| As one of the most important research field of materials science, the ordered porous materials mainly include ordered porous non-metallic materials and ordered porous metal materials, and TiO2, Al2O3, SiO2, ZrO2, SnO2, molecular sieve, zeolite, etc. are the most commonly used porous materials at present. As a important semiconductor material, nanometer TiO2is used in a wide range of applications, such as catalysis, sensors and photoelectric switch because of its excellent electrical, optical and chemical properties. Ordered porous TiO2has the general characteristics of porous materials, such as uniform aperture size, narrow pore size distribution, the orderliness of the pore structure, high porosity and large specific surface area, etc. The hole wall of orderly porous TiO2is usually composed of nanometer TiO2particles, so it can combine the advantages of both ordered porous material and nanoparticles, resulting in more novel features. And the channel structure of mesoporous TiO2is beneficial to the diffusion of the reactants and products, thus increasing the reaction rate. But mesoporous TiO2materials have many deficiencies, such as the low thermal stability, weak surface acidity and so on. In order to improve the catalytic properties of ordered porous TiO2, many researches have been done to modify its properties, and adding other metal oxides is a commonly used method. Among them, the porous Al2O3-TiO2composites can band the superiorities of Al2O3and TiO2together, which showed excellent carrier performance.In our previous work, Pd/γ-AlO3-TiO2catalysts were prepared by combined sol-gel and impregnation methods, and it exhibited a high activity in promoting the complete oxidation of ethanol. But at the same time the insufficiencies such as small specific surface area, low stability, poor selectivity of the catalysts have not been solved yet. In this paper, the porous composite oxide carrier γ-Al2O3-TiO2were prepared using the template method. The catalytic performance and and its selectivity to CO2for ethanol oxidation was studied. X-ray diffraction (XRD), N2adsorption/desorption, Transmission electron microscopy (TEM), FT-IR techniques were carried out to determine the physicochemical properties of the catalysts, the specific details as follows:(1) The catalytic activity tests showed that for the samples calcined at250℃, the performance of the composite carrier catalyst were much better than the single Ti catalysts for the complete oxidation of ethanol.(2) The appropriate pH value was necessary for the improvement of the catalysts activity during the preparation of the catalysts. It turned out that the catalysts prepared in the solution pH=10had the highest activity and selectivity, and higher pH was not conducive to the improvement of catalytic performance, the higher the pH, the lower the catalyst performance.(3) Carbon monoxide, ether, acetaldehyde and methane can all be detected in ethanol oxidation over the catalysts prepared by sol-gel and template method, respectively. The difference was no ethyl acetate produced over the catalysts prepared by the template method for ethanol combustion.(4) The low-angle XRD results showed that the samples calcined at low temperature (<250℃) exhibited the obviously ordered mesoporous structure, and high temperature roasting will lead to the collapse of the pore structure. The diffraction peak intensity of sample Pd/AT-250was nearly three times than that of the Pd/AT-150catalyst, stating that the crystallization degree of the hole wall of sample Pd/AT-250increased with the calcination temperature improving.(5) Wide-angle XRD results showed that the carrier and catalyst calcined at250℃exhibited typical lines of the anatase structure, and the brookite structure has emerged in the TiO2diffraction peak.(6) N2adsorption-desorption results indicated that the specific surface area and pore volum of the composite carrier γ-Al2O3-TiO2were greatly improved when γ-Al2O3was added to the system. The adsorption isotherms of the catalyst and carrier calcined at250℃belonged to the type IV, implying the well mesoporous structure formed.(7) HRTEM characterization results showed that the carriers and catalysts calcined at250℃had wormhole-like mesoporous structure. And TiO2of the carriers and catalysts existed in the form of anatase structure. And the mesoporous structure of the single support TiO2distributed more equally than that of the composite carrier.(8) Fourier infrared spectroscopy results implied that no template agent dodecylamine was residual in the catalyst Pd/AT-250. And TiO2existed mainly in the form of anatase crystal, this is in accordance with the XRD results. |
PDF Full Text Request