The Research On Mesopore Confined Structure Impacting On Sulfur Resistance Performance Of NH₃-SCR Catalyst

With great development of urbanization,the unrestrained consumption of fossil fuels is deemed to aggravate nitrogen oxides(NOx)emission.Currently,selective catalytic reduction of NO with NH₃(NH₃-SCR)is one of most powerful methods to remove NOx from stationary sources like power plant and industrial boiler.However,the practical application of this technique is largely hindered by the deactivation of NH₃-SCR catalyst in SO₂-contained atmosphere due to active centers sulfation,and active site blocking from ammonium bisulfate(ABS)deposition,which is dominant at low temperatures.So getting deep insights into SO₂ poisoning mechanism,nature of surface SO₂-derivatives,thus developing SO₂-resistant catalysts have been essential topics for long-term sustainable denitration.In this thesis,we mainly focus on illustrating the behaviors of ABS on catalyst with mesoporous confined environment,and based on the understanding,novel mesoporous catalyst with superior poisoning resistance was rationally constructed and characterized.The specific content are as follows:1.Activating ABS decomposition is regarded as the ultimate way to alleviate sulfur poisoning.Concerning that most of NH₃-SCR catalysts is porous materials,we investigated the physical structure variation of catalysts impacting on the ABS thermostability and found that ABS decomposition could be simply tailored via adjusting pore size of the material it deposited.We firstly synthesized a series of mesoporous silica SBA-15 with uniform one-dimensional pore structure but different pore sizes,followed by ABS loading to investigate the effect.Results showed that ABS decomposition proceeded more easily on SBA-15 with larger pores,and the decomposition temperature declined as large as 40 ? with increasing pore size of SBA-15 from 4.8 nm to 11.8 nm.To further ascertain the effect in NH₃-SCR reaction,Fe₂O₃/SBA-15 probe catalyst was prepared.It was found the catalyst with larger mesopores exhibited much improved sulfur resistance,and quantitative analysis from FT-IR and ion chromatography further proved the deposited sulfates were greatly alleviated.The result demonstrates for the first time the vital role of pore size engineering in ABS decomposition.2.Furthermore,depth insights of the interaction between ABS and MCM-41 confined Fe₂O₃-WO₃ catalyst were explored and we discovered a novel observation of the dual effects of ABS on the NH₃-SCR reaction.That is,ABS inhibits the NH₃-SCR performance of Fe₂O₃-WO₃/MCM-41 at low temperatures(50-200 ?)but shows apparent and sustainable reaction promotion when the temperature surpasses 250?.X-ray photoelectron spectroscopy(XPS)and NO+O₂ probing adsorption confirmed that when ABS is deposited on the catalyst surface,a partial interaction between ABS and the Fe₂O₃-WO₃ component occurs,resulting in blocking of the active sites and an obvious loss of catalytic activity.With increasing reaction temperature,the ammonium in ABS can be facilely consumed by NO/O₂,thus inducing the disintegration of poisoning species.The sulfate group transforms into metal sulfate and survives at high temperatures.Importantly,owing to the strong inductive effect of sulfate species,both the acidity and redox properties of the catalyst are greatly improved,which contributes to the enhanced activity and also the stable SO₂ resistant ability.3.Based on the above comprehension of sulfur resistance characteristics on innert mesoporous substrate with active sites.We rationally constructed thin-layered titania confined in mesoporous silica via a surface grafting strategy,since Ti O₂ is a famous support for NH₃-SCR catalysts.It exhibits high specific surface area along mesopore channel with amorphous structure,thus much more Br?nsted acid sites are generated than bulk Ti O₂ due to defect induced oxygen-related species.After iron oxide impregnating,both the denitration activity and H₂O/SO₂ tolerance are greatly promoted as compared to conventional Fe/Ti O₂.Further characterizations reveal the novel catalyst displays uniform iron oxide dispersion and intense Fe-Ti interaction,resulting in superior redox behavior and increased acidity.Notably,it is found the introduction of H₂O exhibits a promotional effect on NO conversion,which can be ascribed to enhancement of NH₃ adsorption capability.Besides,SO₂ has negligible disturbance on NO/NH₃ adsorption,which is responsible for superior sulfur tolerance.