Converting CO2 into carbon nanotubes via sequential CO2 methanation and methane pyrolysis

This study presents a sequential thermochemical catalytic process for converting CO 2 into carbon nanotubes (CNTs), achieving nearly 99% overall CO 2 conversion and solid carbon yields of up to 49% in a single pass. The overall transformation is divided into two thermodynamically favorable steps: (1) low-temperature CO 2 methanation to CH 4 over a sol-gel-prepared Ni 87 Ce 6.5 Zr 6.5 -SG catalyst, which achieved >95% CO 2 conversion at 250 °C in a single pass, and (2) subsequent methane pyrolysis to CNTs and H 2 over a Ni@Al 2 O 3 -IE core-shell catalyst, which showed improved stability and carbon yield compared with conventional catalysts. Catalyst characterization revealed the synergistic roles of Ce and Zr in the methanation catalyst and the importance of the core-shell architecture in suppressing deactivation during methane pyrolysis. This CH 4 -bridged strategy avoids intrinsic carbon loss through CO 2 regeneration in CO-mediated routes, enabling high single-pass solid‑carbon yield in a gas-phase sequential process. The resulting product consists predominantly of structurally defined CNTs, which were further validated as functional additives in lithium-ion-battery-related systems. Overall, this work establishes an effective route for converting captured CO 2 into value-added CNT materials.