| Abstract
| - Powders of α-Al1.8Fe0.2O3 solid solution are prepared by combustion and are attrition-milled with different amounts of ammonium heptamolybdate before being transformed into self-supported foams by impregnation of a polyurethane foam. Carbon nanotubes, mostly single- and double-walled, are prepared by catalytic chemical vapor deposition using the foams as catalytic materials. Extensive characterization reveals that the addition of a small amount of molybdenum first favors the formation of double-walled nanotubes over that of single-walled nanotubes and second activates smaller nanoparticles, thus producing smaller-diameter nanotubes. A detailed Mössbauer spectroscopy study reveals that there is no interaction between iron- and molybdenum species, pointing to a role of molybdenum favoring some phenomenon happening in the gas phase, as opposed to any alloying effect.
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