Hierarchical porous catalyst support: Shaping, mechanical strength and catalytic performances

Palladium layered catalysts were reported to have the best performances for selective hydrogenations. A new core/shell bimaterial consisting of low specific surface area α alumina beads coated by a high specific surface area γ alumina layer is proposed and is suitable for a controlled thickness deposition of metallic palladium particles. A coating process was developed for a pan granulator where γ alumina dry powder was added under a boehmite sol pulverisation onto α-Al₂O₃ beads. The material exhibits a uniform and non defective coating (20 μm), a strong resistance against general attrition and local mechanical properties of coating and interface measured by nanoindentation in the order of magnitude of conventional γ-Al₂O₃ beads. Metallic nano-particles deposited by incipient wetness impregnation of palladium nitrate solution are more preferentially located into the γ alumina shell. Activity and selectivity of Pd core/shell bimaterial catalyst are hugely improved compared to traditional catalyst (Pd deposited onto α-Al2O3 beads) in selective hydrogenation of styrene/isoprene model mixture. This metallic core/shell catalysts are thus promising candidates for reactions sensitive to intra-particular diffusion limitations.