The use of different catalysts in the synthesis of carbon nanotubes CNTs through chemical vapor deposition CVD can significantly affect the yield, structure, and properties of the resulting nanotubes. Catalysts play a crucial role in the growth of CNTs by lowering the activation energy required for the reaction and providing nucleation sites for the formation of CNTs. Some of the factors influenced by the choice of catalyst include:1. Yield: The yield of CNTs can be affected by the catalyst's activity, selectivity, and stability. Highly active catalysts can promote the formation of more CNTs, while selective catalysts can help in producing specific types of CNTs. The stability of the catalyst is also important, as it determines the catalyst's lifetime and the duration of CNT growth.2. Diameter and structure: The choice of catalyst can influence the diameter and structure of the CNTs. For example, using catalyst nanoparticles with different sizes can result in CNTs with varying diameters. The catalyst composition can also affect the chirality and electronic properties of the CNTs. Some catalysts may favor the growth of single-walled carbon nanotubes SWCNTs , while others may promote the formation of multi-walled carbon nanotubes MWCNTs .3. Purity: The purity of the synthesized CNTs can be affected by the choice of catalyst. Some catalysts may introduce impurities or amorphous carbon into the CNTs, which can degrade their properties. Using high-purity catalysts and optimizing the CVD process can help in obtaining CNTs with fewer defects and impurities.4. Catalyst support: The choice of catalyst support can also influence the yield and structure of CNTs. The support material can affect the dispersion of catalyst particles, their interaction with the carbon source, and the heat transfer during the CVD process. Some supports may also promote the growth of specific types of CNTs or enhance their properties.Commonly used catalysts for CNT synthesis include transition metals such as iron Fe , cobalt Co , and nickel Ni , as well as their alloys and compounds. The choice of catalyst depends on the desired properties of the CNTs, the carbon source, and the CVD process conditions. By carefully selecting and optimizing the catalyst and CVD process parameters, it is possible to control the yield, structure, and properties of the synthesized CNTs.