The characterization of the coordination geometry of copper ions
included within zeolites has been carried
out with a combination of in-situ XAFS, photoluminescence, and IR
measurements in order to obtain a detailed
description of the formation of isolated Cu+ monomers
with planar 3-coordinate or linear 2-coordinate geometry
in the zeolite channels by thermal treatment under vacuum. The
Cu+ ions within the zeolites were found to
exist as isolated Cu+ monomers and
(Cu+−Cu+) dimers, their relative
concentrations strongly depending on
the type of zeolite used. With ZSM-5 and mordenite zeolites, most
of the copper cations were found to exist
as isolated Cu+ monomers, in contrast to the case of the
Y-zeolite. CO molecules were adsorbed selectively
only on isolated Cu+ monomers, distorting the
coordination geometry to form stable one-on-one
Cu+−CO
complexes.
UV irradiation of the Ag+/ZSM-5 catalyst prepared by an ion-exchange method in the presence of NO led to the photocatalytic decomposition of NO into N2, N2O and NO2 at temperatures as low as 298 K. Investigations of in-situ XANES, ESR, and DRS of the Ag+/ZSM-5 catalyst as well as the effective wavelengths of the irradiated UV light indicated that the excited state of the Ag+ ion included within the zeolite cavities plays a significant role in the photocatalytic decomposition of NO molecules.
The evacuation of the ZrO2 catalyst at higher temperatures led to the appearance of an abnormal absorption and photoluminescence due to the formation of coordinatively unsaturated surface sites. These active ZrO2 catalysts having coordinatively unsaturated surface sites exhibited a high catalytic activity for the selective dimerization of C2H4 to 2-C4H8. In the presence of H2 and C2H4, the formation of C4H10 was observed in place of 2-C4H8. The significant role of the coordinatively unsaturated surface sites in these reactions on the active ZrO2 catalyst has been clarified in detail for the first time.
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