Ab initio molecular dynamics of dissociative chemisorption of CH4 on metal surfaces

Francesco Nattino
Ab initio molecular dynamics of dissociative chemisorption of CH4 on metal surfaces

The methane steam reforming process is the main commercial source for molecular hydrogen. In this process methane and water react over a supported nickel catalyst to produce H2. The first and rate-liming step of the full process is the dissociative chemisorption of methane on the nickel surface, which leads to Hads + CH3 ads. Besides the industrial relevance, this reaction is of fundamental interest, and many experiments have been performed with the aim of understanding the details of the dissociation dynamics. For instance, it was shown that the enhancement in reactivity obtained by putting energy into molecular vibration strongly depends on the vibrational mode that is excited (vibrational mode specificity). From the theoretical side, we are interested in modeling some of the experiments mentioned above, which involve the dissociation of (partially deuterated) methane on platinum and nickel surfaces. In particular, we want to investigate the effect that (i) mode-specific vibrational excitation, (ii) surface temperature and (iii) rotational alignment have on the reactivity of the molecules. The method that we are using is the ab initio molecular dynamics (AIMD) technique, according to which the atoms move according to the classical equations of motion, but forces are computed accurately (quantum mechanically) ‘on-the-fly’ at each time-step of the dynamics.

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