Effect of Various Acid Anions on Potassium Poisoning and the Mechanism of Commercial V₂O₅-WO₃/TiO₂ Catalysts for SCR of NO _x

The poisoning of K2O, KCl, and K2SO4 on commercial V2O5-WO3/TiO(2 )catalysts used for selective catalytic reduction (SCR) of NO x by NH3 was investigated, respectively. The degree of inactivation observed in these catalysts poisoned with different forms of potassium follows K2O approximate to KCl > K2SO4. At 350 C-degrees, the NO x conversion of the K2SO4 poisoning catalyst (0.5 wt % K) was 53%, while that of the K2O and KCl poisoning catalysts was only 2 and 4%, respectively. The atomic ratio of V5+/V4+ (0.76) and the proportion of adsorbed oxygen species (48%) on the surface of the K2SO4 poisoning sample were higher than those of the K2O poisoning sample (0.64, 36%) and the KCl poisoning sample (0.66, 36%). The above phenomena were due to the different poisoning mechanisms caused by K2O, KCl, and K2SO4. K2O decreased the number of Bronsted and Lewis acid sites and, moreover, reduced V5+ to V4+; K in KCl preferred to occupy Bronsted acid sites and Cl in KCl reduced Lewis acid sites. SO42- in K(2)SO(4 )counteracted the impact of K on the surface acid sites and V5+ of the poisoned catalyst and generated new Bronsted acid sites.