Analysis of CO hydrogenation pathways using the bond-order-conservation method

The bond-order-conservation (BOC) method has been used to identify the energetics associated with the hydrogenation of CO over (111) surfaces of Ni, Pd, and Pt. In the formation of CH 4, the CO bond of CO is cleaved. BOC calculations for Ni indicate that cleavage of the CO bond occurs primarily by direct dissociation of molecularly adsorbed CO. The activation energy for direct dissociation of CO on Pd and Pt is significantly greater than that for hydrogen assisted dissociation, and hence the latter process is more significant. The BOC calculations indicate that for these metals the species from which CO bond cleavage occurs is CH 3O s Because the activation barriers for CH 3O s dissociation and hydrogenation to form CH 3OH are close for Pd and Pt, these metals are effective catalysts for both CH 4 and CH 3OH synthesis. By contrast, the BOC method predicts that CH 4 should be the principal product formed over Ni.