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 deter mining the structure and catalytic chemistry of multimetallic catalyst s, kinetic and calorimetric studies of FeRh particles supported on a n umber of refractory oxide supports were conducted. Kinetic studies (l- butene hydroisomerization) showed that selectivity and activity were i nfluenced by a number of parameters, particularly support identity, bu t also reduction temperature, and time on stream. To explain the obser ved kinetics it is postulated: (i) catalysis takes place both at metal sites and at acid sites on the surface, and that the selectivity of e ach site type is very different, (ii) the presence of metal enhances t he rate of reaction at the acid sites by providing hydrogen atoms via a spillover mechanism, (iii) the metal loses activity more rapidly tha n the acid sites and (iv) due to the relative strengths of iron and rh odium interactions with the support, rhodium is preferentially reduced . Microcalorimetric studies of the surface composition support the pos tulate that rhodium is preferentially reduced and found at the surface . In sum, this study clearly shows that the structural and hence catal ytic behavior of refractory oxide supported FeRh is distinctly differe nt than that observed for the same metals on a graphitic support, thus demonstrating the critical importance of metal-support interactions i n determining the catalytic character of multimetallic particles.