Study On The Regulation Of Active Metal Adjacent Environment And Glycerol Oxidation Performance Of Platinum Based Catalysts

With the development of the biodiesel industry,the production of glycerol continues to rise.However,the current utilization of glycerol is not sufficient to consume the glycerol produced annually.Consequently,it is necessary to find new ways to utilize glycerol.Glycerol has three hydroxyl groups and active chemical properties,meaning that it can be converted to high-value-added chemicals such as dihydroxyacetone and glycerol acid by catalytic oxidation.The process of glycerol oxidation involves multiple parallel and consecutive reactions,which leads to difficulty in controlling the degree of reaction and many side reactions.Therefore,it is of great significance for improving the economic value of the biodiesel industrial chain by constructing reactive dominant active sites during catalyst preparation to effectively control the glycerol oxidation reaction path and improve the yield of the target product during the reaction.This paper focuses on the glycerol selective oxidation reaction and aims to solve the prominent problem of difficulty in controlling the primary/secondary hydroxyl selective oxidation path.This paper innovatively proposes a control strategy for dominant active centers induced by the adjacent atom of active metal in Pt-based catalysts.The active centers for highly selective catalytic conversion of primary/secondary hydroxyl groups are constructed by introducing Cu species and Co species to regulate the adjacent environment of active metal Pt,to achieve efficient directional high-value-added conversion of glycerol.Further,the scientific nature of the Pt adjacent environment in the catalyst affecting the selective oxidation of glycerol is revealed by catalyst structure characterization,in-situ monitoring of the reaction process and DFT calculation.（1）The Pt-sol,Pt Cu-sol catalysts and the supported Pt/Cu O,Pt-Cu/Cu O catalysts were prepared by sol-gel and sol-immobilization methods,respectively.All the catalysts were evaluated in glycerol oxidation and the results revealed that the supported catalysts showed high selectivity for dihydroxyacetone（2-OH/1-OH 2.2-5.5）,while the sol catalysts tended to generate glyceraldehyde and glycerate acid（2-OH/1-OH 0.1）.The alloying of active metal Pt also had an important influence on the catalytic performance.Compared with the Pt/Cu O catalyst,glycerol conversion increased significantly over the Pt-Cu/Cu O alloy catalyst（9.2%→66.2%）.The study on the structure-activity relationship of catalysts found that the change in product distribution was caused by the different adsorption sites of glycerol.For the Pt Cu-sol catalyst,the primary and secondary hydroxyl groups of glycerol were co-adsorbed on the Pt⁰-Cu⁰ sites,and the activation energy barrier of the primary hydroxyl group was the lowest（0.7950 e V）,which was beneficial to the production of glyceraldehyde and glycerate acid.However,for the Pt/Cu O catalyst,the primary and secondary hydroxyl groups of glycerol were co-adsorbed on the Pt⁰-Cu^Ⅱ site,and the activation energy barrier of the secondary hydroxyl group of glycerol is the lowest（0.8560 e V）,resulting in a higher selectivity for dihydroxyacetone.In addition,alloying of active metal increased the content of Pt⁰ in the catalyst（58.4%→77.3%）,which improved the ability to activate oxygen and promoted the conversion of glycerol effectively.Further study showed that when Pt⁰-Cu⁰and Pt⁰-Cu^Ⅱ sites are both present in the catalyst,the oxidation of glycerol primary and secondary hydroxyl groups occurs simultaneously,but the oxidation of glycerol secondary hydroxyl groups dominates.（2）To solve the problem of the high activation energy barrier of intermediate species in glycerol directional conversion to glycerol acid,Co species were introduced into Pt-based catalysts to enhance the performance of consecutive reactions by the construction of Pt adjacent active interfaces.The Pt/Zr O₂ and Pt/Co Zr O₂ catalysts were prepared by stepwise impregnation method.Compared with the Pt/Zr O₂ catalyst,the Pt/Co Zr O₂ catalyst（16.7%→65.2%）had a higher yield of glycerol acid.Furthermore,the catalytic performance evaluation was conducted using glyceraldehyde as the reaction substrate.Compared with the Pt/Zr O₂ catalyst,the Pt/Co Zr O₂ catalyst effectively promoted the conversion of glyceraldehyde to glyceric acid,and the conversion of glyceraldehyde increased from 37.2%to 70.1%.Kinetic studies showed that the activation energies of the Pt/Co Zr O₂ catalyst for glycerol and glyceraldehyde were 47.7 k J/mol and 27.3 k J/mol,respectively,which were higher than those of the Pt/Zr O₂ catalyst for glycerol and glyceraldehyde（62.6k J/mol and 70.7 k J/mol）,indicating that the introduction of Co species effectively reduced the activation energy barrier of glycerol and glyceraldehyde.The characterization of the catalysts showed that the Co species in the precursor was Co₃O₄.During the reduction,electron transfer occurred between Co₃O₄ and Pt,forming a Pt Co alloy.At the same time,Co₃O₄ interacted with Zr O₂,forming a Co-Zr active interface and rich oxygen vacancies.The study of structure-activity relationship showed that the controllable construction of Pt Co-V_o[Co-Zr]sites with low coordination on the Co-Zr interface effectively promoted the activation of glyceraldehyde,thereby greatly improving the efficiency of catalytic oxidation of glycerol to produce glyceric acid.