L.D. Schmidt

Production of Syngas by Direct Catalytic Oxidation of Methane

The reaction between methane and oxygen over platinum and rhodium surfaces in metalcoated ceramic monoliths can be made to produce mostly hydrogen and carbon monoxide (greater than 90% selectivity for both) with almost complete conversion of methane and oxygen at reaction times as short as 10–3 seconds. This process has great promise for conversion of abundant natural gas into liquid products such as methanol and hydrocarbons, which can be easily transported from remote locations. Rhodium was considerably superior to platinum in producing more H2 and less H2O, which can be explained by the known chemistry and kinetics of reactants, intermediates, and products on these surfaces.

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 SH2 ≈ 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 SH2 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.

Synthesis gas formation by direct oxidation of methane over Rh monoliths

AbstractThe production of H2 and CO by catalytic partial oxidation of CH4 in air or O2 at atmospheric pressure has been examined over Rh-coated monoliths at residence times between 10−4 and 10−2 s and compared to previously reported results for Pt-coated monoliths. Using O2, selectivities for H2 (

Binding states and decomposition of NO on single crystal planes of Pt

S_{H_2 }

binding states of CO and H2 on clean and oxidized (111)Pt

) as high as 90% and CO selectivities (SCO) of 96% can be obtained with Rh catalysts. With room temperature feeds using air, Rh catalysts give

Interaction of H2 with (100) W. I. Binding States

S_{H_2 }