Fabrication And Catalytic Performance Of Macroporous Cobalt-based Perovskite Oxides For The Catalytic Combustion Of Diesel Soot

Diesel vehicles have been widely used in transportation because of their high combustion efficiency,strong endurance and low CO₂ emissions.However,the large amount of soot particles emitted from the exhaust gas is one of the main sources of PM2.5 pollution in the urban atmosphere,which seriously threatens the environment and human health.At present,catalytic purification treatment technology is the most effective technical means to reduce the emission of soot particles in diesel exhaust.Due to the low temperature of diesel exhaust emissions,it is of great significance to develop a highly active soot combustion catalyst.Based on the use of various macroporous templating agents,a series of cobalt-based perovskite oxide catalysts with different pore structures were prepared,and the physicochemical properties and reaction properties of the catalysts were systematically investigated by various characterization techniques.The main research contents and results are as follows:（1）A series of disordered macroporous-mesoporous Ce-doped La_1-xCe_xCo O₃（x=0～0.15）catalysts with high specific surface area were prepared at a lower calcination temperature using ethylene glycol as template.The results show that,due to the use of templating agent,the oxidation catalyst with lower temperature calcination has a good crystal structure of perovskite phase.In addition,it can effectively increase the specific surface area of the catalyst and has a rich pore structure.The maximum specific surface area of the catalyst can reach 18.6 m²/g.The Ce ion introduced into the La Co O₃ framework mainly exists in a tetravalent form.The introduction of Ce species enhances the redox performance of the catalyst and the mobility of reactive oxygen species in the structure,which effectively increases the catalytic activity of the catalyst for soot combustion.Under the NO_x-free reaction atmosphere,the catalysts showed good catalytic activity when they were in loose contact with soot.The La_0.9Ce_0.1Co O₃catalyst had the highest activity,and T₁₀,T₅₀ and T₉₀ were 372°C,444°C and 497°C,respectively.Based on the above results,a possible catalytic mechanism of soot combustion was proposed by combining XRD,ex-situ XPS and isothermal reaction characterization techniques.（2）For the first time,silica colloidal crystal template was applied to the preparation of three-dimensional ordered macroporous（3DOM）cobalt-based perovskite oxides.The results show that the excellent thermal resistance of silica colloidal crystal templates breaks through the limitations of glass transition temperature and complete decomposition temperature existing in previous polymer templates,and enhances the upper temperature limit for the preparation of composite metal oxides by colloidal crystal templates.In terms of textural,the use of silica colloidal crystal template greatly increased the specific surface area of cobalt-based perovskite oxides,and the catalyst prepared had a high specific surface area of 76.0m²/g.At the same time,it showed a three-dimensional ordered macroporous structure different from PMMA template method,which effectively improved the contact efficiency of the catalyst to soot particles.In terms of chemical properties,the alkali treatment steps in the preparation of silica template can increase the number of active sites of the catalyst,and the in-situ formation of La（OH）₃ with strong adsorption performance can effectively improve the adsorption and conversion performance of NO over the catalyst.At the same time,the surface of the cobalt-based perovskite oxide prepared by the silica template method has higher content of cobalt ions with high valence and higher content of chemical adsorption oxygen content.These characteristics favor an enhancement of the intrinsic activity of the cobalt-based perovskite oxide.The activity test results show that the S-3DOM La Co O₃ catalyst prepared by the silica template method exhibits the highest catalytic activity relative to the PMMA template and the ethylene glycol template,and its T₁₀,T₅₀ and T₉₀ are310°C,350°C and 382°C,respectively.Further cyclic tests and activity tests under different reaction atmospheres showed that S-3DOM La Co O₃catalyst had good stability,water resistance and sulfur resistance.