Abstract:

Nonoxidative decomposition of ethane was conducted over monometallic Ni and bimetallic Fe–Ni catalysts on basic Mg(Al)O support to produce H₂ free of CO and CO₂ and easily purified carbon nanotubes, a potentially valuable byproduct. The Mg(Al)O support was prepared by calcination of synthetic MgAl–hydrotalcite with a Mg to Al ratio of 5. The catalysts were prepared by incipient wetness with total metal loadings of 5 wt %. The dehydrogenation of undiluted ethane was conducted at temperatures of 500, 650, and 700 °C. At 500 °C, the Ni/Mg(Al)O catalyst was highly active and very stable with 100% conversion of ethane to 20 vol % H₂ and 80 vol % CH₄. However, the bimetallic Fe–Ni/Mg(Al)O exhibited its best performance at 650 °C, yielding 65 vol % H₂, 10 vol % CH₄, and 25 vol % unreacted ethane. The product carbon was in the form of carbon nanotubes (CNT) at all three reaction temperatures, but the morphology of the CNT depended on both the catalyst composition and reaction temperature. The CNTs were formed by a tip-growth mechanism over the Mg(Al)O supported catalysts and were easily purified by a one-step dilute nitric acid treatment. Mössbauer spectroscopy, X-ray absorption fine structure spectroscopy, N₂ adsorption–desorption isotherms, TEM, STEM, TGA, and XRD were used to characterize the catalysts and the CNT, revealing the catalytic mechanisms.