Cu-Cr-Ce/TiO₂-SiO₂ And CuSO₄-V₂O₅/TiO₂ Catalysts For Catalytic Reduction Of NO_x At Low Temperature

NO_x is one of the major air pollutants, which jeopardize the ecological environment and human health badly. The selective catalytic reduction (SCR) of NO_x with NH₃ is used widely to reduce nitrogen oxide emissions from stationary sources. V₂O₅-(WO₃)/TiO₂ catalyst operate at temperature above 350℃, where catalyst was eroded, wore and contaminated by high concentrations of dust and SO₂, so its life expectancy is shortened. Therefore developing the low-temperature SCR catalyst which can configure SCR device following with the flue gas desulfurization (FGD) and match with our existing boiler system, especially low temperature SCR catalyst of high activity and high resistance to SO₂, H₂O poisoning properties is of great significance.TiO₂-SiO₂ (TS) support was prepared by the co-precipitation method and a novel Cu-Cr-Ce/TS catalyst was prepared by impregnation method. The effects of preparation conditions including active component ratio, loading along with calcination temperature and operating conditions as reaction temperature, NH₃/NO_x molar ratio, NO_x input concentrations, space velocity and O₂ concentrations on activity of catalyst Cu-Cr-Ce/TS for selective catalytic reduction of nitric oxides by NH₃ at low temperature were investigated. The influences of H₂O, SO₂ were also discussed. The results showed that catalyst with n(Cu):n(Cr):n(Ce) 1:1:3, loading 30%, calcination temperature 450℃? performed high NO_x conversion of over 98.9% at the conditions of NO_x input concentrations 0.08%, O₂ concentrations 6%, space velocity 5000 h^-1, reaction temperature 180℃and NH₃/NO_x molar ratio 1.1. NO_x conversion could be kept over 98% in 35 h stability test. The catalyst activity was unaffected in a separate anti-water experiment above 200℃, while at the same time in a separate anti-sulfur or sulfur and water resistance test, the catalyst was poisoned quickly, and the activity was unrecoverable.The catalysts were characterized by specific surface area (BET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry (TG). Results indicated that when Cu and Cr existed at the same time, there would generate CuCr₂O₄ spinel, which had some role on promoting the catalytic activity. The reasons for catalyst poisoning were: (1) the formation of ammonium sulfate salt covered catalyst active sites; (2) the sulfation of catalyst active component.The low-temperature activity and resistance ability to sulfur and water of CuSO₄-V₂O₅/TiO₂ catalyst was also study preliminarily. Results showed that when the loading of CuSO₄ and V₂O₅ were 5%, calcination temperature was 350℃, reaction temperature was 210℃, the NO_x conversion rate was 97.3%. The catalyst had good resistance to water or sulfur separately and can maintain high activity for a long time at 220℃. When the catalyst was examined under sulfur and water simultaneously condition, its conversion rate started to decline after 6 h because of the formation of ammonium sulfate salt. The conversion rate was less than 40% after 22 h. The results also suggested that the presence of CuSO₄ can improve the catalyst own performance of resistance to sulfur and water.