Presentation Information
[U17-10]Interaction between defect-introduced FeS2 (pyrite) surfaces and small Molecules: a study using surface spectroscopy and first-principles calculations
*Jun Yoshinobu1, Wei-chih Hsiao1, Kozo Mukai1, Takuji Iimori1, Hirobumi Umeyama1, Masahiro Fukuda1, Taisuke Ozaki1 (1.The Institute for Solid State Physics, The University of Tokyo)
Keywords:
Pyrite,surface,defect,X-ray photoelectron spectroscopy,DFT calculation
Sulfur vacancies (Svac) are known to modulate the electronic structure and reactivity of transition metal sulfides, yet the microscopic mechanisms in catalytic reactions remain poorly understood. Pyrite (FeS2) is an abundant sulfide in the Earth's crust and it has also shown catalytic activity. Furthermore, pyrite is discussed in studies on the origin of life. In this study, we systematically investigated the adsorption and reaction mechanisms of small molecules such as NO, CO2, and HCOOH at the Svac sites on the FeS2(100) surface.
We prepared FeS2(100) surfaces with controlled high/low sulfur defect densities and studied the interactions with small molecules (NO, HCOOH, CO2) using in situ XPS and density functional theory (DFT-D3) calculations with dispersion force correction. Natural FeS2(100) single crystal surfaces were prepared by cutting, polishing, and cleaning. Svac concentration was controlled by Ar ion sputtering at 200 and 600 eV. SR-XPS was performed at Photon Factory BL-13B, measuring Fe 2p, S 2p, N 1s, and O 1s after controlled exposure to NO and HCOOH. CO2 experiments were conducted using laboratory XPS at the The Institute for Solid State Physics. Theoretical calculations were performed using OpenMX and GGA-PBE with DFT-D3, and the O 1s binding energy was calculated using the ΔSCF method. The reaction pathway was evaluated by analyzing sequential reaction intermediates.
SR-XPS and laboratory XPS revealed different responses to gas exposure between low-defect and high-defect surfaces. During NO exposure, oxidation of Fe, reduction of sulfur species (Smono, Ssurf), and formation of Fe–N bonds were observed on the highly defective surface, confirming enhanced dissociation. Furthermore, the decrease in the N/O atomic ratio suggests oxygen accumulation progressing in parallel with N2 recombination desorption. The observed O 1s peaks were assigned to multiple oxygen species near Svac (including S-atop, Fe–S bridges, and O–O dimers formed at Svac), based on absolute binding energy calculations using the ΔSCF method. In the case of HCOOH exposure, significant decomposition reactions were observed in the initial stage on both defect surfaces. This reaction occurs even on the low-defect surface, and the defect sites are unsaturated in the initial stage. For CO2 exposure, while oxygen-related species increased significantly on the high-defect surface, the increase in carbon species was small, suggesting that CO2 activation/conversion is proceeding on FeS2(100) with Svac.
We prepared FeS2(100) surfaces with controlled high/low sulfur defect densities and studied the interactions with small molecules (NO, HCOOH, CO2) using in situ XPS and density functional theory (DFT-D3) calculations with dispersion force correction. Natural FeS2(100) single crystal surfaces were prepared by cutting, polishing, and cleaning. Svac concentration was controlled by Ar ion sputtering at 200 and 600 eV. SR-XPS was performed at Photon Factory BL-13B, measuring Fe 2p, S 2p, N 1s, and O 1s after controlled exposure to NO and HCOOH. CO2 experiments were conducted using laboratory XPS at the The Institute for Solid State Physics. Theoretical calculations were performed using OpenMX and GGA-PBE with DFT-D3, and the O 1s binding energy was calculated using the ΔSCF method. The reaction pathway was evaluated by analyzing sequential reaction intermediates.
SR-XPS and laboratory XPS revealed different responses to gas exposure between low-defect and high-defect surfaces. During NO exposure, oxidation of Fe, reduction of sulfur species (Smono, Ssurf), and formation of Fe–N bonds were observed on the highly defective surface, confirming enhanced dissociation. Furthermore, the decrease in the N/O atomic ratio suggests oxygen accumulation progressing in parallel with N2 recombination desorption. The observed O 1s peaks were assigned to multiple oxygen species near Svac (including S-atop, Fe–S bridges, and O–O dimers formed at Svac), based on absolute binding energy calculations using the ΔSCF method. In the case of HCOOH exposure, significant decomposition reactions were observed in the initial stage on both defect surfaces. This reaction occurs even on the low-defect surface, and the defect sites are unsaturated in the initial stage. For CO2 exposure, while oxygen-related species increased significantly on the high-defect surface, the increase in carbon species was small, suggesting that CO2 activation/conversion is proceeding on FeS2(100) with Svac.