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Published November 26, 2009 | Supplemental Material
Journal Article Open

Structures, Energetics, and Reaction Barriers for CH_x Bound to the Nickel (111) Surface

Abstract

To provide a basis for understanding and improving such reactive processes on nickel surfaces as the catalytic steam reforming of hydrocarbons, the decomposition of hydrocarbons at fuel cell anodes, and the growth of carbon nanotubes, we report quantum mechanics calculations (PBE flavor of density functional theory, DFT) of the structures, binding energies, and reaction barriers for all CH_x species on the Ni(111) surface using periodically infinite slabs. We find that all CH_x species prefer binding to μ3 (3-fold) sites leading to bond energies ranging from 42.7 kcal/mol for CH_3 to 148.9 kcal/mol for CH (the number of Ni-C bonds is not well-defined). We find reaction barriers of 18.3 kcal/mol for CH_(3,ad) → CH_(2,ad) + H_(ad) (with ΔE = +1.3 kcal/ mol), 8.2 kcal/mol for CH_(2,ad) → CH_(ad) + H_(ad) (with ΔE = -10.2 kcal/mol) and 32.3 kcal/mol for CH_(ad) → C_(ad) + H_(ad) (with ΔE = 11.6 kcal/mol). Thus, CH_(ad) is the stable form of CH_x on the surface. These results are in good agreement with the experimental data for the thermodynamic stability of small hydrocarbon species following dissociation of methane on Ni(111) and with the intermediates isolated during the reverse methanation process.

Additional Information

© 2009 American Chemical Society. Received: December 1, 2008; Revised Manuscript Received: August 3. Publication Date (Web): October 29, 2009. This research was partially supported by Intel Components Research (Program managers: Dr. Kevin O'Brien, Dr. Sadasivan Shankar). The computer facilities were provided by grants from ONR-DURIP and ARO-DURIP. Supporting Information Available: Pseudopotential parameters, relaxed geometries for all species with charge and spin analysis, relaxed geometries for reference state species, geometries along nudged elastic band reaction pathways, spin optimization calculation inputs, parameters and results, and frequencies and thermodynamic data from cluster calculations. This material is available free of charge via the Internet at http:// pubs.acs.org.

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