Kinetics of hydrogen peroxide reduction by hydrogen in a microreactor

An overall rate expression for the formation of hydrogen peroxide by direct combination (DC) of H₂ and O₂ is required for a rational design of a microreactor and for the determination of the optimum operating conditions for this process. Since the formation of H₂O₂ by the DC process involves four simultaneous reactions (synthesis of H₂O₂, synthesis of water, decomposition of H₂O₂, and reduction of H₂O₂ by H₂), the overall rate expression must take into account the rate expressions of these reactions. In this work, we investigate the mechanism and the rate expression for reduction of H₂O₂ by H₂. Kinetic experiments were carried out to measure the effects of H₂O₂ concentration and H₂ partial pressure on the rate of reaction. The reaction was shown to be free of mass transfer limitations at the conditions of the kinetic experiments. A Langmuir-Hinshelwood mechanism for the reduction of H₂O₂ over Pd/SiO₂ catalyst was adopted since the simple power-law expression could not explain the obtained kinetic data. A rate expression based on this mechanism was shown to accurately correlate experimental data over a wide range of H₂O₂ concentration, H₂ partial pressure, and temperature.