Controllable synthesis of carbon nanotubes by changing the Mo content in bimetallic Fe-Mo/MgO catalyst

► Increasing the Mo content in the Fe-Mo/MgO catalysts resulted in an increase in wall number, diameter and growth yield of carbon nanotubes. ► The Fe interacts with MgO to form complex (MgO)x(FeO)1−x (0 < x < 1) and is then dispersed into the MgO support uniformly, resulting in very small Fe nanoparticles after reduction. ► The Mo interacts with MgO to form stoichiometry compound MgMoO4 and relative large metal Mo particles can be generated after reduction. ► The avalanche-like reduction of MgMoO4 makes the catalyst particles to be small thus enhances the utilize efficiency of Fe nanoparticles.