3358 J. Phys. Chem. B, Vol. 101, No. 17, 1997
Ohtani et al.
tively, and also to Mr. Masahiro Naito (Kyoto University) for
his skillful work in the preparation of an electric furnace for
H2 reduction and photoirradiation apparatuses. Professor Akiko
Aramata (Hokkaido University) is acknowledged for permission
to use the FT-IR spectrometer.
References and Notes
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Figure 11. Selectivity of PCA production as a function of r(Pt/TiO2).
Several procedures have been reported for the platinization
of TiO2, e.g., impregnation followed by reduction,17,27 photo-
deposition,15,16 mechanical mixing with platinum black23,64 or
precipitation from platinum sol,68 but few reports compared the
efficiency of platinization onto TiO2 particles. Mills has
described in a communication that among these platinization
techniques the sol precipitation and photodeposition methods
gave the efficient TiO2-Pt catalyst for photocatalytic H2
evolution from aqueous EDTA solution.68 For several TiO2
powders sol precipitation afforded photocatalytic activity, which
was comparable to photodeposition. On the basis of the results
in present studies, these previous results may be interpreted
reasonably in terms of the distribution of Pt deposits on the
TiO2 particles, not of the total number of loadings. Comparison
of photocatalytic activity of TiO2 platinized via several proce-
dures is now being investigated along this line.
Conclusion
The dependence of the rate on the amount of Pt was
semiquantitatively simulated with a kinetic model by using the
surface area of Pt as a parameter representing the physical
property of Pt deposits. The selectivity of PCA from Lys
strongly depended on the Pt amount, while the rate of H2
evolution from 2-propanol was rather insensitive. From the
distribution of Pt deposits on TiO2 particles, it has been
presumed that only one Pt deposit on a small (a few dozen
nanometers in size) TiO2 particle is required for H2 evolution,
but a larger amount of Pt is necessary for the adsorption and
reduction of the intermediate CSB by photoexcited electrons.
For the Lys system, it was presumed from the data analysis
that the deposited Pt can reduce the intermediate produced at
the TiO2 surface sites located within ca. 5 nm. In both cases
of 2-propanol and Lys, excess loading of Pt that reduced the
overall rate may be due to the decrease in light absorption by
TiO2 or enhanced recombination of electron-hole pairs. Thus,
we have shown the role of Pt deposited on TiO2 in the
photocatalytic reaction system under deaerated conditions and
the optimum amount of loading for two different kinds of
reactions. These results should be useful and applicable to the
preparation of a wide range of noble-metal-loaded semiconduc-
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Acknowledgment. Financial support by the Kawakami
Memorial Foundation and Kansai Research Foundation for
Technology Promotion is gratefully acknowledged. This in-
vestigation was partly supported by the Grant-in-Aid on Priority-
Area-Research on “Photoreaction Dynamics” from the Ministry
of Education, Science, Sports, and Culture of Japan (No.
07228233). Part of this study was achieved under the support
of the Joint Research Program of Catalysis Research Center,
Hokkaido University. The authors are indebted to Professor
Masashi Inoue and Dr. Kenji Wada (Kyoto University) for their
technical advice on the TEM and XPS measurements, respec-
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