Insights into the poisoning mechanisms of zinc compounds on V2O5-WO3/TiO2 catalyst for NH3-SCR: Effect of the anion species

Abstract

V2O5-WO3/TiO2 is commercial catalyst for controlling NOx emissions from municipal solid waste incineration by NH3 Selective Catalytic Reduction (NH3-SCR). However, the flue gas contains a large amount of zinc compounds, which would lead to the deactivation of the catalyst. Therefore, in this work we studied the effect of different zinc species (ZnSO4, ZnO and ZnCl2) on a V2O5-WO3/TiO2 catalyst, investigating the deactivation mechanism. The different compounds negatively affected the activity in the order ZnCl2 >ZnO>ZnSO4, indicating an important influence of the anions. The characterization results points to the evidence that Zn2+ would interact with the active V-OH and OV structure, reducing the content of active Brønsted acid sites and influencing the V5+⇄V4+ redox cycle, as well as inhibiting the activation of NH3. Cl- would interact with V-OH, possibly forming V-Cl and also suppress the formation and mobility of surface adsorbed oxygen, which further exacerbates the negative effect. On the other hand, SO42- would weaken the poisoning effect of Zn2+ by a strong anion/cation interaction and likely form V-O-SO3OH by reaction with V-OH, which is proposed to be an active Brønsted acid site able to active NH3 in the NH3-SCR reaction. Finally, the introduction of Zn2+ increased the adsorption of NOx species to form a stable and inactive nitro species, the formation of which is inhibited by the presence of SO42-.