Decoupling plasma-compatible CO-to-graphitic-carbon conversion from H2-rich feeding over Fe–Mn/Al2O3

Abstract

CO-to-graphitic-carbon conversion is the decisive downstream step in CO 2 –CO–C chemical looping, linking CO 2 fixation to sustainable nanocarbon production. However, this gas-to-solid transformation typically relies on H 2 -rich feeds containing 20–50% H 2 to maintain catalytic activity and stability and promote graphitic carbon growth. Whether such H 2 -rich conditions are fundamentally required remains unclear. Here, we demonstrate stable, graphitic, and plasma-compatible CO-to-C conversion without H 2 -rich feeding using a fluidized-bed Fe–Mn/Al 2 O 3 catalyst. At 2% H 2 , the system sustains Boudouard-dominated CO conversion (∼55%), stable operation (>100 min), and graphitic carbon nanofiber growth ( L c ≈ 8–9 nm), with H 2 acting mainly as a kinetic regulator of carbon growth. The kinetic operability boundary between 1% and 2% H 2 coincides with a transition from compact to filamentous carbon growth, while Fe 3 C and (Fe,Mn)O are identified as coexisting post-reaction phases. The same H 2 -lean regime is compatible with plasma assistance, producing an approximately 66% relative increase in CO conversion and a decrease in the apparent activation energy from 75 to 37 kJ mol −1 , while preserving catalyst stability throughout the 180-min test and maintaining graphitic carbon quality. These findings establish a proof-of-possibility benchmark, showing that catalytic activity, operational stability, carbon crystallinity, and compatibility with plasma electrification can be achieved without H 2 -rich feeding.