Applications of bimetallic PdCu catalysts

Abstract

Bimetallic PdCu nanoparticles can be applied as catalysts in a wide range of chemical and electrochemical reactions. This review article overviews the preparation and synthetic applications of these bimetallic nanoparticles (BNPs) developed mainly over the last 20 years. These BNPs show better catalytic activity and selectivity than the monometallic counterparts due to their electronic and structural interactions. Simple general preparation methods include reduction of the corresponding salt precursors by different agents, solvothermal processes and galvanic replacement. In the case of supported catalysts, mainly wet impregnation and in situ reduction processes are used. In addition, these nanomaterials are prepared with different Pd/Cu compositions and with different morphologies. In the case of supported materials, many solid supports especially alumina, silica, titania, ceria, magnetite, zeolites, active carbon, graphene, carbon nanotubes, resins and polymers are employed allowing the recovery and reuse of the supported catalyst. In addition, the presence of copper reduces the economic cost of using palladium in industrial processes. Among several synthetic applications, C–C bond forming reactions such as Suzuki–Miyaura, Sonogashira–Hagihara, Heck–Mizoroki, Guerbet and A³-coupling are efficiently performed with PdCu BNPs. Reduction reactions under PdCu catalysis such as nitrate reduction for water purification, hydrodechlorination of organic pollutants, hydrogenation of CO₂ and CO to methanol, semihydrogenation of alkynes to alkenes, and hydrogenation of CC double bonds, furfural to furfuryl alcohol, polyols, levulinic and succinic acids to lactones, styrene oxide to 2-phenylethanol and nitroaromatics to aromatic amines can be successfully performed. In the case of electrocatalytic reductions, oxygen reduction to water, CO₂ reductions to CO, to alcohols, to hydrocarbons and to formate and hydrogen generation from water splitting can be highlighted. In the field of oxidation reactions using oxygen, CO can be transformed into CO₂, alcohols into aldehydes, cyclopentene to cyclopentanone, ethylene and acetic acid to vinyl acetate, and aromatic compounds can be hydroxylated to phenols. Electrooxidation reactions are useful processes especially for direct alcohol and formic acid fuel cells. The oxygen-assisted water gas shift reaction can be efficiently performed under PdCu catalysis. In the field of chemical sensors, PdCu BNPs can detect hydrogen in low concentrations, liquefied petroleum gas, formaldehyde, glucose, thiocyanate and phenols. Other applications such as catalysts in hydrosilylation of acetylenes to vinylsilanes and the use of PdCu NPs as antimicrobial agents are also described.