The temperature dependence of methane dissociation on Ni(111) and Pt(111): Mixed quantum-classical studies of the lattice response

Abstract

The barrier to the dissociative adsorption of methane on metal surfaces is generally large, and its height can vary with the motion of the lattice atoms. One fully quantum and three different mixed quantum-classical approaches are used to examine this reaction on Ni(111) and Pt(111) surfaces, using potential energy surfaces derived from density functional theory. The three approximate methods are benchmarked against the exact quantum studies, and two of them are shown to work reasonably well. The mixed models, which treat the lattice motion classically, are used to examine the lattice response during the reaction. It is found that the thermal motion of the lattice atoms strongly modifies the reactivity, but that their motion is not significantly perturbed. Based on these results, new models for methane reactions are proposed based on a sudden treatment of the lattice motion and shown to agree well with the exact results. In these new models, the reaction probability at different surface temperatures is computed from static surface reaction probabilities, allowing for a quantum calculation of the reaction probability without having to explicitly treat the motion of the heavy lattice atoms.

On the origin of mode- and bond-selectivity in vibrationally mediated reactions on surfaces

“…Indeed, recent calculations show that lattice distortion resulting from surface phonon excitation promotes reactivity by directly exciting a motion that enhances transition state access, suggest that there is minimal energy exchange between the methane molecule and the active surface atom during the reactive encounter. 36,37,40,74,75 Another simulation suggests any enhancement of the reaction rate via phonons diminishes with increasing translational or vibrational energy of the incident methane. 76 Recent experimental results support this theory 77 and we plan to explore the role of phonon excitation on methane activation more fully in a future publication.…”

Methane dissociation on Pt(111): Searching for a specific reaction parameter density functional

“…By using the AIMD method, in addition to avoiding fitting/interpolation inaccuracies in the pre-calculated potential due to the 'on-the-fly' computation of the forces, no dynamical approximation with respect to the time evolution of any of the molecular degrees of freedom has to be made a priori [40,45]. Finally, the motion of the surface atoms and their thermal displacement from the equilibrium positions, which has been shown to play a role in the dissociation dynamics of methane on metal surfaces [30,40,46], can be explicitly included in the dynamics. In fact, the movement of the first layer surface atoms towards the impinging molecules significantly lowers the dissociation barrier for methane on metals [47][48][49], and this finding has been used to explain [46,49] the extent to which the reactivity is enhanced by increasing the surface temperature (T s ) [9,11,[50][51][52][53].…”

Vibrationally Promoted Dissociation of Water on Ni(111)

“…The total reaction probability was computed with a flux method on a dividing surface placed beyond the saddle point. The effects of surface corrugation, impact site, and lattice motion are approximately treated based on the approaches of Jackson and co-workers (14,36,37). A more detailed description of the theoretical calculations is given in the SM (30).…”