Effect of co-existing SO
2 on the catalytic activity of Sn supported alumina catalyst was investigated for the reduction of NO in the presence of high concentrations of oxygen and water vapor. Although the catalytic activity decreased at the initial stage of the activity test in the presence of SO
2 over Al
2O
3, Sn/Al
2O
3 and Co/Al
2O
3, a stable NO conversion was observed afterwards. The steady state catalytic activity was in the order of Sn/Al
2O
3 > Co/Al
2O
3 > Al
2O
3. The catalytic activity of Sn/Al
2O
3 for NO
x reduction in the low temperature region was increased with increasing Sn loading. 5 wt%Sn/Al
2O
3 showed the highest activity among Sn supported alumina catalysts. The accumulation of sulfur was observed on the spent catalyst, and its amount was closely related to the co-existing SO
2 concentration and NO
x conversion level. XPS and IR spectra measurements suggested the formation of Al
2 (SO
4)
3-like species on the catalyst surface. The efficiency of the reducing agent was in the following order methanol > ethanol > propylene > propane. In particular, methanol reduced NO most effectively on Sn/Al
2O
3.
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