The role of sulfur vacancies on FeS2(100) in NO dissociative adsorption: a combined in situ SR-XPS and DFT calculation study

Abstract

Sulfur vacancies (S_vacs) are known to change the reactivity of transition metal sulfides, but their mechanistic role in small-molecule activation remains poorly understood. Here, we carried out synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) and dispersion-corrected density functional theory (DFT-D3) calculations to elucidate how S_vac sites on FeS₂(100) surfaces promote nitric oxide (NO) dissociation. SR-XPS results reveal progressive Fe oxidation, Fe–N formation, and the growth of adsorbed oxygen species as a function of NO exposure. The N/O atomic ratio evolution suggests recombinative N₂ desorption from the surface. DFT-D3 calculations show that the dissociative adsorption of NO is thermodynamically more stable on the defective FeS₂(100) surface than on the defect-free surface. Based on the Brønsted–Evans–Polanyi relationship, dissociative adsorption of NO may be kinetically favorable on the defective FeS₂(100) surface. Two possible pathways are proposed: (1) O–O bond formation at S_vac sites and (2) oxygen-induced S–S bond cleavage to yield O–S species and new S_mono. The present experimental–computational study demonstrates the atomic-level role of S_vacs in NO activation on FeS₂(100) and provides chemical insight into defect engineering of sulfide-based catalysts for selective nitrogen oxide conversion.