Theoretical study of methane reforming on molybdenum carbide

Abstract

The adsorption of methane and the subsequent reaction of two dissociatively adsorbed CH3 species on a β-Mo2C (0 0 1) slab to form either ethylene or ethane were studied using density functional theory (DFT) calculations. Four methane-adsorption models of β-Mo2C (0 0 1) with different methane adsorption profiles were investigated. Following structural optimization for adsorption, methane was dissociated into CH3 and H at the three-fold site for the surface Mo atoms, without the underlying carbon atoms of the second layer and the two-fold site position for the surface Mo atoms before optimization. For the two adsorption positions, the adsorption energy of methane was identical at 289 kJ/mol. The other two adsorption positions were unstable relative to these two positions. After optimization of the two methanes for dissociation into 2CH3 and 2H, with one CH3 approaching the another CH3, C2H5 (Intermediate 2) was formed, together with the formation of ethylene through the release of one hydrogen. The first principle molecular dynamics (MD) of Intermediate 2 produced ethylene with one hydrogen, while the MD of Intermediate 2 with the addition of two hydrogen molecules produced ethane following the restricted attack of one hydrogen on the C2H5 species at approximately 2 Å from the surface after its desorption.