Metal-support interactions during the CO2 reforming of CH4 over model TiOx/Pt catalysts

To obtain insight into the importance of metal-support interactions (MSI) in the CO2 reforming of CH4, the reaction was studied using pure TiO2, high-purity Pt powder, and two model TiOx/Pt systems. The latter two TiOx/Pt catalysts, prepared by oxidation of Ti nonylate deposited on the Pt powder surface, contained either one (theta = 1) or ten (theta = 10) theoretical monolayers of TiO2. The H-2 and CO chemisorption capacities showed respective decreases of 1/3 and 1/2 on the latter two catalysts although the N-2 BET surface areas were essentially unchanged. XRD analysis of either TiOx/Pt sample detected no TiOx structures. Specific rates (mu mol/(s g(cat))), areal rates (mu mol/(s m(2))) and turnover frequencies (s(-1)) for the CO2 reforming of CH4 decreased in the order TiOx/Pt (theta = 10) TiOx/Pt (theta = 1) much greater than Pt powder > TiO2. Neither pure Pt powder nor pure TiO2 showed appreciable activity for CH4-CO2 reforming; thus the dramatic increase in activity is attributed to the creation of new sites in the metal-support interfacial region which promote CH4 dissociation, CO2 dissociation and reduction, and subsequent CHxO decomposition. In addition, temperature-programmed hydrogenation of used catalyst samples clearly showed that TiOx overlayers on the Pt surface suppress carbon deposition during reaction via an ensemble effect, thus improving activity maintenance.