Encapsulation Of Metal Nanoparticles Within UiO-67 For Catalytic Hydrogenation Of Nitroarene

Metal-organic frameworks?MOFs?have been widely used to encapsulate metal nanoparticles?MNPs?to fabricate MNPs@MOFs nanocomposites with excellent activity,thanks to their high porosity,abundant chemical sites and adjustable structures.However,the diffusion of reactants and the accessibility of MNPs located in the center of MOFs may be hindered to some extend due to the inherent microporous structures of MOFs,which would decrease the catalytic efficiency and utilization of MNPs.Therefore,it is significant to encapsulate MNPs within the shallow layers of MOFs as close to their outer surface as possible,so as to shorten the diffusion distance of reactants and improve the accessibility of overall MNPs.Consequently,the catalytic efficiency and utilization of MNPs could be enhanced significantly.In this thesis,a solvent assisted ligand exchange-hydrogen reduction?SALE-HR?strategy was proposed,through which MNPs could be successfully encapsulated within the shallow layers of MOFs and hence the catalytic efficiency and utilization of MNPs could be promoted.The main contents and findings of the thesis are as follows:In terms of the SALE-HR strategy,the Pd²⁺-chelating 2,2'-bipyridine-5,5'-dicarboxylic ligands were controllably introduced into the shallow layers of Ui O-67 under moderate conditions.Afterwards,the introduced Pd²⁺precursors were reduced by H₂ and the obtained ultrafine Pd NPs were successfully encapsulated within the shallow layers of Ui O-67concentratedly,producing a series of LE-Pd@Ui O-T-t materials.Besides,the mechanisms of synthesis processes were thoroughly verified through theoretical calculation and experimental characterizations.The impacts of temperatures and durations for SALE on the properties of LE-Pd@Ui O-T-t were investigated by using various characterizations.The results confirmed that the LE-Pd@Ui O-T-t samples preserved good crystallinity and porosity.In addition,different temperatures and durations for SALE made a difference to some properties of the samples,such as the component contents as well as the distribution and particle size of Pd NPs.Furthermore,considering the distribution and particle size of Pd NPs as well as the structural properties of the as-prepared materials,80?was selected as the proper temperature for SALE.Subsequently,the LE-Pt@Ui O-80-1 material was also synthesized via this strategy,with ultrafine Pt NPs encapsulated within the shallow layers of Ui O-67.Finally,the materials with different distributions of Pd NPs were used as catalysts for the catalytic hydrogenation of nitroarenes to anilines at room temperature and 1 atm H₂.The reaction results showed that the LE-Pd@Ui O-80-t samples exhibited remarkable catalytic performances?nearly 100%conversion and selectivity?.Besides,the LE-Pd@Ui O-80-0.5catalyst with the thinnest Pd-embedded layers displayed the highest catalytic efficiency with a TOF value of 600 h^-1,as well as good recyclability and substrate tolerance.The results obtained in this thesis demonstrated that the catalytic efficiency and utilization of MNPs could be effectively improved by encapsulating MNPs within the shallow layers of MOFs as close to their outer surface as possible.