Metal-Free Low-Temperature Water-Gas Shift Catalysis over Small, Hydroxylated Ceria Nanoparticles

The water-gas shift (WGS) reaction is an important process for the production of H₂ either for industrial use as, e.g.; an ammonia precursor or to produce low-CO concentration H₂ gas streams for use in fuel cells. Hybrid metal/metal oxide catalysts have permitted low-temperature WGS reaction by promoting associative reaction mechanisms in which -OH groups adsorbed at the metal oxide surface combine with reactant CO to form metastable intermediates. Here we show that sufficiently small, hydroxylated ceria nanoparticles (CNPs) can directly catalyze the WGS reaction without requiring the presence of a metal cocatalyst. Hydroxyl groups intrinsically present at the surfaces of such CNPs allow associative mechanisms with activation barriers on the order of 0.5 eV, low enough to allow metal-free low-temperature catalysis of the WGS reaction.