(638e) The Contribution of Acid and Redox Sites during the Catalytic Oxidation Scission of Ketones over Supported Vanadium Oxide: An in Situ FTIR Study.
AIChE Annual Meeting
Thursday, November 11, 2021 - 4:24pm to 4:42pm
FTIR spectra of pyridine saturated VOx/Al2O3 samples show two distinct peaks corresponding to Lewis (â 1450 cm-1) and Bronsted (â 1540 cm-1) sites. When co-feeding pyridine during the oxidation of 3-methyl-2-butanone, its competitive adsorption at Lewis and Bronsted sites results in a decreased coverage of ketone and acetate species and reduced oxidative scission rates compared to normal steady-state conditions. Ketone could substitute weakly adsorbed pyridine at Lewis sites, and we observe partial recovery of acetate coverage upon removal of the titrant co-feed. In contrast, pyridine remains bound at Bronsted sites after removal of the pyridine co-feed. These observations suggest that Lewis sites are involved directly in the ketone oxidation, whereas Bronsted sites appear to bind spectator species. Introducing an ammonia co-feed during the oxidative scission of 3-methyl-2-butanone results in the formation of a distinct set of reaction products that include acetone, acetamide, and acetonitrile. Under these conditions, we observe the appearance of V-O-N bands at 930 cm-1 and 965 cm-1, which are consumed rapidly upon stopping the ammonia co-feed. These observations suggest that incorporation of nitrogen into the vanadium oxide lattice leads to the formation of acetamide and acetonitrile, helping to resolve the role of lattice oxygens during the oxidative scission of 3-methyl-2-butanone on vanadium oxides.