Heterogeneously catalyzed processes consist of several elementary reactions. Accurately calculating their rates requires the availability of accurate barriers for the rate controlling steps. Unfortunately, currently no first principles methods can be relied upon to deliver the required accuracy. To solve this problem, in 2009 we came up with a novel implementation of the specific reaction parameter approach to density functional theory (SRP-DFT). This allowed us to reproduce experiments for H2 reacting on copper surfaces, and to determine barrier heights for H2-Cu systems, with chemical accuracy. The original procedure used was not extendable to reactions of molecules heavier than H2 with surfaces, because the metal surface was treated as static. This problem has been solved by combining SRP-DFT with Density Functional Molecular Dynamics (DFMD). This method was applied to the dissociative chemisorption of methane on a Ni surface, a rate-limiting step in the steam reforming reaction. We were able to reproduce experiments on CHD3 + Ni(111) with chemical accuracy, and have predicted a value of the reaction barrier height that we claim to be chemically accurate. Results for CHD3 + Pt(111) are even better, and show that the SRP density functional for methane interacting with Ni(111) is transferable to methane interacting with another group X metal surface, i.e., Pt(111). Even more interestingly for applications to catalysis, the SRP functional derived for methane reacting with Ni(111) also gives a very accurate description of molecular beam sticking experiments on CHD3 + Pt(211). Finally, thanks to a collaboration with Jörg Behler (University of Göttingen) we are now able to develop potential energy surfaces also depending on the degrees of freedom associated with the surface phonons, for polyatomic molecules interacting with metals. This has enabled us to compute statistically accurate reaction probabilities for highly activated reactions not yet open to investigation with DFMD, for which reaction probabilities are less than 0.01. Quasi-classical simulations of diatomic and polyatomic molecules reacting with metals (in systems like N2 + Ru(0001), NH3 + Ru(0001), CH4 + Cu(111)) are revealing interesting insights into the reaction mechanisms of these systems.

Towards a chemically accurate description of reactions of molecules with transition metal surfaces

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.