Nonthermal plasma-assisted catalytic NOx reduction over Ba-Y,FAU: the effect of catalyst preparation

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 nonthermal 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+/Na+ 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 773 K calcination step was implemented after each solution ion exchange. The reaction profile was also altered as a result of the ion-exchange/calci nation 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,FAU catalysts were found in NO2 adsorption and TPD experiments. The amount of chemisorbed NO2 is about twice as high in Ba-Y,FAU than in Na-Y,FAU, and Ba-Y,FAU holds NOx much stronger than Na-Y,FAU. Published by Elsevier Inc