Progress and challenges of direct conversion of methane and carbon dioxide into C2+ oxygenates under mild conditions

Converting greenhouse gases into C2+ oxygenates with high-added value is an effective method for reducing carbon emissions. Due to the molecular structure and stability of methane and carbon dioxide, it is difficult to activate the C–H bond and C = O bond which limits the co-conversion of methane and carbon dioxide into C2+ oxygenates, such as acetic acid and ethanol. The reaction still faces thermodynamic limitations, posing a major challenge in C1 chemical utilization. This paper reviews the literature on the progress of direct conversion of C2+ oxygenates from CH4 and CO2 through thermo- and non-thermal plasma catalysis. It discusses the performance and the corresponding reaction mechanisms over different metal-based catalysts. For thermal catalysis, Cu, Zn, and Pd-based catalysts are the main active metals to generate more active intermediate species and multifunctional catalysts can be prepared to avoid competitive adsorption of two gases. For non-thermal plasma catalysis technology, has the advantage of co-conversion of CH4 and CO2 under mild conditions, but the target product selectivity is extremely low which hinders the practical application. Furthermore, the review discusses the impact of the skeleton environment and the promotion of different acid centers on the active center, the influence of the catalyst support, and the optimization of plasma reaction parameters. Facially, the existing challenges and opportunities for the catalyst design and technical route of methane and carbon dioxide conversion to C2+ oxygenates under mild conditions are summarized.