Studies of NO Reduction with Ammonia Over Copper Species Deposited on MCM‐41 Nanospheres ‐ Experimental Evidence of Reaction Mechanism

Abstract

Nanospheres of MCM-41 were modified with copper by template ion-exchange (TIE) and cocondensation methods. In the samples modified by TIE, dispersion of copper was significantly improved by their post-treatment in ammonia solutions. Highly dispersed copper species were significantly more active in low-temperature NH 3 -SCR than CuO aggregates. Copper dispersed on silica MCM-41 catalytically operated at lower temperatures than copper deposited on silica-alumina MCM-41. The studies of reaction mechanism showed that ammonia and NO x species compete for these same adsorption sites (copper cations) and NH 3 can remove NO x from such sites. Dispersed copper species are more active in NO to NO 2 oxidation than CuO aggregates. Accumulation of oxidised NO x species in the absence of ammonia was more privileged on CuO aggregates. It is postulated that the main reaction pathway in the lowtemperature range is reaction of ammonia bounded to copper with NO x from gas phase or loosely bounded to the catalyst surface.