Adsorption and dissociation of H2S on Co-Cu (1 1 1) and (2 1 1) catalyst surfaces: A first-principles study.

[Display omitted] • Three types of surface models were constructed to study the different behaviors of H 2 S on Co-Cu catalyst surfaces. • The adsorption configurations and properties of related species on three Co-Cu catalyst surfaces were calculated by DFT. • The energy variations in the dissociation of H 2 S on Co-Cu surfaces were studied and compared with that on pure metal. • The factors impacting H 2 S dissociation reaction were explained in terms of adsorption structures, PDOS and Mulliken charge. Co-decorated Cu-based catalysts prepared on the basis of modified Fischer-Tropsch catalysts have high selectivity towards higher alcohols synthesis from syngas. However, H 2 S from syngas can easily deactivate the catalysts containing Co or Cu. In order to explore the interaction between Co-Cu catalyst and H 2 S and to clarify the sulfur poisoning mechanism on this catalyst, the dissociation process of H 2 S and adsorption properties of involved species (H 2 S, HS, S and H) on three surfaces (Cohcp-Cu (1 1 1), Cofcc-Cu (1 1 1) and Co-Cu (2 1 1)) were studied using Density Functional Theory (DFT) calculations. The interactions between S/H and Co are stronger than that Cu. The adsorption energy follows an order of S > HS > H > H 2 S, and the trend of adsorption abilities of three surfaces is Co-Cu (2 1 1) > Cofcc-Cu (1 1 1) ≈ Cohcp-Cu (1 1 1). The dissociation of H 2 S is thermodynamically spontaneous on three surfaces. It was found that the energy barrier of the first dissociation step is lower on Co-Cu (2 1 1) (0.12 eV). The energy barrier of the second dissociation step is relatively high on Co-Cu (2 1 1) (0.53 eV) but extremely low on Cohcp-Cu (1 1 1) (0.01 eV) and Cofcc-Cu (1 1 1) (0 eV). The results show that H 2 S is a bit harder to dissociate on Co-Cu (2 1 1) at low temperature. The difference in the H 2 S dissociation on three surfaces is explained in terms of adsorption configurations, PDOS and Mulliken charge distribution. In general, Co-decorated Cu-based catalyst surfaces are sensitive to H 2 S, which puts forward higher requirements for further improvement in sulfur tolerance of Co-Cu catalysts. [ABSTRACT FROM AUTHOR]