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.

Modifying the Substrate-Dependent Pd/Fe2O3 Catalyst–Support Synergism with ZnO Atomic Layer Deposition

“…It is remarkable that with ZnO-Pd/Fe 2 O 3 , whose low-coordinate sites (along with some terraces and planes, see Figures B and C) at Pd, which are traditionally associated with higher hydrogenation reactivity, , are predominantly overcoated, the catalytic performance appears to be superior. The observation of remaining styrene at 18 h for ZnO-Pd/Fe 2 O 3 further corroborates the overcoating of the low-coordinate sites on the catalyst, which are expected to be more reactive toward alkene hydrogenation …”

“…However, increasing the substrate loading to 2 mmol again yielded complete conversion, in this case with 14% and 50% selectivity toward 4-vinylanisole for Pd/Fe 2 O 3 and ZnO-Pd/Fe 2 O 3 , respectively (Table ). This is commensurate with enhanced selectivity toward vinyl product ( vide supra ) …”