Catalysts

14 pages, 1394 KiB

Open AccessEditor’s ChoiceReview

Catalytic Systems for 5-Hydroxymethylfurfural Preparation from Different Biomass Feedstocks: A Review

by Jiao Tao, Yunchuan Pan, Haiyang Zhou, Yufei Tang, Guoquan Ren, Zhihao Yu, Jiaxuan Li, Rui Zhang, Xiaoyun Li, Yina Qiao, Xuebin Lu and Jian Xiong

Catalysts 2024, 14(1), 30; https://doi.org/10.3390/catal14010030 - 29 Dec 2023

Cited by 11 | Viewed by 3882

Abstract

The preparation of high-value-added platform compounds from biomass materials provides an important method for solving fossil energy shortages. Known as the “sleeping giant”, 5-HMF is one of the most important biomass platform compounds with promising applications. At present, raw materials for the preparation [...] Read more.

The preparation of high-value-added platform compounds from biomass materials provides an important method for solving fossil energy shortages. Known as the “sleeping giant”, 5-HMF is one of the most important biomass platform compounds with promising applications. At present, raw materials for the preparation of 5-HMF mainly comprise sugar compounds and non-food biomass. The current systems for preparing 5-HMF are disadvantaged by poor selectivity and a low conversion rate. This paper focuses on the catalytic mechanisms and catalytic systems for the synthesis of 5-HMF from different biomass feedstocks and reviews a series of existing techniques for the preparation of 5-HMF. Catalytic systems for the synthesis of 5-HMF from different feedstocks are also discussed in depth, providing theoretical support for its subsequent in-depth study. The development of efficient catalysts and catalytic systems for the conversion of polysaccharide raw materials into 5-HMF is anticipated. Full article

(This article belongs to the Special Issue Recent Advances in Catalytic Conversion of Biomass Resources into Chemicals and Fuels)

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20 pages, 3867 KiB

Open AccessEditor’s ChoiceReview

Solid Acid–Base Catalysts Based on Layered Double Hydroxides Applied for Green Catalytic Transformations

by Xiaolu You, Lishi Chen, Shan He and Guiju Zhang

Catalysts 2024, 14(1), 28; https://doi.org/10.3390/catal14010028 - 28 Dec 2023

Cited by 10 | Viewed by 3977

Abstract

Layered double hydroxides (LDHs) have emerged as promising catalysts for various acid–base catalytic reactions. Due to their unique structure and regulatable dual acid–base properties, they offer more environmentally friendly and sustainable alternatives to traditional liquid acid and base catalysts. This study introduces the [...] Read more.

Layered double hydroxides (LDHs) have emerged as promising catalysts for various acid–base catalytic reactions. Due to their unique structure and regulatable dual acid–base properties, they offer more environmentally friendly and sustainable alternatives to traditional liquid acid and base catalysts. This study introduces the structural composition, preparation methods, and acid–base catalytic properties of LDH-based catalysts. Recent application progress in LDHs and rehydrated LDHs, LDH-based metal nanocatalysts, and LDH-based mixed metal oxide catalysts used as solid acid–base catalysts in acid–base green catalytic conversion is reviewed. The challenges and prospects of LDH-based catalysts as green and sustainable catalysts are summarized and proposed. Full article

(This article belongs to the Section Catalytic Materials)

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14 pages, 6373 KiB

Open AccessEditor’s ChoiceArticle

Catalytic Oxidation Mechanism of Toluene on the Ce_0.875Zr_0.125O₂ (110) Surface

by Yuning Leng, Xuesong Cao, Xiaomin Sun and Chenxi Zhang

Catalysts 2024, 14(1), 22; https://doi.org/10.3390/catal14010022 - 27 Dec 2023

Cited by 2 | Viewed by 2432

Abstract

Aromatic volatile organic compounds (VOCs) are toxic to public health and contribute to global air pollution; thus, it is urgent to control VOC emissions. Catalytic oxidation technology has been widely investigated to eliminate aromatic VOCs; this technology exhibits high catalytic efficiency even at [...] Read more.

Aromatic volatile organic compounds (VOCs) are toxic to public health and contribute to global air pollution; thus, it is urgent to control VOC emissions. Catalytic oxidation technology has been widely investigated to eliminate aromatic VOCs; this technology exhibits high catalytic efficiency even at low temperatures. However, the reaction mechanism of aromatic VOCs’ total oxidation over metal-oxide-based catalysts, which is of great significance in the design of catalysts, is not yet clear. In this study, we systemically calculated the catalytic oxidation mechanism of toluene over the Ce_0.875Zr_0.125O₂ catalyst using density functional theory (DFT). The results show that toluene first loses hydrogen from the methyl group via oxy-dehydrogenation and is gradually oxidized by lattice or adsorbed oxygen to benzyl alcohol, benzaldehyde, and benzoic acid following the Mars-van Krevelen (MVK) mechanism. Afterwards, there is a decarboxylation step to produce phenyl, which is further oxidized to benzoquinone. The rate-determining step then proceeds via the ring-opening reaction, leading to the formation of small molecule intermediates, which are finally oxidized to CO₂ and H₂O. This work may provide atomic-scale insight into the role of lattice and adsorbed oxygen in catalytic oxidation reactions. Full article

(This article belongs to the Section Computational Catalysis)

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14 pages, 7130 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Density Functional Theory Study of CuAg Bimetal Electrocatalyst for CO₂RR to Produce CH₃OH

by Sensen Xue, Xingyou Liang, Qing Zhang, Xuefeng Ren, Liguo Gao, Tingli Ma and Anmin Liu

Catalysts 2024, 14(1), 7; https://doi.org/10.3390/catal14010007 - 20 Dec 2023

Cited by 6 | Viewed by 2221

Abstract

Converting superfluous CO₂ into value-added chemicals is regarded as a practical approach for alleviating the global warming problem. Powered by renewable electricity, CO₂ reduction reactions (CO₂RR) have attracted intense interest owing to their favorable efficiency. Metal catalysts exhibit high [...] Read more.

Converting superfluous CO₂ into value-added chemicals is regarded as a practical approach for alleviating the global warming problem. Powered by renewable electricity, CO₂ reduction reactions (CO₂RR) have attracted intense interest owing to their favorable efficiency. Metal catalysts exhibit high catalytic efficiency for CO₂ reduction. However, the reaction mechanisms have yet to be investigated. In this study, CO₂RR to CH₃OH catalyzed by CuAg bimetal is theoretically investigated. The configurations and stability of the catalysts and the reaction pathway are studied. The results unveil the mechanisms of the catalysis process and prove the feasibility of CuAg clusters as efficient CO₂RR catalysts, serving as guidance for further experimental exploration. This study provides guidance and a reference for future work in the design of mixed-metal catalysts with high CO₂RR performance. Full article

(This article belongs to the Special Issue Theoretical and Computational Studies of Catalytic Reactions)

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24 pages, 1424 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Heterogeneous Catalysts for Carbon Dioxide Methanation: A View on Catalytic Performance

by Mazhar Ahmed Memon, Yanan Jiang, Muhammad Azher Hassan, Muhammad Ajmal, Hong Wang and Yuan Liu

Catalysts 2023, 13(12), 1514; https://doi.org/10.3390/catal13121514 - 15 Dec 2023

Cited by 21 | Viewed by 7125

Abstract

CO₂ methanation offers a promising route for converting CO₂ into valuable chemicals and energy fuels at the same time as hydrogen is stored in methane, so the development of suitable catalysts is crucial. In this review, the performance of catalysts for [...] Read more.

CO₂ methanation offers a promising route for converting CO₂ into valuable chemicals and energy fuels at the same time as hydrogen is stored in methane, so the development of suitable catalysts is crucial. In this review, the performance of catalysts for CO₂ methanation is presented and discussed, including noble metal-based catalysts and non-noble metal-based catalysts. Among the noble metal-based catalysts (Ru, Rh, and Pd), Ru-based catalysts show the best catalytic performance. In the non-noble metal catalysts, Ni-based catalysts are the best among Ni-, Co-, and Fe-based catalysts. The factors predominantly affecting catalytic performance are the dispersion of the active metal; the synergy of the active metal with support; and the addition of dopants. Further comprehensive investigations into (i) catalytic performance under industrial conditions, (ii) stability over a much longer period and (iii) activity enhancement at low reaction temperatures are anticipated to meet the industrial applications of CO₂ methanation. Full article

(This article belongs to the Special Issue New Insights into Catalysis for Hydrogen Production and Fuel Conversion)

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16 pages, 3213 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Progress on Ruthenium-Based Electrocatalysts towards the Hydrogen Evolution Reaction

by Lulu Li, Fenyang Tian, Longyu Qiu, Fengyu Wu, Weiwei Yang and Yongsheng Yu

Catalysts 2023, 13(12), 1497; https://doi.org/10.3390/catal13121497 - 7 Dec 2023

Cited by 76 | Viewed by 4751

Abstract

Hydrogen has emerged as an important candidate for clean energy, owing to its environmentally friendly advantages. Electrolytic hydrogen production stands out as the most promising technology for hydrogen production. Therefore, the design of highly efficient electrocatalysts is significant to drive the application of [...] Read more.

Hydrogen has emerged as an important candidate for clean energy, owing to its environmentally friendly advantages. Electrolytic hydrogen production stands out as the most promising technology for hydrogen production. Therefore, the design of highly efficient electrocatalysts is significant to drive the application of hydrogen technologies. Platinum (Pt)-based catalysts are famous for their outstanding performance in the hydrogen evolution reaction (HER). However, the expensive cost limits its wide application. Ruthenium (Ru)-based catalysts have received extensive attention due to their relatively lower cost and HER performance similar to that of Pt. Nevertheless, the performance of Ru-based catalysts is still unable to meet industrial demands. Therefore, improving HER performance through the modification of Ru-based catalysts remains significant. In this review, the reaction mechanism of HER is analyzed and the latest research progress in the modification of Ru-based electrocatalysts is summarized. From the reaction mechanism perspective, addressing the adsorption of intermediates on the Ru-based electrocatalyst surface, the adsorption–activation of interface water molecules, and the behavior of interface water molecules and proposing solutions to enhance performance of Ru-based electrocatalyst are the main findings, ultimately contributing to promoting their application in the field of electrocatalysis. Full article

(This article belongs to the Special Issue Noble Metal-Based Nanomaterials for Heterogeneous Catalysis)

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13 pages, 2484 KiB

Open AccessEditor’s ChoiceArticle

Novel Ionic Liquid Synthesis of Bimetallic Fe–Ru Catalysts for the Direct Hydrogenation of CO₂ to Short Chain Hydrocarbons

by Marina Maddaloni, Ander Centeno-Pedrazo, Simone Avanzi, Nayan Jyoti Mazumdar, Haresh Manyar and Nancy Artioli

Catalysts 2023, 13(12), 1499; https://doi.org/10.3390/catal13121499 - 7 Dec 2023

Cited by 6 | Viewed by 5689

Abstract

The selective hydrogenation of CO₂ for the production of net-zero fuels and essential chemical building blocks is a promising approach to combat climate change. Key to this endeavor is the development of catalysts with high activity and selectivity for desired hydrocarbon products [...] Read more.

The selective hydrogenation of CO₂ for the production of net-zero fuels and essential chemical building blocks is a promising approach to combat climate change. Key to this endeavor is the development of catalysts with high activity and selectivity for desired hydrocarbon products in the C2–C5 range. The process involves a two-step reaction, starting with the reverse water–gas shift (RWGS) reaction and proceeding to the Fischer–Tropsch reactions under high pressure. Understanding the catalyst features that control the selectivity of these pathways is crucial for product formation, as well as identifying morphological changes in the catalysts during the reaction to optimize their performance. In this study, an innovative method for synthesizing iron–ruthenium bimetallic catalysts is introduced, capitalizing on the synergistic effects of these metals as active phases. This method leverages ionic liquids as solvents, allowing for the precise and uniform distribution of active metal phases. Advanced characterizations and extensive catalytic tests have demonstrated that the use of ionic liquids outperformed traditional colloid-based techniques, resulting in superior selectivity for target hydrocarbons. The success of this inventive approach not only advances the field of CO₂ hydrogenation catalysis, but also represents a significant stride towards sustainable e-fuel production. Full article

(This article belongs to the Special Issue Advancing Catalysis with Lonic Liquids: Current Research and Future Opportunities)

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35 pages, 7530 KiB

Open AccessEditor’s ChoiceReview

Recent Advances in Catalyst Design for Carboxylation Using CO₂ as the C1 Feedstock

by Sagarkumar Rajendrakumar Shah, Nayan Jyoti Mazumdar, Ander Centeno-Pedrazo, Dhanapati Deka, Nancy Artioli and Haresh Manyar

Catalysts 2023, 13(12), 1489; https://doi.org/10.3390/catal13121489 - 30 Nov 2023

Cited by 3 | Viewed by 5185

Abstract

Carbon dioxide is ideal for carboxylation reactions as a renewable and sustainable C1 feedstock and has significant recognition owing to its low cost, non-toxicity, and high abundance. To depreciate the environmental concentration of CO₂, which causes the greenhouse gas effect, developing [...] Read more.

Carbon dioxide is ideal for carboxylation reactions as a renewable and sustainable C1 feedstock and has significant recognition owing to its low cost, non-toxicity, and high abundance. To depreciate the environmental concentration of CO₂, which causes the greenhouse gas effect, developing new catalytic protocols for organic synthesis in CO₂ utilization is of great importance. This review focuses on carboxylation reactions using CO₂ as a C1 feedstock to synthesize value-added functionalized carboxylic acids and their corresponding derivatives via catalytically generated allyl metal intermediates, photoredox catalysis, and electrocatalysis with a focus on recent developments and opportunities in catalyst design for carboxylation reactions. In this article, we describe recent developments in the carboxylation of C–H bonds, alkenes, and alkynes using CO₂ as the C1 source for various reactions under different conditions, as well as the potential direction for the further development of CO₂ utilization in organic synthesis. Full article

(This article belongs to the Special Issue Advances in Green Catalysis for Sustainable Organic Synthesis, 2nd Edition)

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39 pages, 6032 KiB

Open AccessFeature PaperEditor’s ChoiceReview

A Review on the Use of Catalysis for Biogas Steam Reforming

by Sergio Nogales-Delgado, Carmen María Álvez-Medina, Vicente Montes and Juan Félix González

Catalysts 2023, 13(12), 1482; https://doi.org/10.3390/catal13121482 - 29 Nov 2023

Cited by 7 | Viewed by 4167

Abstract

Hydrogen production from natural gas or biogas, at different purity levels, has emerged as an important technology with continuous development and improvement in order to stand for sustainable and clean energy. Regarding biogas, which can be obtained from multiple sources, hydrogen production through [...] Read more.

Hydrogen production from natural gas or biogas, at different purity levels, has emerged as an important technology with continuous development and improvement in order to stand for sustainable and clean energy. Regarding biogas, which can be obtained from multiple sources, hydrogen production through the steam reforming of methane is one of the most important methods for its energy use. In that sense, the role of catalysts to make the process more efficient is crucial, normally contributing to a higher hydrogen yield under milder reaction conditions in the final product. The aim of this review is to cover the main points related to these catalysts, as every aspect counts and has an influence on the use of these catalysts during this specific process (from the feedstocks used for biogas production or the biodigestion process to the purification of the hydrogen produced). Thus, a thorough review of hydrogen production through biogas steam reforming was carried out, with a special emphasis on the influence of different variables on its catalytic performance. Also, the most common catalysts used in this process, as well as the main deactivation mechanisms and their possible solutions are included, supported by the most recent studies about these subjects. Full article

(This article belongs to the Special Issue Biomass Derived Heterogeneous and Homogeneous Catalysts, 2nd Edition)

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22 pages, 7672 KiB

Open AccessEditor’s ChoiceArticle

Photocatalytic Applications of SnO₂ and Ag₂O-Decorated SnO₂ Coatings on Cement Paste

by Danilo da Silva Vendramini, Victoria Gabriela Benatto, Alireza Mohebi Ashtiani and Felipe de Almeida La Porta

Catalysts 2023, 13(12), 1479; https://doi.org/10.3390/catal13121479 - 28 Nov 2023

Cited by 3 | Viewed by 2275

Abstract

Recently, the production of new photocatalytic materials has attracted considerable attention as a promising strategy to mitigate anthropogenic environmental degradation. In this study, cement paste composites (water/cement ratio = 0.5) were prepared using a coating based on nanoparticles of SnO₂ (SnO₂ [...] Read more.

Recently, the production of new photocatalytic materials has attracted considerable attention as a promising strategy to mitigate anthropogenic environmental degradation. In this study, cement paste composites (water/cement ratio = 0.5) were prepared using a coating based on nanoparticles of SnO₂ (SnO₂/cement paste) and SnO₂ decorated with Ag₂O (Ag₂O-decorated SnO₂/cement paste) for photocatalytic applications. These coatings were prepared in this study by using the hydrothermal method as the strategy. Thus, photocatalyst efficiency was evaluated through the degradation of methylene blue (MB) and methyl red (MR) as cationic and anionic dyes, respectively, and the simultaneous degradation of MB/MR (1:1 v/v) dyes. Moreover, the photocatalytic mechanism was investigated in the presence of scavengers. Notably, an increase in pH in the range of 2–6 resulted in selective degradation of the MB/MR dye mixtures. Overall, the photocatalytic performance of these materials provides a novel platform technology focused on advanced civil engineering applications, which consequently facilitates the mitigation of various environmental problems. Full article

(This article belongs to the Special Issue Theoretical and Experimental Investigation of Catalytic Materials)

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21 pages, 1907 KiB

Open AccessFeature PaperEditor’s ChoiceReview

TiO₂-Based Photocatalytic Building Material for Air Purification in Sustainable and Low-Carbon Cities: A Review

by Yuanchen Wei, Hong Meng, Que Wu, Xiaoyu Bai and Yongqing Zhang

Catalysts 2023, 13(12), 1466; https://doi.org/10.3390/catal13121466 - 24 Nov 2023

Cited by 18 | Viewed by 8259

Abstract

TiO₂-based building materials possess air purification, self-cleaning, and sterilization functionalities, making them innovative green building materials with significant potential for future energy-saving and emission-reduction applications. However, the transition from laboratory-scale to practical applications poses substantial challenges in improving the photocatalytic efficiency [...] Read more.

TiO₂-based building materials possess air purification, self-cleaning, and sterilization functionalities, making them innovative green building materials with significant potential for future energy-saving and emission-reduction applications. However, the transition from laboratory-scale to practical applications poses substantial challenges in improving the photocatalytic efficiency and stability of TiO₂-based building materials. In recent years, researchers have made considerable efforts to enhance their efficiency and stability. This paper provides a concise overview of the photocatalytic principles employed in buildings for air purification, discusses preparation techniques for TiO₂-based building materials, explores strategies to improve their efficiency, outlines key factors influencing their performance in practical applications, analyzes limitations, and discusses future development trends. Finally, we propose recommendations for further research on photocatalytic buildings and their real-world implementation as a valuable reference for developing highly efficient and stable photocatalytic building materials. The aim of this paper is to guide the application of TiO₂-based photocatalysts in green buildings towards creating more efficient and stable low-carbon buildings that support sustainable urban growth. Full article

(This article belongs to the Section Catalytic Materials)

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30 pages, 9516 KiB

Open AccessEditor’s ChoiceReview

Application of Unconventional External-Field Treatments in Air Pollutants Removal over Zeolite-Based Adsorbents/Catalysts

by Haodan Cheng, Xiaoning Ren, Yuan Yao, Xiaolong Tang, Honghong Yi, Fengyu Gao, Yuansong Zhou and Qingjun Yu

Catalysts 2023, 13(12), 1461; https://doi.org/10.3390/catal13121461 - 23 Nov 2023

Cited by 5 | Viewed by 2802

Abstract

Zeolite-based materials are widely used as adsorbents and catalysts for purifying air pollutants like NO_x and VOCs due to abundant pore structure, regular pore distribution, and numerous ion exchange sites. Thermal treatment is a necessary procedure for both removing impurities in pores [...] Read more.

Zeolite-based materials are widely used as adsorbents and catalysts for purifying air pollutants like NO_x and VOCs due to abundant pore structure, regular pore distribution, and numerous ion exchange sites. Thermal treatment is a necessary procedure for both removing impurities in pores and promoting the metal active dispersed evenly before the zeolite-based adsorbents/catalysts were applied for purifying the NO_x/VOCs. Nevertheless, the conventional thermal field treatment (i.e., high-temperature calcination, high-temperature purging, etc.) takes large energy consumption. In contrast, unconventional external-field treatments such as non-thermal plasma and microwave show significant advantages of high efficiency, low energy consumption as well and low pollution, which were used to substitute the traditional thermal treatment in many fields. In this paper, the roles of non-thermal plasma or microwave in the adsorption/catalysis of the NO_x/VOCs are reviewed from three aspects assisting activation of materials, cooperative catalysis process, and assisting zeolites synthesis. The reasons for unconventional treatments in improving textural properties, active sites, performance, etc. of zeolite-based materials were illuminated in detail. Moreover, the influences of various parameters (i.e., power, time, temperature, etc.) on the above aspects are elaborated. It is hoped that this review could provide some advanced guidance for the researchers to develop highly efficient materials. Full article

(This article belongs to the Special Issue Catalysts for Mobile Source: Low-Carbon and Pollution Emission Control)

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14 pages, 4290 KiB

Open AccessEditor’s ChoiceArticle

RuO₂@IrO₂/C Core-Shell Structure Catalyst for Efficient and Durable Acidic Oxygen Evolution

by Xin Teng, Junan Gao, Zuobo Yang, Xin Liang, Xiaokuan Wu, Jimmy Yun and Jie Zhang

Catalysts 2023, 13(12), 1456; https://doi.org/10.3390/catal13121456 - 22 Nov 2023

Cited by 4 | Viewed by 3056

Abstract

Proton exchange membrane (PEM) water electrolysis for hydrogen production has a high current density and overall efficiency, and is a very promising hydrogen production strategy. However, its application is limited by the high anodic overpotential for oxygen evolution and the instability of catalysts. [...] Read more.

Proton exchange membrane (PEM) water electrolysis for hydrogen production has a high current density and overall efficiency, and is a very promising hydrogen production strategy. However, its application is limited by the high anodic overpotential for oxygen evolution and the instability of catalysts. Therefore, anodic catalysts with a high activity and durability under acidic conditions need further research. Herein, we first synthesized the key intermediate Ru@Ir core-shell structures by controlling nanocrystals, then loaded them onto a carbon support and calcined to obtain a RuO₂@IrO₂/C core-shell nanocatalyst with a size smaller than 5 nm, whose activity exceeded that of commercial RuO₂ and commercial IrO₂. After a 200 h stability test, the catalyst did not show significant performance degradation or structural degeneration. Finally, the prepared catalyst was assembled into a PEM electrolyzer showing the same results as the three-electrode tests, demonstrating its potential for practical applications and providing new insights for designing nanocatalysts suitable for industrialized PEM water electrolysis to produce hydrogen Full article

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26 pages, 5995 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Catalysis for CO₂ Hydrogenation—What We Have Learned/Should Learn from the Hydrogenation of Syngas to Methanol

by Zixu Yang, Derun Guo, Shengbin Dong, Jiayi Wu, Minghui Zhu, Yi-Fan Han and Zhong-Wen Liu

Catalysts 2023, 13(11), 1452; https://doi.org/10.3390/catal13111452 - 20 Nov 2023

Cited by 9 | Viewed by 5242

Abstract

This short review provides an in-depth analysis of the achievements and further developments of the catalytic hydrogenation of carbon dioxide (CO₂) to methanol from those that are worth learning about based on the transformation of syngas into methanol. We begin by [...] Read more.

This short review provides an in-depth analysis of the achievements and further developments of the catalytic hydrogenation of carbon dioxide (CO₂) to methanol from those that are worth learning about based on the transformation of syngas into methanol. We begin by exploring the environmental and energy-related implications of utilizing CO₂ as a feedstock for methanol production by emphasizing its potential to mitigate greenhouse gas emissions and facilitate renewable energy integration. Then, different catalytic formulations focusing on precious metals, copper-based catalysts, and metal oxides are summarized, and insights into their advantages and limitations in the aspects of catalytic activity, selectivity, and stability are discussed. Precious metal catalysts, such as platinum and iridium, exhibit high activity but are cost-prohibitive, while copper-based catalysts present a promising and cost-effective alternative. Metal oxides are considered for their unique properties in CO₂ activation. Mechanistic insights into reaction pathways are explored, with a particular emphasis on copper-based catalysts. Moreover, the complex steps involved in CO₂ hydrogenation to methanol are discussed to shed light on the key intermediates and active sites responsible for catalysis, which is crucial for catalyst design and optimization. Finally, we stress the importance of ongoing research and development efforts to enhance catalyst efficiency, mechanistic comprehension, and process optimization. This review serves as a valuable resource for researchers, engineers, and policymakers working toward a more sustainable and carbon-neutral energy future. By harnessing CO₂ as a carbon feedstock for methanol synthesis, we have the potential to address environmental concerns and advance the utilization of renewable energy sources, further contributing to the transition to a cleaner and more sustainable energy landscape. Full article

(This article belongs to the Special Issue Catalysis for Selective Hydrogenation of CO and CO₂)

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24 pages, 1866 KiB

Open AccessEditor’s ChoiceReview

Green Synthesis of Biocatalysts Based on Nanocarriers Promises an Effective Role in Pharmaceutical and Biomedical Fields

by Doaa S. R. Khafaga, Mohamed G. Radwan, Ghazala Muteeb, Mohammad Aatif and Mohd Farhan

Catalysts 2023, 13(11), 1448; https://doi.org/10.3390/catal13111448 - 17 Nov 2023

Cited by 13 | Viewed by 3176

Abstract

Nanobiocatalysts (NBCs) are a promising new class of biocatalysts that combine the advantages of enzymes and nanomaterials. Enzymes are biological catalysts that are highly selective and efficient, but they can be unstable in harsh environments. Nanomaterials, on the other hand, are small particles [...] Read more.

Nanobiocatalysts (NBCs) are a promising new class of biocatalysts that combine the advantages of enzymes and nanomaterials. Enzymes are biological catalysts that are highly selective and efficient, but they can be unstable in harsh environments. Nanomaterials, on the other hand, are small particles with unique properties that can improve the stability, activity, and selectivity of enzymes. The development of NBCs has been driven by the need for more sustainable and environmentally friendly bioprocessing methods. Enzymes are inherently green catalysts, but they can be expensive and difficult to recover and reuse. NBCs can address these challenges by providing a stable and reusable platform for enzymes. One of the key challenges in the development of NBCs is the immobilization of enzymes on nanomaterials. Enzyme immobilization is a process that attaches enzymes to a solid support, which can protect the enzymes from harsh environments and make them easier to recover and reuse. There are many different methods for immobilizing enzymes, and the choice of method depends on the specific enzyme and nanomaterial being used. This review explores the effective role of NBCs in pharmaceutical and biomedical fields. Full article

(This article belongs to the Special Issue Recent Advances in Nanobiocatalysts Design, and Their Industrial and Biomedical Applications)

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17 pages, 3641 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Advances and Prospects of d-Tagatose Production Based on a Biocatalytic Isomerization Pathway

by Peiyu Miao, Qiang Wang, Kexin Ren, Zigang Zhang, Tongtong Xu, Meijuan Xu, Xian Zhang and Zhiming Rao

Catalysts 2023, 13(11), 1437; https://doi.org/10.3390/catal13111437 - 14 Nov 2023

Cited by 17 | Viewed by 5492

Abstract

d-tagatose is a low-calorie alternative to sucrose natural monosaccharide that is nearly as sweet. As a ketohexose, d-tagatose has disease-relieving and health-promoting properties. Due to its scarcity in nature, d-tagatose is mainly produced through chemical and biological methods. Compared to [...] Read more.

d-tagatose is a low-calorie alternative to sucrose natural monosaccharide that is nearly as sweet. As a ketohexose, d-tagatose has disease-relieving and health-promoting properties. Due to its scarcity in nature, d-tagatose is mainly produced through chemical and biological methods. Compared to traditional chemical methods, biological methods use whole cells and isolated enzymes as catalysts under mild reaction conditions with few by-products and no pollution. Nowadays, biological methods have become a very important topic in related fields due to their high efficiency and environmental friendliness. This paper introduces the functions and applications of d-tagatose and systematically reviews its production, especially by l-arabinose isomerase (L-AI), using biological methods. The molecular structures and catalytic mechanisms of L-AIs are also analyzed. In addition, the properties of L-AIs from different microbial sources are summarized. Finally, we overview strategies to improve the efficiency of d-tagatose production by engineering L-AIs and provide prospects for the future bioproduction of d-tagatose. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Green Catalysts)

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32 pages, 3029 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Developments in Lignocellulosic Biofuel Production with Nanotechnological Intervention: An Emphasis on Ethanol

by Swagata Dutta, Sarveshwaran Saravanabhupathy, Anusha, Rajiv Chandra Rajak, Rintu Banerjee, Pritam Kumar Dikshit, Chandra Tejaswi Padigala, Amit K. Das and Beom Soo Kim

Catalysts 2023, 13(11), 1439; https://doi.org/10.3390/catal13111439 - 14 Nov 2023

Cited by 13 | Viewed by 4633

Abstract

Biofuel, an inexhaustible fuel source, plays a pivotal role in the contemporary era by diminishing the dependence on non-renewable energy sources and facilitating the mitigation of CO₂ emissions. Due to the many constraints in existing technology and the resulting increased costs, the [...] Read more.

Biofuel, an inexhaustible fuel source, plays a pivotal role in the contemporary era by diminishing the dependence on non-renewable energy sources and facilitating the mitigation of CO₂ emissions. Due to the many constraints in existing technology and the resulting increased costs, the production of biofuels on a large scale is a laborious process. Furthermore, the methods used to convert varied feedstock into the intended biofuel may vary based on the specific techniques and materials involved. The demand for bioethanol is increasing worldwide due to the implementation of regulations by world nations that mandates the blending of bioethanol with petrol. In this regard, second-generation bioethanol made from lignocellulosic biomass is emerging at a rapid rate. Pre-treatment, hydrolysis, and fermentation are some of the technical, practical, and economic hurdles that the biochemical conversion method must overcome. Nanoparticles (NPs) provide a very effective approach to address the present obstacles in using biomass, due to their selectivity, energy efficiency, and time management capabilities, while also reducing costs. NPs smaller dimensions allow them to be more effective at interacting with lignocellulosic components at low concentrations to release carbohydrates that can be utilized to produce bioethanol. This article provides a concise overview of various biofuels and the nanotechnological advancements in producing it, with a particular emphasis on ethanol. It provides a detailed discussion on the application of nanotechnology at each stage of ethanol production, with a particular emphasis on understanding the mechanism of how nanoparticles interact with lignocellulose. Full article

(This article belongs to the Special Issue Catalytic Processes in Biofuel Production and Biomass Valorization, 2nd Edition)

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14 pages, 1057 KiB

Open AccessEditor’s ChoiceReview

An Approach towards the Conversion of Biomass Feedstocks into Biofuel Using a Zeolite Socony Mobil-5-Based Catalysts via the Hydrothermal Liquefaction Process: A Review

by Thandiswa Jideani, Emmanuel Chukwuchendo and Lindiwe Khotseng

Catalysts 2023, 13(11), 1425; https://doi.org/10.3390/catal13111425 - 9 Nov 2023

Cited by 6 | Viewed by 2831

Abstract

The conversion of biomass to biofuels as a renewable energy source is continuously gaining momentum due to the environmental concerns associated with using fossil fuels. Biomass is a cost-effective, long-term natural resource that may be converted to biofuels such as biodiesel, biogas, bio-oil, [...] Read more.

The conversion of biomass to biofuels as a renewable energy source is continuously gaining momentum due to the environmental concerns associated with using fossil fuels. Biomass is a cost-effective, long-term natural resource that may be converted to biofuels such as biodiesel, biogas, bio-oil, and biohydrogen using a variety of chemical, thermal, and biological methods. Thermochemical processes are one of the most advanced biomass conversion methods, with much potential and room for improvement. Among various thermochemical processes, hydrothermal liquefaction (HTL) is a promising technology that can convert higher water-content feedstocks into biofuel with significantly lower oxygen content and higher calorific value without requiring the biomass to be dried first. In HTL, temperature, pressure, residence time, catalyst, and solvent all play a vital role in bio-oil quality. This study provides a comprehensive review of the research and development on the effects of catalysts and the need to optimise existing catalysts for optimum biomass conversion into high-value bio-oil and other products. The catalyst of interest is ZSM-5, a heterogenous catalyst that has been seen to increase the hydrocarbon content and decrease oxygenated compounds and other unwanted by-products. The use and modification of this catalyst will play a vital role in generating renewable and carbon-neutral fuels. Full article

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36 pages, 9272 KiB

Open AccessEditor’s ChoiceReview

Heterobimetallic Complexes of Bi- or Polydentate N-Heterocyclic Carbene Ligands and Their Catalytic Properties

by Csilla Enikő Czégéni, Ferenc Joó, Ágnes Kathó and Gábor Papp

Catalysts 2023, 13(11), 1417; https://doi.org/10.3390/catal13111417 - 5 Nov 2023

Viewed by 3279

Abstract

This review summarizes developments in the synthesis and catalytic applications of those heterobimetallic carbene complexes in which at least two different metals are bound to the same ligand by at least one M-C(carbene) bond each. Several new synthetic methods for such complexes yielding [...] Read more.

This review summarizes developments in the synthesis and catalytic applications of those heterobimetallic carbene complexes in which at least two different metals are bound to the same ligand by at least one M-C(carbene) bond each. Several new synthetic methods for such complexes yielding well-defined and thoroughly characterized compounds are presented. The new complexes were found to be catalytically active in several (most often tandem) reactions. In certain cases, the incorporation of two different metals into the same imidazole- or triazol-based NHC-carbene complex resulted in the substantially higher catalytic activity of the heterobimetallic complex compared either to its homobimetallic analogs or to mixtures of comparable mononuclear complex fragments containing the two metals independently. This is a clear demonstration of advantageous metal–metal cooperation within the catalyst. Opposite examples are also discussed, where the heterobimetallic carbene complex proved inferior in relation to its homobimetallic analogs or to mixtures of homonuclear fragments. Full article

(This article belongs to the Special Issue Organometallic Homogeneous Catalysis)

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20 pages, 3196 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Sustainably Sourced Mesoporous Carbon Molecular Sieves as Immobilization Matrices for Enzymatic Biofuel Cell Applications

by Federica Torrigino, Marcel Nagel, Zhujun Peng, Martin Hartmann and Katharina Herkendell

Catalysts 2023, 13(11), 1415; https://doi.org/10.3390/catal13111415 - 4 Nov 2023

Cited by 3 | Viewed by 2827

Abstract

Ordered mesoporous carbon CMK-3 sieves with a hexagonal structure and uniform pore size have recently emerged as promising materials for applications as adsorbents and electrodes. In this study, using sucrose as the sustainable carbon source and SBA-15 as a template, CMK-3 sieves are [...] Read more.

Ordered mesoporous carbon CMK-3 sieves with a hexagonal structure and uniform pore size have recently emerged as promising materials for applications as adsorbents and electrodes. In this study, using sucrose as the sustainable carbon source and SBA-15 as a template, CMK-3 sieves are synthesized to form bioelectrocatalytic immobilization matrices for enzymatic biofuel cell (EFC) electrodes. Their electrochemical performance, capacitive features, and the stability of enzyme immobilization are analyzed and compared to commercially available multi-walled carbon nanotubes (MWCNT) using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The anodic reaction in the presence of glucose oxidase (GOx) and ferrocene methanol (FcMeOH) on the sustainably sourced CMK-3-based electrodes produces bioelectrocatalytic current responses at 0.5 V vs. saturated calomel electrode (SCE) that are twice as high as on the MWCNT-based electrodes under saturated glucose conditions. For the cathodic reaction, the MWCNT-based cathode performs marginally better than the CMK-3-based electrodes in the presence of bilirubin oxidase (BOD) and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS²⁻). The CMK-3-based EFCs assembled from the GOx anode and BOD cathode results in a power output of 93 μW cm⁻². In contrast, the output power of MWCNT-based EFCs is approximately 53 μW cm⁻². The efficiency of CMK-3 as a support material for biofuel cell applications is effectively demonstrated. Full article

(This article belongs to the Special Issue Biocatalytic Processes: A Multidisciplinary Platform for Future Biorefineries and Energy Conversion Systems)

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20 pages, 19051 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Engineering of GH11 Xylanases for Optimal pH Shifting for Industrial Applications

by In Jung Kim, Soo Rin Kim, Uwe T. Bornscheuer and Ki Hyun Nam

Catalysts 2023, 13(11), 1405; https://doi.org/10.3390/catal13111405 - 30 Oct 2023

Cited by 14 | Viewed by 3499

Abstract

Endo-1,4-β-xylanases belonging to the glycoside hydrolase (GH) 11 family hydrolyze the β-1,4-glycosidic linkages in the xylan backbone to convert polymeric xylan into xylooligosaccharides. GH11 xylanases play an essential role in sugar metabolism and are one of the most widely used enzymes in various [...] Read more.

Endo-1,4-β-xylanases belonging to the glycoside hydrolase (GH) 11 family hydrolyze the β-1,4-glycosidic linkages in the xylan backbone to convert polymeric xylan into xylooligosaccharides. GH11 xylanases play an essential role in sugar metabolism and are one of the most widely used enzymes in various industries, such as pulp and paper, food and feed, biorefinery, textile, and pharmaceutical industries. pH is a crucial factor influencing the biochemical properties of GH11 xylanase and its application in bioprocessing. For the optimal pH shifting of GH11 xylanase in industrial applications, various protein engineering studies using directed evolution, rational engineering, and in silico approaches have been adopted. Here, we review the functions, structures, and engineering methods developed for the optimal pH shifting of GH11 xylanases. The various GH11 engineering techniques and key residues involved in pH shifting are discussed based on their crystal and modeled structure. This review provides an overview of recent advancements in the characterization and engineering of GH11 xylanases, providing a guide for future research in this field. Full article

(This article belongs to the Special Issue New Trends in Industrial Biocatalysis)

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18 pages, 4532 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Bimetallic Single-Atom Catalysts for Electrocatalytic and Photocatalytic Hydrogen Production

by Mengyang Zhang, Keyu Xu, Ning Sun, Yanling Zhuang, Longlu Wang and Dafeng Yan

Catalysts 2023, 13(11), 1409; https://doi.org/10.3390/catal13111409 - 30 Oct 2023

Cited by 7 | Viewed by 3616

Abstract

Electrocatalytic and photocatalytic hydrogen evolution reactions (HERs) provide a promising approach to clean energy generation. Bimetallic single-atom catalysts have been developed and explored to be advanced catalysts for HER. It is urgent to review and summarize the recent advances in developing bimetallic single-atom [...] Read more.

Electrocatalytic and photocatalytic hydrogen evolution reactions (HERs) provide a promising approach to clean energy generation. Bimetallic single-atom catalysts have been developed and explored to be advanced catalysts for HER. It is urgent to review and summarize the recent advances in developing bimetallic single-atom HER catalysts. Firstly, the fundamentals of bimetallic single-atom catalysts are presented, highlighting their unique configuration of two isolated metal atoms on their supports and resultant synergistic effects. Secondly, recent advances in bimetallic single-atom catalysts for electrocatalytic HER under acidic/alkaline conditions are then reviewed, including W-Mo, Ru-Bi, Ni-Fe, Co-Ag, and other dual-atom systems on graphene and transition metal dichalcogenides (TMDs) with enhanced HER activity versus monometallic analogs due to geometric and electronic synergies. Then, photocatalytic bimetallic single-atom catalysts on semiconducting carbon nitrides for solar H₂ production are also discussed. Finally, an outlook is provided on opportunities and challenges in precisely controlling bimetallic single-atom catalyst synthesis and gaining in-depth mechanistic insights into bimetallic interactions. Further mechanistic and synthetic studies on bimetallic single-atom catalysts will be imperative for developing optimal systems for efficient and sustainable hydrogen production. Full article

(This article belongs to the Section Nanostructured Catalysts)

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23 pages, 9202 KiB

Open AccessEditor’s ChoiceArticle

Acid-Catalyzed Etherification of Glycerol with Tert-Butanol: Reaction Monitoring through a Complete Identification of the Produced Alkyl Ethers

by Alfonso Cornejo, Inés Reyero, Idoia Campo, Gurutze Arzamendi and Luis M. Gandía

Catalysts 2023, 13(10), 1386; https://doi.org/10.3390/catal13101386 - 23 Oct 2023

Viewed by 2942

Abstract

Higher tert-Butyl glycerol ethers (tBGEs) are interesting glycerol derivatives that can be produced from tert-butyl alcohol (TBA) and glycerol using an acid catalyst. Glycerol tert-butylation is a complex reaction that leads to the formation of five tBGEs [...] Read more.

Higher tert-Butyl glycerol ethers (tBGEs) are interesting glycerol derivatives that can be produced from tert-butyl alcohol (TBA) and glycerol using an acid catalyst. Glycerol tert-butylation is a complex reaction that leads to the formation of five tBGEs (two monoethers, two diethers, and one triether). In order to gain insight into the reaction progress, the present work reports on the monitoring of glycerol etherification with TBA and p-toluensulfonic acid (PTSA) as homogeneous catalysts. Two analytical techniques were used: gas chromatography (GC), which constitutes the benchmark method, and ¹H nuclear magnetic resonance (¹H NMR), whose use for this purpose has not been reported to date. A method for the quantitative analysis of tBGEs and glycerol based on ¹H NMR is presented that greatly reduced the analysis time and relative error compared with GC-based methods. The combined use of both techniques allowed for a complete quantitative and qualitative description of the glycerol tert-butylation progress. The set of experimental results collected showed the influence of the catalyst concentration and TBA/glycerol ratio on the etherification reaction and evidenced the intrinsic difficulties of this process to achieve high selectivities and yields to the triether. Full article

(This article belongs to the Special Issue Biomass Derived Heterogeneous and Homogeneous Catalysts, 2nd Edition)

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14 pages, 4179 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Noble Metal Single-Atom Coordinated to Nitrogen, Oxygen, and Carbon as Electrocatalysts for Oxygen Evolution

by Jianhua Wang, Jiangdong Bai, Yaqi Cang, Qing Li, Xing Fan and Haiping Lin

Catalysts 2023, 13(10), 1378; https://doi.org/10.3390/catal13101378 - 19 Oct 2023

Cited by 4 | Viewed by 2217

Abstract

Tuning the coordination environment centering metal atoms has been regarded as a promising strategy to promote the activities of noble metal single-atom catalysts (SACs). In the present work, first-principle calculations are employed to explore the oxygen evolution reaction (OER) performance of Ir and [...] Read more.

Tuning the coordination environment centering metal atoms has been regarded as a promising strategy to promote the activities of noble metal single-atom catalysts (SACs). In the present work, first-principle calculations are employed to explore the oxygen evolution reaction (OER) performance of Ir and Ru SACs with chemical coordination being nitrogen (M-N₄-C), oxygen (M-O₄-C), and carbon (M-C₄-C) in graphene, respectively. A “three-step” strategy was implemented by progressively investigating these metrics (stability, catalytic activity, structure–activity relationship). A volcano plot of reactivity is established by using the adsorption-free energy of O* (∆G_O*) as a theoretical descriptor. The intrinsic OER activity is IrN₄-C > IrO₄-C > RuO₄-C > RuN₄-C > IrC₄-C > RuC₄-C. The in-depth tuning mechanism of ∆G_O* can be indicated and interpreted by the d-band centers of the active sites and the crystal orbital Hamilton population analysis of metal-oxygen bonds, respectively. Full article

(This article belongs to the Special Issue Theory-Guided Electrocatalysis and Photocatalysis)

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19 pages, 4579 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A New Ammonia Kinetic Model in Ru-Catalyzed Steam-Reforming Reaction Containing N₂ in Natural Gas

by Chulmin Kim, Juhan Lee and Sangyong Lee

Catalysts 2023, 13(10), 1380; https://doi.org/10.3390/catal13101380 - 19 Oct 2023

Cited by 1 | Viewed by 3093

Abstract

Hydrogen for building fuel cells is primarily produced by natural-gas steam-reforming reactions. Pipeline-transported natural gas in Europe and North America used to contain about 1% to 5% N₂, which reacts with H₂ in steam-reforming reactions to form NH₃. [...] Read more.

Hydrogen for building fuel cells is primarily produced by natural-gas steam-reforming reactions. Pipeline-transported natural gas in Europe and North America used to contain about 1% to 5% N₂, which reacts with H₂ in steam-reforming reactions to form NH₃. In the case of Ru, one of the catalysts used in natural-gas steam-reforming reactions, the activity of the NH₃-formation reaction is higher than that of Ni and Rh catalysts. Reforming gas containing NH₃ is known to poison Pt catalysts in Polymer Electrolyte Membrane Fuel Cells (PEMFCs) and also poison catalysts in preferential oxidation (PROX). In this study, Langmuir–Hinshelwood-based models of the NH₃-formation reaction considering H₂ and CO were proposed and compared with a simplified form of the Temkin–Pyzhev model for NH₃-formation rate. The kinetic parameters of each model were optimized by performing multi-objective function optimization on the experimental results using a tube-type reactor and the numerical results of a plug-flow one-dimension simple SR (steam-reforming) reactor. Full article

(This article belongs to the Topic Hydrogen Production Processes)

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20 pages, 3931 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Research Progress of the Selective Catalytic Reduction with NH₃ over ZSM-5 Zeolite Catalysts for NO_x Removal

by Wangxiang Pan, Jingping He, Guanlin Huang, Wentao Zhang and De Fang

Catalysts 2023, 13(10), 1381; https://doi.org/10.3390/catal13101381 - 19 Oct 2023

Cited by 8 | Viewed by 3585

Abstract

Nitrogen oxides (NO_x) are very common air pollutants that are harmful to the environment and human bodies. Selective catalytic reduction with ammonia (NH₃-SCR) is considered an effective means to remove NO_x emissions due to its good environmental adaptability, [...] Read more.

Nitrogen oxides (NO_x) are very common air pollutants that are harmful to the environment and human bodies. Selective catalytic reduction with ammonia (NH₃-SCR) is considered an effective means to remove NO_x emissions due to its good environmental adaptability, high catalytic activity, and remarkable selectivity. In this paper, the preparation methods, types, advantages, and challenges of ZSM-5 catalysts are reviewed. Special attention is paid to the catalytic properties and influence factors of ZSM-5 catalysts for NH₃-SCR. The SCR performances of ZSM-5 catalysts doped with single or multiple metal ions are also reviewed. In addition, the environmental adaptabilities (sulfur resistance, alkali resistance, water resistance, and hydrothermal stability) of ZSM-5 catalysts are discussed, and the development of ZSM-5 catalysts in denitrification is summarized. Full article

(This article belongs to the Special Issue Zeolites as Catalysts: Applications in Chemical Engineering, Energy Sources and Environmental Protection)

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32 pages, 5499 KiB

Open AccessFeature PaperEditor’s ChoiceReview

A Mini-Review on Lanthanum–Nickel-Based Perovskite-Derived Catalysts for Hydrogen Production via the Dry Reforming of Methane (DRM)

by Amvrosios G. Georgiadis, Nikolaos D. Charisiou and Maria A. Goula

Catalysts 2023, 13(10), 1357; https://doi.org/10.3390/catal13101357 - 10 Oct 2023

Cited by 10 | Viewed by 3962

Abstract

Given that the attempts to head toward a hydrogen economy are gathering pace, the dry reforming of methane (DRM) to produce hydrogen-rich syngas is a reaction that is worthy of investigation. Nickel-based catalysts have been extensively examined as a cost-effective solution for DRM, [...] Read more.

Given that the attempts to head toward a hydrogen economy are gathering pace, the dry reforming of methane (DRM) to produce hydrogen-rich syngas is a reaction that is worthy of investigation. Nickel-based catalysts have been extensively examined as a cost-effective solution for DRM, though they suffer from fast deactivation caused by coke accumulation. However, a number of published studies report high catalytic performance in terms of both activity and stability for La–Ni-based perovskite-derived catalysts used in DRM in comparison to other corresponding materials. In the work presented herein, a thorough analysis regarding the application of La–Ni-based perovskite catalysts for DRM is carried out. LaNiO₃ is known for its anti-coking ability owing to the strong interaction between CO₂ and La₂O₃. A further modification to improve the catalytic performance can be achieved by the partial or complete substitution of A or/and B sites of the perovskite catalysts. The latest developments with respect to this topic are also discussed in this manuscript. Even though the low surface area of perovskite catalysts has always been an obstacle for their commercialization, new supported and porous perovskite materials have recently emerged to address, at least partly, the challenge. Finally, conclusions and future outlooks for developing novel perovskite catalysts that may potentially pioneer new technology are included. Full article

(This article belongs to the Special Issue Perovskite-Type Oxides-Based Catalysts in Hydrogen Production Application)

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25 pages, 14513 KiB

Open AccessFeature PaperEditor’s ChoiceReview

The Acquisition of Primary Amines from Alcohols through Reductive Amination over Heterogeneous Catalysts

by Hao Huang, Yuejun Wei, Yuran Cheng, Shuwen Xiao, Mingchih Chen and Zuojun Wei

Catalysts 2023, 13(10), 1350; https://doi.org/10.3390/catal13101350 - 7 Oct 2023

Cited by 6 | Viewed by 6656

Abstract

The synthesis of primary amines via the reductive amination of alcohols involves a hydrogen-borrowing or hydrogen-transfer mechanism, which consists of three main steps: alcohol hydroxyl dehydrogenation, carbonyl imidization, and imine hydrogenation. Heterogeneous catalysts are widely used for this reaction because of their high [...] Read more.

The synthesis of primary amines via the reductive amination of alcohols involves a hydrogen-borrowing or hydrogen-transfer mechanism, which consists of three main steps: alcohol hydroxyl dehydrogenation, carbonyl imidization, and imine hydrogenation. Heterogeneous catalysts are widely used for this reaction because of their high performance and amenability to separation and reuse. However, the efficiency of reductive amination is limited by the dehydrogenation step, which is severely affected by the competitive adsorption of NH₃. We hope to improve the efficiency of reductive amination by increasing dehydrogenation efficiency. Therefore, in this overview, we introduce the research progress of alcohol reductive amination reaction catalyzed by heterogeneous metal catalysts, focusing on methods of enhancing dehydrogenation efficiency by screening the metal component and the acidity/alkalinity of the support. Finally, we propose some new strategies for the preparation of catalysts from the perspective of overcoming the competitive adsorption of NH₃ and speculate on the design and synthesis of novel catalysts with high performance in the future. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Green Catalysts)

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44 pages, 5378 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Advanced Electrocatalysts for the Oxygen Evolution Reaction: From Single- to Multielement Materials

by América Higareda, Diana Laura Hernández-Arellano, Luis Carlos Ordoñez, Romeli Barbosa and Nicolas Alonso-Vante

Catalysts 2023, 13(10), 1346; https://doi.org/10.3390/catal13101346 - 5 Oct 2023

Cited by 20 | Viewed by 9882

Abstract

The proton exchange membrane water electrolyzer (PEM-WE) is a well-known green technology for hydrogen production. The main obstacle to its development, on a large scale, is the sluggish kinetics of the oxygen evolution reaction (OER). At present, the design of acid-stable electrocatalysts with [...] Read more.

The proton exchange membrane water electrolyzer (PEM-WE) is a well-known green technology for hydrogen production. The main obstacle to its development, on a large scale, is the sluggish kinetics of the oxygen evolution reaction (OER). At present, the design of acid-stable electrocatalysts with low overpotential and excellent stability for the OER constitutes an important activity in electrocatalysis. This review presents an analysis of the fundamentals and strategies for the design of advanced electrocatalysts for oxygen evolution, reaction mechanisms, and OER descriptors. The scrutiny of OER electrocatalysts, with elemental composition from single- to multielemental, are presented. In addition, the purpose of high-entropy alloys (HEAs), a recent research strategy, for the design of advanced materials is summarized. Briefly, the effect of support materials, which are beneficial for modulating the electronic properties of catalysts, is presented. Finally, the prospects for the development of acidic OER electrocatalysts are given. Full article

(This article belongs to the Special Issue Exclusive Papers of the Editorial Board Members and Topical Advisory Panel Members of Catalysts in Section Electrocatalysis)

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21 pages, 1851 KiB

Open AccessEditor’s ChoiceReview

A Comprehensive Overview on Biochar-Based Materials for Catalytic Applications

by Mattia Bartoli, Mauro Giorcelli and Alberto Tagliaferro

Catalysts 2023, 13(10), 1336; https://doi.org/10.3390/catal13101336 - 30 Sep 2023

Cited by 16 | Viewed by 3443

Abstract

The development of heterogeneous catalysts is one of the pillars of modern material science. Among all supports, carbonaceous ones are the most popular due to their high surface area, limited cost, and tunable properties. Nevertheless, materials such as carbon black are produced from [...] Read more.

The development of heterogeneous catalysts is one of the pillars of modern material science. Among all supports, carbonaceous ones are the most popular due to their high surface area, limited cost, and tunable properties. Nevertheless, materials such as carbon black are produced from oil-derived sources lacking in sustainability. Pyrolytic carbon produced from biomass, known as biochar, could represent a valid solution to combine the sustainability and performance of supported catalysts. In this review, we report a comprehensive overview of the most cutting-edge applications of biochar-based catalysts, providing a reference point for both experts and newcomers. This review will provide a description of all possible applications of biochar-based catalysts, proving their sustainability for the widest range of processes. Full article

(This article belongs to the Special Issue Advanced Carbon Nanomaterials in Catalysis)

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14 pages, 4076 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Promoting Bifunctional Oxygen Catalyst Activity of Double-Perovskite-Type Cubic Nanocrystallites for Aqueous and Quasi-Solid-State Rechargeable Zinc-Air Batteries

by Yijun Zhong, Xiaomin Xu, Chao Su, Moses Oludayo Tadé and Zongping Shao

Catalysts 2023, 13(10), 1332; https://doi.org/10.3390/catal13101332 - 29 Sep 2023

Cited by 7 | Viewed by 1846

Abstract

Transition metal oxide materials are promising oxygen catalysts that are alternatives to expensive and precious metal-containing catalysts. Integration of transition metal oxides with high activity for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is an important pathway for good bifunctionality. In [...] Read more.

Transition metal oxide materials are promising oxygen catalysts that are alternatives to expensive and precious metal-containing catalysts. Integration of transition metal oxides with high activity for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is an important pathway for good bifunctionality. In contrast to the conventional physical mixing and hybridization strategies, perovskite-type oxide provides an ideal structure for the integration of the transition metal element atoms on an atomic scale. Herein, B-site ordered double-perovskite-type La_1.6Sr_0.4MnCoO₆ nanocrystallites with ultra-small cubic (20–50 nm) morphology and high specific surface areas (25 m² g⁻¹) were proposed. Rational designs were integrated to promote the ORR-OER catalysis, e.g., introducing oxygen vacancies via A-site cation substitution, further increasing surface oxygen vacancies via integration of a small amount of Pt/C and nanosizing of the material via a facile molten-salt method. The batteries with the La_1.6Sr_0.4MnCoO₆ nanocrystallites and an aqueous alkaline electrolyte demonstrate decent discharge−charge voltage gaps of 0.75 and 1.10 V at 1 and 30 mA cm⁻², respectively, and good cycling stability of 250 h (1500 cycles). A coin-type battery with a gel−polymer electrolyte also presents a good performance. Full article

(This article belongs to the Special Issue New Electrocatalytic Materials for Energy Conversion and Storage: Fuel Cells, Electrolysis, and Metal-Air Batteries)

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26 pages, 5987 KiB

Open AccessEditor’s ChoiceArticle

Plasmonic Photocatalysts Based on Au Nanoparticles and WO₃ for Visible Light-Induced Photocatalytic Activity

by Margaux Desseigne, Virginie Chevallier, Véronique Madigou, Marie-Vanessa Coulet, Olivier Heintz, Hassan Ait Ahsaine and Madjid Arab

Catalysts 2023, 13(10), 1333; https://doi.org/10.3390/catal13101333 - 29 Sep 2023

Cited by 8 | Viewed by 2544

Abstract

In this work, we report the application of Au/WO₃ composite as a photocatalyst for the degradation of dyes under solar light irradiation. Au/WO₃ nanocomposites were synthesized using an acid precipitation method followed by an impregnation/reduction at room temperature. Two composites were [...] Read more.

In this work, we report the application of Au/WO₃ composite as a photocatalyst for the degradation of dyes under solar light irradiation. Au/WO₃ nanocomposites were synthesized using an acid precipitation method followed by an impregnation/reduction at room temperature. Two composites were obtained by loading gold nanoparticles on two morphologies of nanostructured WO₃, nanoplatelets (NP), and pseudospheres (PS). The elaboration parameters of the nanocomposites were optimized according to the gold mass percentage, the HAuCl₄ precursor concentration, and the impregnation time. The structural, microstructural, and textural characterization were conducted using advanced techniques: XRD, SEM/TEM microscopies, and XPS and DRS spectroscopies. The optimal synthesis parameters are a 48 h impregnation of a five mass percentage of gold from a HAuCl₄ precursor with a concentration of 10⁻³ mol·L⁻¹. The obtained composites were formed with Au nanoparticles of 7 nm in size. The XRD analyses did not reveal any modification of the oxide supports structure after gold grafting, contrary to the sorption analyses, which evidenced a change in the state of the materials surface. XPS analysis revealed the reduction of W⁶⁺ ions into W⁵⁺, favoring the presence of oxygen vacancies. Furthermore, a localized surface plasmon resonance effect was observed in the composite at 540 nm. The photocatalysis results of several dye pollutants have shown a selective degradation efficiency depending on the charge of the polluting molecules, pH medium, and mass loading of the catalysts. At the native pH, the photocatalysis process is highly efficient on a cationic molecule, with a low adsorption capacity. Au/WO₃ PS composite appears to be the most efficient, degrading almost the whole RhB and MB only in 60 min and 90 min, respectively, while, for the MO anionic dye, the degradation is more efficient in acidic medium (80%) than in basic medium (0%). Trap tests of the main active species were investigated and a photodecomposition mechanism is proposed. Full article

(This article belongs to the Special Issue Catalytic Materials for Hazardous Wastewater Treatment)

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39 pages, 7936 KiB

Open AccessFeature PaperEditor’s ChoiceReview

A Review on Biolubricants Based on Vegetable Oils through Transesterification and the Role of Catalysts: Current Status and Future Trends

by Sergio Nogales-Delgado, José María Encinar and Juan Félix González

Catalysts 2023, 13(9), 1299; https://doi.org/10.3390/catal13091299 - 16 Sep 2023

Cited by 21 | Viewed by 6165

Abstract

The use of biolubricants as an alternative to petroleum-based products has played an important role in the last decade. Due to the encouragement of global policies, which mainly support green chemistry and circular economy, there has been an increasing interest in bio-based products, [...] Read more.

The use of biolubricants as an alternative to petroleum-based products has played an important role in the last decade. Due to the encouragement of global policies, which mainly support green chemistry and circular economy, there has been an increasing interest in bio-based products, including biolubricants, from scientific and industrial points of view. Their raw materials, production, and characteristics might vary, as biolubricants present different applications for a wide range of practical uses, making this field a continuously changing subject of study by researchers. The aim of this work was to study biolubricant production from vegetable oil crops from a bio-refinery perspective, paying attention to the main raw materials used, the corresponding production methods (with a special focus on double transesterification), the role of catalysts and some techno-economic studies. Thus, the main factors affecting quality parameters such as viscosity or oxidative stability have been covered, including catalyst addition, reaction temperature, or the use of raw materials, reagents, or additives were also analyzed. In conclusion, the search for suitable raw materials, the use of heterogeneous catalysts to improve the effectiveness and efficiency of the process, and the optimization of chemical conditions seem to be the most interesting research lines according to the literature. Full article

(This article belongs to the Special Issue Biomass Derived Heterogeneous and Homogeneous Catalysts, 2nd Edition)

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34 pages, 5856 KiB

Open AccessEditor’s ChoiceReview

Overview of Ni-Based Catalysts for Hydrogen Production from Biogas Reforming

by Robinson L. Manfro and Mariana M. V. M. Souza

Catalysts 2023, 13(9), 1296; https://doi.org/10.3390/catal13091296 - 14 Sep 2023

Cited by 15 | Viewed by 3800

Abstract

The environmental impact and the forecasted scarcity of fossil fuels have intensified research on renewable energy sources. Hydrogen is a versatile energy carrier that can be produced from renewable sources and plays a key role in achieving global decarbonization targets. Biogas, produced by [...] Read more.

The environmental impact and the forecasted scarcity of fossil fuels have intensified research on renewable energy sources. Hydrogen is a versatile energy carrier that can be produced from renewable sources and plays a key role in achieving global decarbonization targets. Biogas, produced by anaerobic digestion of organic compounds, is rich in methane and carbon dioxide and can be used to produce renewable hydrogen by dry reforming. This review focuses on the recent advances in Ni-based catalysts for biogas reforming. The effect of supports and promoters on catalyst activity, stability, and resistance to carbon deposition will be systematically discussed. This review provides a better understanding of the influence of the synthesis method, metal-support interaction, acid/base sites, and oxygen mobility on catalytic activity. Special emphasis will be given to the development of core-shell structure catalysts and bimetallic catalysts of Ni with other transition metals and noble metals. Full article

(This article belongs to the Topic Catalysts for Hydrogen Production from Renewable Sources)

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25 pages, 4827 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Molecular Catalysts for OER/ORR in Zn–Air Batteries

by Evgeny V. Rebrov and Peng-Zhao Gao

Catalysts 2023, 13(9), 1289; https://doi.org/10.3390/catal13091289 - 10 Sep 2023

Cited by 38 | Viewed by 6115

Abstract

Zn–air batteries are becoming the promising power source for small electronic devices and electric vehicles. They provide a relatively high specific energy density at relatively low cost. This review presents exciting advances and challenges related to the development of molecular catalysts for cathode [...] Read more.

Zn–air batteries are becoming the promising power source for small electronic devices and electric vehicles. They provide a relatively high specific energy density at relatively low cost. This review presents exciting advances and challenges related to the development of molecular catalysts for cathode reactions in Zn–air batteries. Bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play the main role in improving performance of reversible fuel cell and metal–air batteries. The catalyst development strategies are reviewed, along with strategies to enhance catalyst performance by application of magnetic field. Proper design of bifunctional molecular ORR/OER catalysts allows the prolongment of the battery reversibility to a few thousand cycles and reach of energy efficiencies of over 70%. Full article

(This article belongs to the Special Issue State of the Art in Molecular Catalysis in Europe)

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18 pages, 2645 KiB

Open AccessEditor’s ChoiceReview

Progress in Developing LnBaCo₂O_5+δ as an Oxygen Reduction Catalyst for Solid Oxide Fuel Cells

by Fa Zheng and Shengli Pang

Catalysts 2023, 13(9), 1288; https://doi.org/10.3390/catal13091288 - 9 Sep 2023

Cited by 7 | Viewed by 2376

Abstract

Solid oxide fuel cells (SOFCs) represent a breed of eco-friendly, weather-independent, decentralized power generation technologies, distinguished for their broad fuel versatility and superior electricity generation efficiency. At present, SOFCs are impeded by a lack of highly efficient oxygen reduction catalysts, a factor that [...] Read more.

Solid oxide fuel cells (SOFCs) represent a breed of eco-friendly, weather-independent, decentralized power generation technologies, distinguished for their broad fuel versatility and superior electricity generation efficiency. At present, SOFCs are impeded by a lack of highly efficient oxygen reduction catalysts, a factor that significantly constrains their performance. The double perovskites LnBaCo₂O_5+δ (Ln = Lanthanide), renowned for their accelerated oxygen exchange and conductivity features, are widely acclaimed as a promising category of cathode catalysts for SOFCs. This manuscript offers a novel perspective on the physicochemical attributes of LnBaCo₂O_5+δ accumulated over the past two decades and delineates the latest advancements in fine-tuning the composition and nanostructure for SOFC applications. It highlights surface chemistry under operational conditions and microstructure as emerging research focal points towards achieving high-performance LnBaCo₂O_5+δ catalysts. This review offers a comprehensive insight into the latest advancements in utilizing LnBaCo₂O_5+δ in the field of SOFCs, presenting a clear roadmap for future developmental trajectories. Furthermore, it provides valuable insights for the application of double perovskite materials in domains such as water electrolysis, CO₂ electrolysis, chemical sensors, and metal–air batteries. Full article

(This article belongs to the Special Issue Advanced Electrocatalysts for Fuel Cells and Metal–Air Batteries)

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25 pages, 3621 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Methane Combustion over Zeolite-Supported Palladium-Based Catalysts

by Jinxiong Tao, Yuxi Liu, Jiguang Deng, Lin Jing, Zhiquan Hou, Lu Wei, Zhiwei Wang and Hongxing Dai

Catalysts 2023, 13(9), 1251; https://doi.org/10.3390/catal13091251 - 29 Aug 2023

Cited by 10 | Viewed by 3172

Abstract

The emission of methane leads to the increase in the methane concentration in the atmosphere, which not only wastes resources but also intensifies the greenhouse effect and brings about serious environmental problems. Catalytic combustion can completely convert methane into carbon dioxide and water [...] Read more.

The emission of methane leads to the increase in the methane concentration in the atmosphere, which not only wastes resources but also intensifies the greenhouse effect and brings about serious environmental problems. Catalytic combustion can completely convert methane into carbon dioxide and water at low temperatures. However, the catalytic activities of the conventional supported palladium catalysts (e.g., Pd/Al₂O₃ and Pd/ZrO₂) are easy to decrease or the two catalysts can even be deactivated under actual harsh reaction conditions (high temperatures, steam- and sulfur dioxide-containing atmospheres, etc.). Recently, noble metal catalysts supported on zeolites with ordered pores and good thermal stability have attracted much attention. This review article summarizes the recent progress on the development and characteristics of zeolite-supported noble metal catalysts for the combustion of methane. The effects of framework structures, silica/alumina ratios, acidity, doping of alkali metals or transition metals, particle sizes and distributions, and their locations of/in the zeolites on methane combustion activity are discussed. The importance of developing high-performance catalysts under realistic operation conditions is highlighted. In addition, the related research work on catalytic methane combustion in the future is also envisioned. Full article

(This article belongs to the Special Issue Catalytic Combustion - From Laboratory Tests to Practical Applications)

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71 pages, 50530 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Copper-Catalyzed/Hypervalent Iodine-Mediated Functionalization of Unactivated Compounds

by Marta Papis, Francesca Foschi, Sara Colombo, Egle Maria Beccalli, Camilla Loro and Gianluigi Broggini

Catalysts 2023, 13(9), 1243; https://doi.org/10.3390/catal13091243 - 26 Aug 2023

Cited by 5 | Viewed by 4481

Abstract

The functionalization of unactivated substrates through the combination of copper catalysts and hypervalent iodine reagents represents a versatile tool in organic synthesis to access various classes of compounds. The hypervalent iodine derivatives can be used simply as oxidizing agents to regenerate the catalytic [...] Read more.

The functionalization of unactivated substrates through the combination of copper catalysts and hypervalent iodine reagents represents a versatile tool in organic synthesis to access various classes of compounds. The hypervalent iodine derivatives can be used simply as oxidizing agents to regenerate the catalytic species or they can associate the functionalization of the starting material. In this review, special attention will be paid to methodologies which provide the introduction of nucleophiles into the reagent by use of suitable benziodoxol(on)es or iodonium salts. Many reactions concern C- and N-arylations, but may also involve formation of different carbon–carbon and carbon–nitrogen bonds, carbon–oxygen as well as carbon–halogen and carbon–phosphorus bonds. Full article

(This article belongs to the Special Issue Advancements in Catalytic Oxidations in Organic Synthesis)

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21 pages, 4812 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Advances in Synergistic Modulation of Transition-Metal-Based Electrocatalysts for Water Oxidation: A Mini Review

by Zhen Li, Ying Wang and Lawrence Yoon Suk Lee

Catalysts 2023, 13(9), 1230; https://doi.org/10.3390/catal13091230 - 22 Aug 2023

Cited by 10 | Viewed by 3279

Abstract

Synergistic modulation has been extensively explored to develop highly efficient transition-metal-based electrocatalysts for oxygen evolution reaction (OER) because coupling effects among intrinsic activity, conductivity, mass transfer, mass diffusion, and intermediates adsorption can further promote catalytic activity. In this review, recent progress in both [...] Read more.

Synergistic modulation has been extensively explored to develop highly efficient transition-metal-based electrocatalysts for oxygen evolution reaction (OER) because coupling effects among intrinsic activity, conductivity, mass transfer, mass diffusion, and intermediates adsorption can further promote catalytic activity. In this review, recent progress in both experimental and theoretical research on synergistic modulation for transition-metal-based alkaline OER electrocatalysts is focused. Specifically, synergistic effects will be presented in the following aspects: (1) metal reactive sites and heterogeneous atoms; (2) heterogeneous atoms and crystallographic structure; (3) electronic structure and morphology; (4) elementary reaction steps; and (5) external fields. Finally, the remaining challenges and prospects of synergistic modulation for efficient OER are further proposed. Full article

(This article belongs to the Special Issue Materials and Phenomenology for Electrocatalysis and Redox Reactions)

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14 pages, 3691 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Metal-Doped HZSM-5 Zeolite Catalysts for Catalytic Cracking of Raw Bio-Oil: Exploring Activity toward Value-Added Products

by María Eugenia Chiosso, Iratxe Crespo, Andrea Beatriz Merlo and Beatriz Valle

Catalysts 2023, 13(8), 1198; https://doi.org/10.3390/catal13081198 - 10 Aug 2023

Cited by 4 | Viewed by 3784

Abstract

Catalytic cracking of bio-oil, conducted at atmospheric pressure without hydrogen supply, is a cost-effective and versatile approach for the targeted synthesis of biofuels and platform chemicals. The conversion of raw bio-oil follows intricate reaction pathways strongly influenced by the catalyst properties. In this [...] Read more.

Catalytic cracking of bio-oil, conducted at atmospheric pressure without hydrogen supply, is a cost-effective and versatile approach for the targeted synthesis of biofuels and platform chemicals. The conversion of raw bio-oil follows intricate reaction pathways strongly influenced by the catalyst properties. In this work, we explore the use of various transition metals (Cr, Fe, and Zn) to modify the properties of HZSM-5 zeolite and assess their impact on the catalytic cracking of real raw bio-oil feedstock. The effect of metal loading on physical and chemical characteristics of metal-doped zeolite catalysts was studied through XRD, XRF, N₂ physisorption, NH₃-TPD, FTIR, H₂-TPR. The behavior of each catalyst was evaluated in a continuous two-step catalytic cracking system (TS-CC) operating at 450 °C and space-time 0.7 g_catalysth/g_feed. The results highlight the importance of carefully selecting active metal species to optimize the performance of HZSM-5 in the catalytic cracking of bio-oil. Cr and Fe were found to be effective metals in increasing the selectivity of C₂–C₄ olefins in the gas product and mono-aromatics in the hydrocarbon liquid product, whereas the Zn-doped catalyst exhibits poor activity compared to bulk zeolite. Furthermore, a significant impact of the metal oxidation state on catalytic activity was observed, with reduced metals promoting the formation of H₂, CO, and CO₂ at the expense of hydrocarbon production. Full article

(This article belongs to the Special Issue Catalysis in Biomass Valorization for Fuel and Chemicals)

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17 pages, 5817 KiB

Open AccessEditor’s ChoiceArticle

Visible-Light-Induced Photocatalytic Degradation of Rhodamine B Dye Using a CuS/ZnS p-n Heterojunction Nanocomposite under Visible-Light Irradiation

by Rachel Mugumo, Emmanuel Ichipi, Shepherd M. Tichapondwa and Evans M. Nkhalambayausi Chirwa

Catalysts 2023, 13(8), 1184; https://doi.org/10.3390/catal13081184 - 3 Aug 2023

Cited by 26 | Viewed by 2984

Abstract

The aim of this work was to investigate a new, simple, one-pot combustion synthesis technique for creating sulphur-based CuS/ZnS p-n heterojunction nanocomposite photocatalysts. This study examined the photocatalytic activity and reusability of these nanocomposites in removing rhodamine B (RhB) dye under visible-light irradiation. [...] Read more.

The aim of this work was to investigate a new, simple, one-pot combustion synthesis technique for creating sulphur-based CuS/ZnS p-n heterojunction nanocomposite photocatalysts. This study examined the photocatalytic activity and reusability of these nanocomposites in removing rhodamine B (RhB) dye under visible-light irradiation. Various methods of characterisation were employed to determine the properties of the materials, including particle morphology, crystalline phases, and bandgap energy. The intrinsic reaction parameters, such as catalyst loading, the pH level of the solution, and initial pollutant concentration, were varied to establish the optimal photodegradation conditions. The results showed that a binary CuS/ZnS catalyst with a 10 g L⁻¹ loading, at pH 5, degraded 97% of 5 ppm RhB dye after 270 min of visible light irradiation. Additionally, this composite catalyst exhibited excellent chemical stability and reusability, achieving 83% RhB dye removal after five recycling runs. Scavenger tests identified the photogenerated holes (h⁺) and superoxide free radicals (•O₂) as the primary reactive species responsible for degradation. This study provides valuable insight into the design of highly efficient nanomaterials for removing organic pollutants in wastewater, and a possible reaction mechanism is proposed. Full article

(This article belongs to the Special Issue Catalytic Elimination of Toxic Environmental Pollutants and Toxic Recalcitrant Organic Compounds from Aqueous Solution)

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15 pages, 2471 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Identifying the Active Phase of RuO₂ in the Catalytic CO Oxidation Reaction, Employing Operando CO Infrared Spectroscopy and Online Mass Spectrometry

by Phillip Timmer, Lorena Glatthaar, Tim Weber and Herbert Over

Catalysts 2023, 13(8), 1178; https://doi.org/10.3390/catal13081178 - 1 Aug 2023

Cited by 9 | Viewed by 2839

Abstract

Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is combined with online mass spectrometry (MS) to help to resolve a long-standing debate concerning the active phase of RuO₂ supported on rutile TiO₂ (RuO₂@TiO₂) during the CO oxidation [...] Read more.

Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is combined with online mass spectrometry (MS) to help to resolve a long-standing debate concerning the active phase of RuO₂ supported on rutile TiO₂ (RuO₂@TiO₂) during the CO oxidation reaction. DRIFTS has been demonstrated to serve as a versatile probe molecule to elucidate the active phase of RuO₂@TiO₂ under various reaction conditions. Fully oxidized and fully reduced catalysts serve to provide reference DRIFT spectra, based on which the operando CO spectra acquired during CO oxidation under various reaction conditions are interpreted. Partially reduced RuO₂@TiO₂ was identified as the most active catalyst in the CO oxidation reaction. This is independent of the reaction conditions being reducing or oxidizing and whether the starting catalyst is the fully oxidized RuO₂@TiO₂ or the partially reduced RuO₂@TiO₂. Full article

(This article belongs to the Special Issue Advances in Catalytic Oxidation of Methane and Carbon Monoxide, 2nd Edition)

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12 pages, 6066 KiB

Open AccessEditor’s ChoiceArticle

Metal Bi Loaded Bi₂Ti₂O₇/CaTiO₃ for Enhanced Photocatalytic Efficiency for NO Removal under Visible Light

by Diyuan Du, Menglin Shi, Qingqing Guo, Yanqin Zhang, Ahmed A. Allam, Ahmed Rady and Chuanyi Wang

Catalysts 2023, 13(8), 1169; https://doi.org/10.3390/catal13081169 - 30 Jul 2023

Cited by 6 | Viewed by 1875

Abstract

NO has caused many serious environmental problems and even seriously threatened human health. The development of a cheap and efficient method to remove NO from the air has become an urgent need. In this paper, a novel nanocomposite metal-semiconductor photocatalyst Bi-Bi₂Ti [...] Read more.

NO has caused many serious environmental problems and even seriously threatened human health. The development of a cheap and efficient method to remove NO from the air has become an urgent need. In this paper, a novel nanocomposite metal-semiconductor photocatalyst Bi-Bi₂Ti₂O₇/CaTiO₃ was prepared. Compared to the original Bi₂Ti₂O₇/CaTiO₃, the modification by the metal Bi increased its photocatalytic activity from 25% to 64% under visible light irradiation. The improved photoactivity owns to the SPR effect and the electron capture effect of Bi metals in metal-semiconductor loaded systems improving the separation efficiency of electron-hole pairs and significantly improving the light absorption capacity of the composite photocatalyst. The capture experiment of active species showed that •OH, •O₂⁻, h⁺ and e⁻ are the main active species in the photocatalytic conversion of NO. This work provides new insights into the conformational relationships of Ti-based photocatalysts for NO removal. Full article

(This article belongs to the Special Issue Photocatalysis in Air Purification)

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18 pages, 5117 KiB

Open AccessEditor’s ChoiceArticle

Photocatalytic Systems Based on ZnO Produced by Supercritical Antisolvent for Ceftriaxone Degradation

by Stefania Mottola, Antonietta Mancuso, Olga Sacco, Vincenzo Vaiano and Iolanda De Marco

Catalysts 2023, 13(8), 1173; https://doi.org/10.3390/catal13081173 - 30 Jul 2023

Cited by 9 | Viewed by 1941

Abstract

Emerging contaminants are a significant issue in the environment. Photocatalysis is proposed as a solution for the degradation of pollutants contained in wastewater. In this work, ZnO-based photocatalysts have been produced and tested for the photocatalytic degradation of an antibiotic; specifically, ceftriaxone has [...] Read more.

Emerging contaminants are a significant issue in the environment. Photocatalysis is proposed as a solution for the degradation of pollutants contained in wastewater. In this work, ZnO-based photocatalysts have been produced and tested for the photocatalytic degradation of an antibiotic; specifically, ceftriaxone has been used as a model contaminant. Moreover, there is particular interest in combining small-size ZnO particles and β-cyclodextrin (β-CD), creating a hybrid photocatalyst. Zinc acetate (ZnAc) (subsequently calcinated into ZnO) and β-CD particles with a mean diameter of 0.086 and 0.38 µm, respectively, were obtained using the supercritical antisolvent process (SAS). The produced photocatalysts include combinations of commercial and micronized particles of ZnO and β-CD and commercial and micronized ZnO. All the samples were characterized through UV–Vis diffuse reflectance spectroscopy (DRS), and the band gap values were calculated. Raman and FT-IR measurements confirmed the presence of ZnO and the existence of functional groups due to the β-cyclodextrin and ZnO combination in the hybrid photocatalysts. Wide-angle X-ray diffraction patterns proved that wurtzite is the main crystalline phase for all hybrid photocatalytic systems. In the photocatalytic degradation tests, it was observed that all the photocatalytic systems exhibited 100% removal efficiency within a few minutes. However, the commercial ZnO/micronized β-CD hybrid system is the photocatalyst that shows the best performance; in fact, when using this hybrid system, ceftriaxone was entirely degraded in 1 min. Full article

(This article belongs to the Special Issue Photocatalytical Technology in Europe: State-of-the-Art)

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21 pages, 403 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Synthesis and Specific Properties of the Ceria and Ceria-Zirconia Nanocrystals and Their Aggregates Showing Outstanding Catalytic Activity in Redox Reactions—A Review

by Roman Dziembaj, Marcin Molenda and Lucjan Chmielarz

Catalysts 2023, 13(8), 1165; https://doi.org/10.3390/catal13081165 - 29 Jul 2023

Cited by 8 | Viewed by 3173

Abstract

Non-stoichiometric CeO_2−y, especially in the form of nanocrystal aggregates, exhibits exceptional catalytic activity in redox reactions. It significantly improves the activity of transition metals and their oxides dispersed on/or in it, also acting as an oxygen buffer. Particularly, active oxygen species [...] Read more.

Non-stoichiometric CeO_2−y, especially in the form of nanocrystal aggregates, exhibits exceptional catalytic activity in redox reactions. It significantly improves the activity of transition metals and their oxides dispersed on/or in it, also acting as an oxygen buffer. Particularly, active oxygen species (O₂ⁿ⁻, O⁻) are generated at the M/CeO_2−y nanoparticle interface, as well as in the surface layer of their solid-state solutions M_xCe_1−xO_2−y. The crystal structure of CeO₂, ZrO₂ and (Ce, Zr)O₂ and its defects are discussed in connection with the resulting specific catalytic activity. All the methods (simple precipitation and co-precipitation from mother liquors, sol–gel methods, precipitation from nanoemulsions, hydrothermal and solvothermal techniques, combustion and flame spray pyrolysis, precipitation using molecular and solid-state matrices, 3D printing and mechanochemical methods) used for the synthesis of these nanomaterials are comprehensively reviewed, describing the rules of individual procedures and preparation details. Methods of deposition of metal catalysts and their oxides on CeO₂ nanoparticles, such as impregnation, washcoating and precipitation deposition, were also discussed. This review contains more than 160 references to representative papers wherein the reader can find further details on individual syntheses of effective ceria-based catalysts for redox reactions. Full article

(This article belongs to the Special Issue Nano-Porous Materials for Catalytic Systems in Green Chemistry Processes)

15 pages, 3703 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Au Clusters Supported on Defect-Rich Ni-Ti Oxides Derived from Ultrafine Layered Double Hydroxides (LDHs) for CO Oxidation at Ambient Temperature

by Ayu Takahashi, Akihiro Nakayama, Toru Murayama, Norihito Sakaguchi, Tetsuya Shimada, Shinsuke Takagi and Tamao Ishida

Catalysts 2023, 13(8), 1155; https://doi.org/10.3390/catal13081155 - 26 Jul 2023

Cited by 1 | Viewed by 1658

Abstract

Ultrafine layered double hydroxides (LDHs) have abundant hydroxy groups at their edge sites, serving as anchor sites for metal NPs. Furthermore, transformation of ultrafine LDHs into mixed metal oxides (MMOs) generates abundant oxygen vacancies, which are advantageous for O₂ activation during Au-catalyzed [...] Read more.

Ultrafine layered double hydroxides (LDHs) have abundant hydroxy groups at their edge sites, serving as anchor sites for metal NPs. Furthermore, transformation of ultrafine LDHs into mixed metal oxides (MMOs) generates abundant oxygen vacancies, which are advantageous for O₂ activation during Au-catalyzed CO oxidation. We used ultrafine Ni-Ti LDHs with low crystallinity or Ni-Ti MMOs supported on SiO₂ onto which Au NPs were deposited by deposition–precipitation (DP) and DP–urea (DPU). The catalytic activity of the Au catalysts was significantly affected by the preparation method, with the highest activity obtained by depositing Au onto LDH/SiO₂ by DPU, followed by transformation of LDH to MMO (Au/Ni-Ti MMO/SiO₂ (LDH-DPU)). The presence of Au on LDHs affected the transformation of LDHs into MMOs, resulting in LDH-DPU having the greatest number of oxygen vacancies in the TiO₂ domain in MMOs. Consequently, the adsorbed or the lattice oxygen on the surface of LDH-DPU can be easily utilized for CO oxidation at low temperatures. Moreover, the catalytic activity of LDH-DPU increased with water vapor concentration up to 100% relative humidity at room temperature, suggesting the potential of Au/Ni-Ti MMO/SiO₂ as an air purification catalyst. Full article

(This article belongs to the Special Issue Advances in Catalytic Oxidation of Methane and Carbon Monoxide, 2nd Edition)

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13 pages, 4232 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Insights into SnO₂ Nanoparticles Supported on Fibrous Mesoporous Silica for CO Catalytic Oxidation

by Guobo Li, Yingying Zhang, Jie Yan, Yiwei Luo, Conghui Wang, Weiwei Feng, Shule Zhang, Wenming Liu, Zehui Zhang and Honggen Peng

Catalysts 2023, 13(8), 1156; https://doi.org/10.3390/catal13081156 - 26 Jul 2023

Cited by 1 | Viewed by 1896

Abstract

A large surface area dendritic mesoporous silica material (KCC-1) was successfully synthesized and used as a support to confine SnO₂ nanoparticles (NPs). Owing to the large specific surface area and abundant mesoporous structure of dendritic KCC-1, the SnO₂ NPs were highly [...] Read more.

A large surface area dendritic mesoporous silica material (KCC-1) was successfully synthesized and used as a support to confine SnO₂ nanoparticles (NPs). Owing to the large specific surface area and abundant mesoporous structure of dendritic KCC-1, the SnO₂ NPs were highly dispersed, resulting in significantly improved CO catalytic oxidation activity. The obtained Sn_x/KCC-1 catalysts (x represents the mass fraction of SnO₂ loading) exhibited excellent CO catalytic activity, with the Sn₇@KCC-1 catalyst achieving 90% CO conversion at about 175 °C. The SnO₂ NPs on the KCC-1 surface in a highly dispersed amorphous form, as well as the excellent interaction between SnO₂ NPs and KCC-1, positively contributed to the catalytic removal process of CO on the catalyst surface. The CO catalytic removal pathway was established through a combination of in situ diffuse reflectance infrared transform spectroscopy and density-functional theory calculations, revealing the sequential steps: ① CO → CO₃²⁻_ads, ② CO₃²⁻_ads → CO_2free+SnO_x₋₁, ③ SnO_x₋₁+O₂ → SnO_x₊₁. This study provides valuable insights into the design of high-efficiency non-precious metal catalysts for CO catalytic oxidation catalysts with high efficiency. Full article

(This article belongs to the Special Issue Environmental Catalysis/Adsorption for Organic Waste Resource Disposal)

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15 pages, 2181 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Phosphate Coordination in a Water-Oxidizing Cobalt Oxide Electrocatalyst Revealed by X-ray Absorption Spectroscopy at the Phosphorus K-Edge

by Si Liu, Shima Farhoosh, Paul Beyer, Stefan Mebs, Michael Haumann and Holger Dau

Catalysts 2023, 13(8), 1151; https://doi.org/10.3390/catal13081151 - 25 Jul 2023

Cited by 5 | Viewed by 2439

Abstract

In the research on water splitting at neutral pH, phosphorus-containing transition metal oxyhydroxides are often employed for catalyzing the oxygen evolution reaction (OER). We investigated a cobalt–phosphate catalyst (CoCat) representing this material class. We found that CoCat films prepared with potassium phosphate release [...] Read more.

In the research on water splitting at neutral pH, phosphorus-containing transition metal oxyhydroxides are often employed for catalyzing the oxygen evolution reaction (OER). We investigated a cobalt–phosphate catalyst (CoCat) representing this material class. We found that CoCat films prepared with potassium phosphate release phosphorus in phosphate-free electrolytes within hours, contrasting orders of magnitude’s faster K⁺ release. For P speciation and binding mode characterization, we performed technically challenging X-ray absorption spectroscopy experiments at the P K-edge and analyzed the resulting XANES and EXAFS spectra. The CoCat-internal phosphorus is present in the form of phosphate ions. Most phosphate species are likely linked to cobalt ions in Co–O–PO₃ motifs, where the connecting oxygen could be a terminal or bridging ligand in Co-oxide fragments (P–Co distance, ~3.1 Å), with additional ionic bonds to K⁺ ions (P–K distance, ~3.3 Å). The phosphate coordination bond is stronger than the ionic K⁺-binding, explaining the strongly diverging ion release rates of phosphate and K⁺. Our results support a structural role of phosphate in the CoCat, with these ions binding at the margins of Co-oxide fragments, thereby limiting the long-range material ordering. The relations of catalyst-internal phosphate ions to cobalt’s redox-state changes, proton transfer, and catalytic activity are discussed. Full article

(This article belongs to the Special Issue Electrocatalytic Water Oxidation)

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15 pages, 3859 KiB

Open AccessEditor’s ChoiceArticle

Photothermal-Assisted Photocatalytic Degradation of Tetracycline in Seawater Based on the Black g-C₃N₄ Nanosheets with Cyano Group Defects

by Loic Jiresse Nguetsa Kuate, Zhouze Chen, Jialin Lu, Huabing Wen, Feng Guo and Weilong Shi

Catalysts 2023, 13(7), 1147; https://doi.org/10.3390/catal13071147 - 24 Jul 2023

Cited by 70 | Viewed by 3307

Abstract

As a broad-spectrum antibiotic, tetracycline (TC) has been continually detected in soil and seawater environments, which poses a great threat to the ecological environment and human health. Herein, a black graphitic carbon nitride (CN-B) photocatalyst was synthesized by the one-step calcination method of [...] Read more.

As a broad-spectrum antibiotic, tetracycline (TC) has been continually detected in soil and seawater environments, which poses a great threat to the ecological environment and human health. Herein, a black graphitic carbon nitride (CN-B) photocatalyst was synthesized by the one-step calcination method of urea and phloxine B for the degradation of tetracycline TC in seawater under visible light irradiation. The experimental results showed that the photocatalytic degradation rate of optimal CN-B-0.1 for TC degradation was 92% at room temperature within 2 h, which was 1.3 times that of pure CN (69%). This excellent photocatalytic degradation performance stems from the following factors: (i) ultrathin nanosheet thickness reduces the charge transfer distance; (ii) the cyanogen defect promotes photogenerated carriers’ separation; (iii) and the photothermal effect of CN-B increases the reaction temperature and enhances the photocatalytic activity. This study provides new insight into the design of photocatalysts for the photothermal-assisted photocatalytic degradation of antibiotic pollutants. Full article

(This article belongs to the Special Issue Development of g-C₃N₄-Based Photocatalysts: Environmental Purification and Energy Conversion)

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18 pages, 2124 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Advances in Platinum and Palladium Solvent Extraction from Real Leaching Solutions of Spent Catalysts

by Ana Paula Paiva

Catalysts 2023, 13(7), 1146; https://doi.org/10.3390/catal13071146 - 24 Jul 2023

Cited by 7 | Viewed by 6169

Abstract

The strategic importance of platinum and palladium, two platinum-group metals (PGMs), is particularly supported by their technological applications, one of the most relevant being the role they perform as catalysts for several sorts of chemical reactions. The cumulative demand for these two PGMs [...] Read more.

The strategic importance of platinum and palladium, two platinum-group metals (PGMs), is particularly supported by their technological applications, one of the most relevant being the role they perform as catalysts for several sorts of chemical reactions. The cumulative demand for these two PGMs to be used as catalysts more than justifies increasing research efforts to develop sustainable recycling processes to maintain their supply. This critically appraised topic review describes the recent research trends (since 2010) developed by the world’s research communities to reach sustainable methods to recover platinum and palladium from spent catalysts in the liquid phase, namely those involving a solvent extraction (SX) step. The selected recycling processes are based on extensive fundamental research, but this paper intends to focus on information collected about SX procedures applied to real leaching samples of spent catalysts, either from automobile or industrial sources. A critical appraisal of the claimed success levels, the identified constraints, and open challenges is carried out, together with some perspectives on possible ways to redirect research efforts and minimize the gap between academia and industry on this matter. Full article

(This article belongs to the Special Issue Recent Advances Utilized in the Recycling of Catalysts II)

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