Direct synthesis of hydrogen peroxide from hydrogen and oxygen over activated-carbonsupported Pd-Ag alloy catalysts

A series of bimetallic PdAg catalysts on an activated carbon support were prepared and assessed for the direct synthesis of hydrogen peroxide from hydrogen and oxygen. The ensemble effect and electronic effect between Pd and Ag were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and temperature-programmed desorption of H-2/O-2 (H-2-/O-2-TPD), etc. Our results showed that the Ag additive increased the monomeric Pd sites which were the primary active sites for H2O2 formation. In addition, the content of Pd2+ was increased via the electronic interaction between Pd and Ag, which prevented the decomposition and hydrogenation of H2O2 to some extent. Therefore, the selectivity of this reaction was increased using bimetallic PdAg catalysts, as compared with the monometallic Pd catalyst. The optimal PdAg-40 catalyst achieved a H2O2 productivity of 7022 mol kgPd(-1) h(-1) and a high selectivity of 70.9%, which were superior to those of the Pd/C catalyst.