Topics in Catalysis最新文献

We report the effect of the carbon/nitrogen ratio (C/N), from 0 to 26.2, on the activity and selectivity of the NO Selective Catalytic Reduction with propane and hydrogen (H₂-C₃H₈-SCR) over 2 wt% Ag/γ-Al₂O₃ between 25 and 500 °C. The gas composition included 3% (v/v) O₂ and 6% (v/v) H₂O at GHSV = 70,651 h⁻¹. There are two NO conversion zones as a function of temperature, previously reported. The low temperature ranged from 60 to 180 °C and reached 100% conversion of NO to N₂ at 140 °C. The addition of C₃H₈ had a small effect, decreasing NO conversion to 90–95%, and the temperature window about 10 °C. The H₂ conversion increased as a sigmoidal curve with temperature in all cases, and it shifted to low temperature too. This NO reduction range corresponds to the H₂-SCR. The high temperature activity region involves competition for O₂ between NO and C₃H₈. When C/N = 0 there was only oxidation to NO₂. At C/N = 3.2 and 6.5 there was emission of NO₂ between 160 and 440 °C. At higher temperatures the selectivity to N₂ was > 88%. Above C/N = 13.1 the NO conversion reached 90 to 98%. The N₂O concentration was negligible. The optimum C/N value was 13.1, with high NO conversion at low and high temperatures, and nearly 100% selectivity to N₂. Analysis by XPS and UV–Vis–NIR showed the coexistence of Ag⁺ and Ag⁰ moieties that helps explain the variations and competition of the oxidation–reduction reactions of the NO–H₂–C₃H₈–O₂ system with temperature and with the C/N feed values.

Direct synthesis of hydrogen peroxide (H₂O₂, DSHP) from hydrogen (H₂) and oxygen (O₂) is considered the most promising preparation method due to its atomic economy and compliance with the requirements of green chemistry. However, the poor H₂O₂ yield and selectivity still greatly limit its practical application. Herein, we synthesized a series of oxidized palladium and metal palladium composites (Pd²⁺–Pd) using a controlled decomposition method, to develop efficient catalysts for DSHP. The optimized 4% PdBr₂–Pd/C-250-2 catalyst exhibited the excellent catalytic performance for DSHP, with H₂O₂ selectivity of 99.2%, H₂O₂ yield of 346.53 mol·({text{kg}}_{{{text{cat}}{text{.}}}}^{{ - 1}})·h^− 1, and H₂ conversion of 50.7%. The finding indicates that the enhanced catalytic performance of 4% PdBr₂–Pd/C-250-2 is due to the coexistence of PdBr₂, PdO, and Pd, which not only effectively activates H₂ and O₂, but also effectively inhibits the breaking of O–O bonds, greatly reducing the decomposition and hydrogenation activity of H₂O₂, thereby achieving high H₂O₂ yield and selectivity. This article provides important ideas for the development of efficient DSHP catalysts and will promote their industrial applications.

The growing global demand for sustainable energy has made electrocatalytic water splitting an essential method for efficient hydrogen production and storage. Perovskite oxides are becoming increasingly recognized as effective electrocatalysts for the hydrogen evolution reaction (HER) due to their tunable composition, diverse band structure, outstanding charge transport properties, and beneficial electronic characteristics. Nevertheless, their practical use is frequently limited by issues like inadequate intrinsic activity, stability problems, and cost-related concerns. This review thoroughly evaluates the latest advancements in perovskite oxide-based HER catalysts, emphasizing strategies to improve their electrocatalytic performance. Various techniques, including surface modification, elemental doping, and defect engineering, are investigated to optimize electronic structures, enhance active site density, and boost electrochemical durability. Furthermore, the review addresses improvements aimed at increasing the scalability and cost-effectiveness of perovskite oxide-based electrocatalysts for hydrogen production. Lastly, the article outlines existing challenges and future outlooks to inform the strategic advancement of next-generation perovskite materials for sustainable hydrogen energy endeavors.

Graphical Abstract

The electrochemical reduction of CO₂ stands out as a groundbreaking approach to transform CO₂ into valuable fuels and chemicals, heralding the prospect of a carbon-neutral energy landscape and making strides in climate change mitigation. Among the various catalytic systems available, bimetallic alloys created through the intentional integration of metals showcase highly tunable active sites and remarkable catalytic performance. This research presents the innovative design of bimetallic CuSn alloys derived from metal-organic frameworks, leveraging their engineered surfaces and synergistic metal interactions to finely tune product selectivity. Cu drives alcohol formation, while Sn enhances formate production by stabilizing critical reaction intermediates and effectively suppressing the competing hydrogen evolution reaction. Notably, our Cu-rich CuSn/C-A catalyst achieves an impressive Faradaic efficiency of 71.1% for methanol, while the Sn-rich CuSn/C-B sets a near-record with 89.16% FE for formic acid in 0.1 M KHCO₃ at -0.7 V vs. RHE. These significant results highlight the critical role of alloy composition in directing CO₂ reduction selectivity, offering a powerful framework for the strategic design of high-performance, adaptable electrocatalysts.

Heavy-duty and marine transport will continue to rely on robust, high energy–density, combustion engine technology. Sustainable fuels, fuel-flexible engines and stricter future emission standards all call for further development of catalytic aftertreatment systems (ATSs). This paper reviews progress and evaluates emission removal methods, based on synthetic gas bench (SGB) experiments simulating characteristic lean and stoichiometric conditions in hydrogen, ammonia, methanol and methane engine exhaust gases. The oxidation reactivity of fuel compounds on tailored catalysts showed the following light-off temperatures (T₅₀, °C) in lean conditions: hydrogen(140) < methanol(170) ~ CO < diesel-hydrocarbons, reference(180) < ammonia(250) < methane(380). NO_x removal in mobile applications will be challenging, due to NO_x limits and varying fuel types/mixtures. Urea/NH₃-SCR will remain the main NO_x removal method, with an option of double SCR widening its temperature window. NO_x storage catalysts based on metal oxides or zeolites, increased NO_x removal at 100–200 °C by passive adsorption–desorption. NO_x reduction by hydrogen (H₂-SCR) showed NO_x reduction of up to 60–70% on platinum catalysts at 100–160 °C, before NH₃-SCR reactions at higher temperatures. Selective ammonia slip catalysts (ASCs) were effective to cut NH₃ emissions. High selectivity to N₂ with low N₂O formation was challenging with H₂-SCR and ASC. Three-way catalysts, applied with stoichiometric hydrogen combustion, were operating below 200 °C. More efficient catalytic methods for methane and N₂O removal are required to improve the feasibility of methane and ammonia as future fuels. Integration of different properties in the same units is essential to minimise ATS volume and costs. The flexible use of green fuels requires flexible ATSs too.

A coaxial dielectric barrier discharge (DBD) as a non-thermal plasma reactor was utilized for the non-oxidative coupling of methane into higher hydrocarbons under ambient conditions. The DBD reactor was subsequently performed as a packed-bed dielectric barrier discharge using non-catalytic materials, including glass beads, glass wool, and glass capillary, which were introduced to investigate the non-catalytic reaction mechanism. Typical observation demonstrated that the dielectric glass materials packed with DBD might successfully activate the stable C–H bond to produce hydrogen and C₂–C₄ higher hydrocarbons without the application of any oxidants and additional thermal energy. Among the packing materials investigated, the DBD reactor packed with a glass capillary obtained a maximum CH₄ conversion of 6.1%, with the energy efficiency reaching a maximum of 0.66 mmol kJ⁻¹ at a discharge power of 1.38 W with an SEI of 4.14 J mL⁻¹. The enhanced CH₄ conversion was attributed to an alternation in the plasma discharge behavior with non-catalytic glass materials. Moreover, under these conditions, the low temperature of the discharge zone resulted in minimal solid carbon accumulation on the inner electrode surface of the plasma reactor.

Oxygen vacancy defects can serve as an effective strategy for developing high-performance metal oxide-based catalysts. The formation of oxygen vacancies depends on the reducibility of the metal oxide materials. In this study, we selected three metal oxides (MO_xs): iron oxide (Fe₂O₃), chromium oxide (Cr₂O₃), and zirconium oxide (ZrO₂), with varying degrees of reducibility to investigate oxygen vacancy formation and its consequent impact on platinum (Pt) dispersion and catalytic performance. An oxy-hydrogen flame treatment, characterized by high treatment temperatures and rapid heating and cooling rates, was employed to create oxygen vacancy defects in these metal oxides. The flame treatment promoted defect formation in the order of Fe₂O₃ > Cr₂O₃ > ZrO₂. These defects significantly influenced Pt dispersion and metal-support interactions. The catalytic performance of Pt/MO_x catalysts, both untreated and treated with the oxy-hydrogen flame, was evaluated in the chemoselective hydrogenation of 3-nitrostyrene. The selectivity toward 3-vinylaniline increased with the reducibility of the metal oxide support in the defective Pt/MO_x catalysts. Higher reducibility facilitated oxygen vacancy formation, enhanced Pt dispersion through metal-support interactions, and ultimately improved chemoselective hydrogenation performance.

Metal support interaction (MSI) and oxygen vacancies have a significant impact on the performance of the Ni catalyst for dry reforming of methane (DRM) reaction. In this paper, the synergistic effect between chelating agents and dielectric barrier discharge (DBD) technology was systematically investigated by adding different chelating agents and combining with DBD during the catalyst preparation process. The introduction of the chelating agents improved the dispersion of Ni species exposing more active sites to participate in the reaction. On this basis, DBD technology significantly increased the number of oxygen vacancies on the catalyst surface while further strengthening the MSI by reducing the size of Ni nanoparticles. Notably, ethylene glycol and DBD demonstrated excellent synergistic effects in promoting the activity, stability, and carbon resistance of Ni catalysts, which could be related to the relative content of NiAl₂O₄ in catalysts. This research makes a substantial contribution to enhancing the reactivity of DRM catalyst by using chelating agents and DBD to alter the MSI and increase the number of oxygen vacancies.

The oxidation of sulfur-containing amino acids, particularly methionine and cysteine, is central to numerous biological processes and is associated with oxidative stress, neurodegenerative diseases such as Parkinson’s and Alzheimer’s, and aging. Methionine sulfoxide reductase (Msr) plays a key role in mitigating oxidative damage by reversing methionine oxidation. This review examines the oxidation of sulfur-containing amino acids and peptides by iron complexes, focusing on their mechanistic pathways via electron transfer or oxygen atom transfer. Kinetic and mechanistic studies highlight the reactivity of methionine, cysteine, and methionine peptides with these oxidants. Density functional theory (DFT) calculations provide insights into the geometry and electronic transitions of metal-salen and oxometal-salen complexes. Electrochemical studies, using differential pulse and cyclic voltammetry, reveal the electrocatalytic properties of L-cysteine, L-methionine, and methionine peptides, demonstrating high sensitivity, low detection limits, and stability. Additionally, the antibacterial activity of Fe(III)-salen complexes is evaluated, identifying minimum inhibitory concentrations against bacterial pathogens. This comprehensive review elucidates the intricate oxidation mechanisms of sulfur amino acids and their relevance in redox chemistry, with implications for biomedical applications.