Carbon nanofibers synthesized from carbon dioxide by catalytic hydrogenation on Ni-Na/Al₂O₃ catalysts

In this work, CO₂ gas was used as a source of carbon to produce carbon nanofibers (CNFs). Sodium was used as a promoter to induce the formation of CNFs on a Ni/Al₂O₃ catalyst during a CO₂ hydrogenation reaction. The novel Ni-Na/Al₂O₃ catalyst not only effectively produced solid carbon from CO₂ but also led to high reaction rates for the formation of CO. It was found that the added Na ⁺ ions strongly covered the Ni surface. Calcination and reduction pretreatments led to new Na-related species that participated in the synthesis of CNFs. The structure of CNF materials obtained from CO₂ varied with the reaction time and high-temperature thermal treatment. Initially, oxygen-rich functional groups, such as carboxylic acids, anhydrides, and phenols favored the formation of carbon. However, with increasing reaction times, the carbon growth became more graphite-like and oxygen-containing functional groups disappeared. The process of removal of oxygen-rich functional groups through a high-temperature treatment can lead to reduce the numbers of disorder sp ² carbon materials and enhance the greater graphitic character for CNFs.