Influence of Pr-doping on the sulfur tolerance of Pd-ceria catalysts for complete methane oxidation

In this work, the influence of praseodymium doping on the sulfur tolerance of Pd/CeO2 catalysts for total methane oxidation was systematically investigated. Pd catalysts supported on nanostructured ceria, praseodymia, and mixed oxides (10 or 50 at% Pr) were exposed to SO2 (20 ppm) under dry or wet reaction conditions, followed by high-temperature regeneration cycles up to 900 C. The Pr loading strongly affected the sulfur-catalyst interactions. Undoped Pd/CeO2 underwent fast deactivation due to preferential sulfation of Pd particles, although sulfates were almost completely removed during thermal treatment. In contrast, Pr-doped catalysts exhibited enhanced sulfur resistance, as sulfur preferentially accumulated on the support rather than on Pd. Mild Pr doping (10 at%) provided the best compromise, ensuring limited sulfate accumulation and effective regeneration under the investigated conditions, while preserving the ability of Pr to stabilize PdO species at high temperature, even in the presence of water. Higher Pr loadings promoted extensive sulfate formation, which resulted in Pr segregation from the ceria lattice, weakening of Pd-support interactions, and Pd sintering on pure praseodymia; moreover, sulfates were not completely removed upon regeneration but reorganized into stable bulk aggregates, inducing structural distortion. These results demonstrate that controlled Pr doping effectively tunes sulfur affinity and metal-support interactions, providing useful guidelines for the design of sulfur-tolerant Pd-based catalysts for methane oxidation.