HYDROGEN-PEROXIDE SYNTHESIS OVER METALLIC CATALYSTS

The energetics of the elementary reactions involved in the synthesis of hydrogen peroxide over noble metal catalysts have been investigated using the bond order conservation-Morse potential approach (BOC-MP). Enthalpy changes as well as activation energies for forward and reverse reactions were calculated for the different elementary steps which may occur by reaction of H-2 and O2 on the noble metal series Pd, Pt, Ag and Au. According to the BOC-MP model, under low surface coverage conditions the reaction proceeds along a water channel in which hydroxyl radicals are the main intermediates. No hydrogen peroxide is produced under these conditions. The model indicates that the formation of hydroxyl radicals should be blocked and adsorbed hydroxyls should be destabilized for the reaction to proceed along the hydrogen peroxide channel in which OOH radicals play a fundamental role. In the metal series investigated the production of H2O2 is more favorable on gold and silver than on the other metals. Experimental conditions such as hydrogen and oxygen loading of the catalyst are simulated and the role of promoters is discussed.