Thermodynamic insights on the direct transformation of methane and CO2 into value-added coupling products

• Effect of temperature, pressure, co-reactants, and parallel reactions is theoretically assessed for direct CH 4 and CO 2 coupling. • Equilibrium constants, enthalpies, and Gibbs free energies for assessed reactions are provided. • Optimal C2-C3 oxygenates formation is achieved in absence of O 2 and H 2 O. • The highest equilibrium yields are reached for acetone. • Parallel reactions strongly affect methane conversion and selectively suppress dimethyl ether formation. The indiscriminate anthropogenic emissions of methane (CH 4 ) and carbon dioxide (CO 2 ), the two major greenhouse gases directly involved in global warming, remain a critical environmental challenge. The processes for their combined transformation into value-added chemicals, without relying on energy-intensive and unsustainable syngas generation, are still inefficient for industrial implementation. Achieving significant progress requires a thorough understanding of the thermodynamic aspects governing the reactions involved. To this end, a thermodynamic study on the direct coupling of CH 4 and CO 2 into oxygenated hydrocarbons (O-HCs), for which atom economy is maximized and/or exhibiting potential applications as sustainable energy carriers, has been performed. The analysis, carried out with Aspen Plus using Gibbs free energy minimization, evaluates the influence of reaction temperature (300-1000 K), pressure (1-150 atm), and presence of co-reactants (O 2 , H 2 O, CO) on product distribution and methane conversion. Parallel reactions were also considered, revealing that the complete combustion reaction of methane does not hinder O-HC formation under the studied conditions, whereas reactions leading to CO production do. Equilibrium constants, enthalpies, and Gibbs free energies have been additionally calculated from models using Barin equations according to Aspen Physical Property System parameters. Finally, selected modelling results are contrasted with recent experimental findings for CH 4 and CO 2 coupling reactions, highlighting their potential relevance.