INFRARED STUDY OF THE CO INSERTION REACTION ON REDUCED, OXIDIZED, AND SULFIDED RH/SIO2 CATALYSTS

The reaction of adsorbed CO with C2H4/H2 and ethylene hydroformylation over reduced, oxidized, and sulfided Rh/SiO2 catalysts has been investigated under reaction conditions by in situ infrared spectroscopy. Both reactions involve the CO insertion step resulting in the formation of propionaldehyde. The linear CO adsorbed on the Rh0 site of the reduced Rh/SiO2 and the linear CO adsorbed on the Rh+ site of the oxidized Rh/SiO2 are consumed and propionaldehyde is produced as the adsorbed CO reacts with C2H4 and H2. The results show that both single Rh0 atoms and Rh+ ion sites are active for the CO insertion reaction. In situ infrared observations of steady-state ethylene hydroformylation show that the oxidized Rh/SiO2 containing considerable amounts of Rh+ sites exhibits rate and selectivity for the formation of propionaldehyde higher than those of the reduced Rh/SiO2; the sulfided Rh/SiO2 comprising mainly single Rh sites shows rate and selectivity for the formation of propionaldehyde higher than that of the reduced Rh/SiO,. The low selectivity of the reduced Rh/SiO2 for ethylene hydroformylation is attributed to the high hydrogenation activity of the Rh crystallite surface on the reduced Rh/SiO2. © 1992.