An improved method for the synthesis of hydrogen peroxide from carbon monoxide, water and oxygen catalyzed by palladium complexes in presence of a quinone co-catalyst is described. Even if the reaction balance is formally the same, the mechanism of formation of hydrogen peroxide in the new process is totally different to that proposed for the reaction carried out in absence of quinones. Using 1,10-phenanthroline as a palladium ligand in a water/organic biphasic reaction medium, a dramatic enhancement of the catalyst stability was obtained operating in presence of 1,4-naphthoquinone, which prevented the formation of inactive binuclear palladium species. Additional improvements, with respect to the reaction carried out in absence of quinone, are the use of cheaper palladium ligands and the safer process conditions, since air can be used as a reagent instead of pure oxygen.