Utilisation of CO2 to Carbon Nanotubes

Abstract Capturing and converting CO2 into value-added chemicals and materials is of great interest for decarbonization. Among them, the CO2 conversion to advanced materials such as carbon nanotubes (CNTs) is a promising CO2 utilization. CNTs can be used in many applications, owing to its exceptional properties of high electrical conductivity, high thermal conductivity, high tensile strength, and high surface area. In this work, we have successfully developed catalysts and process to convert CO2 to CNTs. Active transition metal catalysts supported on zeolites were developed for the synthesis of CNTs using CO2 as raw material. The synthesis of CNTs from CO2 over the developed catalyst was carried out via a chemical vapor deposition (CVD) process. The quantity and quality of the carbon nanotubes synthesized from CO2 were determined using thermogravimetric analysis (TGA), scanning electron microscope (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. A comparison between the current response of the synthesized CNTs and commercial CNTs were performed using cyclic voltammetry (V vs. Ag/AgCl) method. By optimizing metal type, metal loading, zeolite topologies and pore structures (hierarchically porous or conventionally microporous), the best CNTs were obtained over the 25wt%Fe on hierarchical FAU catalyst. The qualification and quantification of resulting CNTs were based on an average diameter size of 23.1 nm, a high yield of 15.4%, and ID/IG ratio (CNTs quality) of 0.56 as characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and Raman spectroscopy, respectively. The synthesized CNTs demonstrated improved performance in terms of current response compared to commercial CNTs when evaluated using cyclic voltammetry (V vs. Ag/AgCl) with a 0.5 M H2SO4 supporting electrolyte. This enhanced performance can be attributed to the small diameter and high quality of the synthesized CNTs. This work demonstrates the industrially relevant utilization of CO2 towards highly conductive CNTs-based materials, which have many potential applications including energy storages, sensors, electronic circuits, composite materials, etc. Transition metals like Fe and Ni play a crucial role as catalysts in the decomposition of CO2 during the CNTs synthesis. Well-dispersed distribution of metal nanoparticles on the hierarchical zeolite can enhance catalytic activity, consequently resulting in more favorable CNTs synthesis outcomes.