Preparation Of Gold Catalysts And Its Effect On The Catalytic Activity In Glucose Oxidation

More attention is now paid to nano-gold catalysts due to their specific performance.However,relatively more studies focus on the catalytic oxidation in gas phase using nano-gold catalysts.Relatively few investigations regarding the influence of preparation conditions on the activity of nano-gold catalysts in the liquid phase oxidation have been carried out.In this paper,the influence of the preparation conditions of the Au/TiO₂ has been systematically investigated using the liquid-phase oxidation of glucose to gluconic acid as the probe reaction.The nano-Au/TiO₂ catalysts were prepared by deposition-precipitation(DP) method.The influence of the preparation conditions such as the loading of gold,the type of precipitating agent, the gold ion concentration,the temperature and pH during the precipitation as well as the calcinations atmosphere and calcinations temperature on the activity of the catalysts in the liquid oxidation of glucose to gluconic acid have been investigated.The optimal conditions for the preparation of the Au/TiO₂ was found as following:loading of gold = 1%,concentration of gold ion = 3.5×10^-3g·L^-1,DP temperature = 70℃,pH = 7.calcined in air were more active than that reduced in H₂. The appropriate calcinations temperature was 300℃.Using the catalyst prepared at such conditions,the conversion of glucose to gloconic acid amount 90%when the oxidation reaction was carried out at temperature of 65℃,the value of pH was 9,the mass ration of catalyst to glucose was 2:500 and the flow rate of oxygen was 25ml·min^-1. In order to understand the influence of the preparation conditions on the activity of the Au/TiO₂ in the micro-scale,the catalysts have been characterized using TEM,XRD and XPS.The results show that,the reaction of catalytic oxidation of glucose was non-structure sensitive reaction,the catalyst activity was increased with lowering the size of the gold particles.However,the particle size of nano-gold was not the soly factor that determine the activity,the content of Au^δ+ in the catalyst also plays an important role.Based on the results of the XPS curve regression, it was found that the catalyst prepared under the optimal conditions showed a ratio of Au^δ+/Au⁰ being approximate 0.59.