Transition Metal Oxide Supported Platinum Catalysts Toward Base-free Glycerol Oxidation

With the increasing demand for biodiesel in the market,glycerol,a by-product of biodiesel production,is in excess.Using relatively inexpensive glycerin as a raw material to produce high-value-added fine chemicals has greatly aroused interest.Among a wide variety of methods,the selective oxidation process via O₂ is one of the promising paths to transform glycerol into valuable chemicals.However,the problems of catalyst deactivation and poor selectivity have not been effectively solved.In addition,the oxidation process of glycerin usually requires strong alkaline reaction conditions which demand high requirements for reaction equipment and product separation.Therefore,the development of heterogeneous catalysts with high activity and selectivity to achieve glycerol oxidation under alkali-free conditions remains challenging.This thesis aims to develop glycerol oxidation catalysts with high activity and specific selectivity,and focuses on the relationship between the support property（composition,morphology,oxygen vacancy concentration and crystal form）and catalytic performance.The main research contents and conclusions are as follows:（1）CeO₂ has been introduced into the Pt/CNT catalyst to construct the"Pt-CeO₂-CNT"ternary interface,which has effectively solved the problem of Pt catalyst deactivation in the glycerol oxidation reaction.The conversion of glycerol over Pt-CeO₂/CNT catalyst reached 97.2%,significantly higher than those of Pt/CNT（70.0%）and Pt/CeO₂（63.1%）.Meanwhile,the selectivity of glyceric acid was improved significantly.Combining in-depth structural characterizations,anti-poisonous experiments,and catalytic reaction kinetics researches,the catalytic mechanism of CeO₂ was clearly revealed for the first time.On one hand,CeO₂ weakened the adsorption of the poisonous substance glyceric acid on the surface of Pt by regulating the electronic structure of Pt,making the catalyst highly resistant to toxicity.On the other hand,CeO₂ generated large number of active species by accelerating the dissociation of water at the ternary interface,greatly reducing the energy barrier of the primary glycerol oxidation reaction on 1-OH of glyerol,thereby accelerating the reaction rate and increasing the selectivity for glyceric acid.（2）Six kinds of Pt-CeO₂/CNT catalysts containing CeO₂ with different morphologies were synthesized by hydrothermal method.The catalysts with CeO₂nanoparticles had significant higher catalytic activity and anti-toxicity toward glycerol oxidation than those with other CeO₂ morphologies.Accordingly,the ternary catalyst has the most ternary interfaces,and the Pt⁰ content therein is highest.（3）The transition and rare earth ion-doped M-CeO₂/CNT（M=Zr,Sc,Y,La,Pr,Eu）supports were prepared by the ammonia precipitation method,and catalysts were prepared by loading Pt through the NaBH₄ reduction method.The catalytic activity and selectivity of Pt-Pr_0.2Ce_0.8O₂/CNT catalyst for glycerol oxidation are significantly higher than those of undoped or other metal ion doped catalysts.We believe that the high content of oxygen vacancies in Pr_0.2Ce_0.8O₂ and the high content of Pt⁰ in the catalyst are the main reasons for the excellent catalytic performance of Pt/Pr_0.2Ce_0.8O₂/CNT.（4）The black rutile TiO₂-supported Pt catalyst was synthesized by ultraviolet irradiation and NaBH₄ reduction method.The catalytic activity and selectivity for glycerol oxidation of black rutile TiO₂-supported Pt catalyst were much higher than those of anatase-type TiO₂ and white TiO₂ supported Pt catalyst.This is first report about the synergy of TiO₂ crystal form and the surface oxygen vacancy to improve the catalytic performance of Pt/TiO₂.