Exploring adsorption behavior of sulfur and nitrogen compounds on transition metal-doped Cu(100) surfaces: insights from DFT and MD simulations

Abstract

We conducted an extensive investigation using density functional theory (DFT) calculations and ReaxFF molecular dynamics (MD) simulations to elucidate the mechanisms of desulfurization and denitrogenation on Cu(100) surfaces. This study encompassed both pristine surfaces and those modified with Pt or Rh transition metals. Our primary objective was to gain a deep understanding of the adsorption behavior of thiophene (C₄H₄S) and pyridine (C₅H₅N) molecules on stepped Cu(100) surfaces, which serve as models for sulfur and nitrogen compounds. We systematically explored the interplay among water, adsorption efficiency, and surface regeneration capabilities. Using DFT, we thoroughly examined various aspects, including interaction energies, charge transfers, changes in electron density, and alterations in work function upon molecule adsorption. Notably, we observed a decrease in the interaction energy of thiophene, whereas that of pyridine increased when adsorbed on Pt/Rh-doped surfaces compared to pristine ones. Thiophene adsorption reduced the work function, potentially enhancing detectability, without causing inhibitory effects on any surface. Stepped Cu(100) surfaces demonstrated a strong affinity for thiophene, exhibiting an energy difference of approximately 86 kJ mol⁻¹. However, this trend reversed on doped surfaces, where pyridine displayed stronger adsorption than thiophene, resulting in energy differences of around 123 kJ mol⁻¹ and 62 kJ mol⁻¹ on Pt–Cu and Rh–Cu surfaces, respectively. Moreover, our investigation highlighted the regeneration capacity of these surfaces, indicating that all surfaces can be considered promising candidates for desulfurization, while only Cu and Pt–Cu surfaces were found to be suitable for denitrogenation. Furthermore, results from MD simulations in combination with potential of mean force (PMF) simulations at 300 K, aligned with DFT calculations, confirmed the adsorption configurations of pyridine and thiophene. This analysis demonstrated the competitive advantage of thiophene over pyridine in adsorption and highlighted the inhibitory effect of water on pyridine adsorption on the Cu(100) surface.