Selective CO Methanation on Ru/TiO2 Catalysts: Role and Influence of Metal-Support Interactions

Aiming at a detailed understanding of the role of metal-support interactions in the selective methanation of CO in CO2-rich reformate gases, we have investigated the catalytic performance of a set of Ru/TiO2 catalysts with comparable Ru loading, Ru particle size, and TiO2 phase composition but very different surface areas (ranging from 20 to 235 m(2) g(-1)) in this reaction. The activity for CO methanation, under steady-state conditions, was found to strongly depend on the TiO2 support surface area, increasing first with increasing surface area up to a maximum activity for the Ru/TiO2 catalyst with a surface area of 121 m(2) g(-1) and TiO2 surface area then decreasing for an even higher surface area; however, the selectivity is mainly determined by the Ru particle size, which slightly decreases with increasing support surface area. This goes along with an increase in selectivity for CO methanation, in agreement with a model proposed previously for nonreducible supports. In situ infrared measurements further revealed that also the adsorption properties for these catalysts, as evidenced by the CO adsorption strength, change significantly with increasing catalyst surface area and that strong metal-support interactions cause a partial overgrowth of the Ru nanoparticles for the highest surface area catalyst. The interplay between catalyst surface area and reaction characteristics and the important role of metal-support interactions in the reaction, in addition to particle size effects, will be elucidated and discussed.