Impact of Aliovalent/Isovalent Ions (Gd, Zr, Pr, and Tb) on the Catalytic Stability of Mesoporous Ceria in the HCl Oxidation Reaction

CeO2 is a promising material in the catalytic recovery of Cl2 from HCl by oxidation with O2 due to its beneficial redox properties (Ce3+/Ce4+) and accompanied oxygen storage capacity (OSC). Two options to tailor the OSC are the usage of dopants and nanostructuring. In this work, we report the synthesis of mesoporous doped Ce0.9M0.1O2 (M = Zr, Gd, Pr, and Tb) powders with identical mesopore size, shape, and specific surface area (≈90 m2 g–1) to investigate the impact of aliovalent (Gd), isovalent (Zr), and aliovalent/isovalent (Pr and Tb) dopants on the OSC as well as on the catalytic activity/stability. The cubic arrangement of spherical 12 nm mesopores surrounded by a crystalline framework is obtained by using a diblock copolymer as structure directing agent in the sol-gel-based preparation approach, indicated by small angle X-ray scattering (SAXS) and scanning electron microscopy (SEM). Pr-doped CeO2 revealed the highest oxygen storage capacity but the lowest catalytic activity/stability in the HCl oxidation together with the Tb- and Gd-doped samples. By contrast, the Zr-doped mesoporous CeO2 powders showed the highest catalytic performance and stability in the CO and HCl oxidation of all samples but a lower OSC. These findings suggest that the OSC should therefore be treated with caution when relating to the catalytic performance in oxidation reactions. The differences in the stability are in agreement with recent studies of the HCl oxidation on model cerium oxide films with defined stoichiometry: the low stability of the aliovalent doped CeO2 materials in the HCl oxidation reaction can be attributed to a large number of oxygen vacancies.