Preparation And Properties Of V-W-Ti DeNOx Catalyst For Selective Catalytic Reduction Of NOx With NH₃

The flue gas de-NOx technology is one of the effective methods of controllingNOx emission of coal-fired power plant. In flue gas denitrification technology, becauseof high denitration efficiency, good selectivity, stable and reliable running, selectivecatalytic reduction （SCR） technology has been widely used. Catalyst is the key elmentof the whole SCR system. Effects of the whole SCR system were directly affected bycatalytic activities of catalyst. Most of the SCR catalysts are imported in China. TiO₂account is about80%of the total weight of catalysts in monolithic catalysts. There arestill some problems. These problems involve high costs and underutilization of activecomponent. Monolithic catalysts was prepared by means of substrate that is activecomponents and carrier mixed with adhesives, pore-forming agent and lubricants, thenand kneading, extrusion moulding, drying and calcining. However, catalytic activity stillexists varying degrees reducing in the process of the catalyst forming.In order to make up for the deficiency, a series of V₂O₅-WO₃/TiO₂（VWTi）catalysts was prepared by impregnation method for the selective catalytic reduction（SCR）of NO with NH₃. In VWTi catalyst, analytical reagent TiO₂that made in chinais carrier, V₂O₅is active ingredient and WO₃is secondary catalyst. Effect of the quantityof V₂O₅and WO₃on the catalyst was investigated. Meanwhile, A V₂O₅-WO₃/TiO₂（VWTi） monolithic catalyst was prepared using different molding agent （PAM, PVA andKaolin）. These catalysts were characterized by BET, X-ray diffraction （XRD）, scanningelectron microscope （SEM）, X-ray fluorescence（XRF） techniques. Under the differentconditions of simulated flue gas, the actual DeNOx performance was evaluated bycatalyst activity evaluation device. During this process, the effect of preparationmethods, molding agent and a number of factors（temperature, NO concentration, spacevelocity, NH₃/NO and SO₂, etc.） were researched.Under the condition of vanadium loading within0.4¹wt.%, WO₃of8wt.%, O₂concentration greater than1%, NH₃/NO of0.8¹, space velocity （SV） of10000h-1, theresults showed that the NO conversion of the VWTi catalyst can be more than85%inthe temperature range of300⁴00℃. And VWTi catalyst has well ability to adapt todifferent initial NO concentrations; Addition of MoO₃has little contribution forincreasing of DeNOx activity of VW8Ti catalysts. However, the thermal stability andsulfur resistant performance of the catalyst are improved; The organic molding agent that appropriate molecular weight is conducive to hold BET specific surface area of thecatalyst. Meanwhile, the mechanical strength of catalyst was increased. The mechanicalstrength of catalyst was strengthened significantly by addition of inorganic moldingagent. But the crystal morphology of catalyst carrier was larger influenced; With theincrease of Kaolin and PAM, catalytic activities for SCR reactions decreased gradually.Under PAM and Kaolin achieved4wt.%respectively, the highest DeNOx ratio was only75%. However, PVA has little negative influence on the catalytic activity of VWTi. AsPVA of2wt.%, NO coversion reached above90%at400℃and the mechanical strengthreached above0.7MPa. Among these catalysts by three molding agents （PAM, PVA andKaolin）, PVA exhibited the best molding effect. Meanwile, temperature window of thecatalyst was broaden by addition of PVA. And the PVA agent has little negativeinfluence on physical and chemical properties of the catalyst.