Solid-electrolyte-aided study of methane oxidation on polycrystalline silver

Abstract

The oxidation of methane on porous polycrystalline Ag films supported on yttria-stabilized zirconia was studied in a CSTR at temperatures between 450 and 600 °C and atmospheric total pressure. The technique of solid-electrolyte-potentiometry (SEP) was used to monitor the chemical potential of oxygen adsorbed on the catalyst. The kinetic and potentiometric results are consistent with an Eley-Rideal reaction model with adsorbed atomic oxygen reacting with gaseous methane. The rate of CH 4 combustion was found to satisfy r = K RP CH 4 · K 0a 0 (1 + K 0a 0) with K R = 1.97 exp(−10,300/ T) mol/ s · bar and K 0 = 7.56 × 10 −5 exp(8500/T) bar −1 2 on a porous film that could adsorb a total of 2.5 × 10 −6 moles O 2. The steady state atomic oxygen activity satisfies the equation P O 2 1 2 /a 0 − 1 = K R P CH 4 K D with K D = 0.172 exp(−9500/ T) g atom O/s. A simple mechanism is proposed which explains all the experimental observations.