Versatile Roles of Metal Species in Carbon Nanotube Templates for the Synthesis of Metal–Zeolite Nanocomposite Catalysts

Metal–zeolite nanocomposites are extensively used in heterogeneous catalysis. The small size of zeolite micropores and nonuniform distribution of the metal component within the zeolite structure can severely reduce the efficiency of these catalysts. In this work, we propose a new single-pot synthesis strategy for the design of metal–zeolite nanocomposites with specific shape, enhanced mesoporosity, and uniform distribution of highly dispersed metals such as cobalt, nickel, and magnesium within the zeolite crystals. The strategy involves using metal carbon nanotubes as a secondary hard template. The presence of metal species in carbon nanotube templates is crucial and indispensable for the synthesis of metal zeolite nanocomposites. The multiple roles of the metal carbon nanotubes in the zeolite synthesis are revealed. First, they serve as a replica to create zeolites with specific fibrous morphology. Second, they fulfill the role of a mesoporogen and markedly increase the zeolite secondary porosity. Finally, they act as a vehicle to uniformly introduce the metal functions inside the mesoporous zeolites. Nanocomposites prepared using metal carbon nanotubes have shown enhanced catalytic performance in Fischer–Tropsch synthesis, hydrogenation of aromatics, and anisole acylation.