Adsorption and activation of CO and H2, the corresponding equilibrium phase diagrams under different temperature and partial pressures over Cu(100) surface: Insights into the effects of coverage and solvent effect

- The saturated coverage of CO adsorption is 8/12 ML on Cu(100) surface.
- Solvent effect can improve the stability of CO adsorption at low coverage.
- Only molecular adsorption CO exists in syngas conversion on Cu catalyst.
- Solvent effect makes more H2 molecules become the dissociative adsorption.
- H2 exists in the form of H atoms on Cu catalyst under the realistic condition.

The adsorption and activation of CO and H2 at different coverage over Cu(100) surface under the vacuum and liquid paraffin conditions have been investigated using DFT calculations together with ab initio thermodynamics. It is found that the stepwise adsorption energies of CO decrease with the increasing of coverage, and CO prefers to desorption rather than its dissociation in vacuum and liquid paraffin, which are independent on the reaction environment. H2 in vacuum is the dissociative adsorption at the coverage less than or equal to 3/12 ML, but until to the coverage of 6/12 ML in liquid paraffin, indicating that solvent effect can make more H2 molecules become the dissociative adsorption; moreover, solvent effect is in favor of stabilizing the adsorption configurations of dissociated H atoms. Further, the equilibrium phase diagrams illustrate the relationship between the stable CO(H2) adsorption with the temperatures and CO(H2) partial pressure on Cu(100) surface in vacuum and liquid paraffin. It is concluded that H2 exists in the form of H atoms, and CO is the molecular adsorption, which provide the reasonable explanations for many studies related to CO and H2 on Cu catalyst under the realistic condition.

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