Akio Nishida

Catalytic activity of PdO/ZrO2 catalyst for methane combustion

Abstract Catalytic activity of ZrO2 supported PdO catalysts for methane combustion has been investigated in comparison with Al2O3 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 ZrO2 support. Temperature-programmed reduction (TPR) measurements of the catalyst with hydrogen revealed that the PdO of PdO/Al2O3 catalyst was reduced at the temperature less than 100°C, whereas in PdO/ZrO2 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/ZrO2 catalyst. In order to confirm the formation of the solid solution of PdO and ZrO2, X-ray diffraction (XRD) analyses of the mixtures of ZrO2 and PdO calcined at 700–900°C in air were carried out. The lattice volume of ZrO2 in the mixture was larger than that of ZrO2. Furthermore, the Pd thin film on ZrO2 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 ZrO2 support might be stabilized by the formation of the solid solution of PdO and ZrO2.

Catalytic properties of PdO/δ-Al2O3 catalysts prepared by hot isostatic pressing

Abstract The catalytic properties of PdO/δ-Al2O3 catalysts prepared by hot isostatic pressing (HIP) have been investigated. The HIP treated catalysts (HIPed catalysts) showed higher catalytic activity for the oxidation of methane in the temperature range 973-1173 K than the catalysts calcined in atmosphere (non-HIPed catalysts). These catalysts were characterized by thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, CO adsorption and temperature-programmed desorption of oxygen. It was found that the palladium oxide stable against reduction was formed by the HIP treatment, and that oxygen in the HIP atmosphere played an important role for the formation of the stabilized palladium oxide species. The temperature dependence of catalytic activity was explained in connection with the palladium oxide species on the support.