Theoretical Study of the Water–Gas Shift Reaction on a Au/Hematite Model Catalyst

Using the density functional theory, the mechanism of the water–gas shift reaction has been investigated employing a model catalyst formed by a Au5 cluster supported on the Fe-terminated (0001) face of hematite (α-Fe2O3), to better understand the role played by the metal–oxide interface in this reaction. Our results indicate that the Au5/hematite model catalyst has a good performance to catalyze the reaction following the so-called adsorptive mechanism. The presence of Au favors the development of the reaction due mainly to the following factors: (i) H2O dissociates very easily at the metal–oxide interface producing OH species; (ii) CO adsorbs strongly on a Au site nearby the position of OH; (iii) the hydroxycarbonyl intermediate (HOCO) is formed at the interface from CO and OH with a low activation barrier; and (iv) after hydrogen releasing, CO2 is desorbed with relative facility from the interface region. The formation of H2 is the stage of the whole reaction that more energy demands; however, this process is favored if one hydrogen atom comes directly from HOCO, instead of from two hydrogen atoms bound to surface oxygen anions.