Study The Morphology Effect Of Oxide Catalyst On Soot Combustion

Due to the high thermal,excellent fuel efficiency and low price the diesel engines have been widely used in vehicle.However,soot particles emitted from diesel engines can cause serious health and environmental problems,which calls for efficient treatment systems for soot particles.So,effective ways should be conducted to solve the problems.Meanwhile,one of the most effective ways to removal the soot particles is to reduce the thermal oxidation temperature,so it has become a hot topic to removal of catalytic soot particles at low temperature by catalyst.（1）Three-dimensionally ordered macroporous CuO-CeO₂ catalysts were successfully synthesized by the colloidal crystal template route and systematically characterized by means of XRD,FESEM,HRTEM,BET,XPS,FTIR,H₂-TPR and O₂-TPD.The 3DOM CeO₂ with CuO loading amount of 9.7 wt%exhibited the optimal catalytic activity,giving T_m of 427^oC and exceptional high CO₂ selectivity of nearly 100%.This superior activity was attributed to the enlarged contact area between catalyst and soot particles,the improved mass transfer caused by the well-defined 3DOM structure and the enhanced redox capability at low temperatures mainly associated with the highly dispersed copper species.Meanwhile,the effect of feed compositions on soot combustion efficiencies revealed that NO and H₂O played the crucial promoting effect on catalytic oxidation of soot particles because NO₂ formed via in-situ NO oxidation during reaction and H₂O significantly reduce the activation energy of carbon.Furthermore,this catalyst also demonstrated strong durability against structural collapse owning to the well-defined and robust 3DOM structure,indicating its potential applications in practical working conditions.（2）A series ofα-Mn₂O₃ micro crystals with different morphologies and crystal shapes were successfully prepared by hydrothermal method and has been investigated as potential soot combustion catalysts for the first time.The activity data showed that the soot combustion efficiency were markedly affected by the shape of the preparedα-Mn₂O₃catalysts,among which their activity ranked asα-Mn₂O₃-cubic>α-Mn₂O₃-truncated octahedral>α-Mn₂O₃-octahedra.As revealed by various physicochemical characterization techniques such as XRD,SEM,HR-TEM,FT-IR,BET,H₂-TPR,O₂-TPD,NO-and NO+O₂-TPSR,the enhanced activity as well as selectivity overα-Mn₂O₃-cubic is originated with the nature of the exposedα-Mn₂O₃（001）surface facets,on which the higher concentration of low-coordinated surface oxygen sites facilitates the oxygen activation and improves surface redox properties,thereby accelerating the formation of the crucial intermediate i.e.,NO₂ formation by NO oxidation and thus promoting the overall soot combustion efficiency.Moreover,the kinetic study performed under isothermal condition provided solid evidence and proof to support that it is the exposed crystal facet,rather than surface area,to be critical to determine the catalytic performance of soot combustion.Under loose contact condition,soot combustion efficiency over best performingα-Mn₂O₃-cubic catalyst was further enhanced in the presence of water,CO and hydrocarbons,which are essential components in real diesel exhaust.Furthermore,the cubicα-Mn₂O₃ displayed excellent durability against structural collapse upon repeated recycling test and accelerated deactivation test,demonstrating its promise for the practical use in diesel soot combustion.