One-step preparation of highly dispersed metal-supported catalysts by fluidized-bedMOCVD for carbon nanotube synthesis

Abstract

A new technique of fluidized-bed metal–organic chemical vapour deposition(FB-MOCVD) is developed as a one-step method to prepare highly dispersedmetal-supported catalysts for carbon nanotube synthesis. By using ultrafinepowder of gamma-alumina (70 nm Sauter mean in size) as the support withFe(CO)5 andMo(CO)6 as the metalprecursors, Fe/Al2O3, Mo/Al2O3 and Fe–Mo/Al2O3 catalysts have been prepared in an FB-MOCVD reactor. Compared with theconventional catalyst-preparation methods such as impregnation, ion exchange,co-precipitation and co-crystallization, the one-step FB-MOCVD technique is advantageousin many aspects. These include eliminating the solid–liquid separation and thesubsequent operations of drying and high-temperature calcination/reduction,thus minimizing the aggregation or the crystalline size-growing problem for thesupported metal particles caused by these operations. The metal-supported catalystsobtained by FB-MOCVD are characterized with various techniques includingICP-AES, SEM-EDX, XRD and nitrogen isothermal adsorption. Some catalystsare selected and used for carbon nanotube synthesis by CVD from acetylene(C2H2) in a fluidizedbed at 650 or 850 °C. The formation of the entangled multi-walled carbon nanotubes (MWNTs), around 50 nmin outer diameter and 10 nm in inner diameter, and several to tens of microns in length, hasbeen confirmed by the TEM and SEM analyses. High CNT selectivity () with the carbon yield ranging widely from about 10% to over 60%, depending on thetype of catalyst used and the CNT deposition temperature, has been demonstrated withTGA tests.