Direct H2O2 synthesis over Pd membranes at elevated temperatures

H2O2 was directly synthesized from the elements over supported Pd membranes in O2-saturated, aqueous H2SO4 (0.03 mol/l) between 303 and 348 K while feeding H2 through the membrane. The H2O2 yield increased with temperature despite H2O2 selectivity declining simultaneously due to faster H2O2 decomposition. Both H2O2 yield and selectivity improved with H2 feed pressure, however. Comparison of H2 consumption during H2O2 synthesis with the intrinsic membrane H2 permeability and the energetics of H2 oxidation on Pd surfaces revealed that the H2O2 productivity gain with temperature was primarily owed to the acceleration of reaction kinetics. The H2O2 selectivity enhancement with H2 feed pressure is attributed to the inhibition of direct H2O formation as a result of hindered O2 dissociation due to blocking of O atom adsorption sites on the membrane surface because of increasing occupation by H atoms. H2O2 decomposition and reduction on the Pd membrane surface accelerate much faster with temperature than H2O2 formation and need to be suppressed in order to maximize H2O2 yield and H2 utilization at higher temperatures.