Epitaxial Growth of Unconventional 2H Noble Metals and Crystal Phase-Dependent Selectivity of Pt in Hydrogenation Catalysis

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