Preparation, Characterization And Catalytic Properties In Hydrocarbon Selective Oxidation Of Mof Catalysts With Multiple Active Sites

Metal-organic frameworks (MOFs), which are formed by coordination self-assembly of metal ions and organic ligands, are crystalline porous materials with regular channels. MOFs have abundant chemical and structure diversity. Moreover, they can act as hosts for a variety of guest molecules. These features provide multiple opportunities to create desirable active sites and determine MOFs as excellent candidates for catalysis application.This paper adopts MOFs as platforms to prepare multi-sites and cooperative catalysts through introducing metal nanoparticles, complex or exchanging node metal of framework. The catalytic performances of these catalysts for selective oxidation of cyclohexane to cyclohexanone and cyclohexanol (KA-oil) or selective oxidation of toluene to benzaldehyde were studied. The main contents of the dissertation are listed as follows:A series of Au/MOF were prepared by urea deposition-precipitation. The catalytic performances of these catalysts were investigated via selective oxidation of cyclohexane to cyclohexanone and cyclohexanol. Au/MIL-53(Cr) and Au/MIL-101(Cr) exhibit superior catalytic performance:the KA-oil selectivities are above80%and the conversions of cyclohexane are above30%. It is believed that both Au nanoparticles and framework Cr ions are effective catalytic sites in cyclohexane selective oxidation. The confinement effect of MIL-101(Cr) cages to Au nanoparticles results in <2nm Au particles, which accounts for that Au/MIL-101(Cr) presents higher selectivity than Au/MIL-53(Cr).A series of salen-MOF catalysts, metal-salen complexes incorporated into amino-functionalized MIL-101matrices by salicylaldehyde condensed to amino group and coordinated metal ion through postsynthetic modification (PSM), have been prepared. The catalytic performances of prepared catalysts were investigated via selective oxidation of cyclohexane to KA-oil. NH2-MIL-101(Cr)-Sal-Co exhibits best catalytic performance:when the KA-oil selectivity is91.7%, the conversion of cyclohexane reaches36.1%. It was believed that NH2-MIL-101(Cr)-Sal-Co behaves as cooperative catalyst for cyclohexane selective oxidation. That is, salen-Co(Ⅱ) attached to framework of MOF is able to assist in the generation of new radicals from peroxides via a Haber-Weiss catalytic cycle to promote conversion of cyclohexane while framework Cr ion is able to catalyze the dehydration of intermediate product cyclohexyl hydroperoxide (CHHP) to improve KA-oil selectivity. Therefore, both high KA-oil selectivity and high cyclohexane conversion are obtained.Ag-Cu-BTC was prepared by a postsynthetic exchange (PSE) method. The catalytic performance of this catalyst was investigated via selective oxidation of toluene to benzaldehyde by molecular oxygen in the absence of solvent and initiator. Ag-Cu-BTC exhibits excellent catalytic performance in this reaction:the conversion of toluene reached to12.7%while the selectivity of benzaldehyde maintained above99%. This demonstrates that Ag ions can replace Cu ions in Cu-BTC by PSE successfully. This method can be used to produce mixed nodes MOF materials. The introduction of Ag improved the conversion of toluene from6.5%to12.7%while kept the highly selective catalytic performance of Cu-BTC for oxidation of toluene to benzaldehyde.