SYNTHESIS GAS-FORMATION BY DIRECT OXIDATION OF METHANE OVER PT MONOLITHS

The production of H2 and CO by catalytic partial oxidation of CH4 in air at atmospheric pressure has been examined over Pt and Pt-Rh coated monoliths at residence times between 10-4 and 1-2 sec. With these short contact times, the direct oxidation reaction can be studied independent of reforming reactions. We observe high conversions to H2 and CO, which strongly suggests that the primary surface reaction is methane pyrolysis, CH4 → C + 4H, from which H2 desorbs and C is oxidized to CO. With room-temperature feeds using air, the optimal feed composition for H2 and CO occurs between 15 and 20% CH4 with optimal selectivities of up to SH ≈ 0.5 and Sco ≈ 0.95 at 80% conversion of the CH4 at ≈100°C. Increasing the adiabatic reaction temperature by preheating the reactant gases or by using O2 instead of air improves SH to as much as 0.7 for a Pt catalyst and shifts the optimal feed composition toward the stoichiometric feed composition for H2 and CO production. By examining several catalyst configurations, including Pt-10% Rh woven gauzes and Pt-coated ceramic foam and extruded monoliths, several reaction and reactor variables in producing H2 and CO have been examined. These experiments show that the selectivity is improved by operating at higher gas and catalyst temperatures, by maintaining high rates of mass transfer through the boundary layer at the catalyst surface, and by using catalysts with high metal loadings. At flow rates high enough to minimize mass-transfer limitations, the gauze, foam monoliths, and extruded monoliths all give similar selectivities and conversions, but with important differences resulting from different catalyst geometries and thermal conductivities. © 1992.