Preparation And Catalytic Performance Of Ruthenium-based Diesel Oxidation Catalysts?DOC? Using Metal Modified TiO₂ Supports

Diesel engines are widely applied the files of transportation,mining and engineering machinery due to these advantages of low fuel consumption,high thermal efficiency and good stability.However,carbon monoxide?CO?,unburned hydrocarbons?HCs?,various oxides of nitrogen?NO_x?and the particulate matter?PM?in diesel vehicle exhaust have caused serious harm to the environment and human body.The diesel oxidation catalysts?DOC?of integrated exhaust after-treatment system can oxidize CO,HCs and NO to CO₂,NO₂ and H₂O.Compared with commercialized noble metal Pt,Pd and Rh catalysts,Ru has excellent low temperature activity and anti-toxicity,importantly,the price of Ru is relatively low.Many studies show that RuO₂and rutile phase TiO₂ have similar cell parameters and RuO₂ can be highly dispersed on the surface of TiO₂ to improve the reaction activity.However,the specific surface area of rutile phase TiO₂ is small and the thermal stability is poor.Therefore,it is necessary to modify TiO₂ by indroduction other metal,which can effectively improve thermal stability and the dispersion of Ru particles,increase the oxygen vacancies of catalysts,promote the mobility of lattice oxygen,and create more active site,and then enhance the catalytic activity.Moreover,most studies are limited to the preparation of DOC catalysts by co-precipitation method,which has a small grain size,but poor crystallinity,multiple crystal phases,and the subsequent heat treatment process of mixture by co-precipitation method are required,so the operation is complicated.Hydrothermal treatment at the selfgenerated pressure was adopted in the preparation process to avoid the traditionally followed calcination processes and the formation of hard aggregation of the products.The purpose of this paper is to prepare M_xTi_1-xO₂?MxTy,M=Sn,Ce,Zr;x/y represents the molar ratio of M/Ti?supports by modified TiO₂,and then supposed active component Ru to synthesis a series of RuMxTy catalysts.Therefore,the preparation conditions of catalysts were optimized.The morphology and microstructure of these catalysts were characterized systematically to explore the interaction between supports and active component,and the effect on the DOC activity.The main research contents of this paper are as follows:?1?The rutile SxTy solid solution were prepared by one-step hydrothermal method and impregnated with Ru.The oxidation of CO and C₃H₈ was used as the target reaction.The effect of supports composition and structure on DOC activity of RuSxTy catalysts were investigated.Firstly,the CO oxidation as probe to explore the effect of hydrothermal temperature,hydrothermal time and calcination temperature of RuS2T1on the CO performance.The optimum preparation conditions were obtained as follows:hydrothermal temperature is 180 ?,hydrothermal time is 24 h and calcination temperature is 400 ?.Subsequently,a series of RuSxTy?x/y=1/2,1/1 and 2/1?catalysts were synthesized under the optimal preparation conditions.The DOC activity of RuSxTy,RuT and RuS were investigated.RuS2T1 gives the best activity.Conversion of 50%and 90%of CO is achieved at 180 ? and 240 ?,and conversion of 50%and100%of C₃H₈ is achieved at 320 ? and 500 ?,respectively.The stability of RuS2T1was better,and the activity of RuSxTy catalysts did not decrease at 240 ??CO?and500 ??C₃H₈?for 12 h.The excellent properties of RuS2T1 are attributed to the larger specific surface area?83.3 m²/g?,smaller grain size?7.6 nm?and RuO_x size?5.49 nm?,more surface Ru content?0.69wt.%?and bulk Ru content?0.40wt.%?as well as the strong interaction between active component RuO_x and support S2T1.?2?M2T1?M=Sn,Ce,Zr?supports were prepared by one-step method and loaded with active component Ru.The DOC activity of RuM2T1 catalysts was investigated for CO and C₃H₈ oxidation.The effects of support modification elements on the structure and performance of catalysts were explored.M2T1-W and M2T1-E?M=Sn,Ce,Zr,W and E represent water and ethanol,respectively?carriers were prepared using hydrothermal/ethanol heating at 180 ? for 24 h,respectively.A series f RuM2T1-W/E catalysts were prepared by loading Ru.The effect of solvents by RuM2T1 on the oxidation of CO was investigated using CO as a probe.The CO oxidation activity of RuM2T1-E catalysts at low temperature was better than RuM2T1-W catalysts.The 50%conversion temperature of CO was 11-18 ?,lower than RuM2T1-W samples,which is attrubuted to the RuM2T1-E catalysts had smaller grain size.Among all the samples,the conversion of CO and C₃H₈ on RuZ2T1 was the best.The CO conversion of 50%and 90%were achieved at 136 ? and 240 ?,the C₃H₈ conversion of 50%and 100%were achieved at 180 ? and 500 ?,respectively.The stability of RuM2T1 was better,and the activity of RuM2T1 catalysts did not decrease at 240 ??CO?and 500 ??C₃H₈?for 12 h.The excellent properties of RuZ2T1 are attributed to the smaller grain size?4.2 nm?and RuO_x size?2.29 nm?,more surface Ru content?0.98wt.%?and bulk Ru content?0.91wt.%?as well as the strong interaction between active component RuO_x and support Z2T1.