HYDROISOMERIZATION PROBE OF THE CATALYTIC AND STRUCTURAL BEHAVIOR OF IRON-RHODIUM PARTICLES SUPPORTED ON REFRACTORY OXIDE SUPPORTS

In order to understand the role of metal-support interactions in determining the structure and catalytic chemistry of multimetallic catalysts, kinetic and calorimetric studies of FeRh particles supported on a number of refractory oxide supports were conducted. Kinetic studies (l-butene hydroisomerization) showed that selectivity and activity were influenced by a number of parameters, particularly support identity, but also reduction temperature, and time on stream. To explain the observed kinetics it is postulated: (i) catalysis takes place both at metal sites and at acid sites on the surface, and that the selectivity of each site type is very different, (ii) the presence of metal enhances the rate of reaction at the acid sites by providing hydrogen atoms via a spillover mechanism, (iii) the metal loses activity more rapidly than the acid sites and (iv) due to the relative strengths of iron and rhodium interactions with the support, rhodium is preferentially reduced. Microcalorimetric studies of the surface composition support the postulate that rhodium is preferentially reduced and found at the surface. In sum, this study clearly shows that the structural and hence catalytic behavior of refractory oxide supported FeRh is distinctly different than that observed for the same metals on a graphitic support, thus demonstrating the critical importance of metal-support interactions in determining the catalytic character of multimetallic particles.