Pd-Au-Cu Ternary Alloy Nanoparticles: Highly Tunable and Economical Nitrite Reduction Catalysts

Solid-solution ternary Pd-Au-Cu nanoparticles (NPs) with broadly tunable compositions (PdxAuyCu100-(x+y); where x = 30-70 and y = 15-35) were prepared by a microwave-assisted polyol reduction method. Commercially available Pd2+, Au3+, and Cu2+ salts were directly co-reduced by ethylene glycol and NaBH4 in a one-pot process to generate near-monodisperse ternary alloy NPs with mean sizes between 2 and 4 nm. Using the same synthetic approach, the corresponding binary alloy PdCu NPs with similar monodispersities and particle sizes were also prepared. The comparative catalytic performances of PdCu NPs and PdAuCu NPs were assessed for the aqueous-phase reduction of nitrate (NO3-) anions and were compared to previously published results for analogous binary PdAu NPs. The experimental catalytic results and theoretical studies reveal that the resulting catalytic activity of Pd surface sites are highly sensitive to the relative amounts of Au and Cu also present. We ultimately prove that the hitherto unstudied ternary PdAuCu NPs are highly active and selective as NO2- reduction catalysts and effectively utilize Cu as an economically viable dilutant metal, without sacrificing the activity or stability of industrially important and well-studied PdAu alloy catalysts. From an economic perspective, the ternary alloy nanocatalysts show superior price-to-activity ratios: the measured turnover rates of Pd63Au22Cu16 NPs (3.353 min(-1) $(-1)) outperform not only monometallic Pd NPs (0.797 min(-1) $(-1)) but also binary PdAu NPs and PdCu NPs of all accessible compositions.