Structure sensitivity of CH4 formation from successive hydrogenation of C on cobalt: Insights from density functional theory

Methods lowering methane selectivity are highly encouraged for Fisher-Tropsch synthesis. To unravel the correlation between the intrinsic surface properties and the ability of suppressing CH4 formation, process of hydrogenation from C to CH4 over HCP-Co(10 -10), HCP-Co(10 - 11), HCP-Co(10 -12), HCP-Co(11 - 21), FCC-Co(111), FCC-Co(311) and FCC-Co(110) surfaces have been investigated with density functional theory calculations. Hydrogenation reactions manifest significant structural sensitivity over Co catalysts since the variation of overall barriers and reaction energies is huge over seven surfaces. There is no convinced evidence to judge whether HCP Co or FCC Co is more advantageous for suppressing hydrogenation from C to CH4 . However, according to the calculated effective barriers and reaction energies, the ability of suppressing CH4 formation should be as follow: HCP(10 -11) > HCP(10 -12) > FCC(111) > FCC(311) > FCC(110) similar to HCP (10 -10) > HCP(11 - 21). More importantly, CH3 hydrogenation is rate-limiting step in CH4 formation over all considered surfaces. It is revealed that activation barriers of CH3 hydrogenation exhibit a well linear relationship with the d-band center of Co surfaces. The correlation between intrinsic surface property of catalysts and the ability for suppressing CH4 formation were established, therefore further guide the catalyst design and screening of efficient catalysts in FTS.