Low Temperature Selective Catalytic Reduction(SCR) Of NOx On Manganese-Based Catalysts

NOxis one of the main air pollutants discharge from coal-fired powerplants, it is also the important reason to cause pollution such as acid rain,photochemical smog and so on. Selective catalytic reduction (SCR) technologyis an effective method to control the emission of NOxfrom stationary sources.Vanadium-based catalyst is widely used in industry department, but the catalystis active within a narrow temperature window of300-400℃, easily to bedeactived by the flue gas and toxicity of vanadia may cause secondarypollution.This paper, we use manganese oxide as the main active component,try to develop suitable catalysts for low temperature SCR reaction, so that SCRdevice can be placed after the electric precipitation or desulfurization system, itwould help to reduce the deactivation caused by harmful components of fluegas, prolong the service life of catalyst, it also can narrow the volume of SCRdevice and reduce the cost of flue gas denitration.This paper using sol-gel method prepared a series of manganese-based lowtemperature SCR catalysts, the catalytic activity and sulfur resistance at lowtemperature was tested, and the catalysts are characterized by XRD diffractionanalysis, BET surface area analysis and H2-TPR and NH3-TPD temperatureprogrammed technology methods, systematically studied the low temperatureSCR catalyst performance.Firstly studied the influence of preparation conditions for Mn-Cu/TiO2catalysts’ catalytic properties at low temperature, it found that exorbitantmanganese load and calcination temperature would against the low temperaturecatalytic properties of catalysts, mainly because they lead to the unscattered andsintering of catalyst’s active component, and the phenomenon of catalyst tunnelcollapse.Based on above study, we compared the catalytic properties of thecatalysts which used Mn-Cu oxides as the main active component and loadingon TiO2and Al2O3these two kinds of catalyst carrier at low temperature. Thecatalyst supported at TiO2in the whole experiment temperature window has thebetter SCR activity and sulfur resistance at low temperature than it supported atAl2O3. NH3-TPD test results show that the TiO2carrier contributes to theformation of Lewis acid centers, while Al2O3carrier are more likely to form theBronsted acid centers. Then, in view of TiO2carrier showed good experimental phenomenon andthe Ce element was frequently reported at other literatures, this paper studiedthe catalyst poisoning of Mn-Ce/TiO2caused by Na and Ca these two kinds ofalkali metals loading. The results showed that, Na or Ca loading has inhibitoryeffect on the activity of catalysts, and the poisoning effect of Na was moresignificantly than Ca.The main reasons for the catalyst activity reducing afterNa doping may be the increased of catalyst crystallinity and the decreased ofcatalyst specific surface area, redox capacity and surface acidity.Finally, using quantum chemistry theory set up and optimize the model ofMn-Cu/TiO2and Mn-Cu/Al2O3catalysts surface adsorption with ammonia, andcalculated the adsorption energy, compared the bonding situation of two kindsof carrier catalysts with ammonia molecules on the surface, it was found thatthe adsorption energy and bonding situation of catalyst which supported onTiO2is better than that on Al2O3. The result is consistent with the experiment, itindicated that the quantum chemistry calculation result is in conformity withthe actual situation, it is reasonable.In this article, through the combining of experimental research andtheoretical calculation methods, we studied the catalytic properties ofmanganese-based low temperature SCR catalyst at low temperature.Revealingthe denitration reaction mechanism in-depth by using characterizationexperiments and quantum chemical calculation method, it also providing thetheoretical basis for the design and improvement of low temperature SCRcatalysts in the future.