| Benzoic acid and sodium benzoate are important commodity chemicals, with wide use in food additive, preservative, spicery, plasticizer and mordant. The commercial production of benzoic acid and sodium benzoate via the catalytic oxidation of toluene is achieved by heating mixture of the substrate, cobalt acetate and bromide promoter in acetic acid to 250℃at high pressure. The process gives rise to problems such as difficult separation of products and homogeneous catalyst, large amount of toxic waste and equipment corrosion. In addition, requirement of expensive and specialized equipments also makes the cost of production very high, along with large amount of energy consumed by operation under extreme conditions. In this dissertation, the gold-based catalysts were used to catalyze the benzyl alcohol under one-pot solvent-free condition to find new and environmental-friendly routes, which is by performing the reaction under mild conditions using a variety of solid catalysts, ionic liquids or supercritical fluids.Nobel metal nanostructures have recently received much attention because of their unique optical, catalytic, and electrochemical properties which make them suitable materials for potential applications in various field. Supported bimetallic nanoclusters have been at the focus of interest for decades due to their unique catalytic properties. Gold-based bimetallic NPs exhibit interesting electronic, optical, chemical, and biological properties due to their new bifunctional or synergistic effects. The introduction of second metal into Au NPs has been expected to enhance the catalytic activity and selectivity.Their reactivity is affected by chemical compositions, for the addition of a second metallic element often modifies the stability and catalytic activity of the pure metal clusters by affecting both geometry and electronic properties.A novel efficient gold-based bimetallic catalysts were developed with high stability for one-pot solvent-free synthesis of sodium benzoate and benzoic acid from the green oxidation of benzyl alcohol using air as the oxidant under ambient pressure without any wastes emission. The preparation conditions of the catalysts, support crystal phase and the mole ratio of the two metal were optimized, and finally we prepared the gold-based bimetallic catalysts with high activity and stability were obtained. The conclusions are as follows:1. By optimizing the reaction temperature, reaction time and catalyst amount, the best reaction condition is as follows:1.08 g benzyl alcohol,0.5 g NaOH, bimetal: benzyl alcohol molar ratio 0.004,200℃,10 h. Precipitation order of An and Ag also has influence on the activity of gold catalysts. Activity results reveal that loading Ag before the precipitation of Au gives better catalytic activity than the catalyst obtained by precipitation of Au and Ag simutaneously. By altering the pretreatment temperature Au-Ag catalyst, e.g. drying, calcination and reduction, the AuAg/P25(500)-C catalyst which is calcined at 500℃after impregnation of Ag, followed by precipitation of Au and calcining at 300℃shows the highest activity. Au-Ag catalysts with different Au/Ag molar ratio are also prepared. It is found that the activity of Au-Ag bimetallic catalysts is better than that of monometallic ones. Meanwhile, catalyst with Au/Ag molar ratio of 1:3 shows the best activity. It is concluded that there is synergistic effect between Au and Ag.2. The AuPd/CeO2 bimetallic catalysts were prepared for the application in the oxidation of benzyl alcohol. In particular, the Pd promotional effects are studied through the systematic investigation set of AuPd/CeO2 bimetallic catalysts with a range of Au/Pd ratios. The addition, Pd nano-species show great influence on the gold catalysts, including changes in particle size, electronic structure and etc. The reaction activity increases with the increase of the Pd content. The optimum performance for the synthesis of benzoic acid from benzyl alcohol is observed over a catalyst with the Au/Pd of 3:1 molar ratio. |
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