Multifunctional Catalysts for Singlewall Carbon Nanotube Synthesis

Single-wall carbon nanotubes (SWNTs) are usually produced with the help of metal catalysts that first break down various carbon species such as graphite, carbon clusters, amorphous carbon, or hydrocarbons and then release them in the form of SWNTs. These catalysts therefore must perform several functions in order to produce high quality, high yield, long SWNTs, and the finesse of these catalysts is controlled by the balance between those functions. Such a production is critical to future applications such as telecommunication, molecular electronics, sensing, and mechanical devices. In general, multicomponent materials such as bimetallic nanoparticles (bi-MNPs) are much better catalysts than those made of single component materials because the two metals in the biMNPs can enhance certain functions by playing complementary catalytic roles. Furthermore, some functions can only be offered by bi-MNPs because the two metals are structurally arranged in such specific manners that the combined properties would otherwise be impossible to access by monometallic nanoparticles (mono-MNPs). Bimetallic catalysts have been proven superior with improved activity, selectivity, stability, and resistance to poisoning than their monometallic counterparts.1,2 For example, bi-MNPs are preferred heterogeneous catalysts in petroleum reforming processes.3 Bi-MNPs of large diameters (>50 nm) have also been used to catalyze the growth of carbon filaments.4 Those catalysts have also been used in ammonia synthesis