Impact of the Pd incorporation method on the kinetics of the CH₄/O₂ reaction on Natural-Gas-Vehicle model Pd-doped LaMnO₃ catalysts

The kinetics of the CH4/O-2 reaction was studied in lean conditions on Natural-Gas-Vehicle Pd-doped LaMnO3 catalysts. The impact of the method for Pd incorporation, sol-gel vs. impregnation, has been examined. The calcination temperature to obtain the perovskite structure turned out to be a key to determine the strength of the interaction between Pd and LaMnO3. Steady-state kinetic measurements at 400 degrees C have been modeled according to a single site or a dual site reaction mechanism representative of the cooperation between Pd and surface lattice oxygen species supplied by the support material. Impregnated catalysts are found sensitive to particle sintering inducing a deterioration of the metal-support interface. On the contrary, aging leads to strenghening of the metal-support interaction on sol-gel Pd catalysts which promotes methane conversion notably near three-way operating conditions.