The effect of cations (NH4+, Na+, K+, and Ca2+) on chemical deactivation of commercial SCR catalyst by bromides

Alkali and alkaline-earth metals from fly ash have a significant deactivation effect on catalysts used for selective catalytic reduction of NOx by NH3 (NH3-SCR). Bromides are considered effective additives to improve Hg-0 oxidation on SCR catalysts. In this work, the effects of different bromides (NH4Br, NaBr, KBr, and CaBr2) on a commercial V2O5-WO3/TiO2 catalyst were studied. NOx conversion decreased significantly over the KBr-poisoned catalyst (denoted as L-KBr), while that over NaBr- and CaBr2-poisoned catalysts (denoted as L-NaBr and L-CaBr, respectivity) decreased to a lesser extent compared with the fresh sample. Poor N-2 selectivity was observed over L-NaBr, L-KBr and L-CaBr catalysts. The decrease in the ratio of chemisorbed oxygen to total surface oxygen (O-alpha/(O-alpha + O-beta+ O-w)), reducibility and surface acidity might contribute to the poor activity and N-2 selectivity over L-KBr catalyst. The increased O-alpha ratio was conducive to the enhanced reducibility of L-CaBr. Combined with enhanced surface acidity, this might offset the negative effect of the loss of active sites by CaBr2 covering. The overoxidation of NH3 and poor N-2 selectivity in NH3 oxidation should retard the SCR activity at high temperatures over L-CaBr catalyst. The increased basicity might contribute to increased NOx adsorption on L-KBr and L-CaBr catalysts. A correlation between the acid-basic and redox properties of bromide-poisoned catalysts and their catalytic properties is established. (C) 2018, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.