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  • Author or Editor: Yuhan Sun x
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Abstract  

The reaction of urea with ZnO was investigated by FTIR and TPD. It was found that urea was thermally decomposed into isocyanic acid on ZnO, and the adsorbed isocyanic acid reacted with ZnO to form zinc isocyanate. Catalytic evaluation showed that ZnO had high activity towards urea methanolysis in a batch reactor, and zinc element and isocyanate were all detected in the product solution. Furthermore, the soluble zinc content was proportional to the DMC yield. Sample analyses suggested that the soluble zinc existed in the form of Zn(NCO)2(NH3)2, which originated from the reaction of ZnO with urea. It was the complex (not ZnO) that catalyzed the urea methanolysis. Based on these observations, a possible mechanism was suggested.

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Abstract

A novel carbon modified Fe–Mn–K catalyst for light olefin synthesis from CO hydrogenation was prepared by the sol–gel method. The effect of carbon contents on the structure and performance of the catalysts was investigated. With the incorporation of carbon, the catalysts showed much different morphology from that prepared by co-precipitation. At the carbon contents between 0.23 and 6.66 wt%, the catalyst particles were around 10 nm while the carbon phase was amorphous. The activity test results indicated that the catalysts (Fe/Mn/K molar ratio = 60/20/1) with carbon modification showed high conversion of CO and selectivity to light olefins with low CH4 selectivity. At the carbon content of 2.43 wt%, the total C2–C4 content in all hydrocarbons and O/P (olefin/paraffin) in the C2–C4 fraction was 49 wt% and 4.89, respectively. Furthermore, when the K content in the catalyst was reduced by half, the C2–C4 olefin yield raised from 60 to 71 g/Nm3 syngas. The formation of carbon provided a more hydrophobic surface, which inhibited the water gas shift reaction (WGSR) and caused a decrease in CO2 selectivity. The dispersion of carbon favored the formation and stabilization of small particles, and promoted the production of light olefins via suppressing the chain propagation.

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Abstract

The influence of pore regularity in Fischer–Tropsch synthesis over Co/SiO2 catalysts was investigated by using two series of silica with comparable pore sizes: mesoporous silica (SBA-15) and amorphous silica. It was found that cobalt dispersion was largely influenced by the support porous structure. The cobalt particles on mesoporous silica showed much more homogeneous size distribution and the increase of cobalt loadings did not result in a noticeable increase of Co3O4 particle size on SBA-15, while most of those on amorphous silica agglomerated into clusters. As a result, SBA-15 supported Co catalysts showed higher cobalt-time yield and C5+ selectivity in Fischer–Tropsch synthesis, particularly higher C12–18 fraction. However, the average particle size of Co3O4 supported on amorphous silica increased with the cobalt loadings, which led to lower cobalt-time yield and higher CH4 selectivity.

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Abstract

Sol–gel Co/SiO2 catalysts were prepared using Co–en (ethylenediamine) complex precursors with different cobalt introduction order. More highly reduced catalysts were obtained by gelling the silica support followed by depositing cobalt nanoparticles on silica surface, and then catalysts exhibited higher FT activity and concomitant higher C18+ selectivity. Meanwhile, both series of catalysts prepared with en/Co molar ratio of 2/1 exhibited higher activity due to their high cobalt reduction.

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Emasculation and bagging of flowers, which are widely used in the controlled pollination of monoclinous plants, may induce premature senescence, flower abscission and low fruit set. To determine the mechanism responsible for these phenomena, levels of abscisic acid (ABA), jasmonic acid (JA), indole-3-acetic acid (IAA), ethylene, soluble sugars, reducing sugars and free amino acids in black locust (Robinia pseudoacacia) flowers subjected to different treatments were quantified at different developmental stages. The phytohormones and assimilates were also quantified in untreated flowers to investigate the presence of discernible patterns. The levels of ethylene and ABA in emasculated and bagged (EB) flowers increased prematurely compared with those of untreated flowers, whereas the content of reducing sugars in EB flowers decreased compared with that of untreated flowers. These results indicated that the premature increase in ethylene and ABA synthesis, and the decrease in reducing sugars content, in EB flowers may cause flower abscission and result in low fruit set, which may be relevant for assimilate applications and future research on the regulation of controlled pollinations with exogenous phytohormones.

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