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

Analytical electron microscopy was used in the preceding paper to dete rmine 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 t he reduction of NO with CO between 25 and 300 degrees C is presented h ere. The performance of one catalyst that contained alloy particles wi th compositions centered at approximately 10 wt% Pt and 90 wt% Pt was intermediate to that observed for Pt and Rh monometallic catalysts. Ad ditional catalysts were prepared to separately test the kinetic perfor mance of Pt-rich and Rh-rich alloy particles. One catalyst that was pr epared at a 95/5 weight ratio of Pt to Rh contained Pt-rich alloy part icles in the composition range of 80 wt% Pt-100 wt% Pt. Another cataly st was prepared at a 17/83 weight ratio of Pt to Rh and contained most ly Rh-rich alloy particles in the composition range of 70 wt% Rh-100 w t% Ph. For both the NO-H-2 and NO-CO reactions, the 95/5 catalyst disp layed an activity greater than that expected from the sum of the alloy components. It is therefore concluded that for the Pt-rich alloy part icles of the 95/5 catalyst, a synergistic effect due to particle alloy ing is present. The kinetic performance of the Rh-rich particles in th e 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 Acade mic Press, Inc.