FTIR STUDY OF CO INTERACTION WITH RU TIO2 CATALYSTS/

A Ru/TiO2 (anatase) sample prepared by ion-exchange was studied by TPR and FTIR spectroscopy of CO adsorbed at different temperatures. Two k inds of Run+ species, differing in their reducibility, are present on the sample surface. The IR spectra of the sample and of CO adsorbed re veal the existence of a RuO2-like phase and Run+ (1 less than or equal to n less than or equal to 3) cations. The supported ruthenium is com pletely reduced to Ru-0 after treatment with hydrogen at 523 K. Simult aneously, a large part of the initial anatase sites are liberated for exchange. Therefore, a second ion-exchange of Ru/TiO2 is possible whic h allows to double ruthenium concentration. Low-temperature CO adsorpt ion on the reduced Ru/TiO2 catalyst reveals the existence of Ru-0 site s as well as different sites typical of the bare titania. At temperatu res close to the ambient one, CO interacts with the RuO clusters causi ng disruption of some Ru-Ru bonds and increase in dispersion of ruthen ium particles. At higher temperatures, CO dissociates on particular Ru O sites, thus oxidizing some Ru-0 atoms to Run+ ions. Subsequently, Ru n+(CO)(3) species are formed after adsorption of additional CO molecul es on these latter species. Simultaneously, the titania sites that hav e been liberated during the reduction are re-occupied. On the Ru/TiO2 catalyst whose dispersion has been modified by CO contact, further red uction with hydrogen at 523 K leads to a new drop of the metal dispers ion (similar to that of freshly reduced catalyst) showing that the met al sintering/increase in dispersion are reversible effects. When CO ad sorption is performed on an oxidized catalyst, both Run+(CO)(3) and Ru m+(CO)(2) species are formed on the surface. All these phenomena are a lso observed on the Ru/TiO2 (anatase) catalyst prepared by impregnatio n. The results differ only in some quantitative values. (C) 1998 Acade mic Press.