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Nature of SO3 poisoning on Cu/SAPO-34 SCR catalysts

Shen, Meiqing, Zhang, Yun, Wang, Jianqiang, Wang, Chen, Wang, Jun
Journal of catalysis 2018 v.358 pp. 277-286
aluminum, aluminum sulfate, catalysts, copper, copper sulfate, nitrogen oxides, oxidation, sulfur oxides
To reveal the nature of SO3 poisoning of Cu/SAPO-34 selective catalytic reduction (SCR) catalysts, CHA structure, copper species, and NOx conversion were probed. The Cu/SAPO-34 catalyst was treated with different ratios of SO3 to SOx (0, 6, 13, and 20%) at 250 °C. The breakage of SiO(H)Al bonds takes place and leads to aluminum sulfate formation upon SOx sulfation. More isolated Cu²⁺ transform to copper sulfate with an increment of the SO3/SOx ratio. Catalysts poisoned with SOx show lower NOx conversion at 150–300 °C, the reason for which is a reduced number of isolated Cu²⁺ sites, as their turnover frequencies (TOFs) are identical. The loss of isolated Cu²⁺ and SiO(H)Al bonds is responsible for the inferior activity above 300 °C. The presence of SO3 cannot be ignored because of the irreversible reaction with Cu/SAPO-34 when diesel oxidation catalysts are applied upstream of the SCR.