Water Mediated Deactivation of Co3O4 Naonrods Catalyst for CO Oxidation and Resumption of Activity at and Above 373 K: Electronic Structural Aspects by NAPPES

The catalytic activity of the Co 3 O 4 nanorods (NRs) for the CO oxidation reaction and the effect of water on the catalytic reaction have been explored with near-ambient pressure photoelectron spectroscopy (NAPPES) and mass spectral analysis. Comparative NAPPES studies have been employed to understand the elucidation of the catalytic reaction pathway and the evolution of various surface species. The results confirm the suppression of the CO oxidation activity on the Co 3 O 4 NRs in the presence of water vapor. Various type of surface species, such as CO(ads), hydroxyl, carbonate, formate, are found to be present on the catalyst surface depending on the reaction conditions. Vibrational features of CO, O 2, and CO 2 were observed and shift in binding energy of these features under the reaction conditions directly suggests a change in work function of the catalyst surface. Under dry conditions, CO couples with labile O atoms to form CO 2; however, under wet conditions, CO predominantly interacts with surface OH groups resulting in the formation of carbonate and formate intermediates. In situ studies of oxidation of CO on Co 3 O 4 shows that CO oxidation depends not only on surface Co 3+ concentration but also influenced by Co 3+ /Co 2+ ratio on the catalyst surface. The carbonate was found to be a reaction inhibitor at room temperature; however, it acts as an active intermediate at 375 K and above. Above the boiling point of water, Co 3 O 4 NR surfaces begin to show the oxidation activity even in the presence of water vapor. The intrinsic role of intermediate species was used to derive a possible reaction mechanism under different reaction conditions.