A Study On The Gas-phase Selective Oxidation Of Bioethanol Over Unreducible Metal-doped OMS-2 And Its Supported Gold Catalysts

With the rapid development of the technology of bioethanol by biomass fermentation,the research on the production of high value-added chemicals using bioethanol as a platform compound has drawn much attention.Among them,the preparation of acetaldehyde by selective oxidation of bioethanol promises to be practical application prospect.The superior performance of manganese oxide octahedral molecular sieves?OMS-2?in the field of catalytic oxidation has attracted our attention.As far as we know,there are few reports on selective oxidation of gas-phase ethanol by manganese oxide octahedral molecular sieves?OMS-2?and their supported gold nanoparticle catalysts.In this dissertation,a series of M-OMS-2 catalysts were prepared by doping various unreducible-metal cations into the tunnel of manganese oxide octahedral molecular sieves?OMS-2?by using“one-pot”refluxing method,and then the"urea deposition"method was applied to the surface of M-OMS-2 support to prepare Au-M-OMS-2 catalyst for the selective oxidation of ethanol to acetaldehyde.The effect of catalytic activity by acidity and redox of the catalyst was studied,so did the mechanism of activation of O₂ and ethanol on the catalyst surface.We found that the activity of the M-OMS-2 catalysts was demonstrated to be proportional to the surface basicity.Na-OMS-2 exhibited the highest catalytic activity at200?,which is higher than and comparable to the previously reported preferred Fe-OMS-2 and Ag-OMS-2 catalysts,respectively.The beneficial effect of Na⁺-doping is related to the enhancement of surface oxygen vacancies,basicity and reducibility,which also result in better catalytic stability.Kinetic studies indicate that ethanol O-H and?-C-H bond cleavages are both kinetically-relevant,with the latter being the more difficult step.O₂ is the most efficient oxidant and is thought to be activated at oxygen vacancies of Mn²⁺/Mn³⁺species to form superoxide-type O₂^-and lattice-oxygen-type O^2-species,which act as dual active sites for the rate-controlling ethanol activation steps.The"urea deposition"method can well load AuNP on M-OMS-2 nanorods.Due to the metal-support interaction,the loaded AuNP significantly improved the reducibility of the M-OMS-2 catalyst,and the ethanol conversion rate of the Au-M-OMS-2 catalyst was significantly higher than that of the corresponding M-OMS-2.Moreover,the activity of all supported gold nanoparticle catalysts is relatively close.