Mechanism and Active Site Density Elucidation for Ethanol Oxidation Over Supported V Ox , Mo Ox , and W Ox Catalysts
Hari Nair and Chelsey D. Baertsch. School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, West Lafayette, IN 47907-2100
A novel system of anaerobic titrations by stoichiometric titration of lattice oxygen with ethanol reactant in the absence of gas phase O2 was used to quantify the redox site density on supported catalysts containing VOx, MoOx, and WOx domains. The intrinsic turn-over frequency is independent of the metal oxide composition and surface density. Differences in redox rates arise due to differences in the number of active redox sites available under reaction conditions. Active redox site densities for the conversion of ethanol to acetaldehyde at 453 K range from ~ 0.05-1.0 active sites per metal atom and intrinsic acetaldehyde turn-over frequencies over all supported oxide catalysts are approximately 1e-03 s-1. Detailed mechanisms for acetaldehyde and diethyl ether formation were also determined using a combination of in-situ FTIR, isotopic labeling, and acid site titration using pyridine. Both redox (acetaldehyde) and acid (diethyl ether) products form through a chemisorbed ethoxy species, which can form either acetaldehyde or diethyl ether depending on the nature of the metal oxide domain.