Subject Number : S-20-KU-0055
Support Type : Common use (including technical support necessary for the training),
Proposal Title (English) : Chemical Analysis of Au Species Supported on Monoclinic ZrO2
Username (English) :Q.-A. Huang1), H. Murayama1)
Affiliation (English). :1) Department of Chemistry, Kyushu University

1. Summary
Supported Au nanoparticles (NPs) catalysts were wildly applied in the fine chemical synthesis field1. One of the important applications using the supported Au NPs is working as a soft Lewis acid (SLA) in heterogeneous catalysts. In recent years, we have developed several efficient catalytic reactions in the SLA mechanism with Au NPs supported on monoclinic ZrO2 (Au/m-ZrO2). However, the authentic active sites or species for these reactions were still unclear. Here, we utilized the X-ray photoelectron spectroscopy (XPS) and precisely investigate the active sites on the surface of Au NPs, which may boost up the high soft Lewis acidity.
2. Experimental
Sample Au/ZrO2_DP was prepared by the deposition-precipitation method using (NH4)2CO3. Then the catalysts were calcined under 200°C. Samples Au/ZrO2_IP and Au/SiO2_IP were prepared by the impregnation method using the Au–-ala complex as a precursor reported in our previous research2. The obtained catalysts were calcined under 300°C. XPS spectra were measured by a Shimadzu AXIS-ULTRA spectrometer equipped with an Al Kα anode. In the XPS analysis process, all the powder samples were stuck on the carbon tape. The binding energies in the XPS spectra were calibrated with the C 1s peak at 284.3 eV. The spectra were fitted using XPSPEAK4.1 software based on a Gaussian-Lorentzian function.
3. Results and Discussion
Au 4f spectra were mainly investigated for the target samples. The Au 4f2/7 peak for Au/ZrO2_DP was mainly observed at around 83.3 eV, which was approximated to the standard value of Au0. Besides, the Au/ZrO2_IP showed the 4f2/7 peak at around 82.1 eV, which was 1.2 eV lower than that of Au/ZrO2_DP. Interestingly, both of them could act as SLA in their reactions. It revealed that Au- might also work as an SLA instead of the Au+. Hence, further investigation should be carried out to uncover the reason for this phenomenon.

Figure. Au 4f XPS spectra for various supported Au catalysts.
4. Others
References
1) Corma, A.; Garcia, H. Chem. Soc. Rev. 2008, 37, 2096–2126.
2) Murayama, H.; Hasegawa, T.; Yamamoto, Y.; Tone M.; Kimura, M.; Ishida, T.; Honma, T.; Okumura, M.; Isogai, A.; Fujii, T.; Tokunaga, M. J. Catal. 2017, 353, 74-80.
Acknowledgments
This work was financially supported by JSPS KAKENHI Grant Number JP19H02755. The authors thank Dr. F. Toshimitsu for his assistance to measure the XPS spectra.
5. Publication/Presentation
N/A
6. Patent
N/A