Characterization of zirconium-silicon binary oxide catalysts prepared by the sol-gel method and their photocatalytic activity for the isomerization of 2-butene

Article abstract of DOI:10.1021/jp961523p

Zirconium-silicon binary oxide catalysts having different Zr concentrations were prepared by the sol-gel method and used as photocatalysts. The photocatalytic activity of these catalysts was investigated for the isomerization of cis-2-butene and was found to be enhanced in regions of lower Zr content. In situ photoluminescence, UV-vis reflectance, XRD, EXAFS, and XPS spectroscopic investigations of these zirconium-silicon oxide catalysts indicated that the Zr ions in the oxides which have a low Zr concentration exist separately as extremely small zirconium oxide species in the SiO₂ matrix while the radiative decay from the charge-transfer excited state of these species results in a characteristic photoluminescence. These results and the quenching of the photoluminescence by the added butene molecules showed that the higher photocatalytic activity of the zirconium-silicon binary oxides having a low Zr content is linked to the catalytic activity of the charge-transfer excited state of the zirconium oxide species, [Zr³⁺-O^-]*, in the catalysts.

Full text of DOI:10.1021/jp961523p

J. Phys. Chem. B 1997, 101, 369-373
369
Characterization of Zirconium-Silicon Binary Oxide Catalysts Prepared by the Sol-Gel
Method and Their Photocatalytic Activity for the Isomerization of 2-Butene
Sang-Chul Moon, Mutsuko Fujino, Hiromi Yamashita, and Masakazu Anpo*
Department of Applied Chemistry, College of Engineering, Osaka Prefecture UniVersity, 1-1 Gakuen-cho,
Sakai, Osaka 593, Japan
ReceiVed: May 24, 1996; In Final Form: August 23, 1996X
Zirconium-silicon binary oxide catalysts having different Zr concentrations were prepared by the sol-gel
method and used as photocatalysts. The photocatalytic activity of these catalysts was investigated for the
isomerization of cis-2-butene and was found to be enhanced in regions of lower Zr content. In situ
photoluminescence, UV-vis reflectance, XRD, EXAFS, and XPS spectroscopic investigations of these
zirconium-silicon oxide catalysts indicated that the Zr ions in the oxides which have a low Zr concentration
exist separately as extremely small zirconium oxide species in the SiO2 matrix while the radiative decay
from the charge-transfer excited state of these species results in a characteristic photoluminescence. These
results and the quenching of the photoluminescence by the added butene molecules showed that the higher
photocatalytic activity of the zirconium-silicon binary oxides having a low Zr content is linked to the catalytic
activity of the charge-transfer excited state of the zirconium oxide species, [Zr3+-O-]*, in the catalysts.
Introduction
oxide catalysts nor a clarification of the role of coordinatively
unsaturated surface species on zirconium oxide particles.
ZrO2 is well-known as an active catalyst for the hydrogenation
of carbon monoxide to produce alcohol and isobutene. The
reaction mechanism for the synthesis of alcohol and isobutene
on ZrO2 has been reported by Onishi et al.1-5 and Ekerdt et
al.6-9 Tanabe et al. have also reported that ZrO2 catalysts
exhibit catalytic activity for the isomerization of 1-butene to
cis- and trans-2-butenes at 373 K.10 Furthermore, it has been
established that coordinatively unsaturated surface sites are
produced on the powdered oxides by evacuation at higher
temperatures and that they not only play a significant role in
the appearance of abnormal absorption and photoluminescence
in insulating materials such as MgO and SrO but are also vital
as active sites for catalytic reactions on these oxides.11-14 We
have observed the abnormal absorption and photoluminescence
spectra with ZrO2 catalysts degassed at temperatures higher than
600 K, suggesting that such coordinatively unsaturated surface
sites which correspond to the abnormal absorption and photo-
luminescence are also formed on the powdered ZrO2 catalysts
by evacuation at higher temperatures. Furthermore, we have
also observed that on these ZrO2 catalysts, hydrogen molecules
adsorb dissociatively and the hydrogenation of carbon monoxide
and ethylene proceed effectively and efficiently.15-17
The sol-gel process offers unique advantages for the
preparation of highly dispersed transparent catalysts, coating
materials, active thin film photocatalysts, and multicomponent
ceramics. Recently, Anthony et al. have reported that Zr/Si
binary oxides prepared by the sol-gel method exhibit catalytic
activity for the selective formation of isobutane and isobutene
from synthesis gas.18 Zr/Si binary oxides having strong acid
sites have also been found to exhibit catalytic activity for the
dehydrogenation of cyclohexanol.19 Also, coordinatively un-
saturated surface species on magnesium oxide particles are
known to be generated on the Mg/SiO2 oxides prepared by an
impregnation method as well as to play a significant role in the
photocatalytic oxidation reaction of propylene with O2 on the
catalyst.20 However, until now there have been no investigations
on the photocatalytic properties of zirconium-silicon binary
In the present study, we deal with the characterization of
zirconium-silicon binary oxide catalysts prepared by the sol-
gel method by means of in situ photoluminescence, UV-vis
reflectance, EXAFS, XPS, and XRD spectroscopic techniques
and their photocatalytic activity for the isomerization of cis-2-
butene into trans-2-butene and 1-butene at 295 K using a
photocatalytic flow reaction system.
Experimental Section
Preparation of Catalysts. Zirconium-silicon (Zr/Si) binary
oxides having different Zr contents were prepared by the sol-
gel method from mixtures of tetraethyl orthosilicate (TEOS)
and zirconium oxychloride in ethanol. The Zr/Si gels were
obtained by keeping the mixture at room temperature for 3 days.
The Zr/Si oxide gels formed in this way were washed with
sufficient amounts of boiled water and then calcined in O2 at
773 K for 5 h. The Zr/Si binary oxide samples were crushed
and sieved to 0.25-mm-size particles. The ZrO2 powdered
catalysts were prepared by the precipitation of the ZrO(NO3)2
solution with NH4OH after which the precipitates were dried
and calcined in O2 at 773 K. Prior to the spectroscopic
measurements and photocatalytic reactions, the catalysts were
evacuated for 5 h at the desired temperatures in the region of
300-1073 K.
Characterization. The photoluminescence spectra of the
catalyst were measured at 295 and 77 K using a Shimadzu RF-
5000 spectrophotofluorometer. The UV-vis reflectance spectra
were measured at 295 K by a Shimadzu UV-2200A double-
beam digital spectrophotometer equipped with conventional
components of a reflectance spectrometer. X-ray diffraction
patterns of the catalysts were obtained with a Rigaku RDA-γA
X-ray diffractometer using Cu KR radiation with a Ni filter.
The XPS spectra were measured at 295 K with a V.G. Scientific
ESCASCOPE photoelectron spectrometer using Mg KR radia-
tion. The X-ray absorption fine spectra of the Zr/Si binary oxide
catalysts were obtained in the transmission mode using an
EXAFS at the BL10B facility of the Photon Factory in the
National Laboratory for High Energy Physics (KEK-PF),
Tsukuba. A Si(311) channel-cut crystal was used to mono-
* To whom correspondence should be addressed.
X Abstract published in AdVance ACS Abstracts, December 15, 1996.
S1089-5647(96)01523-4 CCC: $14.00 © 1997 American Chemical Society

370 J. Phys. Chem. B, Vol. 101, No. 3, 1997
Moon et al.
Figure 1. X-ray diffraction patterns of powdered ZrO2 and Zr/Si
binary oxides: (a) Zr/Si binary oxide of 17.0 wt % as ZrO2 (Zr/Si )
0.19), (b) 45.1 wt % (Zr/Si ) 0.4), (c) 55.2 wt % (Zr/Si ) 0.6), (d)
67.2 wt % (Zr/Si ) 1.0), and (e) powdered ZrO2 catalyst.
Figure 2. UV-vis reflectance spectra of Zr/Si binary oxides: (a) Zr/
Si binary oxide of 3.9 wt % as ZrO2 (Zr/Si ) 0.02), (b) 9.3 wt %
(Zr/Si ) 0.05), (c) 45.1 wt % (Zr/Si ) 0.4), (d) 67.2 wt % (Zr/Si )
1.0), and (e) powdered ZrO2 catalyst.
chromatize the X-rays from the 2.5 GeV electron storage ring.
The Fourier transformation was performed on the k3-weighted
EXAFS oscillation in the range of 3-12 Å-1
.
Photocatalysis. The photocatalytic isomerization of cis-2-
butene was performed in a quartz tube cell connected to a
flowing system. Prior to the photocatalytic reaction experi-
mentation, the Zr/Si binary oxide catalysts were pretreated under
the flow of 7 vol % O2 in Ar at 573 K. The reactant gas flow
of 0.3 vol % cis-2-butene in Ar was then introduced into the
quartz tube reactor. UV-irradiation was carried out with a high-
pressure Hg lamp (λ > 250 nm) at 295 K. The reaction products
were collected at defined reaction intervals and analyzed by
gas chromatography.
Results and Discussion
The crystalline structures of Zr/Si binary oxide catalysts
having different Zr contents were investigated by XRD mea-
surements. The XRD patterns obtained are shown in Figure 1.
The crystalline structures of the Zr/Si binary oxides were
different from that of ZrO2 powders having a monoclinic phase
and changed with the Zr content in the oxides. As shown in
Figure 1, the X-ray patterns of the Zr/Si binary oxide catalysts
show only the diffraction lines attributed to the two crystalline
phases of ZrO2, the monoclinic phase and the tetragonal phase.
When the Zr content is decreased, the diffraction lines due to
the monoclinic phase decreased in intensity, and simultaneously
the diffraction lines due to the tetragonal phase of ZrO2 appeared
in the oxides having Zr contents lower than 67.2 wt % as ZrO2.
A further decrease in the Zr content led to the disappearance of
the X-ray diffraction lines attributed to these monoclinic and
tetragonal phases of ZrO2. Such features indicate that in Zr/Si
oxide catalysts, the crystallinity of the zirconium oxide species
decreases dramatically and then disappears in the low Zr content
region. Especially, in the Zr/Si binary oxide catalysts having
Zr contents lower than 17.0 wt % as ZrO2, zirconium oxide
species are present in amorphous structures in the SiO2 matrices.
Figure 2 shows the UV-vis reflectance spectra of the Zr/Si
binary oxides. It is clear that with decreasing Zr content the
absorption band of the binary oxides shifts remarkably toward
shorter wavelengths. Similar studies were carried out on the
Ti/Si and Ti/Al binary oxides having various compositions of
Ti:Si and Ti:Al, and a considerable shift toward shorter
wavelengths was observed for the absorption band of the highly
dispersed titanium oxide species.21-22 Therefore, it can be said
Figure 3. Fourier transforms of EXAFS spectra of powdered ZrO2
catalyst and Zr/Si binary oxides: (a) Zr/Si binary oxide of 3.9 wt % as
ZrO2 (Zr/Si ) 0.05), (b) 17.0 wt % (Zr/Si ) 0.1), (c) 45.1 wt % (Zr/Si
) 0.4), (d) 55.2 wt % (Zr/Si ) 0.6), (e) 67.2 wt % (Zr/Si ) 1.0), and
(f) powdered ZrO2 catalyst.
that such a large shift toward shorter wavelengths observed with
the Zr/Si oxides having a low Zr concentration indicates the
formation of ultrafine zirconium oxide species in the binary
oxides, its extent strongly depending on the Zr content. These
results obtained by XRD and UV-vis reflectance measurements
clearly show that with decreasing Zr content in the Zr/Si binary
oxide catalysts the crystalline structure of zirconium oxides
changes from aggregates in a monoclinic phase to those in a
tetragonal phase and then to ultrafine zirconium oxide species.
These ultrafine zirconium oxide species have an amorphous
structure in which the local coordinate geometry is different
from those of the crystalline ZrO2, as shown in the EXAFS
studies (vide infra).
Figure 3a-e shows the Fourier transformation of the k3-
weighted EXAFS (FT-EXAFS) spectra of the Zr/Si binary oxide
catalysts. Figure 3f shows the Fourier transformation of the
ZrO2 powders as a reference. As can be expected from the
XRD studies, the FT-EXAFS spectra of the Zr/Si binary oxide
catalysts with a high Zr content were similar to those of the

Characterization of Zr-Si Binary Oxide Catalysts
J. Phys. Chem. B, Vol. 101, No. 3, 1997 371
TABLE 1: Structure Parameters Determined from the
Curve-Fitting Analysis of the EXAFS Spectra of the Zr/Si
Binary Oxide Catalysts and the Powdered ZrO2 Catalyst
TABLE 2: Binding Energies of Zr(3d3/2), Zr(3d5/2), and
Si(2p1/2) XPS Bands and the Ratio of the Signal Intensity of
Zr(3d5/2) vs Si(2p1/2) in the Zr/Si Binary Oxides
sample
shell coordination number R/Åa
surface characterization
ZrO2
Zr/Si binary oxide
(Zr/Si ) 1.0) (67.2 ZrO2 wt %)
Zr/Si binary oxide
(Zr/Si ) 0.05) (9.3 ZrO2 wt %)
a Bond distance.
Zr-O
Zr-O
7.0
6.0
2.20
2.12
binding energy (eV)
sample Zr/Si
binary oxide
Zr(3d5/2)/Si(2p1/2) Zr(3d3/2) Zr(3d5/2) Si(2p1/2)
pure ZrO2
100% of ZrO2
0.33
184.2
184.7
181.8
182.3
Zr-O
4.5
2.05
Zr/Si ) 0.6
(55.2 ZrO2 wt %)
Zr/Si ) 0.1
(17.0 wt %)
Zr/Si ) 0.05
(9.3 wt %)
103.1
102.8
103.1
104.0
0.09
185.0
185.5
182.6
183.1
0.06
pure SiO2
100% of SiO2
energy for highly dispersed zirconium oxide species as compared
to the powdered bulk ZrO2 catalysts.
Table 2 shows the ratio of the Zr(3d5/2) to Si(2p1/2) XPS band
intensity. It is clear that there is a steady decrease in the
intensity of Zr(3d5/2) signals as the Zr content in the Zr/Si binary
oxides decreases. Furthermore, the ratio of the Zr(3d5/2) to
Si(2p1/2) peak intensity is higher than what can be expected from
the original composition of the sols in a lower content region
of the Zr ion, suggesting the enrichment of Zr ions in the surface
region of binary oxide catalysts having low Zr concentrations.
As has been reported in previous papers,15-17 the ZrO2
powders degassed at 1073 K exhibit a photoluminescence
spectrum at around 500 nm upon excitation at around 285 nm.
An abnormal absorption at around 285-300 nm and the
photoluminescence at around 500 nm of the well-degassed ZrO2
powders are attributed to the charge-transfer processes associated
with coordinatively unsaturated surface sites in a manner similar
to those for MgO and SrO powders:
Figure 4. X-ray photoelectron spectra of the Zr (3d3/2 and 3d5/2) level
for the powdered ZrO2 catalyst and Zr/Si binary oxides: (a) Zr/Si binary
oxide of 9.3 wt % as ZrO2 (Zr/Si ) 0.05), (b) 17.0 wt % (Zr/Si ) 0.1),
(c) 55.2 wt % (Zr/Si ) 0.6), and (d) powdered ZrO2 catalyst.
ZrO2 powder. The peak at around 1.6 Å in Figure 3 is assigned
to the neighboring oxygen atoms (Zr-O), and this peak can
clearly be observed with all Zr/Si binary oxides. However, as
shown in Figure 3, it is clear that there is a steady decrease in
the intensity of the peak at around 1.6 Å as the Zr content of
the binary oxides decreases, indicating that the coordinatively
unsaturated sites are formed on the zirconium oxide species. In
fact, as shown in Table 1, the coordination numbers of the oxide
determined from the curve-fitting analysis are found to change
from 7 to 5 when the concentration of Zr in the oxides is
decreased. On the other hand, the peak appearing at around
3.0 Å which is attributed to the neighboring Zr atoms (Zr-Zr)
is observed only with Zr/Si binary oxides having Zr contents
higher than 17.0 wt % as ZrO2. These results indicate that
zirconium oxide species are highly dispersed in Zr/Si binary
oxides having lower Zr concentration and the aggregated ZrO2
fine particles are formed in the SiO2 matrices with increasing
Zr content.
hν′
(Zr4+sO2-)LC y z (Zr3+sO-)*LC
(1)
hν
where LC ) low coordination
In the present study, both Zr/Si binary oxides prepared by the
sol-gel method and the Zr/SiO2 catalyst prepared by an
impregnation method exhibit photoluminescence spectra at
around 430-480 nm when the absorption bond was excited at
around 300 nm. These photoluminescence spectra are very
similar to those of the powdered bulk ZrO2 catalyst degassed
at higher temperatures. However, as shown in Figure 5, the
band positions of the photoluminescence of these Zr/Si binary
oxides and Zr/SiO2 catalysts can be observed at wavelengths
much shorter than for those of the well-degassed ZrO2 powders.
The addition of oxygen onto the Zr/Si binary oxides leads to
an efficient quenching of the photoluminescence, indicating that
the emitting sites, i.e., [Zr4+-O2-
]LC coordinatively unsaturated
In order to obtain information on the binding energy of the
zirconium oxide species in the Zr/Si binary oxides, the XPS
spectra of the catalysts were measured. Figure 4a-c shows
the XPS spectra of the Zr 3d band for the Zr/Si binary oxide
catalysts having different Zr contents. The resolution of the
peaks in the Zr(3d3/2) and Zr(3d5/2) XPS signals gradually
becomes better as the Zr content increases and finally approaches
the peaks of the powdered ZrO2 catalyst when the Zr content
reaches 55.2 wt % as ZrO2. It can also be seen that the binding
energy of the Zr(3d5/2) band shifts by 0.8 eV to a higher value
with catalysts having less than 17.0 wt % as ZrO2. A similar
tendency has been observed for the Ti(2p3/2) XPS signals of
the Ti/Si and Ti/Al binary oxides mentioned above. Considering
surface species, are present at the surface and/or near the surface
regions to allow the added oxygen molecules access to the sites
in a manner similar to those for various supported metal oxide
catalysts.
Figure 6 shows the effect of the Zr content on the peak
position and intensity of the photoluminescence spectrum due
to the presence of highly dispersed zirconium oxide species in
a state of coordinative unsaturation in the Zr/Si binary oxides.
With decreasing Zr content, the intensity of the photolumines-
cence spectrum increases and the band position shifts to shorter
wavelength regions. These findings indicate that decreasing the
Zr content in the Zr/Si binary oxides causes the catalyst to exist
in a highly dispersed state in the SiO2 matrices with coordination
numbers lower than those of ZrO2 powders. Similar phenomena
have been observed for the Ti/Si binary oxide catalysts prepared
these results, such a shift in the binding energy of the Zr(3d5/2
)
band to higher values can be attributed to the smaller relaxation

372 J. Phys. Chem. B, Vol. 101, No. 3, 1997
Moon et al.
Figure 5. Effect of the addition of cis-2-butene or oxygen on the
photoluminescence spectrum of the Zr/Si binary oxides (a). The amounts
of added cis-2-butene (b) at 0.1 Torr, (c) at 1.0 Torr, and (d) at 10.0
Torr. The amounts of added oxygen (e) at 0.1 Torr and (f) at 1.0 Torr.
(Photoluminescence spectra were recorded at 77 K. Addition of 2-butene
or oxygen onto the catalysts was carried out at 295 K.)
Figure 7. Relationship between the specific intensity of the photolu-
minescence of the Zr/Si binary oxide catalysts and the specific
photocatalytic reactivities for the isomerization of cis-2-butene of these
catalysts.
In fact, UV-irradiation of the Zr/Si binary oxides in the
presence of cis-2-butene led to the photocatalytic isomerization
of cis-2-butene to produce trans-2-butene (geometrical isomer-
ization) as the major product and 1-butene (double-bond shift
isomerization) as the minor product. After prolonged UV
irradiation time, the number of the photoinduced isomerization
products becomes larger than the number of Zr ions in the
catalyst, indicating that the reaction proceeds photocatalytically
at 298 K. At the reaction temperature, the thermal isomerization
reaction scarcely proceeded and the reaction products were
negligible as compared to the photocatalytic isomerization
reactions.
It was also found that the photocatalytic activity of the Zr/Si
binary oxide catalysts increased when the Zr content is
decreased. As described above, the intensity of the photolu-
minescence of these catalysts attributed to the radiative decay
from the charge-transfer excited state of the coordinatively
unsaturated zirconium oxide species increased in regions of
lower Zr content, and its peak position shifted to shorter
wavelength regions indicating that the zirconium oxide species
are highly dispersed in the SiO2 matrices. Figure 7 shows the
relationship between the specific photocatalytic activity per
weight of the Zr/Si binary oxide catalysts for the isomerization
of cis-2-butene and the specific photoluminescence yields per
weight of the catalysts. The former was calculated from the
conversions of butenes measured during the reaction period
when the stable photocatalytic reactions proceeded steadily and
constantly. As shown in Figure 7, the photocatalytic activity
is in a good relationship with the photoluminescence yield of
the catalysts, directly indicating that the charge-transfer excited
state of the coordinatively unsaturated zirconium oxide species
plays a significant role in the photocatalyzed isomerization
reaction on the Zr/Si binary oxides.
From these results, it can be concluded that the interaction
of cis-2-butene with the coordinatively unsaturated zirconium
oxide species in their charge-transfer excited state occurs easily
and the interaction of cis-2-butene with the charge-transfer
excited state of the [Zr3+-O-]* paired state or the O- species
of the pair state of the zirconium oxide results in the opening
of its CdC double bond which in turn results in the geometrical
isomerization of cis-2-butene into trans-2-butene in a manner
similar to that proposed for the photocatalytic isomerization of
Figure 6. Photoluminescence spectrum of powdered ZrO2 catalyst and
Zr/Si binary oxides having different Zr contents at 77 K: (a) Zr/Si
binary oxide of 9.3 wt % as ZrO2 (Zr/Si ) 0.05), (b) 17.0 wt % (Zr/Si
) 0.1), (c) 55.2 wt % (Zr/Si ) 0.6), and (d) powdered ZrO2 catalyst.
by the sol-gel method; decreasing the Ti content in the Ti/Si
binary oxides caused the photoluminescence intensity to in-
crease, and its band position shifted to shorter wavelength
regions, indicating that titanium oxide species are highly
dispersed in the Ti/Si binary oxides.23
Figure 5 also shows the effect of the addition of cis-2-butene
on the photoluminescence spectrum of the Zr/Si (Zr/Si ) 0.02)
binary oxide catalyst. Spectrum a was recorded after the
evacuation of the oxide at 573 K. As shown in Figure 5b-d,
the addition of cis-2-butene onto the Zr/Si binary oxide catalysts
was found to lead to an efficient quenching of the photolumi-
nescence, its extent strongly depending on the pressure of the
added cis-2-butene. The addition of cis-2-butene (0.2 Torr) onto
the Zr/Si binary oxide led to the shortening of the lifetime of
the photoluminescence from 2.52 ns to 1.75 ns, its extent
depending on the pressure of butene. These findings suggest
that the charge-transfer excited state of the coordinatively
unsaturated zirconium oxide species easily interacts with the
added cis-2-butene.

Characterization of Zr-Si Binary Oxide Catalysts
J. Phys. Chem. B, Vol. 101, No. 3, 1997 373
(3) Kondo, J.; Abe, H.; Sakata, Y.; Maruya, K. I.; Domen, K.; Onishi,
T. J. Chem. Soc., Faraday Trans. 1 1988, 84, 511.
2-butene on well-degassed MgO powders with coordinatively
unsaturated surface sites.
(4) Maruya, K. I.; Maehashi, T.; Haraoka, T.; Narui, S.; Asakawa, Y.;
Domen, K.; Onishi, T. Bull. Chem. Soc. Jpn. 1988, 61, 667.
Conclusions
(5) Maruya, K. I.; Fujisawa, T.; Takasawa, A.; Domen, K.; Onishi, T.
Bull. Chem. Soc. Jpn. 1989, 62, 11.
Using the sol-gel technique, Zr-Si binary oxide catalysts
having different Zr concentrations were prepared in a homo-
geneous structure. When the Zr concentration is decreased, the
crystalline structure of the zirconium oxides in the Zr/Si binary
oxide catalysts caused the structure to change from monoclinic
to tetragonal and then to an amorphous state while a simulta-
neous enrichment of the Zr ions in the surface region was also
observed. In the Zr/Si binary oxide having lower Zr content,
the ultrafine zirconium oxide species were found to exist
separately from each other in the SiO2 matrices and exhibited
a typical photoluminescence spectrum attributed to the radiative
decay from the charge-transfer excited state of these species.
The efficient quenching of the photoluminescence with the
addition of cis-2-butene indicated the interaction of butene with
the charge-transfer excited state of the coordinatively unsaturated
surface sites of the zirconium oxide species, i.e., [Zr3-O-]*.
These ultrafine zirconium oxide species in the Zr/Si binary oxide
exhibited a specific photocatalytic activity for the isomerization
of cis-2-butene. The good parallelism between the photolumi-
nescence yield and the photocatalytic activity obtained with the
Zr/Si binary oxide catalysts having different Zr contents clearly
indicated that the charge-transfer excited state of the emitting
sites of the zirconium oxide species plays a significant role in
the photocatalytic isomerization of cis-2-butene on the catalysts.
(6) He, M. Y.; Ekerdt, J. G. J. Catal. 1984, 87, 238.
(7) He, M. Y.; Ekerdt, J. G. J. Catal. 1984, 87, 381.
(8) Jackson, N. B.; Ekerdt, J. G. J. Catal. 1986, 101, 90.
(9) Tseng, S. C.; Jackson, N. B.; Ekerdt, J. G. J. Catal. 1988, 109,
284.
(10) Yamaguchi, T.; Sakai, H.; Tanabe, K. Chem. Lett. 1973, 1017.
(11) Anpo, M.; Yamada, Y.; Kubokawa, Y. J. Chem. Soc., Chem.
Commun. 1986, 714.
(12) Anpo, M.; Yamada, Y. Shokubai (Catalysis) 1987, 29, 470.
(13) Anpo, M.; Yamada, Y.; Kubokawa, Y.; Coluccia, S.; Zecchina,
A.; Che, M. J. Chem. Soc., Faraday Trans. 1 1988, 84, 751.
(14) Anpo, M.; Moon, S. C.; Chiba, K.; Martra’s, G.; Coluccia, S. Res.
Chem. Intermed. 1993, 19, 495.
(15) Anpo, M.; Nomura, T.; Kondo, J.; Maruya, K. I.; Onishi, T. Res.
Chem. Intermed. 1990, 13, 195.
(16) Moon, S. C.; Yamashita, H.; Anpo, M. Acid-Base Catalysis II;
Hattori, H., Misono, M., Ono, Y., Eds.; Kodansha: Tokyo, 1994; pp 479-
484.
(17) Moon, S. C.; Tsuji, K.; Nomura, T.; Anpo, M. Chem. Lett. 1994,
2241.
(18) Feng, Z.; Postula, W. S.; Erkey, C.; Philip, C. V.; Akgerman, A.;
Anthony, R. G. J. Catal. 1994, 148, 84.
(19) Bosman, H. J. M.; Kruissink, E. C.; van der Spoel, J.; van den
Brink, F. J. Catal. 1994, 148, 660.
(20) Tanaka, T.; Yoshida, H.; Nakatsuka, K.; Funabiki, T.; Yoshida, S.
J. Chem. Soc., Faraday Trans. 1992, 88, 2297.
(21) Anpo, M.; Nakaya, H.; Kodama, S.; Kubokawa, Y.; Domen, K.;
Onishi, T. J. Phys. Chem. 1986, 90, 1633.
(22) Anpo, M.; Kawamura, T.; Kodama, S. J. Phys. Chem. 1988, 92,
438.
References and Notes
(1) Abe, H.; Maruya, K. I.; Domen, K.; Onishi, T. Chem. Lett. 1984,
1875.
(2) Maruya, K. I.; Inabe, A.; Maehashi, T.; Domen, K.; Onishi, T. J.
Chem. Soc., Chem. Commun. 1985, 487.
(23) Yamashita, H.; Kawasaki, S. I.; Anpo, M.; Stewart, G.; Fox, M.
A.; Arendt, M. F.; White, J. M. In Abstracts of International Conference
on Photochemical ConVersion & Storage of Solar Energy (ISP-10);
Calzaferri, G., Ed.; Interaken, Switzerland, 1994; p 403.