Staged oxidation of hydrocarbons with simultaneously enhanced conversion and selectivity employing O2 as oxygen source catalyzed by 2D metalloporphyrin-based MOFs possessing bimetallic active centers

With the objective to realize efficient and selective oxidation of hydrocarbons with O2 to partial oxidation products, 2D metal–organic frameworks (2D MOFs) possessing bimetallic active centers (Co&Cu, Co&Zn, Cu&Zn) were prepared to construct confined catalytic domains and staged oxidation sites. All the 2D MOFs were characterized systematically through FT-IR, XPS, PXRD, SEM, TEM, EDS, BET and TG analyses. Applied to the partial oxidation of C-H bonds with O2, superior catalytic performance was observed in the employment of 2D MOF Co-TCPPCu as catalyst, in which both of the conversion and selectivity towards partial oxidation products were enhanced simultaneously. The superior performance of oxidation system employing Co-TCPPCu as catalyst was mainly because of the decreased disordered autoxidation at lower reaction temperature, suppressed free radical diffusion in the confined catalytic domains of Co-TCPPCu, and enhanced oxidation of C-H bonds with oxidation intermediate product R-OOH catalyzed by second metal center Cu(II). For the important and classical oxidation of cyclohexane in chemical industry, the conversion was increased from 4.39% to 5.31% with the selectivity towards partial oxidation products being enhanced from 85% to 95% compared with homogeneous metalloporphyrin T(4-COOCH3)PPCo as catalyst. The staged oxidation paths and catalytic mechanism were also explored systematically through control experiments, free radical capture and electron paramagnetic resonance (EPR) analyses. This work presented an intelligent and valuable reference not only for the selective and efficient oxidative functionalization of hydrocarbons with O2 in both of the industrial application and academic research, but also for other important chemical transformations involved in free radicals.