Conversion of waste carbon dioxide into fuels by plasma-assisted catalysis

A prototype reactor devoted to carbon dioxide methanation was developed to produce carbon neutral methane via chemical conversion of CO2 waste flue gases using renewable energy, in a circular economy strategy [1,2]. It was characterized in its best operative conditions determining yields of methanation by the Sabatier reaction of about 84%, where a Ni-based solid catalyst has been employed. An experimental effort aimed to investigate new reaction pathways avoiding the use of the solid catalyst, has been undertaken. Interesting and promising data collected exploring mechanisms via plasma generation using microwave discharges over CO2+H2 gas mixtures are presented. They demonstrate the production of simple hydrocarbons as methane, formic acid and/or di-methyl ether, small amount of HCO+, H2CO+, H3CO+, HCO2+ ions, and considerable quantities of CO+ and O+ having a high kinetic energy content (2-6 eV). These ions formed by Coulomb explosion of CO22+ molecular dications, could be the responsible of the enhanced chemical reactivity of the generated plasmas. Further experimental efforts will be done in two directions: i) to make the use of the methanation prototype reactor suitable to be employed in the industrial chain in order to treat waste gases and convert them into valuable fuels in a circular economy logic; ii) to develop a hybrid plasma-catalytic solid system or a homogeneous gas-phase process where CO2/H2 reagent mixtures activated by a plasma generation could realize the methanation reaction by new microscopic mechanisms more favorable from both a kinetic and energetic point of view.