Plasma-catalytic CH4 reforming with CO2 over biochar in a dielectric barrier discharge reactor

Plasma-catalytic CH4 reforming with CO2 is a highly promising technology for converting two greenhouse gases into high-value chemical products under mild conditions. Developing efficient catalysts with low-cost is essential for scaling up this process. Herein, coconut shell biochar and nitrogen-doped biochar (prepared via co-calcination with melamine) are employed as the catalyst for this reaction. The results show that packing biochar promotes the charge generation and transfer capability and therefore enhances the conversion of reactant molecules CH4 and CO2. The maximum conversion of 18.7% for CH4 and 13.7% for CO2 together with the maximum selectivity of 24.3% for acetic acid are obtained when using the N1-biochar sample with the lowest melamine-to-biochar mass ratio (1/5). Increasing the melamine-to-biochar mass ratio gradually increases the selectivity of syngas (H2 and CO) and main gaseous hydrocarbon (C2H6) but decreases that of total liquid components. Catalyst characterizations indicate that both original and nitrogen-doped biochar features hierarchical porous structure, and the nitrogen doping enhances the basic characteristics. These properties collectively facilitate the adsorption, activation and mass transfer of reactant molecules and intermediates. Notably, the N1-biochar sample exhibits the highest specific surface area to provide the most active site for plasma reaction. In addition, its high nucleophilicity and electron transfer capability resulted from the highest content of pyridinic-N facilitate the cleavage and reformation of C-H and C-O bonds in CH4 and CO2 molecules. These two factors account for its superior reaction performance with respect to reactant conversion and energy efficiencies.