Steam Reforming on Transition-Metal Carbides from Density-Functional Theory

Abstract

A screening study of the steam reforming reaction on clean and oxygen covered early transitionmetal carbides surfaces is performed by means of density-functional theory calculations. It is found that carbides provide a wide spectrum of reactivities, from too reactive via suitable to too inert. Several molybdenum-based systems are identified as possible steam reforming catalysts. The findings suggest that carbides provide a playground for reactivity tuning, comparable to the one for pure metals.

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

“…These results suggest that the most relevant Mo 2 C(001) surface to use for studying syngas reactions is the oxygen passivated surface or hydrocarbon terminated surface. Previous work has suggested that the oxygen passivated surface may temper the high reactivity of the Mo-terminated Mo 2 C(001) surface, leading to improved catalytic activity [52]. Adsorbed oxygen, carbon, or hydrocarbons can desorb as part of catalytic cycles, therefore the termination will depend on both thermodynamic conditions and reaction kinetics.…”

“…In order to further improve the performance of molybdenum carbide catalysts it is of value to understand the reactivity, selectivity, and stability of molybdenum carbide under various conditions. Numerous theoretical studies have investigated the surface stability [38,39,40,41], adsorption energies [42,43,44,45,46,47,48,49,50,51,40,52], reaction energetics [53,54,46,55,52], and alkali-doping [40,50] on Mo 2 C. The most well-studied surface is the Mo 2 C(001) surface, and both orthorhombic and hexagonal close packed Mo 2 C have been investigated. The results have indicated that the non-polar (011) surface is the most stable regardless of carbon chemical potential, but that the surface energies are sufficiently close that all surfaces are expected to be present on nanoparticles [40,39].…”

Computational Identification of Descriptors for Selectivity in Syngas Reactions on a Mo2C Catalyst

“…27,[32][33][34][35] Recently, Medford et al applied ab initio thermodynamics and DFT to study the stability of surface structures of Mo 2 C and adsorption of reactive intermediates as well as C-O bond dissociation on the Mo 2 C surface. 36 Pistonesi et al studied adsorption of alkali metal on Mo 2 C surfaces and its effect on CO adsorption and dissociation.…”

Phase and Facet Control of Molybdenum Carbide Nanosheet Observed by In Situ TEM

“…Figure c presents the (111) facet, which has Mo‐terminated or C‐terminated surface. It has been reported that the MoC (111) surface has a higher reactivity in the catalyzed reduction than the MoC (100) surface, which, however, makes the (111) surface easily oxidized . We calculated the surface energy of these surfaces (see details in the Experimental Section).…”

“…Different surfaces of carbides also possess different electrochemical properties. The Mo‐terminated or C‐terminated fcc MoC (111) surface is easily oxidized though it has higher reactivity compared to fcc MoC (100) surface …”