Three-dimensional PdAu nanoflowers have been designed and effectively synthesized through a procedure of dropping addition of the reductant, in which morphology evolution was recorded by capturing HRTEM images at continuous synthetic stages. HRTEM, positron annihilation spectroscopy, and in situ CO-IR results showed that synthesized flowerlike PdAu nanoalloys with a size of 30-55 nm were composed of several small PdAu building units and have abundant crystal defects as well as synergetic effects. The obtained colloidal PdAu nanoflowers were then immobilized onto MgAl mixed metal oxides as a novel catalyst for partial hydrogenation of acetylene. Due to its complex morphology, rich defective sites, and synergetic effect caused by the cooperation between building units, supported PdAu nanoflower-like catalyst exhibited not only much higher activity and selectivity but also preferable stability compared with the catalyst whose active component was shape- and size-similar to the building units of PdAu nanoflowers. (C) 2014 Elsevier Inc. All rights reserved.