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

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 deNO_x 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 deNO_x 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 deNO_x 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 deNO_x efficiency of the best compatibility of the five ions doping was TiW_0.1O_x-630 > TiMo_0.12O_x-630 > TiAl_0.11O_x-487 > TiZr_0.06O_x-538 ≈ TiSi_0.04O_x-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 TiW_0.1O_x-630 ≈ TiMo_0.12O_x-630 > TiSi_0.04O_x-582 > TiZr_0.06O_x-538 > TiAl_0.11O_x-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 (1 0 1) crystal plane in TiW_0.1O_x-630 was the highest, which was beneficial to NH₃-SCR of NO_x. Furthermore, the concentration of chemisorbed oxygen O_α was in the order of TiW_0.1O_x-630 > TiMo_0.12O_x-630 > TiAl_0.11O_x-487 > TiZr_0.06O_x-538 > TiSi_0.04O_x-582. The higher the concentration of O_α is, the more conducive to the oxidation of NO to NO₂ and the promotion of NH₃ adsorption and dehydrogenation oxidation.