Catalysts

12 pages, 7657 KiB

Open AccessArticle

Cation Vacancies Anchored Transition Metal Dopants Based on a Few-Layer Ti₃C₂T_x Catalyst for Enhanced Hydrogen Evolution

by Xiangjie Liu, Xiaomin Chen, Chunlan Huang, Sihan Sun, Ding Yuan and Yuhai Dou

Catalysts 2025, 15(7), 663; https://doi.org/10.3390/catal15070663 (registering DOI) - 7 Jul 2025

Abstract

This study addresses the efficiency and cost challenges of hydrogen evolution reaction (HER) catalysts in the context of carbon neutrality strategies by employing a synergistic approach that combines cation vacancy anchoring and transition metal doping on two-dimensional (2D) MXenes. Using an in situ [...] Read more.

This study addresses the efficiency and cost challenges of hydrogen evolution reaction (HER) catalysts in the context of carbon neutrality strategies by employing a synergistic approach that combines cation vacancy anchoring and transition metal doping on two-dimensional (2D) MXenes. Using an in situ LiF/HCl etching process, the aluminum layers in Ti₃AlC₂ were precisely removed, resulting in a few-layer Ti₃C₂T_x MXene with an increased interlayer spacing of 12.3 Å. Doping with the transition metals Fe, Co, Ni, and Cu demonstrated that Fe@Ti₃C₂ provided the optimal HER performance, characterized by an overpotential (η₁₀) of 81 mV at 10 mA cm⁻², a low Tafel slope of 33.03 mV dec⁻¹, and the lowest charge transfer resistance (R_ct = 5.6 Ω cm²). Mechanistic investigations revealed that Fe’s 3d⁶ electrons induce an upward shift in the d-band center of MXene, improving hydrogen adsorption free energy and reducing lattice distortion. This research lays a solid foundation for the design of non-precious metal catalysts using MXenes and highlights future avenues in bimetallic synergy and scalability. Full article

(This article belongs to the Special Issue Novel Electrocatalysts for Boosting Oxygen/Hydrogen Evolution Reactions)

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18 pages, 10208 KiB

Open AccessArticle

Development of Ni-P-N-C/Nickel Foam for Efficient Hydrogen Production via Urea Electro-Oxidation

by Abdullah M. Aldawsari, Maged N. Shaddad and Saba A. Aladeemy

Catalysts 2025, 15(7), 662; https://doi.org/10.3390/catal15070662 (registering DOI) - 7 Jul 2025

Abstract

Electrocatalytic urea oxidation reaction (UOR) is a promising dual-purpose approach for hydrogen production and wastewater treatment, addressing critical energy and environmental challenges. However, conventional anode materials often suffer from limited active sites and high charge transfer resistance, restricting UOR efficiency. To overcome these [...] Read more.

Electrocatalytic urea oxidation reaction (UOR) is a promising dual-purpose approach for hydrogen production and wastewater treatment, addressing critical energy and environmental challenges. However, conventional anode materials often suffer from limited active sites and high charge transfer resistance, restricting UOR efficiency. To overcome these issues, a novel NiP@PNC/NF electrocatalyst was developed via a one-step thermal annealing process under nitrogen, integrating nickel phosphide (NiP) with phosphorus and nitrogen co-doped carbon nanotubes (PNCs) on a nickel foam (NF) substrate. This design enhances catalytic activity and charge transfer, achieving current densities of 50 mA cm⁻² at 1.34 V and 100 mA cm⁻² at 1.43 V versus the reversible hydrogen electrode (RHE). The electrode’s high electrochemical surface area (235 cm²) and double-layer capacitance (94.1 mF) reflect abundant active sites, far surpassing NiP/NF (48 cm², 15.8 mF) and PNC/NF (39.5 cm², 12.9 mF). It maintains exceptional stability, with only a 16.3% performance loss after 35 h, as confirmed by HR-TEM showing an intact nanostructure. Our single-step annealing technique provides simplicity, scalability, and efficient integration of NiP nanoparticles inside a PNC matrix on nickel foam. This method enables consistent distribution and robust substrate adhesion, which are difficult to attain with multi-step or more intricate techniques. Full article

(This article belongs to the Special Issue Advances in Catalysis for Sustainable Energy and Environmental Remediation)

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10 pages, 1115 KiB

Open AccessArticle

Ab Initio Study of Ti Segregation on the Pd–Ti Alloy Surface in the Presence of Adsorbed Atomic Oxygen

by Yufeng Wen, Yanlin Yu, Huaizhang Gu, Yaya Shi, Guoqi Zhao, Yuanxun Li and Qiuling Huang

Catalysts 2025, 15(7), 661; https://doi.org/10.3390/catal15070661 (registering DOI) - 7 Jul 2025

Abstract

Surface segregation in bimetallic systems plays a critical role in material functionality, as electrochemical activity and catalytic performance are governed by the surface composition. To explore the influence of atomic oxygen on the surface composition of Pd–Ti alloys, density functional theory (DFT) simulations [...] Read more.

Surface segregation in bimetallic systems plays a critical role in material functionality, as electrochemical activity and catalytic performance are governed by the surface composition. To explore the influence of atomic oxygen on the surface composition of Pd–Ti alloys, density functional theory (DFT) simulations were utilized to analyze Ti segregation within Pd matrices. The adsorption behavior of atomic oxygen on Pd–Ti low-index (111), (100), and (110) surfaces was systematically investigated through energetic and electronic analyses. Simulation results reveal that Ti atoms prefer to remain in the bulk of the alloy under vacuum conditions, whereas oxygen adsorption induces significant Ti segregation to the surface layer. This oxygen-driven segregation is mechanistically linked to oxygen-surface bonding strength, as evidenced by correlating adsorption energetics with electronic structure modifications. These results provide a theoretical basis for engineering Pd–Ti alloys as high-performance catalysts in the oxygen reduction reaction. Full article

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15 pages, 4061 KiB

Open AccessFeature PaperArticle

Influence of Metal Compounds on Structural and Electrochemical Characteristics of Chars from PVC Pyrolysis

by Jiayou Sun, Tianyang Ding, Xue Zhao, Guorong Xu, Chang Wen and Jie Yu

Catalysts 2025, 15(7), 660; https://doi.org/10.3390/catal15070660 (registering DOI) - 6 Jul 2025

Abstract

This study aims to investigate the influence of various metal compounds (ZnO, ZnCl₂, Zn(OH)₂, MgO, MgCl₂, and Mg(OH)₂) on the structural and electrochemical properties of chars derived from the pyrolysis of polyvinyl chloride (PVC). Raw [...] Read more.

This study aims to investigate the influence of various metal compounds (ZnO, ZnCl₂, Zn(OH)₂, MgO, MgCl₂, and Mg(OH)₂) on the structural and electrochemical properties of chars derived from the pyrolysis of polyvinyl chloride (PVC). Raw PVC samples mixed with different metal compounds were firstly pyrolyzed at 500 °C in a fixed-bed reactor. The produced chars were further pyrolyzed at 800 °C. The objective was to evaluate the impact of these metal compounds on the char structure through comparative analysis. The pyrolytic chars were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy, and Brunauer–Emmett–Teller (BET) analysis. Zinc-based additives notably increased carbon yield to 32–34 wt.%, attributed to ZnCl₂-induced cross-linking. Specifically, ZnO facilitated porous architectures and aromatic structures with six or more rings. Mg-based compounds induce the formation of a highly stacked carbon structure primarily composed of crosslinked cyclic alkenes, rather than large polyaromatic domains. Upon further thermal treatment, these aliphatic-rich stacked structures can be progressively transformed into aromatic frameworks through dehydrogenation reactions at elevated temperatures. A high-surface-area porous carbon material (PVC/ZnO-800, SSA = 609.382 m² g⁻¹) was synthesized, demonstrating a specific capacitance of 306 F g⁻¹ at 1 A g⁻¹ current density. Full article

(This article belongs to the Special Issue Catalysis Accelerating Energy and Environmental Sustainability)

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18 pages, 4065 KiB

Open AccessArticle

Comparative Study on Ni/MgO-Al₂O₃ Catalysts for Dry and Combined Steam–CO₂ Reforming of Methane

by Tingting Zheng, Yuqi Zhou, Hongjie Cui and Zhiming Zhou

Catalysts 2025, 15(7), 659; https://doi.org/10.3390/catal15070659 (registering DOI) - 6 Jul 2025

Abstract

The dry reforming of methane (DRM) and the combined steam–CO₂ reforming of methane (CSCRM) are promising routes for syngas production while simultaneously utilizing two major greenhouse gases—CO₂ and CH₄. In this study, a series of Ni/MgO-Al₂O₃ [...] Read more.

The dry reforming of methane (DRM) and the combined steam–CO₂ reforming of methane (CSCRM) are promising routes for syngas production while simultaneously utilizing two major greenhouse gases—CO₂ and CH₄. In this study, a series of Ni/MgO-Al₂O₃ catalysts with varying Mg/Al molar ratios (Ni/MgAl(x), x = 0.5–0.9), along with Ni/MgO and Ni/Al₂O₃, were synthesized, characterized, and evaluated in both the DRM and CSCRM. Ni/MgO and Ni/Al₂O₃ exhibited a lower activity due to fewer active sites and a poor CH₄/CO₂ activation balance. In contrast, Ni/MgAl(0.6), Ni/MgAl(0.7), and Ni/MgAl(0.8) showed an enhanced activity, attributed to more abundant active sites and a more balanced activation of CH₄ and CO₂. Ni/MgAl(0.7) delivered the best DRM performance, whereas Ni/MgAl(0.8) was optimal for the CSCRM, likely due to its greater number of strong basic sites promoting CO₂ and H₂O adsorption. At 750 °C and 0.1 MPa over 100 h, Ni/MgAl(0.7) maintained a stable DRM performance (77% CH₄ and 86% CO₂ conversion; H₂/CO = 0.9) at 120 L/(g_cat·h), while Ni/MgAl(0.8) achieved a stable CSCRM performance (80% CH₄ and 62% CO₂ conversion; H₂/CO = 2.1) at 132 L/(g_cat·h). This study provides valuable insights into designing efficient Ni/MgO-Al₂O₃ catalysts for targeted syngas production. Full article

(This article belongs to the Section Catalytic Reaction Engineering)

15 pages, 3237 KiB

Open AccessFeature PaperArticle

A Simple Fabrication of Tourmaline-Supported Ni-NiAl₂O₄ Nanocomposites for Enhanced Methane Dry Reforming Activity

by Jin Wang, Xianku Wang, Pengfei Zhou, Liang Bian and Fei Wang

Catalysts 2025, 15(7), 658; https://doi.org/10.3390/catal15070658 (registering DOI) - 6 Jul 2025

Abstract

Ni-based catalysts have been widely used in catalytic reactions by researchers due to their advantages such as abundant resources, high catalytic activity and lower prices than precious metals. However, the problems of easy agglomeration and poor dispersion of Ni-based catalysts have hindered their [...] Read more.

Ni-based catalysts have been widely used in catalytic reactions by researchers due to their advantages such as abundant resources, high catalytic activity and lower prices than precious metals. However, the problems of easy agglomeration and poor dispersion of Ni-based catalysts have hindered their large-scale application. Therefore, it is necessary to select a suitable preparation method to reduce the agglomeration of the catalyst and improve its dispersion. In this paper, the Ni-NiAl₂O₄/tourmaline composite material was prepared by using the microwave hydrothermal reduction method. The most favorable conditions for preparing NiAl₂O₄/tourmaline are as follows: using TEOA as the additive, the microwave hydrothermal temperature is 220 °C, the calcination temperature is 800 °C, and the addition amount of tourmaline is 7.4 wt.%. NiAl₂O₄ has a good dispersion over the surface of tourmaline support and the optimal NiAl₂O₄/tourmaline catalyst exhibits a specific surface area of 106.5 m²/g. Metallic nickel was reduced at 650 °C to further obtain Ni-NiAl₂O₄/tourmaline composites. Finally, the Ni-NiAl₂O₄/tourmaline composites showed significantly improved catalytic dry reforming of methane (DRM) activity compared to Ni-NiAl₂O₄ sample under low-temperature conditions (500–600 °C), meaning that the tourmaline carrier could effectively optimize the low-temperature catalytic performance of Ni-NiAl₂O₄. Full article

(This article belongs to the Special Issue Catalytic Reforming and Hydrogen Production: From the Past to the Future, 2nd Edition)

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17 pages, 989 KiB

Open AccessFeature PaperArticle

Combination of aza-Friedel Crafts MCR with Other MCRs Under Heterogeneous Conditions

by Giovanna Bosica and Roderick Abdilla

Catalysts 2025, 15(7), 657; https://doi.org/10.3390/catal15070657 (registering DOI) - 6 Jul 2025

Abstract

Multicomponent reactions (MCRs) enable the efficient assembly of complex small molecules via multiple bond-forming events in a single step. However, individual MCRs typically yield products with similar core structures, limiting access to larger, more intricate scaffolds. Strategic selection of reactants allows the combination [...] Read more.

Multicomponent reactions (MCRs) enable the efficient assembly of complex small molecules via multiple bond-forming events in a single step. However, individual MCRs typically yield products with similar core structures, limiting access to larger, more intricate scaffolds. Strategic selection of reactants allows the combination of distinct MCRs, thus facilitating the synthesis of advanced molecular architectures with potential biological significance. Using our previously reported method for performing the aza-Friedel Crafts multicomponent reaction under green heterogeneous conditions, we have incorporated some of the obtained products into diverse multicomponent reactions to generate, in an unprecedent approach, eight novel products, some of which were also characterized by two-dimensional NMR techniques. The biological properties of such products are under investigation. Full article

(This article belongs to the Special Issue Multicomponent Catalytic Reactions Under Green Conditions, 2nd Edition)

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30 pages, 3496 KiB

Open AccessFeature PaperArticle

Production of 5-Hydroxymethylfurfural (HMF) from Sucrose in Aqueous Phase Using S, N-Doped Hydrochars

by Katarzyna Morawa Eblagon, Rafael G. Morais, Anna Malaika, Manuel Alejandro Castro Bravo, Natalia Rey-Raap, M. Fernando R. Pereira and Mieczysław Kozłowski

Catalysts 2025, 15(7), 656; https://doi.org/10.3390/catal15070656 (registering DOI) - 5 Jul 2025

Abstract

5-Hydroxymethylfurfural (HMF) is a versatile platform molecule with the potential to replace many fossil fuel derivatives. It can be obtained through the dehydration of carbohydrates. In this study, we present a simple and cost-effective microwave-assisted method for producing HMF. This method involves the [...] Read more.

5-Hydroxymethylfurfural (HMF) is a versatile platform molecule with the potential to replace many fossil fuel derivatives. It can be obtained through the dehydration of carbohydrates. In this study, we present a simple and cost-effective microwave-assisted method for producing HMF. This method involves the use of readily available sucrose as a substrate and glucose-derived bifunctional hydrochars as carbocatalysts. These catalysts were produced via hydrothermal carbonisation using thiourea and urea as nitrogen and sulphur sources, respectively, to introduce Brønsted acidic and basic sites into the materials. Using a microwave reactor, we found that the S, N-doped hydrochars were active in sucrose dehydration in water. Catalytic results showed that HMF yield depended on the balance between acidic and basic sites as well as the types of S and N species present on the surfaces of these hydrochars. The best-performing catalyst achieved an encouraging HMF yield of 37%. The potential of N, S-co-doped biochar as a green solid catalyst for various biorefinery processes was demonstrated. A simple kinetic model was developed to elucidate the kinetics of the main reaction pathways of this cascade process, showing a very good fit with the experimental results. The calculated rate constants revealed that reactions with a 5% sucrose loading exhibited significantly higher fructose dehydration rates and produced fewer side products than reactions using a more diluted substrate. No isomerisation of glucose into fructose was observed in an air atmosphere. On the contrary, a limited rate of isomerisation of glucose into fructose was recorded in an oxygen atmosphere. Therefore, efforts should focus on achieving a high glucose-to-fructose isomerisation rate (an intermediate reaction step) to improve HMF selectivity by reducing humin formation. Full article

(This article belongs to the Special Issue Carbon-Based Catalysts to Address Environmental Challenges)

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19 pages, 3246 KiB

Open AccessFeature PaperArticle

Direct Conversion of 1,3-Butanediol to 1,3-Butadiene over ZSM-22 Catalysts: Influence of the Si/Al Ratio

by Loïc Eloi, Jeroen Poissonnier, Arne De Landsheere, Dhanjay Sharma, Jaouad Al Atrach, Valérie Ruaux, Valentin Valtchev, Maarten K. Sabbe, Joris W. Thybaut and An Verberckmoes

Catalysts 2025, 15(7), 655; https://doi.org/10.3390/catal15070655 (registering DOI) - 5 Jul 2025

Abstract

ZSM-22 zeolites with different Si/Al ratios (38, 50, 80) were prepared via a hydrothermal synthesis method, investigated for the catalytic dehydration of 1,3-butanediol (1,3-BDO) to butadiene (BD) at 300 °C. The catalytic performance of the synthesized materials was related to their properties and [...] Read more.

ZSM-22 zeolites with different Si/Al ratios (38, 50, 80) were prepared via a hydrothermal synthesis method, investigated for the catalytic dehydration of 1,3-butanediol (1,3-BDO) to butadiene (BD) at 300 °C. The catalytic performance of the synthesized materials was related to their properties and compared to a commercial ZSM-22 zeolite (Si/Al = 30). ZSM-22 (50) exhibited a quick decline in conversion, a lower BD selectivity, and higher propylene selectivity compared to the other materials, which could be attributed to the presence of strong Lewis acid sites and silanol nests. The Lewis sites favor the cracking of the intermediate 3-buten-1-ol (3B1OL) into propylene, while the silanol nests interact with the free hydroxyl group of 3B1OL, potentially inhibiting further dehydration towards BD. The highest initial BD yield of 74% was observed over ZSM-22 (80), while the highest initial BD productivity of 2.7 g_BD·g⁻¹_cata·h⁻¹ was achieved over ZSM-22 (38). After 22 h time on stream (TOS), c-ZSM-22 and ZSM-22 (38) outperformed previously reported catalysts from the literature, with productivities amounting to 1.3 g_BD·g⁻¹_cata·h⁻¹ and 1.2 g_BD·g⁻¹_cata·h⁻¹, respectively, at a site time of 6.6 mol_H+·s·mol⁻¹_1,3-BDO. Full article

(This article belongs to the Special Issue Zeolites as Catalysts: Applications in Chemical Engineering, Energy Sources and Environmental Protection, 2nd Edition)

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22 pages, 1883 KiB

Open AccessFeature PaperArticle

Preparation and Screening of Ni-Based Catalysts for the Olive Oil Mill Wastewater Steam Reforming Process

by Cláudio Rocha, Miguel A. Soria and Luís M. Madeira

Catalysts 2025, 15(7), 654; https://doi.org/10.3390/catal15070654 (registering DOI) - 4 Jul 2025

Abstract

Olive mill wastewater (OMW) is a highly polluting effluent rich in organic pollutant compounds derived from olive oil production. In this work, the steam reforming reaction of OMW (OMWSR) was performed in a traditional reactor at 400 °C and different pressures (1–4 bar) [...] Read more.

Olive mill wastewater (OMW) is a highly polluting effluent rich in organic pollutant compounds derived from olive oil production. In this work, the steam reforming reaction of OMW (OMWSR) was performed in a traditional reactor at 400 °C and different pressures (1–4 bar) to treat and valorize this effluent. A commercial catalyst (Rh/Al₂O₃) was used as a reference sample and several new catalysts were prepared (Ni-Ru/Ce-SiO₂) using different preparation methods to study their effect on the activity and stability. The best-performing catalysts were also subjected to long-term operation experimental tests (24 h). It was observed that the preparation method used for the catalysts synthesis influenced the catalytic performance of the samples. In addition, temperature-programmed oxidation (TPO) analysis of the used catalyst showed the presence of carbon deposits: the results showed that periodic oxidative regeneration improved the catalyst stability and sustained H₂ production. Finally, it was verified that the Ni-Ru/Ce³ catalyst stood out during the experimental tests, exhibiting high catalytic activity along the stability test at 400 °C and 1 bar: H₂ yield always over 7 mol_H2·mol_OMW⁻¹ and total organic carbon (TOC) conversion always higher than 94%. Despite these promising results, further research is needed to assess the economic feasibility of scaling up the process. Additionally, future work could explore the development of catalysts with enhanced resistance to deactivation by carbon deposition. Full article

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

38 pages, 6778 KiB

Open AccessReview

Challenges and Opportunities for g-C₃N₄-Based Heterostructures in the Photodegradation of Environmental Pollutants

by Eduardo Estrada-Movilla, Jhonathan Castillo-Saenz, Benjamín Valdez-Salas, Álvaro Ortiz-Pérez, Ernesto Beltrán-Partida, Jorge Salvador-Carlos and Esneyder Puello-Polo

Catalysts 2025, 15(7), 653; https://doi.org/10.3390/catal15070653 (registering DOI) - 4 Jul 2025

Abstract

Graphitic carbon nitride (g-C₃N₄) is emerging as one of the most promising non-metallic semiconductors for the degradation of pollutants in water by photocatalytic processes. Its exceptional reduction–oxidation (redox) potentials and adequate band gap of approximately 2.7 eV give it [...] Read more.

Graphitic carbon nitride (g-C₃N₄) is emerging as one of the most promising non-metallic semiconductors for the degradation of pollutants in water by photocatalytic processes. Its exceptional reduction–oxidation (redox) potentials and adequate band gap of approximately 2.7 eV give it the ability to absorb in the visible light range. However, the characteristic sensitivity to light absorption is limited, leading to rapid recombination of electron–hole pairs. Therefore, different strategies have been explored to optimize this charge separation, among which the formation of heterostructures based on g-C₃N₄ is highlighted. This review addresses recent advances in photocatalysis mediated by g-C₃N₄ heterostructures, considering the synthesis methods enabling the optimization of the morphology and active interface of these materials. Next, the mechanisms of charge transfer are discussed in detail, with special emphasis on type II, type S, and type Z classifications and their influence on the efficiency of photodegradation. Subsequently, the progress in the application of these photocatalysts for the degradation of water pollutants, such as toxic organic dyes, pharmaceutical pollutants, pesticides, and per- and polyfluoroalkyl substances (PFAS), are analyzed, highlighting both experimental advances and remaining challenges. Finally, future perspectives oriented towards the optimization of heterostructures, the efficiency of synthesis methods, and the practical application of these in photocatalytic processes for environmental remediation. Full article

(This article belongs to the Special Issue Design and Synthesis of Nanostructured Catalysts, 3rd Edition)

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19 pages, 5983 KiB

Open AccessArticle

Fabrication of CoP@P, N-CNTs-Deposited Nickel Foam for Energy-Efficient Hydrogen Generation via Electrocatalytic Urea Oxidation

by Hany M. Youssef, Maged N. Shaddad, Saba A. Aladeemy and Abdullah M. Aldawsari

Catalysts 2025, 15(7), 652; https://doi.org/10.3390/catal15070652 (registering DOI) - 4 Jul 2025

Abstract

The simultaneous generation of hydrogen fuel and wastewater remediation via electrocatalytic urea oxidation has emerged as a promising approach for sustainable energy and environmental solutions. However, the practical application of this process is hindered by the limited active sites and high charge-transfer resistance [...] Read more.

The simultaneous generation of hydrogen fuel and wastewater remediation via electrocatalytic urea oxidation has emerged as a promising approach for sustainable energy and environmental solutions. However, the practical application of this process is hindered by the limited active sites and high charge-transfer resistance of conventional anode materials. In this work, we introduce a novel CoP@P, N-CNTs/NF electrocatalyst, fabricated through a facile one-step thermal annealing technique. Comprehensive characterizations confirm the successful integration of CoP nanoparticles and phosphorus/nitrogen co-doped carbon nanotubes (P, N-CNTs) onto nickel foam, yielding a unique hierarchical structure that offers abundant active sites and accelerated electron transport. As a result, the CoP@P, N-CNTs/NF electrode achieves outstanding urea oxidation reaction (UOR) performance, delivering current densities of 158.5 mA cm⁻² at 1.5 V and 232.95 mA cm⁻² at 1.6 V versus RHE, along with exceptional operational stability exceeding 50 h with negligible performance loss. This innovative, multi-element-doped electrode design marks a significant advancement in the field, enabling highly efficient UOR and energy-efficient hydrogen production. Our approach paves the way for scalable, cost-effective solutions that couple renewable energy generation with effective wastewater treatment. Full article

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

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35 pages, 3949 KiB

Open AccessFeature PaperReview

The Influence of Defect Engineering on the Electronic Structure of Active Centers on the Catalyst Surface

by Zhekun Zhang, Yankun Wang, Tianqi Guo and Pengfei Hu

Catalysts 2025, 15(7), 651; https://doi.org/10.3390/catal15070651 - 3 Jul 2025

Abstract

Defect engineering has recently emerged as a cutting-edge discipline for precise modulation of electronic structures in nanomaterials, shifting the paradigm in nanoscience from passive ‘inherent defect tolerance’ to proactive ‘defect-controlled design’. The deliberate introduction of defect—including vacancies, dopants, and interfaces—breaks the rigid symmetry [...] Read more.

Defect engineering has recently emerged as a cutting-edge discipline for precise modulation of electronic structures in nanomaterials, shifting the paradigm in nanoscience from passive ‘inherent defect tolerance’ to proactive ‘defect-controlled design’. The deliberate introduction of defect—including vacancies, dopants, and interfaces—breaks the rigid symmetry of crystalline lattices, enabling new pathways for optimizing catalysis performance. This review systematically summarizes the mechanisms underlying defect-mediated electronic structure at active sites regulation, including (1) reconstruction of the electronic density of states, (2) tuning of coordination microenvironments, (3) charge transfer and localization effects, (4) spin-state and magnetic coupling modulation, and (5) dynamic defect and interface engineering. These mechanisms elucidate how defect-induced electronic restructuring governs catalytic activity and selectivity. We further assess advanced characterization techniques and computational methodologies for probing defects-induced electronic states, offering deeper mechanistic insights at atomic scales. Finally, we highlight recent breakthroughs in defect-engineered nanomaterials for catalytic applications, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and beyond, while discussing existing challenges in scalability, defect stability, and structure–property causality. This review aims to provide actionable principles for the rational design of defects to tailor electronic structures toward next-generation energy technologies. Full article

(This article belongs to the Special Issue Effect of the Modification of Catalysts on the Catalytic Performance, 2nd Edition)

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19 pages, 5973 KiB

Open AccessFeature PaperArticle

Chitosan-Modified SBA-15 as a Support for Transition Metal Catalysts in Cyclohexane Oxidation and Photocatalytic Hydrogen Evolution

by Assemgul S. Auyezkhanova, Alima K. Zharmagambetova, Eldar T. Talgatov, Aigul I. Jumekeyeva, Sandugash N. Akhmetova, Zhannur K. Myltykbayeva, Imge Kalkan, Atıf Koca, Akzhol A. Naizabayev and Aigul T. Zamanbekova

Catalysts 2025, 15(7), 650; https://doi.org/10.3390/catal15070650 - 3 Jul 2025

Abstract

This work aims to study the catalytic properties of Fe, Cr, and Cu catalysts deposited on chitosan–silica (SBA-15) composites in liquid phase oxidation of cyclohexane (CH) with H₂O₂ and photocatalytic hydrogen evolution reaction. The catalysts were obtained by consecutive adsorption [...] Read more.

This work aims to study the catalytic properties of Fe, Cr, and Cu catalysts deposited on chitosan–silica (SBA-15) composites in liquid phase oxidation of cyclohexane (CH) with H₂O₂ and photocatalytic hydrogen evolution reaction. The catalysts were obtained by consecutive adsorption of chitosan (CS) and metal ions (Fe³⁺, Cr³⁺, Cu²⁺) on SBA-15 at ambient conditions. Characterization of the catalysts by XRD, IR spectroscopy, XPS, TEM, SEM, etc., showed the CS and metal ion adsorption on the solid support. Modification with CS provided better immobilization of the metal ions on SBA-15. The synthesized catalysts demonstrated different performance in liquid phase oxidation of cyclohexane with H₂O₂ under mild conditions at 40 °C and atmospheric pressure. Cyclohexane conversion on Fe–CS/SBA-15 (18.5%) and Cr–CS/SBA-15 (21.6%) was higher than on Cu–CS/SBA-15 (9.3%). The influence of different conditions of the reaction such as time, temperature, catalyst dosage, substrate and oxidant ratio on cyclohexane conversion in the presence of the most efficient Cr–CS/SBA-15 catalyst was also studied. The optimal reaction conditions were found to be the following: duration of reaction—4 h, temperature of reaction—50 °C, m_cat—0.03 g, a substrate/H₂O₂ ratio of 1:3. In addition, Cr–CS/SBA-15 and Fe–CS/SBA-15 catalysts were studied in a photocatalytic H₂ evolution reaction. The Fe-containing catalyst demonstrated superior efficiency in photocatalytic H₂ evolution. The total volume of hydrogen produced within 3 h was 103 mL/g. Thus, this study demonstrates that chitosan possesses promising potential in the design of the supported catalysts for cyclohexane oxidation and photocatalytic hydrogen evolution reactions. Full article

(This article belongs to the Special Issue Homogeneous and Heterogeneous Catalytic Oxidation and Reduction)

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12 pages, 3285 KiB

Open AccessArticle

Ceria Promoted Ni/SiO₂ as an Efficient Catalyst for Carbon Dioxide Reforming of Methane

by Hua-Ping Ren, Lin-Feng Zhang, Yu-Xuan Hui, Xin-Ze Wu, Shao-Peng Tian, Si-Yi Ding, Qiang Ma and Yu-Zhen Zhao

Catalysts 2025, 15(7), 649; https://doi.org/10.3390/catal15070649 - 2 Jul 2025

Abstract

The Ni/SiO₂ and the ceria-promoted Ni-CeO₂/SiO₂ were prepared by the impregnation method and co-impregnation method, respectively. The performance of the carbon dioxide reforming of methane (CDR) over Ni/SiO₂ and Ni-CeO₂/SiO₂ was investigated under the conditions [...] Read more.

The Ni/SiO₂ and the ceria-promoted Ni-CeO₂/SiO₂ were prepared by the impregnation method and co-impregnation method, respectively. The performance of the carbon dioxide reforming of methane (CDR) over Ni/SiO₂ and Ni-CeO₂/SiO₂ was investigated under the conditions of CH₄/CO₂ = 1.0, T = 800 °C, and GHSV = 60,000 mL·g⁻¹·h⁻¹. As a result, a high CDR performance, especially stability, was obtained over Ni-CeO₂/SiO₂, in which the conversion of CH₄ was very similar to that of the thermodynamic equilibrium (88%), and a negligible decrease in CH₄ conversion was observed after 50 h of the CDR reaction. Ni/SiO₂ and Ni-CeO₂/SiO₂ before and after the CDR reaction were subjected to structural characterization by XRD, TEM, TG–DSC, and physical adsorption. It was found that the addition of CeO₂ into Ni/SiO₂ significantly affected its surface area, the size and dispersion of Ni, the reduction behavior, and the coking properties. Moreover, the redox property of Ce³⁺-Ce⁴⁺, which accelerates the gasification of the coke, made Ni-CeO₂/SiO₂ successfully operate for 50 h without observable deactivation. Thus, the developed catalyst is very promising for the CDR. Full article

(This article belongs to the Special Issue Trends and Prospects in Catalysis for Sustainable CO₂ Conversion)

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28 pages, 3287 KiB

Open AccessReview

Recent Progress in Photocatalytic Hydrogen Production Using 2D MoS₂ Based Materials

by Khursheed Ahmad and Tae Hwan Oh

Catalysts 2025, 15(7), 648; https://doi.org/10.3390/catal15070648 - 2 Jul 2025

Abstract

Due to the increase in energy demand, photocatalytic hydrogen (H₂) production has received enormous interest from the scientific community due to its simplicity and cost-effectiveness. The photocatalyst (PC) plays a vital role in H₂ evolution, and it is well understood [...] Read more.

Due to the increase in energy demand, photocatalytic hydrogen (H₂) production has received enormous interest from the scientific community due to its simplicity and cost-effectiveness. The photocatalyst (PC) plays a vital role in H₂ evolution, and it is well understood that an efficient PC should have a larger surface area and better charge separation and transport properties. Previously, extensive efforts were made to prepare the efficient PC for photocatalytic H₂ production. In some cases, pristine catalyst could not catalyze the catalytic reactions due to a fast recombination rate or poor catalytic behavior. Thus, cocatalysts can be explored to boost the photocatalytic H₂ production. In this regard, a promising cocatalyst should have a large surface area, more active sites, decent conductivity, and improved catalytic properties. Molybdenum disulfide (MoS₂) is one of the two-dimensional (2D) layered materials that have excellent optical, electrical, and physicochemical properties. MoS₂ has been widely utilized as a cocatalyst for the photocatalytic H₂ evolution under visible light. Herein, we have reviewed the progress in the fabrication of MoS₂ and its composites with metal oxides, perovskite, graphene, carbon nanotubes, graphitic carbon nitrides, polymers, MXenes, metal-organic frameworks, layered double hydroxides, metal sulfides, etc. for photocatalytic H₂ evolution. The reports showed that MoS₂ is one of the desirable cocatalysts for photocatalytic H₂ production applications. The challenges and future perspectives are also mentioned. This study may be beneficial for the researchers working on the design and fabrication of MoS₂-based PCs for photocatalytic H₂ evolution applications. Full article

(This article belongs to the Special Issue Catalytic Reforming and Hydrogen Production: From the Past to the Future, 2nd Edition)

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15 pages, 1943 KiB

Open AccessArticle

Theoretical Study on the Influence of Building Blocks in Benzotrithiophene-Based Covalent Organic Frameworks for Optoelectronic Properties

by Xu Li, Yue Niu, Kexin Ma, Xin Huang, Qingji Wang and Zhiqiang Liang

Catalysts 2025, 15(7), 647; https://doi.org/10.3390/catal15070647 - 2 Jul 2025

Abstract

Covalent organic frameworks (COFs) have emerged as unique catalysts for photocatalysis; however, the relationship between their building block units and optoelectronic properties remains elusive. Herein, we explored the influence of building blocks on the optoelectronic properties of benzotrithiophene-based COFs (BTT-COFs) using density functional [...] Read more.

Covalent organic frameworks (COFs) have emerged as unique catalysts for photocatalysis; however, the relationship between their building block units and optoelectronic properties remains elusive. Herein, we explored the influence of building blocks on the optoelectronic properties of benzotrithiophene-based COFs (BTT-COFs) using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The calculation results suggested that three critical factors—the conjugated structure, planarity, and the introduction of nitrogen heteroatoms—significantly influenced charge separation and transfer within BTT-COFs. Structure–property relationships were established through several critical quantitative parameters, such as Sr, t, and CT. Among seven BTT-COFs, BTT-Tpa (Tpa: 4,4′,4″-triaminotriphenylamine) exhibited the most efficient charge separation and the highest charge transfer capability due to the electronegativity of triphenylamine, the delocalization of its lone pair electrons, and its unique star-shaped configuration. These theoretical results will provide an essential foundation for selecting donor–acceptor units in the design of novel COF materials for photocatalytic reaction applications. Full article

(This article belongs to the Section Computational Catalysis)

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14 pages, 3484 KiB

Open AccessArticle

Al₂O₃@SiO₂ Supported NiMo Catalyst with Hierarchical Meso-Macroporous Structure for Hydrodemetallization

by Weichu Li, Jun Bao, Shuangqin Zeng, Jinbao Zheng, Weiping Fang, Xiaodong Yi, Qinghe Yang and Weikun Lai

Catalysts 2025, 15(7), 646; https://doi.org/10.3390/catal15070646 - 1 Jul 2025

Abstract

The pore structure of a hydrotreating catalyst plays a pivotal role in hydrodemetallization (HDM) reactions. To effectively construct a meso-macroporous catalyst, we employed a CTAB-guided in situ TEOS hydrolysis approach to prepare silica-coated γ-Al₂O₃@SiO₂ composite supports. The silica [...] Read more.

The pore structure of a hydrotreating catalyst plays a pivotal role in hydrodemetallization (HDM) reactions. To effectively construct a meso-macroporous catalyst, we employed a CTAB-guided in situ TEOS hydrolysis approach to prepare silica-coated γ-Al₂O₃@SiO₂ composite supports. The silica shell incorporation significantly enhances specific surface area and reduces the metal–support interactions, thereby improving the dispersion of NiMo active components and boosting the deposition of metal impurity. Hence, the NiMo/Al₂O₃@SiO₂ catalyst (2.8 wt.% NiO, 4.3 wt.% MoO₃) exhibits much higher HDM activity than that of NiMo/Al₂O₃. This is evidenced by markedly higher demetallization rate constant (1.38 h⁻¹) and turnover frequency (0.56 h⁻¹) of the NiMo/Al₂O₃@SiO₂. The NiMo/Al₂O₃@SiO₂ catalyst further demonstrates excellent recyclability during sequential HDM reactions. This superior catalytic behavior stems from the hierarchical meso-macroporous structure, which simultaneously facilitates the deposition of metal impurities and mitigates deactivation by pore blockage. Full article

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18 pages, 5074 KiB

Open AccessFeature PaperArticle

A Novel Polymer-Derived Ni/SiOC Catalyst for the Dry Reforming of Methane

by Rachel Olp, Keith L. Hohn and Catherine B. Almquist

Catalysts 2025, 15(7), 645; https://doi.org/10.3390/catal15070645 - 1 Jul 2025

Abstract

Nickel (Ni)-based catalysts, prepared by pyrolyzing Ni-containing polydimethylsiloxane (Ni-PDMS), were evaluated for their activity in the dry reforming of methane (DRM) reaction. The pyrolyzed PDMS support was found to be largely microporous, and the active nickel particles were nano-sized but were not dispersed [...] Read more.

Nickel (Ni)-based catalysts, prepared by pyrolyzing Ni-containing polydimethylsiloxane (Ni-PDMS), were evaluated for their activity in the dry reforming of methane (DRM) reaction. The pyrolyzed PDMS support was found to be largely microporous, and the active nickel particles were nano-sized but were not dispersed evenly in the resulting catalysts. The catalysts were prepared with 0 wt%, 2 wt%, 4 wt%, and 6 wt% Ni in PDMS prior to pyrolysis. The resulting catalysts demonstrated notable activity in the DRM reaction, comparable to many of those described in the published literature. The catalyst with 6 wt% Ni (prior to pyrolysis) displayed the highest conversion of methane (47%) and the lowest loss of activity (9.8%) over 11 h of continuous operation. This research was successful in exploring novel polymer-derived catalysts, specifically pyrolyzed Ni-PDMS catalysts, in the dry reforming of methane (DRM) reaction. Full article

(This article belongs to the Special Issue Catalysis for the Future)

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