Effect Of Sulfation Temperature On The Catalytic Performances Of CeO₂ Nanocubes,Nanorods And Nano-octahedral In NH₃-Selective Catalytic Reduction Conditions

The distribution of resources in our country has determined that for a long time in the future,we are still a big coal-burning country.Therefore,the pollution of nitrogen oxides caused by coal combustion has become an urgent problem to be solved.Ammonia-selective catalytic reduction(NH3-SCR)technology is one of the most effective means to reduce or eliminate nitrogen oxide pollution.Ceria-based and ceria-containing NH3-SCR catalysts are widespread researched because of their excellent storage and release properties and environmentally friendly.In this paper,three different morphologies of CeO2(nano-octahedron,nanocube,nanorod)were pretreated by SO2(sulfated)at different temperatures to investigate the source of their activity changes,for providing some theoretical understanding for the discovery of ceria-based catalysts with resistance to SO2 poisoning.The main research contents are as follows:(1)The CeO2 nano-octahedron was sulfated at different temperatures and its NH3-SCR performance was investigated.The results showed that the best activity appears after sulfation at 350 ℃.HRTEM shows that excessive sulfation temperature will destroy the octahedral morphology.The results of XRD and Raman indicate that the sulfate species gradually penetrate from the surface to the bulk phase.H2-TPR and TG-DTA indicate that the amount of sulfate species increased with the elevating sulfation temperature.Abundant surface oxygen vacancies are the main reasons for the superior activity of ceria nano-octahedra after sulfation at 350 ℃.The formation of bulk sulfate inhibited the interation between surface sulfate and bulk CeO2,thus sulfation at higher temperature will decrease the activity of catalysts.(2)The CeO2 nanocubes(expose(100)facial)and nanorods(mainly expose(110)facial)were sulfated at 150,350,550℃,and it was found that there was a NH3-SCR activity reversal point at the same sulfation temperature.HRTEM showed that the sulfation treatment did not significantly affect these two morphologies.The XRD,Raman,and SO2+ O2 in-situ DRIFTs qualitatively indicated that the sulfate species on both CeO2 were deep from the surface to the bulk,but the form of sulfate species present at the same sulfation temperature are the same;H2-TPR,TG-DTA quantitative indicates that the amount of sulfate species between them increases with elevating sulfation temperature.The location of reversal point is closely related to the amount of sulfate species.Sulfate species are more easily forming at(110)facial,and the proper amount of sulfate species can increase the content of surface Ce3+ and O specie,forming more low-coordination sulfate species,adjust the redox properties of catalysts,which is beneficial to the NH3-SCR reaction.