Study On The Effect Of Crystalline Structure Of Cobalt-based And Cerium-based Catalysts On Soot Oxidation

In recent years,exhaust pollutants from diesel vehicles have brought great harm to the atmospheric environment and human life and health.Soot particles are not only the main component of Urban Haze,but also easily enter the lungs and blood through the human respiratory system,resulting in lung cancer,asthma,cardiovascular diseases,etc.At present,the combination of catalytic combustion technology and diesel exhaust particle capture technology is the most commonly used post-treatment technology,and the core of this technology is to develop catalysts with high soot catalytic activity.In recent years,Co and Ce based metal oxides have been widely studied in the field of catalysis because of their good catalytic activity and excellent redox performance.In this paper,pure phase metal oxides（Co₃O₄and CeO₂）with different crystal structures and nano needle Co based composite metal oxide(Mn_0.5Co_0.5-xNi_xO_y)catalysts were prepared by hydrothermal method.The bulk structure and surface physicochemical properties of the catalysts were characterized,and the relevant reaction mechanism was discussed.The specific research contents are as follows:（1）Three pure phase Co₃O₄（nano cube,nano plate and nano flower）catalysts with different crystal structures were synthesized by hydrothermal method.The results showed that compared with Co₃O₄nanocubes and nanoplates,Co₃O₄nanoflowers showed better low-temperature oxidation activity of soot,whether in loose contact or close contact.In close contact,T₅₀and T₉₀were only 369℃and 474℃respectively.This was because there were more CO³⁺cations and lattice oxygen on the surface of Co₃O₄nanoflower structure,which made it more prone to low-temperature redox reaction.In addition,the excellent soot oxidation activity of Co₃O₄nanoflowers was also related to its small grain diameter and good crystal structure,which increased its contact efficiency with soot.（2）Nano needle Co based composite metal oxide(Mn_0.5Co_0.5-xNi_xO_y)catalyst was synthesized by hydrothermal method.Under the condition of controlling the introduction amount of Mn unchanged,the introduction of a small amount of Ni was conducive to improve the activity of the catalyst,but with the further increase of the introduction amount of Ni,the activity of the catalyst decreased.The results showed that there was an optimal value x=0.1 for the amount of Ni,and the catalyst showed the highest soot oxidation activity.This was because there was a strong interaction between Mn-Co-Ni,Mn_0.5Co_0.4Ni_0.1could resolve a large amount of lattice oxygen at low temperature,and its nano needle structure promoted the contact between the catalyst and soot.（3）Two pure phase CeO₂（nano cube and nano rod）catalysts with different crystal structures were synthesized by hydrothermal method.The results showed that under the same calcination temperature,the catalytic activity of nanorod CeO₂to soot was better than that of nanocube CeO₂.Further research showed that among nanorod CeO₂,nanorod CeO₂（Ce-r-300）calcined at 300℃showed the best soot catalytic activity,and its T₅₀and T₉₀were 358℃and 458℃respectively.This was because the nanorod CeO₂（Ce-r-300）had more surface defect structures and oxygen vacancies,the small grain diameter and the nanorod structure promoted its full contact with soot.（4）By comparing the catalytic oxidation of soot with Co₃O₄and CeO₂with nano cube structure,it was found that nano cube CeO₂（Ce-c-500）had higher catalytic oxidation activity than nano cube Co₃O₄.This was because the nano cube CeO₂（Ce-c-500）could resolve a large amount of lattice oxygen at lower temperature,which was more prone to low-temperature redox reaction,and its grain size was the smallest,which was conducive to contact with soot and promoted soot oxidation.Figure[46]Table[18]Reference[124]...