Study on the relationship of catalytic activities and o-Ps annihilation properties of supported palladium species chelated by different functional groups

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.