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 low-cost catalysts 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 charge generation and transfer capability and therefore enhances the conversion of the 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 selectivities of syngas (H₂ and CO) and the main gaseous hydrocarbon (C₂H₆) but decreases that of total liquid components. Catalyst characterizations indicate that both original and nitrogen-doped biochar feature a hierarchical porous structure, and 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 and the largest number of basic sites to provide the strongest capability for adsorption, activation and reaction of reactant molecules. In addition, its high nucleophilicity and electron transfer capability, resulting 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 factors account for its superior reaction performance with respect to reactant conversion and energy efficiency. The presence of defects in the nitrogen-doped biochar samples promotes the catalytic activity of pyridinic-N by modulating the local electron density and ultimately exhibits long-time stable reaction performance.