Nanoporous Metal Catalyzed Synthesis Of New Carbon Nanomaterials

Nanocarbon materials,such as fullerene,carbon nanotubes and graphene,can be widely used in many fields,including structural materials,catalysis,sensing,energy storage and conversion because of their unique structures and excellent mechanical strength,thermal stability and electrical properties.There are many methods have been developed.Among them,the most widely used is chemical vapor deposition(CVD).A typical CVD method involves the catalytic cracking of a carbon source,which involves the catalytic decomposition of a carbon source into carbon atoms on the surface of an active transition metal particle supported by a matrix.Then the nanocarbons were grown directly in the matrix result from the interaction between the transition nanoparticles and the carbon atoms.Although the traditional supported metal nanoparticles,such as Fe,Ni,Co and Cu,are generally excellent catalysts for CVD synthesis of nanocarbons,due to the complicated preparation process,high cost,and easy agglomeration,it is hard to meet the mass production of carbon nanomaterials.Nanoporous metals(NPM)have great potential as catalyst for CVD growth of carbon nanomaterials in large quantities instead of the traditional metal nanoparticles,due to their inherent metal property and unique nanostructured and self-surported framework.In this paper,Cu-Mn alloy,Ni-Mn alloy and Ni-Co-Mn alloy system were used as raw materials,and the nano-porous metals,prepared by dealloying the raw materials,were used as catalysts for graphene,carbon nanotubes and their hybrids growth by CVD.This method provides an effective approach for the large scale synthesis of carbon nanomaterials using NPM as the growth support and catalyst.We studied systematically the effect of reduction time,growth time and temperature on the growth of carbon nanomaterials.The experimental results suggest that the free-standing nanoporous Cu(NPC),nanoporous Ni(NPN)and np-NiCo composite catalysts have high catalytic activity for the pyrolysis of acetylene into carbon nanomaterials.Through the control of carbon source,flow rate,reduction time and temperature and growth time,NPM can catalyze the synthesis of graphene with different quality.Carbon nanotubes with an average diameter of only tens of nanometers(the smallest diameter is only 14 nm)can be synthesized using Ni/Y catalyst supported on NPC/G composite.NPC can also catalyze the synthesis of carbon nanotubes with a diameter of 9-30 nm in one step.Nanoporous nickel can catalyze the cleavage of acetylene to generate porous carbon nanotubes with larger specific surface area.When the CVD perfomed with a gas flow of Ar:H2:C2H2 = 200:100:5 and growth time of 30 min,the flaky carbon nanotubes with an average diameter of about 20 nm can be obtained.Although dealloying method can not remove fully the manganese elements in the nickel-cobalt-manganese alloy system,and the prepared nanoporous nickel-cobalt composite catalyst can catalyze the synthesis of scaly porouscarbon nanotubes with an average diameter of about 35 nm.