Selectivity considerations in methane catalytic combustion

In the catalytic combustion of methane, both the catalytic reactions and the downstream radical combustion processes can influence the selectivity to CO and CO2, Assuming CH4 is oxidized to CO2 via a CO intermediate, the CO level exiting a supported palladium monolithic catalyst was modeled assuming that the CO was a gas phase intermediate and using literature kinetics for both CH4 and CO surface reaction rates. The. model predicts a CO selectivity independent of the methane oxidation rate and CO levels in the range of 1 to 6 ppm. This agrees with experimental measurements that showed levels of 5 to 8 ppm at practical gas turbine conditions. The radical reaction process just downstream of the catalyst was also explored using a kinetic reaction sequence that describes the homogeneous radical combustion of CH4. To achieve CO levels in the range of 10 ppm in a reaction time adequate for use in a gas turbine combustor, reaction temperatures above 1100 degrees C are required.