Ultrathin Two-Dimensional Pd-Based Nanorings as Catalysts for Hydrogenation with High Activity and Stability.

Despite a few reports on the synthesis of ultrathin 2D nanosheets made of noble metals, it still remains a tremendous challenge to generate their ultrathin hollowed nanostructures, which are of particular interest in highly active catalysis due to their unique structural features. Here, the synthesis of ultrathin 2D Pd nanorings is reported with a hollow interior by selective epitaxial growth of Pd atoms on the periphery of the as-preformed Pd nanosheets in combination with oxidative etching. This approach can be extended to fabricate Pd-based bimetallic ultrathin nanorings such as Pd-Pt. The Pd nanorings exhibit substantially enhanced activity toward the hydrogenation of p-nitrophenol, which is 2.2 and 33.4 times higher than that of the Pd nanosheets and commercial Pd black, respectively. Significantly, the Pd nanorings are highly stable with only less than 11% loss in activity compared to 45.7% loss of the Pd nanosheets and 72.2% loss of the Pd black after ten cycles.