Dual-copper catalytic site formed in CuMFI zeolite makes effective activation of ethane possible even at room temperature

The role of dual-cation sites in zeolites has received a renaissance in chemistry and industry directed toward fixation and activation of various gases; such sites may be expected to be more efficient than a single-cation site. We aimed to clarify the real active centers in the copper-ion-exchanged MFI-type zeolite (CuMFI) for ethane (C ₂H ₆). A peculiar feature was found in the appearance of the characteristic IR bands at 2644 and 2582 cm ^-1 when C ₂H ₆ was adsorbed on Cu ⁺ formed in CuMFI. The existence of dual species composed of two Cu ⁺ ions bridging C ₂H ₆ was clearly indicated by extended X-ray absorption fine structure (EXAFS) data. Density functional theory calculations gave clear evidence that the two IR bands are distinctly due to C ₂H ₆ adsorbed on the dual-Cu ⁺ site and not on a single site; this agrees with the EXAFS data. These data lead us to conclude that the dual-Cu ⁺ site in the CuMFI sample is indispensable for efficient activation of C ₂H ₆ through the simultaneous interaction of C ₂H ₆ with two Cu ⁺ ions.