A critical review of heterogeneous catalyst design for carbon nanotubes synthesis: Functionalities, performances, and prospects

Carbon nanotubes (CNTs) can be employed for many practical applications. However, the challenges regarding the scalability, and choice of catalyst for generating high-yield and quality CNTs persist. Thus, this review intends to discuss the catalyst design strategies based on different elements covering types of catalysts and supports. To date, Ni catalysts are superior in generating high yield of CNTs, but much focus is required on controlling the rate of carbon deposition and catalyst sintering issues. As such, bimetallic catalysts and promoters with high carbon solubilities are desirable to enhance metal catalyst dispersion and CNTs yield. At the same time, catalyst supports with high surface roughness and surface basicity, such as MgO and La2O3, are encouraged due to their strong metal-support interaction and surface oxidative properties for controlled carbon deposition. To achieve successful scale up CNTs productions, four research directions are identified, which cover: (1) the statistical modeling of the growth and termination of the CNTs process via quantitative and qualitative measures, (2) the optimum catalyst design strategies covering types of catalysts, supports, and catalysts precursors, (3) the evaluation of the sustainability of CNTs productions via life cycle assessments, and (4) the development of optimum process flows with high robustness.