High H ₂O ₂ yield in the direct oxidation of H ₂ with O ₂ on mono dispersed Pd-Au nano colloid under pressurized conditions

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 H ₂O ₂ by direct oxidation of H ₂ with O ₂. The yield of H ₂O ₂ increased with increasing reaction pressure and at 1 MPa, H ₂O ₂ yield achieved a value of 30%. Under these conditions, H ₂ conversion is as high as 80%. H ₂O ₂ yield was further improved by increasing H ₂ partial pressure, and the optimum H ₂ partial pressure was 10% at 1 MPa because of safety (out of the explosion limit concentration in reactor) and the formation rate of H ₂O ₂. Because H ₂O ₂ decomposition is prevented, H ₂O ₂ yield also increased with decreasing reaction temperature and at 268 K, H ₂O ₂ yield and production rate are achieved as high as 46% and 25 mmol h ^-1, respectively, in aqueous solution. H ₂O ₂ concentration reaches a value of 5.8% in aqueous solution after 20 h at 268 K.