| Alcohol selective oxidation reaction is one of the important reactions in the field of fine chemicals.Its product aldehyde and ketone has a wide range of applications in the production fields such as pharmaceuticals,coatings,cosmetics,food additives and flavors.With further research,02 as the oxygen source in selective oxidation of alcohol has received more and more attention.However,it is hard to react due to the high activation energy of molecular oxygen which makes it is difficult to dissociate.Therefore,it is essential to use a suitable catalyst to reduce the activation energy of molecular oxygen,so that the molecular oxygen can be rapidly dissociate and achieve the purpose of promoting the reaction rate.Supported precious metal catalysts have attracted much attention due to their excellent catalytic performance.Pd-based and Au-based catalysts are most widely used in the traditional alcohol selective oxidation reaction,but their application is limited by the problems of low precious metal reserves and high prices and are limited by carriers and preparation methods.It can be reduced by increasing the utilization of precious metals.As an important component of the supported precious metal catalyst,the carrier can not only support the active component,but also various groups and sites on the surface can participate in the reaction process as the active center in the reaction system.The active metal component synergistically promotes the occurrence of the reaction.Therefore,it is of great significance to find a suitable carrier and select a suitable preparation method to prepare a supported noble metal catalyst with high activity and high atom utilization.Layered composite metal hydroxides(LDHs)are a class of functional two-dimensional layered materials that have found wide applications as catalyst supports,catalysts or precursors in the catalytic field.LDHs can be used as a supported precious metal catalyst carrier in alcohol oxidation reaction.The hydroxyl group on the surface can promote the reaction as the adsorption site of benzyl alcohol;and the defect sites on the surface with metal coordination unsaturation can also participate.The active metal component is assisted in the reaction to promote the reaction.However,there is a low utilization of the LDHs laminate due to it's layer spacing,and the metal components and active sites located in the other laminates are less accessible than the outermost laminate.Therefore,the accessibility of LDHs surface sites can be improved by ultra-thinning of LDHs.Simultaneously,the ultra-thinning of LDHs can generate a large number of surface defects to improve the catalytic performance of the catalyst.Based on the characteristics of LDHs laminate thickness and layer metal variability,the ultra-thin TiMgAl-LDHU(Ti-LDHu)carrier was prepared.According to the surface structure of the carrier,the preparation and research of various high-efficiency supported noble metal catalysts were carried out.The relationship between the synergistic effect of metal and carrier and the catalytic performance in the catalyst was discussed.1.Ultrathin Ti-LDHu was prepared by inhibitor method,and Pd/Ti-LDHu catalyst was prepared by sol-immobilization method.The effects of surface defect strcture on active component structure and the performance of selective oxidation of benzyl alcohol was investigated by comparing with the Pd/Ti-LDHN catalyst which was prepared by using TiMgAl-LDHN(Ti-LDHN)as carrier.The catalytic result shows that the Pd/Ti-LDHU catalyst has higher reactivity than the Pd/Ti-LDHN catalyst,and its TOF value can reach 19,000 h-1.The surface defect structure of the catalysts is analyzed by UV-vis DRS,PL spectrum and XPS,there are abundant defect structure(Ti3+-Vo)at the surface of the ultra-thin Ti-LDHu has been found which has a strong promoting effect on the adsorption and activation of O2.The active oxygen species generated by the activation of Ti3+-Vo site can rapidly reacted with the active metal hydride to complete the entire alcohol oxidation process.2.Based on the ultra-thin Ti-LDHu carrier structure,a new P-Au/Ti-LDHu catalyst with strong metal-support interaction is prepared by photodeposition method and used in the benzyl alcohol oxidation reaction,and its TOF was up to 4083 h-1.By compared with the catalysts prepared by the impregnation method IM-Au/Ti-LDHU catalyst(2881 h-1)and the precipitation deposition method DP-Au/Ti-LDHU catalyst(2468 h-1),its reactivity was increased by 41.7%and 65.4%and catalyst stability studies show that the catalyst prepared by photodeposition has the best reaction stability,respectively.The characterization of the catalysts showed that the high activity and stability of the photodeposition ultra-thin catalyst is mainly attributed to the strong absorption capacit for light of the ultra-thin Ti-LDHU carrier,which is beneficial to generation of photogenerated electrons.The high concentration of Ti3+-Vo site on the surface that can anchor the active metal particles in the photodeposition process,and effectively inhibiting the agglomeration of the active components.In addition,the metal Au as a reactive site of the catalyst plays a decisive role in the a-C-H elimination of alcohol.The strong metal-carrier interaction increases the electron cloud density on the Au surface,which can effectively promote the elimination of alcohol a-C-H and enhance the reactivity of P-Au/Ti-LDHU catalyst. |
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