Mesocrystalline PdAg nanoalloys have been assembled from PdAg nanoparticle units via an oriented attachment pathway and subsequently immobilized on hydrotalcite a support that offers the advantages of tunable basicity and acidity, as well as high adsorption capacity. Pd and Ag atoms were homogeneously distributed throughout the sea urchin-like mesocrystals. The supported PdAg mesociystals showed a significant enhancement in catalytic performance in the partial hydrogenation of acetylene when compared with the conventional PdAg nanoparticles, with a fourfold increase in turnover frequency. The high activity can be ascribed to the presence of grain boundaries in the mesocrystalline PdAg catalyst, which facilitate H-2 activation/dissociation. In addition, the increase in the selectivity toward ethene over supported PdAg mesocrystals catalyst may be ascribed to the potential ordered facets, which originated from the oriented attachment of building units. (C) 2015 Elsevier Inc. All rights reserved.