The Role of Lewis and Brønsted Acid Sites in NO Reduction with NH3 on Sulfur Modified TiO2-Supported V2O5 Catalyst

V 2 O 5 /S-doped TiO 2 was prepared by the sol-gel and impregnation methods. The adsorption of NO, NH 3 , and O 2 over the catalyst was studied by in situ DRIFTS spectroscopy to elucidate the reaction mechanism of the low-temperature selective catalytic reduction of NO with NH 3 . Exposing the catalyst to O 2 and NO, three types of nitrates species appeared on the surface. The introduction of S to TiO 2 could generate large amounts of acid sites for ammonia adsorption on the catalyst, which was believed to be an important role in the SCR reaction and hereby improved the catalytic activity. The results indicated two possible SCR reaction pathways for catalyst. One was that NO was absorbed to form nitrite species, which could react with NH 3 on Lewis acid sites, producing N 2 and H 2 O. Another way was that NH 3 was adsorbed, then reacted with gas phase NO (E–R) and nitrite intermediates on the surface (L–H).