Hydrogen production by non-oxidative decomposition of methane
Dr. Naresh Shah
University of Kentucky
Chemical and Materials Engineering (CME) and
Consortium for Fossil Fuel Liquefaction Science (CFFLS)
Friday, June 15, 2001 3:00 pm
Ben Bandy Conference Center
Center for Applied Energy Research
Production of pure hydrogen from hydrocarbons, particularly methane, the major component of natural gas, has great practical importance. Traditionally, reforming and partial oxidation of methane are employed to produce synthesis gas, and CO in synthesis gas is converted to CO2 using the water-gas shift reaction to produce a relatively pure hydrogen stream. However, this hydrogen still contains enough CO to poison the catalysts used in PEM electrochemical fuel cells. A reverse methanation reaction has to be carried out to reduce the CO concentration to sub-ppm levels.
This talk presents results for the catalytic decomposition of undiluted methane to pure hydrogen and carbon using a variety of alumina supported binary metal (Fe, Pd, Mo and Ni) catalysts. Fe based binary metal catalysts showed higher conversion to hydrogen at lower temperatures than the pure iron catalyst. All binary catalysts reduced methane decomposition temperature by 400-500 degrees C as compared to non-catalytic thermal decomposition. The product stream comprised of over 75-volume % of hydrogen and unconverted methane at reaction temperatures of 700 C.
All catalysts showed reduction in hydrogen production with temperature above 700 C before increasing again due to non-catalytic thermal decomposition. High resolution SEM and TEM characterization indicated that almost all carbon produced at 700 C is in the form of potentially useful multi-walled nanotubes. At higher temperatures (>900C) carbon is deposited in the form of carbon fibers and whiskers on the catalysts. In non-catalytic thermal decomposition mode, at temperatures over 1100C, 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.