In this work, a simple co-deposition strategy for the synthesis of carbon-supported Pd-Au alloy was reported. Our approach involves the co-reduction of Au and Pd ions using ethylene glycol and sodium citrate as the reducing and stabilizing reagents. Both alloy and non-alloy bimetallic Pd-Au nanoparticles are produced using a right rate-limiting strategy. For example, when ethylene glycol and sodium citrate are the limiting reagent with Au and Pd ions in excess, the synthesis environment favors preferential nucleation and growth of Au nanoparticles followed by deposition of Pd either as the shell of Au core or as separate Pd clusters. On the other hand, if the supply of metal ions (not the reducing reagents) limits the reaction, it creates a synthesis condition for Pd-Au alloy particles. The as-prepared Pd-Au alloys exhibit higher Pd-specific activities towards formic acid oxidation compared with the non-alloy counterpart or individual Pd catalyst and an easier removal of adsorbed oxygen species (e.g., O-ads or OHads) was observed from the surface of Pd-Au alloy with a higher content of Au. (C) 2010 Elsevier Ltd. All rights reserved.