Effects of thiophene and SO 2 on acrolein hydrogenation over Co/SiO 2 catalysts

Abstract

Infrared spectra are reported of adsorbed species and gaseous products in the reactions over SO 2-modified Co/SiO 2 of acrolein, propanal, allyl alcohol and propan-1-ol with and without hydrogen. Low coordination edge or step sites in high index planes contain Co n+ Co ○ sites which are active for CO hydrogenation but are completely poisoned by SO 2 pretreatment. Formation of 2-methylpenten-2-al from propanal by an aldol reaction over oxidic cobalt sites was promoted by SO 2 but inhibited by hydrogen. Low index planes contain Co ○ sites which are available for CC hydrogenation of acrolein but are inactive for allyl alcohol hydrogenation because of strong chemisorption of allyl alcohol on the SO 2-treated surface. Propanol was the dominant product from acrolein, propanal and allyl alcohol hydrogenation over unmodified Co/SiO 2 but was not formed over SO 2 modified catalyst. The acrolein reaction gave propanal alone. Thiophene caused partial poisoning of both low coordination and high coordination sites on Co/SiO 2, the hydrogenation of acrolein giving propanal and propan-1-ol but at lower rates than for unmodified Co/SiO 2.