Fabrication Of PtGa Alloy Catalysts With Oxide Or Amorphous Carbon Interface Structure For Hydrogenation Of ?,?-Unsaturated Aldehyde

?,?-unsaturated aldehyde is an important chemical material,and its C=O bond selective hydrogenation product,unsaturated alcohol,is widely used in spices and medicine producing as a chemical intermediate.Study on selective ?,?-unsaturated aldehyde hydrogenation has important economic value.As a typical ?,?-unsaturated aldehyde probe molecule,cinnamaldehyde is widely used to reveal the competitive hydrogenation mechanism of C=C bond and C=O bond.At the same time,selective hydrogenation of cinnamaldehyde also is a good model reaction,which is widely used in the study of the structure-activity relationship of catalysts.Therotically,hydrogenating the conjugated C=C bond is thermodumaically favored than C=O bond.Therefore,the selective hydrogenation of C=O bond without attacking C=C bond is a knotty problem.Supported metal catalysts are widely used in chemical industry.The surface structure and interface structure of supported metal catalysts are the key factor to determine the performance of catalyst.Fabrication of interface structure could alter electronic structure through charge transfer and decorate geometric structure to enable the steric effect,which contributes to the improvement of selectivity in hydrogenation of ?,?-unsaturated aldehyde.This thesis aims at selective hydrogenation of cinnamaldehyde.On basis of high dispersion alloy catalyst obtained by LDH precursor method,aiming at the insufficient C=O selectvity of alloy catalysts,a new improving strategy to enchance the C=O selectivity based on in-situ construction of oxide@alloy interface structure by H2-O2 cycle atmosphere induction was created.Morevoer,facing the problem of decreased activity due to the coverage of active sites on oxide@alloy interface structure,a new strategy to improve the C=O selectivity while maintain the activity by constructing amorphous-carbon@alloy interface structure by H2/O2 mixed atmosphere induction was proposed.Meanwhile,the influence mechanism of interfacial effect on catalytic performance caused by different interface structure was revealed.(1)Aiming at the improvement of C=O bonds selectivity,PtGa alloy catalyst with Ga2O3@PtGa interface structure was obtained under H2-O2 cycle atmosphere by using PtCl62-/MgAlGa-LDHs as precursor.The adjustment of encapsulation extent of interface structure could be realized by tuning atmosphere cycle times.Furthermore,the interfacial effect of Ga2O3@PtGa interface structure on catalytic performance was studied.Cs-corrected STEM,CO adsorption and CO infrared spectroscopy revealed that the PtGa alloy nanoparticles are partially encapsulated by Ga2O3 interface layer which is characteristics of impermeable and reduced the exposure of the active metal.The C=O selectivityof Ga2O3@PtGa catalyst(87.5%)is higher than that of bare PtGa alloy catalyst(71.7%).In situ absorbed cinnamaldehye DRIFT demonstrated that the improvement of C=O selectivity could be ascribed to Ga2O3@PtGa interface structure optimizing reactant adsorption mode by steric effect.However,due to the construction of Ga2O3 interface layer leading to decrease of active sites,the 2h conversion decreased from 58.7%(bare PtGa alloy catalyst)to 46.6%,resulting in the unchanged yielding of cinnamyl alcohol(42.1%and 40.8%).(2)Aiming at the improvement of C=O bonds selectivity while maintaining the activity,PtGa alloy catalyst with C@PtGa interface structure was obtained under H2/CO2 atmpshere by using PtCl62-/MgAlGa-LDHs as precursor.The adjustment of encapsulation extent of interface structure could be realized by tuning atmosphere induction time and temperature.Furthermore,the interfacial effect of C@PtGa interface structure on catalytic performance was studied.Cs-corrected STEM,EELS and CO chemisorption clearly confirmed the PtGa alloy particles were well covered by amorphous carbon thin layer with the characteristics of porous and permeable,and the exposure of the active metal has no obvious decline.C@PtGa catalyst showed 2h conversion of 90.75,a turnover frequency(TOF)of 1546 h-1 and C=O selectivity of 93.6%,which are much higher than the bare PtGa(58.7%,891 h-1 and 71.7%)and also Ga2O3@PtGa(46.6%,866 h-1 and 87.5%)catalyst.XPS,XAFS and in situ absorbed cinnamaldehye DRIFT and XPS revealed the steric effect of C@PtGa interface structure and formed electron-enriched active sites could improve selectivity of C=O by optimizing reactant adsorption mode.More importantly,the impermeable characteristic of amorphous carbon layer is benefical for maintaining the accessibility of active sites,and the optimized adsorption mode of cinnamaldehyde exhibit higher C=O activation ability,which both contributed to the enhancement of activity.