A Plasma-Catalytic Approach to Upscaling Industrial Flue Gases into Sustainable Fuels

Industrial process heating with fossil fuels significantly contributes to greenhouse gas emissions. While electrification reduces the carbon footprint, it overlooks valuable components like unconverted methane (CH₄) and CO₂ in flue gases. We propose a synergistic plasma-catalysis approach to transform these gases into valuable fuels like methanol (MeOH). Optimizing plasma-catalysis requires careful consideration of its design space, as not all catalysts synergize effectively with plasmas under all conditions. In this work, we explore plasma excitations, catalyst activation, and species transport to study their influence on reaction pathways. While vibrational excitations result in selective reactant interactions in the gas-phase, adding a catalyst can either promote desired reactions or lead to undesired reaction intermediates, such as converting bound CH₃ to CH₂, CH, or C. For instance, we show a polycrystalline Cu catalyst with a dielectric barrier discharge (DBD) shows a 5-fold increase in MeOH selectivity compared to plasma alone, while polycrystalline Ni exhibits an antagonistic effect, decreasing selectivity by 5-fold. In-situ characterization using Fourier-Transform Infrared Spectroscopy (FTIR) in Diffuse Reflectance (DRIFTS) and transmission mode provides insight into the reaction mechanisms. We observe that Cu promotes the formation of key intermediates like CH₃* and O*, which recombine to form CH₃O*, a crucial step in MeOH synthesis. However, adding trace amounts of H₂O makes CH₃O* concentration rapidly decline, suggesting that OH* prevents CO₂ dissociation on a catalyst. Another critical factor is the interplay between species excitation and transport, quantified by the Damköhler number (Da). Decreasing Da resulted in a 13-fold improvement in MeOH selectivity, suggesting that optimizing the rate of product removal from the catalyst surface before further reactions is essential for maximizing the desired product yield.