Surface Reaction Barriometry: Methane Dissociation on Flat and Stepped Transition-Metal Surfaces

Abstract

Accurately simulating heterogeneously catalyzed reactions requires reliable barriers for molecules reacting at defects on metal surfaces, such as steps. However, first-principles methods capable of computing these barriers to chemical accuracy have yet to be demonstrated. We show that state-resolved molecular beam experiments combined with ab initio molecular dynamics using specific reaction parameter density functional theory (SRP-DFT) can determine the molecule-metal surface interaction with the required reliability. Crucially, SRP-DFT exhibits transferability: the functional devised for methane reacting on a flat (111) face of Pt (and Ni) also describes its reaction on stepped Pt(211) with chemical accuracy. Our approach can help bridge the materials gap between fundamental surface science studies on regular surfaces and heterogeneous catalysis in which defected surfaces are important.

CHD3 dissociation on Pt(111): A comparison of the reaction dynamics based on the PBE functional and on a specific reaction parameter functional

“…The theoretical methods employed in the current work have been described in detail previously 22,39 and only the most relevant aspects will be presented here. In brief, we ran between 500 and 1000 quasi-classical trajectories for CHD 3 colliding with Pt(111) for a range of incident energies using the Vienna ab initio simulation package (VASP) version 5.3.5.…”

“…As discussed in more detail in the supplementary material, the maximum error this introduces in the E b for the reaction calculated using the PBE functional is 0.4 kJ/mol which is not significant enough to change the results of the PBE trajectories presented here. The Pt(111) surface has been modeled using a 5 layer (3 × 3) supercell slab 36,39 with each slab separated from its first periodic replica by 13 Å of vacuum. A 0.1 eV Fermi smearing has been used to facilitate the convergence.…”

“…Extensive tests of the parameters used in the calculations have been performed, the results of which can be found in the supplementary material of Ref. 39.…”

“…30 We have also demonstrated that an SRP exchange correlation functional can be used to reproduce the experimental sticking coefficients for CHD 3 on Ni(111) for both molecules prepared with a quantum of C-H stretch vibration and those without vibrational excitation. 22 The same SRP functional, which uses the RPBE 29 and PBE 27 for exchange and van der Waals for correlation, 38 was also shown to give chemically accurate results for the sticking coefficients for CHD 3 dissociation on Pt(111) and Pt(211), 39 demonstrating the transferability of the SRP functional among systems in which methane reacts with group 10 transition metals of the periodic table and also from a flat to a stepped transition metal surface. In recent work, the same SRP functional has been shown to accurately describe sitespecific reactivity by reproducing the sticking coefficients for the dissociation of CH 4 on the step sites of Pt(211).…”

“…Previous work by Jackson and co-workers using their reaction path Hamiltonian model presented in the supplementary material of Ref. 39 has suggested that the coupling of translational motion along the minimum energy path (MEP) to vibrational motion is larger with the SRP functional than the PBE functional due to the presence of the van der Waals well. The effect of this may be to remove energy from motion along the MEP and convert it to motion away from the MEP, reducing the observed reactivity with the SRP functional.…”