Comparing the CO oxidation activity of free PdO and Pd2+ ions over PdO-CeO2/SiO2 catalysts

Abstract Aiming at comparing the CO oxidation activity of free PdO and Pd 2+ ions, a series of PdO-CeO 2 /SiO 2 catalysts were prepared via an impregnation method and the turnover frequencies of them were quantitatively evaluated. The catalysts were further characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), temperature-programmed reduction (TPR), Raman technique and CO chemisorption. It was found that free PdO species and Pd 2+ ions could be segregated efficiently by nitric acid treatment. The PdO-CeO 2 /SiO 2 catalyst calcined at 600 °C showed the highest activity. The results of CO chemisorption suggested that free PdO species had a higher activity than Pd 2+ ions, and the turnover frequencies of them were 3.27 × 10 −2  s −1 and 0.49 × 10 −2  s −1 , respectively. The activity of PdO-CeO 2 /SiO 2 catalyst was higher than that of PdO/SiO 2 catalyst. Moreover, the CO catalytic activity of PdO-CeO 2 /SiO 2 catalyst could be assigned to the synergetic effect of free PdO and Pd 2+ ions, and this effect could improve the CO catalytic activity of catalysts.