BL5S1

実験番号：2018D4008（4hr）

XAFS study of the defective boron nitride
with atomically dispersed Pt atoms
Yu Lei1,2, Kazunori Fujisawa2,3, Rodolfo Cruz-Silva4, Morinobu Endo4, Mauricio Terrones1,2,3,4
1

Department of Materials Science and Engineering & Materials Research Institute,2
Center for 2-Dimensional and Layered Materials and 3 Department of Physics,
The Pennsylvania State University, University Park, PA 16802, United States;
4
Institute of Carbon Science and Technology, Shinshu University, Wakasato 4-17-1, Nagano, 380-8553, Japan.
Keywords: defective boron nitride, single Pt atoms, single atom catalysts (SAC)
1. Background and research purpose
Atomically dispersed metal catalyst has emerged as a promising approach tomaximize the metal utilization, especially for the earth-scarce metals such as Pt.
To ensure a robust binding site, a strong metal-support interaction is necessary;a promising route is defects, for which it has been observed that metal cations
tend to migrate and be reduced at vacancies to form a stronger interaction thandefect-free supports1,2. In this study, we demonstrate how the defect engineeringin hexagonal boron nitride (BN) can be used to spontaneously reduce the ionicplatinum (Pt4+) and silver (Ag+) into isolated Pt atoms and AgPt subnanocluster
at the defective region, which contributes to efficient and stable catalytic
behavior. As a complementary part of the study, we must understand the bonding
environment of the Pt atoms which are responsible to the catalytic reactivity.
2. Experimental method
Platinum and silver cations were reduced by the defective BN (90BN) inaqueous solution at the room temperature. Then, the powder was washed with
distilled water three times by centrifugation, followed by drying process at 60°C.
The samples analyzed by XAFS at the Aichi Synchrotron facility at the BL5S1line. The resulting patterns were analyzed using Athena software.

Figure 1 (a) The Fouriertransformed R-space plot ofEXAFS spectra and (b) Pt L3edge XANES spectra of 90BN-Pt,
90BN-Ag1Pt1, Pt foil and PtO2.

3. Results and discussion
To verify the atomically dispersed Pt atoms, extended X-ray absorption fine structure (EXAFS) spectra at thePt L3-edge was obtained for 90BN-Pt and 90BN-Ag1Pt1, as well as Pt foil and PtO2 as the references. As seen in theFourier transformed spectra (Figure 1a), there is one prominent peak at ~1.63 Å in 90BN-Pt and 90BN-Ag1Pt1
which is shorter length than Pt-Pt bonding (~2.55 Å) in Pt foil. Thus, the lack of Pt-Pt bond confirms the atomicallydispersed Pt in 90BN-Pt and 90BN-Ag1Pt1 that no Pt particles or clusters are presented. Compared to PtO2 reference
spectra, the first peak of 90BN-Pt or 90BN-Ag1Pt1 (Figure 1a) is believed to be the contribution from the Pt-Obonding. Figure 1b is the normalized X-ray absorption near-edge structure (XANES) spectra of the samples 90BNPt and 90BN-Ag1Pt1 with the reference spectra of Pt and PtO2. The white-line intensities of 90BN-Pt and 90BNAg1Pt1 are between those of Pt-foil and PtO2, which indicates the positive charges on Pt in 90BN-Pt and 90BNAg1Pt1 due to the Pt-O bonds. These results confirm that the oxygen functional groups work as the nucleation siteto form metal-O bonds, so that the charge transfer is allowed between metal and defective BN and ensure a strong
metal-support interaction3.
4. References
1Tauster, S. J., Fung, S. C., Baker, R. T. K. & Horsley, J. A. Strong-interactions in supported-metal catalysts.
Science 211, 1121-1125, doi:10.1126/science.211.4487.1121 (1981).
2Sanchez, M. G. & Gazquez, J. L. Oxygen vacancy model in strong metal support interaction. Journal ofCatalysis 104, 120-135, doi:10.1016/0021-9517(87)90342-3 (1987).
3
Qiao, B. et al. Single-atom catalysis of CO oxidation using Pt1/FeOx. Nature chemistry 3, 634-641 (2011).