Competition between C-O bond scission and retention in methanol reaction on Co-covered Mo(110)

Methanol reaction on Co overlayers (1.0-1.3 ML) deposited on Mo(110) yields CO and H-2 as the gaseous products. Isotopic labeling and vibrational studies show that molecular methanol desorption around 210 K competes with O-H bond scission to form methoxide. Methoxide is identified as the major surface intermediate at 250 K using electron energy loss spectroscopy. Vibrational data also indicate that methoxide decomposes to adsorbed CO by 350 K. The formation of C-O bond retention products such as CO on the Co overlayers is consistent with the intermediate Co-O bond strength and is characteristic of methanol reaction on other mid transition metal surfaces. However, C-O bond dissociation to produce atomic carbon and oxygen accounts for similar to 54% of the total methanol reaction. The C-O bond dissociation pathway is attributed mainly to reaction at defects on the overlayer, based on comparison with studies of CO on Co(0001), The dependence of the CO yield on Co coverage suggests that there is no special reactivity associated with mixed Co-Mo sites that gives rise to new product formation. Defects in the Co overlayers exhibit a higher activity for C-O bond dissociation, suggesting that the reactivity of Co itself is structure-sensitive.