Photon Factory Activity Report 2016 #34 (2017)

BL-12C/2014G548,2016G643

Role of Pt nanoparticles on TiO2 in the photocatalytic cross-coupling between THF
and cyclohexane
1Akanksha Tyagi,1 Akira Yamamoto,1,2 and Hisao Yoshida1,2*
Graduate School of Human and Environmental Studies, Kyoto University, Yoshida Nihonmatsu-cho,Sakyo-ku, Kyoto 606-8501, Japan
2ESICB, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8520, Japan

1 Introduction
Titanium oxide catalyzed organic reactions is anemerging field to develop sustainable techniques forchemical synthesis.1 Recently, we reported a
photocatalytic cross-coupling between tetrahydrofuran(THF)
andcyclohexane
togive2cyclohexyltetrahydrofuran with Pt loaded TiO2 (Pt/TiO2)
photocatalysts (Scheme 1).2 We also clarified the role ofPt nanoparticles in the photocatalytic reaction. For this,
we performed the reaction with either Pt/TiO2 or aphysical mixture of TiO2 and Pt/Al2O3 catalyst. Pt/TiO2
photocatalyst gave a larger product yield than the physicalmixture of the two catalysts.
To investigate the relationship between the state of Pt
nanoparticles on the two supports and their catalytic
activity, they were analyzed by XAFS.

and Pt/Al2O3, the Pt nanoparticles could not function aselectron receiver. So, they remain electron deficient.
Thus, the primary role of Pt nanoparticles wasproposed to be an electron receiver to reduce therecombination of electron and hole on TiO2. Due todecreased recombination, the holes are available for theoxidation of tetrahydrofuran and cyclohexane, to generate
their corresponding radicals and protons. The radical cancombine to give the cross-coupling product while theprotons are reduced to hydrogen radicals and ultimatelyto hydrogen gas.
Thus, the XAFS measurements clarified the role of Pt
nanoparticles on TiO2 in the photocatalytic cross-coupling
reaction between THF and cyclohexane.

Scheme 1 Direct cross-coupling reaction between
THF and cyclohexane with Pt/TiO2 photocatalyst
2 Experiment
The Pt/TiO2 (ST01, Catalyst Society of Japan JRCTIO-8) photocatalyst was prepared by a photodeposition
method. The Pt/Al2O3 (JRC ALO-7) catalyst wasprepared by an impregnation method. The loading amountof Pt was fixed to 0.1 weight% in both catalysts. The
reaction between THF and cyclohexane was carried out
using these catalysts and the samples were recovered afterthe reaction. The recovered samples were analysed bymeasuring Pt LIII-edge XAFS. A Pt foil and PtO2 weremeasured in the transmission mode, while the samples
were measured in the fluorescence mode.
3 Results and Discussion
Fig. 1 shows the result of the normalized XANES of Pt
LIII-edge in the recovered samples, Pt foil, and PtO2. The
analysis revealed that the Pt nanoparticles on TiO2 weresimilar to Pt foil and different from PtO2 (Fig.1, a, b, andd). On the other hand, Pt nanoparticles on Al2O3 werecloser to PtO2 and quite different from Pt foil (Fig.1, a, c,and d).
So, it can be proposed that Pt nanoparticles on TiO2
could work as an electron receiver to accept the electrons
from the conduction band of TiO2, thus becoming
electron rich. However, in the physical mixture of TiO2

Fig. 1: Normalized XANES spectra of Pt-LIII edge. (a) Pt
foil (b) Pt(0.1)/TiO2-AR, (c) Pt(0.1)/Al2O3-AR, and (d)PtO2References[1] Y. Shiraishi, T. Hirai, J. Photochem. Photobiol., C,
2008, 9, 157.
[2] A. Tyagi, A. Yamamoto, T. Kato, H. Yoshida, Catal.
Sci. Technol., 10.1039/c7cy00535k.
* yoshida.hisao.2a@kyoto-u.ac.jp