High H2O2 yield in the direct oxidation of H2 with O2 on mono dispersed Pd–Au nano colloid under pressurized conditions

Abstract

Pd–Au (75 : 25) nano colloid was prepared by using various reductants and it was found that the mono dispersed Pd–Au nano colloid with 4.7 nm in diameter was prepared by reduction with oxalic acid and this Pd–Au nano colloid is highly active for the synthesis of H₂O₂ by direct oxidation of H₂ with O₂. The yield of H₂O₂ increased with increasing reaction pressure and at 1 MPa, H₂O₂ yield achieved a value of 30%. Under these conditions, H₂ conversion is as high as 80%. H₂O₂ yield was further improved by increasing H₂ partial pressure, and the optimum H₂ partial pressure was 10% at 1 MPa because of safety (out of the explosion limit concentration in reactor) and the formation rate of H₂O₂. Because H₂O₂ decomposition is prevented, H₂O₂ yield also increased with decreasing reaction temperature and at 268 K, H₂O₂ yield and production rate are achieved as high as 46% and 25 mmol h⁻¹, respectively, in aqueous solution. H₂O₂ concentration reaches a value of 5.8% in aqueous solution after 20 h at 268 K.