(704d) Kinetics of the Oxidative Cleavage of Methyl Ketones over Supported Vanadium Oxide Catalysts

The oxidative cleavage of methyl ketones over VO_x/SiO₂ was studied over the temperature range of 323-723 K under atmospheric pressure. Our experiments show that methyl ketones cleave over supported reducible vanadium clusters in both the presence and absence of molecular O₂. The reaction network of methyl propyl ketone (MPK), which includes three parallel reactions (terminal cleavage, internal cleavage and combustion), was investigated based on observations from contact time studies and activities of all the observed products. Temperature programmed surface oxidation experiments were carried out to investigate the role of gas phase oxygen in the formation of both aldehyde and carboxylic acid products during oxidative cleavage. In absence of oxygen, the temperature required for aldehyde formation increased, and the remaining acetate species on the catalyst surface were either further oxidized or underwent combustion into carbon oxides. Specifically, the addition of oxygen initiates cleavage reactions at low temperatures, and appears to promote desorption of the acetic acid product, which is slow under anaerobic conditions. Our ongoing investigations in this area are aimed at further resolving the exact mechanism of oxidative ketone scission using in-situ or operando experiments and microkinetic analysis.