Spectroscopic investigation of species arising from CO chemisorption on titania-supported manganese

The nature of manganese species on the surface of TiO2 (anatase) has been i nvestigated by means of XPS, visible absorption spectroscopy, and FTIR spec troscopy of adsorbed CO. The catalysts were prepared by ion-exchange from a queous manganese(II) chloride solution and impregnation. The application of ion-exchange results in a loading of manganese oxide phase corresponding t o a monolayer coverage. On the surface of the ion-exchanged sample two kind s of Mn3+ ions are stabilized, differing in their coordinative saturation a nd localization. The Mn3+ ions form two kinds of linear carbonyls character ized by absorption at 2194 and 2187 cm(-1), respectively The impregnated ca talyst contains a mixture of Mn3+ and Mn2+ species. The latter ions produce a carbonyl band at 2114 cm(-1). The adsorption of CO at room temperature o n the catalysts studied results in formation of formate, carbonate, and hyd rogen carbonate structures as web. It is found that the formation of format e species is associated with the Mn3+ ions and the possible mechanism is di scussed. The stabilization of the hydrogen carbonates is favored by Mn2+ io ns. The reduction of the catalyst studied with hydrogen strongly suppresses the adsorption of CO and is indicative of the occurrence of a strong metal -support interaction. (C) 2000 Academic Press.