Construction Of Noble Metal Catalysts From Amino Acid Complexes And Studies On Selective Hydrogenation Of Unsaturated Aldehydes

The selective hydrogenation of unsaturated aldehydes is an important industrial process for the production of fine chemicals such as perfumes,fragrances and pharmaceuticals.However,due to the unique reaction pathway of unsaturated aldehyde,the hydrogenation reaction product of unsaturated aldehyde is not unique.In addition,the hydrogenation of C=C bond is better than that of C=O bond in thermodynamics,which makes it more difficult to obtain the hydrogenation products of single C=O bond.Traditional metal-organic frameworks（MOFs）as supports support metal nanoparticles（NPs）,which can promote the selective hydrogenation of C=O bonds through steric confinement and metal nodes,but metal NPs confined in pores tend to exhibit low catalytic activity.Therefore,this paper intends to use amino acids as organic ligands to prepare coordination polymer-supported metal NPs with amorphous structure.Meanwhich,the C=O selectivity of the catalyst was improved by enhancing the interaction of metal NPs with the support and introducing the second metal.It is hoped that the catalyst can effectively catalyze the selective hydrogenation of unsaturated aldehydes to unsaturated alcohols at lower temperatures.1.Co（Ⅱ）-amino acid coordination polymers（Co-Dacp:Co-Asp,Co-Glu,Co-Aa）were prepared by hydrothermal method using Co（Ⅱ）ion as metal site and L-aspartic acid,L-glutamic acid and D-2-aminoadipic acid succinic acid as organic ligand to load PtNPs to prepare amorphous Pt/Co-Dacp catalysts.At low Ptloading（1.0wt.%）,Pt/Co-Dacp catalysts showed high catalytic performance(TOF>900 h^-1).The microstructure and PtNPs state of the catalysts were characterized by XRD,HRTEM,XPS and BET,etc.;the effects of supports,Ptloading,reaction temperature,H₂ pressure,reaction time and solvent on catalytic performance were investigated.The results showed that ethanol was used as the reaction solvent at 60°C and P（H₂）=20 bar for 2 h,the hydrogenation conversion of cinnamaldehyde was 87.9%and the selectivity was 89.3%of cinnamyl alcohol on 1.0 wt.%Pt/Co-Asp catalyst,which is attributed to the formation of Pt^δ+by electron transfer between PtNPs and support,as a potentiophilic point,promotes the polarization of the C=O bond at the active center.2.To enhance the interaction between the carriers and metal NPs,the amorphous coordination polymer Fe-Asp was prepared using adenine（A）modified Fe（III）with L-aspartic acid to obtain a functionalized Fe-Asp-A coordination polymer and used as a catalytic carrier for PtNPs to obtain Pt/Fe-Asp-A catalysts.The surface morphology,crystal structure and interaction between PtNPs and Fe-Asp-A catalyst were analyzed by XRD,HETEM,SEM,XPS and BET,etc..Due to the electron transfer between Fe-Asp-A and PtNPs and the existence of Lewis acid sites(Fe³⁺),the conversion of cinnamaldehyde and selectivity of cinnamol by 3.0wt.%Pt/Fe-Asp-A_0.25 catalyst reached 93.1%and 91.2%,respectively,when isopropanol was used as the reaction solvent and the reaction time was 2 h at 50°C,P（H₂）=20 bar.In addition,the catalyst maintained good catalytic performance after10 cycles of testing with 90.2%conversion of cinnamaldehyde and 91.3%selectivity for the generation of cinnamyl alcohol.3.PtCo intermetallic nanoparticles（IMNs）were prepared by adjusting the surface electronic properties of PtNPs with a trace amount of Co;Co Pt/Cr-Glu-His catalyst was prepared by using Cr-Glu-His coordination polymer prepared by Cr（Ⅲ）,L-Glu and L-His as PtCo IMNs support.The microstructure,crystal structure,electronic state and structure-activity relationship of the PtCo/Cr-Glu-His catalyst was analyzed by XRD,HETEM,XPS,etc.,the effects of different factors on the catalytic performance of 3wt.%Pt0.6 wt.%Co/Cr-Glu-His_0.25 were investigated.Under the optimum reaction condition of 100°C,15 bar H₂,5 m L isopropanol,the conversion of cinnamaldehyde and the selectivity of cinnamyl alcohol are 96.2%and 90.8%,respectively.In addition,3 wt.%Pt0.6wt.%Co/Cr-Glu-His_0.25 catalyst also has excellent catalytic effect on other unsaturated aldehydes,which is attributed to the interaction of PtCo IMNs and the activation of C=O bond by Lewis acid sites(Cr³⁺).