SELECTIVE REDUCTION OF NITRIC-OXIDE OVER CU ZSM-5 - THE ROLE OF OXYGEN IN SUPPRESSING CATALYST DEACTIVATION BY CARBONACEOUS DEPOSITS/

The role of oxygen in the selective reduction of nitrogen monoxide by either propane or propene over ''excessively'' ion-exchanged Cu/ZSM-5 has been studied. In a wide temperature region and in the absence of a dditives such as steam, propane is a more effective reductant than pro pene; with propane and in the presence of oxygen reduction of nitric o xide to nitrogen approaches 100% above 600 K. The difference in effect iveness is due to the different degree of catalyst deactivation by car bonaceous deposits: more carbonaceous material is deposited from prope ne than from propane. Temperature-programmed oxidation shows that abov e 600 K the rate of oxidation of carbonaceous deposits by oxygen is si gnificant. The amount of such carbonaceous deposits is, therefore, low er when catalytic tests above 600 K are done in the presence of oxygen . At very high temperatures, the in situ volatilization of the deposit s by reaction with oxygen keeps the catalyst surface clean in the stea dy state of nitric oxide reduction.