Adsorption and dissociation of molecular hydrogen on orthorhombic β-Mo2C and cubic δ-MoC (001) surfaces

Abstract

Molybdenum carbides are increasingly used in heterogeneously catalyzed hydrogenation reactions, which imply the adsorption and dissociation of molecular hydrogen. Here a systematic density functional theory based study, including or excluding dispersion terms, concerning the interaction and stability of H2 with cubic δ-MoC(001) and orthorhombic β-Mo2C(001) surfaces is presented. In the latter case the two possible C or Mo terminations are considered. In addition, different situations for the H covered surfaces are examined. Computational results including dispersive forces predict as essentially spontaneous dissociation of H2 on β-Mo2C(001) independently of the surface termination, whereas on δ-MoC(001) molecular hydrogen dissociation implies a small but noticeable energy barrier. Furthermore, the ab initio thermodynamics formalism has been used to compare the stability of different H coverages. Finally, core level binding energies and vibrational frequencies are presented with the aim to assist the interpretation of yet unavailable data from X-ray photoelectron and infrared spectroscopies.

Hydrogen adsorption on transition metal carbides: a DFT study

“…For all four carbides, the increase in coverage leads to a decrease in the adsorption energy per atom, which is consistent with the results found for other carbides by previous work. 59 This effect is not unexpected, and insight comes from the analysis of the work function (F), which steadily decreases with coverage as electrons are inserted in the conduction band (Fig. 4).…”

Diversity of Adsorbed Hydrogen on the TiC(001) Surface at High Coverages

“…13,14 In this aspect, TiC can be regarded as a textbook example within the family of transition metal carbide (TMC) materials. 14,15 It has also been shown that TiC can be useful as a material for hydrogen storage, although the low gravimetric content prevents its technological use. [6][7][8][9] Under electrochemical conditions H is found to be absorbed on defective TiC x compounds.…”

Liquid-Phase Hydrodeoxygenation of Guaiacol over Mo2C Supported on Commercial CNF. Effects of Operating Conditions on Conversion and Product Selectivity

“…It is particularly suitable as electrocatalyst in reducing processes, as well as heterogeneous catalyst in reactions where electron transfer is needed from the catalyst to adsorbed reactant, characteristic of bond breaking reactions [11]. Another DFT study [12] revealed that dispersive forces predict an essentially spontaneous dissociation of hydrogen molecules on β-Mo 2 C (001), independently of the surface termination. These studies show that molybdenum carbides present an interesting potential as catalyst material for HDO [8].…”