Preparation Of Sn-doped Cu/CeZrO₂/γ-Al₂O₃ Automobile Exhaust Catalysts And Study On Their Sulfur Resistance Performance

Motor vehicle pollution has become one of the most significant contributors to air pollution,with pollutants mainly coming from exhaust emissions of CO,NO and HC.The most effective method for treating vehicle exhaust is catalytic purification technology,which usually uses the precious metals of platinum（Pt）,palladium（Pd）and rhodium（Rh）as the active components of the catalyst to achieve the removal of these three pollutants from exhaust gases.However,the precious metals are expensive and they are prone to react with SO₂containing in the exhaust gaswhich could result in the irreversible sulphur poisoning,thus reducing their catalytic performance and shortening their service life.Therefore,it is imperative to develop a three-way catalyst with low cost and excellent sulfur resistance to effectively remove CO,NO,HC and other pollutants in vehicle exhausts.In this paper,a three-way catalyst named as Cu/CeZrSnO₂/γ-Al₂O₃was prepared using a two-step impregnation method,thereinγ-Al₂O₃is the support,Cu O is the active component and tin-doped ceria-zirconia solid solution（CeZrO₂）is used as additive.The effects of the preparation conditions of catalyst and the reaction conditions on their reactivity and sulphur resistance performance were investigated.Based on the collected results on XRD,XPS,H₂-TPR,O₂-TPD and TG characterisations and combined with DFT calculations,the catalytic mechanism of Cu/CeZrSnO₂/γ-Al₂O₃on the removal of CO,NO and HC and its sulphur resistance mechanism were proposed.combined.The obtained conclusions were as follows:（1）By comparing the effects of different preparation methods and Sn doping on the catalytic performance and sulfur resistance of the three-way catalysts,it was found that their catalytic activity and anti-sulfur performance were following the orders:Cu/CeZrSnO₂/γ-Al₂O₃-I>Cu/CeZrSnO₂/γ-Al₂O₃-A>Cu/CeZrO₂/γ-Al₂O₃-I.Therein,the Cu/CeZrSnO₂/γ-Al₂O₃-I catalysts achieved conversion efficiencies of 75.5%,82.5%and100%for CO,NO and HC,respectively,with only 13%,0.2%and 22%decreases in CO,NO and HC conversion after introduction of 100 ppm SO₂.The Cu/CeZrO₂/γ-Al₂O₃-I and Cu/CeZrSnO₂/γ-Al₂O₃-I were characterized by XRD,XPS,H₂-TPR and O₂-TPD,and it was found that Sn doping could improve the structure-activity relationship between the active component and the additive,meanwhile could increase the concentrations of oxygen vacancies,improve the oxygen mobility and also provide a larger buffer space for the redox process.The TG results indicated that Sn modification inhibited the formation of sulphate on the surface of the active component of the catalyst,thus improving their sulphur resistance performance.（2）By investigating the effects of Cu loading,Sn doping and the calcination temperature on the catalytic performance of Cu/CeZrSnO₂/γ-Al₂O₃three-way catalysts,it was found that the prepared catalysts had the best catalytic performance when the active component loading was 7 wt.%,the Sn doping was 0.1 and the calcination temperature was 700°C.The Cu/CeZrSnO₂/γ-Al₂O₃catalyst showed the conversion efficiencies for CO,NO and HC were88%,92%and 100%,respectively,when theλvalue of air-fuel ratio was maintained near 1,the air velocity was 40,000 h^-1and the catalyst reaction temperature was at 600°C.（3）The relationship between the electronic structure and SO₂anti-sulphur performance of Sn-doped Cu/CeZrO₂（110）catalysts was investigated using density functional theory calculations.The results show that the most stable adsorption site of Cu on the surface of CeZrO₂（110）is the oxygen bridge site,its adsorption energy is-3.52 e V.By analysing the Cu-d band centre,charge change,partial density of state（PDOS）and SO₂adsorption energy,it was found that Sn doping enhanced the positive charge of the active component Cu and the interaction between Cu-O,which inhibited the adsorption of SO₂on the Cu active sites,thus improving the catalytic performance of the catalyst and its sulfur poisoning resistance,and improving.