Catalytic Oxidation Of Soot And CO On Ceria Based Solid Solution With CTAB Assisted Synthesis

Diesel engines have been widely used due to their low fuel consumption,high power,and high durability.However,the main emissions of their pollutants,such as soot particulates,nitrogen oxides,carbon monoxide,and hydrocarbons have caused severe environmental problems and threatened our living conditions.The control of diesel engine emission has become a research hotspot in recent years.Nowadays,catalytic combustion of soot and CO is one of the most efficient methods to eliminate exhaust pollutants,and the key is catalyst.Ceria gains favor in the field of catalysis due to its appreciable oxygen storage capacity and good catalytic performance.Transition metals have excellent redox properties,which can be used to achieve catalytic oxidation at lower temperature.In this paper,the transition metal doped ceria-based solid solutions with mesoporous structure were prepared by CTAB assisted method.The physicochemical properties of the prepared catalysts were characterized using a variety of methods.The soot combustion and CO oxidation were used as model reactions.And the correlation between their physicochemical properties and catalytic performance catalytic reaction mechanism also were systematically investigated.The transition metal doped ceria-based solid solutions(M_0.1Ce,M=Mn,Fe,Co,Cu)with mesoporous structure were prepared by the CTAB-assisted co-precipitation method.Compared with CeO₂-co?57 m²/g?synthesized without CTAB,CeO₂ prepared by CTAB assisted method has larger surface area?105 m²/g?.The obtained samples maintain the cubic fluorite structure of CeO₂ and small crystallite size.Transition metals doping enhances the oxygen vacancies and improves redox properties of the solids,resulting in the increased NO oxidation capacity and NOx adsorption capacity.The soot oxidation activity in the presence of O₂ is enhanced by doping transition metal,which may be related to their high surface area,increased oxygen vacancies and improved redox properties.The soot combustion is accelerated by the NO₂-assisted mechanism under NO+O₂ atmosphere,facilitating an intimate contact between the soot and the catalyst.The nanosized copper-doped ceria catalysts?Cu_xCe,x=0,0.05,0.1,0.2,0.3,1?were synthesized by a CTAB-assisted co-precipitation method.The influence of Cu contents on their crystal phase,pore structure,surface properties and catalytic performance was studied.The lower Cu content doped samples maintain the cubic fluorite structure of CeO₂ and small crystallite size,whereas a higher Cu doping causes the formation of bulk CuO.Cu doping favors the increase of surface area of CuCe?105-131 m²/g?and the formation of oxygen vacancies,thereby improving the redox properties.The CuCe samples exhibit higher catalytic performance compared to the bare CeO₂ and CuO catalysts.Particularly,the Cu_0.1Ce catalyst shows the highest catalytic performance(T₅₀=59°C),as well as an excellent stability.The in situ DRIFTS results show that CO adsorbed on surface Cu⁺?Cu⁺-CO species?can easily react with the active oxygen,while stronger adsorption of carbonate-like species cause catalyst deactivation during the reaction.The Mn and Cu doped cerium-based solid solutions MnCuCe,CuCe,MnCe and CeO₂were successfully prepared by CTAB-assisted hydrothermal method.The doping of transition metals influenced the lattice parameters,surface oxygen vacancies and redox properties of the catalysts.The doped catalysts have a single CeO₂ crystal phase and high crystallinity,forming Ce-based solid solutions.The catalysts synthesized by this method have large mesoporous structure?average pore size,10-14 nm?.The doping of transition metal induces more oxygen vacancies,promoting the increase of redox properties,thereby enhancing the catalytic activity and selectivity for soot and CO.Compared to single-metal-doped catalysts,MnCuCe exhibits the highest catalytic activity for soot and CO,which is attributed to the synergistic interaction between double-doped metals.The doping of Mn and Cu metal induces more oxygen vacancies,promoting the increase of oxygen adsorption and the transfer rate of bulk oxygen of catalyst,thereby enhancing the catalytic activity and selectivity for soot and CO.The Co-doped ceria-based catalysts?CoxCe,x=0,0.1,0.2,0.3?were successfully prepared by CTAB+PEG2000 dual template assisted co-precipitation method.The lower Cu content doped samples still maintain a single CeO₂ crystal phase with decreased crystallinity.As the doping amount increased,the dispersion of Co₃O₄ particles decreased and some of the particles remained on the surface of CeO₂ which is confirmed by Raman.The synthesized samples had a larger specific surface area?81-117 m²/g?and mesoporous structure?average pore size,9-16 nm?.According to Raman and H₂-TPR characterization,the Co doping facilitates the formation of more oxygen vacancies and improves the redox performance.The results of catalytic activity show that the Co doped catalysts possess increased activity,and Co_0.1Ce has the best catalytic activity(T₅₀ is 345 ^oC and 337 ^oC under O₂ and NO+O₂atmospheres,respectively).More Co doping leads to more Co₃O₄ particles produced,which reduced synergy between Co-O and Ce-O and low-temperature redox properties,thereby resulting in lower catalytic activity.Compared with the samples prepared by single template Co_0.1Ce-C and Co_0.1Ce-P,the catalytic activity order results:Co_0.1Ce>Co_0.1Ce-P>Co_0.1Ce-C,which illustrated that the dual template assisted synthesis contribute to prepare catalyst with higher catalytic activity.