Synthesis Of Mesoprous Silica With Special Morphology And Its Utilization As Support For Catalysts

Mesoporous silica with nanoflower morphology(MSNF) not only has general characteristics of mesoporous materials, such as high surface area, well-defined mesopore structure, good hydrothermal stability, non-toxicity and easily modifiable surface, but also is featured with radially opened hierarchical pore structure, which is beneficial to the mass transfer and diffusion greatly. Therefore, MSNF material is widely recognized as a type of important material, which can be used as ideal support for catalysts, etc.In this paper, a MSNF material with well-defined morphology and uniform size distribution is synthesized by a hydrothermal method, in which a mixture of cyclohexane and water has been used as the solvent, with cetylpyridinium bromide(CPB) as the template. The material presents uniform particle size of ca. 200 nm, and its surface area is up to 502 m2·g-1. The effects of solvent composition, hydrothermal temperature, and molar ratio of Si to CPB on morphology and structure have been investigated. It is found that the existence of cyclohexane is vital to form nanoflower morphology and structure. In addition, the influence of the addition of second polymer template on morphology has been studied. Furthermore, a hard-template method has been used to design and synthesize a cotton-like nanoflower materials. The morphology and pore structure have been characterized by SEM, TEM, XRD, TG, FTIR, N2 adsorption-desorption, and a possible forming mechanism is suggested.Using MSNF as support, a Pd Au0.2/MSNF catalyst has been prepared by a facile impregnation-hydrogen reduction method, and its catalysis towards the hydrogenation of phenol has been explored. It is found that the Pd Au0.2/MSNF catalyst showed 4 times and 13 times higher activity than mono-Pd/MSNF catalyst and commercial Pd/C catalyst respectively. To investigate the influences of support on catalytic performance, XC-72 R, MCM-41, SBA-15 and MCM-48 have been selected as support to prepare a series of supported Pd Au0.2 catalysts, it is found that the catalytic activity of mono-Pd is higher than Pd Au0.2 when XC-72 R as support. Interestingly, the bimetallic Pd Au0.2 catalyst shows greatly enhanced catalytic activity when MSNF has been used as support. The activity of the catalysts with different mesoporous silica supports follows the order as: SBA-15> MSNF> MCM-48> MCM-41.Furthermore,a series of Pd Irn/MSNF bimetallic catalysts has been prepared by impregnation-hydrogen reduction method and applied to the hydrogenation of nitrobenzene to aniline for the first time. It is found that when the catalyst with the Ir/Pd molar ratio of 0.4 showed the highest catalytic activity, which is 5 times and 33 times higher than that of mono-Pd and mono-Ir catalysts respectively. By the characterization results of TEM, H2-TPR, and XRD, we find it that the addition of Ir could decreases the particle size of catalyst and strengthen its anti-aggregation performance.