INFLUENCE OF METAL-PARTICLE SIZE AND SUPPORT ON THE CATALYTIC PROPERTIES OF SUPPORTED RHODIUM - CO-O2 AND CO-NO REACTIONS

The effects of metal particle size and support material on the kinetics of the COO2 and CONO reactions over Rh have been investigated. For the COO2 reaction in the CO-inhibition regime, both the specific rate and the apparent activation energy were found to be virtually independent of the Rh particle size, but moderately sensitive to the nature of the support material (with the low-temperature oxidation activity decreasing in the order Rh/α-Al2O3 > Rh/SiO2 > Rh/φ-Al2O3). The specific rate of the CONO reaction increased drastically with increasing Rh particle size; a 45-fold increase in specific rate was observed as the Rh particle size increased from 10 to 676 Å. However, support material had only a small effect on both the activity and selectivity of Rh for the CONO reaction. © 1991.