Water-Gas Shift Mechanism Revealed

Brookhaven National Laboratory scientists have uncovered key pieces of the mechanism that drives the water-gas shift (WGS) reaction on gold/metal-oxide catalysts (Science 2007, 318, 1757). Critical to industrial H₂ production, the WGS reaction (H₂O + CO — H₂ + CO₂) is used to remove the CO impurity from H₂ that's generated during reforming of crude oil, coal, and other materials. Conventional WGS catalysts based on oxides of copper or iron-chromium are air sensitive and require elaborate activation procedures before they can be used. Recent studies showed that novel WGS catalysts based on Au-CeO₂ and Au-TiO₂ nanomaterials may sidestep those problems, but the basic mechanism through which these catalysts mediate the reaction was poorly understood. Now, José A. Rodriguez, Jan Hrbek, and coworkers have determined that water dissociates at oxygen vacancies on the metal oxide surface and CO adsorbs at adjacent gold sites. Reactions then proceed at the interface between gold and the oxide, they say.