High and low surface area NiO-MgO and CoO-MgO solid solutions: a study of XPS surface composition and CO oxidation activity

Oxide solid solutions NiO-MgO of high surface area were studied by XPS. The surface Ni2+ concentration was found to be equal, within experimental erro rs, to the bulk concentration. The result is analogous to that found previo usly for the low surface area NiO-MgO system and for both the high and low surface area systems of CoO-MgO. The catalytic oxidation of CO by O-2, on h igh and low surface area NiO-MgO and CoO-MgO materials, was investigated wi th the aim of relating the catalytic activity with transition metal ion nat ure and concentration. Turnover frequency data (CO2 molecules produced per second per surface atom) show that the activity is due primarily to the tra nsition metal ions and is not subject to the ions being in special configur ations (dimers or trimers) or in special positions (edges, corners). The ac tivity of CoO-MgO is higher than that of NiO-MgO solid solution.