Crotonaldehyde Hydrogenation on Rh/TiO2 catalysts: In situ DRIFTS studies

the surface and catalytic properties in the vapor-phase hydrogenation of crotonaldehyde on rh/tio2 has been studied. it was found that a partial reduction of the support produces a surface decoration of the metal component. thus, interfacial sites are created, which are responsible of an increase in the selectivity to crotyl alcohol, via enhancement of the polarization of the c=o bond. photoelectron spectra revelead that rhodium is in different oxidation states, with a contribution of ca. 20 % rhd + and 80 % rho species for ltr catalyst and only a slight increase of rhd + for htr catalyst. tem studies revelead that rh has metal particle size close 3 nm with small increases in the catalyst reduced at high temperature. drifts essayed carried out under reaction conditions allowed to identify crotonaldehyde species strongly adsorbed through the c=c bond and weakly coordinated through both the c=c and c=o bonds. after reduction at 723 k an increase in the peak at 1660 cm-1 ascribed to an interaction between the carbonyl group and the surface, was observed. this peak seems to be stabilized at interfacial rh/tiox sites the deactivation in crotyl alcohol formation can be ascribed to the generation of strongly chemisorbed asymmetric carboxylate species detected by band at 1740 cm-1. this band grows at expense of crotonaldehyde o s - bonded intermediate chemisorbed on coordinatively unsaturated sites (lewis acid sites) responsible of the crotyl alcohol obtaintion (detected by a band at 1653 cm-1). additionally, a small band at 2068 cm-1 assigned to co adsorbed on transition metals, which increases with time on-stream may explain the deactivation of the catalysts in flow systems.