Hydrothermal stability of Pd/ZrO2 catalysts for high temperature methane combustion

A monoclinic ZrO2 support was synthesized via a precipitation technique for the investigation of the effects of calcination temperature on methane combustion over Pd/ZrO2 and Pd/γ-Al2O3 catalysts at 600 °C, in the absence and presence of water vapor. In comparison with Pd/γ-Al2O3, all the Pd/ZrO2 catalysts studied showed superior performances. With the exception of Pd/ZrO2 (ZrO2 support calcined at 1000 °C), all the Pd/ZrO2 catalysts showed higher methane conversions in the presence of water vapor than in its absence. The Pd/ZrO2 catalyst with a ZrO2 support calcined at 900 °C exhibited the highest activity as well as the greatest durability under both conditions, in spite of its low surface area. Transmission electron microscopy indicated that the activity of methane combustion is unrelated to Pd particle size. In addition, the results of temperature-programmed decomposition of Pd oxide on Pd/support and X-ray photoelectron spectroscopy showed that the activity of Pd/ZrO2 was strongly dependent on the oxidation state of the Pd species.