Systematic Theoretical Study of Ethylene Adsorption on δ-MoC(001), TiC(001), and ZrC(001) Surfaces

Abstract

A systematic study of ethylene adsorption over δ-MoC(001), TiC(001), and ZrC(001) surfaces was conducted by means of calculations based on periodic density functional theory. The structure and electronic properties of each carbide pristine surface had a strong influence in the bonding of ethylene. It was found that the metal and carbon sites of the carbide could participate in the adsorption process. As a consequence of this, very different bonding mechanisms were seen on δ-MoC(001) and TiC(001). The bonding of the molecule on the TMC(001) systems showed only minor similarities to the type of bonding found on a typical metal like Pt(111). In general, the ethylene binding energy follow the trend in stability: ZrC(001) < TiC(001) < δ-MoC(001) < Pt(111). The van der Waals correction to the energy produces large binding energy values, modifies the stability orders and drives the ethylene closer to the surface but the adsorbate geometry parameters remain unchanged. Ethylene was activated on clearly defined binding geometries, changing its hybridization from sp 2 to sp 3 with an elongation (0.16−0.31 Å) of the CC bond. On the basis of this theoretical study, δ-MoC(001) is proposed as a potential catalyst for the hydrogenation of olefins, whereas TiC(001) could be useful for their hydrogenolysis.

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

“…Similar conclusions were obtained for methane adsorption on the same surfaces[47]. Not unexpectedly, the adsorbate molecular geometry remains unchanged[16,47].…”

“…Owing to their activity and the fact that they do not require special conditions for their synthesis [15], Mo carbides have stood out among other TMCs. Very recently it has been shown that the interaction of ethylene with -MoC(001) and Pt(111) exhibits a similar adsorption energy [16], further reinforcing the idea that early TMCs exhibit chemical features of late transition metals. On the other hand, Mo2C phases have been proposed as alternative to commercial catalyst for water gas shift reaction (WGS) [17] and Pt/Mo2C based catalyst also display very high rates for WGS [18].…”

Acetylene and Ethylene Adsorption on a β-Mo2C(100) Surface: A Periodic DFT Study on the Role of C- and Mo-Terminations for Bonding and Hydrogenation Reactions

“…5,21,22 Among the crystal phases of molybdenum carbide, 23 three of them are the most used in catalysis, viz. cubic, 13,22,[24][25][26][27][28][29] hexagonal 11,[30][31][32] and orthorhombic. 14,20,22,28,33 In general, molybdenum carbides can be represented as MoC y , where the most investigated system is y = 0.5 (Mo 2 C), i.e.…”

“…However, phases with y = 1 (MoC) have also been reported. 22,25,28,29,34,35 Moreover, y also could be a non-integer number, leading to nonstoichiometric carbides. 13 The chemistry of molybdenum carbides depends on their C/Mo ratio, with a significant effect in the activity, stability, and selectivity in hydrogenation reactions.…”

Surface and Interface Engineering: Molybdenum Carbide–Based Nanomaterials for Electrochemical Energy Conversion

“…[117] Crystal phase plays a significant role in the intrinsic characteristics of molybdenum carbide including the type of supersaturation, catalyst geometry, and interfacial energy. [117,[148][149][150] A series of phases in molybdenum carbides (Mo x C), such as α-Mo 2 C, β-Mo 2 C, γ-MoC, η-MoC, δ-MoC, and α-MoC 1−x , show quite different electrochemical performances due to the varied electronic configurations. [116] Rodriguez and co-workers revealed the different d-band center values on δ-MoC (−4.79 eV), α-MoC (−3.18 eV), and β-Mo 2 C (−3.02 eV) by the DFT calculations, [42] which were related to the binding strength of H-binding on the surface and consequently lead to the different HER activity.…”