Infrared study of CO and 2-butenal co-adsorption on Zn modified Pt/CeO2–SiO2catalysts

Abstract

Infrared spectra of CO alone and CO followed by the introduction of 2-butenal (crotonaldehyde) have been recorded for Pt/CeO₂–SiO₂ and Zn doped Pt/CeO₂–SiO₂ catalysts which had been pre-reduced at 473, 623 and 773 K. Samples treated at the highest reduction temperature showed the greatest selectivity toward the unsaturated alcohol although no clear spectroscopic evidence for the formation of an SMSI state was obtained. Although 773 K reduced Zn containing catalysts showed the greatest yield, there was no IR spectroscopic evidence to support the formation of significant quantities of a Pt–Zn alloyed phase or that the addition of Zn enhanced Pt-support interactions beyond increasing the amount of surface reduced ceria. Results show that, contrary to popular opinion, the development of an SMSI state which enhances the density of support-metal interface sites is not essential in order to increase the yield of unsaturated alcohol and the presence of reduced cationic sites at the interface zone may be the crucial factor. Although IR spectra in the νCO region were dominated by dipole coupling effects, enhanced intensity of carbonyl bands in the 2030–1950 cm⁻¹ region for 773 K reduced samples and for Zn containing samples reduced at lower temperatures suggests that sites responsible for these carbonyl bands may be the active sites in the selective hydrogenation reaction.