Support Effect In The Gas-phase And Liquid-phase Oxidation Of Bioethanol Over Cu-containing Spinel Supported Gold Nanoparticle Catalysts

Catalytic oxidation of alcohols is one of the most important catalytic reactions.With the rapid development of ethanol production by biomass fermentation,bioethanol has attracted wide attention as a platform compound for the preparation of value-added chemicals.Aerobic oxidation of bioethanol to acetaldehyde or acetic acid is promising in practical application.Our previous studies found that the ternary spinel Mg Cu Cr2O4(prepared by co-precipitation method)supported gold nanoparticle(Au NP)catalyst showed excellent catalytic performance in the gas phase oxidation of ethanol to acetaldehyde,mainly due to the synergistic effect of Au0-Cu+.However,it is still unknown whether there is a similar synergistic effect in the liquid-phase oxidation of ethanol.In this dissertation,three different series of spinel MCr2O4,MAl2O4 and MFe2O4(M=Mg and/or Cu)supported Au NP catalysts were prepared by changing the composition and preparation conditions of spinel supports.The eleven catalysts were applied to the gas-phase oxidation of ethanol to acetaldehyde and the liquid-phase oxidation to acetic acid.The differences in the metal-support interaction between gas phase oxidation and liquid phase oxidation were investigated.The main results are listed below:1.In the gas phase oxidation of ethanol,the Au NP catalysts supported by Mg Cu Al2O4 and Cu Al2O4 calcined at 900 oC showed higher catalytic activity than Au/Mg Cu Cr2O4.Under the conditions of 200 oC,2.5 vol% ethanol,7.5 vol% O2,GHSV = 100 000 m L gcat-1 h-1,a yield of >92% of acetaldehyde was obtained.The activity of Fe-based spinelsupported Au NP catalysts was poor,mainly because Al-and Cr-based Cu-containing spinels can stabilize surface Cu+ species under reaction conditions to form effective Au0-Cu+ synergy.2.In the liquid phase oxidation of ethanol,however,the order of activity of the catalysts is Fe>Al>Cr.This distinct difference is attributed to the instability of the Cu+ species under the hydrothermal reaction conditions,which is not the active site for O2 activation any more.The Au/Cu Fe2O4 catalyst showed the best catalytic activity and acetic acid selectivity,with the TOF value up to 315 h-1.This catalyst could be reused multiple times by facile magnetic recovery.Through the characterization of the recovered catalyst,it was proved that the superior performance of Au/Cu Fe2O4 catalyst was mainly attributed to the novel Au?--Fe2+ synergistic effect promoting the activation of O2 and ethanol,while the alloying effect of Cu0 and Au0 improved the hydrothermal stability of the catalyst.Through kinetic and radical capture experiments,the reaction path and mechanism have been unequivocally proposed.It is pointed out that the liquid phase oxidation of ethanol over Au/Cu Fe2O4 is essentially a heterogeneous Fenton system.It provides new ideas for designing and preparing more efficient and stable ethanol oxidation catalysts.