Synthesis gas formation by direct oxidation of methane over Pt monoliths

• Published in: Journal of catalysis 1992, Vol.138 (1), p.267-282
• Main Authors: Hickman, D.A., Schmidt, L.D.
• Format: Article
• Language: English
• Subjects: 03 NATURAL GAS; 034000 - Natural Gas- Combustion; 400201 - Chemical & Physicochemical Properties; ALKANES; CATALYSIS; CATALYST SUPPORTS; CATALYSTS; CATALYTIC EFFECTS; Catalytic reactions; CHEMICAL PREPARATION; CHEMICAL REACTIONS; Chemistry; DECOMPOSITION; ELEMENTS; Exact sciences and technology; FLUIDS; GASES; General and physical chemistry; GEOMETRY; HETEROGENEOUS CATALYSIS; HYDROCARBONS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; MATHEMATICS; METALS; METHANE; ORGANIC COMPOUNDS; OXIDATION; PHYSICAL PROPERTIES; PLATINUM; PLATINUM METALS; PYROLYSIS; RHODIUM; SYNTHESIS; SYNTHESIS GAS; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; THERMAL CONDUCTIVITY; THERMOCHEMICAL PROCESSES; THERMODYNAMIC PROPERTIES; TRANSITION ELEMENTS
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/0021-9517(92)90022-A

The production of H 2 and CO by catalytic partial oxidation of CH 4 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 H 2 and CO, which strongly suggests that the primary surface reaction is methane pyrolysis, CH 4 → C + 4H, from which H 2 desorbs and C is oxidized to CO. With room-temperature feeds using air, the optimal feed composition for H 2 and CO occurs between 15 and 20% CH 4 with optimal selectivities of up to S H 2 ≈ 0.5 and S co ≈ 0.95 at 80% conversion of the CH 4 at ≈100°C. Increasing the adiabatic reaction temperature by preheating the reactant gases or by using O 2 instead of air improves S H 2 to as much as 0.7 for a Pt catalyst and shifts the optimal feed composition toward the stoichiometric feed composition for H 2 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 H 2 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.