Atomistic thermodynamics study of the adsorption and the effects of water–gas shift reactants on Cu catalysts under reaction conditions

Density-functional theory (DFT) calculations were performed to determine the structure and stability of oxygen, carbon monoxide and sulfur adsorption on Cu(111), (100) and (110) surfaces that are in equilibrium with a water–gas shift (WGS) reactive environment of H2, H2S, H2O and CO. An atomistic thermodynamic framework based on DFT was used for describing the phase behaviors of the adsorbates on different Cu facets. Phase diagrams of each possible adsorbate on each surface were constructed as a function of the corresponding chemical potential which showed sulfur poisoning occurs even at ppm levels of H2S in the environment at low temperatures. Under reaction conditions relevant to WGS at low temperature, CO and S adsorbed surface structures were found to be more stable then the clean catalyst surfaces. At high temperatures and high hydrogen pressures, a poisoned surface can be regenerated back to a clean surface. The shapes of a Cu nanoparticle in the WGS reaction conditions under various sulfur chemical potentials were determined using the Wulff construction. We found that the crystal shape changes significantly from one dominated by (111) and (100) facets at very low sulfur chemical potentials to a shape dominated by (110) facets at higher sulfur chemical potentials, suggesting that reactive site distributions may change under reaction conditions.