Photoassisted methanation using Cu2O nanoparticles supported on graphene as a photocatalyst

Abstract

Photoassisted CO₂ methanation can be carried out efficiently at 250 °C using Cu₂O nanoparticles supported on few layer graphene (Cu₂O/G) as a photocatalyst. The Cu₂O/G photocatalyst has been prepared by chemical reduction of a Cu salt (Cu(NO₃)₂) with ethylene glycol in the presence of defective graphene obtained from the pyrolysis of alginic acid at 900 °C under Ar flow. Using this photocatalyst a maximum specific CH₄ formation rate of 14.93 mmol g_Cu2O⁻¹ h⁻¹ and an apparent quantum yield of 7.84% were achieved, which are among the highest reported values for the gas-phase methanation reaction at temperatures below the Sabatier reaction temperature (>350 °C). It was found that the most probable reaction mechanism involves photoinduced electron transfer from the Cu₂O/G photocatalyst to CO₂, while evidence indicates that light-induced local temperature increase and H₂ activation are negligible. The role of the temperature in the process has been studied, the available data suggesting that heating is needed to desorb the H₂O formed as the product during the methanation. The most probable reaction mechanism seems to follow a dissociative pathway involving detachment of oxygen atoms from CO₂.