K+ deactivation of V2O5-WO3/TiO2 catalyst during selective catalytic reduction of NO with NH3: Effect of vanadium content.

• 3 V catalyst presents the best performance for both NO x reduction and K+ resistance ability. • Increasing V 2 O 5 content reduces the Lewis acid sites, but increases the amount of BrØnsted acid sites. • Isolated vanadyl (V = O) are advantageous to high-temperature catalytic activity. • Polymeric vanadia species present priority to ammonia adsorption and K+ occupation. The effect of vanadium content on the resistance to K+ deactivation of V 2 O 5 -WO 3 /TiO 2 SCR catalyst in biomass-fired flue gas was investigated. Catalytic activity and ammonia oxidation were measured, and the properties of fresh and K+-deactivated catalysts were characterized by XRD, N 2 physisorption, H 2 -TPR, NH 3 -TPD and NH 3 -DRIFT. The BET surface area decreases with increased vanadium content for both fresh and K+-poisoned samples, but it is not responsible for catalyst deactivation. Ammonia oxidation starts from 300 °C and becomes more important with increasing vanadium content and at higher temperature. K+ can inhibit ammonia oxidation, but inactivates the newly generated NO 2 to be reduced. The increase of vanadium content reduces mainly the Lewis acid sites, while the amount of BrØnsted acid sites increases. Monomeric and polymeric vanadium are the dominant species on the TiO 2 support, and the amount of isolated vanadyl (V = O) species decreases with V 2 O 5 content while the amount of V-OH species in polymeric vanadia increases. Isolated vanadyl species are advantageous to high-temperature catalytic activity while polymeric vanadia species increase ammonia and K+ adsorption. The (3 wt% V 2 O 5)-WO 3 /TiO 2 catalyst shows the best performance for both NO reduction and K+ resistance due to it containing both monomeric and polymeric vanadia species (or V = O and V-OH). Catalysts with 3 wt% V 2 O 5 are preferable for flue gases with high alkali metal contents. Finally, the mechanism of reaction for different vanadium contents and corresponding K+-poisoning are also discussed. [ABSTRACT FROM AUTHOR]