The use of probe molecules in the study of CO hydrogenation over SiO2-supported Ni, Ru, Rh, and Pd

Abstract CO hydrogenation over Ni SiO 2 , Ru SiO 2 , Rh SiO 2 and Pd SiO 2 was studied by the addition of various probe molecules (C 2 H 4 , CH 3 CH 2 OH, and CH 3 CHO) to the reactant stream under synthesis conditions. The well-known differences among these catalysts in product formation (methane, higher hydrocarbons, C 2+ oxygenates and methanol) were shown to be due to differences in their activities to catalyze hydrogenation, hydrogenolysis, dehydrogenation, decarbonylation, CH x insertion, and CO insertion rather than just CO dissociation. Ni SiO 2 and Pd SiO 2 exhibited weak activities for the incorporation of these probe molecules into higher hydrocarbons and oxygenates. Rh SiO 2 , a good catalyst for the production of C 2 oxygenated compounds, showed strong activity for CO insertion and for the incorporation of ethylene and ethanol into C 3+ oxygenated compounds. Ru, a higher hydrocarbon synthesis catalyst, displayed fairly strong activities for the incorporation of ethanol and acetaldehyde into C 3+ hydrocarbons. Probing of the surface under reaction conditions by the addition of certain reacting molecules provides an excellent method for developing a better understanding of reaction mechanisms as well as of fundamental properties of catalysts under those conditions.