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

Abstract

Co-decorated Cu-based catalysts prepared on the basis of modified Fischer-Tropsch catalysts have high selectivity towards higher alcohols synthesis from syngas. However, H2S from syngas can easily deactivate the catalysts containing Co or Cu. In order to explore the interaction between Co-Cu catalyst and H2S and to clarify the sulfur poisoning mechanism on this catalyst, the dissociation process of H2S and adsorption properties of involved species (H2S, HS, S and H) on three surfaces (Cohcp-Cu (111), Cofcc-Cu (111) and Co-Cu (211)) 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 > H2S, and the trend of adsorption abilities of three surfaces is Co-Cu (211) > Cofcc-Cu (111) ≈ Cohcp-Cu (111). The dissociation of H2S is thermodynamically spontaneous on three surfaces. It was found that the energy barrier of the first dissociation step is lower on Co-Cu (211) (0.12 eV). The energy barrier of the second dissociation step is relatively high on Co-Cu (211) (0.53 eV) but extremely low on Cohcp-Cu (111) (0.01 eV) and Cofcc-Cu (111) (0 eV). The results show that H2S is a bit harder to dissociate on Co-Cu (211) at low temperature. The difference in the H2S 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 H2S, which puts forward higher requirements for further improvement in sulfur tolerance of Co-Cu catalysts.