Mild generation of surface oxygen vacancies on CeO for improved CO photoreduction activity.

The vacancy defects of semiconductor photocatalysts play key roles in enhancing their photocatalytic CO reduction activity. In this work, CeO was chosen as a model catalyst and oxygen vacancies were introduced on its surface by a facile and mild oxalic acid treatment followed by moderate heating in N. Such a treatment resulted in a much increased ratio of Ce/Ce in CeO, and the oxygen vacancy-enriched CeO showed remarkably enhanced photocatalytic activity in CO reduction, with CO being the dominant reduction product, whose yield was about 8 times that on the pristine CeO. In situ FT-IR spectra showed that the abundant oxygen vacancies substantially improved the CO adsorption/activation on the surface of CeO, which facilitated the subsequent reduction of CO. However, the carbonates strongly adsorbed on the photocatalyst surface might be the main obstacle to maintaining the high CO reduction activity and stability of CeO with O vacancies.