Reaction kinetics and mechanism of complete methane oxidation on Pd/Mn2O3 catalyst

摘要

A Pd/Mn2O3 catalyst highly active in the reaction of complete methane oxidation has been prepared by supporting palladium on nanosized Mn2O3. The nanosized Mn2O3 particles have been obtained by calcination of finely divided Mn3O4, synthesized by advanced wet chemical procedure. The very high activity manifested by the Pd/Mn2O3 catalyst (in the presence of 20000 pm water vapor and gaseous hourly space velocity of 25000 h(-1) the catalyst bed temperature for reaching 50% conversion degree is 430 A degrees C) is explained based on the nature of the active species: PdO clusters stabilized on Mn2O3. The role of Mn2O3 is to maintain the palladium in its oxidized state, acting as a high capacity storage of the oxygen species. The Langmuir-Hinshelwood or Eley-Rideal mechanisms are most probable over pure Mn2O3, while the addition of palladium to Mn2O3 changes reaction mechanism to Mars-van Krevelen whereupon water molecules are competing with the methane molecules for the oxidized adsorption sites, accompanied by a slow desorption of products (rate-limiting step).