Effect of moisture on the active species in Cu-CeO2 catalyst

The influence of moisture present in air on the CO oxidation activity of 10% Cu-CeO2 catalysts was studied, and the active Cu species in the catalyst were examined by high-resolution transmission electron microscopy (HRTEM). It was found that the catalyst is highly sensitive to the moisture in air. The fresh oxidized catalyst was deactivated after exposure to air with the light-off temperature increasing from 30 to 70 °C. A large amount of small Cu(OH)2 nanocrystals in the size of 1-4 nm were observed in the exposed catalyst in this study, rather than the copper oxide clusters proposed in the literature. The transformation of the active CuOx nanocrystals to Cu(OH)2 nanocrystals is believed to be the cause of catalyst deactivation when moisture is present. The driving force for this transformation is the lower surface energy of Cu(OH)2 as compared to copper oxides. The results highlight the important role of surface energy in the stability and reactivity of the active cluster species in the catalysts.