日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

Copper (II)-exchanged zeolites act as effective catalysts for the selective photooxidation of cyclohexane and benzene with hydrogen peroxide. The structure of active species in the H₂O₂-treated copper(II)-exchanged Y zeolite (CuY-H₂O₂) was characterized by in situ UV-vis, in situ XAFS, and Raman spectroscopies. This review describes the structure, dynamic behavior, and photo-reactivity of the dicopper(II) complexes whose structure is similar to that of active species in copper-enzymes. The reaction of H2O2 with isolated Cu(II) ions in the zeolite yields the bis (μ-oxo)dicopper(II) (1) and the O₂²⁻ or HOO⁻- bridged dicopper(II) (2). The complex 2 is partly converted to superoxodicopper(II) (3) at ambient temperature. At higher temperature, the thermal desorption of the bridged dioxygen species in the complexes 2 and 3 occurs to yield two monomeric Cu(II) complexes and O2, while the complex 1 remains unchanged up to 473 K. Under photoirradiation the dioxygen species in complexes 2 and 3 react with cyclohexane, suggesting that this reaction step is an important step of the selective cyclohexane oxidation.