A series of Schiff-base functional groups modified MCM-41 materials have been synthesized and used as the supports of palladium species. The chemical structures of MCM-41 functionalized by nine Schiff-base functional groups were characterized by Fourier transform infrared spectroscopy (FT-IR), whereas their grafting densities of functional groups were achieved from the results of thermogravimetric analysis (TGA) and elemental analysis (EA). Small angle powdered X-ray (SAX) patterns demonstrate that the ordered mesoporous structures of MCM-41 were well retained after modification of functional groups and immobilization of Pd 2+ cations. Moreover, the regular mesoporous structures of supports and homogeneous dispersions of Pd 2+ cations were characterized by transmission electron microscopy (TEM). The positron annihilation lifetime spectroscopic (PALS) results revealed that the electronic and steric factors of functional groups could affect the o -Ps annihilation properties of support Pd 2+ cations. Meanwhile, the catalytic activities of these supported Pd 2+ cations chelated by different functional groups were determined by the Heck reaction of iodobenzene with n -butyl acrylate. At last, the catalytic activities of these supported Pd 2+ cations were linearly correlated to their o -Ps annihilation properties. This result demonstrates that the catalytic activities of supported Pd 2+ cations chelated by different functional groups can be readily determined by the o -Ps annihilation, which can be potentially used in the design and preparation of highly active palladium catalysts.
Li Linbo,Du Yijun,Li Yao,Shao Linjun,Qi Chenze,Zhou Shujing,Li Jinjing
Abstract Developing a facile and accurate method for assessing catalytic activities of supported metals can significantly promote the preparation and application of supported metal catalysts. Herein, we synthesized five MCM-41 materials functionalized with Schiff-base groups, which were employed as the supports for copper cations. The chemical structures and coordination of copper cations on the supports were characterized by Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The grafting densities were calculated by analyzing the results of thermal gravimetric analysis (TGA) and elemental analysis (EA). The microstructures of these supported copper catalysts were analyzed by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The oxidation of thioanisole to methylphenyl sulfoxide was employed to determine the catalytic activities of these supported copper catalysts while their o -Ps annihilation properties were evaluated by the positron annihilation lifetime spectroscopy. It is found that the o -Ps annihilation properties were linearly correlated with their catalytic activities. Therefore, the catalytic activities of supported copper species surrounded by different functional groups can be easily determined through o -Ps annihilation.
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