Activity and stability of molybdenum carbide as a catalyst for CO2 reforming

The activity for CO2 reforming of methane over a Mo2C catalyst was studied at 8 and 1.6 bar total pressure using a plug flow reactor and a differential plug flow reactor with external recycle operated as a continuously stirred tank reactor (CSTR), respectively. In the plug flow reactor, the catalyst deactivation started from the top of the reactor and proceeded downward, while it was stable in the CSTR at high conversions. Comparison of the activity of the Mo2C with that of a 1.8% Ru/MgAl2O4 catalyst demonstrates that this noble metal catalyst is more than two orders of magnitude more active than the Mo2C catalyst on the basis of weight. Thermodynamic calculations of the stability of Mo2C catalysts during CO2 reforming conditions show that Mo2C is only stable at high product concentrations. Finally, the carbon resistance of Mo2C is calculated to be higher than that of nickel-based catalysts. Carbon formation on a Mo2C catalyst at 700 degreesC requires an extra Gibbs-free energy of 4.5 kJ/mole compared to a nickel catalyst with nickel particles up to 2500 Angstrom. (C) 2001 Academic Press.