A method for synthesizing carbon nanotubes having a narrow distribution of diameter and/or chirality is presented. The method comprises providing catalyst particles to a reactor for synthesizing the carbon nanotubes, wherein the catalyst particles are characterized by a narrow distribution of catalyst-particle diameters and a narrow distribution of catalyst-particle compositions. Preferably, the catalyst particles are characterized by a mean catalyst-particle diameter of 2.6 nm or less and a composition of NixFe1-x, wherein x is less than or equal to 0.5.