(134g) Direct Versus Hydrogen Assisted CO Dissociation On Metal Surfaces

We present computational investigations of the formation of
precursor hydrocarbon species relevant to production of liquid hydrocarbons on
low index surfaces of various important noble and transition metals. The
formation could occur via the so-called carbide mechanism. In this mechanism, direct
carbon monoxide dissociation takes place, followed by stepwise hydrogenation of
C yielding CH_x precursor species.
Formation of precursor CH_x species could also potentially take place
through hydrogen assisted route giving rise to hydrogenated carbon monoxide
intermediates. First-principles calculations of energetics and barriers of carbon
monoxide conversion to hydrocarbons species were performed using plane-wave
periodic density functional theory. Our calculations indicate that the hydrogen
assisted route is competitive, particularly on transition metals. An in-house microkinetic computer code, with input
thermodynamics and kinetic parameters estimated from electronic structure
calculations, was developed. The two
pathways were examined on representative surfaces using microkinetic approach
and it was found that the aforementioned finding holds true at realistic
conditions.

.