(621b) Impact of Feed Composition on the Spatial Features of Coupled Methane Oxidation and Reforming

Increased interest in utilizing natural gas as a fuel and chemical feedstock necessitates development of catalytic technologies for methane abatement via oxidation and conversion via reforming (steam and dry). Here we study coupled methane oxidation and steam/dry reforming in multifunctional structured catalyzed monoliths through in situ spatial measurements of temperature and species concentration profiles. We combine optical frequency domain reflectometry (OFDR) for temperature and spatially resolved capillary inlet mass spectrometer (SpaciMS) for concentration. The experiments were performed on a Pt/Pd/Al₂O₃ washcoated monolith with feeds containing varied compositions of CH₄, O₂, H₂O, and CO₂ to simulate both stoichiometric natural gas vehicle emission control and conversion of flared streams from shale gas production facilities.

Figure 1a shows the dependence of methane conversion on O₂ feed concentration. As O₂ increases from zero, the conversion increases from a reforming dominated regime, exhibits a maximum, then drops sharply due to O₂ self-inhibition. For the excess H₂O concentrations shown, the conversion is rather insensitive. However, as H₂O is decreased to zero (not shown here) the conversion drops dramatically at low O₂ concentration. The temperature profiles in Figure 1b at the conversion maximum (3000 ppm O₂) reveal an overall exothermic reaction system due to methane oxidation and water gas shift. As the amount of water in the feed is increased, the water-gas shift reaction becomes more important, underscored by the decrease in CO selectivity indicated in Figure 1c. In an ongoing study, spatially-resolved species concentrations and temperature are being collected spanning a wide range of conditions. These data provide deep insight into the competing reactions.