Synthesis And Catalytic Performance Of Non - Silica Mesoporous Materials

The mesoporous molecular sieve materials show the broad application prospects in petrochemistry, fine chemistry and other fields, owing to their large specific surface areas and pore volumes, uniform and adjustable pore sizes, diversified mesostructures, etc. In recent years, mesoporous silica-based materials have been extensively used as catalysts and catalyst supports. However, as mesoporous silica lacks of catalytic active sites, additional catalytic active species need to be introduced. Compared with the silica-based mesoporous materials, the non-siliceous mesoporous materials, such as mesoporous metal oxides, mesoporous metals and mesoporous amorphous alloys with high surface areas and narrow pore size distributions, hold promise for a wide range of potential application. However, the preparation of non-siliceous mesoporous materials is more difficult than that of mesoporous silica materials. Therefore, the study on the synthesis of the mesoporous non-siliceous materials attracts much attention.In this thesis, we studied the preparation of worm-like, two-dimensional hexagonal and mesoporous foamlike alumina materials via the solvent evaporation induced self-assembly method (EISA). The obtained mesoporous alumina materials were employed as supports of vanadium catalysts for the oxidative dehydrogenation of propane. We also prepared the3D gyroidal structure mesoporous Pd catalysts with different topologies and pore sizes and the mesoporous Pd nanowire arrays with different morphologies via the ultrasound-assisted two solvents strategy by using mesoporous silica molecular sieves as hard template. The Pd catalysts were tested in the enantioselective hydrogenation of acetophenone derivatives and the formic acid electrooxidation. In addition, the uniform mesoporous Ni-P amorphous alloy nanospheres were synthesized via liquid templated strategy and employed in the hydrogenation of nitrobenzene.1. The synthesis of mesoporous alumina for oxidative dehydrogenation of propane to propeneThe mesoporous alumina (m-Al2O3) was fabricated by the EISA method. A series of m-Al2O3with different mesostructure and pore size were synthesized by modulating synthesis conditions, such as humidity, solvents and the type of surfactant. When the surfactants of CTAB and DMA were applied, the worm-like mesostructure was obtained with the pore size between2and4nm. On the other hand, the PI23and F127could induce two-dimensional hexagonal mesoporous alumina with pore size between5and7nm, under the low humidity of15%and using ethanol and isopropanol as solvent. If appropriate amount of TMB was added, mesoporous celluar alumina foams were formed with large pore size of40nm. Through the co-synthesis method, Mg, Zr, Si, Ti and V doped mesoporous alumina materials could be synthesized with little effect to the mesoporous structure.The highly ordered hexagonal mesoporous alumina supported vanadia catalysts (V/m-Al2O3) with different vanadium contents were prepared by the impregnation method and tested in the oxidative dehydrogenation of propane. The characterization results showed that suitable loading of vanadia led to high dispersion of vanadium species and weak acidity of catalyst, which improved the propane conversion and propene selectivity. V/m-Al2O3also exhibited better catalytic performance than the vanadia-incorporated mesoporous alumina prepared by a co-synthesis method and γ-Al2O3supported vanadia by an impregnation method.2. The synthesis of3D gyroidal structural mesoporous Pd catalysts for asymmetric hydrogenation of acetophenone and its derivativesThe3D gyroidal structural mesoporous Pd catalysts with different topologies and pore sizes were prepared via an ultrasound-assisted two solvents strategy by using mesoporous molecular sieves KIT-6as hard template. The topology and pore size of the replicated Pd catalysts can be adjusted by using KIT-6treated at different hydrothermal temperature. When KIT-6prepared above373K were used as the template, the resulted mesoporous Pd replicated the structure of the parent silica perfectly and the Ia3d symmetry was preserved. When KIT-6was prepared at lower hydrothermal temperatures (<353K), the symmetry of the replicated Pd transformed from cubic Ia3d to I4132. The KBH4-reduced mesoporous Pd catalyst exhibits more ordered gyroidal structure and preferred orientation of low index planes than the H2-, N2H4·H2O-reduced samples.The relationship between topology, pore size, reduction method of a series of mesoporous Pd catalysts and their catalytic performances in enantioselective hydrogenation of acetophenone and its derivatives were studied systematically. We found for the first time that the enantiomeric excesses (ee) of the acetophenone hydrogenation reaction could be significantly enhanced by simultaneously manipulating the topology, pore size and reduction method of the mesoporous Pd catalysts. The double gyroid structure (Ia3d symmetry) was found superior to single gyroid (I4132) and hexagonal structure (P6mm) in obtaining high ee. The KBH4-reduced Pd catalyst exhibited higher ee than the N2H4·H2O and H2-reduced ones. The optimized catalyst exhibited ee of40-73%in the hydrogenation of acetophenone and some derivatives at atmospheric pressure. DFT study reveals that the double gyroid structure Pd catalysts with the desired lattice structure formed by KBH4reduction may lead to the formation of R-isomer preferentially.3. The synthesis of mesoporous Pd nanowire arrays catalysts for formic acid electrooxidationThe mesoporous Pd nanowire arrays with different morphologies were prepared by using mesoporous silica (Regular-SBA-15, Rod-SBA-15) as hard templates. When Regular-SBA-15was served as hard template, the1D Pd nanowires (1D-Wire-Pd) of several microns length and2D Pd nanowire array (2D-Wire-Pd) could be obtained by modulating synthesis conditions such as precursor contents, reductant and thermal treatment before reducing. For Rod-SBA-15, the short rod Pd (2D-Rod-Pd) was obtained.The catalytic activities of1D-Wire-Pd,2D-Wire-Pd and2D-Rod-Pd were tested in the formic acid electrooxidation. We found that the1D-Wire-Pd exhibited the best electroactivity with the peak current of324mA mg-1and the2D-Rod-Pd showed the worst electroactivity (205mA mg-1). However, the current decay on the2D-Rod-Pd and2D-Wire-Pd were significantly slower than that on the1D-Wire-Pd. At the end of the1000s test, the oxidation current on2D Pd nanowires array was about60%of the initial value. Considering the catalytic activity and stability, the2D-Wire-Pd has good application prospect.4. The synthesis of mesoporous Ni-P amorphous alloy nanospheres for hydrogenation of nitrobenzeneThe uniform mesoporous Ni-P amorphous alloy nanospheres were synthesized via a liquid templated strategy. The effects of synthesis conditions, such as the molar ratio of H2PO2/Ni2+, the reaction temperature, the type of surfactant, and the amount of the CTAB on the morphology and composition of the mesoporous Ni-P amorphous alloy were systematically studied. When the DMA was used as template, the core shell structure of Ni-P amorphous alloy could be obtained. As for CTAB, the wormlike mesoporous Ni-P amorphous alloy nanospheres could be produced at lower concentration. And the P contents (19.5-27.6at.%) and diameter (90-30nn) could be adjusted by change molar ratio of H2PO2-/Ni2+and the reaction temperature respectively. Interestingly, increasing the amount of CTAB, the core-shell, yolk-shell and hollow structure Ni-P amorphous alloy were obtained.The catalytic behavior of mesoporous Ni-P amorphous alloy was tested in the hydrogenation of nitrobenzene, and compared with that of regular Ni-P amorphous alloy. It shows that the mesoporous Ni-P amorphous alloy exhibits higher activity and aniline selectivity than regular Ni-P amorphous alloy.