(591b) Rich CH4 Oxidation on Pt/Pd/Al2O3 Monolith: Performance, Multiplicity, and Spatial Effects

The increased interest in natural gas as a fuel requires improved oxidation catalysts to minimize the slip of methane, a potent greenhouse gas. Under rich conditions (O₂/CH₄ < 2) CH₄ is converted to a mixture of total oxidation products (CO₂, H₂O) and partial oxidation products (CO, H₂). We describe the results of an experimental study of rich methane oxidation on Pt/Pd/Al₂O₃ washcoated monolith.

This monolith was introduced to feeds containing a range of different compositions (O₂, CO₂, H₂O) and temperatures. To assess the behaviors of this system, spatial measurement techniques were utilized. Spatial temperature was recorded using optical frequency domain reflectometry (OFDR) and concentration by capillary inlet mass spectrometry (SpaciMS). Figure 1 shows the impact of both variances in inlet O₂ and H₂O. Spatial concentration profiles for a dry feed in the O₂-starved regime (< 2000 ppm) reveals that complete oxidation occurs upstream while anaerobic chemistry such as steam reforming occurs downstream. Increases in O₂ result in initial increases in conversion across all conditions followed by eventual decline in conversion to an oxygen-insensitive value. This decrease occurs due to inhibition by site blockage by oxygen adatoms. Increasing the amount of H₂O present results in increased methane conversion. Figure 2 shows spatial methane conversion profiles for a condition corresponding to the region of declining methane conversions. This profile shows the existence of two separate steady states, one inhibited and one active. The combination of these profiles produces the bulk conversion previously observed with the decline occurring due to more channels being inhibited as opposed to active. A kinetic model to describe this system is being worked on and results will be presented and discussed.