Effect of metal doping on multi-step electron transfer and oxygen species of silicon-based nanocomposite aerogel supported Pd catalysts in oxidative carbonylation of phenol

Abstract

A series of new metal/silicon-based nanocomposite aerogel supported Pd catalysts were prepared using ambient pressure drying method with low energy consumption, which was applied in the synthesis of diphenyl carbonate (DPC) by oxidative carbonylation. New PS-MnCe nanocomposite areogel catalyst with better activity and stability than traditional metal oxide, which the single pass yield of DPC reached 34.2% with selectivity above 99.2% and TOF (turnover frequency) 100.6 molDPC/molPd h−1. The regeneration of the catalyst maintained the yield 16.6% in the third run with selectivity 97.9%. The prepared nanocomposite areogel catalysts were characterized by power X-ray diffraction pattern, FTIR spectrum, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller and Transmission electron microscopy, in order to make clear the effects of metal doping on multi-step electron transfer, oxygen species and active Pd2+ in the oxidative carbonylation of phenol by as-prepared nanocomposite aerogel supported Pd catalysts. The results showed that this kind of catalyst had a typical structure of aerogel stereoscopic three-dimensional network with high specific surface area and high metal dispersion, which effectively increased the number of active site (Pd2+). Different kinds of metal complexes can adjust the ratio of oxygen species, raise the efficiency of multi-step electron transfer and improve the performance of oxidation properties at low temperatures of the catalyst. The strong SMSI effect between the active center Pd and the support can effectively promote the recycling of Pd2+ so as to improve the activity and stability of the catalyst which may suite for industrial experiments in fixed-bed reactor in future.