Investigation On The Preparation And Properties Of Si Doped V₂O₅/TiO₂Catalyst For Low And Moderate Temperature SCR

With the development of power industry in China, the discharges of polluted gas and dust released from coal-based power plant increase every year. Among the polluted gas, the discharges of NOx catch our eye especially. SCR technique is the traditional way to remove NOx by transfer it into the non-polluted gas N2. However, the removal efficiency of NOx will decrease with the existence of dust and SO2in high concentration. Utill now, the direction of the attempt and exploration is that how to solve the above problem. The paper studied the catalytic performance of new Si-doped V2O5/TiO2catalyst, aiming to improve the activity and the ability of toxin immunity. Moreover, the best preparation conditions of the catalysts, the best process conditions of the reaction and the catalytic mechanism of the reaction are also investigated.The performance of catalysts was investigated in a catalytic fixed-bed reactor. The preparation conditions contained preparation method of the catalysts, the effect of Si doping amount and the calcination temperature were explored, and finally the best preparation conditions of the catalysts were obtained. The results showed that under the experimental conditions of GHSV41000h-1,5%O2(volume fraction), NO concentration600×10-6,[NH3]/[NO] ratio1.2, and when [Si]/[Ti] was0.2(mole ratio), V loading was1%(mass fraction) and the calcination temperature was350℃, the best catalysts were obtained. While the reaction temperature was300℃, the best NO conversion reached94%, about30%higher than that on V2O5/TiO2.The characterizations of XRD, FT-IR, BET, TEM, Raman, XPS and EPR were explored to analyze the crystal structure, surface area, grain size, electronic structure and surface properties of catalysts. The results showed that Si4+was doped into the lattice of TiO2, and replaced of partial Ti4+to make the warping of TiO2lattice. Hence, the structure of the catalytsts changed from the micropores to the mesopores, leading to the increase of the surface area and the dispersion of V2O5on the surface of the support. Meanwhile, the doping of Si benefitted for the restrained-process of transfer from anatase TiO2to rutile TiO2, thus increasing the catalytic activity. Moreover, the lattice defects were generated while Si4+entered into the TiO2lattice, and the caused lattice defects were conducive to the generation of oxygen vacancies. The oxygen vacancies could adsorb O2to produce the superoxide radicals, which could oxidize NO to the reactive intermediates NO3-and NO2-, thus enhancing the rate of catalytic reaction and improving the catalytic activity. The effects of operating conditions such as the concentration of O2, GHSV,[NH3]/[NO] and the inlet concentration of NO on NO conversion over Si-doped V2O5/TiO2were studied. The effects of SO2and H2O on NO conversion were also investigated. The results showed that under the experimental conditions of GHSV41000h-1,O25%, NO concentration600×10-6,[NH3]/[NO]1.2, the NO conversion on Si-doped V2O5/TiO2could reach over94%at300℃What’s more, compared to pure V2O5/TiO2, the NO conversion on Si-doped V2O5/TiO2reduced11%and8%separately under the individual addition of4%H2O or600ppm SO2, far below that on pure V2O5/TiO2.