Synthesis Of Metal-Organic Frameworks Materials And The Application In Hydrogen Sorption And Conversion Of Biomass

Hydrogen as a renewable energy is considered as one of the most potential alternativeenergy source for fossil fuels. However, hydrogen storage remains as the bottleneck ofconstraining the effective use of hydrogen. Metal-Organic Frameworks (MOFs) have showngreat potentials in gas storage and catalysis, owing to their large surface area and low crystaldensity. Hydrogen spillover has been demonstrated as a promising approach to enhance thehydrogen storage capacities in nanostructured materials including carbons, zeolites, andMOFs at ambient tempreture. From the reports on hydrogen storage in MOFs by spillover, itis noted that the spillover enhancements are remarkably different on various MOF samples.The difference in storage capacity by spillover could be largely related to the structural andsurface characteristics of the MOFs, such as particle sizes, metal ions, or organic linking units.To understand the key factors that affect storage capacity by spillover, a fundamentalexamination of the structure-property relationships of MOFs is needed. However, to date,such a systematic study on the effects of structural and surface properties of MOFs onspillover storage is scarce.In this dissertation, the influencing factors of the hydrogen storage via spillover and thenew preparation methods for MOFs material featuring spillover were systematicallyinvestigation. To gain insights into the correlation between the chemical composition ofMOFs (e.g., metal ion and organic linker) and the H2adsorption capacity by spillover, wechosed two series of terephthalate-based MOFs materials(MILs and IRMOFs) that had veryclose surface areas and chemical formula units, respectively. Four MIL type MOFs, with asimilar formula unit (M(OH)BDC; M=Al, Cr, Fe, and V, BDC=terephthalate), wereinvestigated to elucidate the influence of constituent metal ions on spillover storage; and fiveIRMOFs, with a similar formula unit Zn4OL3(L=BDC, Br-BDC, NH2-BDC, NO2-BDC, and(CH3)2-BDC) were examined to disclose the impacts of organic ligands on H2uptakes.The hydrogen adsorption isotherms of the pristine MOFs and Pt/C-MOF mixtures weremeasured at298K and up to7.3MPa. It was found that the MOFs with different metal ions(but having the same BDC ligand) exhibited very close hydrogen capacities, suggesting thatmetal ions may not play an important role in the hydrogen uptakes of MOF materials by spillover. However, ligand functionalization was demonstrated to affect the storage capacitiesof MOFs by spillover significantly. Pt/C-IRMOF-2physical mixture had the highest H2adsorption capacity among the IRMOF structures, and the hydrogen adsorption capacity ofthe Pt/C-MTV-MOF-5-AF materials containing–(CH3)2functional groups exhibited thelowest H2capacity. The results suggest that the decoration of functional groups with strongelectrophilicity (i.e., electron-withdrawing ability) on the organic linkers in MOFs couldfacilitate the adsorption of spiltover hydrogen atoms on the ligands and thus enhance thehydrogen uptakes by spillover. The experimental results were in line with the DFTcalculations, which showed that the hydrogenation energies of the ligands withelectron-withdrawing groups were much higher than those with electron-donating ones on theMOF structures.MIL-101was chosen as the receptor for spillover hydrogen atoms owing to its largesurface area and acceptable thermal and water stability. Here Pd/MIL-101materials loadedwith different loading quatity (1wt%,3wt%,4wt%and5wt%) were prepared by usingdifferent methods (e.g. excessive impregnation, equal impregnation, organosol,deposition-precipitation and sol-gel method). The results of hydrogen adsorption showed thatdoing method and loading amount had a greater impact on the hydrogen storage of thePd/MIL-101materials by spillover, and the3wt%Pd/MIL-101prepared by the excessiveimpregnation method had the highest hydrogen storage capacity at room temperature.The catalytic conversion of biomass to useful chemicals by MOFs was investigated in thisdissertation. Biomass is considered as one of the most potential alternative energy source forfossil fuels because it is abundant, renewable, and environment-friendly. Moreover, lactic acidis an important chemicals and it is critical important to develop an efficient strategy for thepreparation of lactic acid from renewable biomass resource.MIL-101with open Lewis acidic Cr site was used as catalyst in anti-aldol condensationreaction of biomass glucide to synthesize lactic acid. The yield of glucose converting to lacticacid is up to68.9%at160℃and20atm oxygen. A high lactic acid yield was obtained inone-pot synthesis, which was friendly to environment. More importantly, this methodprovided highly selective for L-lactic acid, which has brought a new dawn for pharmaceuticaland food industry.