Water gas shift reaction on supported noble metal catalysts is an essential process for upgrading hydrogen source industrially. Here a series of Pd/FeOx catalysts were detected for this reaction with Pd/Al2O3 as reference. It was found that Pd/FeOx exhibited higher CO conversion than Pd/Al2O3 with a good stability even in the presence of CO2 and H-2. Along the loading decreasing, the turnover frequency of exposed Pd atoms increased with the dispersion from subnanometer (similar to 1 nm) to single atoms. Various characterizations suggested that Pd single atoms greatly enhanced the reducibility of FeOx and facilitated the formation of oxygen vacancies, which served as sites to promote the dissociation of H2O to form H-2 and atomic O. The atomic O was ready to react with the linear adsorbed CO species on Pd single-atom sites through a redox mechanism, which resulted in low activation energy of similar to 30 kJ mol(-1). (C) 2017 American Institute of Chemical Engineers