Towards coupling direct activation of methane with in situ generation of H2O2

Abstract

Due to the explosive nature of H₂, O₂ and CH₄ mixtures, the concept of coupling in situ synthesis of H₂O₂ with low-temperature single-step methane conversion to methanol has not received sufficient attention. This study aimed to investigate this process using a microchannel reactor, which offers the opportunity to explore the process under a wide range of concentrations. Direct methane activation with in situ generation of H₂O₂ was successfully demonstrated in a microcapillary containing Au–Pd nanoparticles embedded on its silica-coated walls. The effect of H₂, O₂ and CH₄ partial pressures, H₂/O₂ molar ratio, gas-to-liquid (G/L) ratio and liquid phase weight-hourly-space-velocity (WHSV) on the productivity and product distribution was investigated. CH₄ partial pressure had the most significant effect on the productivity, while H₂ and O₂ partial pressures influenced the productivity less. The methane activation rate was found to be correlated with the H₂O₂ formation rate. With only O₂ or pre-formed stabilized H₂O₂ methane activation was not found, in situ H₂O₂ synthesis was therefore essential. G/L affected neither the product distribution nor the productivity, however, lowering WHSV altered the product distribution favoring methanol formation.