In situ time-resolved DXAFS for the determination of kinetics of structural changes of H-ZSM-5-supported active Re-cluster catalyst in the direct phenol synthesis from benzene and O-2

Dynamic structural changes and their kinetics of a Re-10-cluster catalyst in the direct phenol synthesis from benzene and O-2 were investigated by in situ time-resolved Re L-III-edge energy-dispersive XAFS (DXAFS). We have successfully monitored the structural transformation of active Re-10 clusters to inactive Re monomers in the course of the selective oxidation of benzene with O-2 on the catalyst by the DXAFS technique in a real time. The results obtained suggested that the Re-10 cluster transformed directly to the Re monomers, which showed first order kinetics with respect to the quantity of Re-10 clusters. The absence of undesirable intermediate structures with low phenol selectivity during the structural transformation may be an advantageous issue for the high phenol selectivity of 93.9% at 9.9% conversion in a pulse reaction and 87.7% at 5.8% conversion in a steady-state reaction on the Re-10-cluster catalyst. The reactant benzene inhibited the unfavorable structural transformation of the Re-10 cluster to the Re monomers during the selective benzene oxidation to phenol.