Preparation, Characterization And Catalytic Studies Based On Mg-Al LDH Nanosheets Catalysts

Layered double hydroxides is a typical kind of inorganic material which is constituted by electro-positive metal hydroxides brucite, interlayered balanced anions and water molecular, and the uniformal formula is [M2+1-xM3+x(OH)2]x+(An--x/nyH2O. LDH are extensively applied in adsorption, pharmaceuticals, catalysis and functional material fields due to the special properties of LDH:the controlling property of the layers constitution, the exchangeability of interlayer anions, the excellent thermostability and the acidity and basicity. However, because of the high charge density of the layers, heavily aggregation of the brucites and the narrow interlayer space, the surface area of LDH was quite low and the intercalated active sites was poorly accessible. In this paper, the highly dispersive LDH nanosheets were prepared and the effect of silane modification on the propertities of LDH was studied. Besides, the catalytic performances of the silylated LDH nanosheets and the silylated LDH nanosheets immobilized with Cu complexes were investigated. The main results are as following:1) Preparation, characterization and the catalytic performance of APTS functionalized LDH nanosheetsThe functionalized LDH catalysts with high surface area and large pore volume were prepared by modifying the brucite surface of the LDH nanosheets with aminopropyltriethoxysilane (APTS). The obtained catalysts APTS-MgAl-LDH-del were characterized by XRD、 FTIR、SEM、CO2 adsorption and N2 adsorption-desorption in detail. The results showed that the prepared LDH nanosheets were highly dispersive with high surface area and APTS was successfully grafted onto the LDH nanosheets surface via the condensation between APTS and the hydroxyl groups on LDH surface. And the catalytic study showed that APTS-MgAl-LDH-del exhibited superior catalytic performance in the Knoevenagel condensation reaction between benzaldehyde and malononitrile than the homogeneous catalyst APTS. These indicated that there had a synergistic effect between the LDH support and APTS.2) Preparation, characterization and the catalytic performance study of PTES modified LDH immobilized with copper complexesA novel strategy to prepare LDH immobilized with active component catalyst was proposed. The strategy involved preparing LDH nanosheets by AMOST method, modifying the brucite surface with PTES and immobilizing the copper complexes onto the modified LDH. The property of the catalyst was characterized by XRD、FTIR、N2 adsorption-desorption、SEM、TG\ ICP and contacting angle tests. The results showed that PTES modification improved the hydrophobicity of the surface and hindered the layered structure of the LDH from recovering during the copper complexes immobilization which is beneficial to improve the accessibility of the active sites and at the same time the substrate and the product could easily diffuse in the reaction system. Therefore, the catalyst MgAl-PTES-BDA/Cu showed better catalytic performance and stability in the alkene oxidation.The work in this paper provides a new route for novel functionalized hybrids and heterogeneous catalysts based on LDH nanosheets.