Study On The Oxidation Of Glucose To Sodium Gluconate Over Supportd Nano Gold Catalyst

Glucose, an environment friendly and low cost substance, is the most widely existing source in nature. Gluconate such as zinc, sodium, calcium and ferrite salts have a wide range of applications in chemical industry, food, medicine, light industry, etc.. With the development of the fine chemical industry, increasing demand for gluconate has been grown up. Five hydroxyls and one aldehyde exist in one molecule of glucose. How to selectively oxidize of aldehyde fast and efficiently and retain hydroxyl at the same time, has become a major focus of current research. Using gold nanoparticles as heterogeneous catalysts of glucose oxidation represents high activity and high selectivity under mild conditions, which has drawn widely attention of academia and industry fields.In order to get high-performance nano-gold catalyst for catalytic oxidation of glucose, considerable literature has been investigated. It is found that supporting materials and preparation method of catalyst are the most effective factors for the catalyst performance. On this basis, two types of material were carefully selected to be the main subject of study:activated carbon and titanium silicalite (TS-1). The catalytic reactions were carried under mild conditions with low temperature and atmospheric pressure. In each catalytic system, the influences of all carriers were inspected separately according to the physical structure, surface chemical properties, preparation methods and the amount of gold content. Based on the above, the best activity of the nano-gold catalyst were chosen and used to optimize the reaction conditions. The main conclusions are as follows:(1) Catalysts Au/C prepared by sol-immobilization (SI method) showed a high catalytic activity in the oxidation of glucose, which were better than the Au/C prepared by deposition-precipitation (DP method) or impregnation method (IM method). Graphite is not suitable to support nano-gold for glucose oxidation. Using SI method and C2(more than200mesh, specific surface area1068.0m2/g) as the support, the1wt%Au/C represented uniform particle size distribution of gold, ranging2-5nm, with well dispersion and exhibited the highest catalytic activity in the catalytic oxidation of glucose. In alkaline solution, using oxygen as the oxidant, the reaction conditions:50℃, pH9.5, O2flowrate40mL/min, catalyst0.22g, rotational speed of magneton1200r/min,7.5wt%glucose solution (2.64g glucose dissolved in30mL water), reaction time1h, both the conversion and the selectivity of glucose were up to100%and the TOF (glucose conversion rate per loaded Au) was up to1559h-1. No characteristic peaks of gold could be observed in the XRD pattern and ICP-AES test showed that surface, the efficiency of gold loading on Au/C catalyst was low (<1%). The hydrophobic surface of activated carbon might caused by the poor adsorption ability of the gold ion or gold sol in water solution.(2) Comparing to the commonly used oxide supports such as SiO2, AI3O2, TiO2, etc., nano-gold catalyst supported on TS-1showed a higher catalytic activity in the heterogeneous oxidation of glucose. Gold particles on TS-1prepared by the deposition-precipitation (DP method) were uniformly distributed, ranging from10to20nm in diameter, exhibited obvious characteristic diffraction peaks in the XRD patterns with high-load efficiency of more than80%. Therefore, DP method can be used to prepare high loading of gold nanoparticle catalysts. At the same time, catalytic activity of Au/TS-1prepared by DP method was better than that of Au/TS-1prepared by SI method or IM method. The Au/TS-1with4wt%gold-loading amount prepared by DP prepared showed the highest catalytic activity in the oxidation of glucose. The optimum reaction conditions were as follows:60℃, pH9.5, O2flowrate40mL/min, catalyst0.18g, glucose concentration5wt%(1.76g glucose dissolved in30mL water). In23min, both the selectivity and conversion of glucose could reach100%. However, the stability of the4wt%Au/TS-1catalyst was poor. In the fourth reuse, the catalytic activity has been greatly reduced. In addition, no synergy effect was found. The catalytic activity of the modified bimetallic catalysts Pd-Au/TS-1and Pt-Au/TS-1in glucose oxidation is lower than the original Au/TS-1catalyst.