H2 Thermal Desorption Spectra on Pt(111): A Density Functional Theory and Kinetic Monte Carlo Simulation Study

Abstract

Theoretical investigation of the static and kinetic behaviors of H and H2 on metal surface plays a key role in the development of hydrogenation catalysts and new materials with high H2 storage capacity. Based on the density functional theory (DFT) calculation of H and H2 adsorption on Pt(111), H(a) adatom strongly interacts with surface Pt; while H2 weakly adsorbs on Pt(111). H(a) adatoms stably occupy the face-centered cubic sites on Pt(111) which agrees with the experimental LERS observations. By using kinetic Monte Carlo (kMC) simulation, the qualitative effects of the kinetic parameters on the H2 TDS spectra indicate that the H2 desorption peaks shift to the low temperature with increasing pre-exponential factor and decreasing desorption barrier. Simultaneously, the desorption peaks shift downwards and broaden to two peaks with the increase of the lateral interaction energy among H(a) adatoms. Using the kMC simulation based on DFT calculation, the predicted H2 TDS spectra are well consistent with the experimental ones. It unanimously proves that the two peaks of TDS spectra are derived from the lateral interactions among H(a). This work provides the intrinsic kinetics of H(a) and H2 on Pt(111) at an atomic level, and gives insight into the development of hydrogenation catalysts.