Regulation Of The Activity And Mechnical Strength Of Vanadium-Titanium Catalyst During Its Preparation

Ammonia selective catalytic reduction (SCR) due to its high selectivity, efficiency and non secondary pollution to the environment, was widely used in the DeNOx engineering and became the mainstream technology for flue gas DeNOx. After more than30years of research, V2O5-WO3/TiO2is the most widely used DeNOx catalyst. The catalyst is operated at350-450℃and the DeNOx rate is more than80%, besides it has a better property of antitoxic and sulfur resistance. HoweVer, the selection of raw materials and the preparation process of the catalyst core technology are dominated by the developed countries, so the cost of the catalyst is high.High performance of the SCR catalyst needs not only high DeNOx activity but also high strength in order to adapt the coal-fired flue gas dust erosion and abrasion. Athough the scholars had a deep study on the influencing factors and operating conditions of the V2O5-WO3/TiO2catalyst, they lack attention on catalyst strength. The raw material selection (choice of titanium powder and binder) and preparation process (titanium tungsten powder preparation, catalyst drying methods, calcination conditions) of V2O5-WO3/TiO2catalyst were disgussed in this paper, we hope that what we studied can provide the basis theory for high strength and activity vanadium-titanium denitration catalyst localization production. Effect of the property of titanium powder, preparation of titanium-tungsten powder, catalyst drying methods, the amount of binder of polyvinyl alcohol and catalyst calcination conditions (different oxygen contents) on the catalyst DeNOx activity and strength were studied in this paper, the main conclusions as follows:(1) TiO2with low BET and pore volume is not suitable for the support of the vanadium-titanium DeNOx catalyst, the catalyst obtained by the this TiO2performs low DeNOx activity and strength. TiO2with high BET and pore volume is suitable for the support of the vanadium-titanium DeNOx catalyst, the catalyst obtained by the TiO2performs high DeNOx activity and strength. The smaller particle size of TiO2with rough surface and rich pore structure is, the higher DeNOx activity and strength of obtained catalyst are. HoweVer, the improving degree of the strength is clear, the improving degree of DeNOx activity is not very clear.(2) With the increasing amount of PVA, surface area and micropore volume decrease. HoweVer, in the range of PVA amount (0-10g PVA/100g cat), the catalyst pore structure does not affect DeNOx activity and SO2oxidation rate, but affect the catalyst strength.5g PVA/100g cat performs the best catalyst strength, so5g PVA of per100g catalyst is the most appropriate dosage.(3) The preparation method of titanium-tungsten powder does not affect the V and W chemical morphology in the catalyst. Although the preparation method of titanium-tungsten powder has an influence on the catalyst Ti chemical morphology,surface area and pore structure, it does not affect the catalyst DeNOx activity and SO2oxidation rate, In the preparation process of titanium tungsten powder, drying and calcination processes make TiO2agglomeration and sintering, so the particles become larger and the catalyst strength is low. With the increasing drying and calcination procedure of the titanium tungsten powder preparation, the catalyst pore volume become bigger and the catalyst strength is lower, so preparation of titanium-tungsten powder firstly is not good for the catalyst strength.(4) The drying methods (the blast drying, vacuum drying, and microwave drying) of the catalyst don’t affect the catalyst DeNOx activity and SO2oxidation rate, but affect the catalyst strength. The faster drying rate of the catalyst is, the worse the catalyst strength is. Blast drying the catalyst strength is equivalent to the vacuum drying, the microwave drying the catalyst strength is the worst. With the increasing pore volume of macro and meso pores of the catalyst, the abrasion rate of the catalyst increases linearly, i.e. the strength of the catalyst has a direct relationship with pore volume of macro and meso pores.(5) As to the same amount vanadium catalyst, the V5+content is more, the V4+content is less, the amount of NH3adsorption on the catalyst surface increases and the degree of NH3oxidation is small, so the catalyst DeNOx activity is higher and SO2oxidation rate is lower. The calcination atmosphere can affect vanadium existence form and shift behaviour, the greater oxygen concentration when calcining the catalyst is, the more V5+content in fresh catalyst is, the less V4+content is, but the result is the opposite in the sample after the activity test, i.e. the greater oxygen concentration when calcining the catalyst is, the less V5+content in uesd catalyst is, the more V4+content is.