A facile synthesis of MPd (M = Co, Cu) nanoparticles and their catalysis for formic acid oxidation

Monodisperse CoPd nanoparticles (NPs) were synthesized and studied for catalytic formic acid (HCOOH) oxidation (FAO). The NPs were prepared by coreduction of Co(acac) ₂ (acac = acetylacetonate) and PdBr ₂ at 260 °C in oleylamine and trioctylphosphine, and their sizes (5-12 nm) and compositions (Co ₁₀Pd ₉₀ to Co ₆₀Pd ₄₀) were controlled by heating ramp rate, metal salt concentration, or metal molar ratios. The 8 nm CoPd NPs were activated for HCOOH oxidation by a simple ethanol wash. In 0.1 M HClO ₄ and 2 M HCOOH solution, their catalytic activities followed the trend of Co ₅₀Pd ₅₀ > Co ₆₀Pd ₄₀ > Co ₁₀Pd ₉₀ > Pd. The Co ₅₀Pd ₅₀ NPs had an oxidation peak at 0.4 V with a peak current density of 774 A/g _Pd. As a comparison, commercial Pd catalysts showed an oxidation peak at 0.75 V with peak current density of only 254 A/g _Pd. The synthesis procedure could also be extended to prepare CuPd NPs when Co(acac) ₂ was replaced by Cu(ac) ₂ (ac = acetate) in an otherwise identical condition. The CuPd NPs were less active catalysts than CoPd or even Pd for FAO in HClO ₄ solution. The synthesis provides a general approach to Pd-based bimetallic NPs and will enable further investigation of Pd-based alloy NPs for electro-oxidation and other catalytic reactions.