Promoting effect of Nb doping on NH₃-SCR of NO_x at high temperature over Zr₅W₁O_x

Driven by the strategy of reducing pollution and CO₂ emissions, high-temperature deNO_x has become a major demand for NO_x treatment of gas exhaust such as gas power generation. This paper intends to further improve the high-temperature deNO_x performance of Zr₅W₁O_x by Nb doping. A series of Zr₅W₁Nb_aO_x with different Nb contents were synthesized by sol–gel method for NH₃-SCR of NO. Combined with characterization analysis of FE-SEM, XRD, XPS, N₂ adsorption–desorption, H₂-TPR, NH₃-TPD and in situ DRIFTS, the influence mechanism of Nb incorporation was discussed. The results showed that the addition of Nb promoted the deNO_x activity temperature window of the catalyst to shift towards high temperature by 30 ℃. Among them, Zr₅W₁Nb_0.09O_x exhibited better high-temperature NH₃-SCR deNO_x activity, and its efficiency of NH₃-SCR of NO reached over 90 % within 480–683 ℃ at a space velocity of 50000 h⁻¹; Moreover, under the coexistence of 5 vol% water vapor and 200 ppm SO₂, its deNO_x activity did not decrease, exhibiting excellent resistance to water vapor and SO₂ poisoning. Analysis showed that there were both Lewis and Brønsted acid sites on the surface of Zr₅W₁Nb_0.09O_x. The addition of Nb increased the strength of the medium and strong acid sites of the catalyst, enhanced its effective adsorption of NH₃ molecules, and broadened the high-temperature deNO_x activity temperature window. in situ DRIFTS analysis confirmed that the high-temperature NH₃-SCR deNO_x reaction of Zr₅W₁Nb_0.09O_x followed both Eley-Rideal and Langmuir-Hinshelwood mechanisms.