Preparation Of De-NOx Catalysts Containing V-W And Their Application In Selective Catalytic Reduction Of NO

Flue gas denitrification is one of effective ways to control NOx emissions from coal-fired power plants. Because of the high efficiency, selectivity, stability and reliability, selective catalytic reduction (SCR) technology has been widely used in the de-NOx processing. Catalyst is the key technology, currently, in China most of the SCR catalysts are imported and monolithic catalysts which used TiO₂ as carrier, TiO₂ account for about 80% of the total weight of catalysts, there are problems like high costs and insufficient use of highly active component in this method.In order to improve the shortcomings, vanadium-based catalysts are modified by WO₃ to investigate the preparation methods and de-NOx applications of tungsten supported vanadium based catalysts. Meanwhile, there are preliminary studies about the performances of supported heteropoly compound catalysts. Respectively, a composite support TiO₂/honeycomb cordierite modified by V₂O₅-WO₃ has been prepared via static impregnation method and used for the preparation of V₂O₅-WO₃ based monolith SCR catalyst, and particle catalysts were prepared by impregnated V₂O₅-WO₃ on TiO₂ powder and then mold it with Al₂O₃. The X-ray diffraction method, X-ray photoelectron spectroscopy and BET technology were applied for catalyst characterization, and the activity for NO catalytic removal by NH₃ has been evaluated. During this process, the effect of preparation methods, temperature and a number of factors to flue gas conditions have been researched.The results showed that a lower NO conversion rate have been evaluated, because of surfaces of the particle catalysts do not have good diffusion conditions for the reaction gases. The influences of impregnation process on SCR activities indicated that the existence of oxalic acid in precursor solution decreased the SCR activity of the resulted catalyst, which is deduced as the major effect of the distribution and accumulation of V₂O₅ on the surface of catalyst. The effects of temperature, initial NO concentration, space velocity and NH₃/NO ratio on the SCR reaction have been investigated. The prepared catalyst showed a good activity, the NO conversion can be more than 97% under the condition of 350℃⁴00℃, NH₃/NO of 0.8¹ and the space velocity of 10000 h-1. The V₂O₅-WO₃/TiO₂/CC catalyst was not obviously inhibited the oxidation of SO2, when CaO was deposited on catalyst, it will undermine the structure of the surface, resulting in lower activity. The Keggin structure is maintained when heteropoly compound is immobilized on TiO₂/CC surface. When the HPC was loaded less than 20%, the main reason of the denitrification activity seems to be the amorphous phase which formed by the strong interaction between HPC and TiO₂.The catalyst was evaluated higher activity when there were more vanadium atoms in heteropoly acid anions. The active center of catalyst was involved in vanadium species.