Taguchi-Optimized Catalytic Growth of Carbon Nanotubes for Applications in Electro-Catalysis

Taguchi method, largely used to optimize processes controlled by manifold parameters, has been utilized to improve the synthesis of carbon nanotubes by chemical vapor deposition of isobutane. Analyzing results obtained in nine suitably designed reactions, the influence of synthesis (773-973 K), calcinations (723-1,023 K) and reduction (773-973 K) temperatures and catalyst-support (alumina, magnesia or Na+-exchanged K10 clay) on specific yield and crystallization degree (i.e., C sp2 content) of the nanotubes has been ranked. After critical examination and adjusting of conditions predicted to give optimal results, ~50 g of nanotubes per gram of metal are obtained at 973 K over Fe/alumina catalysts calcined at 723 K and reduced at 773 K. Under the same conditions, highly crystallized nanotubes (with 73% of C sp2 bonds, as qualitatively estimated from Raman spectroscopy), suitable for electro-catalysis applications, are synthesized over Fe/clay catalysts.