Influence Mechanism Of Structure Of Ce-based Catalyst On Catalytic Performance For NH₃-SCR Reaction

Nitrogen oxides（NOx）emitted from locomotive exhaust and burning of fossil fuels is one of the main atmospheric pollutants,which will cause serious ecological and environmental problems such as acid rain,photochemical smog,ozone layer destruction and global warming,and also threaten human life health and safety.Hence,the emission standards of NOx become stricter.Due to high catalytic activity and wide temperature window,Selective catalytic reduction of NH₃（NH₃-SCR）has been widely used in industry.In the reaction,catalyst is the core of the catalytic system,so it is crucial to the development of the catalyst.Currently,V-based catalysts are used as commercial catalysts in industry due to high catalytic activity and selectivity.However,the toxicity and narrow temperature window of V-based catalyst vanadium.Hence,environmental friendly catalysts are caused great concern and exploration.Therefore,CeO₂-WO₃/TiO₂ catalyst was prepared by using TiO₂ as a support,and loading active components Ce and W to achieve efficient catalytic performance.Secondly,the morphology of Ce-based catalyst and Ce anchoring are further studied.Therefore,it has extremely important significance for the morphology of the support and catalyst,the loading of the active components and the Ce anchoring.This thesis mainly carried out the following work:different support structure morphology was synthesized by changing the reaction conditions,and then loaded active components to further improve the activity of the catalyst;Ce-Fe catalyst was synthesized by co-precipitation method,and then Ce@Ce-Fe is prepared by anchoring Ce on surface of Ce-Fe.On this basis,using SEM,XRD,BET,TEM,H₂-TPR,NH₃-TPD,XPS,Raman and FTIR and other characterization techniques to study the effect of support structure morphology on catalyst activity and catalyst morphology as well as Ce anchoring effect on catalytic activity.The following results were achieved by our study:TiO₂ support with mesoporous microsphere assembly structure and flower sphere structure unit was prepared by adjusting hydrothermal temperature and the volume ratio of tetrabutyl titanate（TTIP）and acetic acid（HAC）.After,the active components Ce and W were loaded on the TiO₂ support by impregnation method,and the effects of hydrothermal temperature and volume ratio on the morphology of the support were studied.At the same time,the effect of the morphology of the support on the activity of the catalyst after loading the active component was investigated.When the hydrothermal time was unchanged,the hydrothermal temperature was adjusted.The carrier-supported catalyst synthesized at 160°C had the best catalytic activity,which presented a mesoporous microsphere assembly structure;the hydrothermal and time unchanged,and the volume ratio of TTIP/HAC was adjusted.When the volume ratio is 1:75,the catalyst had the best denitration activity,and the carrier exhibited a flower-shaped structure unit.Through a series of characterization analysis,it is believed that the size and structural morphology of the support promoted the dispersion of the active component and the load of the active component,improving the catalytic performance of the catalyst.Ce-Fe catalyst was synthesized by co-precipitation method,and Ce@Ce-Fe as well as Ce@CeO₂-Fe₂O₃ catalysts were synthesized by Ce anchoring Ce-Fe catalyst precursors and oxides.Through a series of characterization analysis results,the catalyst’s morphology,structure size,and Ce anchoring played a greater impact on the catalyst activity.Meanwhile,Ce@Ce-Fe catalyst has the best catalytic active.Furthermore,the Ce@Ce-Fe catalyst has a high atomic ratio of Ce³⁺/(Ce³⁺+Ce⁴⁺)and Fe content,which improved the redox performance of the catalyst,so that the catalyst exhibited higher catalytic activity.