The α‐WC(0001) Surface as a Hydrogen Sponge: A First Principle Study of H2 Dissociation and Formation of Low and High Coverages

Abstract

AbstractTungsten carbide (WC) displays a Pt‐like behavior in catalysis, applied in hydrogenation processes. Numerous theoretical studies have modeled the behavior and use of adsorbed hydrogen without obtaining a general picture, missing basic links between H2 dissociation and generation of high surface coverage (ΘH>0.5 ML). Here, the capability of C‐ and W‐terminations of the α‐WC(0001) surface is analyzed to dissociate several H2 molecules to produce coverages, ΘH, ranging from low to very high values (0.13<ΘH<2.00 ML). Density functional theory and an ab initio atomistic thermodynamic were used to achieve the conditions for H2 dissociation. The WC−C surface has higher capacity to dissociate H2 molecules than WC−W. However, both surfaces can reach full surface coverage, ΘH=1 ML, at mild ambient conditions, T=300 K and P=1 atm, and even up to 500 K at low and high pressures. The H‐adatoms on WC−W are more labile than on WC−C. The binding of adsorbates is hindered at high ΘH, implying a need to modulate ΘH according to the application. The results give the basis to understand the capabilities of WC‐based catalysts in hydrogenation‐related reactions, with the advantage of WC being a hydrogen reservoir at mild practical catalytic conditions.