Evaluating the catalytic performances of supported transition metal catalysts by positron annihilation lifetime spectroscopy

Abstract

Supported transition metal catalysts have played a critical role in the modern synthetic chemical industry. Herein, MCM-41 was chemically modified with amino groups and then used as the support of six transition metal cations. The chemical structures, microstructures and dispersions of these supported transition metal cations were carefully characterized by XRD, TEM and BET. The chelations of modified MCM-41 support with these transition metal cations were confirmed by FT-IR and XPS. The reduction reaction of 4-nitrophenol into 4-aminophenol was employed to evaluate the catalytic activities and recyclabilities of these supported transition metal catalysts. Meanwhile, their reactivities with o-Ps species were assessed by positron annihilation lifetime spectroscopy (PALS). It was found that the reduced o-Ps annihilation intensities (ΔI3) were well associated with their catalytic activities while the o-Ps annihilation lifetime values (τ3) were related to their catalytic recyclabilities. In all, the catalytic activities and recyclabilities of supported transition metal cations can be conveniently evaluated by their o-Ps annihilation properties. This method holds great potential in the design and preparation of highly active and stable supported transition metal catalysts.