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

Mn-containing oxide catalysts have wide application and potential use in different catalytic processes of industrial importance. The nature of Mn species on the surface of TiO2 (anatase) was studied using XPS, FTIR, and visible absorption spectroscopy of adsorbed CO. The catalysts were prepared by ion-exchange from aqueous Mn(II) chloride solution and impregnation. The application of ion-exchange led to a loading of Mn oxide phase corresponding to a monolayer coverage. On the surface of the ion-exchanged samples, two types of Mn3+ ions were stabilized, which differed in their coordinative saturation and localization. The Mn3+ ions formed two types of linear carbonyls characterized by absorption at 2194 and 2187/cm, respectively. The impregnated catalyst contained a mixture of Mn3+ and Mn2+ species, with the latter ions generating a carbonyl band at 2114/cm. CO adsorption at room temperature on the catalysts led to the formation of formate, carbonate, and hydrogen carbonate structures as well. The formation of formate species was related to the Mn3+ ions and the possible mechanism was discussed. The stabilization of the hydrogen carbonates was favored by Mn2+ ions. The reduction of the catalyst studied with hydrogen strongly suppressed CO adsorption and was indicative of the occurrence of a strong metal-support interaction