Catalysts

31 pages, 13841 KiB

Open AccessArticle

Activated Carbons as Supports for Sulfided Mo-Based Catalysts Intended for the Hydroprocessing of Lipidic Feedstocks

by Antônio M. de Freitas Júnior, Ruana D. Brandão, Jeremie Garnier, Myller S. Tonhá, Wagner da N. Mussel, Daniel Ballesteros-Plata, Enrique Rodríguez-Castellón and Marcos J. Prauchner

Catalysts 2025, 15(4), 359; https://doi.org/10.3390/catal15040359 (registering DOI) - 6 Apr 2025

Abstract

The production of hydrocarbon-based biofuels has been the target of intense research worldwide. In this context, the core goal of the present work was to investigate the use of mesopore-rich activated carbons (ACs) as support for sulfided Mo-based catalysts intended for the hydroprocessing [...] Read more.

The production of hydrocarbon-based biofuels has been the target of intense research worldwide. In this context, the core goal of the present work was to investigate the use of mesopore-rich activated carbons (ACs) as support for sulfided Mo-based catalysts intended for the hydroprocessing of lipidic feedstocks. The key motivations for the work were that, in comparison to traditional inorganic supports such as Al₂O₃, ACs are less propense to form coke, due to their lower acidity, and are highly resistant to hydrolysis, which is a very important aspect in the hydroprocessing of lipidic feedstocks because water is abundantly produced during the process. Furthermore, the porosity of ACs can be tailored to give rise to a high mesopore content, which is important for improving the access of bulky triglyceride molecules to metallic active sites located inside the pores network. A systematic study on the effects of the preparation conditions on the properties and performance of the obtained catalysts was carried out for the first time. The highest hydrodeoxygenation (HDO) activity was verified for the catalyst prepared through sequential deposition of Mo and Ni by wet impregnation. The prepared catalyst presented better performance for coconut oil HDO than an industrial sulfided NiMo/Al₂O₃ catalyst. Furthermore, it presented good stability, provided that the sulfidation degree was kept high. The obtained results evidenced that ACs have great potential to replace inorganic support in sulfided Mo-based catalysts. Full article

(This article belongs to the Collection Nanocatalysis Towards Energy Transition and Environmental Sustainability)

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15 pages, 3249 KiB

Open AccessFeature PaperArticle

Understanding Lipase-Deep Eutectic Solvent Interactions Towards Biocatalytic Esterification

by Can Liu and Jian Shi

Catalysts 2025, 15(4), 358; https://doi.org/10.3390/catal15040358 (registering DOI) - 6 Apr 2025

Abstract

Deep eutectic solvents (DESs) have shown promise as a medium for extracting polar volatile fatty acids (VFAs) and in situ esterification of the extracted molecules using lipases. This solvent enhanced biocatalysis process can potentially streamline VFA separation from fermentation broth by integrating conversion [...] Read more.

Deep eutectic solvents (DESs) have shown promise as a medium for extracting polar volatile fatty acids (VFAs) and in situ esterification of the extracted molecules using lipases. This solvent enhanced biocatalysis process can potentially streamline VFA separation from fermentation broth by integrating conversion and extraction steps. Two commercial lipases from Aspergillus oryzae (AoL) and Candida rugosa (CrL) were evaluated in reaction systems containing hydrophilic or hydrophobic DESs using a newly optimized lipase assay. The optimal pH for both lipases was around 5.0, with a slight reduction in activity at pH 8.0 and a significant inhibition at pH 2.0. The impact of DES concentration on lipase activity varied depending on the specific DES–lipase pairs. Most hydrophilic DESs show good compatibility with the tested lipases. Specifically for choline chloride/ethylene glycol (1:2) and choline chloride/levulinic acid (1:2), taking into account the influence of pH, CrL activity increased with DES concentration. However, the hydrophobic DES thymol/2,6-dimethoxyphenol (1:2) demonstrated enhanced inhibitory effects on both lipases. Docking simulation helped explain the ligand–protein interactions but showed limited capability in predicting the compatibility of specific DES–lipase pairs due to its constraints in simulating flexible protein structures and the complex interactions between DES components and water. Full article

(This article belongs to the Special Issue Topical Advisory Panel Members' Collection Series: Biomass Catalytic Conversion)

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21 pages, 4493 KiB

Open AccessArticle

Copper Molybdate-Catalyzed Esterification of Levulinic Acid: A Heterogeneous Approach for Biofuel Synthesis

by Alyne Pereira de Oliveira Ribeiro, Wyvirlany Valente Lobo, Talles André Feitosa de Carvalho, José Milton Elias de Matos, Flávio Augusto de Freitas, Yurimiler Leyet Ruiz, Robert S. Matos, Ştefan Ţălu, Henrique Duarte da Fonseca Filho, Lianet Aguilera Domínguez, Walter Ricardo Brito and Francisco Xavier Nobre

Catalysts 2025, 15(4), 357; https://doi.org/10.3390/catal15040357 (registering DOI) - 6 Apr 2025

Abstract

The catalytic esterification of levulinic acid (LA) to methyl levulinate (ML) was investigated using copper molybdate (Cu₃(MoO₄)₂(OH)₂) as a heterogeneous catalyst. The catalyst, synthesized via chemical precipitation, exhibited a monoclinic structure with self-assembled nanoplates forming [...] Read more.

The catalytic esterification of levulinic acid (LA) to methyl levulinate (ML) was investigated using copper molybdate (Cu₃(MoO₄)₂(OH)₂) as a heterogeneous catalyst. The catalyst, synthesized via chemical precipitation, exhibited a monoclinic structure with self-assembled nanoplates forming spherical mesostructures. Structural characterization confirmed its high crystallinity, while textural analysis revealed a BET surface area of 70.55 m² g⁻¹ with pore sizes in the nanometric range (1–6 nm). The catalytic performance was systematically evaluated under varying reaction conditions, including temperature, catalyst dosage, reaction time, methanol-to-LA molar ratio, alcohol type, and catalyst reusability. Optimal conversion of 99.3% was achieved at 100 °C, a 1:20 methanol-to-LA molar ratio, 5% catalyst loading, and a reaction time of 4 h. Comparative analysis with other heterogeneous catalysts demonstrated superior efficiency and stability of Cu₃(MoO₄)₂(OH)₂, with minimal activity loss over four reuse cycles (final conversion of 77.1%). Mechanistic insights suggest that its high activity is attributed to Lewis and Brønsted acid sites, facilitating efficient esterification. This study underscores the potential of copper molybdate as a sustainable and recyclable catalyst for biofuel additive synthesis, advancing green chemistry strategies for biomass valorization. Full article

(This article belongs to the Special Issue Sustainable Catalysis for Green Chemistry and Energy Transition)

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18 pages, 3255 KiB

Open AccessArticle

Heterogeneous Acid Catalytic Filaments for Three-Dimensional Printing: Their Preparation, Characterization, and Reduction of Free Fatty Acids in Crude Palm Oil

by Jarernporn Thawornprasert, Kritsakon Pongraktham and Krit Somnuk

Catalysts 2025, 15(4), 356; https://doi.org/10.3390/catal15040356 (registering DOI) - 5 Apr 2025

Abstract

This study focuses on the fabrication and application of heterogeneous acid catalytic filaments for free fatty acid (FFA) reduction in crude palm oil (CPO) via esterification. Amberlyst-15 catalyst was blended with acrylonitrile butadiene styrene (ABS) using a single-screw filament extruder to produce Amberlyst-15/ABS [...] Read more.

This study focuses on the fabrication and application of heterogeneous acid catalytic filaments for free fatty acid (FFA) reduction in crude palm oil (CPO) via esterification. Amberlyst-15 catalyst was blended with acrylonitrile butadiene styrene (ABS) using a single-screw filament extruder to produce Amberlyst-15/ABS catalytic filaments. A 5 wt.% concentration of fine Amberlyst-15 particles was considered optimal for blending with ABS, making them a suitable acid catalyst for FFA reduction. The mechanical properties, thermal behavior, and morphology of the Amberlyst-15/ABS catalytic filaments were assessed. The esterification process was optimized by varying three independent variables: the methanol-to-oil molar ratio, catalytic filament loading, and reaction time. The results revealed that under the recommended conditions—26.7:1 methanol-to-oil molar ratio, 78.5 wt.% catalytic filament loading, and a reaction time of 20.2 h at 500 rpm and 60 °C—the FFA content in CPO was reduced from 10.05 to 0.83 wt.%. Additionally, the reusability of the catalytic filaments was evaluated under the recommended conditions of the esterification process. The results demonstrated that the filaments remained effective for at least two cycles, achieving FFA levels below 2 wt.%, thereby confirming their stability and catalytic efficiency. The methodology employed in this study for the preparation and characterization of Amberlyst-15/ABS catalytic filaments offers a promising approach for fabricating acid catalytic materials via 3D printing, especially for heterogeneous catalysis in esterification reactions. Full article

(This article belongs to the Section Industrial Catalysis)

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12 pages, 3697 KiB

Open AccessArticle

Ni-Doped Co-Based Metal–Organic Framework with Its Derived Material as an Efficient Electrocatalyst for Overall Water Splitting

by Jingyuan Zhang, Hui Ni, Jianing Yu and Bin Zhao

Catalysts 2025, 15(4), 355; https://doi.org/10.3390/catal15040355 (registering DOI) - 5 Apr 2025

Abstract

Composite catalysts combining a metal–organic framework (MOF) with its derivatives have attracted significant attention in electrocatalysis due to their unique properties. In this study, we report the synthesis of a Ni-doped Co-1,4-benzenedicarboxylate (defined as Co₃Ni₁BDC) metal–organic framework via a [...] Read more.

Composite catalysts combining a metal–organic framework (MOF) with its derivatives have attracted significant attention in electrocatalysis due to their unique properties. In this study, we report the synthesis of a Ni-doped Co-1,4-benzenedicarboxylate (defined as Co₃Ni₁BDC) metal–organic framework via a straightforward solvothermal method, aiming to enhance oxygen evolution reaction (OER) activity. The introduction of Ni modulated the electronic structure, yielding high catalytic activity with an overpotential (η₁₀₀) of 300 mV and excellent stability for the OER. The Co₃Ni₁BDC material was further encapsulated with Co₂P nanoparticles via a controlled phosphating annealing process, forming a hybrid electrocatalyst (Co₃Ni₁BDC@Co₂P) to boost hydrogen evolution reaction (HER) performance. The Co₃Ni₁BDC@ Co₂P catalysts exhibited superior HER performance with low overpotentials of η₁₀ = 20 mV and η₁₀₀ = 127 mV, outperforming the Co₃Ni₁BDC precursor. An alkaline electrolyzer assembled with Co₃Ni₁BDC//Co₃Ni₁BDC@Co₂P achieved a cell voltage of 1.70 V at a current density of 20 mA cm⁻². This work provides a valuable idea for designing efficient electrocatalysts for overall water splitting. Full article

(This article belongs to the Special Issue Catalytic Activity of Two-Dimensional Materials and Their Heterostructures)

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24 pages, 1347 KiB

Open AccessArticle

Aluminum Microspheres Coated with Copper and Nickel Nanoparticles: Catalytic Activity in the Combustion of Ammonium Perchlorate

by Yi Wang and Xiaolan Song

Catalysts 2025, 15(4), 354; https://doi.org/10.3390/catal15040354 (registering DOI) - 4 Apr 2025

Abstract

This study employed an in-situ displacement technique to eliminate the oxide layer present on the surface of micron aluminum (μAl). Utilizing the exposed metallic aluminum, we facilitated the displacement of copper and nickel nanoparticles. These nanoparticles, approximately 90 nanometers in size, were densely [...] Read more.

This study employed an in-situ displacement technique to eliminate the oxide layer present on the surface of micron aluminum (μAl). Utilizing the exposed metallic aluminum, we facilitated the displacement of copper and nickel nanoparticles. These nanoparticles, approximately 90 nanometers in size, were densely adhered to the surface of the μAl particles. The elemental composition and structural characteristics of the composite particles were meticulously analyzed using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Energy Dispersive Spectroscopy (EDS), Vibrating Sample Magnetometry (VSM), and X-ray Photoelectron Spectroscopy (XPS). Subsequently, thermal analysis and combustion performance assessments were conducted to elucidate the catalytic effects of the composite particles ([nCu+nNi]/μAl) on the thermal decomposition and combustion efficiency of ammonium perchlorate (AP). The results elucidate that the nanoparticles immobilized on the surface of μAl are unequivocally metallic copper (nCu) and metallic nickel (nNi). Following the application of nCu and nNi, the oxidation reaction of μAl accelerated by nearly 400 °C; furthermore, the incorporation of [nCu+nNi]/μAl raised the thermal decomposition peak temperature of AP by approximately 130 °C. Notably, the thermal decomposition activation energy of raw AP reached as high as 241.7 kJ/mol; however, upon doping with [nCu+nNi]/μAl, this activation energy significantly diminished to 161.4 kJ/mol. The findings of the combustion experiments revealed that both the raw AP and the AP modified solely with μAl were impervious to ignition via the hot wire method. In contrast, the AP doped with [nCu+nNi]/μAl demonstrated pronounced combustion characteristics, achieving an impressive peak flame temperature of 1851 °C. These results substantiate that the nCu and nNi, when deposited on the surface of μAl, not only facilitate the oxidation and combustion of μAl but also significantly enhance the thermal decomposition and combustion dynamics of ammonium perchlorate. Consequently, the [nCu+nNi]/μAl composite shows considerable promise for application in high-burn-rate hydroxyl-terminated polybutadiene (HTPB) propellants. Full article

(This article belongs to the Collection Nanotechnology in Catalysis)

13 pages, 3866 KiB

Open AccessArticle

Effect of Mn/Cu Molar Ratios on CO Oxidation Activity of Mn-Cu Bimetallic Catalysts

by Cong Liang, Yingchun Sun, Peiyuan Li, Ye Jiang, Xin Sun and Zhengda Yang

Catalysts 2025, 15(4), 353; https://doi.org/10.3390/catal15040353 - 4 Apr 2025

Abstract

The steel manufacturing industry is a major source of global air pollution, with sintering processes contributing over 70% of emissions, primarily carbon monoxide (CO), a significant uncontrolled pollutant. This study explores Mn-Cu bimetallic catalysts as a cost-effective and environmentally friendly alternative to noble [...] Read more.

The steel manufacturing industry is a major source of global air pollution, with sintering processes contributing over 70% of emissions, primarily carbon monoxide (CO), a significant uncontrolled pollutant. This study explores Mn-Cu bimetallic catalysts as a cost-effective and environmentally friendly alternative to noble metal-based systems, addressing the urgent need for efficient CO oxidation catalysts. Mn-Cu catalysts with different Mn/Cu molar ratios were synthesized via hydrothermal methods and systematically characterized using XRD, XPS, BET, H₂-TPR, etc., to assess their physicochemical properties and catalytic performance. The Mn₄Cu₁ catalyst demonstrated the highest CO oxidation activity, achieving complete conversion at 175 °C. This performance is attributed to its optimal Mn/Cu molar ratio, high specific surface area, abundant oxygen vacancies, and superior redox properties. The catalyst’s enhanced performance is further supported by its low reduction temperature and high Mn³⁺ and Cu⁺ content, which promote efficient electron transfer and oxygen activation. These findings highlight the crucial role of Mn/Cu molar ratios in optimizing catalytic performance and offer valuable insights for designing high-efficiency, low-cost catalysts to reduce CO emissions in industrial applications. Full article

(This article belongs to the Special Issue Advanced Catalysts in Environmental Purification)

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9 pages, 1008 KiB

Open AccessCommunication

Computational Search for a Novel Effective Ligand for Ni-Catalyzed Asymmetric Hydrogenation

by Evgeny V. Pospelov, Ivan S. Golovanov, Jianzhong Chen, Wanbin Zhang and Ilya D. Gridnev

Catalysts 2025, 15(4), 352; https://doi.org/10.3390/catal15040352 - 3 Apr 2025

Abstract

Using the DFT method, an analogue of R,R-t-Bu-BenzP* was tried as a potential ligand for Ni-catalyzed asymmetric hydrogenation. This ligand contains benzyl groups instead of the t-Bu groups in R,R-t-Bu-BenzP*. Computational results imply that the R [...] Read more.

Using the DFT method, an analogue of R,R-t-Bu-BenzP* was tried as a potential ligand for Ni-catalyzed asymmetric hydrogenation. This ligand contains benzyl groups instead of the t-Bu groups in R,R-t-Bu-BenzP*. Computational results imply that the R,R-Benz-BenzP* ligand (1) is expected to provide excellent enantioselectivity in the Ni-catalyzed asymmetric hydrogenation of 1-phenylethanone oxime. The computed effectiveness of the R,R-Benz-BenzP* ligand is stipulated by its conformational flexibility, which helps stabilize the crucial transition states via a non-bonding interaction between the substrate and the catalyst. R,R-Benz-BenzP* ligands with CN- and OMe-substituted benzyl rings were also computed to possess the same effectiveness. Full article

(This article belongs to the Section Computational Catalysis)

21 pages, 7030 KiB

Open AccessArticle

Experimental Design and Numerical Optimization of Photochemical Oxidation Removal of Tetracycline from Water Using Fe₃O₄-Supported Fruit Waste Activated Carbon

by Manasik M. Nour, Maha A. Tony, Hossam A. Nabwey and Shaaban M. Shaaban

Catalysts 2025, 15(4), 351; https://doi.org/10.3390/catal15040351 - 3 Apr 2025

Abstract

The ever-increasing importance of sustainable environmental remediation calls for academics’ contribution to satisfy such a need. The 3R’s criteria of recover, recycle and reuse is designed to sustain the waste stream to produce a valuable product. In this regard, the circular economy looks [...] Read more.

The ever-increasing importance of sustainable environmental remediation calls for academics’ contribution to satisfy such a need. The 3R’s criteria of recover, recycle and reuse is designed to sustain the waste stream to produce a valuable product. In this regard, the circular economy looks to deliver banana peel waste as a photocatalyst for pharmaceutical effluent oxidation, which we investigated in this study. Banana peel waste is treated thermally and chemically then augmented with magnetite nanoparticles and labeled as ACBP-Fe₃O₄. The mixture is characterized through Scanning Electron Microscopy (SEM) and the composition of the composite material is attained by energy dispersive X-ray spectroscopy (EDX), and then introduced as a Fenton catalyst. The notable oxidation of tetracycline (TC), evaluated by TC removal and chemical Oxygen Demand (COD) oxidation tenancy, is achieved. The effectiveness of the operational parameters is also assessed and the most influenced parameters are optimized through numerical optimization based on a Response Surface Methodology (RSM) tool. The effects of initial pH value, ACBP-Fe₃O₄ and H₂O₂ concentrations on the oxidation efficiency of the Tetracycline were optimized at pH 6.6 and 350 mg/L and 43 g/L for H₂O₂ and ACBP-Fe₃O₄, respectively. Thermodynamics and kinetics were also studied and the experimental and model data revealed the reaction is spontaneous and exothermic in nature and follows the first-order reaction kinetics. Also, the thermodynamic results the reaction proceeds at a low energy barrier of 34.33 kJ mol⁻¹. Such a system introduces the role of engineers and academics for a sustainable world without a waste stream. Full article

(This article belongs to the Special Issue Remediation of Natural Waters by Photocatalysis)

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14 pages, 4341 KiB

Open AccessArticle

Fabricating Oxygen Vacancy-Rich Bi₂WO₆/Bi₂S₃ Z-Scheme Nano-Heterojunction on Carbon Fiber with Polydopamine for Enhanced Photocatalytic Activity

by Jiantao Niu, Jiaqi Pan, Jianfeng Qiu and Chaorong Li

Catalysts 2025, 15(4), 350; https://doi.org/10.3390/catal15040350 - 2 Apr 2025

Abstract

The use of fibers or fabrics as frameworks for loading photocatalysts is beneficial in solving the problems of photocatalytic nanomaterials, which tend to agglomerate and are difficult to recycle. In this study, Bi₂WO₆/CFb and Bi₂WO₆/Bi [...] Read more.

The use of fibers or fabrics as frameworks for loading photocatalysts is beneficial in solving the problems of photocatalytic nanomaterials, which tend to agglomerate and are difficult to recycle. In this study, Bi₂WO₆/CFb and Bi₂WO₆/Bi₂S₃/CFb photocatalytic fibers rich in oxygen vacancies were prepared using carbon fibers as the framework by the crystal seed attachment method and in situ growth method by using the self-polymerization and strong adhesion properties of dopamine. The results of SEM, TEM and XRD tests showed that Bi₂WO₆ and Bi₂WO₆/Bi₂S₃ nanosheets were uniformly and completely encapsulated on the surface of the carbon fibers. The results of XPS and EPR tests showed that Bi₂WO₆ nanosheets were rich in oxygen vacancies. The PL, transient photocurrent responses and EIS results showed that the introduction of Bi₂S₃ significantly improved the migration efficiency of the photogenerated carriers of Bi₂WO₆/Bi₂S₃/CFb, which effectively hindered the recombination of photogenerated electron–hole pairs. By conducting degradation experiments on p-nitrophenol and analyzing the bandgap structure, it was postulated that the heterojunction structure of Bi₂WO₆/Bi₂S₃/CFb in the Bi₂WO₆/Bi₂S₃ material was not Type-II but Z-scheme. As analyzed by the active species assay, the active species that played a major role in the degradation process were O₂⁻ and h⁺. The incorporation of a small amount of Bi₂S₃ resulted in enhanced photocatalytic degradation activity of Bi₂WO₆/Bi₂S₃/CFb toward tetracycline hydrochloride compared to Bi₂WO₆/CFb. The excellent photocatalytic performance of Bi₂WO₆/Bi₂S₃/CFb photocatalytic fibers can be attributed to the rapid transmission and separation performance and the high oxidation and reduction capacities of photogenerated electron–hole pairs formed by direct Z-scheme heterojunctions. Full article

(This article belongs to the Section Catalytic Materials)

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13 pages, 9751 KiB

Open AccessFeature PaperArticle

Synthesis of Black g-C₃N₄ and Exploration of the Mechanism Underlying the Enhancement of Photocatalytic CO₂ Reduction

by Shaokun Lv, Jun Zhang, Xiaoke Chen, Yue Zou, Qiuli Chen, Yongsheng Yan and Pengxin Li

Catalysts 2025, 15(4), 349; https://doi.org/10.3390/catal15040349 - 2 Apr 2025

Abstract

The use of solar energy to convert CO₂ into value-added chemicals is a promising sustainable development strategy. In this study, a black graphitic carbon nitride (CN-B) photocatalyst was fabricated through a single-step calcination process, employing phloxine B and urea as the precursor [...] Read more.

The use of solar energy to convert CO₂ into value-added chemicals is a promising sustainable development strategy. In this study, a black graphitic carbon nitride (CN-B) photocatalyst was fabricated through a single-step calcination process, employing phloxine B and urea as the precursor materials. The catalysts were characterized using TEM, XRD, FTIR, XPS and so on. The amount of prepolymer phloxine B was 25 mg, 35 mg and 45 mg, respectively, and the obtained samples were CN-B-0.025, CN-B-0.035 and CN-B-0.045. All samples were used for visible-catalyzed CO₂ reduction. The experimental findings indicate that the CO evolution rate of the optimal photocatalyst CN-B-0.035 reaches 27.56 μmol g_cat.⁻¹ h⁻¹. This value is nine-fold higher than that of pure CN, which has a CO evolution rate of 3.22 μmol g_cat.⁻¹ h⁻¹. The excellent photocatalytic reduction performance is due to the following factors: Firstly, the exceedingly thin nanosheet structure of the catalyst enhances the velocity of the charge transfer, and transmission electron microscopy (TEM) analysis shows that the nanosheet thickness of the catalyst CN-B is significantly thinner. Secondly, the light absorption capacity of the catalyst is enhanced. The absorbance of CN-B increases significantly in the ultraviolet region and extends to the near-infrared region, as shown with UV diffuse reflection spectroscopy. Finally, the photothermal effect of CN-B causes the catalyst temperature to rise rapidly from 20 °C to 131 °C within 120 s, which further promotes photogenerated carrier separation. This research offers a novel approach to the development of photocatalysts aimed at the photothermal-assisted photocatalytic conversion of CO₂. Full article

(This article belongs to the Special Issue Mineral-Based Composite Catalytic Materials)

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31 pages, 9891 KiB

Open AccessFeature PaperArticle

Selective Conversion of Glycerol to Acetol: Effect of the Preparation Method of CuAl Catalysts and Reaction Phase

by Francisco Maldonado-Martín, Lucía García, Joaquín Ruiz, Miriam Oliva and Jesús Arauzo

Catalysts 2025, 15(4), 348; https://doi.org/10.3390/catal15040348 - 2 Apr 2025

Abstract

A group of CuAl catalysts were synthesized with a Cu/Al molar ratio of 1:1 using different preparation methods: coprecipitation, surfactant assisted coprecipitation, polymeric precursor, and self-combustion and then screened for the selective dehydration of glycerol to acetol. The catalysts were employed in glycerol [...] Read more.

A group of CuAl catalysts were synthesized with a Cu/Al molar ratio of 1:1 using different preparation methods: coprecipitation, surfactant assisted coprecipitation, polymeric precursor, and self-combustion and then screened for the selective dehydration of glycerol to acetol. The catalysts were employed in glycerol conversion at the same temperature (227 °C) in two different laboratory-scale systems, the first one at atmospheric pressure (gas phase) and the second one in a pressurized system at 34 absolute bar (liquid phase). The preparation method of the CuAl catalysts influenced the carbon yield to liquids and acetol selectivity. However, the reaction phase had a greater influence than the preparation method of the catalyst. In the gas phase, the carbon yield to liquids reached values above 40% and the carbon selectivity to acetol was higher than 90%. The highest acetol yield, 462.6 mg_acetol/g_glycerol, was obtained with the CuAl catalyst prepared by the surfactant-assisted coprecipitation method. This study provides a new perspective on catalyst design by highlighting the crucial role of preparation techniques in determining CuAl catalyst performance in the liquid and gas phases. Full article

(This article belongs to the Special Issue Topical Advisory Panel Members' Collection Series: Biomass Catalytic Conversion)

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9 pages, 2547 KiB

Open AccessArticle

Correlation Between the Apparent Rate Constant and the Dye Concentration—Effect of the Bottom Reflection Ability on the Photocatalytic Reaction Rate

by Emil Lilov, Svetlozar Nedev, Vanya Lilova, Christian Girginov and Stephan Kozhukharov

Catalysts 2025, 15(4), 347; https://doi.org/10.3390/catal15040347 - 2 Apr 2025

Abstract

The dependence of the reaction rate on the solution layer thickness discovered in a previous work could be a powerful tool for investigating photocatalytic reactions. A reduction of the apparent rate constant with the growth of the dye concentration was found using this [...] Read more.

The dependence of the reaction rate on the solution layer thickness discovered in a previous work could be a powerful tool for investigating photocatalytic reactions. A reduction of the apparent rate constant with the growth of the dye concentration was found using this dependence. This decrement follows a hyperbolic law. This dependence is explained based on the observed increment of the solution conductivity. In addition, it is confirmed experimentally that the reaction rate decreases with the solution depth growth. The possibility of independent determination of the reaction rate constant and the adsorption equilibrium constant has been discussed. Additionally, it is demonstrated that the vessel’s reflective bottom could increase the chemical reaction rate. The reason why other authors have not yet reported this effect is also discussed. Full article

(This article belongs to the Section Photocatalysis)

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25 pages, 6515 KiB

Open AccessArticle

Frequency-Resolved Modulation Excitation Spectroscopy Methodology for Identifying Surface Reaction Species in Ethanol Oxidation on Gold Catalysts

by Bhagyesha S. Patil, Alejandra Torres-Velasco and Juan J. Bravo-Suárez

Catalysts 2025, 15(4), 346; https://doi.org/10.3390/catal15040346 - 1 Apr 2025

Abstract

This study used in situ modulation excitation spectroscopy (MES) with varying frequencies in a single experiment to identify surface species during ethanol oxidation on Au/SiO₂, Au/TiO₂, Au/ZnO, and Au/SrTiO₃. Fixed-bed reactor (FBR) tests (1 kPa ethanol, 1.5 [...] Read more.

This study used in situ modulation excitation spectroscopy (MES) with varying frequencies in a single experiment to identify surface species during ethanol oxidation on Au/SiO₂, Au/TiO₂, Au/ZnO, and Au/SrTiO₃. Fixed-bed reactor (FBR) tests (1 kPa ethanol, 1.5 kPa O₂, 513 K) showed that Au/SiO₂ and Au/SrTiO₃ had higher ethanol conversions. Au/SiO₂ favored acetaldehyde, while Au/SrTiO₃ yielded more acetates (acetic acid and ethyl acetate). Operando modulation excitation (ME)–phase sensitive detection (PSD)–DRIFTS, with ethanol and oxygen modulation, identified surface ethanol, acetaldehyde, acetates, ethoxy, and hydroxyl species. Oxygen modulation showed charge transfer to supports in Au/TiO₂ and Au/ZnO. At the fundamental frequency (f₀ = 1/90 Hz), ME–PSD–DRIFTS showed minimal adsorbed ethanol on Au/SiO₂, indicating high ethanol conversion. Au/SrTiO₃ had higher acetaldehyde consumption, correlating with increased acetates, consistent with FBR results. ME–PSD–DRIFTS at lower frequencies (0.07f₀, 0.5 f₀) and higher harmonics (2f₀, 3f₀) showed rapid ethoxy formation/decomposition, and slower acetaldehyde reactions, confirming acetaldehyde as a primary product and acetates as secondary products. Oxygen modulation revealed rapid hydrogen spillover and hydroxyl changes. Overall, operando spectroscopy via mass spectrometry confirmed the FBR findings. Full article

(This article belongs to the Special Issue Spectroscopy in Modern Materials Science and Catalysis)

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14 pages, 1980 KiB

Open AccessArticle

Regulating the Structures of Carbon Cloth and Carbon Nanotubes to Boost the Positive Electrode Reaction of Vanadium Redox Flow Batteries

by Xinyu Huang, Chuanyu Sun, Shuqi Liu, Bangsen Zhao, Mingming Ge and Huan Zhang

Catalysts 2025, 15(4), 345; https://doi.org/10.3390/catal15040345 - 1 Apr 2025

Abstract

Considering the various morphologies of carbon nanotubes (CNTs), it is expected to solve the contradiction between concentration polarization and electrochemical polarization in vanadium redox flow batteries (VRFBs). This paper investigates the structural evolution of CNTs grown on the surface of thermally oxidized carbon [...] Read more.

Considering the various morphologies of carbon nanotubes (CNTs), it is expected to solve the contradiction between concentration polarization and electrochemical polarization in vanadium redox flow batteries (VRFBs). This paper investigates the structural evolution of CNTs grown on the surface of thermally oxidized carbon cloth (TCC) and their impact on the performance of VRFBs. The morphological results indicate that thermal oxidation treatment forms pores on the surface of the TCC, providing nucleation sites for CNT growth. Spiral-shaped CNTs (TCC@s-CNTs) were formed in a short growth time (1 h), and their high defect density originated from the non-steady-state supply of carbon sources and the dynamic behavior of the catalyst. While 3 h of growth forms a network structure (TCC@n-CNT), the van der Waals force drives the self-assembly of its three-dimensional network. Although the TCC@s-CNT exhibits high catalytic activity due to its high defect density and edge active sites, the performance of VRFBs is more dependent on the three-dimensional conductive network of the TCC@n-CNT. At 240 mA/cm², the energy efficiency (EE) of a VRFB assembled with the TCC@n-CNT reaches 71%, and the capacity retention rate is 15% higher than that of the TCC@s-CNT. This work reveals the synergistic mechanism of CNT morphology regulation on electrode performance and provides theoretical guidance for the design of VRFB electrodes. Full article

(This article belongs to the Section Catalysis for Sustainable Energy)

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12 pages, 920 KiB

Open AccessFeature PaperArticle

Nitrone or Oxaziridine? Further Insights into the Selectivity of Imine Oxidation Catalyzed by Methyltrioxorhenium

by Camilla Matassini, Marco Bonanni, Francesca Cardona and Andrea Goti

Catalysts 2025, 15(4), 344; https://doi.org/10.3390/catal15040344 - 1 Apr 2025

Abstract

The oxidation of imines may give several products, such as oxaziridines, nitrones, amides, and other rearranged compounds. Therefore, its selectivity is a challenge that various methods have to face. The controversial selectivity of the oxidation of imines using urea hydrogen peroxide (UHP) catalyzed [...] Read more.

The oxidation of imines may give several products, such as oxaziridines, nitrones, amides, and other rearranged compounds. Therefore, its selectivity is a challenge that various methods have to face. The controversial selectivity of the oxidation of imines using urea hydrogen peroxide (UHP) catalyzed by methyltrioxorhenium (MTO) is addressed by varying the solvent, temperature, reaction time, amount of oxidant, and catalyst used. The reactivity and selectivity of the oxidation of imines proved to be particularly sensitive to the type of solvent. The use of methanol furnished the corresponding nitrones as the exclusive products, except for very hindered N-tert-alkyl substituted substrates. Using the ionic liquid [bmim]BF₄ as a solvent resulted in a complete switch in reactivity and selectivity. N-methyl substituted imines gave the corresponding amides, while imines with bulkier substituents at nitrogen did not show any reactivity. An exception was the C-phenyl,N-tert-butyl imine—the only substrate that was oxidized to the corresponding oxaziridine, albeit with low conversion. The results reported herein reaffirm the oxidation of imines with UHP/MTO in MeOH as the method of choice for their interconversion to nitrones. Full article

(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)

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21 pages, 4523 KiB

Open AccessFeature PaperArticle

ZIF-67-Derived Co−N−C Supported Ni Nanoparticles as Efficient Recyclable Catalyst for Hydrogenation of 4-Nitrophenol

by Juti Rani Deka, Diganta Saikia, Jia-Cheng Lin, Wan-Yu Chen, Hsien-Ming Kao and Yung-Chin Yang

Catalysts 2025, 15(4), 343; https://doi.org/10.3390/catal15040343 - 1 Apr 2025

Abstract

In this study, a novel, highly efficient, environment friendly, and low-cost nanocatalyst, denoted as Ni(x)@Co−N−C, was successfully developed by encapsulating Ni nanoparticles into N-doped porous carbon derived from ZIF-67. A variety of techniques including powder X-ray diffraction (XRD), nitrogen adsorption/desorption, scanning electron microscopy [...] Read more.

In this study, a novel, highly efficient, environment friendly, and low-cost nanocatalyst, denoted as Ni(x)@Co−N−C, was successfully developed by encapsulating Ni nanoparticles into N-doped porous carbon derived from ZIF-67. A variety of techniques including powder X-ray diffraction (XRD), nitrogen adsorption/desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectrometer (XPS) were used to characterize the prepared materials. The TEM images reveal that the nanoparticles were distributed homogeneously in the carbon support. The N atoms in the carbon support serve as the sites for the nucleation and uniform growth of Ni nanoparticles. The catalyst was used for the degradation of environmentally harmful 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). Among all the catalysts investigated, Ni(10)@Co-N-C exhibited the highest catalytic activity for the hydrogenation of 4-NP, with a specific reaction rate of 6.1 × 10⁻³ s⁻¹, activity parameter of 31 s⁻¹g⁻¹, and turn over frequency (TOF) of 1.78 × 10¹⁹ molecules g_metal⁻¹s⁻¹. On the other hand, the specific reaction rate and TOF value were 1.7 × 10⁻³ s⁻¹ and 6.96 × 10¹⁸ molecules g_metal⁻¹s⁻¹, respectively, for Co−N−C. This suggests that Ni(10)@Co−N−C is about three times more catalytically active than the Co−N−C catalyst. The superb activity of Ni(10)@Co−N−C in comparison to Co−N−C can be ascribed to the homogeneous dispersion of small-sized Ni nanoparticles, the interconnected three-dimensional porous arrangement of the support Co−N−C, the presence of N atoms in the carbon framework that stabilize metal nanoparticles, and the synergistic electronic effect between Ni and Co. The Ni(10)@Co−N−C catalyst maintained consistent catalytic activity over multiple cycles, which suggests that porous N-containing carbon support can effectively prevent aggregation and leaching of metal nanoparticles. The ICP-AES analysis of the recycled Ni(10)@Co−N−C revealed a slight reduction in metal content compared to the fresh sample, suggesting almost negligible leaching of metal nanoparticles. Full article

(This article belongs to the Special Issue Nanocatalysts for Degradation of Environmental Pollutants and Hydrogen Generation)

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14 pages, 3629 KiB

Open AccessFeature PaperArticle

Enhanced Nitrate Production via Electrocatalytic Nitric Oxide Oxidation Reaction over MnO₂ with Different Crystal Facets

by Xiaoyu Qin, Dongcai Shen, Quan Li, Xin Liu, Mingrui Wu and Wentai Wang

Catalysts 2025, 15(4), 342; https://doi.org/10.3390/catal15040342 - 1 Apr 2025

Abstract

The synthesis of nitrate (NO₃⁻) via electrocatalytic nitric oxide oxidation reaction (NOOR) is a green and efficient strategy for nitrogen fixation, which has great advantages over conventional nitrate synthesis. Notably, it also presents a promising solution for the remediation of [...] Read more.

The synthesis of nitrate (NO₃⁻) via electrocatalytic nitric oxide oxidation reaction (NOOR) is a green and efficient strategy for nitrogen fixation, which has great advantages over conventional nitrate synthesis. Notably, it also presents a promising solution for the remediation of NO pollutants. In this study, the structure–performance correlations of α-, β-, and δ-MnO₂ catalysts were investigated. These three polymorphs of MnO₂ exhibited disparate surface chemistries, NO adsorption capabilities, and NOOR catalytic activities. In a 1.0 M KOH electrolyte, α-MnO₂, characterized by its large-sized (2 × 2) one-dimensional tunnel structure, demonstrated the most outstanding NOOR catalytic performance, which achieved a remarkable NO₃⁻ yield of 665.2 mg·h⁻¹·mg_cat⁻¹ at a potential of 1.9 V, along with excellent stability and durability. Furthermore, a Zn-NO system was constructed, employing α-MnO₂ as the anode and a Zn plate as the cathode. This innovative setup integrated an energy storage system with NO electrochemical capture, yielding a NO₃⁻ production rate of 265.5 mg·h⁻¹·mg_cat⁻¹. The density functional theory calculations confirm the NO adsorption performance and catalytic activity of three different crystal forms of MnO₂. Full article

(This article belongs to the Section Electrocatalysis)

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19 pages, 3289 KiB

Open AccessArticle

Genome Mining of the Biocontrol Agent Trichoderma afroharzianum Unearths a Key Gene in the Biosynthesis of Anti-Fungal Volatile Sesquiterpenoids

by Fang Zhang, Rui Ma, Yuyang Huang, Yang Cui, Qiong Zhou and Jingang Gu

Catalysts 2025, 15(4), 341; https://doi.org/10.3390/catal15040341 - 1 Apr 2025

Abstract

The volatile organic compounds (VOCs) in Trichoderma afroharzianum ACCC 33109 have the biological activities of both hydrolytic enzymes and antimicrobial peptides to mitigate attack by phytopathogens and spread over long distances in soil. However, the biosynthesis pathway of anti-fungal VOCs has not been [...] Read more.

The volatile organic compounds (VOCs) in Trichoderma afroharzianum ACCC 33109 have the biological activities of both hydrolytic enzymes and antimicrobial peptides to mitigate attack by phytopathogens and spread over long distances in soil. However, the biosynthesis pathway of anti-fungal VOCs has not been elucidated yet. In this study, we identified 15 genes (TaTS1–15) coding for putative terpene synthase with low identities (<79.54%) to functionally characterized homologs through genome mining. Upon Fusarium induction, the relative expression levels of nine TaTS genes were up-regulated by up to 2793-fold (TaTS9). To verify the contribution of TaTS9 to the synthesis of anti-fungal VOCs, the TaTS9 knockout mutant strain was constructed and characterized by its antagonistic activities, transcript profiles, and VOC metabolomes. Heterologous expression of TaTS9 in Escherichia coli produced the target gene product, which converted the precursor farnesyl pyrophosphate (FPP) into β-cubenene (>90%) and γ-amorphene. Thus, TaTS9 was confirmed as the first β-cubenene synthase of Trichoderma, which catalyzes the biosynthesis of various sesquiterpenes with anti-fungal activities. This study provides insight into the key terpene synthase gene in the biosynthesis of anti-fungal sesquiterpenoids for potential applications in the agriculture and food industries. Full article

(This article belongs to the Section Biocatalysis)

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