This
research is designed to fundamentally understand CO activation
acting as a crucial step in the initiation of the Fischer–Tropsch
(FT) process over Co2C catalyst, the intrinsic activity,
and structural sensitivity of the catalyst, which is vital to its
FT performance, but remains unclear. Accordingly, CO activation over
the commonly exposed Co2C(101), (011), (010), (110), and
(111) facets is investigated using density functional theory (DFT)
calculations and microkinetic modeling. Results show that the CH monomer
is the most abundant surface CH
x
species
for CO activation over five Co2C facets, and the mechanism
of CO activation and subsequent CH formation strongly depend on the
Co2C facet. The formation rate of the CH monomer follows
the order of (111) < (010) < (110) < (101) < (011). The
(011) facet accounting for 35.21% of the surface is the most active
for CO direct dissociation into C, followed by C hydrogenation to
CH, which presents a comparable activity with the hexagonal close-packed
(HCP) Co due to the presence of denser B5-type active sites.
Further, Co2C is a multifunctional catalyst for the FT
process because its facets exhibit a different catalytic activity
toward CO dissociation to form the key CH monomer, and as a result,
C2+ hydrocarbons and oxygenates can be formed depending
on the relative reaction rate between CO insertion into CH
x
reaction and CH
x
–CH
x
coupling. The finding of this research may
lead a new avenue for rational design of Co2C-based catalysts
with desirable activities and product selectivity.
Improving the selectivity and activity of C 2 species from syngas is still a challenge. In this work, catalysts with monolayer Cu or Rh supported over WC with different surface terminations (M/WC (M = Cu or Rh)) are rationally designed to facilitate C 2 species generation. The complete reaction network is analyzed by DFT calculations. Microkinetics modeling is utilized to consider the experimental reaction temperature, pressure, and the coverage of the species. The thermal stabilities of the M/WC (M = Cu or Rh) catalysts are confirmed by AIMD simulations. The results show that the surface termination and supported metal types in the M/WC (M = Cu or Rh) catalysts can alter the existence form of abundant CH x (x = 1−3) monomer, as well as the activity and selectivity of CH x monomer and C 2 species. Among these, only the Cu/WC−C catalyst is screened out to achieve outstanding activity and selectivity for C 2 H 2 generation, attributing to that the synergistic effect of the subsurface C atoms and the surface monolayer Cu atoms presents the noble-metal-like character to promote the generation of CH x and C 2 species. This work demonstrates a new possibility for rational construction of other catalysts with the non-noble metal supported by the metal carbide, adjusting the surface termination of metal carbide and the supported metal types can present the noble-metal-like character to tune catalytic performance of C 2 species from syngas.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.