Preparation of a nanostructured iron chromite spinel in the pure form and its catalytic activity for the selective oxidation of benzene to phenol: experimental and DFT studies

Selective oxidation of benzene to phenol in a single step is a long-standing challenge and has been a subject of potential interest for researchers. In this study, a nanostructured iron chromite spinel in the pure form was prepared, and it was found that this catalyst selectively oxidized benzene to phenol in a single step under mild and environmentally friendly conditions. The material was thoroughly characterized by XRD, Raman spectroscopy, BET, TEM, SEM, TPR, XPS and TGA. Under optimum reaction conditions, 71% benzene conversion with a phenol selectivity of 100% was achieved. The recyclability test was conducted and it was found that there was no significant loss of catalytic activity even after 5 recycles confirming the truly heterogeneous nature of the catalyst. For comparison, pure Cr 2 O 3 and Fe 2 O 3 were also prepared by the same hydrothermal method and characterized, and their catalytic activity results were also tested. DFT calculations showed that sp 2 CH bond activation of benzene over FeCr 2 O 4 (102) and Cr 2 O 3 (102) surfaces required an activation energy of 133.6 kJ mol 1 and 144.2 kJ mol 1 , respectively, matching the experimentally calculated activation barrier of 114 kJ mol 1 and 127.4 kJ mol 1 , obtained from kinetic studies. Selective oxidation of benzene to phenol using H 2 O 2 as oxidant, with efficient and recycling FeCr 2 O 4 nanostructured catalyst.