Effect of pore structure of TiO₂ on the SO₂ poisoning over V₂O₅/TiO₂ catalysts for selective catalytic reduction of NO_x with NH₃

We applied 5 wt% V₂O₅/TiO₂ catalysts supported on two types of TiO₂ having distinctive pore structure, mesopore (DT-51) and micropore (microporous TiO₂; micro) to selective catalytic reduction of NO_x with NH₃ (NH₃ SCR) to investigate the effect of pore structure of TiO₂ on sulfur poisoning. During the SCR reaction in the presence SO₂ for 12 h, 5 wt% VT (DT-51) showed more drastic decrease in activity than 5 wt% VT (micro). Larger amount of SO₂ was desorbed over the post-reaction 5 wt% VT (DT-51) sample during the temperature programmed decomposition which was consistent with the elemental analysis. Such larger amount of sulfate formation could be explained by the more active SO₂ oxidation on the 5 wt% VT (DT-51) than 5 wt% VT (micro) because SO₂ oxidation is the key step to generate sulfate species on the catalysts. It could be ascribed to the difference in the tendency of oxidation reaction affected by the vanadium species, since it was known that more V–O–V bonds existed on the surface of 5 wt% VT (DT-51) having bulk-like VO_x species whereas V[dbnd]O bonds were prevalent on 5 wt% VT (micro) having more dispersed VO_x. In situ FT-IR results also provided the evidence about the formation of ammonium bisulfate through strong interaction between NH₃ and SO₃ on 5 wt% VT (DT-51), although 5 wt% VT (micro) did not. It can be summarized that the different vanadium species determined by the pore structure of TiO₂ have a significant effect on the sulfur poisoning during SCR reaction.