CO-2 AND CO+NO REACTIONS OVER PD(O)AL2O3 CATALYSTS/

The kinetics of the CO + NO and CO + O-2 reactions have been studied o ver several different Pd/AL(2)O(3) powder catalysts covering a wide ra nge of average Pd particle sizes. The structure-insensitive nature of the CO + O-2 reaction over Pd has been exploited to determine the rela tive dispersions in several Pd/Al2O3 powder catalysts by measuring the rate of that reaction and normalizing against surface area. This meth od, assuming particles of hemispherical shape, yields average particle sizes that are consistent with observations using TEM. For the CO + N O reaction over the same catalysts, a pronounced structure sensitivity is evident that results in higher reaction activities over larger Pd particles. Differences between CO oxidation rates for the CO + O-2 rea ction prior and subsequent to exposure to the CO + NO reaction are sug gestive of the formation of an inhibiting, site-blocking species durin g the latter reaction. These results are discussed with reference to s urface science and kinetics studies over single crystal and model plan ar Al2O3 supported Pd catalysts which have indicated that the structur e-sensitive formation and stabilization of an inactive atomic N specie s plays a significant role in determining the reaction activity over a particular crystal plane or particle size.