Comparative Studies of Effects of Vapor- and Liquid-Phase AsO on Catalytic Behaviors of VO-WO/TiO Catalysts for NH-SCR.

The role of vapor- and liquid-phase AsO in deactivating commercial VO-WO/TiO catalyst during the NH-selective catalytic reduction (SCR) process was explored and compared. AsO was loaded via vapor deposition (As(vap)) and the wet impregnation (As(imp)) method, respectively. Results demonstrated that the poisoning extent of vapor arsenic was much stronger than in the liquid state. Differences in As distribution on the catalyst surface was one of the main causes. Most vapor AsO could be oxidized to AsO, which underwent stacking and formed a dense covering layer on the catalyst surface. In comparison, liquid AsO could also be oxidized but distributed uniformly and did not change the catalyst pore structure. Loading arsenic would destroy the V-OH and V=O active sites of the catalyst, and less reactive As-OH was generated. Catalyst oxidizability was also enhanced, resulting in NH oxidation enhancement, decreased N selectivity, and a decline in SCR activity. Importantly, the intermediate of NH oxidation, NH-amide, also could react with NO + O, and more NO was generated on the poisoned catalyst during the SCR process, especially on As(imp). Finally, two mechanisms of arsenic poisoning were proposed, in which the role of vapor and liquid AsO over the VO-WO/TiO catalyst was compared.