The X-ray photoelectron spectroscopy of surface composition of aged mixed copper manganese oxide catalysts

A series of copper manganese oxide catalysts of approximate composition Cu1þxMn2 xO4 (x ¼ 0.54 0.04), which was aged at various times and at different pH values, has been studied by X-ray photoelectron spectroscopy (XPS). In all cases, copper (II) and manganese (IV) are the only oxidation states. The copper/manganese concentration ratio exceeds the bulk value (0.5) at short ageing times, but falls to <0.4 on prolonged ageing. Sodium, which is believed to be a poison for the CO oxidation reaction; for which, the copper manganese oxide catalyst is the most useful, is formed on all samples, however, its concentration decreases significantly with increased ageing time.