Existence of dual species composed of Cu(+) in CuMFI being bridged by C(2)H(2).

The interaction of ethyne (C(2)H(2)), as well as of carbon dioxide (CO(2)), with copper-ion-exchanged MFI zeolite (CuMFI) at room temperature was examined. It was found that CuMFI preferentially adsorbs C(2)H(2), while this material does not respond to CO(2). To clarify the specificity of CuMFI, a combination of various experimental techniques and theoretical calculations was adopted. Distinctive interaction energies of 140 and 110 kJ mol(-1) were clearly observed at the initial stage of C(2)H(2) adsorption on CuMFI, suggesting the presence of two types of adsorbed C(2)H(2). Two distinct IR bands at 1620 and 1814 cm(-1) appeared, which were assigned to the C[triple bond]C stretching vibration modes of C(2)H(2) differing in their adsorbed state. Both photoluminescence and X-ray absorption spectra showed that cuprous ions (Cu(+)) in CuMFI act as efficient sites for a marked C(2)H(2) adsorption. From the analysis of the latter spectra and the calculational results based on the density functional theory, the formation of dual Cu(+)...(C(2)H(2))...Cu(+) complexes was indicated for the first time for CuMFI, and such a special configuration of the Cu(+) sites contributed to the extremely strong adsorption of C(2)H(2). In contrast, it was necessary for the linear CO(2) molecule to take a bent structure to be adsorbed on Cu(+) in CuMFI. It was concluded that the difference in the adsorption response of Cu(+) in CuMFI towards C(2)H(2) and CO(2) is due to the chemistry between the nature of electron donation of Cu(+) and the hybrid orbitals of the respective molecules. This work promotes further understanding of the states of active centres in CuMFI for C(2)H(2) activation, as well as for N(2) fixation.