Crotonaldehyde Hydrogenation on Pt/TiO2and Ni/TiO2SMSI Catalysts

A kinetic and DRIFTS (diffuse reflectance FTIR) investigation of crotonaldehyde adsorption and hydrogenation was conducted over TiO2-supported Pt and Ni with the intent of gaining insight into the adsorption modes of molecules with carbonyl groups on these catalysts in the SMSI and non-SMSI states. Significant enhancement in selectivity toward crotyl alcohol was observed with each catalyst after reduction at 773 K. DRIFT spectra under reaction conditions identified crotonaldehyde species strongly adsorbed through the C=C bond and weakly coordinated through both the C=C and the C=O bonds on these catalysts after reduction at 573 K, which gave a peak at 1693 cm−1. After reduction at 773 K, an additional adsorbed species with a strong band at 1660 cm−1, indicating a significant interaction between the carbonyl group and the surface, was observed, which is presumed to be stabilized at interfacial Pt–TiOxand Ni–TiOxsites. A decrease in the surface coverage of this species paralleled a drop in selectivity to crotyl alcohol with time on stream. After reduction at 573 K, decarbonylation occurred during the initial few minutes on stream to create adsorbed CO on Pt/TiO2in addition to carbon deposition, but these reactions were significantly suppressed after reduction at 773 K, presumably due to a TiOxoverlayer which covers part of the Pt surface and breaks up the ensembles of Pt atoms required for these reactions.