3520
Energy & Fuels 2007, 21, 3520–3529
Catalytic Nonoxidative Dehydrogenation of Ethane over Fe–Ni and Ni Catalysts Supported on Mg(Al)O to Produce Hydrogen and Easily Purified Carbon Nanotubes Wenqin Shen,*,† Yuguo Wang,†,‡ Xuebei Shi,† Naresh Shah,† Frank Huggins,† Shilpa Bollineni,§ Mohindar Seehra,§ and Gerald Huffman† Consortium for Fossil Fuel Science, UniVersity of Kentucky, Lexington, Kentucky 40506-0043; Research & DeVelopment Center, Saudi Aramco, Dhahran 31311, Saudi Arabia; and Physics Department, West Virginia UniVersity, Morgantown, West Virginia 26506 ReceiVed July 12, 2007. ReVised Manuscript ReceiVed September 12, 2007
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.
1. Introduction An energy economy based on hydrogen could alleviate growing concerns about energy supply, air pollution, and greenhouse gas emissions. Currently, the most widely used method of hydrogen production is steam reforming or partial oxidation of fossil fuels, particularly natural gas, followed by the water gas shift reaction (WGS) and separation and purification steps. However, the hydrogen purity requirement for use in polymer electrolyte membrane (PEM) fuel cells is demanding (
