Study On Catalytic Oxidation Of Glycerol At Room Temperature With Au Catalyst Supported On UiO-66 Derived Carbon Material

The depletion and non-renewability of fossil fuels have prompted urgent need for a new alternative renewable resource to solve the increasingly serious demand for living and production.In recent years,biodiesel has been regarded as a safe and reliable renewable resource.However,when biodiesel is produced by transesterification,the by-product glycerol also increases.Therefore,how to use the excess glycerol reasonably has become an urgent problem to be solved.Therefore,it is significant to convert glycerol into products with added value,which can be used in the industrial production of food additives and cosmetics.Heterogeneous catalytic oxidation is the most common method for the effective conversion of glycerol,the key of this way is to design a high-efficiency catalyst,which consisted of the carbon material as the support and noble metals as the support metals.Then it is applied to the liquid phase catalytic oxidation of the glycerol system and has obtained a relatively ideal catalytic effect.But the catalytic system is generally carried out at the reaction temperature of 60～100℃,which is bound to cause energy waste.In this paper,UiO-66 and Ce-doped UiO-66 were selected as the precursor,calcination at high temperature under the protection of inert atmosphere to obtain ZrO₂@C and Ce-ZrO₂@C support.The supported Au catalyst was successfully prepared by the colloidal deposition method,and this catalyst was applied to the catalytic oxidation of the glycerol system at room temperature.XRD,BET,TG,XPS,TEM,and other characterization methods were used to analyze the influence of the catalysts on the catalytic performance.In addition,the catalytic mechanism and deactivation reasons of the two catalysts were also studied.（1）The UiO-66 was synthesized by hydrothermal method,and the derivative ZrO₂@C was obtained by calcination at high temperature under inert atmosphere.Then the Au/ZrO₂@C catalyst was prepared by colloidal deposition method,and used for liquid phase catalytic oxidation of the glycerol system at room temperature.In order to reflect the advantages of Au/ZrO₂@C catalyst,this chapter took Au/ZrO₂,Au/C and Au/ZrO₂-C catalysts as comparison.According to the result,the Au/ZrO₂@C catalyst showed the best catalytic effect（69%glycerol conversion and 77%glyceric acid selectivity）at the reaction temperature of 25℃,the reaction time of 6 h and the molar ratio of GLY/Au of750 mol/mol.Combining XRD,TEM,XPS and other characterization methods,it was found that the catalytic activity of Au/ZrO₂@C catalyst mainly depends on the special structure of ZrO₂@C,the interaction between Au and ZrO₂@C,the size and dispersion of Au particles.At the same time,the catalytic mechanism of the catalyst was proposed by various characterization methods.In addition,the stability of the catalyst was also discussed,and the reason for its inactivation was briefly discussed.（2）In order to improve the serious problem of deactivation of the Au/ZrO₂@C catalyst,the support was further modified to obtain Ce-ZrO₂@C support,and the Au/Ce-ZrO₂@C catalyst was prepared.The results showed that the catalyst showed the most optimal catalytic effect under the conditions of Zr-Ce molar ratio of 5:1,support calcination temperature of 600℃,reaction temperature of 25℃,reaction time of 6 h,glycerol/Au molar ratio of 750 mol/mol,and the conversion rate of glycerol was 69%,and the selectivity of main product glyceric acid was 67%.XRD and TEM demonstrated that the introduction of Ce did not change the existing form of Zr,and the support continued the octahedral shape of UiO-66.From the analysis of XPS and TPR test results,it was known that there was electron transfer between Zrand Ce,indicating that there is interaction between Zrand Ce.At the same time,it was found that the calcination temperature of the support affected the distribution and size of Au nanoparticles,and then affected the catalytic effect of liquid phase catalytic oxidation of glycerol.It is worth noting that the catalyst stability after the Ce doping has greatly increased,the glycerol conversion rate remained stable at 69%and the selectivity of glyceric acid remained the same after four cycles.Through XPS characterization found Ce element diffraction peak is obvious,because the Ce from the inside of Au/Ce-ZrO₂@C gradually exposed during repeated use,in favor of the interaction with Zr.