Promotional effect of nickel doping on the W/Fe2O3 catalyst for selective catalytic reduction of NOx with NH3

Abstract

Herein, nickel species have been used to optimize the NH3-SCR activity of the tungsten-impregnated 7.5W/Fe2O3 catalyst. The doping of nickel species helps to the formation of spinel NiFe2O4 and also promotes the growth of γ-Fe2O3 and α-Fe2O3 crystals in Fe2O3 supports fabricated via the anaerobic solution followed by the chemical oxidization of hydrogen peroxide, although it decreases the BET surface areas and pore volumes of supports sharply. However, the induced interaction between the formed spinel NiFe2O4 and the impregnated tungsten species depresses the disadvantageous effect of the high-temperature calcination on the formation/growth of γ-Fe2O3/α-Fe2O3 crystals in 7.5W/Fe2O3 catalysts and the collapse of the pore structure of catalyst effectively. Furthermore, the formation of spinel NiFe2O4 after nickel doping contributes to promoting the redox equilibrium of Fe3++Ni2+ ↔ Fe2++Ni3+ via the electronic inductive effect between Fe and Ni ions, thereby improves the surface molar ratio of Oα/(Oα+Oβ), the redox properties as well as the higher molar ratio of Brønsted/Lewis acid sites formed on the surface of 7.5W/Fe2O3 catalyst, but nickel doping is not conducive to the bulk oxygen vacancies of catalyst. Interestingly, the decrease of glucose/urea molar ratio from 10:20 to 7.5:20 strengthens the optimized role of nickel doping on the physical-chemical properties of 7.5W/Fe2O3 catalyst, and there exists a synergetic promotional effect of nickel doping and glucose dosage on its NH3-SCR activity.