1. Alkane C-H Bond Breaking at Catalytic Metal Surfaces: Theory
Alkane C-H Bond Breaking at Catalytic Metal Surfaces: Theory
Development Coupled with Effusive Molecular Beam Experiments
Ian Harrison, Department of Chemistry, University of Virginia
Microcanonical unimolecular rate theory (MURT) has been developed to treat activated dissociative chemisorption at surfaces – a reactive step that can rate-limit important petrochemical processes such as hydrogen production via steam reforming of alkanes over Ni catalysts. Non-equilibrium dissociative sticking coefficients S(Tg, Ts) for increasingly complex alkanes on single crystal metal surfaces were measured using effusive molecular beams and modeled by MURT.
Over the grant period, we:
demonstrated the ability of MURT to treat two benchmark systems for gas-surface reaction dynamics where detailed balance can be applied: (i) the dissociation and associative desorption of H2 on Cu(111), and (ii) the dissociation of CO2 and CO oxidation on Rh(111). Catalytic processes that can activate or produce H2, CO, and CO2 are important for clean energy technologies.
used the MURT to predict the thermal reactivity of methane on flat metal surfaces based on analysis of non-equilibrium molecular beam experiments such that direct comparisons to nanocatalyst reactivity could be made.
developed experimental methods to measure the non-equilibrium reactivity of alkanes on metals when the impinging gas temperature Tg differs from the surface temperature Ts. Gas-surface energy transfer was found to be increasingly coupled to reactivity for the higher alkanes, such as propane on Pt(111).
Metal nanocatalysts are apparently much less reactive than flat metal surfaces, suggesting that H2 production via CH4 reforming might be substantially improvable.