The promotional effect of HSiW doping on CeNb for NH3 selective catalytic reduction of NOx

Abstract

The selective catalytic reduction of NO by NH₃ was investigated using a series of CeNbW_x catalysts synthesised by co-precipitation and characterised in different ways. Experimental investigation demonstrated that doping with HSiW significantly enhanced the activity of the CeNb catalysts. The CeNbW₂₀ catalyst exhibited the best NH₃-SCR activity and strong tolerance to H₂O and SO₂. This was mainly attributed to the introduction of a certain amount of HSiW, which endowed the CeNbW₂₀ catalyst with more acidic sites, oxygen vacancies, chemisorbed oxygen species and Ce³⁺/Ce⁴⁺ redox pairs. In situ DRIFT results indicated that HSiW modification on the surface of CeNb provided additional acidic and surface-active sites, facilitating the adsorption of NO_x and NH₃ species. HSiW-doped CeNbW₂₀ exhibited enhanced E–R and L–H mechanism reaction rates, yielding significantly higher NO_x conversion rates than CeNb at 175–275 °C. This stemmed from the “fast SCR” pathway, which demonstrated markedly higher low-temperature reaction rates and dominated the reaction mechanism in CeNbW₂₀. Raman and XPS analyses revealed the highest concentrations of oxygen vacancies and O_α ratios within this catalyst. Both features promoted the oxidation of NO to NO₂, supplying ample intermediates that further substantiate the dominance of the “fast SCR” pathway.