Microfabricated multiphase reactors for the direct synthesis of hydrogen peroxide from hydrogen and oxygen

Hydrogen peroxide synthesis is demonstrated by direct combination of hydrogen and oxygen over supported palladium catalysts in a microchemical reactor. The direct combination process is chemically simple and environmentally benign for producing hydrogen peroxide, but the risk of handling the explosive gas mixture of hydrogen and oxygen over an active palladium catalyst limits implementation. By using a multichannel microchemical reactor with packed-bed catalyst, we realize the direct reaction of hydrogen and oxygen at hydrogen/oxygen ratios in the explosive regime at pressures of 2-3 MPa. As long as millimeter-sized void spaces are avoided, the microchannel structure and catalyst packaging effectively promote the heterogeneous reaction over the homogeneous free radical branching reactions that otherwise would lead to an explosion. Among the Pd/Al2O3, Pd/SiO2, and Pd/C catalysts investigated, Pd/C selectively yields hydrogen peroxide. The decomposition of peroxide is shown to be suppressed by the addition of bromide. Analysis of the microreactor data reveals significantly enhanced mass transfer relative to conventional reactors, consistent with previous multiphase microreactor studies.