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

A Pd/Mn 2 O 3 catalyst highly active in the reaction of complete methane oxidation has been prepared by supporting palladium on nanosized Mn 2 O 3 . The nanosized Mn 2 O 3 particles have been obtained by calcination of finely divided Mn 3 O 4 , synthesized by advanced wet chemical procedure. The very high activity manifested by the Pd/Mn 2 O 3 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 °C) is explained based on the nature of the active species: PdO clusters stabilized on Mn 2 O 3 . The role of Mn 2 O 3 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 Mn 2 O 3 , while the addition of palladium to Mn 2 O 3 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).