| Mesoporous materials as new materials have potential applications in the field of catalysis, adsorption and separation, due to the high surface area, narrow pore size distribution. Therefore, these materials have attracted much attention since first synthesis of the ordered mesoporous materials. Alumina (Al2O3) has been widely used as catalyst support and absorbents in industry owing to its unique properties such as multiple phases (amorphous,α,β,γ,δand so on), cheap price and good physical and chemical features. Mesoporous alumina (hereafter denoted as M-Al2O3) not only has excellent performance of normal Al2O3, but also has the characteristics of mesoporous materials, thus it possesses more promising potentials compared with normal Al2O3. Therefore, synthesis of M-Al2O3 is of special importance. In this work, M-Al2O3 with high specific surface area, uniform pore size and thermal stabilities was synthesized and used as the support of Pd catalysts for methane catalytic combustion. Also, synthesis of mesoporousβ-AIF3 derived from M-Al2O3 was conducted. The detailed results are as follows:1. M-Al2O3 with high thermal stability and high specific surface area was synthesized by a sol-gel method using nonionic block copolymer P123 as the template, aluminum isopropoxide as aluminum source under acidic conditions. The influences of the surfactant amount, pH, aging temperature and calcination temperature on the M-Al2O3 surface area and pore structure were investigated. Small-angle XRD, TEM, N2 adsorption and desorption results show that the M-Al2O3 has a highly ordered 2D hexagonal mesostructure. Under optimized conditions, the M-Al2O3 has a large surface area (230 m2/g) and pore volume (0.49 cm3/g) after calcination at 800℃.2. Pd catalysts supported on M-Al2O3 were prepared and tested for CH4 catalytic combustion. After the loading of Pd, the M-Al2O3 support remained good mesoporous pore structure. When calcined at low temperature, Pd species were mainly in mesoporous channels of the support, in form of highly dispersed PdO particles; however, at the elevated calcinations temperature, Pd species are in forms of crystalline Pd and PdO. The best catalytic performance was obtained on a Pd/M-Al2O3 catalyst calcined at 700℃, with a CH4 conversion of 91% at 400℃. A higher calcinations temperature such as 900℃resulted in a drop of reactivity but a higher turnover frequency, which might be due to the interaction between Pd phase and Carrier and the co-existance of metallic Pd and PdO in catalyst.3. Pureβ-AIF3 with high surface area was prepared derived from M-Al2O3, using a carbon template methodcombined with gas phase fluorination. The effects of fluorination temperature and fluorination method on the resultingβ-AIF3 were investigated. It was found that both the removal of carbonized P123 and direct fluorination of M-Al2O3 led to pure B-AIF3, provided that the fluorination temperature was carefully controlled, however, the surface areas of the resulting B-AIF3 by these two methods were low, being 17 m2/g and 60 m2/g. When carbonized sucrose was used as the hard template, the surface area of the resultingβ-AIF3 slightly increased. However, the pore structures collapsed after the template was removed, due to the fact that the 2D hexagonal structure of M-Al2O3 could not be remained after fluorination. |
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