Selective catalytic reduction of NOx with NH3 over short-range ordered W[sbnd]O[sbnd]Fe structures with high thermal stability

Abstract

The selective catalytic reduction (SCR) of NOx with NH3 was studied over poorly-crystalline WFe composite oxides (WaFeOx). The short-range order present within the WOFe structure was found to be responsible for the excellent SCR activity, in which the strong atomic-level interaction between Fe and W atoms promoted the formation of both Lewis and Brønsted acidity. The WOFe structure existed as amorphous overlayers, approximately 2 nm thick over the surface of crystalline particles after high-temperature aging as shown by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). After treatment at 800 °C for 5 h, the WaFeOx catalysts still showed almost 100% NO conversion in the range 300–450 °C with 100% N2 selectivity, despite the loss in surface area. This resistance to the impacts of high temperature ageing guarantees high activity of SCR catalysts which often suffer during high-temperature excursions as in the case of diesel exhaust due to diesel particulate filter (DPF) regeneration.