Total oxidation of methane over Pd catalysts supported on silicon nitride

Non-oxide refractory materials such as silicon nitride showing high thermal stability and thermal conductivity can be used as catalytic supports. Silicon nitride with different specific area and crystallinity: amorphous silicon nitride (SiN-am), amorphous silicon nitride annealed at 1450 °C (120 min) under nitrogen flow (SiN-annl) and α-Si3N4 were chosen as supports for Pd catalysts. Commercial amorphous silicon nitride contains a small amount of crystalline phase with α/β Si3N4 ratio of 2.3. Annealing of the amorphous silicon nitride leads to changes in the phase composition, as well as in the morphology of the powder. An increase of the amount of crystalline phases up to 80% with α/β Si3N4 ratio of 6.6 was obtained after annealing. Palladium catalysts were prepared by impregnation of Pd(II) acetylacetonate in toluene solution of silicon nitride powder and were tested in the methane total oxidation reaction. A strong influence of the phase composition and the crystalline state of supports on the catalytic properties of Pd catalysts was found. The activity of Pd catalysts deposited on the amorphous Si3N4 is very poor. It increases with the α-Si3N4 content of the support.