Synergy of KCl and Hg^el on selective catalytic reduction of NO with NH₃ over V₂O₅-WO₃/TiO₂ catalysts

The synergy effects of KCl and Hg^el on selective catalytic reduction of NO with NH₃ over V₂O₅-WO₃/TiO₂ catalysts were studied. KCl was doped by impregnation, and Hg^el was added by dry-gas adsorption method. Catalytic activity was tested under the condition of simulated flue gas. XRD, SEM, BET, FT-IR, NH₃-TPD and NH₃ chemisorption were used to characterize the changes of the phase composition, microstructure, surface acidity and functional groups. Deactivation was observed obviously for the catalysts of KCl loadings, while Hg^el showed weakly negative effect. KCl caused agglomeration to the catalysts, but Hg^el did not. For KCl poisoning catalysts, Brønsted acid sites were neutralized evidently and it was related to the KCl loading amounts. KCl could react with V-OH to ultimately form -V-O-K and Cl-V-O-K, resulting in the deactivation of the active sites substantially. Synergy effect was observed that Hg^el could increase the amount of chemisorbed NH₃ and retard the deactivation caused by KCl. Hg^el would combine with Cl that introduced from KCl to form HgCl or HgCl₂, and partly replace K. Then, -V-O⋯Hg or -V-O-Hg-Cl produced, causing the amount of adsorbed NH₃ increased due to their competition for the active sites. Based on the experimental results and theoretical analysis, the probable synergy mechanism model of KCl and Hg^el poisoning V₂O₅-WO₃/TiO₂ catalysts was proposed.