CONTRIBUTION OF PHYSICAL BLOCKING AND ELECTRONIC EFFECT TO ESTABLISHMENT OF STRONG METAL SUPPORT INTERACTION IN RH/TIO2 CATALYSTS

Establishment of strong metal-support interaction in Rh/TiO2 catalysts has been studied by H-1 NMR spectroscopy as a function of conditions of reduction in H-2: temperature (373-773 K), time, and type of reduction (static or dynamic). Two consecutive stages have been identified: one when the catalyst is reduced below 673 K and the other when the temperature is above 673 K. In the first stage, elimination of hydrogen incorporated into the metal-support interface, by outgassing at 773 K, recuperates hydrogen adsorption on the metal. In the second stage, the outgassing treatment does not recover metal adsorption capacity. Physical blocking of metal adsorption sites by TiO(x) species and electronic perturbation of the metal are responsible for the irreversible loss of hydrogen adsorption. From analysis of the NMR line assigned to hydrogen adsorbed on the metal, the relative contribution of both effects to adsorption suppression has been estimated.