Synthesis, Structural Analysis And Properties Of Ordered Mesoporous Alumina-Based Mixed Metal Oxides

Since the early 1990s, mesoporous materials are widely used in adsorption, catalysis, sensors, electrochemical and other aspects because of their unique structure. Following the mesoporous silica, a variety of mesoporous materials, such as ZrO2, WO3, TiO2, Al2O3, HfO2, Nb2O5, Ta2O5, SnO2 have been developed. Mesoporous alumina are attracting widespread attention due to its large surface area, tunable pore sizes over a considerably wide range, large amounts of Lewis acid sites on the surface and other structural advantages. In this paper, the controllable preparation of composite oxides was achieved by using solvent evaporation induced self-assembly (EISA) method. The microstructures of Cu-Mg-Al composite oxides were regulated under different atmosphere. Using a series of characterization methods to prove the different state of copper species, we also researched its application in CO oxidation reaction. The research contents are as follows:To begin with, Mg-Al and Cu-Mg-Al composite oxides were prepared by solvent evaporation induced self-assembly method. SXRD patterns show two diffraction peaks, a strong one and a weak one. Through TEM images, we can see a long-range ordered mesoporous structure. Based on the above two phenomena, we can conclude that Mg-Al and Cu-Mg-Al composite oxides with 2 D hexagonal mesoporous structure were prepared. Cu-Mg-Al composite oxides show a good thermal stability, it maintain a large BET surface area of 137 m2/g, a pore volume of 0.30 cm3/g and an average pore size in 7.1 nm after 4h-calcination under 800 ℃.Furthermore, Cu-Mg-Al composite oxides were treated at different atmosphere:based on XRD and TEM results, Cu-Mg-Al composite oxides with spinel structure were obtained at air atmosphere. The reduction peak was around 305 ℃ in the TPR patterns, this indicated copper was incorporated into the spinel skeleton; Then it was treated at reduced atmosphere, XRD and TEM results show metallic copper particles with sizes of 6-10 nm were uniformly distributed over the mesoporous surface. The reduction peak at 220 ℃ of the TPR patterns revealed the truth that copper migrate from skeleton to surface. The sample was further treated at oxidic atmosphere, only the diffraction peak of spinel was found in XRD patterns. Reduction peak of CuO at 290 ℃ was demonstrated in TPR patterns, illustrating the surface of copper on the surface was again incorporated into the spinel skeleton. In the test of CO catalytic performance test, we found that the CO conversion temperature of Cu-Mg-Al with spinel structure was at 270 ℃, whereas Cu-Mg-Al with Cu on the surface was at 165 ℃, indicating that the catalytic property of cooper on the surface is more active than the cooper in the skeleton.In this paper, mesoporous Cu-Mg-Al composite oxides with different states of copper species were synthesized by EISA method. Our study finds that the copper species convert between the skeleton and surface. Experimental results of CO oxidation show that there is a certain structure-activity relationship between the microstructure of Cu species and the catalytic effect.