Enhancing direct hydroxylation of benzene to phenol on Fe1/PMA single-atom catalyst: a comparative study of H2O2vs. O2-assisted reactions†
Abstract
In this study, systematic first-principles calculations were carried out to ascertain the optimal single-atom catalyst (SAC) among the 3d-transition metals (TM1 = Fe1, Co1, Ni1, Cu1, and Zn1) anchored on a phosphomolybdic acid (PMA) cluster for efficient benzene oxidation to phenol, which is otherwise challenging at ambient temperature. Strong binding due to substantial charge transfer between Fe1 and PMA, and the adsorption energies of H2O2 and O2 oxidants enabled significant bonding within the Fe1/PMA cluster, facilitating enhanced catalytic performance compared to that of 3d-TM1 (Co1, Ni1, Cu1, and Zn1). The Fe1/PMA cluster demonstrated enhanced reactivity towards H2O2 supported by lower activation barriers and rate-determining steps for H2O2 (0.84 and 0.67 eV) compared to O2 (1.02 and 0.66 eV). The spontaneous dissociation of H2O2 on Fe1/PMA, in contrast to O2, is a crucial step to initiate iron–oxo (Fe1–O) active site formation, easing benzene to phenol oxidation at ambient temperature. Thus, the proficient coordination environment of Fe1 atoms as SACs adsorbed on the PMA cluster is found to influence catalytic performance, especially in the case of H2O2. The proposed mechanism is reminiscent of hydrocarbon hydroxylation in enzymatic processes, establishing Fe1/PMA as an environmentally friendly, heterogeneous and non-noble metal green catalyst for electrocatalytic phenol production.