Crystal orientation-dependent activity of tungsten-based catalysts for selective catalytic reduction of NOx with NH3

Abstract Hexagonal WO 3 crystals with [1 1 0] and [0 0 1] orientations (denoted as H-110 & H-001) were synthesized and impregnated with 5 wt% V 2 O 5 for NH 3 -SCR catalysis. H-110 with dominant (0 0 1) exposed facet possesses 72% NO x conversion at 400 °C while H-001 with dominant (1 0 0) exposed facet only achieves 17%. The maximal NO x conversion over V/H-110 and V/H-001 catalysts was enhanced to 96% and 47%, respectively. The catalysts were characterized by H 2 temperature-programmed reduction (TPR), temperature-programmed desorption (TPD) of NH 3 , X-ray photoelectron spectroscopy (XPS), Raman, ultraviolet-visible (UV-vis) and diffuse reflection infrared Fourier transform (DRIFT) spectroscopy. The more coordinative unsaturated W 6+ atoms on (0 0 1) facet generated more acid sites and NH 3 was more strongly adsorbed on H-110 surface. The better match relationship between vanadia and WO 3 (0 0 1) exposed facets led to the formation of more polymeric vanadates on V/H-110 catalyst. The higher proportioned V 4+ and chemisorbed oxygen on V/H-110 catalyst also facilitated NH 3 -SCR reaction.