State Resolved Measurements of Methane Reactivity on Ni(111) and Ir(111) Surfaces
Abstract: The initial sticking probability for methane dissociation on Ir(111) and Ni(111) surfaces are measured using molecular beam surface scattering techniques. State-resolved measurements coupling infrared laser excitation to the incident methane beam allowed for the reactivity of a single ro-vibrational state to be probed. A precursor-mediated reaction pathway is highlighted on Ir(111) ... read moredemonstrating the first mode-selective behavior for a physisorbed molecule leading to dissociation. Despite the different interaction times between the molecule and surface, the direct dissociative and precursor-mediated mechanisms had identical vibrational efficacies for the (v3, v=1) vibrational state. The reaction of CHD3 on Ni(111) in the (v1, v=1) vibrational state was used as a model system for direct comparison with ab-initio molecular dynamics simulations to obtain the first chemically accurate description of a polyatomic molecule-surface reaction. Surface temperature effects for the dissociative chemisorption of methane on Ni(111) are explored for both the initial sticking probability and diffusion of carbon into the nickel lattice. It was observed that methane dissociation was insensitive to surface temperatures at and above 800 K and exciting the methane to the (v3, v=1) vibrational state enhanced reactivity even at the highest methane internal energies. Diffusion of carbon into the nickel bulk was observed to turn on rapidly around a surface temperature of 780 K under the conditions studied. Under these conditions the studied reactivities and diffusivities were much closer to those used in industrial steam reforming reactors.
Thesis (Ph.D.)--Tufts University, 2018.
Submitted to the Dept. of Chemistry.
Advisor: Arthur Utz.
Committee: Charles Sykes, Samuel Thomas, and Bret Jackson.
Keywords: Chemistry, and Physical chemistry.read less