Topics in Catalysis最新文献

Series of nickel catalysts, supported on γ-alumina and promoted with different Ce loading (1–5%), have been studied in conventional and sorption-enhanced CO₂ methanation reaction. In addition, a detailed kinetic water adsorption study has been performed on commercial zeolite (13X, 4 A, 3 A). The decrease in adsorption capacity is observed for all zeolites with increasing temperature. The highest water adsorption capacity is observed for the 13X zeolite for all investigated temperatures (100–350 °C). However, the 13X zeolite showed loss of 50% of its capacity after 100 adsorption/desorption cycles while the 4 A and 3 A zeolites are almost unchanged. The catalyst characterization results indicate that upon addition of a small amount of ceria, dispersion of the Ni catalyst is improved as well as CO₂ conversion in conventional methanation. The catalyst that showed best performance was further tested for sorption-enhanced methanation, where water sorbents (13X, 4 A, 3 A) are mixed with catalysts. All the tests performed in presence of zeolites showed an increase in CO₂ conversion compared to those carried out in their absence. In addition, a 34% increase in CO₂ conversion was observed when increasing the H₂/CO₂ ratio to 8 for the system with 13X zeolite. This indicates the enhancement effect when water is removed from the reaction.

Investigation of methane bi-reforming over Ni-impregnated La₂O₃-ZrO₂ mixed oxide catalysts to produce hydrogen-rich syngas. A series of supports with varying molar ratios of La-Zr were synthesized using the co-precipitation method, and the metal addition was carried out using the impregnation method. The properties of the materials are characterized by different characterization techniques such as BET, XRD, H₂-TPR, and CO₂-TPD analyses. The overall characterization illustrated that the change in the mole ratio of La₂O₃-ZrO₂ support improves catalyst performance by enhancing CO₂ adsorption and metal-support interactions and reducing carbon deposition. 12 wt% Ni loading catalyst with La₂O₃-ZrO₂ molar ratio of 3:1 showed optimal performance, yielding high methane and CO₂ conversion rates (90% and 75%, respectively) and achieving H₂ yield of 82%. Further, the catalyst demonstrated stability over a 100 h reaction time, ascribed to the strong metal-support interaction along with the change in the basicity with change in the La₂O₃, which improves the overall bi-reforming methane reactivity and enhances syngas production.

A series of CeO_x–CrO_x catalysts were synthesized via the sol-gel method for the oxidation of toluene. A comprehensive set of characterization techniques, including XRD, N₂ adsorption, Raman spectroscopy, HRTEM, H₂-TPR, O₂-TPD, XPS, and in situ DRIFTS, was employed to investigate the structure-performance relationships of the catalysts. Among the catalysts, the one with a Ce/Cr molar ratio of 1:3 exhibited the best performance in toluene oxidation, with the activation energy for toluene degradation decreasing from 54.5 kJ mol⁻¹ for CeO_x to 31.3 kJ mol⁻¹ for the CeO_x–CrO_x (1:3) and CO₂ selectivity reaching 100% at temperatures above 250 °C. This enhancement was primarily attributed to an increased specific surface area, an elevated concentration of highly active Cr⁶⁺ species, and improved reducibility and mobility of surface oxygen species. During the reaction, toluene was rapidly adsorbed and converted into benzoate intermediates, which were subsequently oxidized to form the final products, CO₂ and H₂O.

This work reports the successful synthesis of a highly stable and durable non-PGM catalyst Co₃O₄/Co_xCe_1−xO_2−δ/C via a simple solvothermal process. The electrocatalytic ability of Co₃O₄/C, CeO₂/C and Co₃O₄/Co_xCe_1−xO_2−δ/C are tested for oxygen reduction and oxygen evolution reaction (ORR, OER). Under identical conditions, the electrochemical studies of the catalysts reveal enhanced performance of the Co₃O₄/Co_xCe_1−xO_2−δ/C. It shows the highest geometric current density (j_geo = ̶ 4.1 mAcm⁻² ) at 0.33 V vs. RHE. Moreover, Co₃O₄/Co_xCe_1−xO_2−δ/C has the earliest onset for OER with a bifunctionality index of ΔE = 1.05 V and has the highest turnover frequency. The catalyst was compared with benchmarks like 20 wt% Pt/C for ORR and RuO₂ for OER. Chronoamperometry studies (CA) reveals superior performance of Co₃O₄/Co_xCe_1−xO_2−δ/C over Pt/C for ORR and accelerated durability test (ADT) shows no observable shift of half-wave potential (E_1/2). This enhancement of electrocatalytic ability of Co₃O₄/Co_xCe_1−xO_2−δ/C are attributed to (1) higher degree of Co²⁺:Co³⁺ ratio (3.6) in Co₃O₄/Co_xCe_1−xO_2−δ/C than in Co₃O₄/C (0.8) as revealed from XPS. This is a result of doping of cobalt into CeO₂, and (2) presence of crystalline-amorphous interfaces as observed from HRTEM.

The influence of the type of carbon support on the catalytic activity of Ru/graphitized carbon systems in carbon dioxide methanation was evaluated. Four partly graphitized carbons with varying surface areas (from 50 to 1417 m²/g) were used as supports. The prepared samples were characterized by N₂ physisorption, TG-MS studies, H₂-TPR, CO₂-TPD, XRD, XAS, TEM/STEM, Raman spectroscopy and CO chemisorption. Both the mode of particle size distribution and the dispersion of the active phase clearly depend on the carbon texture; dispersion changes from 27% to almost 90% with increasing carbon support surface area. The degree of support graphitization affects its resistance to undesired methanation under reaction conditions. The activity tests conducted in a model H₂–rich stream with very low CO₂ concentration (1 vol% CO₂) show that the catalysts exhibit good activity, achieving a 20% conversion of CO₂ at a temperature of 270 °C. The increase of the average Ru particle size leads to about sevenfold increase in the CO₂ conversion and a nearly 20-fold increase in TOF values. The catalytic activity or Ru/carbon catalysts is also associated with the presence of basic sites on their surface.

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.