Effect of acidic components (SO42- and WO3) on the surface acidity, redox ability and NH3-SCR activity of new CeO2-TiO2 nanoporous aerogel catalysts: A comparative study

Abstract

• New CeTiSO 4 2- and WO 3 -CeTi nanoporous aerogel catalysts for NH 3 -SCR reaction. • SO 4 2- modifies the nature of Ce species and increases the acidity of the CeTi aerogel. • WO 3 generates more reactive surface oxygen and active redox sites at CeTi surface. • WO 3 -CeTi displays the highest SCR activity at 320–400 °C (NO conversion > 90 %) • CeTiSO 4 2- exhibits superior SCR performance at 450–500 °C (NO conversion > 90 %) Selective catalytic reduction (SCR) of nitrogen oxide (NO) by ammonia (NH 3 ) was studied in this work over new sulfate (SO 4 2- ) or tungsta (WO 3 ) modified CeO 2 -TiO 2 aerogel catalysts. The catalytic systems were elaborated via sol gel method then characterized by: XRD, N 2 -Physisorption at 77 K, DRUV–vis, NH 3 -TPD and H 2 -TPR. It was revealed that the nature of acidic components influences differently the texture, surface oxygen concentration, acidity, reducibility and NH 3 -SCR activity of new Ce-based catalysts. Hence, the incorporation of sulfate modifies the nature of Ce species, improves their dispersion through the Ce-SO 4 2- interactions and, particularly, generates new strong acid sites which display superior catalytic performance at high temperature NO reduction (NO conversion into N 2 > 90 % between 450 and 500 °C over CeO 2 -TiO 2 -SO 4 2- catalyst). However, the addition of tungsta affects slightly the surface acidity of CeO 2 -TiO 2 catalyst but it induces the creation of more reactive surface oxygen and new redox sites at its surface (mainly due to the existence of W-Ce interactions) leading to highly active WO 3 -CeO 2 -TiO 2 system for the low temperature NH 3 -SCR reaction with above 90 % NO conversion into N 2 between 320 and 400 °C.