Victor Baldovino-Medrano - Establishing the Role of Graphite as a Shaping Agent of Vanadium–Aluminum Mixed (Hydr)oxides and Their Physicochemical Properties and Catalytic Functionalities

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      ACS Catalysis   2012,    2,   pp 322–336


        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–aluminum 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═O species. Calcination of   VAlO-xG   caused further polymerization of vanadium species into decavanate   chains and V2O5-like   structures connected to a γ-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 COx    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 χ-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.

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