Hydrogen Production by Catalytic Decomposition of Methane

Abstract

Traditionally, hydrogen is produced by reforming or partial oxidation of methane to produce synthesis gas, followed by the water-gas shift reaction to convert CO to CO2 and produce more hydrogen, followed in turn by a purification or separation procedure. This paper presents results for the catalytic decomposition of undiluted methane into hydrogen and carbon using nanoscale, binary, Fe−M (M = Pd, Mo, or Ni) catalysts supported on alumina. All of the supported Fe−M binary catalysts reduced methane decomposition temperature by 400−500 °C relative to noncatalytic thermal decomposition and exhibited significantly higher activity than Fe or any of the secondary metals (Pd, Mo, and Ni) supported on alumina alone. At reaction temperatures of approximately 700−800 °C and space velocities of 600 mL g-1 h-1, the product stream was comprised of over 80 volume % of hydrogen, with the balance being unconverted methane. No CO, CO2, or C2 and higher hydrocarbons were observed in the product gas. High-resolution SEM and TEM characterization indicated that almost all carbon produced in the temperature range of 700−800 °C is in the form of potentially useful multiwalled nanotubes. At higher temperatures (>900 °C), hydrogen production decreases and carbon is deposited on the catalyst in the form of amorphous carbon, carbon flakes, and carbon fibers. In the noncatalytic thermal decomposition mode, at temperatures above 900 °C, graphitic carbon film is deposited everywhere in the reactor. Thus, the morphology of the carbon produced may be the controlling parameter in catalytic decomposition of methane. The efficient removal of the carbon from the catalyst surface in the form of nanotubes may be the key factor influencing catalyst performance.