Evaluation of the Catalytic Activities of Supported Copper Catalysts Surrounded with Different Functional Groups by o-Ps Annihilation

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.