Plasma catalytic process for CO₂ methanation

The limited resources of oil and natural gas, together with an increasing energy demand, forces us to seek more and more efficient and cleaner energy production alternatives. Hydrogen has been recently considered as a promising energy carrier. However, there are several inherent problems to the utilization of H₂, from its transportation to its distribution. Transformation of the H₂ molecule by fixing into a carbon-containing compound, i.e. CH₄, will offer the possibility of using the conventional transportation network. Indeed, the Sabatier reaction, which is highly exothermic, involves the reaction of carbon dioxide and hydrogen gas in order to produce methane and water. This process, called methanation, represents a feasible approach contributing to the reduction of the CO₂ emissions in our atmosphere, through a closed carbon cycle involving the valorization of CO₂, i.e. from capture. However, below a temperature of 250 C, the conversion becomes practically close to 0 %, whereas at higher temperatures, i.e., (≥300 C), the co-existence of secondary reactions favours the formation of CO and H₂. This is the reason why new catalysts and process conditions are continuously being investigated in order to maximize the methane selectivity at low reaction temperatures at atmospheric pressure. Therefore, by using catalysts combined to Dielectric Barrier Discharge plasmas (DBD), the activation of the methanation reaction can be enhanced and overcome the drawbacks of existing conventional processes. Several Ni-containing catalysts were prepared using various ceria-zirconia oxides as supports, with different Ce/Zr ratios. The results obtained in the adiabatic conditions at low temperatures (ranging between 100-150 C), in the presence of catalysts activated by plasma, are promising. Indeed, the conversion of CO₂ to CH₄ is about 85 % with a selectivity close to 100 %. The same conversion in the absence of the plasma activation of the catalyst is observed at 350 C. At low temperatures (120-150 C) and without plasma, conversion is almost close to zero. This low consumption energy system helps reduce the cost of production of synthetic methane together with an extended life of the catalyst. (author)