A Study On The Liquid-phase Aerobic Oxidation Of Alcohols Over Spinel-supported Gold Nanoparticles

Energy and environment problems have become a bottleneck restricting the social sustainable development, thus, green chemistry has become the basic requirement of the development of modern chemistry. Selective oxidation of liquid alcohols to aldehydes or ketones is a kind of important organic chemical reactions, and also, one of the most polluted reactions, which has an urgent requirement to adopt a clean catalytic oxidation technology to replace the traditional stoichiometric oxidation process in which toxic, expensive metal oxide have been used. Therefore, to develop a clean and cheap molecular oxygen as oxidant of heterogeneous catalytic oxidation is an important route to realize achieve green oxidation of alcohols.Supported gold nanoparticles show a high catalytic activity and selectivity in the aerobic oxidation of alcohols, and studies have shown that the interaction between gold nanoparticles and support is the important factor which affects the catalytic activity. Hence, taking advantage of synergistic effect of support to improve the activity of gold nanoparticles is the focus of the research. In this paper, based on the in-depth analysis of the research progress of oxidation of alcohols catalyzed by gold, we propose a synergy catalyst, Au/MgCuCr2O4, which used for catalyzing vapor-phase oxidation of ethanol, as the research point, and investigate reactivity of liquid phase oxidation of alcohols catalyzed by gold nanoparticles supported on spinel which contains different transition metals. The research results are as follows:Firstly, We have synthesized two different series of spinel carrier, MCr2O4 and MFe2O4(M = Mg, Co, Ni, Cu, Zn), by using Coprecipitation-calcination method, and by using Urea uniform deposition precipitation method, we synthesized the supported gold nanoparticles as the catalyst. Then, the catalysts were characterized by methods of XRD, UV-Vis, N2 adsorption, Atomic Absorption Spectrum, SEM, TEM, XPS, et al, and we found that carrier have little impact on dispersion of gold nanoparticles, with 2-4 nm size.Secondly, when putting Au/MCr2O4 catalyst into liquid-phase oxidation of benzene alcohol, we found that Au/MgCuCr2O4 catalyst has a higher catalytic activity, under the condition of no alkali additives,and Au/MgCoCr2O4 shows the highest performance with the alkali additives exist. This, indicates that there are two different synergistic catalytic action, Au-Cu and Au-Co. Cu is helpful to activate the oxygen, while Co is conducive to the breaking of alpha-C-H bondThirdly, In the absence of alkali additives, Au/MFe2O4 catalyst shows a similar regularity to Au/MCr2O4, but after adding alkali additives, the catalytic activity of Au/MFe2O4 is obviously higher than that of Au/MCr2O4, and Au/CoFe2O4 has the highest performance in liquid-phase oxidation of benzene alcohol. This indicates that except Au-Co synergistic catalytic action, there are also some synergistic effect between Au and Fe. On the basis of Au/CoFe2O4 catalyst, we has carried on the optimized reaction conditions.