We investigated the interactions between nickel oxide and silica–alumina supports, which were applied to the catalytic oligomerization of ethylene by powder X-ray diffraction, UV diffuse reflectance spectroscopy, H2 temperature-programmed reduction, and X-ray photoelectron spectroscopy. The catalytic activity was also correlated with the acidity of catalysts determined by NH3 temperature-programmed desorption and pyridine FT-IR spectroscopy. Although all the catalysts had similar Ni contents, their catalytic performances were strongly influenced by the strength of the metal oxide–support interaction. Strong interaction promoted the formation of nickel aluminate on the catalyst surface, and resulted in low catalytic activity due to reducing the amount of nickel oxide active sites. However, weak interaction favored the aggregation of nickel oxide species into larger particles, and thus resulted in low ethylene conversion and selectivity to oligomers. Eventually, the optimal activity was realized at the medium interaction strength, preserving a high amount of both active nickel oxides and acid sites.
Stable, high-performance noble-metal catalysts have proven effective for obtaining lactate (LA) and formate (FA) from simultaneous conversion of glycerol and carbonate as a CO 2 source. For this purpose, we developed a novel method reported herein for the synthesis of Ru nanoparticles (NPs) supported on graphitic nanoporous carbon (Ru/NCT, T = pyrolysis temperature). The Ru/NCT catalysts were prepared by in situ encapsulation of trimeric ruthenium clusters in ZIF-11 pores, with a subsequent pyrolysis process. The pyrolysis temperature affected the size and crystallinity of Ru NPs and the textural properties of the ZIF-11-derived carbon. Optimization of reaction parameters such as CO 2 source, reaction temperature, reaction time, and glycerol/carbonate ratio resulted in Ru/ NCTs with significantly higher turnover number (TON) and space-time yield (STY) of the desired products (LA and FA). Moreover, these Ru/NCTs were stable even after three consecutive recycle tests without leaching of active metal or notable structural change. The correlation of reaction performance and detailed characterization revealed that large Ru NPs with high crystallinity exhibit superior catalytic activity for the combined dehydrogenation−hydrogenation reactions that yield the desired products.
This paper proposes a kinetic model of the chlorination of methane in the presence of a catalyst. As the reaction involves both gas-phase and catalytic chlorination, the reaction mechanisms with and without the catalyst were considered in this study. Experiments were conducted for the case of the gas phase and with catalysts separately, and kinetic parameters for each phase were estimated independently by fitting the experimental data. The proposed model accurately describes the experimental data (means of absolute relative residual values for the conversions of CH 4 and Cl 2 and the selectivities of methyl chloride, dichloromethane, and trichloromethane were 9. 60, 12.91, 7.79, 19.18, and 16.14%, respectively), in which the presence of the catalyst increased the conversion of methane, while it decreased the selectivity of methyl chloride, which is the desired product in this work. Further analysis showed that a high temperature increased the conversion and reduced the size of the reactor. The production rate of methyl chloride was strongly influenced by the methane fraction in the feed. An optimal fraction exists (70% methane) because an excess amount of methane decreased the conversion. Under optimal conditions, toxic chlorine was completely consumed. It was concluded that the developed model can be used to design an effective reactor for catalytic methane chlorination and determine the optimal operating conditions.
The existence of various surface active sites within a nanocrystal (NC) catalyst complicates understanding their respective catalytic properties and designing an optimal catalyst structure for a desired catalytic reaction. Here, we developed a novel approach that allows unequivocal investigation on the intrinsic catalytic reactivity of the edge and terrace atoms of NCs. Through the comparison of the catalytic behaviors of edge‐covered Pd NCs, which were prepared by the selective deposition of catalytically inactive Au atoms onto the edge sites of rhombic dodecahedral (RD) Pd NCs, with those of the pristine RD Pd NCs toward alkyne hydrogenation and Suzuki–Miyaura coupling reactions, we could decouple the activity of the edge and {110}‐plane atoms of the Pd NCs without uncertainties. We expect that this study will provide an opportunity to scrutinize the surface properties of various NC catalysts to a more precise level and devise ideal catalysts for intended catalytic reactions.
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