ALUMINA-SUPPORTED PT-RH CATALYSTS .2. KINETIC CHARACTERIZATION AND SYNERGISTIC EFFECTS

Analytical electron microscopy was used in the preceding paper to determine the composition distribution of individual catalytically active particles on several supported Pt-Ph bimetallic catalysts. The kinetic performance of these catalysts for the reduction of NO with H-2 and the reduction of NO with CO between 25 and 300 degrees C is presented here. The performance of one catalyst that contained alloy particles with compositions centered at approximately 10 wt% Pt and 90 wt% Pt was intermediate to that observed for Pt and Rh monometallic catalysts. Additional catalysts were prepared to separately test the kinetic performance of Pt-rich and Rh-rich alloy particles. One catalyst that was prepared at a 95/5 weight ratio of Pt to Rh contained Pt-rich alloy particles in the composition range of 80 wt% Pt-100 wt% Pt. Another catalyst was prepared at a 17/83 weight ratio of Pt to Rh and contained mostly Rh-rich alloy particles in the composition range of 70 wt% Rh-100 wt% Ph. For both the NO-H-2 and NO-CO reactions, the 95/5 catalyst displayed an activity greater than that expected from the sum of the alloy components. It is therefore concluded that for the Pt-rich alloy particles of the 95/5 catalyst, a synergistic effect due to particle alloying is present. The kinetic performance of the Rh-rich particles in the 17/83 catalyst was less favorable, and less than that expected from the sum of the alloy components for the NO-CO reaction. (C) 1995 Academic Press, Inc.