An infrared study of CO adsorption on reduced and oxidized Ru/SiO2

Three infrared bands are observed for CO adsorbed on RuSiO2. The two highest frequency bands are assigned to the A1 and E stretching modes of tricarbonyl species. On a reduced sample, the tricarbonyl species are associated with Ru ions bonded directly to the support. Such structures are produced by corrosive chemisorption of CO on Ru crystallites [Rus + 2 SiOH + 3 CO = (SiO)2Ru(CO)3 + H2]. A separate set of tricarbonyl species is observed on partially oxidized samples of RuSiO2. In this case, the partially oxidized sites occur on the surface of the Ru particles. The lowest frequency band is assigned to the CO stretch of linearly adsorbed CO on Ru particles. Evidence is also found for linearly adsorbed CO on partially oxidized Ru sites.