jp9b06745_si_001.pdf (2.79 MB)
Surface Carbon Hydrogenation on Precovered Fe(110) with Spectator-Coverage-Dependent Chain Initiation and Propagation
journal contribution
posted on 2019-10-10, 13:34 authored by Teng Li, Xiaodong Wen, Yong-Wang Li, Haijun JiaoExperimentally,
surface carbon hydrogenation on metallic iron forms
CH4, ethylene/ethane, and propene/propane, while previous
density functional theory studies showed that these reactions are
highly endothermic. This disagreement can be attributed to the shortcoming
of low coverage of surface carbon atoms and the underestimated role
of surface hydrogen. On a p(4 × 4) Fe(110) surface
with 0.25 ML carbon coverage (4 C atoms) and other free sites filled
with H atoms, we studied surface C hydrogenation with spectators and
found that the formation of CH4, ethylene/ethane, and propene/propane
becomes exothermic. Coupling of CH + CH and CH3C + CH to
acetylene and propylene is favored thermodynamically. Next, CHCH and
CH3CCH can be hydrogenated into CH2CH and CH3CHCH, and the subsequent hydrogenation of CH2CH
and CH3CHCH determines the formation and selectivity of
alkenes and alkanes. The most important surface species is carbide
HC for chain initiation or CH3C (RC for higher homolog)
for chain propagation. This model of high coverage with spectators
may help understand the mechanism of heterogeneous catalysis under
real conditions.