Catalysis Letters最新文献

CO esterification to dimethyl carbonate (DMC) routes holds significant economic and environmental value. Nevertheless, industrial routes suffer from drawbacks, such as raw material methyl nitrite (MN) was decomposed into by-products dimethoxymethane (DMM) and methyl formate (MF), which caused subsequent separation problem for the product/reactant mixture, which results in additional production cost. Previous studies have demonstrated that the acid site of NaY play an essential role in promoting the decomposition of MN. Herein, a series of Na₂HPO₄ -modified Pd/NaY catalysts were prepared to solve these problems. The results indicated that the introduction of Na₂HPO₄ increased the DMC selectivity (from 55% to 83%) and decreased the by-products selectivity [DMM (from 22% to 10%), MF (from 23% to 7%)] of Pd/PNaY-12 significantly. Based on the results of Py-IR, the amounts of Lewis acidic sites decreased, and NH₃-TPD analysis shown that the amounts of weak acid sites (from 0.33 mmol/g to 0.14 mmol/g) and medium strong acid sites (from 0.46 mmol/g to 0.10 mmol/g) also reduced obviously. The outstanding performance should be attributed to the fact that the important intermediate *COOCH₃ was more readily obtained after Na₂HPO₄ was incorporated. This work provides a convenient strategy for developing catalysts with high selectivity and low by-products.

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High-entropy materials, which integrate five or more metal species into single-phase crystal structures, have garnered significant interest across various fields. In this study, we synthesized a low-cost, non-noble metal-based electrocatalyst known as a high-entropy metal–organic framework (HEMOF) for the oxygen evolution reaction (OER). The HEMOF was prepared via a solution-phase method utilizing transition metals and exhibited a single-phase, thin-sheet structure. Five distinct metals—iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), and copper (Cu)—were uniformly dispersed within the framework, with concentrations ranging from 5 to 35 atomic percent. The HEMOF demonstrated a high surface area and exceptional OER performance, achieving a low overpotential of 305 mV at 10 mA cm⁻², a Tafel slope of 68.5 mV dec⁻¹, and remarkable stability over 10 h. These findings suggest that the HEMOF represents a straightforward and cost-effective alternative to noble-metal-based OER electrocatalysts, contributing to sustainable energy conversion and storage.

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A low-cost, non-noble metal-based electrocatalyst, high-entropy metal-organic framework(MOF@FeCoNiMnCu), was synthesized for oxygen evolution reaction, achieving a low overpotential of 319 mV at 10 mA cm⁻² and excellent stability for 10 h. This study demonstrates high-entropy metal-organic framework (HEMOF) as a promising alternative to noble-metal-based electrocatalysts for sustainable energy conversion and storage.

Low-cost electrocatalysts with high catalytic activity for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are essential for electrochemical water splitting to produce hydrogen. In this study, we report the combination of porosification and doping strategy to improve the catalytic activity of NiCo₂O₄-based electrocatalysts for HER and OER. A facile porosification method was proposed and demonstrated by annealing the NiCo₂O₄ nanosheets in a reductive atmosphere to synthesize porous NiCo₂O₄ nanosheets. In order to further improve the catalytic activity for HER and OER, the porous NiCo₂O₄ nanosheets were doped with P and Fe, respectively, which tailored the electronic structure of the electrocatalysts, improved the intrinsic catalytic activity, and increased the number of active sites. HER or OER experiments were performed on the porous P-NiCo₂O₄ nanosheets or the porous NiCo_1.5Fe_0.5O₄ nanosheets, which required an overpotential of 160 mV or 222 mV to deliver a current density of 10 mA/cm², respectively. Furthermore, overall water splitting was achieved using the porous P-NiCo₂O₄ nanosheet cathode and the porous NiCo_2-xFe_xO₄ nanosheet anode with a Faraday Efficiency of 98.22%. The present paper proposes a strategy to fabricate doped porous electrocatalysts with a view to providing insights for the design and synthesis of efficient and inexpensive electrocatalysts for water splitting.

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The practical application of Cu₂O in the field of photoelectrocatalytic (PEC) hydrogen production has been limited by its relatively low photoconversion efficiency and electron mobility. Plasmonic metal nanoparticles have been utilized to enhance the charge separation of semiconductors through resonance energy transfer from metal nanoparticles to semiconductors. In this study, Ag nanosphere (Ag NS)@SiO₂ were combined with Cu₂O to form triple core–shell nanocomposites, aiming to enhance the photoelectrochemical activity of Cu₂O under visible-light irradiation. The microstructures of the Ag@SiO₂@Cu₂O nanocomposites were regulated by controlling the thickness of SiO₂ interlay and Cu₂O shell in order to optimize the PEC efficiency. It was found that Ag NS@SiO₂ (5 nm)@Cu₂O (29 nm) NCs exhibited the highest photocurrent intensity, showing 3.3 times, 11.9 times, and 17.8 times higher values than pure Cu₂O, pure Ag NS, and AgNS@SiO₂ NPs respectively. Furthermore, the photoelectrocatalytic hydrogen production velocity of Ag NS@SiO₂ (5 nm)@Cu₂O (29 nm) NCs was around 25 mmol·g⁻¹·h⁻¹, which has been improved around 4.2 times compared to pure Cu₂O. This enhanced performance is attributed to plasmon-induced resonance energy transfer from Ag metal nanoparticles to Cu₂O semiconductor, which may improve the separation efficiency of electron–hole pairs and lead higher photoelectrocatalytic efficiency.

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The Ag NS@SiO₂ was integrated with Cu₂O to form triple core–shell nanocomposites, aiming to enhance the photoelectrochemical activity of Cu₂O under visible-light irradiation through plasmon-induced resonance energy transfer from Ag to Cu₂O. And their photoelectrocatalytic performances were optimized by controlling the thickness of SiO₂ interlay and Cu₂O shell. Ag NS@SiO₂ (5 nm)@Cu₂O (29 nm) NCs exhibited superior photocurrent intensity and enhanced photoelectrocatalytic hydrogen production rate compared to pure Cu₂O.

Electro-reduction of CO₂ (CO₂RR) to formic acid is one of the most efficient and promising technologies for the utilization of CO₂, however, designing catalysts with high reactivity and selectivity to achieve the conversion of CO₂ to formic acid is still a great challenge. Therefore, in this study, Bi₂O₃-ZnO/ZnAl₂O₄ composite oxide catalysts were constructed using layered double hydroxides as precursors to enhance the interfacial stability and utilize the synergistic effect of zinc-bismuth dual active sites for the efficient electrocatalytic reduction of CO₂ to formate. The product formate bias current density reached up to 25.8 mA·cm^− 2 at -1.3 V (vs. RHE) in an H-type electrolytic cell and the Faraday efficiency of formate was maintained at about 93% under stability tests up to 14 h, which was superior to most other reported catalysts. In the formation of the Bi₂O₃-ZnO/ZnAl₂O₄ interface, zinc promotes the electroreduction of CO₂ to produce *CO₂⁻ intermediates, while bismuth reduces CO production and improves formic acid selectivity by providing more reactive sites. In addition, the interface between zinc and bismuth optimizes electron and proton flow, helping to maintain a lower energy threshold during the reaction and thus improving catalytic efficiency. This interface engineering approach utilizes zinc-bismuth dual active sites to achieve high selectivity and stability of CO₂ electrocatalytic reduction, providing insights for the development of large-scale efficient CO₂RR catalysts in the future.

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Aromatic hydrocarbons are important components of jet fuels mainly due to their effects on lowering the freeze point, enhancing the lubricity, and preventing the fuel leakage in the engines and fueling systems by interacting with their polymer seals. Produced from fossil resources, jet fuel consumption contributes to rising atmospheric CO₂ levels. Therefore, efficient utilization of renewable resources, such as biomass, to produce jet fuel components is an important step toward building a sustainable society. Hence, structure-modified zeolite catalysts that determine a high selective production of aromatic HCs in the range of jet fuel chemicals from biomass via catalytic pyrolysis were synthesized and engineered in a PyroGC-MS/FID system. The structure-modified catalysts of hierarchical HBeta (HRCHY HBeta) and defect-free nano-sized crystals ZSM-5 (ZSM-5-F) were used to selectively deoxygenate the reactive species in biomass pyrolysis vapors leading to a high production of renewable jet fuels (bio jet fuels; BJFs). The morphology of zeolites were designed for an enhanced diffusion of biomass pyrolysis vapors and upgraded products, in and out of the catalyst, to selectively produce monoaromatic HCs. A comprehensive comparison of the experimental and theoretical results obtained from biomass pyrolysis using the commercial catalyst of HBeta and the structure-modified catalysts of hierarchical HBeta and defect-free ZSM-5 was accomplished in in-situ and ex-situ catalytic configurations. Meanwhile, the catalytic performance of the ZSM-5-F catalyst in the conversion of a biomass pyrolysis oil model into jet fuel chemicals was investigated using a fixed bed catalytic reactor.

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Previous studies have employed density functional theory (DFT) modeling to investigate hydrodesulfurization (HDS) pathways for heavy aromatic sulfides, typically focusing on hydrogenation to assist in C-S bond cleavage on both pristine and promoted MoS₂ catalysts. These investigations, which primarily examine the reduced Mo- and sulfur-terminated edges of MoS₂ slabs, generally categorize the reaction pathways into two types: direct desulfurization (DDS) and hydrogenation-desulfurization (HYD). Traditionally, these models assume that C-S bond cleavage occurs through interactions with edge sulfur atoms, with less attention given to the role of promoter metals like Co. However, our recent work indicates that Co atoms on the S-edges of MoS₂ slabs may play a crucial role in activating and dissociating C-S bonds, particularly through an α-carbon transfer. This process has been identified as key in the desulfurization of small thiols like methanethiol, prompting further investigation into its relevance for aromatic thiols such as thiophene, dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (DMDBT). In the DFT calculations presented in this article, we demonstrate that the activation barrier for C-S bond cleavage to Co remains consistent at 1.0-1.1 eV/atom for the unsubstituted aromatic sulfides with a higher 1.67 eV for DMDBT. This oxidative addition mechanism of Co is strongly favored by the presence of dissociated hydrogen on adjacent sites and the aromatic nature of the molecule being desulfurized, while self-desulfurization through this pathway is found to be unfavorable. Our findings provide new insights into the chemistry of promoter atoms in the HDS of heavy aromatic sulfides.

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Silver nanoparticles are highly active for low-temperature CO oxidation reactions. Herein, we report the synthesis of Ag nanoparticles dispersed over mesoporous SiO₂ via a green approach. The Ag nanoparticles were dispersed over mesoporous silica using bay leaf extract to prepare a 2% Ag/SiO₂ (G) catalyst. The formation of the catalyst was confirmed by UV-Vis spectroscopy, transmission electron microscopy and X-ray diffraction analysis. The activity of the 2% Ag/SiO₂ (G) catalyst was tested for CO oxidation reaction in a packed bed reactor. The catalyst showed excellent activity for low-temperature CO oxidation, and 100% conversion was achieved at 125 ^oC. The higher conversion and stable activity for 100 h is ascribed to the strong metal support interaction, homogenous dispersion of nano-particles and formation of easily reducible metal oxides. The strong metal support interaction is confirmed by temperature programmed reduction analysis.

Azoxybenzene is an essential substance for the chemical industry. The catalytic reduction of nitroarenes from hydrogenation transfer is a mild, green and environment-friendly reaction process. Here, we synthesize nanorod CeO₂ catalysts, which present a stable 28% nitrobenzene conversion and 90% azoxybenzene selectivity without additives during the 22 h reaction time at 140 ^oC and 5wt.% Nitrobenzene/ethanol fluid solution in a fixed bed reactor. In contract, nanoparticle CeO₂ only present about 2% nitrobenzene conversion at the same condition. Oxygen vacancies generated in CeO₂ (110) are critical for the adsorption and activation of nitrobenzene and ethanol, lead to a lower reaction energy barrier of r-CeO₂.

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