Research On The Structure And Performance Of Manganese-based Oxides Macroscopic Assemblies

Since the increasingly stringent environmental regulation for vehicles emissions has been issued,the catalytic elimination of hydrocarbons emitted during the cold-start period has been imperative and compelling.In this thesis,the propane was employed as gaseous pollutant and manganese dioxide nanomaterials were modified on the microscopic and macroscopic levels.The effect of modification on the structural properties and catalytic activities of propane oxidation was studied.This will provide strategies for the development of novel catalysts.The main results include:(1)On the microscopic level,the modification of cobalt on the manganese dioxide was studied.The results showed that the phase structure and morohologies of the obtained manganese cobalt oxides did not change significantly.However,the redox properties and chemical states on the surface of manganese cobalt oxides were changed significantly.Furthermore,their catalytic activities of propane oxidation were significantly improved,and the 1/5 Co-MnO2 sample showed the highest catalytic activity.During the propane oxidation,the 1/5 Co-MnO2 sample provided dual reaction sites,which synergistically accelerated the dehydrogenation of propane and propylene oxidation,thus significantly improving the catalytic activity.(2)On the microscopic level,the modification of nickel on the manganese dioxide was studied.The results showed that the incorporation of nickel resulted in the formation of large quatities of defects.Correspondingly,the morphologies,the relative content of Mn4+and adsorbed oxygen species were changed.Among the four as-prepared manganese nickel oxides samples,the 1/1 Ni-MnO2 sample showed the highest catalytic activity of propane oxidation.During the propane oxidation,the nickel was inactive,but played an important role in the increase of reactive sites through changing the coordination environment of manganese.Thus,the adsorption,dehydrogenation and deep oxidation of propane were enhanced,which resulted in the improved catalytic activity.(3)On the macroscopic level,the manganese dioxide nanomaterials were assembled into macroscopic three-dimensional assembly.It was found that the macroscopic assembly of manganese dioxide nanomaterials prepared by the chemical cross-linking method showed self-standing structure,excellent mechanical property and thermal shock resistant,which provided potential for practical applications.In order to improve its catalytic activity of propane oxidation,the structural unit of manganese cobalt oxide and manganese nickel oxide nanomaterials were employed to construct macroscopic three-dimensional assemblies.The obtained macroscopic assemblies of manganese cobalt oxide and manganese nickel oxide exhibited lower temperatures at which 50%propane was converted and they decreased by 37? and 26?,respectively,compared with that of macroscopic assembly of manganese dioxide.