Kinetic Monte Carlo Studies of Hydrogen Abstraction from Graphite

TL;DR

This study uses kinetic Monte Carlo simulations informed by density functional theory to analyze hydrogen abstraction mechanisms on graphite, revealing a novel dimer-mediated Eley-Rideal process that explains coverage-dependent reaction behaviors.

Contribution

It introduces a new dimer-mediated Eley-Rideal mechanism and demonstrates its significance in hydrogen abstraction from graphite, supported by simulation and experimental comparison.

Findings

Good agreement between simulations and experiments on cross sections.

Identification of a dimer-mediated Eley-Rideal mechanism.

Coverage dependence explained by two combined mechanisms.

Abstract

We present Monte Carlo simulations on Eley-Rideal abstraction reactions of atomic hydrogen chemisorbed on graphite. The results are obtained via a hybrid approach where energy barriers derived from density functional theory calculations are used as input to Monte Carlo simulations. By comparing with experimental data, we discriminate between contributions from different Eley-Rideal mechanisms. A combination of two different mechanisms yields good quantitative and qualitative agreement between the experimentally derived and the simulated Eley-Rideal abstraction cross sections and surface configurations. These two mechanisms include a direct Eley-Rideal reaction with fast diffusing H atoms and a dimer mediated Eley-Rideal mechanism with increased cross section at low coverage. Such a dimer mediated Eley-Rideal mechanism has not previously been proposed and serves as an alternative explanation to the steering behavior often given as the cause of the coverage dependence observed in Eley-Rideal reaction cross sections.