Comparison of Several Metal Catalysts in the Hydrogenation of Carbon Monoxide

Hydrogenation of CO was carried out by using a pulse technique on α-alumina supported Ni, Fe, Co, and Ru catalysts. When a CO pulse was introduced to the catalyst at around 473 K by H₂ carrier gas, hydrocarbons were produced of which chromatographic peaks showed pronounced tailings. The amount of H₂O produced during the slow formation of hydrocarbons was compared with that of hydrocarbons. When CO was pulsed to a catalyst stabilized by the pretreatment with CO pulse, H₂O and hydrocarbons were produced with almost equal reaction rate. On the other hand, when CO was pulsed to a freshly reduced catalyst of Fe, Co, and Ru, H₂O was produced much slower than hydrocarbons. The uptake of oxygen from CO molecule by such catalysts occurred and the metal surface was consequently considered to be partially oxidized. This leads to stabilization of the catalyst surface. In case of Ni catalyst such an oxygen uptake was not observed and the reaction took place in the metallic state. The rate of H₂O formation was equal to that of CH₄. Although the C-O bond dissociation process of the adsorbed CO species was recognized to be a rate-determining step in the hydrogenation of CO over all metal catalysts used, the surface state during the reaction was observed to be different between Ni and other metals such as Fe, Co, and Ru.