DFT study of Ni-catalyzed plasma dry reforming of methane

- The presence of surface-bound H-atoms:
- Facilitates associative desorption of methanol by increasing the rate of H-transfer to the adsorbed fragments.
- Facilitates associative formation of C1 and C2 hydrocarbons by increasing the rate of H-transfer to the formed fragment.
- Impedes hydrogenation of ethylene to ethane.
- The retention of methane fragments, in the presence of surface-bound H-atoms can be regarded as an identifier.

We investigated the plasma-assisted catalytic reactions for the production of value-added chemicals from Ni-catalyzed plasma dry reforming of methane by means of density functional theory (DFT). We inspected many activation barriers, from the early stage of adsorption of the major chemical fragments derived from CH4 and CO2 molecules up to the formation of value-added chemicals at the surface, focusing on the formation of methanol, as well as the hydrogenation of C1 and C2 hydrocarbon fragments. The activation barrier calculations show that the presence of surface-bound H atoms and in some cases also remaining chemical fragments at the surface facilitates the formation of products. This implies that the hydrogenation of a chemical fragment on the hydrogenated crystalline surface is energetically favoured compared to the simple hydrogenation of the chemical fragment at the bare Ni(111) surface. Indeed, the presence of hydrogen modifies the electronic structure of the surface and the course of the reactions. We therefore conclude that surface-bound H atoms, and to some extent also the remaining chemical fragments at the crystalline surface, induce the following effects: they facilitate associative desorption of methanol and ethane by increasing the rate of H-transfer to the adsorbed fragments while they impede hydrogenation of ethylene to ethane, thus promoting again the desorption of ethylene. Overall, they thus facilitate the catalytic conversion of the formed fragments from CH4 and CO2, into value-added chemicals. Finally, we believe that the retention of methane fragments, especially CH3, in the presence of surface-bound H atoms (as observed here for Ni) can be regarded as an identifier for the proper choice of a catalyst for the production of value-added chemicals.

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