Cu-Doped ZIF-8 metal organic framework as heterogeneous solid catalyst for aerobic oxidation of benzylic hydrocarbons
Mixed-metal metal organic frameworks have received considerable attention in recent years and it has been shown that the activity of the parent MOF is often enhanced upon doping with external metal ions in the metal organic framework. In this context, Cu2+ ions with different loadings were incorporated within the framework of ZIF-8 to obtain series of Cu-doped ZIF-8 and their activity was examined in the aerobic oxidation of hydrocarbons. The as-synthesized Cu-doped solids were characterized by powder XRD, UV-DRS, SEM, FT-IR, EPR and ICP analysis. The experimental results revealed that the activity of Cu-doped ZIF-8 is much higher than the parent ZIF-8 in all the substrates studied at 120 oC. Further, the activity of Cu-doped ZIF-8 with the highest Cu loading was eight fold higher than the parent ZIF-8 in the aerobic oxidation of cyclooctane at 120 oC with more than 80 % selectivity to the corresponding ol/one mixture. Cu-doped ZIF-8 was reused two times with no significant drop in its activity under identical conditions. Further, the comparison of the two times reused solid with that of the fresh solid by powder XRD and SEM analysis revealed that the structural integrity and morphology are retained during the oxidation reactions.