Boosting the Conversion of CO2 with Biochar to Clean CO in an Atmospheric Plasmatron: A Synergy of Plasma Chemistry and Thermochemistry

In this work, the conversion of CO 2 into O 2 -free CO has been investigated in an atmospheric plasmatron via the reaction with biochar. The effects of the biochar source, pyrolysis temperature for biochar preparation, and gas–solid reaction patterns (fixed bed and fluidized bed) on the reaction performance were evaluated under different feed flow rates. The underlying mechanisms were explored using in situ optical emission spectroscopy focusing on understanding the role of plasma chemistry and thermochemistry in CO 2 conversion. The results revealed that the presence of both biochar and plasma significantly facilitate CO 2 conversion. In comparison to thermal CO 2 splitting, the plasmatron CO 2 + C process dramatically enhanced the CO 2 conversion from 0 to 27.1%. Walnut shell biochar prepared at relatively high pyrolysis temperatures favored CO 2 conversion due to a high carbon content. A fixed bed surprisingly provided remarkably better performance than a fluidized bed for the CO 2 + C reaction, benefiting from a prompt consumption of the generated O 2 by biochar. The high electron density achieved in the plasmatron (10 15 cm –3 ) allows for a high processing capacity, and the moderate electron temperature (1.1–1.5 eV) with enhanced vibrational energy (6300–8200 K) obtained stimulates the most efficient CO 2 activation routes through vibrational excitation. The relatively high rotational (gas) temperatures in the core plasma area (2100–2400 K) and in the gas–solid reaction region (<1573 K) detrimentally drive the reverse reactions of CO 2 splitting and advantageously boost the biochar-involved reactions, respectively, by thermochemistry. The synergy of plasma-chemistry-dominated CO 2 dissociation and the thermochemistry-dominated CO 2 + C and O 2 + C reactions accounts for the high CO 2 conversion obtained in the plasmatron CO 2 + C process. The immediate study provides a novel route for efficient CO 2 conversion by coupling plasma chemistry and thermochemistry.