Titanium oxide species anchored within the Y-zeolite cavities by
an ion-exchange method exhibit a high and
unique photocatalytic reactivity for the reduction of CO2
with H2O at 328 K with a high selectivity for
the
formation of CH3OH in the gas phase. The in situ
photoluminescence, ESR, diffuse reflectance absorption,
and XAFS (XANES and FT-EXAFS) investigations indicate that the titanium
oxide species are highly dispersed
within the zeolite cavities and exist in a tetrahedral coordination.
The charge transfer excited state of the
anchored titanium oxide species plays a significant role in the
reduction of CO2 with H2O with a high
selectivity
for the formation of CH3OH, while the catalysts
involving the aggregated octahedrally coordinated titanium
oxide species show a high selectivity to produce CH4, being
similar to reactions on the powdered TiO2
catalysts.
The addition of Pt to the anchored titanium oxide catalysts
promotes the charge separation which leads to an
increase in the CH4 yields in place of
CH3OH formation.
Highly dispersed titanium oxide photocatalysts anchored onto transparent plates of porous silica glass were
successfully prepared by metal ion implantation, and their photocatalytic reactivity for the liquid-phase
photocatalytic degradation of an aqueous 2-propanol solution was compared with that in an aqueous TiO2
dispersion. The titanium ions implanted into the porous silica glass are found to be present on the surface
layer as isolated tetrahedral titanium oxide moieties by diffuse reflectance absorption, SIMS, XPS, and XAFS
analyses. The specific photocatalytic reactivity of the anchored catalyst was much higher than that for TiO2
powder, which may be attributed to the tetrahedrally coordinated titanium oxide moieties. Metal ion implantation
is one of the novel and useful techniques to prepare highly efficient photocatalysts on glass plates.
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