Catalysis Surveys from Asia最新文献

FeC_x catalysts (Fe-CN-Py) were synthesized by co-pyrolyzing the mixture of iron nitrate and a CN source (melamine, bulk g-C₃N₄ (b-C₃N₄), or defective g-C₃N₄ (d-C₃N₄)). The physicochemical properties of Fe-CN-Py catalysts and their activities of CO₂ hydrogenation to light hydrocarbon (C₂-C₆) were analyzed. The results indicated that Fe-d-C₃N₄-(0.3)-Py is the most promising with the highest CO₂ conversion (47.2%), olefin yield (10.8%), and olefin space-time yield (STY = 4.5 µmol olefin/s/g_Fe). The promising activity of Fe-d-C₃N₄-(0.3)-Py was attributed to its high concentration of surface FeC_x. The correlation between surface FeC_x and the STY of hydrocarbons and olefins was established.

The conversion of ethanol and acetaldehyde to 1,3-butadiene has been an emerging process to produce key chemicals. The preparation of highly efficient catalysts and the understanding of reaction mechanism are current research priority. Herein, mesoporous silica framework confining zirconia (Zr-HMS) was prepared and act as catalyst for 1,3-butadiene production from ethanol and acetaldehyde. The prepared catalysts were characterized by Low-angle X-ray powder diffraction, transmission electron microscopy, N₂ physical adsorption-desorption, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and UV–vis spectra. It has been shown that the Zr-HMS exhibits similar textural properties to supported catalyst (ZrO₂/HMS). However, regardless of their comparable activities, higher 1,3-butadiene selectivity is obtained over Zr–HMS, which can be due to the different active zirconia species in two catalysts. Mesoporous framework confining character of Zr-HMS can achieve uniformly dispersed zirconia species. Further investigation toward the reaction process has presented new viewpoints for formation and consumption of some typical intermediates and byproducts, which will help to understand the reaction mechanism and construct efficient catalysts for conversion of ethanol and acetaldehyde to 1,3-butadiene.

The fabrication of a proficient and durable electrocatalyst for the OER process is the most crucial parameter in the water splitting process. A simple and basic procedure was used in this study to create Cu-substituted ZnMn₂O₄/rGO spinel nanosized composite as an electrode for OER. The morphological and structural investigations indicate that the carbon based spinel successfully bonds, and the addition of copper into rGO results in a substantial change in its electrocatalytic process for the oxygen evolution process. Zn_1−xCu_xMn₂O₄/rGO with x = 0.6 has a minimal overpotential of 150 mV at a current density of 10 mAcm⁻², low onset potential of 1.40 V and a smaller Tafel slope of 31 mV dec⁻¹ than other substitution. The electrocatalyst also exhibits high ECSA (632.5 cm²), R_f (1580), and exceptional stability, all of which improve OER performance. These analysis confirm the enhanced electrocatalytic efficiency of the hybrid material to catalyze OER for energy generation, and other fields.

In this work, we report for the first time, the tungstic acid-catalyzed oxidation of terpene alcohols with hydrogen peroxide. This simple, solid, and commercially available catalyst efficiently promoted the conversion of borneol, geraniol and nerol to camphor and epoxide products, respectively. Effects of main reaction parameters, such as catalyst load, the molar ratio of oxidant to the substrate, time, and reaction temperature were investigated. Conversions and selectivity greater than 90% were achieved using 1.0 mol % of H₂WO₄ after 2 h of reaction at 90 °C. The activation energy was equal to 66 kJmol⁻¹. We propose a reaction mechanism based on the experimental results. This solid catalyst was easily recovered and reused without loss of activity. As far as we know, it is the first time that tungstic acid was used as the catalyst in the oxidation reactions of terpene alcohols.

Graphical Abstract

Chlorine species, widely presented in industrial flue gas such as the waste incineration plants, can poison the catalysts and affect the selective catalytic reduction (SCR) performance. In this work, effects of Cl on the SCR performance of V₂O₅–WO₃/TiO₂ (VW/Ti) catalysts were investigated by NH₄Cl deposition. The results showed that the NO_x conversion efficiency at low reaction temperature (< 300 °C) decreased with the loading of NH₄Cl after calcination. It was found that instead of causing the chlorination of VW/Ti catalyst the NH₄Cl decomposed into volatile Cl species due to the weak V–Cl bonding. Such decomposition reduced significantly the surface non-lattice oxygen species to inhibit NO adsorption and activation, but hardly affected the redox ability and acidity of VW/Ti catalyst. Time–resolved in situ DRIFTs results indicated that NH₃ activation and the SCR process predominated by Eley–Rideal mechanism were not influenced with NH₄Cl impregnation, while the SCR at low temperature following a Langmuir–Hinshelwood path was limited by the decreased and weaker binding sites for NO activation.

Mesoporous silica-alumina spheres were used to create macro- and mesoporous bimodal silica-aluminas. Before removing the surfactant template for mesopores, the silica-alumina spheres were neatly stacked by sedimentation, and the contact points between the spheres were reinforced by silica. The bimodal silica-alumina was used as an acid catalyst for transesterification of triglyceride with methanol. The bimodal catalyst was readily separated from the reaction mixture. It showed the same catalytic activity as the non-sedimented spheres and higher activity than the catalyst prepared by pelletizing the silica-alumina spheres with colloidal silica binders. The bimodal materials were utilized as an adsorbent with an indicator of adsorption amount since the color changed with the amount of toluene that was adsorbed on them.

Nitrogen oxides (NO_x) are major contaminant causing environmental pollution in atmosphere. The most effective method for NO_x removal is ammonia selective catalytic reduction (NH₃-SCR), and catalysts play a crucial role. Cu-based zeolite catalysts are commonly used for the removal of NO_x from diesel engine exhaust, but the complex composition of diesel exhaust and the harsh operating environment of catalysts make zeolite catalysts susceptible to deactivation, thus limiting their practical application. This manuscript focuses on the negative effects of actual working conditions associated with diesel vehicle exhausts and analyses the influence of composition structure that Cu-based zeolite catalysts have on NH₃-SCR reaction, which refers mainly to the effects brought by topology, Si/Al ratio and Cu species. The strategies for developing Cu-based zeolite catalysts are summarized, and the current development bottlenecks such as improving catalytic performance, reducing synthesis cost and enhancing production efficiency are discussed, and the future research directions of Cu-based zeolite are prospected.

Selective hydrogenation of anthraquinone is critical in producing H₂O₂, the strong oxidant widely used in most industrial areas. More efforts were made on the selective hydrogenation of C=O in the anthraquinone process because the sides-product will negatively affect continuous H₂O₂ production and significantly reduce the project economics. A crucial step toward high H₂O₂ yield is the rational design of heterogeneous catalysts. In this review, the metal-based catalyst design for the selective anthraquinone hydrogenation is cataloged into two significant strategies: active metal regulation and support property regulation. Research accomplished in the past decade on the catalyst design for selective anthraquinone hydrogenation is systematically reviewed. The focus is on the catalytic performance-enhancing mechanism and the factors that influence the mechanism. In addition, the limitations and barriers encountered for supported catalysts in the current study, as well as potential research trends, are discussed.

Co-based catalysts were derived from CoAl-layered double hydroxide (LDH), LDH/melamine, LDH/activated carbon, and LDH/g-C₃N₄. The use of these catalysts for the hydrogenation of γ-valerolactone into 1,4-pentanediol was investigated. The catalyst derived from CoAl-LDH/g-C₃N₄ contained higher concentrations of strong Brønsted acid, Lewis acid (Co^δ+, δ > 2), and Lewis base (N with a lone pair of electrons) sites, resulting in improved turnover frequency.

Nitrogen-doped carbon with and without Fe additives is a promising alternative for commercial Pt/C catalysts for the oxygen reduction reaction (ORR) in proton and anion exchange membrane fuel cells. To understand the nature of the rate-determining steps (RDSs) of the ORR over newly developed catalysts, the analysis of the Tafel slopes of ORR voltammograms is beneficial for elucidating the number of electrons involved in the RDS. Conventionally, the Tafel slope is evaluated from the measured total current, which involves several different reaction pathways: the four-electron pathway from O₂ to H₂O described with a kinetic constant k₁, the two-electron pathway from O₂ to H₂O₂ with k₂, and the two-electron pathway from H₂O₂ to H₂O with k₃. This method provides reasonable Tafel slopes as long as the measured ORR is selective to a particular reaction pathway, such as the four-electron pathway over a Pt/C catalyst; however, typical Fe/N/C and N/C catalysts have mixed reaction pathways and analyzing the Tafel slopes from the total current does not provide meaningful information. To address this, we propose a new methodology for analyzing Tafel slopes. In this study, the measured ORR currents were converted into inherent kinetic constants (k₁⁰, k₂⁰, and k₃⁰) using the Nabae model, which was previously developed by our group, and the Tafel plots for k₁⁰, k₂⁰, and k₃⁰ were analyzed to determine the Tafel slopes of each reaction pathway. Four ORR systems (Fe/N/C and N/C catalysts in acid and base) were analyzed using the proposed method, and the differences in the reaction mechanisms were successfully reflected in the determined parameters.