| As a technology-intensive industry,fine chemical industry has a wide range of applications,and it is the most dynamic emerging field in the chemical industry today.Therefore,the development of fine chemicals has become one of the strategic priorities for the development of chemical.In the process of fine chemicals synthesis,80%are related with the conversion of carbon-oxygen bond.However,the upstream raw reactants often contain a variety of functional groups,and the carbon-oxygen bond has high bond energy and relatively complex bond types.This leads to a reduction in the priority of carbon-oxygen bond conversion,which often accompanied by the competing conversion of other bonds.Therefore,the the directional transformation of carbon-oxygen bonds has become a challeng in the field of fine chemicals systhesis.Recent studies have shown that the metal-support interface structure of catalyst has unique physical and chemical properties,and thus paly a key role in the improvement of catalytic performance.According to the characteristics of the target reaction,constructing the interface sites that are conducive to the adsorption of reactants and the interface electronic structure that matches the orbitals of the reactants molecular,through the adjustment of interface electrons and geometric effects,has become an effective method to achieve catalytic performance improvement.Therefore,the construction of the metal-support interface structure provides an innovative way for the breakthrough of the C=O bond selective transform.This dissertation foucuses on the C=O bond hydrogenation reaction in the field of fine chemicals,especially the cinnamaldehyde(CAL)selective hydrogenation and the anthraquinone(EAQ)selective hydrogenation.Using the typical two-dimensional material—Layered double hydroxides(LDHs)as an innovation platform,controllable construct the metal-support interface structure catalyst based on the controllable characteristics of the chemical composition and structure of the LDHs materials.The effect on the C=O bond adsorption and activation behavior of the interface coordination unsaturated structure has been revealed by regulating the interface electronic and geometric effects.Based on the exchangeability of interlayer anions of LDHs,a new method for the controllable construction of the defect-enriched sandwich Pd-LDHs interface structure was carried out,and a breakthrough in the catalytic performance of the anthraquinone selective hydrogenation was achieved.Based on the controllability of the stacking degree of LDHs layers,a new method for constructing of di-vacancy metal/ultrathin LDHs interface structure has been developed,so as to obtain high selectivity with the high activity of the cinnamaldehyde selective hydrogenation.Based on the structural topological characteristics of LDHs materials,a new strategy for the controllable construction of MOx/metal interface structure was proposed,the influence of topological conditions on the MOx/metal interface structure and the synergistic strengthening mechanism of electronic and geometric effects in the anthraquinone reaction has been revealed.(1)Based on the exchangeability of interlayer anions of LDHs,a Pd/MgAlLDHs nanocatalysts with sandwich interface structure were prepared by ion exchange and liquid phase reduction methods,taking impregnated IMPd/MgAl-LDH as a control.A combination study verifies that more Pd-LDH interface sites appear in the sandwich interface structure resulting from high intimacy between the layers and Pd located in the interlayer space.More importantly,the loss of surface hydroxyl groups on the layer during the ionexchange process results in a significant increase of oxygen vacancies concentration and thus leading to the emergence of new defect-riched Pdoxygen vacancy interfacial sites.As expected,the optimized sandwich interface structure catalyst gives significant catalytic performance in the selective hydrogenation of anthraquinone,its TOF value(37375 h-1)is 2.7 times than the conventional IM-Pd/MgAl-LDH samples,and the selectivity of the former is also much higher than the latter.Such a high activity was attributed to the improved hydrogen spillover ability due to the promotion effect of increased Pd-LDH interfacial sites and oxygen vacancy concentration,which facilitated hydrogen activation/dissociation.Preferred selectivity was owing to the Pdriched oxygen vacancy interfacial sites which promote the activation of the C=O bonds due to the special adsorption mode.(2)Based on the controllability of the stacking degree of LDHs layers,an ultrathin Pt/CoAl-LDHs catalyst was prepared by using the one-pot method.A combination study shows the thickness of the ultrathin catalyst is 2.7-4.4 nm,which only contains only 3-5 layers.Moreover,the ultrathin LDHs not only contains oxygen vacancies due to the loss of surface hydroxyl groups,but also contains Co vacancies due to the loss of surface Co atoms.Strong interface electronic interaction between Pt and LDHs was induced by the abundant defect sites of the untrathin structure,resulting in electron-riched Pt-Vo-Co?+ and PtVco-OH?-interface sites.In the cinnamaldehyde selective hydrogenation process,the ultrathin Pt/CoA1-LDHs catalyst exhibits excellent catalytic performance,the TOF of it(1650.5 h-1)is 2.18 times that of the bulk catalyst(755.7 h-1).The ultrathin catalyst also exhibits excellent towards C=O bond(91.9%C=O selectivity under 94.3%conversion).The improved activity of the catalyst can be attributed to the enhanced ability of active hydrogen transformation which is promoted by the electron-riched Pt-VCo-OH?-interface sites,and the increasement in the interface sites number.The excellent selectivity can be attributed to the fact that the electron-enriched Pt-Vo-Co?+interface sites change the adsorption mode of the reactant molecules at the interface,which facilitates the activation of the C=O bond.In addition,the electronic effect between the Pt-LDHs interface can promote the desorption of the resulting product,thereby further preventing the formation of excessive hydrogenation products,so that the catalyst exhibits good reusability,and the conversion rate and the selectivity of the C=O bond remains above 90%after 6 times reuse.(3)Based on the topological effect of the LDHs structure,the coprecipitation method was used to introduce the transition metal Ti element into the MgAl-LDHs layers as the precursor of the oxide carrier.By precisely controlling the topological conditions,a series of Pd/MgTiAl-MMO catalyst with inverted TiOx/Pd interface structure was obtained.Compared with the Pd/TiO2 catalyst,the LDHs-based catalyst realizes the effective control of the migration and aggregation degree of TiOx during the interface construction,thereby inhibiting the excessive encapsulation of the active metal by the interface coating layer.During the anthraquinone hydrogenation process,the Pd/MgTiAl-MMO catalyst showed excellent catalytic performance,the H2O2 yield was 11.3 g/L which is 6 times than that of the Pd/TiO2 catalyst.More interestingly,the catalytic performance of the MMO catalyst exhibits the characteristics of a volcanic curve as the reduction temperature increases.This catalytic performance can be attributed to the special interface electronic and geometric effects brought by the TiOx/metal interface structure.As the reduction temperature increases,the increasing electronic effects in the MMO catalyst and the increasing number of Pd-Ti3+-Vo interface sites promote the activation of the C=O bond.However,the increase of the reduction temperature promotes the encapsulation of Pd by the TiOx coating layer,thereby reducing the accessibility of the reactant molecules to the active sites.Therefore,under the synergistic effect of interface electronic effect and geometric effect,the MMO catalyst with moderate reduction temperature shows the best catalytic performance. |
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