Ultrathin Atomic Layer Deposited Al₂O₃ Overcoat Stabilizes Al₂O₃-Pt/Ni-Foam Hydrogenation Catalysts

Abstract

Galvanic exchange seeds the growth of Pt nanostructures on the Ni foam monolith. Subsequent atomic layer deposition of ultrathin Al₂O₃ followed by annealing under air affords supported Pt catalysts with ultralow loading (0.020 ppm). In addition to the expected enhancement of the stability of the Pt particles on the surface, the ∼2 nm Al₂O₃ overcoat appears to also play a crucial role in the overall structural integrity of the NiO_x nanoplates that grow on the Ni foam surface as a result of the preparative route. The resulting material is physically robust toward repeated handling and showcases retention of catalytic activity over 10 standard catalyst recycling trials, standing in marked contrast to the uncoated samples. Catalyst activity was tested via the hydrogenation of various functionalized styrenes at low temperatures and low hydrogen pressure in ethanol as a solvent, with a TOF as high as 9.5 × 10⁶ h^-1 for unfunctionalized styrene. Notably, the catalysts show excellent tolerance toward F, Cl, and Br substituents and no hydrogenation of the aromatic ring.