Epitaxial\nGrowth of Unconventional 2H Noble Metals\nand Crystal Phase-Dependent Selectivity of Pt in Hydrogenation Catalysis

Crystal\nstructure plays an important role in tuning the\nphysicochemical\nproperties of noble metal nanomaterials. However, it remains challenging\nto synthesize unconventional-phase noble metal nanocrystals, particularly\nwith well-defined facets. Here, we develop a series of noble metal\nshells, including Pt, Au, and Ag, with the novel hexagonal close-packed\n(2H) phase via a phase-based epitaxial growth on predesigned 2H Pd<sub><i>x</i></sub>B nanoseeds, resulting in 2H Pd<sub><i>x</i></sub>B@Pt, 2H/face-centered cubic (<i>fcc</i>, or 3C) heterophase Pd<sub><i>x</i></sub>B@Au, and Pd<sub><i>x</i></sub>B@Ag core–shell nanostructures. Impressively,\nthe unconventional 2H Pt shells show high phase purity with well-defined\n2H facets, which provide an excellent model to investigate the crystal\nstructure-dependent catalytic properties of Pt nanocatalysts. Significantly,\n 2H Pd<sub><i>x</i></sub>B@Pt exhibits a remarkably high\ncatalytic selectivity (93%) toward 4-aminostyrene in the hydrogenation\nof 4-nitrophenylacetylene, outperforming conventional 3C Pd@Pt and\ncommercial Pt/C. This work provides a general strategy to design and\nsynthesize unconventional-phase metal nanocatalysts and study the\ncrystal structure-dependent catalytic behaviors.