ones through a domino palladium-catalyzed reaction of indol-2-ylmethyl acetates with 1,3-dicarbonyl derivatives is described. The key role of the features of the 1,3-dicarbonyls on the reaction outcome has been explored. The employment of 2-methylcyclohexan-1,3-dione [...] Read more.

A straightforward assembly of polysubstituted 1,2-dihydro-3H-pyrrolo[1,2-a]indol-3-ones through a domino palladium-catalyzed reaction of indol-2-ylmethyl acetates with 1,3-dicarbonyl derivatives is described. The key role of the features of the 1,3-dicarbonyls on the reaction outcome has been explored. The employment of 2-methylcyclohexan-1,3-dione as the dicarbonyl source could allow further challenging indole nucleus functionalizations. Full article

(This article belongs to the Special Issue Advances in Transition Metal Catalysis)

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16 pages, 24519 KiB

Open AccessEditor’s ChoiceArticle

A Brønsted Acidic Deep Eutectic Solvent for N-Boc Deprotection

by Debora Procopio, Carlo Siciliano, Roberta De Rose, Sonia Trombino, Roberta Cassano and Maria Luisa Di Gioia

Catalysts 2022, 12(11), 1480; https://doi.org/10.3390/catal12111480 - 19 Nov 2022

Cited by 8 | Viewed by 8367

Abstract

The tert-butyloxycarbonyl (Boc) group is one of the most widely used amine-protecting groups in multistep reactions in synthetic organic chemistry as well as in peptide synthesis. Traditional methods to remove the Boc group have disadvantages in terms of high acidity, the use of [...] Read more.

The tert-butyloxycarbonyl (Boc) group is one of the most widely used amine-protecting groups in multistep reactions in synthetic organic chemistry as well as in peptide synthesis. Traditional methods to remove the Boc group have disadvantages in terms of high acidity, the use of expensive reagents, excessive amounts of catalysts and harmful solvents as well as high temperatures, making them environmentally unsustainable. Therefore, more efforts must be stepwise tightened to make Boc removal practical, clean, and minimize any potential impact. We describe an efficient and sustainable method for N-Boc deprotection by means of a choline chloride/p-toluenesulfonic acid deep eutectic solvent (DES), which is used as a reaction medium plus catalyst. The adopted conditions allow the deprotection of a wide variety of N-Boc derivatives in excellent yields. The strategy has found advantages in greening, simplicity, and short reaction times, resulting in a useful alternative to standard methods. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts: Recent Advances in the Use of Catalysts for Pharmaceuticals)

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16 pages, 3608 KiB

Open AccessEditor’s ChoiceArticle

Magnetron Sputtered Al Co-Doped with Zr-Fe₂O₃ Photoanode with Fortuitous Al₂O₃ Passivation Layer to Lower the Onset Potential for Photoelectrochemical Solar Water Splitting

by Tae Sik Koh, Periyasamy Anushkkaran, Jun Beom Hwang, Sun Hee Choi, Weon-Sik Chae, Hyun Hwi Lee and Jum Suk Jang

Catalysts 2022, 12(11), 1467; https://doi.org/10.3390/catal12111467 - 18 Nov 2022

Cited by 5 | Viewed by 2915

Abstract

In this paper, we investigate the magnetron sputtering deposition of an Al-layer on Zr-doped FeOOH (Zr-FeOOH) samples to fabricate a Zr/Al co-doped Fe₂O₃ (Al-Zr/HT) photoanode. An Al-layer is deposited onto Zr-FeOOH through magnetron sputtering and the thickness of the Al [...] Read more.

In this paper, we investigate the magnetron sputtering deposition of an Al-layer on Zr-doped FeOOH (Zr-FeOOH) samples to fabricate a Zr/Al co-doped Fe₂O₃ (Al-Zr/HT) photoanode. An Al-layer is deposited onto Zr-FeOOH through magnetron sputtering and the thickness of the Al deposition is regulated by differing the sputtering time. Electrochemical impedance spectroscopy, intensity-modulated photocurrent spectroscopy, Mott-Schottky and time-resolved photoluminescence spectra analyses were used to study, in depth, the correlations between sputtered Al-layer thicknesses and PEC characteristics. High-temperature quenching (800 °C) assists in diffusing the Al³⁺ in the bulk of the Zr-doped Fe₂O₃ photoanode, whilst an unintended Al₂O₃ passivation layer forms on the surface. The optimized Al-Zr/HT photoelectrode achieved 0.945 mA/cm² at 1.0 V_RHE, which is 3-fold higher than that of the bare Zr/HT photoanode. The Al₂O₃ passivation layer causes a 100 mV cathodic shift in the onset potential. Al co-doping improved the donor density, thus reducing the electron transit time. In addition, the passivation effect of the Al₂O₃ layer ameliorated the surface charge transfer kinetics. The Al₂O₃ passivation layer suppressed the surface charge transfer resistance, consequently expediting the hole migration from photoanode to electrolyte. We believe that the thickness-controlled Al-layer sputtering approach could be applicable for various metal oxide photoanodes to lower the onset potential. Full article

(This article belongs to the Special Issue Theme Issue in Honor of Prof. Dr. Jae Sung Lee)

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18 pages, 6652 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Highly Active Ag-Cu Nanocrystal Catalyst-Coated Brewer’s Spent Grain Biochar for the Mineralization of Methyl Orange and Methylene Blue Dye Mixture

by Lahcen Boubkr, Arvind K. Bhakta, Youssef Snoussi, Cora Moreira Da Silva, Laurent Michely, Mohamed Jouini, Souad Ammar and Mohamed M. Chehimi

Catalysts 2022, 12(11), 1475; https://doi.org/10.3390/catal12111475 - 18 Nov 2022

Cited by 17 | Viewed by 3739

Abstract

The aim of the present work is to valorise the brewing industry’s waste, i.e., brewer’s spent grain (BSG), into functional biocarbon for environmental catalysis applications. In this context, cost-effective and environmentally friendly biochar support coated with in-situ-generated Ag-Cu nanocrystals, was developed via the [...] Read more.

The aim of the present work is to valorise the brewing industry’s waste, i.e., brewer’s spent grain (BSG), into functional biocarbon for environmental catalysis applications. In this context, cost-effective and environmentally friendly biochar support coated with in-situ-generated Ag-Cu nanocrystals, was developed via the wet impregnation of BSG biomass powder with copper (II) nitrate trihydrate and silver nitrate aqueous solution prior to pyrolysis at moderate temperature (500 °C). Small-size homogenously distributed Ag-Cu nanocrystals (≤80 nm) on the surface of the biochar (Biochar@Ag-Cu) were observed by field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). Elemental compositions were determined by X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX). The crystalline nature of the nanoparticles was confirmed by X-ray powder diffraction (XRD). Information about the thermal stability of the materials and quality were obtained by thermogravimetric analysis (TGA) and Raman, respectively. The potentiality of the Biochar@Ag-Cu catalyst in the field of pollutant removal is demonstrated by taking methyl orange and methylene blue as model dyes. A kinetics study was performed and analyzed by UV–vis spectroscopy. Its highly active catalytic nature is proved by the complete mineralization of the methyl orange dye (100%) through oxidative degradation. The reusability of the catalyst has shown 96% removal efficiency after 3 cycles. The linear plot of −Ln (C_A/C₀) vs. time (R² = 0.9892) reveals that the mineralization of the methyl orange dye follows pseudo-first-order kinetics (k = 0.603 × 10⁻² min⁻¹). A methyl orange + methylene blue dye mixture degradation study has revealed the faster kinetics of the present catalyst towards methylene blue degradation. The current study suggests that BSG Biochar@Ag-Cu can be a potential candidate in contribution towards SDG 6. Full article

(This article belongs to the Special Issue Nanoparticles in the Catalysis)

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23 pages, 4101 KiB

Open AccessEditor’s ChoiceReview

A Critical Review of the Use of Bismuth Halide Perovskites for CO₂ Photoreduction: Stability Challenges and Strategies Implemented

by Edith Luévano-Hipólito, Oscar L. Quintero-Lizárraga and Leticia M. Torres-Martínez

Catalysts 2022, 12(11), 1410; https://doi.org/10.3390/catal12111410 - 11 Nov 2022

Cited by 17 | Viewed by 4490

Abstract

Inspired by natural photosynthesis, the photocatalytic CO₂ reduction reaction (CO2RR) stands as a viable strategy for the production of solar fuels to mitigate the high dependence on highly polluting fossil fuels, as well as to decrease the CO₂ concentration in the [...] Read more.

Inspired by natural photosynthesis, the photocatalytic CO₂ reduction reaction (CO2RR) stands as a viable strategy for the production of solar fuels to mitigate the high dependence on highly polluting fossil fuels, as well as to decrease the CO₂ concentration in the atmosphere. The design of photocatalytic materials is crucial to ensure high efficiency of the CO2RR process. So far, perovskite materials have shown high efficiency and selectivity in CO2RR to generate different solar fuels. Particularly, bismuth halide perovskites have gained much attention due to their higher absorption coefficients, their more efficient charge transfer (compared to oxide perovskites), and their required thermodynamic potential for CO2RR. Moreover, these materials represent a promising alternative to the highly polluting lead halide perovskites. However, despite all the remarkable advantages of bismuth halide perovskites, their use has been limited, owing to instability concerns. As a consequence, recent reports have offered solutions to obtain structures highly stable against oxygen, water, and light, promoting the formation of solar fuels with promising efficiency for CO2RR. Thus, this review analyzes the current state of the art in this field, particularly studies about stability strategies from intrinsic and extrinsic standpoints. Lastly, we discuss the challenges and opportunities in designing stable bismuth halide perovskites, which open new opportunities for scaling up the CO2RR. Full article

(This article belongs to the Special Issue Photocatalysts for Pollutants Disposals, CO₂ Reduction, Hydrogen Evolution Reaction)

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14 pages, 4983 KiB

Open AccessEditor’s ChoiceArticle

Co(OH)₂ Nanoflowers Decorated α-NiMoO₄ Nanowires as a Bifunctional Electrocatalyst for Efficient Overall Water Splitting

by Zhiying Xu, Minghui Hao, Xin Liu, Jingjing Ma, Liang Wang, Chunhu Li and Wentai Wang

Catalysts 2022, 12(11), 1417; https://doi.org/10.3390/catal12111417 - 11 Nov 2022

Cited by 16 | Viewed by 2833

Abstract

The development of bifunctional electrocatalysts with high catalytic activity and cyclic stability is an effective method for electrocatalytic water splitting. Herein, a promising hydroxide/oxide Co(OH)₂/α-NiMoO₄ NWs/CC heterostructure with nanoflowers decorating the nanowires was fabricated on a carbon cloth (CC) substrate [...] Read more.

The development of bifunctional electrocatalysts with high catalytic activity and cyclic stability is an effective method for electrocatalytic water splitting. Herein, a promising hydroxide/oxide Co(OH)₂/α-NiMoO₄ NWs/CC heterostructure with nanoflowers decorating the nanowires was fabricated on a carbon cloth (CC) substrate via hydrothermal and calcination methods. In contrast to one-dimensional nanomaterials, the interfaces of Co(OH)₂ nanoflowers and α-NiMoO₄ nanowires on CC provide more active sites for electrocatalytic reactions; therefore, they exhibit obviously enhanced electrocatalytic activities in overall water splitting. Specifically, the Co(OH)₂/α-NiMoO₄ NWs/CC electrodes exhibit an overpotential of 183.01 mV for hydrogen evolution reaction (HER) and of 170.26 mV for oxygen evolution reactions (OER) at the current density of 10 mA cm⁻² in 1.0 M KOH. Moreover, the electrocatalytic oxygen evolution reaction (OER) activity of the Co(OH)₂/α-NiMoO₄ NWs/CC electrocatalyst was enhanced after long-term stability tests. Full article

(This article belongs to the Special Issue Synthesis and Application of Catalytic Materials in Energy and Environment)

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18 pages, 2232 KiB

Open AccessEditor’s ChoiceReview

Recent Progress of Ga-Based Catalysts for Catalytic Conversion of Light Alkanes

by Yuming Li, Shuting Fu, Qiyang Zhang, Hongyu Liu and Yajun Wang

Catalysts 2022, 12(11), 1371; https://doi.org/10.3390/catal12111371 - 5 Nov 2022

Cited by 11 | Viewed by 4303

Abstract

The efficient and clean conversion of light alkanes is a research hotspot in the petrochemical industry, and the development of effective and eco-friendly non-noble metal-based catalysts is a key factor in this field. Among them, gallium is a metal component with good catalytic [...] Read more.

The efficient and clean conversion of light alkanes is a research hotspot in the petrochemical industry, and the development of effective and eco-friendly non-noble metal-based catalysts is a key factor in this field. Among them, gallium is a metal component with good catalytic performance, which has been extensively used for light alkanes conversion. Herein, we critically summarize recent developments in the preparation of gallium-based catalysts and their applications in the catalytic conversion of light alkanes. First, we briefly describe the different routes of light alkane conversion. Following that, the remarkable preparation methods for gallium-based catalysts are discussed, with their state-of-the-art application in light alkane conversion. It should be noticed that the directional preparation of specific Ga species, strengthening metal-support interactions to anchor Ga species, and the application of new kinds of methods for Ga-based catalysts preparation are at the leading edge. Finally, the review provides some current limitations and future perspectives for the development of gallium-based catalysts. Recently, different kinds of Ga species were reported to be active in alkane conversion, and how to separate them with advanced in situ and ex situ characterizations is still a problem that needs to be solved. We believe that this review can provide base information for the preparation and application of Ga-based catalysts in the current stage. With these summarizations, this review can inspire new research directions of gallium-based catalysts in the catalysis conversion of light alkanes with ameliorated performances. Full article

(This article belongs to the Special Issue Photocatalysis for Energy Transformation Reactions)

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13 pages, 2631 KiB

Open AccessEditor’s ChoiceArticle

Spark Ablation for the Fabrication of PEM Water Electrolysis Catalyst-Coated Membranes

by Foteini M. Sapountzi, Marek Lavorenti, Wilbert Vrijburg, Sofia Dimitriadou, Beata Tyburska-Pueschel, Peter Thüne, Hans Niemantsverdriet, Tobias V. Pfeiffer and Mihalis N. Tsampas

Catalysts 2022, 12(11), 1343; https://doi.org/10.3390/catal12111343 - 2 Nov 2022

Cited by 11 | Viewed by 6299

Abstract

Proton-exchange-membrane (PEM) electrolyzers represent a promising technology for sustainable hydrogen production, owing to their efficiency and load flexibility. However, the acidic nature of PEM demands the use of platinum-group metal-electrocatalysts. Apart from the associated high capital costs, the scarcity of Ir hinders the [...] Read more.

Proton-exchange-membrane (PEM) electrolyzers represent a promising technology for sustainable hydrogen production, owing to their efficiency and load flexibility. However, the acidic nature of PEM demands the use of platinum-group metal-electrocatalysts. Apart from the associated high capital costs, the scarcity of Ir hinders the large-scale implementation of the technology. Since low-cost replacements for Ir are not available at present, there is an urgent need to engineer catalyst-coated membranes (CCMs) with homogeneous catalyst layers at low Ir loadings. Efforts to realize this mainly rely on the development of advanced Ir nanostructures with maximized dispersion via wet chemistry routes. This study demonstrates the potential of an alternative vapor-based process, based on spark ablation and impaction, to fabricate efficient and durable Ir- and Pt-coated membranes. Our results indicate that spark-ablation CCMs can reduce the Ir demand by up to five times compared to commercial CCMs, without a compromise in activity. The durability of spark-ablation CCMs has been investigated by applying constant and dynamic load profiles for 150 h, indicating different degradation mechanisms for each case without major pitfalls. At constant load, an initial degradation in performance was observed during the first 30 h, but a stable degradation rate of 0.05 mV h⁻¹ was sustained during the rest of the test. The present results, together with manufacturing aspects related to simplicity, costs and environmental footprint, suggest the high potential of spark ablation having practical applications in CCM manufacturing. Full article

(This article belongs to the Special Issue Advanced Nanomaterials for Electrocatalysis: Synthesis, Characterization and Application)

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17 pages, 3032 KiB

Open AccessEditor’s ChoiceArticle

Large-Scale Synthesis of Iron Ore@Biomass Derived ESBC to Degrade Tetracycline Hydrochloride for Heterogeneous Persulfate Activation

by Tingting Tian, Xinfeng Zhu, Zhongxian Song, Xindong Li, Jinhui Zhang, Yanli Mao, Junfeng Wu, Wei Zhang and Chaohai Wang

Catalysts 2022, 12(11), 1345; https://doi.org/10.3390/catal12111345 - 2 Nov 2022

Cited by 4 | Viewed by 2464

Abstract

Iron-based catalysts are widely used in water treatment and environmental remediation due to their abundant content in nature and their ability to activate persulfate at room temperature. Here, eggshell biochar-loaded natural iron slag (IO@ESBC) was successfully synthesized to remove tetracycline hydrochloride (TCH) by [...] Read more.

Iron-based catalysts are widely used in water treatment and environmental remediation due to their abundant content in nature and their ability to activate persulfate at room temperature. Here, eggshell biochar-loaded natural iron slag (IO@ESBC) was successfully synthesized to remove tetracycline hydrochloride (TCH) by activated persulfate. The morphology, structure and chemical composition of IO@ESBC were systematically characterized. The IO@ESBC/PS process showed good performance for TCH removal. The decomposition rate constant (k) for IO@ESBC was 0.011 min⁻¹ and the degradation rate was 3690 mmol/g/h in this system. With the increase of PS concentration and IO@ESBC content, the removal rate of TCH both increased. The IO@ESBC/PS process can effectively remove TCH at pH 3–9. There are different effects on TCH removal for the reason that the addition of water matrix species (humic acid, Cl⁻, HCO₃⁻, NO₃⁻ and HPO₄²⁻). The IO@ESBC/PS system for degrading TCH was mainly controlled by both the free radical pathway (SO₄^•−, •OH and O₂^•−) and non-free radical pathway (¹O₂). The loading of ESBC slows down the agglomeration between iron particles, and more active sites are exposed. The removal rate of TCH was still above 75% after five cycles of IO@ESBC. This interesting investigation has provided a green route for synthesis of composite driving from waste resources, expanding its further application for environmental remediations. Full article

(This article belongs to the Special Issue Advanced Catalytic Material for Water Treatment)

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16 pages, 3252 KiB

Open AccessEditor’s ChoiceArticle

Activity and Structure of Nano-Sized Cobalt-Containing Systems for the Conversion of Lignin and Fuel Oil to Synthesis Gas and Hydrocarbons in a Microwave-Assisted Plasma Catalytic Process

by Mark V. Tsodikov, Olga V. Bukhtenko, Alexander V. Naumkin, Sergey A. Nikolaev, Andrey V. Chistyakov and Grigory I. Konstantinov

Catalysts 2022, 12(11), 1315; https://doi.org/10.3390/catal12111315 - 27 Oct 2022

Cited by 2 | Viewed by 1871

Abstract

In this study, we present the results of lignin and fuel oil conversion to hydrogen, synthesis gas, and liquid hydrocarbons in the presence of nano-sized cobalt-containing systems in a microwave-assisted plasma catalytic process. The deposition of a small amount of cobalt on lignin [...] Read more.

In this study, we present the results of lignin and fuel oil conversion to hydrogen, synthesis gas, and liquid hydrocarbons in the presence of nano-sized cobalt-containing systems in a microwave-assisted plasma catalytic process. The deposition of a small amount of cobalt on lignin increases its microwave absorption capacity and provides plasma generation in the reaction zone. The role of Co-containing particles in the above catalytic reactions is probably to activate the carbon bonds of lignin, which substantially increases the microwave absorption capacity of the system as a whole. The subsequent use of the cobalt-containing residue of lignin conversion as a catalytic system and MWI-absorbing material results in active fuel oil pyrolysis in a plasma catalytic process to afford gaseous and liquid hydrocarbons. In the plasma catalytic pyrolysis, fuel oil conversion is probably accompanied by the conversion of the organic matter of the residue and agglomeration of cobalt oxide particles. Full article

(This article belongs to the Special Issue Nanoparticles in the Catalysis)

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15 pages, 1805 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Inactivation and Degradation of Influenza A Virus on the Surface of Photoactive Self-Cleaning Cotton Fabric Functionalized with Nanocrystalline TiO₂

by Dmitry Selishchev, Grigory Stepanov, Mariia Sergeeva, Maria Solovyeva, Evgenii Zhuravlev, Andrey Komissarov, Vladimir Richter and Denis Kozlov

Catalysts 2022, 12(11), 1298; https://doi.org/10.3390/catal12111298 - 23 Oct 2022

Cited by 6 | Viewed by 2855

Abstract

Chemical modification of cotton-rich fabrics with TiO₂ nanoparticles results in photoactive self-cleaning textiles, which can provide, under UV or solar radiation, complete oxidation of low-molecular compounds, degradation of supramolecular structures, and inactivation of microorganisms due to the photocatalytic effect. In this paper, [...] Read more.

Chemical modification of cotton-rich fabrics with TiO₂ nanoparticles results in photoactive self-cleaning textiles, which can provide, under UV or solar radiation, complete oxidation of low-molecular compounds, degradation of supramolecular structures, and inactivation of microorganisms due to the photocatalytic effect. In this paper, we describe, based on the example of influenza A (H1N1) virus, a photoinduced antiviral effect of cotton fabric functionalized with nanocrystalline TiO₂. Fast inactivation of influenza virus occurs on the irradiated surface of photoactive fabric due to adsorption and photocatalytic degradation. The TiO₂ component in the prepared fabric increases the adsorption effect compared to initial cotton due to a high specific area of TiO₂ nanocrystallites. Long-term irradiation leads to destruction of all virion structures to the point of RNA molecules. In contrast to pristine cotton, no virus RNA is detected using the polymerase chain reaction (PCR) technique after long-term irradiation of photoactive fabric. The results of this study underline the potential of photoactive self-cleaning fabrics for application in air purification systems and personal protective clothes to provide permanent protection of people against harmful chemical and biological pollutants. Full article

(This article belongs to the Special Issue Photocatalytic Nanomaterials for Abatement of Microorganisms)

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16 pages, 6982 KiB

Open AccessEditor’s ChoiceArticle

Computational Insights into Ru, Pd and Pt fcc Nano-Catalysts from Density Functional Theory Calculations: The Influence of Long-Range Dispersion Corrections

by Marietjie J. Ungerer and Nora H. De Leeuw

Catalysts 2022, 12(10), 1287; https://doi.org/10.3390/catal12101287 - 21 Oct 2022

Cited by 5 | Viewed by 4012

Abstract

Ruthenium, palladium and platinum fall within the group of noble metals that are widely used in catalysis, especially for the electrocatalytic production of hydrogen. The dominant phase of the bulk Ru metal is hexagonal close-packed (hcp), which has been studied extensively. [...] Read more.

Ruthenium, palladium and platinum fall within the group of noble metals that are widely used in catalysis, especially for the electrocatalytic production of hydrogen. The dominant phase of the bulk Ru metal is hexagonal close-packed (hcp), which has been studied extensively. However, significantly less attention has been paid to the face-centred cubic (fcc) phases, which have been observed in nanoparticles. In this study, we have carried out density functional theory calculations with long-range dispersion corrections [DFT-D2, DFT-D3 and DFT-D3-(BJ)] to investigate the lattice parameters, surface energies and work functions of the (001), (011) and (111) surfaces of Ru, Pd and Pt in the fcc phase. When investigating the surface properties of the three metals, we observed that the DFT-D2 method generally underestimated the lattice parameters by up to 2.2% for Pt and 2.8% for Ru. The surface energies followed the observed trend (111) < (001) < (011) for both Ru and Pd with all three methods, which is comparable to experimental data. For Pt the same trend was observed with DFT-D2 and DFT-D3(BJ), but it deviated to Pt (111) < Pt (011) < Pt (001) for the DFT-D3 method. DFT-D2 overestimated the surface energies for all three Miller Indexes by 82%, 73%, and 60%, when compared to experimental values. The best correlation for the surface energies was obtained with the DFT-D3 and DFT-D3(BJ) methods, both of which have deviate by less than 15% deviation for all surfaces with respect to experiment. The work function followed the trend of Φ (111) < Φ (001) < Φ (011) for all three metals and calculated by all three methods. Five different types of Ru, Pd and Pt nanoparticles were considered, including icosahedral, decahedral, cuboctahedral, cubic and spherical particles of different sizes. The bulk, surface and nanoparticle calculations showed that the DFT-D2 method for Pt overestimated the exchange-correlation, leading to higher energy values that can be contributed erroneously to a more stable structure. The calculations showed that as soon as the surface-to-bulk ratio > 1, the energy per atom resembles bulk energy values. Full article

(This article belongs to the Special Issue Application of Heterogeneous Catalysts in Energy Conversion and Storage Systems)

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24 pages, 4024 KiB

Open AccessEditor’s ChoiceArticle

Synthesis of Novel Key Chromophoric Intermediates via C-C Coupling Reactions

by Laila M. Nhari, Elham N. Bifari, Aisha R. Al-Marhabi, Huda A. Al-Ghamdi, Sameera N. Al-Ghamdi, Fatimah A. M. Al-Zahrani, Khalid O. Al-Footy and Reda M. El-Shishtawy

Catalysts 2022, 12(10), 1292; https://doi.org/10.3390/catal12101292 - 21 Oct 2022

Cited by 6 | Viewed by 4810

Abstract

The fundamentals of Pd-catalyzed Csp²−Csp² Miyaura borylation, Suzuki cross-coupling, and Stille cross-coupling reactions for a variety of borylated precursors based on phenothiazine (PTZ), phenoxazine (POZ), carbazole (Cz), and quinoxaline (QX) units have been explored. Three palladium-based catalysts were chosen for [...] Read more.

The fundamentals of Pd-catalyzed Csp²−Csp² Miyaura borylation, Suzuki cross-coupling, and Stille cross-coupling reactions for a variety of borylated precursors based on phenothiazine (PTZ), phenoxazine (POZ), carbazole (Cz), and quinoxaline (QX) units have been explored. Three palladium-based catalysts were chosen for this study: Pd(PPh₃)₄, Pd(PPh₃)₂Cl₂, and Pd(dppf)Cl₂, applying different reaction conditions. Around 16 desired chromophores were successfully designed and synthesized using C-C cross-coupling reactions in moderate to excellent yields, including PTZ, POZ, and Cz units coupled with QX, indolinium iodide, thienyl, phenyl, or triphenylamine moieties. Additionally, PTZ, POZ, and Cz have been employed in synthesizing various pinacol boronate ester derivatives in good to moderate yields. Interestingly, Pd(dppf)Cl₂ was found to be the best catalyst for borylation, and C-C cross-coupling reactions occurred in as little as 30 min, with an excellent yield exceeding 98%. Pd(PPh₃)₄ and Pd(PPh₃)₂Cl₂ catalyzed the reaction to obtain the desired products in moderate to good yields after a long time (20–24 h). On the other hand, the Suzuki-Miyaura cross-coupling between N-(2-methyl)hexyl carbazole pinacol boronate ester derivative 10c and three halogenated quinoxaline derivatives—4-(3-(5-bromothiophen-2-yl)quinoxalin-2-yl)benzaldehyde (27), 4-(5-(3-(5-bromothiophen-2-yl)quinoxalin-2-yl)thiophen-2-yl)benzaldehyde (30), and 4-(3-chloroquinoxalin-2-yl)benzaldehyde (25) catalyzed by Pd(PPh₃)₄—afforded three carbazole-quinoxaline chromophores (28, 30, and 31, respectively) in 2–3 h, with good to excellent yields reaching 86%. The electron-deficient QX couplers proved to be coupled efficiently using the Stille coupling reaction, which involves the coupling between electron-rich orgaostannane and electron-deficient halide. The synthesized precursors and desired chromophores were characterized by FTIR, ¹H-NMR, ¹³C-NMR, and HRMS. Full article

(This article belongs to the Special Issue The Role of Catalysts in Functionalization of C-H and C-C Bonds)

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12 pages, 7398 KiB

Open AccessEditor’s ChoiceArticle

Photo-Charging a Zinc-Air Battery Using a Nb₂O₅-CdS Photoelectrode

by Tatiana S. Andrade, Antero R. S. Neto, Francisco G. E. Nogueira, Luiz C. A. Oliveira, Márcio C. Pereira and Panagiotis Lianos

Catalysts 2022, 12(10), 1240; https://doi.org/10.3390/catal12101240 - 15 Oct 2022

Cited by 6 | Viewed by 2874

Abstract

Integrating a photoelectrode into a zinc-air battery is a promising approach to reducing the overpotential required for charging a metal-air battery by using solar energy. In this work, a photo-fuel cell employing a Nb₂O₅/CdS photoanode and a Zn foil [...] Read more.

Integrating a photoelectrode into a zinc-air battery is a promising approach to reducing the overpotential required for charging a metal-air battery by using solar energy. In this work, a photo-fuel cell employing a Nb₂O₅/CdS photoanode and a Zn foil as a counter-electrode worked as a photoelectrochemical battery that saves up to 1.4 V for battery charging. This is the first time a Nb₂O₅-based photoelectrode is reported as a photoanode in a metal-air battery, and the achieved gain is one of the top results reported so far. Furthermore, the cell consumed an organic fuel, supporting the idea of using biomass wastes as a power source for sunlight-assisted charging of metal-air batteries. Thus, this device provides additional environmental benefits and contributes to technologies integrating solar energy conversion and storage. Full article

(This article belongs to the Special Issue Advanced Catalysts for Electrochemical Energy Storage and Conversion)

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15 pages, 3458 KiB

Open AccessEditor’s ChoiceArticle

Assessment of a Euro VI Step E Heavy-Duty Vehicle’s Aftertreatment System

by Barouch Giechaskiel, Tommaso Selleri, Roberto Gioria, Anastasios D. Melas, Jacopo Franzetti, Christian Ferrarese and Ricardo Suarez-Bertoa

Catalysts 2022, 12(10), 1230; https://doi.org/10.3390/catal12101230 - 14 Oct 2022

Cited by 8 | Viewed by 3198

Abstract

The latest generation of heavy-duty vehicles (Euro VI step E) have to respect low emission limits both in the laboratory and on the road. The most challenging pollutants for diesel vehicles are NO_x and particles; nevertheless, NH₃ and N₂O [...] Read more.

The latest generation of heavy-duty vehicles (Euro VI step E) have to respect low emission limits both in the laboratory and on the road. The most challenging pollutants for diesel vehicles are NO_x and particles; nevertheless, NH₃ and N₂O need attention. In this study, we measured regulated and unregulated pollutants of a Euro VI step E Diesel vehicle. Samples were taken downstream of (i) the engine, (ii) the Diesel oxidation catalyst (DOC) and catalyzed Diesel particulate filter (cDPF), and (iii) the selective catalytic reduction (SCR) unit for NO_x with an ammonia slip catalyst (ASC). In addition to typical laboratory and real-world cycles, various challenging tests were conducted (urban driving with low payload, high-speed full-load driving, and idling) at 23 °C and 5 °C. The results showed high efficiencies of the DOC, DPF, and SCR under most testing conditions. Cold start cycles resulted in high NO_x emissions, while high-temperature cycles resulted in high particle emissions. The main message of this study is that further improvements are necessary, also considering possible reductions in the emission limits in future EU regulations. Full article

(This article belongs to the Special Issue Catalytic Removal and Resource Utilization of NOx)

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21 pages, 3831 KiB

Open AccessEditor’s ChoiceReview

Recent Strategies in Nickel-Catalyzed C–H Bond Functionalization for Nitrogen-Containing Heterocycles

by Ke Yang, Zhi Li, Qingyue Hu, Mazen Elsaid, Chong Liu, Jun Chen and Haibo Ge

Catalysts 2022, 12(10), 1163; https://doi.org/10.3390/catal12101163 - 2 Oct 2022

Cited by 13 | Viewed by 4330

Abstract

N-heterocycles are ubiquitous in natural products, pharmaceuticals, organic materials, and numerous functional molecules. Among the current synthetic approaches, transition metal-catalyzed C–H functionalization has gained considerable attention in recent years due to its advantages of simplicity, high atomic economy, and the ready availability [...] Read more.

N-heterocycles are ubiquitous in natural products, pharmaceuticals, organic materials, and numerous functional molecules. Among the current synthetic approaches, transition metal-catalyzed C–H functionalization has gained considerable attention in recent years due to its advantages of simplicity, high atomic economy, and the ready availability of starting materials. In the field of N-heterocycle synthesis via C–H functionalization, nickel has been recognized as one of the most important catalysts. In this review, we will introduce nickel-catalyzed intramolecular and intermolecular pathways for N-heterocycle synthesis from 2008 to 2021. Full article

(This article belongs to the Special Issue The Role of Catalysts in Functionalization of C-H and C-C Bonds)

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26 pages, 2437 KiB

Open AccessEditor’s ChoiceReview

Membrane Bioreactors: A Promising Approach to Enhanced Enzymatic Hydrolysis of Cellulose

by Saleha Al-Mardeai, Emad Elnajjar, Raed Hashaikeh, Boguslaw Kruczek, Bart Van der Bruggen and Sulaiman Al-Zuhair

Catalysts 2022, 12(10), 1121; https://doi.org/10.3390/catal12101121 - 27 Sep 2022

Cited by 11 | Viewed by 4555

Abstract

The depletion of fossil fuel resources and the negative impact of their use on the climate have resulted in the need for alternative sources of clean, sustainable energy. One available alternative, bioethanol, is a potential substitute for, or additive to, petroleum-derived gasoline. In [...] Read more.

The depletion of fossil fuel resources and the negative impact of their use on the climate have resulted in the need for alternative sources of clean, sustainable energy. One available alternative, bioethanol, is a potential substitute for, or additive to, petroleum-derived gasoline. In the lignocellulose-to-bioethanol process, the cellulose hydrolysis step represents a major hurdle that hinders commercialization. To achieve economical production of bioethanol from lignocellulosic materials, the rate and yield of the enzymatic hydrolysis of cellulose, which is preferred over other chemically catalyzed processes, must be enhanced. To achieve this, product inhibition and enzyme loss, which are two major challenges, must be overcome. The implementation of membranes, which can permeate molecules selectively based on their size, offers a solution to this problem. Membrane bioreactors (MBRs) can enhance enzymatic hydrolysis yields and lower costs by retaining enzymes for repeated usage while permeating the products. This paper presents a critical discussion of the use of MBRs as a promising approach to the enhanced enzymatic hydrolysis of cellulosic materials. Various MBR configurations and factors that affect their performance are presented. Full article

(This article belongs to the Special Issue Enzymatic Catalysis in Bio-Based Chemicals Production)

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23 pages, 2553 KiB

Open AccessEditor’s ChoiceReview

Catalytic Dehydration of Isopropanol to Propylene

by Jean-Luc Dubois, Georgeta Postole, Lishil Silvester and Aline Auroux

Catalysts 2022, 12(10), 1097; https://doi.org/10.3390/catal12101097 - 22 Sep 2022

Cited by 17 | Viewed by 9271

Abstract

Catalytic dehydration of isopropanol to propylene is a common reaction in laboratories to characterize the acid–base properties of catalysts. When acetone is produced, it is the sign of the presence of basic active sites, while propylene is produced on the acid sites. About [...] Read more.

Catalytic dehydration of isopropanol to propylene is a common reaction in laboratories to characterize the acid–base properties of catalysts. When acetone is produced, it is the sign of the presence of basic active sites, while propylene is produced on the acid sites. About 2/3rd of the world production of isopropanol is made from propylene, and the other third is made from acetone hydrogenation. Since the surplus acetone available on the market is mainly a coproduct of phenol synthesis, variations in the demand for phenol affect the supply position of acetone and vice versa. High propylene price and low demand for acetone should revive the industrial interest in acetone conversion. In addition, there is an increasing interest in the production of acetone and isopropanol from CO/CO₂ via expected more environmentally friendly biochemical conversion routes. To preserve phenol process economics, surplus acetone should be recycled to propylene via the acetone hydrogenation and isopropanol dehydration routes. Some critical impurities present in petrochemical propylene are avoided in the recycling process. In this review, the selection criteria for the isopropanol dehydration catalysts at commercial scale are derived from the patent literature and analyzed with academic literature. The choice of the process conditions, such as pressure, temperature and gas velocity, and the catalysts’ properties such as pore size and acid–base behavior, are critical factors influencing the purity of propylene. Dehydration of isopropanol under pressure facilitates the downstream separation of products and the isolation of propylene to yield a high-purity “polymer grade”. However, it requires to operate at a higher temperature, which is a challenge for the catalyst’s lifetime; whereas operation at near atmospheric pressure, and eventually in a diluted stream, is relevant for applications that would tolerate a lower propylene purity (chemical grade). Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts: Feature Papers in Catalytic Reaction Engineering)

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9 pages, 2996 KiB

Open AccessEditor’s ChoiceArticle

Self-Supported Polymeric Ruthenium Complexes as Olefin Metathesis Catalysts in Synthesis of Heterocyclic Compounds

by Adam A. Rajkiewicz, Anna Kajetanowicz and Karol Grela

Catalysts 2022, 12(10), 1087; https://doi.org/10.3390/catal12101087 - 21 Sep 2022

Cited by 2 | Viewed by 2128

Abstract

New ruthenium olefin metathesis catalysts containing N-heterocyclic carbene (NHC) connected by a linker tether to a benzylidene ligand were studied. Such obtained self-chelated Hoveyda–Grubbs type complexes existed in the form of an organometallic polymer but could still catalyze olefin metathesis after being dissolved [...] Read more.

New ruthenium olefin metathesis catalysts containing N-heterocyclic carbene (NHC) connected by a linker tether to a benzylidene ligand were studied. Such obtained self-chelated Hoveyda–Grubbs type complexes existed in the form of an organometallic polymer but could still catalyze olefin metathesis after being dissolved in an organic solvent. Although these polymeric catalysts exhibited a slightly lower activity compared to structurally related nonpolymeric catalysts, they were successfully used in a number of ring-closing metathesis reactions leading to a variety of heterocyclic compounds, including biologically and pharmacologically related analogues of cathepsin K inhibitor and sildenafil (Viagra™). In the last case, a good solubility of a polymeric catalyst in toluene allowed the separation of the product from the catalyst via simple filtration. Full article

(This article belongs to the Special Issue Catalysis in Heterocyclic and Organometallic Synthesis II)

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15 pages, 3335 KiB

Open AccessEditor’s ChoiceArticle

Pd-Catalyzed Hirao P–C Coupling Reactions with Dihalogenobenzenes without the Usual P-Ligands under MW Conditions

by Bianka Huszár, Petra Regina Varga, Nóra Á. Szűcs, András Simon, László Drahos and György Keglevich

Catalysts 2022, 12(10), 1080; https://doi.org/10.3390/catal12101080 - 20 Sep 2022

Cited by 2 | Viewed by 2173

Abstract

A literature survey of the P–C coupling reactions of 1,4-and 1,2-bromo-iodobenzenes with diphenylphosphine oxide or diethyl phosphite under different conditions comprising Pd-, Ni-, or Cu-catalysis revealed that, depending on the experimental details, the yields of the corresponding >P(O)-bromobenzenes were rather diverse and occasionally [...] Read more.

A literature survey of the P–C coupling reactions of 1,4-and 1,2-bromo-iodobenzenes with diphenylphosphine oxide or diethyl phosphite under different conditions comprising Pd-, Ni-, or Cu-catalysis revealed that, depending on the experimental details, the yields of the corresponding >P(O)-bromobenzenes were rather diverse and occasionally contradicting. Therefore, the reactivity of a series of 1,4-, 1,3- and 1,2-dibromo- and bromo-iodobenzenes with the above mentioned P-reagents was evaluated under the “P-ligand-free” microwave (MW)-assisted conditions elaborated by us. Starting from dibromobenzenes and iodo-bromoarenes, practical and competent syntheses were developed for phosphonoyl- and phosphinoyl-bromoarenes, and, in a few instances, for arenes with two P-functions. The cheaper dibromobenzenes may be substituted for the bromo-iodo derivatives. In all, 12 products were prepared in yields of 45–82%. They were fully characterized. The method described does not require the use of traditional P-ligands. Full article

(This article belongs to the Special Issue Catalysis in Heterocyclic and Organometallic Synthesis II)

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12 pages, 7538 KiB

Open AccessEditor’s ChoiceArticle

Semi-Hydrogenation of Acetylene to Ethylene Catalyzed by Bimetallic CuNi/ZSM-12 Catalysts

by Song Hu, Chong Zhang, Mingyu Wu, Runping Ye, Depan Shi, Mujin Li, Peng Zhao, Rongbin Zhang and Gang Feng

Catalysts 2022, 12(9), 1072; https://doi.org/10.3390/catal12091072 - 19 Sep 2022

Cited by 9 | Viewed by 3168

Abstract

The purpose of this work is to develop a low-cost and high-performance catalyst for the selective catalytic hydrogenation of acetylene to ethylene. Non-precious metals Cu and Ni were selected as active ingredients for this study. Using ZSM-12 as a carrier, Cu-Ni bimetallic catalysts [...] Read more.

The purpose of this work is to develop a low-cost and high-performance catalyst for the selective catalytic hydrogenation of acetylene to ethylene. Non-precious metals Cu and Ni were selected as active ingredients for this study. Using ZSM-12 as a carrier, Cu-Ni bimetallic catalysts of CuNi_x/ZSM-12 (x = 5, 7, 9, 11) with different Ni/Cu ratios were prepared by incipient wetness impregnation method. The total Cu and Ni loading were 2 wt%. Under the optimal reaction conditions, the acetylene conversion was 100%, and the ethylene selectivity was 82.48%. The CuNi₇/ZSM-12 prepared in this work exhibits good performance in the semi-hydrogenation of acetylene to ethylene with low cost and has potential for industrial application. Full article

(This article belongs to the Special Issue Current State-of-the-Art of Catalysts for Energy and Environmental Applications)

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19 pages, 2114 KiB

Open AccessEditor’s ChoiceReview

Recent Advances in Electrochemical Nitrogen Reduction Reaction to Ammonia from the Catalyst to the System

by Yong Hyun Moon, Na Yun Kim, Sung Min Kim and Youn Jeong Jang

Catalysts 2022, 12(9), 1015; https://doi.org/10.3390/catal12091015 - 7 Sep 2022

Cited by 34 | Viewed by 8541

Abstract

As energy-related issues increase significantly, interest in ammonia (NH₃) and its potential as a new eco-friendly fuel is increasing substantially. Accordingly, many studies have been conducted on electrochemical nitrogen reduction reaction (ENRR), which can produce ammonia in an environmentally friendly manner [...] Read more.

As energy-related issues increase significantly, interest in ammonia (NH₃) and its potential as a new eco-friendly fuel is increasing substantially. Accordingly, many studies have been conducted on electrochemical nitrogen reduction reaction (ENRR), which can produce ammonia in an environmentally friendly manner using nitrogen molecule (N₂) and water (H₂O) in mild conditions. However, research is still at a standstill, showing low performances in faradaic efficiency (FE) and NH₃ production rate due to the competitive reaction and insufficient three-phase boundary (TPB) of N₂(g)-catalyst(s)-H₂O(l). Therefore, this review comprehensively describes the main challenges related to the ENRR and examines the strategies of catalyst design and TPB engineering that affect performances. Finally, a direction to further develop ENRR through perspective is provided. Full article

(This article belongs to the Special Issue Catalysis on Stable Molecules (CO₂, CO, CH₄, N₂, NH₃) Activation and Their Transformation)

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24 pages, 7738 KiB

Open AccessEditor’s ChoiceReview

Achievements and Perspectives in Metal–Organic Framework-Based Materials for Photocatalytic Nitrogen Reduction

by Linkun Fan, Qin Yu, Jiazhen Chen, Usman Khan, Xusheng Wang and Junkuo Gao

Catalysts 2022, 12(9), 1005; https://doi.org/10.3390/catal12091005 - 6 Sep 2022

Cited by 20 | Viewed by 4253

Abstract

Metal–organic frameworks (MOFs) are coordination polymers with high porosity that are constructed from molecular engineering. Constructing MOFs as photocatalysts for the reduction of nitrogen to ammonia is a newly emerging but fast-growing field, owing to MOFs’ large pore volumes, adjustable pore sizes, controllable [...] Read more.

Metal–organic frameworks (MOFs) are coordination polymers with high porosity that are constructed from molecular engineering. Constructing MOFs as photocatalysts for the reduction of nitrogen to ammonia is a newly emerging but fast-growing field, owing to MOFs’ large pore volumes, adjustable pore sizes, controllable structures, wide light harvesting ranges, and high densities of exposed catalytic sites. They are also growing in popularity because of the pristine MOFs that can easily be transformed into advanced composites and derivatives, with enhanced catalytic performance. In this review, we firstly summarized and compared the ammonia detection methods and the synthetic methods of MOF-based materials. Then we highlighted the recent achievements in state-of-the-art MOF-based materials for photocatalytic nitrogen fixation. Finally, the summary and perspectives of MOF-based materials for photocatalytic nitrogen fixation were presented. This review aims to provide up-to-date developments in MOF-based materials for nitrogen fixation that are beneficial to researchers who are interested or involved in this field. Full article

(This article belongs to the Special Issue Current State-of-the-Art of Catalysts for Energy and Environmental Applications)

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13 pages, 1587 KiB

Open AccessEditor’s ChoiceArticle

Silver(I)-Catalyzed C4-H Amination of 1-Naphthylamine Derivatives with Azodicarboxylates at Room Temperature

by Yuxue Zhang, Mengxue Pei, Fan Yang and Yangjie Wu

Catalysts 2022, 12(9), 1006; https://doi.org/10.3390/catal12091006 - 6 Sep 2022

Cited by 2 | Viewed by 2616

Abstract

A highly facile and efficient protocol for silver(I)-catalyzed C4–H amination of 1-naphthylamine derivatives with readily available azodicarboxylates utilizing picolinamide as a bidentate directing group is reported, providing an alternative strategy for the synthesis of 4-aminated 1-naphthylamine derivatives. The reaction proceeded smoothly in acetone [...] Read more.

A highly facile and efficient protocol for silver(I)-catalyzed C4–H amination of 1-naphthylamine derivatives with readily available azodicarboxylates utilizing picolinamide as a bidentate directing group is reported, providing an alternative strategy for the synthesis of 4-aminated 1-naphthylamine derivatives. The reaction proceeded smoothly in acetone at room temperature undergoing a self-redox process under the base and external oxidant-free conditions, affording the desired products with good to excellent yields. Full article

(This article belongs to the Special Issue Advances in Transition Metal Catalysis)

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10 pages, 2817 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Well-Defined Ultrasmall V-NiP₂ Nanoparticles Anchored g-C₃N₄ Nanosheets as Highly Efficient Visible-Light-Driven Photocatalysts for H₂ Evolution

by Mengfan Niu, Liyun Cao, Qianqian Liu, Xiaoyi Li, Qian Chen, Dinghan Liu, Wenbin Li, Jianfeng Huang and Liangliang Feng

Catalysts 2022, 12(9), 998; https://doi.org/10.3390/catal12090998 - 5 Sep 2022

Cited by 2 | Viewed by 2514

Abstract

Exploring low-cost and highly active, cost-effective cocatalysts is of great significance to improve the hydrogen evolution performance of semiconductor photocatalysts. Herein, a novel ultrasmall V-doped NiP₂ nanoparticle, as an efficient cocatalyst, is reported to largely upgrade the photocatalytic hydrogen evolution reaction (HER) [...] Read more.

Exploring low-cost and highly active, cost-effective cocatalysts is of great significance to improve the hydrogen evolution performance of semiconductor photocatalysts. Herein, a novel ultrasmall V-doped NiP₂ nanoparticle, as an efficient cocatalyst, is reported to largely upgrade the photocatalytic hydrogen evolution reaction (HER) of g-C₃N₄ nanosheets under visible-light irradiation. Experimental results demonstrate that V-NiP₂ cocatalyst can enhance the visible-light absorption ability, facilitate the separation of photo-generated electron-hole pairs and boost the transfer ability of electrons of g-C₃N₄. Moreover, the V-NiP₂/g-C₃N₄ hybrid exhibits prominent photocatalytic HER activity 17 times higher than the pristine g-C₃N₄ counterpart, even outperforming the 1 wt.% platinum-loaded g-C₃N₄. This work displays that noble-metal-free V-NiP₂ cocatalyst can serve as a promising and efficient alternative to Pt for high-efficiency photocatalytic H₂ evolution. Full article

(This article belongs to the Special Issue Innovative Strategies for (Photo)Electrocatalytic Water Splitting and CO₂ Reduction)

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20 pages, 2456 KiB

Open AccessEditor’s ChoiceArticle

Understanding 2D-IR Spectra of Hydrogenases: A Descriptive and Predictive Computational Study

by Yvonne Rippers, Barbara Procacci, Neil T. Hunt and Marius Horch

Catalysts 2022, 12(9), 988; https://doi.org/10.3390/catal12090988 - 1 Sep 2022

Cited by 2 | Viewed by 2572

Abstract

[NiFe] hydrogenases are metalloenzymes that catalyze the reversible cleavage of dihydrogen (

H_{2}

), a clean future fuel. Understanding the mechanism of these biocatalysts requires spectroscopic techniques that yield insights into the structure and dynamics of the [NiFe] active site. Due to [...] Read more.

[NiFe] hydrogenases are metalloenzymes that catalyze the reversible cleavage of dihydrogen (

H_{2}

), a clean future fuel. Understanding the mechanism of these biocatalysts requires spectroscopic techniques that yield insights into the structure and dynamics of the [NiFe] active site. Due to the presence of CO and

{CN}^{-}

ligands at this cofactor, infrared (IR) spectroscopy represents an ideal technique for studying these aspects, but molecular information from linear IR absorption experiments is limited. More detailed insights can be obtained from ultrafast nonlinear IR techniques like IR_pump-IR_probe and two-dimensional (2D-)IR spectroscopy. However, fully exploiting these advanced techniques requires an in-depth understanding of experimental observables and the encoded molecular information. To address this challenge, we present a descriptive and predictive computational approach for the simulation and analysis of static 2D-IR spectra of [NiFe] hydrogenases and similar organometallic systems. Accurate reproduction of experimental spectra from a first-coordination-sphere model suggests a decisive role of the [NiFe] core in shaping the enzymatic potential energy surface. We also reveal spectrally encoded molecular information that is not accessible by experiments, thereby helping to understand the catalytic role of the diatomic ligands, structural differences between [NiFe] intermediates, and possible energy transfer mechanisms. Our studies demonstrate the feasibility and benefits of computational spectroscopy in the 2D-IR investigation of hydrogenases, thereby further strengthening the potential of this nonlinear IR technique as a powerful research tool for the investigation of complex bioinorganic molecules. Full article

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

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26 pages, 4601 KiB

Open AccessEditor’s ChoiceReview

The Emergence of the Ubiquity of Cerium in Heterogeneous Oxidation Catalysis Science and Technology

by James F. Brazdil

Catalysts 2022, 12(9), 959; https://doi.org/10.3390/catal12090959 - 29 Aug 2022

Cited by 16 | Viewed by 4434

Abstract

Research into the incorporation of cerium into a diverse range of catalyst systems for a wide spectrum of process chemistries has expanded rapidly. This has been evidenced since about 1980 in the increasing number of both scientific research journals and patent publications that [...] Read more.

Research into the incorporation of cerium into a diverse range of catalyst systems for a wide spectrum of process chemistries has expanded rapidly. This has been evidenced since about 1980 in the increasing number of both scientific research journals and patent publications that address the application of cerium as a component of a multi-metal oxide system and as a support material for metal catalysts. This review chronicles both the applied and fundamental research into cerium-containing oxide catalysts where cerium’s redox activity confers enhanced and new catalytic functionality. Application areas of cerium-containing catalysts include selective oxidation, combustion, NO_x remediation, and the production of sustainable chemicals and materials via bio-based feedstocks, among others. The newfound interest in cerium-containing catalysts stems from the benefits achieved by cerium’s inclusion, which include selectivity, activity, and stability. These benefits arise because of cerium’s unique combination of chemical and thermal stability, its redox active properties, its ability to stabilize defect structures in multicomponent oxides, and its propensity to stabilize catalytically optimal oxidation states of other multivalent elements. This review surveys the origins and some of the current directions in the research and application of cerium oxide-based catalysts. Full article

(This article belongs to the Special Issue Ceria-Based Heterogeneous Catalysis: Experimental and Theoretical Study)

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14 pages, 3716 KiB

Open AccessEditor’s ChoiceArticle

Photocatalytic Oxidative Desulfurization of Thiophene by Exploiting a Mesoporous V₂O₅-ZnO Nanocomposite as an Effective Photocatalyst

by Maha Alhaddad, Ahmed Shawky and Zaki I. Zaki

Catalysts 2022, 12(9), 933; https://doi.org/10.3390/catal12090933 - 24 Aug 2022

Cited by 15 | Viewed by 2680

Abstract

Due to increasingly stringent environmental regulations imposed by governments throughout the world, the manufacture of low-sulfur fuels has received considerable assiduity in the petroleum industry. In this investigation, mesoporous V₂O₅-decorated two-dimensional ZnO nanocrystals were manufactured using a simple surfactant-assisted [...] Read more.

Due to increasingly stringent environmental regulations imposed by governments throughout the world, the manufacture of low-sulfur fuels has received considerable assiduity in the petroleum industry. In this investigation, mesoporous V₂O₅-decorated two-dimensional ZnO nanocrystals were manufactured using a simple surfactant-assisted sol–gel method for thiophene photocatalytic oxidative desulfurization (TPOD) at ambient temperature applying visible illumination. When correlated to pure ZnO NCs, V₂O₅-added ZnO nanocomposites dramatically improved the photocatalytic desulfurization of thiophene, and the reaction was shown to follow the pseudo-first-order model. The photocatalytic effectiveness of the 3.0 wt.% V₂O₅-ZnO photocatalyst was the greatest among all the other samples, with a rate constant of 0.0166 min⁻¹, which was 30.7 significantly greater than that of pure ZnO NCs (0.00054 min⁻¹). Compared with ZnO NCs, and owing to their synergetic effects, substantial creation of hydroxyl radical levels, lesser light scattering action, quick transport of thiophene species to the active recenters, and efficient visible-light gathering, V₂O₅-ZnO nanocomposites were found to have enhanced photocatalytic efficiency. V₂O₅-ZnO nanocomposites demonstrated outstanding stability during TPOD. Using mesoporous V₂O₅-ZnO nanocomposites, the mechanism of the charge separation process was postulated. Full article

(This article belongs to the Special Issue The Role of Catalysts in Functionalization of C-H and C-C Bonds)

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28 pages, 4233 KiB

Open AccessEditor’s ChoiceArticle

Chemical Composition of the Surface and Subsurface of Pt–Pd–Rh–Ru Catalytic Gauzes Used in the NH₃ Oxidation with Air at 1133 K

by Aleksei Salanov, Alexandra Serkova, Alexandr Kalinkin, Lyubov Isupova and Valentin Parmon

Catalysts 2022, 12(9), 930; https://doi.org/10.3390/catal12090930 - 23 Aug 2022

Cited by 3 | Viewed by 2314

Abstract

High-temperature oxidation of NH₃ on Pt alloy gauzes to NO is widely employed in industry for the production of HNO₃, which is used to obtain agricultural fertilizers. Particular attention is paid now to the investigation of the chemical composition of [...] Read more.

High-temperature oxidation of NH₃ on Pt alloy gauzes to NO is widely employed in industry for the production of HNO₃, which is used to obtain agricultural fertilizers. Particular attention is paid now to the investigation of the chemical composition of gauzes used in NH₃ oxidation. X-ray photoelectron and energy-dispersive X-ray spectroscopies with the depth of analysis ca. 5 nm and ca. 500 nm were applied to investigate the chemical composition of surface and subsurface layers of the new and used in NH₃ oxidation with air at T = 1133 K Pt–Pd–Rh–Ru catalytic gauzes (81, 15, 3.5, 0.5 wt.%, respectively). For all the gauzes, adsorption (OH_ad, CO_ad), graphitic (C_gr) and oxide (Rh₂O₃) films were found on the surface of the metallic alloy. Under these films, C_ab, N_ab and O_ab atoms absorbed in the subsurface layers were detected on the gauzes used in NH₃ oxidation. The obtained data testify to the penetration of O_ab and N_ab atoms into deeper layers of the alloy during etching with elevation of the catalyst temperature. O_ab atoms were accumulated predominantly on dislocations, etch pits and grain boundaries, whereas N_ab atoms intercalated mostly into interstitial sites of the alloy lattice. Full article

(This article belongs to the Section Catalytic Materials)

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25 pages, 8379 KiB

Open AccessEditor’s ChoiceArticle

Activity of Catalytic Ceramic Papers to Remove Soot Particles—A Study of Different Types of Soot

by Sabrina Antonela Leonardi, Eduardo Ernesto Miró and Viviana Guadalupe Milt

Catalysts 2022, 12(8), 855; https://doi.org/10.3390/catal12080855 - 3 Aug 2022

Cited by 8 | Viewed by 2588

Abstract

Diesel soot particles are of concern for both the environment and health. To catalytically remove them, it is important to know their structure and composition. There is little described in the literature on how catalysts favor the combustion of different soot fractions. In [...] Read more.

Diesel soot particles are of concern for both the environment and health. To catalytically remove them, it is important to know their structure and composition. There is little described in the literature on how catalysts favor the combustion of different soot fractions. In this work, programmed temperature oxidation (TPO) experiments were carried out using Co,Ce or Co,Ba,K catalysts supported on ceramic papers. Soot particles were obtained by burning diesel fuel in a vessel (LabSoot) or by filtering exhaust gases from a turbo diesel engine in a DPF filter (BenchSoot), and compared with a commercial diesel soot: Printex U. Various characterization techniques were useful to relate the characteristics of both the soot particles and the catalysts with the TPO results. The maximum catalytic soot burn rate (T_M) temperatures were in the range of diesel exhaust temperatures that would facilitate in-situ regeneration of the DPF. The Co,Ba,K catalyst showed a higher catalytic effect in LabSoot, as the latter exhibited the largest primary particles and the higher order of graphene layers, for which the potassium-containing catalyst improves the contact between soot and catalyst and favors the combustion of soot, while the Co,Ce catalyst preferentially enhanced the combustion of commercial soot by supplying active oxygen. Full article

(This article belongs to the Special Issue Catalysts for Air Pollution Control: Present and Future)

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14 pages, 2356 KiB

Open AccessEditor’s ChoiceArticle

High-Efficiency Oxygen Reduction to Hydrogen Peroxide Catalyzed by Oxidized Mo₂TiC₂ MXene

by Ge Li, Bin Zhou, Ping Wang, Miao He, Zhao Fang, Xilin Yuan, Weiwei Wang, Xiaohua Sun and Zhenxing Li

Catalysts 2022, 12(8), 850; https://doi.org/10.3390/catal12080850 - 2 Aug 2022

Cited by 25 | Viewed by 4340

Abstract

The two-electron oxygen reduction reaction (2e⁻ORR) pathway electrochemical synthesis to H₂O₂ has the advantages of low investment and environmental protection and is considered to be a promising green method. Herein, the oxidized Mo₂TiC₂ MXene (O-Mo [...] Read more.

The two-electron oxygen reduction reaction (2e⁻ORR) pathway electrochemical synthesis to H₂O₂ has the advantages of low investment and environmental protection and is considered to be a promising green method. Herein, the oxidized Mo₂TiC₂ MXene (O-Mo₂TiC₂) was successfully synthesized by a facile hydrothermal method as an electrocatalyst in electrocatalytic H₂O₂ production. The O-Mo₂TiC₂ achieved the 90% of H₂O₂ selectivity and 0.72 V vs. RHE of the onset potential. Moreover, O-Mo₂TiC₂ showed high charge transfer ability and long-term stable working ability of 40 h. This significantly enhanced electrocatalytic H₂O₂ production capacity is assigned the oxidation treatment of Mo₂TiC₂ MXene to generate more oxygen-containing groups in O-Mo₂TiC₂. This work provides a promising catalyst candidate for the electrochemical synthesis of H₂O₂. Full article

(This article belongs to the Special Issue Advanced Earth-Abundant Catalysts for Energy Related Electrochemistry)

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19 pages, 3162 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Pd Supported on Pr-Rich Cerium–Zirconium–Praseodymium Mixed Oxides for Propane and CO Oxidation

by Simon Fahed, Rémy Pointecouteau, Mimoun Aouine, Antoinette Boreave, Sonia Gil, Philippe Bazin, Alain Demourgues, Marco Daturi and Philippe Vernoux

Catalysts 2022, 12(8), 827; https://doi.org/10.3390/catal12080827 - 27 Jul 2022

Viewed by 2536

Abstract

The activity of emission control catalysts must be improved in urban mode at low temperatures. One possible way is to tailor the metal-support interaction between platinum group metals (PGMs) and ceria to stabilize small clusters or single atoms, optimizing the utilization of costly [...] Read more.

The activity of emission control catalysts must be improved in urban mode at low temperatures. One possible way is to tailor the metal-support interaction between platinum group metals (PGMs) and ceria to stabilize small clusters or single atoms, optimizing the utilization of costly PGMs. In this study, a small loading of Pd (<0.2 wt.%) was dispersed on Pr-rich cerium–zirconium–praseodymium mixed oxides (CZP45: Ce_0.45Zr_0.10Pr_0.45O_2−x). After the initial calcination at 800 °C, Pd was mainly in the form of dispersed isolated cations which were found to be efficient for low-temperature CO oxidation but inactive for propane combustion. Nevertheless, a pre-reduction step can trigger the formation of Pd nanoparticles and promote the propane oxidation. Pd nanoparticles, formed during the reduction step, coupled with the high oxygen mobility of CZP45, lead to outstanding catalytic activity for propane oxidation starting from 250 °C. However, the re-oxidation of Pd nanoparticles and their partial re-dispersion, promoted by the fast oxygen mobility of the mixed oxide, rapidly deactivate the catalysts in lean conditions. Full article

(This article belongs to the Special Issue Single-Atom Catalysts and MOF/COF Materials for Catalytic Application)

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21 pages, 3414 KiB

Open AccessEditor’s ChoiceArticle

An In-Depth Exploration of the Electrochemical Oxygen Reduction Reaction (ORR) Phenomenon on Carbon-Based Catalysts in Alkaline and Acidic Mediums

by Niladri Talukder, Yudong Wang, Bharath Babu Nunna and Eon Soo Lee

Catalysts 2022, 12(7), 791; https://doi.org/10.3390/catal12070791 - 19 Jul 2022

Cited by 24 | Viewed by 8524

Abstract

Detailed studies of the electrochemical oxygen reduction reaction (ORR) on catalyst materials are crucial to improving the performance of different electrochemical energy conversion and storage systems (e.g., fuel cells and batteries), as well as numerous chemical synthesis processes. In the effort to reduce [...] Read more.

Detailed studies of the electrochemical oxygen reduction reaction (ORR) on catalyst materials are crucial to improving the performance of different electrochemical energy conversion and storage systems (e.g., fuel cells and batteries), as well as numerous chemical synthesis processes. In the effort to reduce the loading of expensive platinum group metal (PGM)-based catalysts for ORR in the electrochemical systems, many carbon-based catalysts have already shown promising results and numerous investigations on those catalysts are in progress. Most of these studies show the catalyst materials’ ORR performance as current density data obtained through the rotating disk electrode (RDE), rotating ring-disk electrode (RRDE) experiments taking cyclic voltammograms (CV) or linear sweep voltammograms (LSV) approaches. However, the provided descriptions or interpretations of those data curves are often ambiguous and recondite which can lead to an erroneous understanding of the ORR phenomenon in those specific systems and inaccurate characterization of the catalyst materials. In this paper, we presented a study of ORR on a newly developed carbon-based catalyst, the nitrogen-doped graphene/metal-organic framework (N-G/MOF), through RDE and RRDE experiments in both alkaline and acidic mediums, taking the LSV approach. The functions and crucial considerations for the different parts of the RDE/RRDE experiment such as the working electrode, reference electrode, counter electrode, electrolyte, and overall RDE/RRDE process are delineated which can serve as guidelines for the new researchers in this field. Experimentally obtained LSV curves’ shapes and their correlations with the possible ORR reaction pathways within the applied potential range are discussed in depth. We also demonstrated how the presence of hydrogen peroxide (H₂O₂), a possible intermediate of ORR, in the alkaline electrolyte and the concentration of acid in the acidic electrolyte can maneuver the ORR current density output in compliance with the possible ORR pathways. Full article

(This article belongs to the Special Issue Graphene in Photocatalysis/Electrocatalysis)

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31 pages, 29703 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Mechanistic Details of the Sharpless Epoxidation of Allylic Alcohols—A Combined URVA and Local Mode Study

by Marek Freindorf and Elfi Kraka

Catalysts 2022, 12(7), 789; https://doi.org/10.3390/catal12070789 - 18 Jul 2022

Cited by 6 | Viewed by 6100

Abstract

In this work, we investigated the catalytic effects of a Sharpless dimeric titanium (IV)–tartrate–diester catalyst on the epoxidation of allylalcohol with methyl–hydroperoxide considering four different orientations of the reacting species coordinated at the titanium atom (reactions R1–R4) as well as [...] Read more.

In this work, we investigated the catalytic effects of a Sharpless dimeric titanium (IV)–tartrate–diester catalyst on the epoxidation of allylalcohol with methyl–hydroperoxide considering four different orientations of the reacting species coordinated at the titanium atom (reactions R1–R4) as well as a model for the non-catalyzed reaction (reaction R0). As major analysis tools, we applied the URVA (Unified Reaction Valley Approach) and LMA (Local Mode Analysis), both being based on vibrational spectroscopy and complemented by a QTAIM analysis of the electron density calculated at the DFT level of theory. The energetics of each reaction were recalculated at the DLPNO-CCSD(T) level of theory. The URVA curvature profiles identified the important chemical events of all five reactions as peroxide OO bond cleavage taking place before the TS (i.e., accounting for the energy barrier) and epoxide CO bond formation together with rehybridization of the carbon atoms of the targeted CC double bond after the TS. The energy decomposition into reaction phase contribution phases showed that the major effect of the catalyst is the weakening of the OO bond to be broken and replacement of OH bond breakage in the non-catalyzed reaction by an energetically more favorable TiO bond breakage. LMA performed at all stationary points rounded up the investigation (i) quantifying OO bond weakening of the oxidizing peroxide upon coordination at the metal atom, (ii) showing that a more synchronous formation of the new CO epoxide bonds correlates with smaller bond strength differences between these bonds, and (iii) elucidating the different roles of the three TiO bonds formed between catalyst and reactants and their interplay as orchestrated by the Sharpless catalyst. We hope that this article will inspire the computational community to use URVA complemented with LMA in the future as an efficient mechanistic tool for the optimization and fine-tuning of current Sharpless catalysts and for the design new of catalysts for epoxidation reactions. Full article

(This article belongs to the Special Issue Catalytic Epoxidation Reaction)

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