Establishing the Role of Graphite as a Shaping Agent of Vanadium鈥揂luminum Mixed (Hydr)oxides and Their Physicochemical Properties and Catalytic Functionalities

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• 作者：V铆ctor G. Baldovino-Medrano ; Benjamin Farin ; Eric M. Gaigneaux
• 刊名：ACS Catalysis
• 出版年：2012
• 出版时间：March 2, 2012
• 年：2012
• 卷：2
• 期：3
• 页码：322-336
• 全文大小：646K
• 年卷期：v.2,no.3(March 2, 2012)
• ISSN：2155-5435

文摘

This work contributes to the establishment of a scientific basis for the understanding of the effect of shaping on the physicochemical properties and functionalities of catalytic powders. In particular, the influence of graphite (G) as a shaping agent for vanadium鈥揳luminum mixed (hydr)oxides, VAlO, is presented herein. Graphite was added in different loadings (x = 1, 3, and 7 wt %). VAlO-xG hydroxides were tableted and then calcined as to obtain VAlO-xG mixed oxides. Both series of materials were characterized and tested in propane oxidative dehydrogenation (ODH). Correlation of X-ray photoelectron spectrometry (XPS) and Raman data permitted establishing that VAlO-xG hydroxides are constituted by graphite particles physically attached to the amorphous VAlO structure. The VAlO hydroxide structure was found to be composed of Al(OH)₃ and AlOOH linked to decavanadates-, metavanadates, and isolated or cluster vanadyl V鈺怬 species. Calcination of VAlO-xG caused further polymerization of vanadium species into decavanate chains and V₂O₅-like structures connected to a 纬-Al₂O₃-like matrix. Though graphite was not incorporated into the structure of VAlO, XPS analysis showed that it actively interacts with the VAlO surface. Such interaction favored propylene selectivity in ODH. Particularly, graphite containing VAlO-xG displayed higher production of propene over CO_x at high propane conversion. On the other hand, though graphite boosts the mechanical resistance of the VAlO-xG tablets, the surface area of the materials, as determined by the application of 蠂-theory, was found to significantly decrease after shaping and further calcination. This trend was explained considering pore widening during tableting. Finally, characterization performed on particles recovered from crushed VAlO-xG tablets showed that graphite particles were randomly distributed within the shaped catalysts.

Keywords:

VAlO mixed (hydr)oxides; graphite; shaping; N₂ physisorption; XPS; Raman; propane ODH