Preparation And CO Catalytic Oxidation Performance Of Ceria-based Catalysts

In recent years,the exhaust emissions of motor vehicles,the incomplete combustion of hydrocarbons,and the air pollution caused by the gas generated in mines are becoming increasingly serious.Air pollutants mainly include sulfur oxides,nitrogen oxides,particulate matter,and carbon monoxide.Carbon monoxide,as a colorless,odorless,flammable and explosive harmful gas,is highly toxic to the blood and nervous system.Therefore,the elimination of carbon monoxide has certain practical significance to protect the environment.At present,converting carbon monoxide to non-polluting carbon dioxide is one of the more ideal and effective methods.Catalysts for converting carbon monoxide are mainly classified into noble metal catalysts and non-precious metal catalysts.Although noble metal catalysts have high catalytic activity for carbon monoxide oxidation at low temperatures,their high price and complicated preparation process have limited their wide application.Therefore,more research has been focused on non-precious metal catalysts,among which ceria-based catalysts received widespread attention,because of its popular prices,excellent oxygen storage and thermal stability.This paper mainly focuses on the synthesis of cerium oxides with different morphology of cerium-based coordination compounds as precursors,and the use of cerium oxide catalysts with different morphologies as substrate materials for loading or doping with different transition metal oxides.Modifications explored the effects of different transition metal oxides and their different contents on catalytic performance.The main research contents in the full text are as follows:?1?The core-shell structure Ce-asparagine coordination polymer precursor was prepared by the reaction of L-asparagine and cerium salt under hydrothermal condition.After pyrolysis of the precursor,the morphology of the mesoporous core-shell structure CeO₂ was obtained.Then,upon a sheath-coating process via solvothermal treatment with Co?CH₃COO?₂·4H₂O,Co₃O₄ species were uniform dispersed onto the CeO₂ core-shell microsphere surface to generate CeO₂@Co₃O₄composite.The effects of different contents of Co₃O₄ on the catalytic oxidation of carbon monoxide were investigated.The results showed that for CeO₂ and CeO₂@Co₃O₄-20wt%core-shell microspheres,the full carbon monoxide conversion temperatures were 280 ^oC and 170 ^oC,respectively.Moreover,CeO₂@Co₃O₄core-shell microsphere exhibited a excellent cyclical stability.The feature of core-shell and porous structures provide a larger surface area and abundant oxygen vacancies to absorb and activate CO gases,resulting the high catalytic activity.The excellent CO conversion performance of the core-shell microsphere CeO₂@Co₃O₄was ascribed to the synergistic interaction between Co₃O₄ and CeO₂.?2?A simple and economical route based on solvothermal method was developed to synthesize three-dimensional?3D?flowerlike Ce-based coordination polymer precursor using cerium chloride,terephthalic acid and fumaric acid as reactants.CeO₂with the same flowerlike microstructure was readily obtained by calcination of the precursor.The test result illustrates that the temperature for full CO conversion of as-prepared flowerlike CeO₂ microspheres was 290 ^oC.In order to further improve the catalytic activity,CeO₂@Co₃O₄ and CeO₂@CuO flower-like microspheres were prepared by impregnation method.The results showed that CeO₂@CuO flower-like microspheres had excellent performance.Then,a series of CeO₂@CuO composites with different Ce/Cu contents were synthesized by solvothermal synthesis.The flowerlike CeO₂@CuO-2 exhibited an enhanced CO catalytic activity and cyclical stability,demonstrating a promising potential in environmental remediation.Therefore,the as-obtained CeO₂ could be used as not only an effective catalyst to remove CO by catalytic oxidation but also as an excellent support for CuO.The rich oxygen vacancies and synergetic effect play a vital role in catalytic reaction.?3?First,two kinds of morphologies of CeO₂ were obtained by adjusting the ratio of solvent?DMF and ethanol?and organic ligand?fumaric acid?.The dumbbell microflower CeO₂ has a large size and a dense surface.Correspondingly,the performance of the catalyst was slightly worse than that of the smaller,thin flakes of snowflake CeO₂.Snowflake CeO₂ completes CO conversion at 310 ^oC.Therefore,we dope different metal salts during the preparation of the snowflake CeO₂ precursor.The morphology of the catalyst changes greatly after the doping,from the snow-like configuration directly to the hollow nano-structure of CeO₂-NiO and the hollow core-shell structure of CeO₂-Co₃O₄.The competitive coordination of metal ions plays an important role in changing the morphology.Even though the nickel salt and cobalt salt has the same molar ratio,CeO₂-Co₃O₄ hollow core-shell spheres have been found to have the most excellent catalytic activity and cycle stability.It can be seen that different metal ion doping has different effects on the catalytic performance.In addition,the influence of the catalyst morphology cannot be neglected.