Microwave-Assisted Pyrolysis of Methane with Iron-Based Alumina Catalysts Fabricated by Solution Combustion Synthesis

FeAlxOy powders, fabricated by solution combustion synthesis (SCS), are promising catalysts for microwave-assisted pyrolysis of methane. However, the effects of SCS parameters on the pyrolysis are not well understood. In the present work, two fuels (citric acid and glycine), two Fe:Al molar ratios, and two heating modes (a hotplate and a muffle furnace) are tested. All catalysts exhibit CH4 conversion of around 70% and H2 composition of about 93%. The process is one to two orders of magnitude more efficient than conventional pyrolysis. Increasing the Fe:Al ratio from 1:1 to 2:1 and using a hotplate improve H2 generation efficiency. Use of glycine decreases the CO2:H2 ratio, but citric acid yields more readily reducible products due to differences in phase evolution, detected by X-ray diffraction analysis. Scanning electron microscopy and energy-dispersive X-ray spectroscopy reveal carbon nanotubes and exsolution of Fe. FeAlxOy catalysts, prepared via incipient wetness impregnation, are ineffective.