| Mesoporous materials have broad application prospects in the fields of catalysis, energy storage and conversion, gas adsorption and separation and so on due to high specific surface area, highly ordered pore structure. KIT-6 is the most typical silica based mesoporous material. It has both the properties of the traditional mesoporous materials, and has a 3-D Ia3 d cubic structure and highly cross-linking of the internal structure of the channel and other unique advantages, as a high-quality alternative material in the field of catalysis and template for a long-term research.Spinel type composite metal oxides with an adjustable degeneration and structural stability, are widely used as a redox catalyst and catalyst carrier in the catalytic field. Spinel supported nano metal catalysts exhibit synergistic catalytic enhancement effect in many reactions. However, spinel which prepared by co-precipitation and calcination usually has a low specific surface area, which leads to the low catalytic efficiency of the catalyst in the liquid phase reaction, which greatly limits the application of this kind of catalyst. Therefore, the preparation of mesoporous spinel supported nano metal catalysts has gradually become a hot research topic. The emergence of hard template method provides an efficient way for the preparation of mesoporous spinel with high specific surface area. In view of this, this paper proposes using mesoporous molecular sieve KIT-6 as the template, variety of methods are used to explore the optimal synthesis conditions of the three element mesoporous spinel. Finally M-MgCoCr2O4 and m-MgCuCr2O4 mesoporous spinel materials were successfully prepared, Meanwhile, the KIT-6 is used as the carrier, and the nano spinel particles are loaded in the pore channels to prepare the composite carrier as comparison. By using Urea uniform deposition precipitation method, we synthesized catalysts supported gold nanoparticles. Then, the catalysts were characterized by methods of XRD, N2 adsorption, AES, TEM, XPS, et al.Under the optimal reaction conditions for the liquid phase oxidation of benzyl alcohol screened in our preliminary work, that is compared to substrate 15 mol% K2CO3, 0.18 mol% catalyst, 90? after 5h reaction. With Au/m-MCr2O4 and Au/MCr2O4@KIT-6 as catalysts, Au/m-MgCoCr2O4 showed the highest catalytic activity, It shows the catalyst has both a large specific surface area and an enhanced synergistic catalytic effect between carrier and gold nanoparticles. Based on this, we compared reaction activity of Au/MgCoCr2O4 and Au/m-MgCoCr2O4. Kinetic studies show that the two have the same synergy mechanism, and the latter activity is significantly improved compared to the former, indicate that the increase of the specific surface area of the carrier can significantly improve its catalytic activity. Then, with Au/m-MgCoCr2O4 as catalyst, selecting different alcohols to expand the substrate, and do Hammett curve, the results show that the reaction is promoted by the electron substituent to the catalytic reaction. It indicates that the rate determining step in the reaction center is positive, and the mechanism of the catalytic reaction was discussed. Au/m-MgCoCr2O4 showed good cycling stability in the circulation experiment. |
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