COMPARISON OF METHANOL FORMATION OVER PALLADIUM AND RHODIUM CATALYSTS.

Recent work has suggested that the synthesis of methanol from CO and H//2 probably proceeds in general by a different mechanism than hydrocarbon and higher oxygenate synthesis. Both Pd and Rh can synthesize methanol with high selectivities using the proper catalyst formulation and reaction conditions. In order to develop a better understanding of the similarities and differences of methanol synthesis on such different catalysts, an investigation of CO hydrogenation over Pd/SiO//2, Rh black, Rh/La//2O//3, Rh/MgO, and Rh/SiO//2 has been carried out. The addition of probe reactant molecules (ethylene and ethanol) to the reaction stream was also utilized to provide increased insight. The results indicate that only those catalysts able to synthesize C//2 oxygenates directly were able to form C//3 oxygenates from ethylene by CO insertion. Catalysts lacking the ability to synthesize methanol were able to form C//3// plus oxygenates from reaction of added ethanol with the CO hydrogenation intermediaties. Based on the results, it appears that the active sites for methanol formation are different from those for C//2 oxygenate formation.