Selective Oxidation Of Glycerol With Modified Zeolite And Ceria Nanosheet Supported Platinum-based Catalysts

In the process of transesterification production of biodiesel,glycerol is the main by-product of transesterification production of biodiesel.Selective oxidation of glycerol into high value-added chemicals through simple catalytic reaction is a feasible green strategy to achieve sustainable resource utilization.Herein,Pt with high activity as the main catalytic oxidation active site,based on the characteristics of Sn-modified zeolite and flake ceria,such as high specific surface area,acid-base properties,oxygen vacancy and defect sites,a series of high-efficiency Pt-base catalyst were designed and prepared.These catalysts have high activity to catalyze the oxidation of glycerol and high selectivity to specific products such as dihydroxyacetone and lactic acid.At the same time,the method for regulating acidic properties of zeolite,the mechanism of acid site of zeolite in catalytic reaction,intermetallic interaction and the influence mechanism of oxygen vacancy on catalytic activity were studied.The main research contents and conclusions are as follows:（1）A series of Sn-MFI with different Sn contents were synthesized by hydrothermal method.PtCu/Sn-MFI bifunctional catalyst which converted glycerol to dihydroxyacetone in a relay reaction mode was prepared by using Sn-MFI as a carrier.In this catalyst,Pt sites with Cu as promoter oxidize the primary hydroxyl of glycerol to glyceraldehyde.Then the Sn Lewis acid sites catalyze glyceraldehyde rearrangement into dihydroxyacetone.The synergistic effect of Cu and Sn makes the catalyst efficiently catalyze the conversion of glycerol into dihydroxyacetone.In this catalyst,the electron interaction between Pt-Cu and the formation of lattice distortion and PtCu alloy greatly improve the catalytic activity of the catalyst.At the same time,by controling the content of Sn,the ratio of Lewis acid and Br（?）nsted acid in zeolite was adjusted,the reaction path of dihydroxyacetone further conversion to lactic acid was blocked and the high selectivity（66.7%）and high yield（38.7%）of dihydroxyacetone were achieved.（2）Using layered cerium hydroxide（LCe H）as the precursor,ultra-thin lamellar ceria nanosheet（LCeO-T,T is the calcination temperature）was obtained by calcination at different temperatures.Through characterization analysis,it was found that with the increase of calcination temperature,the size of cerium oxide particles composed of LCeO increased and the content of Ce³⁺increased which means the oxygen vacancy concentration may also increase.Pt/LCeO-T catalysts were prepared with LCeO-T as supporter through the reduction of Na BH₄.Under the optimized reaction conditions,the selectivity of glyceraldehyde can reach 61.7%in base-free condition over5%Pt/LCeO-400℃catalyst and the selectivity of lactic acid can reach 63.2%in base condition over the 1.5%Pt/LCeO-600℃catalyst.The catalytic activity and lactic acid selectivity of 1.5%Pt/LCeO-600℃were significantly higher than short rod-like ceria,long rod-like ceria and nano-cubic ceria supported Pt catalysts.This may be related to the larger specific surface area,more abundant oxygen vacancies and defects of LCeO.Finally,Sn-MFI was introduced into Pt/LCeO catalyst,which improved the catalytic activity of the catalyst under the base-free condition and successfully converted the main product of glycerol oxidation from glyceraldehyde into dihydroxyacetone.That proved the catalytic effect of Sn-MFI on the isomerization of glyceraldehyde again and reflects its universality.