A First Principles Study of Carbon−Carbon Coupling over the {0001} Surfaces of Co and Ru

Abstract

The coupling of CH (methylidyne) and CH2 (methylene), to form CHCH2 (vinyl), over Co and Ru surfaces has been studied with the nonlocal gradient-corrected density functional theory slab calculations. The results show that this reaction is slightly exothermic on Co while endothermic on Ru within a (2 × 2) surface unit cell. Transition states were isolated on both surfaces, and the reaction barriers were found to be 55.9 and 116.5 kJ/mol on Co and Ru, respectively. The structures of the transition state on the two metal surfaces are similar; both involve the formation of a multicentered bond.

Elementary steps of syngas reactions on Mo2C(001): Adsorption thermochemistry and bond dissociation

“…At high coverages C 2 H 2x formation is thermodynamically favorable, and spontaneous coupling between adjacent sites indicates that it will also be kinetically facile. This attractive interaction between CH x<3 species is unusual; most surface adsorbates exhibit repulsive interactions [40,65], and carbon coupling is often activated even for adjacent adsorption sites [65,66]. This propensity towards coupled carbons is consistent with the activity of Mo 2 C for methane aromatization [7] and FischerTropsch synthesis [15,16,17,22].…”

“…Hydrogen assisted dissociation of CO is the rate-limiting step for methane synthesis on Ni [69], and barriers for carbon-carbon coupling determine the mechanism and average chain length in FischerTropsch synthesis [66]. Thus, the energy barriers for these types of elementary reactions on Mo 2 C(001) provide important information about the catalytic activity of the surface.…”

High coverage CO adsorption and dissociation on the Co(0001) and Co(100) surfaces from DFT and thermodynamics

“…All calculations are spin-polarized due to the magnetic properties of cobalt with a plane wave cutoff energy of 400 eV [33], the reported structures will be converged while the energy differences are smaller than 10 −5 eV, and the forces are less than 0.03 eV/Å. A 5 × 5 × 1 k-points grid generated via the Monkhorst-Pack procedure [22,34] [38,39], respectively. Spin-polarized calculations on the isolated CO molecule, C and O atoms are carried out in a 10 × 10 × 10 Å cubic unit cell with a single k-point [40].…”

Effect of manganese on a potassium-promoted iron-based Fischer-Tropsch synthesis catalyst

“…Fischer-Tropsch synthesis (FTS) is a well-established catalytic process to convert syngas (H 2 and CO) derived from coal or natural gas to transportation fuels and petrochemical substitutes [1][2][3][4]. The iron-based catalysts are often used in the commercial operations, especially for coal derived syngas with low H 2 /CO ratio, due to their high water gas shift (WGS) activity, low cost, flexible operation conditions as well as reasonable products distribution [5][6][7][8].…”