The function of Mo-Ni-MgO catalysts for the synthesis of thin carbon nanotubes

摘要

The function of Mo-Ni-MgO catalysts in the synthesis of carbon nanotubes (CNTs) has been studied as a function of the catalyst composition. Thin CNTs with diameter of 2-15 nm have been produced on the catalysts by the decomposition of methane at 1073 K in a flow reactor. The purity was estimated to be over 90 percent in the carbon products by TEM observation. The carbon yield changed with the content of Mo or Ni in the catalysts. The coexistence of the three components of Mo, Ni, and MgO was found to be necessary for the synthesis of CNTs. The role of MgO with the size of 14-20 nm is to stabilize small alloy particles of Mo and Ni. Without MgO, the particles grew large, showing no longer catalytic ability for the CNT synthesis. The Mo-Ni alloy particle was separated into two phases of Mo_2C and Ni during the CNTs synthesis, which was considered to be essential for the CNT synthesis catalysts. It is thought that the role of Ni is to dissociate methane, while the role of Mo_2C is to reserve carbon and to create graphene sheets at the high synthesis temperature.