The Design And Synthesis Of The Catalysts Involving [AlO₆] Function Groups And Their Catalytic Activities Towards Selective Oxidation Of Glycerol

Glycerol（GLY）is a major by-product during ester transfer reaction for biodiesel formation.The global production of GLY is about 5.2 million tons in 2020,and the crude glycerol price is currently as low as 0.04-0.09$/LB.Therefore,it is of importance and economical interest to develop selective catalysts to upgrade GLY into renewable fuels.1,3-dihydroxyacetone（DHA）and glyceraldehyde（GLAD）are two value-added products in these compounds,which can be produced by selective oxidation of GLY.In this study,heterogeneous catalysts involving[AlO₆]function groups,i.e.,layered double hydroxides（LDH）and aluminum-borate molecular sieves（PKU-1）were synthesized with the hydro-thermal method.Transition metal（TM）ions,i.e.,Fe³⁺or Cr³⁺,were loaded on these two materials to promote their catalytic activities.The results show that the modified catalysts exhibit the high GLY conversion and the satisfying selectivity for DHA and GLAD.The catalytic mechanism was investigated in detail,which including the structure-function relationship between selective activation of H₂O₂ and the physic-chemical properties of catalysts surface（e.g.,acid-based nature and the chemical environment of TM dopants）,and the function mechanism of these oxyradicals for controlling over the reaction pathway and product distribution.（1）A series of Cr-doped LDH catalysts were synthesizes with the hydro-thermal method,the ratio of Mg/Al was also regulated to modify the surface properties of LDH.These materials can promote the conversion from GLY to DHA.And Cr content and the ratio of Mg/Al were evident to dominate material surface properties,i.e.,acid-base nature and the degree of metal dispersion.This can regulate the H₂O₂ activation,thus affect the final reaction results.Under the optimal reaction conditions（Cr doping was 6%,H₂O₂/glycerol=3.5,Mg/Al=1.8,0.6 g catalyst and 5 h）,the best GLY conversion and DHA selectivity reached 90.2%and 86.5%,respectively.（2）In order to control the oxidation sites of glycerol to produce DHA,as well as improve the H₂O₂ utilization efficiency,a series of catalysts,i.e.,different Cr and Fe loading PKU-1,were designed and synthesized.It was founded that Fe and Cr loading could control over the reaction pathway of GLY oxidation.Specially,Fe doping was significantly favorable for the GLAD producing,while Cr doping can improve GLY conversion and promote DHA formation.The GLY conversion and GLAD selectivity could achieve 84.06%and 81.3%catalyzed by Cr_0.05Fe_0.10-PKU-1.Noted that the reaction was driven by the microwave.The reaction results indicates that the microwave/H₂O₂/catalyst system can greatly improve the utilization efficiency of H₂O₂,and enhance the capacity for controlling over oxidation pathway.