Carbon dioxide concentration in the atmosphere is continuously and significantly increasing as a consequence of the combustion of fossil fuels. Due to its abundance, lack of toxicity and relatively low price, CO2 has become an attractive raw material for the synthesis of chemicals and fuels. This work reports initial proof-of-concept studies on the heterogeneous catalytic conversion of CO2 under hydrothermal conditions in the absence of the addition of gas phase H2. Evidence for the feasibility of the transformation of CO2 into higher hydrocarbons and oxygenates over iron-containing minerals comes from studies on the origin of life on Earth, where the hydrothermal conditions present in the primitive oceanic vents were mimicked.
This research focused on the investigation of the influence of different reaction parameters involved in the hydrothermal conversion of CO2 using Fe powder as the catalyst. The conditions explored were the CO2:H2O mole ratio, the temperature, the solvent and the presence or absence of air in the system. The optimal parameters using Fe powder after 4 h of reaction time were a temperature of 300 ºC, a CO2:H2O mole ratio of 0.26 and 0.56 g of catalyst. Under these optimal conditions, Fe-based materials, zeolites, carbons and alumina were also screened. Among them, Fe3O4 exhibited the highest CO2 conversion with a value of 13.8 %. Hence, a reaction mechanism was suggested using this catalyst. In all cases, the major liquid product identified was methanol. Other liquid species detected included ethanol, acetone, phenol, heptanal, 2-octanone and C5-C8 cyclic ketones among others. Gas phase products encompassed C1 and C2 hydrocarbons and oxygenates.
The feasibility of producing valuable species from CO2 under hydrothermal conditions has been successfully demonstrated. Specifically, the performance of Fe-based materials in this reaction may reinforce the hypothesis of the hydrothermal
oceanic vents as a potential system for life to emerge.
