Complete and partial catalytic oxidation of methane over substrates with enhanced transport properties

The development of improved substrate properties for catalytic combustion has been an area of much interest in recent years. Towards this end, Precision Combustion Inc. has developed novel short channel length, high cell density substrates (trademarked Microlith®) and high surface area ceramic coatings for them. These substrates avoid substantial boundary layer buildup and greatly enhance heat and mass transfer rates in reactors. The high cell density of these substrates results in high amount of the catalyst per unit of reactor volume. In this paper we examine the performance of these substrates coated with precious metal catalysts for the catalytic combustion and reforming of methane. Under fuel-lean operating conditions the surface temperature of Pd-based catalyst supported on Microlith® substrate and the temperature of the gas exiting the reactor remain stable at ∼800 °C over a wide range of inlet conditions. This is attributed to combination of enhanced transport properties and characteristics of Pd–PdO transformation. Preheating of the gas mixture in the Microlith® reactor was sufficient to stabilize a downstream premixed flame with NOx, CO, and UHC emissions in the single digit ppm range. Microlith® substrates were also examined for partial oxidation of methane under fuel-rich conditions. The enhanced transport properties of the Microlith® substrate allowed complete conversion of methane with surface temperature not exceeding material limits at 93% selectivity to partial oxidation products. High flow rate of reactants result in extremely high power densities and syngas output. The catalyst performance was observed to be stable over 500 h of operation.