Preparation of Mg1−xFexMoO4 catalyst and its application to grow MWNTs with high efficiency

Synthesis of aligned and length-controlled carbon nanotubes by chemical vapor deposition

“…a-f. The molar ratios of Mo to Mg and Fe to Mg were from 1.0 to 1.2 and from 0.01 to 0.1 in previous works [11][12][13][14], whereas those of Mo to Mg and Fe to Mo were from 0.01 to 0.06 and from 0.04 to 0.14 in our work. In http://carbonlett.org TEM was used to measure the distribution and average diameters of CNTs.…”

“…The growth mechanism of the aligned CNTs on the iron-rich catalyst or molybdenum-poor catalyst, such as were used in our study, would be similar to that of aligned growth on a substrate such as silicon wafer. This means that the metal nanoparticles such as MgO could easily melt and then move from the inside of the ceramic supports to the surface of the ceramic supports when catalysts were synthe- short, previous works [11][12][13][14] used a catalyst with high Mo content; on the other hand, we used a catalyst with low Mo content. In cases of high content of Mo in the catalyst, high temperature was needed to grow CNTs, because the melting point of Mo is higher than 2000°C.…”

“…In cases of high content of Mo in the catalyst, high temperature was needed to grow CNTs, because the melting point of Mo is higher than 2000°C. Wang et al [10] and others [11][12][13][14] carried out experiments to obtain aligned CNTs at more than 900°C with flow of methane gas; however, we could have aligned CNTs at less than 700°C with a flow of ethylene gas instead of methane gas. 3000, 1000, 500 and 300 wt% in the order shown in Figs. 5a-e.…”

“…It was analogized that the amounts of metal nanoparticles compared to the grown CNTs were enriched due to the increase of the preparation temperature of the catalysts. According to the papers of Lie et al [13] and those of several other researchers [14][15][16], the catalysts for aligned CNTs were calcined at a temperature of more than 750°C. Those researchers reported that the growth mechanism of the aligned CNTs grown over molybdenum/magnesium oxide or iron, nickel, and cobalt doped molybdenum/ magnesium oxide catalysts, in which the absorption of hydrogen makes the molybdenum nanoparticles separate out from the inside to the outside of the catalyst, led to the formation of multilayers of molybdenum nanoparticles on the surface of the support.…”

“…The powder form of short and aligned CNTs can be more easily dispersed in a composite matrix than can be normally grown CNTs. Several researchers [8][9][10][11][12][13][14] have succeeded in growing aligned CNTs powders, but there has been no fabrication of a composite with aligned CNTs. Current materials do not seem to be suitable for composites because of the use of high temperature in the CNT growth and high molybdenum contents in the catalysts.…”