| In order to meet the increasingly stringent emission standards of NOx,large scale SCR denitration systems have been put into operation in coal-fired power plants in China,and thus large amounts of waste SCR catalysts will be produced at the same time.By far,the waste SCR catalyst has been classified as hazardous waste,so its disposal will inevitably become a difficult problem for the thermal power industry in the future.In this thesis,the oxalic acid leaching residue of waste SCR catalyst with destroyed honeycomb structure was used as raw material,then,V2O5-WO3/TiO2 catalysts were newly synthesized from the leaching residue,and the denitration(deNOx)activity,SO2/H2O resistance,thermal stability and physicochemical properties of catalysts were systematically studied.The main research contents and conclusions are as follows:(1)The V2O5-W03/TiO2 catalysts with various V2O5 mass fractions were resynthesized from oxalic acid leaching residue,and the effects of V2O5 contents on the activities and physicochemical properties were investigated.The catalystic performances of catalysts revealed that the deNOx activity of newly synthesized 1.0%V2O5-W03/TiO2 catalyst was almost recovered to the level of fresh catalyst,with NO conversion being recovered to 91%at 300 0C,and it also showed a good resistance to SO2 and H2O.The catalyst characterization results showed that the VOm,coverage for the newly synthesized 1.0%V2O5-W03/TiO2 catalyst was optimized to 29%,generating more active sites for the SCR reaction.In addition,the V4+/V5+ ratio and reducibility of vanadium species were significantly improved when compared to the waste catalyst.The investigation of thermal stability showed that when the V2O5 content was no more than 0.7%,the resynthesized catalysts had a good thermal stability,but the change of crystalline phase,particle morphology and pore structure of catalysts was promoted with increasing V2O5 content.(2)The recycling conditions of TiO2 carrier from oxalic acid leaching residue were optimized,and the medium circulation experiment was performed under optimal conditions.The alkali leaching conditions were optimized with rotation speed of 300 r/min,reaction time of 180 min,temperature of 160 ?,liquid to solid ratio of 15 mL/g,NaOH concentration of 2.0 mol/L;meanwhile,the process of washing with dilute H2SO4 was optimized as the follow-up processing after alkali leaching.The medium circulation experiment showed the concentrations of W and Si were gradually accumulated to 3.0 g/L and 6.6 g/L after five cycles,and the purity of the obtained recycled carrier could meet the requirements of industrial WO3/TiO2 powder.(3)The V2O5-WO3/Ti02 catalysts with various V2O5 mass fractions were synthesized by co-impregnation and stepwise impregnation methods from the recycled carrier,which was obtained under the abovementioned optimal conditions.The deNOx activity and physicochemical properties of the resynthesized catalysts were studied.In addition,the SO2/H2O resistance and thermal stability of the optimized catalyst were investigated.The results displayed that the resynthesized catalysts prepared by different methods had similar deNOx activity and physical properties.Moreover,the catalysts prepared by co-impregnation method showed better reducibility but weaker surface acid than that prepared by stepwise impregnation method.The optimized 0.7%V2O5-W03/TiO2 catalyst,which was resynthesized by co-impregnation method,showed almost the same activity as fresh catalyst,and showed good SO2/H2O resistance and thermal stability. |
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