不同阳离子(NH 4 + ,Na + ,K + ,Ca 2+ )溴化物对商用SCR催化剂化学中毒影响机制研究

Alkali and alkaline-earth metals from fly ash have a significant deactivation effect on catalysts used for selective catalytic reduction of NO x by NH 3 (NH 3 -SCR). Bromides are considered effective additives to improve Hg 0 oxidation on SCR catalysts. In this work, the effects of different bromides (NH 4 Br, NaBr, KBr, and CaBr 2 ) on a commercial V 2 O 5 -WO 3 /TiO 2 catalyst were studied. NO x conversion decreased significantly over the KBr-poisoned catalyst (denoted as L-KBr), while that over NaBr- and CaBr 2 -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 α /(O α + O β + O w )), reducibility and surface acidity might contribute to the poor activity and N 2 selectivity over L-KBr catalyst. The increased O α 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 CaBr 2 covering. The overoxidation of NH 3 and poor N 2 selectivity in NH 3 oxidation should retard the SCR activity at high temperatures over L-CaBr catalyst. The increased basicity might contribute to increased NO x 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.