High-temperature selective reduction of NOx into N2 catalyzed by different ion-doped titania

Abstract

The active titanium-based composite oxide carrier with strong thermal stability and surface acidity is the key to ensure the steady operation of high-temperature deNOx catalyst for gas-fired exhaust. In this paper, W6+, Zr4+, Mo6+, Al3+, Si4+, Cu2+, Co2+, Mn2+, Fe3+ doped titanium-based composite oxides were synthesized by sol–gel method. The effects of ion species, doping amount, calcination temperature on NH3-SCR deNOx efficiency and resistance to water vapor and SO2 poisoning were investigated. Results showed that the Cu2+, Co2+, Mn2+, Fe3+ doped titanium-based composite oxides calcined at 630 °C had negligible deNOx activity, while the doping of W6+, Zr4+, Mo6+, Al3+ and Si4+ improved the NH3-SCR activity and anti-water vapor and SO2 poisoning of titanium-based composite oxide. The deNOx efficiency of the best compatibility of the five ions doping was TiW0.1Ox-630 > TiMo0.12Ox-630 > TiAl0.11Ox-487 > TiZr0.06Ox-538 ≈ TiSi0.04Ox-582, which was consistent with the order of total acid amount. The order of resistance to water vapor and SO2 poisoning and resistance to high temperature thermal shock was TiW0.1Ox-630 ≈ TiMo0.12Ox-630 > TiSi0.04Ox-582 > TiZr0.06Ox-538 > TiAl0.11Ox-487. Doping of five ions inhibited the transformation of anatase TiO2 to rutile TiO2 in different degrees. Among them, W6+ doping had the best inhibitory effect and the exposure ratio of TiO2 (101) crystal plane in TiW0.1Ox-630 was the highest, which was beneficial to NH3-SCR of NOx. Furthermore, the concentration of chemisorbed oxygen Oα was in the order of TiW0.1Ox-630 > TiMo0.12Ox-630 > TiAl0.11Ox-487 > TiZr0.06Ox-538 > TiSi0.04Ox-582. The higher the concentration of Oα is, the more conducive to the oxidation of NO to NO2 and the promotion of NH3 adsorption and dehydrogenation oxidation.