PNNL

Abstract

The effects of catalyst preparation on the NOx reduction activity of a series of Ba-Y,FAU zeolites were investigated using a simulated exhaust gas mixture. The introduction of Ba²?ions into Na-Y,FAU results in a large increase in their non-thermal plasma-assisted NOx reduction activity. The NOx reduction activities of Ba-Y,FAU catalysts were found to increase with increasing Ba²? concentration in the aqueous ion exchange solutions, which translated into increased Ba²?/Na² ratios in the resulting materials. Consecutive ion exchange procedures at a given Ba²?concentration in the aqueous solution, however, did not improve the NOx reduction activities of Ba-Y,FAU catalysts, i.e. the activity of the four times ion exchanged material was the same as that of the one that was ion exchanged only once. The reaction profiles for all of these Ba-Y,FAU catalysts were the same. In contrast, a significant increase in NOx reduction activity was observed when a 773K calcination step was implemented after each solution ion exchange. The reaction profile was also altered as a result of the ion exchange/calcination cycles. Calcination that followed each ion exchange step seems to further increase the Ba²?/Na? ratio in the zeolite, and in turn increases the NOx reduction activities of the catalysts prepared this way. Key differences in Na-, and Ba-Y catalysts were found in NO2 adsorption and TPD experiments. The amount of chemisorbed NO2 is about twice as high in Ba-Y than in Na-Y, and Ba-Y holds NOx much stronger than Na-Y.