One-step electrodeposition of Pd–CeO2 on high pore density foams for environmental catalytic processes

Abstract

Environmental catalytic processes are probably the best example for the application of structured catalysts based on activated open-cell metallic foams, and Pd/CeO₂ based materials are one of the most active catalysts for different applications like three-way catalysts, methane combustion and water gas shift. Here, we report the one-step deposition of Pd and CeO₂ on FeCrAlloy foams with very high pore densities (cell sizes equal to 580 and 1200 μm) by the electro-base generation method followed by calcination. The type of Pd and CeO₂ species, the quality of the coating and the catalytic activity in the mass transfer limited CO oxidation as a model reaction were investigated. For comparison purposes, a CeO₂ coating was also prepared. Reproducible and evenly distributed defective nano-CeO₂ coatings containing Pd_xCe_1−xO_2−δ solid solution and Pd⁰ particles were electrodeposited in 500 s regardless of the foam pore size. The structure, morphology, and adhesion of the catalytic layer, as well as the Pd distribution, were almost constant after calcination at 550 °C, only some PdO segregated. The resulting structured catalysts showed high activity and stability after 48 h time-on-stream and different thermal cycles in CO oxidation even at high GHSV values (e.g. 4 × 10⁶ h⁻¹ referred to as the total foam disk volume). High volumetric mass transfer coefficients, widely outperforming those of conventional honeycomb monoliths, were obtained, especially for the small pore (580 μm) foam. The in situ formation of Pd⁰ nanoparticles and the homogeneous distribution and stability of the coating may contribute to the high catalytic performance, although these catalyst features depended on the position in the catalytic bed.