Characterization And Mechanism Study Of V₂o₃/acf Catalysts For No Reduction With Nh₃at Law Temperature

Currently, the power plants of our country rely mainly on coalburning,which release NOX to the atmosphere. This kind of gas is themain precursor of forming acid rain and photochemical fog in theatmosphere, which will cause serious damage to the environment and thehuman's health. Therefore, it is urgent request to control the dischargeamount of NOX in the flue gas. One of the technologies that can effectivelycontrol the emissions of nitrogen oxides from these kinds of sources isselective catalytic reduction (SCR) of NOx with NH3. The purpose of thisstudy was to seek high-efficiency deNOx catalysts in low temperature,which also have sulfur resistance and long service life, and then toexamine the characterization and mechanisms of catalyst for NO reductionat low temperature.In this study, the catalysts were prepared by a solution-impregnationmethod. Activated carbon fiber (ACF) was modified with concentratednitric acid, and then loaded ammonium metavanadate and other activesubstances with HNO3-modified ACF as the carrier. The SCR performanceof V2O5/ACF catalyst was evaluated under varying reaction parameters, such as V₂O₅ loading, the reaction temperature, the volume ratio of NH3and NO, O₂ concentration and an introduction of 500ppm SO₂ intoinspection system. Results showed that the de-NO efficiency could beimproved greatly by ACF oxidized by 20% nitric acid and loaded by V₂O₅ .The catalyst of V₂O₅/ACF had higher de-NO efficiency when theconcentration ratio of NH3 and NO was 1.1, NO concentration was1000×10-6, O₂ concentration was 5%, and the reaction temperature was180℃. It also had a better SO₂ anti-poisoning ability, and the de-NOefficiency was only decreased from 52% to 50% when SO₂ introduced.In order to improve the de-NO efficiency and the catalyst stability ofV₂O₅/ACF, some other elements were introduced into the above catalyst(7% V₂O₅ /ACF). Owing to manganese catalyst has a high denitrificationperformance at low-temperature but poor sulfur resistance, the lowtemperaturecatalyst can be prepared with 7%V₂O₅/ACF catalystssupported Mn. The results showed that the high activity with 69.5% of de-NO efficiency could be obtained under the condition that the volume ratioof NH3 and was 1.1, the flue gas was mixed with 1000×10-6 NO, 1000×10-6NH3, 5% O₂ as well as the carrier gas N2, the reaction temperature was180℃, and the mass of 7%V-Mn/ACF catalyst was 1.0g. When 500ppmSO₂ introduced, the de-NO efficiency still can reach 62%, which showinga relatively strong sulfur anti-poisoning ability. Furthermore, in order toimprove the stability and service life of V₂O₅ /ACF, the rare earth elements (Ce and Zr), with a good stability characteristics, were doped into the 7%V2O5/ACF catalyst. Experimental results showed that 7%V-5% Ce/ACFcatalyst had better stability during denitrification process. The de-NOefficiency by 7%V-5%Ce/ACF was fluctuated from 58% to 54% whenreation time increased from 0 to 600min, which was better than thatdecresed from 52% to 43% by 7%V2O5/ACF.A series of experiments, such as BET surface area analysis, thermalgravimetric analysis (Thermal Gravity, TG), X-ray diffraction analysis(XRD), X-ray photoelectron spectroscopy (XPS), scanning electronmicroscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR)were conducted to estimate the selected catalysts'physical and chemicalcharacters. The results not only supported the datas obtained from thecompared experiments, but also provided some theoretic base of thecatalyst improvement.