When a Low-Temperature Solid Oxide Solution Is the Best Solution: Inserting Guest Ions into the Ceria Host Lattice to Improve Silver Catalyst Activity for Soot Combustion

This study focuses on the application of low-temperature ceria-based solid solutions as silver supports for the catalytic soot combustion. The silver catalysts supported on the solid solutions exhibited activity substantially higher than that on undoped ceria. Although ceria has often been investigated as a catalyst or catalytic support, the present study shows that the proper choice of dopant can further increase the activity of the ceria supports themselves as well as the resulting silver catalysts. This investigation can be a breakthrough in the study of the impact of the selection of the support dopant for a beneficial overall effect of the use of low-temperature solid solutions as supports. All of the synthesized supports contain only one phase, i.e., the fluorite-type structure, typical for undoped ceria with the same lattice parameter and the same dopant concentration. The influence of support composition on the crystallite size (X-ray diffraction, XRD), shape of pores (N₂ physisorption), acid/base properties (Py-FTIR, Hammett indicator tests), and concentration of oxygen vacancies (Raman) was investigated. The distribution of 5 atom % of Sr²⁺, Mg²⁺, Al³⁺, or Zr⁴⁺ in the ceria lattice as well as the distribution of silver on these supports was probed with energy-dispersive X-ray (EDX) and ToF SIMS. Elemental maps show an even distribution of the dopants within the grains of the supports. The silver was mainly present as a metallic silver layer on the supports, though the systems exhibited differences in the concentrations of oxidized silver species on their surface and in the reducibility of the supports, as evidenced by H₂-temperature-programmed desorption studies.