Reaction mechanism and kinetics of CO oxidation over a CuO/Ce0.75Zr0.25O2-δ catalyst.

The CuO/Ce 0.75 Zr 0.25 O 2 - δ and Ce 0.75 Zr 0.25 O δ catalysts were prepared by the sol-gel method, and Cu 0.07 Ce 0.75 Zr 0.25 O 2-δ was obtained by treating CuO/Ce 0.75 Zr 0.25 O 2 - δ with nitric acid to remove the well-dispersed CuO on the surface. Various characterizations were used to reveal the different active sites, such as surface-dispersed CuO and Cu-Ce-Zr-O δ solid solutions in CuO/Ce 0.75 Zr 0.25 O 2 - δ , Cu-Ce-Zr-O δ solid solutions in Cu 0.07 Ce 0.75 Zr 0.25 O 2-δ and Ce-Zr-O δ solid solutions in Ce 0.75 Zr 0.25 O δ . The Raman and O 2 -TPD results showed that the concentration of oxygen vacancies in Cu-Ce-Zr-O δ solid solutions was higher than that in Ce-Zr-O δ solid solutions. CO oxidation testing suggested that the catalytic activity decreases in the order of CuO/Ce 0.75 Zr 0.25 O 2 - δ > Cu 0.07 Ce 0.75 Zr 0.25 O 2-δ > Ce 0.75 Zr 0.25 O δ . Combined with the in situ diffuse-reflectance Fourier transform (in situ DRIFT) results, the reaction sensitivity followed the order of CO linear chemisorption onto dispersed CuO x species (Mars-van Krevelen mechanism) > carbonate species onto a Cu-Ce-Zr-O δ solid solution (Langmuir-Hinshelwood mechanism) > carbonate species onto a Ce-Zr-O δ solid solution (Langmuir-Hinshelwood mechanism). Kinetic studies suggested that the power-law rate expressions and apparent activation energies were r = 6.02 × 10 −7 ×P CO 0.68 P O2 0.03 (53 ± 3 kJ/mol) for CuO/Ce 0.75 Zr 0.25 O 2 - δ , r = 5.86 × 10 −7 ×P CO 0.8 P O2 0.07 (105 ± 5 kJ/mol) for Cu 0.07 Ce 0.75 Zr 0.25 O 2-δ and r = 5.7 × 10 −7 ×P CO 0.75 P O2 0.12 (115 ± 6 kJ/mol) for Ce 0.75 Zr 0.25 O δ . The Mars-van Krevelen mechanism should be the crucial reaction pathway over CuO/Ce 0.75 Zr 0.25 O 2 - δ in CO interfacial reactions, although the Langmuir-Hinshelwood mechanism cannot be ignored, and the Langmuir-Hinshelwood mechanism mainly occurred over the Cu 0.07 Ce 0.75 Zr 0.25 O 2-δ and Ce 0.75 Zr 0.25 O δ catalysts, where the contribution from the Mars-van Krevelen mechanism was negligible due to the absence of surface CuO x species. [ABSTRACT FROM AUTHOR]