Catalysis Letters最新文献

The presence of alkali metals in flue gas can lead to catalyst poisoning, which can significantly impact the de-NOx efficiency of the catalyst. There is a lack of specific studies on the influence of potassium (K) poisoning on the efficiency of γ-Fe₂O₃. In this study, the mechanism of K poisoning on the γ-Fe₂O₃ surface was studied based on DFT, and the influence of K on molecular adsorption and SCR reaction process was analyzed. The results show that the K₂O and KCl provide O, K, and Cl ions when deposited on the catalyst surface. The adsorption and dehydrogenation processes of NH3 were enhanced to varying degrees near the O and Cl iron sites, but the subsequent generation and decomposition of NH₂NO were inhibited. On the sites near K cations, the adsorption, dehydrogenation, and subsequent SCR reaction processes of NH₃ are hindered, and the adverse effects on the reaction are greater on the Fe sites closer to K. As well as the presence of K can to some extent promote the adsorption of NO and O₂.

Graphical Abstract

An extremely efficient green protocol for palladium acetate-catalysed ligand-free Suzuki–Miyaura cross-coupling reactions of aryl/heteroaryl bromides with aryl/substitute aryl boronic acids in neat ‘Water Extract of Leaf Ash of Neem’ (WELAN)’ was developed. This method offers a simple, mild, efficient and highly cost-effective alternative to the existing protocols since the reaction proceeds in natural feedstock WELAN at room temperature in air at very short reaction times (5–60 min) under ligand/external base/promoter/organic medium free conditions. Here WELAN has been found to be the effective base and reaction medium for this cross-coupling reaction with high turnover number (TON). This manuscript also theoretically depicts the probable mechanism of WELAN catalysed cross-coupling reaction.

Graphical Abstract

Based on the first-principles density-functional theory, formation energies, transition energy levels of M (M = Mo, W) doped α-BiNbO₄ systems are studied. The calculation results show that the donor defects form easily under Bi-rich condition. Of these, the W_int (W interstitial) and Mo_int (Mo interstitial) are the two main defects that lead to n-type conductivity. Then, the electronic structures of M-mono-doped and M/O_vac (O vacancy)-codoped α-BiNbO₄ were investigated. Our results show that the band gap of W_int/O_vac-codoped α-BiNbO₄ is reduced by 0.43 eV, and the conduction band minimum and valence band maximum are reduced by 0.20 and 0.23 eV, respectively, compared to pure α-BiNbO₄, with less driving force required for the redox reaction process and then an increased redox rate. The α-BiNbO₄ with W_int+O_vac defects with n-type conductivity has good photocatalytic activity in water splitting.

Graphical Abstract

In this research, microorganisms were used to produce Gd₂ZnMnO₆ NFs in a biological process instead of a chemical method as a nanocatalyst. Considering the capability of the microorganisms to synthesize nanofibrous (NFs) upon exposure to metal ions, microorganisms were employed to produce Gd₂ZnMnO₆ NFs through a biological process. The utilization of chemical modification to fabricate environmentally friendly heterogeneous nanocatalysts has proven to be highly appealing in the context of synthesizing 3-aryl-2-oxazolidinones using alkenes, carbon dioxide, and amines in an aqueous solution. The role of diverse variables in the creation of 3-aryl-2-oxazolidinones has been thoroughly investigated. Notably, Gd₂ZnMnO₆ NFs demonstrates remarkable efficiency in the production of 3-aryl-2-oxazolidinones due to its unique morphology. The morphology of Gd₂ZnMnO₆ NFs contributed to the creation of a desirable outer layer for the creation of 3-aryl-2-oxazolidinones. The findings demonstrated that the utilization of Gd₂ZnMnO₆ nanofibers positively impacts the effectiveness of the creation of 3-aryl-2-oxazolidinones. This can be attributed to the nanofibers' impressive mechanical and ionic internal characteristics, as well as their exceptional thermal sustainability and persistent colloidal sturdiness. Consequently, employing the host–guest method, the system could be regarded as an exemplary nanocatalyst. A diverse array of olefins was successfully transformed into desirable products, independent of the electronic nature of the substitutes. The involvement of heterogeneous mixtures did not impede the progression of the reaction. Moreover, the 3-aryl-2-oxazolidinones were easily distinguished from the Gd₂ZnMnO₆ nanofibers, and the medium exhibited the ability to undergo multiple cycles of usage without experiencing a notable decline in their catalytic activity and selectivity. This approach offers notable advantages, including a strong economic capability and the potential to withstand functional groups.

Graphical Abstract

Synthesis of biogenic Gd2ZnMnO6 nanofibrous for creation of 3-Aryl-2-oxazolidinones from alkenes, carbon dioxide, and aminesSynthesis of biogenic Gd2ZnMnO6 nanofibrous for creation of 3-Aryl-2-oxazolidinones from alkenes, carbon dioxide, and amines

Efficient catalysts for separating electron–hole pairs are crucial for improving the quantum yield and activity of photocatalysts. This study systematically investigates the properties and performance of monolayers of Janus SXSiN₂ (X = Cr, Mo, W) using the first-principles computational methods. The research findings suggest that biaxial strain can induce an indirect-to-direct bandgap transition in Janus SXSiN₂ and can also modulate the bandgap and band edge positions. Surface vacancy defects play a critical role in enhancing the charge carrier separation ability of Janus SXSiN₂, leading to remarkable photocatalytic performance. Moreover, the synergistic effect of biaxial strain and vacancy defects can significantly improve the catalytic performance for the HER. This study provides a theoretical foundation for further development of efficient two-dimensional Janus photocatalysts.

Graphical Abstract

Biaxial strain can modulate the bandgap and band edge positions. Surface vacancy defects play a critical role in enhancing the charge carrier separation ability. Janus SXSiN2 exhibits excellent photocatalytic performance for the HER reaction due to the synergistic effects of strain and vacancy defects.

Sugar compounds are an important part of biomass resources, and their catalytic conversion can prepare a series of platform compounds, such as lactic acid and polyols. One of the key steps is the isomerization of aldoses to ketoses. However, finding a simple method to efficiently convert aldoses to ketoses remains a great challenge. Herein, we report a core–shell structured catalyst, Pt/SiO₂@Mg(OH)₂, for the efficient conversion of xylose as well as the further conversion of xylose to xylulose. Xylose, a five-carbon sugar unit with the highest content in biomass, was used as the object of study to determine the optimal reaction conditions in the aqueous system by adjusting the loading amount of Mg(OH)₂, catalyst addition, reaction temperature, and reaction time: In the optimum aqueous conditions, the yield of xylulose was 23.61%. We also investigated the effect of solvent effects on the hydrothermal reaction and determined the optimal solvent ratio, the yield of xylulose reached 31.74% at H₂O:MeOH (8:2). We anticipate that this research result can provide a theoretical basis and reference for the industrialized production of subsequent sugar isomerization.

Graphical Abstract

Cleaning up carbon monoxide (CO) in water gas shift feedstocks is crucial for fuel cell applications. The catalytic transformation of CO in hydrogen-rich feeds poses a significant challenge in environmental catalysis. To address this issue, a range of Cu–Mn-based monometallic and bimetallic catalysts with diverse supports (such as alumina, silica, zirconia, and titania) were employed. Temperature programming techniques were utilised to observe the reduction and oxidation behaviours of these catalysts. The investigation involved testing CO oxidation at various temperatures over copper and manganese-based supported catalysts in the presence of H₂O and CO₂ (simulating realistic conditions). A positive impact of H₂O on catalytic performance was noted, whereas CO₂ had a suppressive effect. Furthermore, the specific support materials (Al₂O₃, SiO₂, TiO₂, and ZrO₂) were studied to understand their roles in CO oxidation under realistic conditions. In the presence of water, alumina catalysts containing bimetallic metals (Cu–Mn) exhibited 100% CO conversion even at a lower temperature of 160 °C. Conversely, under the predominant influence of CO₂, alumina catalyst (Cu–Mn) showed 55% CO conversion. The exceptional performance was attributed to CO preferential adsorption on highly active Cu–Mn sites and a small H₂-oxidative atmosphere of the catalysts. The activity results highlighted the strong dependence of CO conversion on reaction temperatures, the presence of metals, and the types of supports. Overall, these findings suggest the potential use of these catalysts for H₂ purification under realistic conditions.

Graphical Abstract

Selective catalytic conversion of ammonia to nitrogen is an effective method for reducing ammonia emissions from both stationary and mobile sources. In this study, CeO₂-based catalysts (M/CeO₂, M = Co, Cu, Fe, Zr) were synthesized using the sol–gel method and subsequently tested on a simulated gas experimental platform to assess their performance in NH₃ selective catalytic oxidation (NH₃-SCO). Results showed that Co/CeO₂ and Cu/CeO₂ catalysts exhibited high ammonia oxidation activity at respectively low temperatures, with T₅₀ 196.8 and 229.5 °C, and T₉₀ 239.2 and 292.1 °C. However, it was observed that while Co/CeO₂ displayed poor N₂ selectivity, Cu/CeO₂ demonstrated good N₂ selectivity. The superior catalytic performance of Cu/CeO₂ and Co/CeO₂ catalysts compared to Fe/CeO₂ and Zr/CeO₂ can be attributed to their distinct interactions with Ce. Subsequent characterization experiments were conducted to elucidate these interactions. BET and SEM analyses revealed that all M/CeO₂ catalysts possessed a typical mesoporous structure. XRD and XPS results indicated that the primary phase of each catalyst was CeO₂, and the incorporation of M transition metals did not alter the cubic fluorite structure. The interaction between the M metal and Ce varied, impacting the Ce³⁺ content on the catalyst surface, which in turn influenced oxygen species adsorption and ammonia oxidation activity. H₂-TPR and Raman spectroscopy analyses demonstrated that M metal incorporation shifted the CeO₂ reduction peak, thereby altering reduction properties and affecting oxidation performance. In particular, the Co-metal composite shifted the reduction peak to a lower temperature, thereby enhancing the reduction properties and indirectly increasing oxidation activity.

Graphical Abstract