Dry reforming of methane on grafted-supported Rh catalysts: effect of the metal-support interaction on the reaction rate

Catalysts of rhodium supported on pure oxides and modified alumina with 50, 75 and 100% of ZrO2 were prepared by the impregnation method, to be tested in the reaction of dry reforming of methane in order to study the effect of the metal-support interaction on the reaction rate. The catalysts were characterized by N-2 adsorption isotherms, CO chemisorption, TEM, temperature programmed reduction, XRD and XPS. The reaction rate for CH4 conversion was measured at 500-700 A degrees C, in the absence of transport limitation. The average Rh cluster size in catalysts with modified supports resulted similar as compared with the catalyst Rh/0%ZrO2-Al2O3, so that the modification of the support had no effect on the dispersion of Rh, which is associated with the similarity in the BET surface area of the pure and modified alumina. The Rh-support interaction is determined by the degree of coverage of alumina with zirconia and by the nature of ZrO2 phase formed in the grafted supports. The higher coverage of alumina with zirconia leads to a lower Rh-support interaction. However, the interaction of Rh with the monoclinic phase seems to be weaker than with the tetragonal phase of zirconia, the latter more abundant as the loading of ZrO2 is increased in the grafted supports. Consequently, the Rh-support interaction increases with the content of ZrO2. Despite the different Rh-support interaction, the structural sensitivity of dry reforming of methane on Rh catalysts was still evidenced, i.e., the DRM reaction rate is mainly determined by the coordination degree of Rh atoms on the catalyst surface.