Ab Initio Microkinetics of H2S Interactions with Clean and Sulfided Au(110) at Low Temperature: A Strong Assistance in Partial Dissociation from Single Sulfur Atoms

A microkinetic model built on first-principles calculations is developed to clarify an ongoing experimental controversy regarding whether hydrogen sulfide (H2S) molecules are intact or dissociated on pristine and S-covered Au(110) surfaces at 120 K. From the simulation, we prove that only associative adsorption of H2S on the defect-free, flat (110) facet of gold occurs in the exposure region under investigation, whereas its reaction with sulfur adsorbed as single atoms straightforwardly proceeds to yield relatively strongly bound SH radicals for the surface precovered with elemental S. The sulfur assistance of neighboring H2S to decompose is ascribed to the stability of the corresponding transition state in which three-center hydrogen bonding interactions are being formed. One-dimensional zigzag chains of divalent sulfur are shown as structural units of the c(2 x 4) superstructure observed experimentally in inactive sulfur islands for the S + H2S reaction. The sensitivity of H-S bond cleavage in surface H2S to the aggregation state of coadsorbed sulfur may, in part, be rationalized by the change in valency of these adatoms. This is the first time that a clear theoretical picture of the chemistry of H2S on such an open Au surface is provided, which is beneficial to elucidate more complicated reaction processes, such as sulfur-poisoning tolerance of gold nanocatalysts.