Further evidence for the existence of a dual-Cu+ site in MFI working as the efficient site for C2H6 adsorption at room temperature.

We have recently clarified the following point: a dual-type site, which is composed of a pair of monovalent copper ions (Cu(+)) formed in a copper-ion-exchanged MFI-type zeolite (CuMFI), functions as the active center for strong ethane (C2H6) adsorption even at room temperature rather than a single-type site composed of a Cu(+) ion. However, the character of the dual-Cu(+) site in a CuMFI is not yet fully understood. In this study, we have elucidated the nature of the active sites for C2H6 based on infrared (IR) and calorimetric data. On the basis of the results obtained, we came to the conclusion that the dual-Cu(+) site composed of Cu(+) ions giving the adsorption energy of 100 kJ mol(-1) and the absorption band at 2151 cm(-1) for carbon monoxide (used as a probe molecule) at room temperature functions as an adsorption site for C2H6. We also evaluated, for the first time, the interaction between the dual-Cu(+) site and C2H6 energetically, by the direct measurement of heat of adsorption. The value of 67 kJ mol(-1) that we recorded was higher than that for the single-Cu(+) site in this sample and also for other samples, such as NaMFI and HMFI.