Catalytic activity of PdO/ZrO 2 catalyst for methane combustion

Abstract

Catalytic activity of ZrO 2 supported PdO catalysts for methane combustion has been investigated in comparison with Al 2O 3 supported PdO catalysts. It was found that the drop of catalytic activity owing to decomposition of PdO at a high temperature region (600–900°C) was suppressed by using ZrO 2 support. Temperature-programmed reduction (TPR) measurements of the catalyst with hydrogen revealed that the PdO of PdO/Al 2O 3 catalyst was reduced at the temperature less than 100°C, whereas in PdO/ZrO 2 catalyst the consumption of hydrogen was also observed at 200–300°C. This result indicates that the stable PdO species were present in the PdO/ZrO 2 catalyst. In order to confirm the formation of the solid solution of PdO and ZrO 2, X-ray diffraction (XRD) analyses of the mixtures of ZrO 2 and PdO calcined at 700–900°C in air were carried out. The lattice volume of ZrO 2 in the mixture was larger than that of ZrO 2. Furthermore, the Pd thin film on ZrO 2 substrate was prepared as a model catalyst and the depth profile of the elements in the Pd thin film was measured by Auger electron spectroscopy (AES). It was confirmed that Zr and O as well as Pd were present in the Pd thin film heated at 900°C in air. It was considered that the PdO on ZrO 2 support might be stabilized by the formation of the solid solution of PdO and ZrO 2.