Study On Activity And SO₂Tolerance Over Modified VO_x/TiO₂for Low-Temperaure Selective Of NO_x

NOX is one of the major source of air pollution, which has caused great damage to people’s health and environment, so the control of NOX emission is the key to the successful management of environment. Selective Catalytic Reduction (SCR) of NOx by using NH3as a reductant is considered to be one of the most effective and stable processes to stack gases from stationary sources. In recent years, it has been a hot topic that the research and development of the highly active catalysts which can be used for low-temperature SCR that works downstream of the electrostatic precipitator and desulfurization. Recently the following problems are the main obstacle of the industrial application of low-temperature SCR technology:low catalytic activity and the poor SO2resistance performance. Compared to other catalysts systems, vanadium-based catalysts system is provided with the merits of maturity of production process and SO2resistance. In our previous study, vanadium catalysts are modified by transition metal oxides to get higher denitration activity in the low-temperature condition and excellent SO2resistance.Firstly, VOx-based catalysts were modified by Copper oxides. It was found that the activity was considerably enhanced with Cu additive, Cuo.2-Vo.8/Ti02showed the highest activity and more than90%NOX conversion at180℃. When100ppm SO2was added to the gas flue, the catalyst showed a certain sulfur resistance, but the SCR activity decreased slowly after the12h’s experimental time. The various physico-chemical techniques were used to characterize the catalysts. The results reveal that a little NH4HSO4and CuSCU are formed on surface of the reacted catalyst Cuo.2-Vo.8/Ti02in the short time (4h) exposure of SO2, and vanadium oxides could reduce the effect of SO2to the catalyst, especially to the Copper Oxide. However, a mass of the sulphates may form deposits on the catalytic surface after12h or more. As the active sites on surface gradually be held, the catalytic activity gradually declined.Secondly, the catalytic activity and tolerance to sulfur dioxide of VOx/TiO2modified by Cr ions were studied. No matter SCR activity or sulfur resistance, the results of Cr-V/TiO2catalysts show better than that modified by Cu ions. It was found that the Cr0.2-V0.8/TiO2showed the highest activity of87.5%of NOX conversion at160℃. When100ppm SO2was added to the gas flue, the deactivation did not occur within12h for Cro.2-Vo.8/Ti02catalyst, which gave a good sulfur resistance. The results of the various physico-chemical techniques show that Cr0.2-V0.8/TiO2catalyst has higher specific surface area with more weak acidities on it. Meanwhile it is the interaction of Cr-V that increases the sub-stable state of V ions and enhances the redox ability. The increase of lattice oxygen species and oxygen vacancies on the surface of Cr0.2-V0.8/TiO2catalyst is a great help to the activation of NH3and NO adsorption which is good for the SCR reaction in the low temperatures.