Effect of W on the acidity and redox performance of the Cu0.02Fe0.2WaTiOx (a = 0.01, 0.02, 0.03) catalysts for NH3-SCR of NO

Abstract

A series of tungsten-modified Cu0.02Fe0.2TiOx catalysts (Cu0.02Fe0.2WaTiOx; a = 0.01, 0.02, and 0.03) was synthesized by sol-gel method. Their catalytic activities were investigated for the selective catalytic reduction (SCR) of NO with NH3, in the presence/absence of 5 vol.% H2O. The characterization techniques of XRD, BET, Raman, H2-TPR, NH3-TPD, XPS, in situ DRIFTS, and kinetic studies were used to reveal the effect of tungsten modification on the redox and acidity of the Cu0.02Fe0.2WaTiOx catalysts. The relationship among the species composition, acid property, and oxidation-reduction behavior of the Cu0.02Fe0.2WaTiOx catalysts was established. Results demonstrated that a moderate amount of tungsten doping can markedly enhance the specific surface area, improve the abundant Brönsted and Lewis acid sites, and tune the surface species composition, which all benefited high-performance catalysis. Water/sulfur resistance also improved because of the excellent acidity levels. Among the Cu0.02Fe0.2WaTiOx catalysts, Cu0.02Fe0.2W0.02TiOx showed the highest NO conversion, a wide reaction-temperature window (235–520 °C) with >90% NO conversion, high N2 selectivity, and high water/sulfur resistance even in the presence of 5 vol.% H2O. Moreover, Cu0.02Fe0.2W0.02TiOx retained its outstanding catalytic activity under a rather high gas hourly space velocity (GHSV) of 100,000 h−1. In conclusion, the combined effects of redox and sufficient acidities on catalytic activity played key roles in superior SCR performance and water/sulfur durability. Furthermore, the NH3-SCR reaction over Cu0.02Fe0.2W0.02TiOx may follow the Eley–Rideal reaction pathway according to the in situ DRIFTS and kinetic studies results.