Crotonaldehyde hydrogenation on Pt/TiO2 and Ni/TiO2 SMSI catalysts

A kinetic and DRIFTS (diffuse reflectance FTIR) investigation of crotonalde hyde adsorption and hydrogenation was conducted over TiO2-supported Pt and Ni with the intent of gaining insight into the adsorption modes of molecule s with carbonyl groups on these catalysts in the SMSI and non-SMSI states. Significant enhancement in selectivity toward crotyl alcohol was observed w ith each catalyst after reduction at 773 K. DRIFT spectra under reaction co nditions identified crotonaldehyde species strongly adsorbed through the C= C bond and weakly coordinated through both the C=C and the C=O bonds on the se catalysts after reduction at 573 K, which gave a peak at 1693 cm(-1). Af ter reduction at 773 K, an additional adsorbed species with a strong band a t 1660 cm(-1), indicating a significant interaction between the carbonyl gr oup and the surface, was observed, which is presumed to be stabilized at in terfacial Pt-TiOx and Ni-TiOx sites. A decrease in the surface coverage of this species paralleled a drop in selectivity to crotyl alcohol with time o n stream. After reduction at 573 K, decarbonylation occurred during the ini tial few minutes on stream to create adsorbed CO on Pt/TiO2 in addition to carbon deposition, but these reactions were significantly suppressed after reduction at 773 K, presumably due to a TiOx overlayer which covers part of the Pt surface and breaks up the ensembles of Pt atoms required for these reactions. (C) 1999 Academic Press.