High specific surface area YSZ powders from a supercritical CO2 process as catalytic supports for NOx storage–reduction reaction

Nanometric yttria-stabilized zirconia (3 mol% yttria, SC-3YSZ) was synthesized using an innovative supercritical carbon dioxide-aided sol–gel process and used as a support for NOx storage catalysts. Wash-coats composed of noble metals (Pt and Rh) dispersed on 3YSZ were deposited inside the porosity of mini-diesel particulate filters. Commercial and SC-3YSZ powders were used as supports independently and mixed. NOx storage/reduction performances were compared under cycling conditions according to the YSZ support surface area, the washcoat localization inside the DPF and the metallic dispersions. All the results emphasize that the presence of high specific surface area SC-3YSZ inside the DPF improves the NOx conversion, the N2 selectivity and the NOx storage capacity. This enhancement of the catalytic properties was linked with the increase in both the metallic dispersion and the number of storage sites on the catalyst surface.