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

Abstract

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 Pd2+ cations. Moreover, the regular mesoporous structures of supports and homogeneous dispersions of Pd2+ 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 Pd2+ cations. Meanwhile, the catalytic activities of these supported Pd2+ 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 Pd2+ cations were linearly correlated to their o‐Ps annihilation properties. This result demonstrates that the catalytic activities of supported Pd2+ 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.