Structure Manipulation Of Carbon Nanotubes Supported Pt Catalysts And Their Catalytic Performance In Base-free Oxidation Of Glycerol

Base-free catalytic oxidation of glycerol by carbon supported Pt-based catalysts is a burgeoning green chemical reaction process for production of value-added fine chemicals,in which rational design and optimization of the catalysts are important yet challenging issues.In this thesis,the structure of carbon nanotubes(CNTs)supported Pt catalysts(Pt/CNTs)has been tuned by the surface chemistry of CNTs supports and the addition of amine promoters to achieve high catalytic activity.Furthermore,the effects of product adsorption on catalytic performance have also been studied.The main results are as follows:(1)The Pt/CNTs catalysts with Pt loadings varying from 2%to 5%exhibit similar Pt 4f binding energy,but different average particle size,and thus different catalytic performance.The Pt/CNTs catalyst with an optimal particle size shows a high initial reaction rate.The selectivity of C3 products is found to be insensitive to Pt particle size,but glyceraldehyde(GLYD)prefers to be formed over largely sized Pt/CNTs catalyst.The pristine CNTs support was further treated by acid oxidation and acid oxidation followed by high temperature,respectively,and then used to support Pt nanoparticles.The obtained catalysts(Pt/CNTs-0 and Pt/CNTs-O-HT)possess similar particle size and Pt 4f binding energy with the Pt/CNTs catalyst.However,their catalytic performance is much different,which may be due to the difference in the acid-basic property of the supports.Especially,the Pt/CNTs-O-HT with stronger basic site presents a higher activity.Unfortunately,this catalyst also promotes the cleavage of the C-C bond,leading to a lower C3 product selectivity.(2)The introduction of diethylamine(DEA)and diethanol amine(DEOA)does not significantly change the particle size of the Pt/CNTs catalyst,but resulted in an increased binding energy of Pt 4f and enhanced surface basicity.The Pt/CNTs catalyst promoted by DEOA(Pt/CNTs-DEOA)exhibits higher Pt 4f binding energy and stronger basic site,and thus improving both the initial reaction rate of glycerol oxidation and the selectivity to glyceraldehyde(GLYD).Moreover,there exists optimal values for reaction temperature and GLY/Pt molar ratio for glycerol oxidation over Pt/CNTs-DEOA catalyst.(3)The addition of GLYD in small amounts has been found to benefit the conversion of glycerol,while the dihydroxyacetone inhibits the oxidation of glycerol to a certain extent.The deactivation of Pt/CNTs catalyst is further demonstrated to mainly result from the adsorption of glyceric acid.Most of the adsorbed products can be removed from the first used catalyst by washing,and the catalyst exhibits similar activity as the fresh one.However,after several times recycling,more and more products are adsorbed on the catalysts and cannot be removed,leading to the decrease in catalytic activity.