Infrared spectroscopic studies of adsorption and catalysis: IV. Aliphatic ketones on silica-supported nickel

The adsorption and decarbonylation of acetone, acetone-d₆, and diethylketone on silica-supported nickel have been studied between 25 and 200 °C using infrared spectroscopy. After a short period of adsorption, two surface species were observed spectroscopically at 25 °. The main one is considered to be the associatively adsorbed ketone R₂CM-OM (M = surface metal atom). The minor one is a carbonyl-containing species possibly involving a complete acetone molecule held to a metal site through a relatively weak σ-bonded interaction with the carbon atom of the carbonyl group, or a π-bonded interaction with the carbonyl group as a whole. Over longer periods of time, bands were observed which are attributable to R₂CH · OSi groups (Si = surface silicon atom of the support). These probably result from the reduction of the ketone to R₂CHOH molecules which then react with OH groups of the silica surface. The hydrogen needed for the reduction process may arise from disproportionation of some of the dissociatively adsorbed species.