Direct conversion of CH4 and CO2 to alcohols using plasma catalysis over Cu/Al(OH)3 catalysts

Abstract

The direct conversion of CH4 and CO2 into high-value alcohols is a highly desirable route for efficiently utilizing these two C1 sources while mitigating greenhouse gas emissions. However, this reaction is considered one of the most challenging research topics since it suffers from the contradiction between thermodynamics and kinetics. In this study, plasma-catalytic conversion of CH4 and CO2 for the production of high-value alcohols, with methanol being the major liquid product, was achieved using Cu-based catalysts at ∼190 °C and atmospheric pressure. Herein, the Cu-based catalysts were tuned by controlling the support material (Al(OH)3, γ-Al2O3, TiO2 and CeO2), calcination temperature (400–600 °C) and copper loading (1–20 wt%) to promote alcohol production in this reaction. The results show that the 5 wt% Cu/Al(OH)3 calcined at 540 °C exhibited the highest selectivity of alcohols (∼38%), which is the best result achieved so far in the presence of a catalyst. Catalyst characterization results reveal that the redox capacity and valence state of the copper species play a crucial role in tuning the product distribution. The Cu/Al(OH)3 catalyst with strong redox capacity and abundant Cu2+ species significantly improves the selectivity of alcohols. Interestingly, the predominant alcohol gradually shifts from methanol to ethanol with increasing copper loading, and the optimal copper loading for producing methanol and ethanol was found to be 5 wt% and 15 wt%, respectively. This work provides valuable insights for designing efficient catalysts to tune the production of alcohols through the single-step plasma-catalytic conversion of CH4 and CO2.