Comparative Theoretical Study of the Chemistry of Hydrogen Sulfide on Cu(100) and Au(100): Implications for Sulfur Tolerance of Water Gas Shift Nanocatalysts

(100)-like planes have been thought to play a pivotal role in catalyzing the water gas shift (WGS) reaction on complicated face-centered cubic metal nanoclusters, such as Cu-29 and Au-29 supported over ZnO. Understanding their sulfur poisoning effect is highly desirable yet very challenging. Accordingly, as an important first step toward addressing this interesting issue, we applied a combination of periodic, self-consistent density functional theory (DFT-GGA) calculations and microkinetics to investigate the interaction of H2S with the extended model surfaces Cu(100) and Au(100) under realistic conditions. Through our calculations, a scaling relationship of the adsorption enthalpy for HxS (x = 0-2) on each surface was put forward. On the former substrate, the scission of the H-S bonds was found to be more facile in energy than that on the latter one; however, the recombinative desorption of the dissociated H atoms is less favored. The barrier of the rate-determining step of H2S decomposing to S at the Cu facet is clearly lower than that of the Au counterpart, 0.43 versus 0.95 eV, which makes Cu much more active to the reaction. In fact, our microkinetic model reveals that a notable proportion of the (100) surface of copper was already occupied by S from very low values of the partial pressure of H2S, while the Au(100) surface was essentially free of adsorbates for all examined pressures. Based on the experimental Campbell-Koel principle, the present findings indicate that the Au material exhibits improved catalytic performance for the WGS reaction, which suppresses the formation of undesirable S that deactivates the catalyst. Its related nanomaterials are thus a promising candidate for a WGS catalyst possessing excellent sulfur-resistance.