Dicopper(II)-dioxygen complexes in Y zeolite for selective catalytic oxidation of cyclohexane under photoirradiation

The photooxidation of cyclohexane with hydrogen peroxide is catalytically promoted by copper(II)-exchanged Y zeolite (CuY), resulting in the selective formation of cyclohexanol and cyclohexyl hydroperoxide. Analyses by in-situ UV-vis, in-situ Cu K-edge XAFS, and Raman spectroscopies are used to identify the active species in CuY treated with H2O2 solution. The reaction of H2O2 with isolated Cu(II) ions in Y zeolite yields the bis(mu-oxo)dicopper(II) (complex 1) and the O-2(2-) - or HOO--bridged dicopper(II) (complex 2). The complex 2 is partly converted to superoxodicopper(II) (complex 3) at ambient temperature. At higher temperature, the thermal desorption of the bridged dioxygen species in complexes 2 and 3 occurs to yield two monomeric Cu(II) complexes and O-2, while the complex 1 remains unchanged up to 473 K. Under photoirradiation the dioxygen species in complexes 2 and 3 are consumed, and the consumption rates increased when cyclohexane is added to the gas mixture, suggesting that the photoexcitation of the complexes is, involved in an important step of the selective cyclohexane oxidation.