Synthesis, characterization and catalytic properties of Pt/CeO 2–Al 2O 3 and Pt/La 2O 3–Al 2O 3 sol–gel derived catalysts

Abstract

Platinum supported on La 2O 3–Al 2O 3 and CeO 2–Al 2O 3 were prepared by the sol–gel method. High specific surface areas between 572–418 m 2/g were obtained. FTIR-pyridine absorption band proved the formation of Lewis sites with comparable intensity in the supports. The stabilization of the γ-Al 2O 3 in the La 2O 3–Al 2O 3 support was observed by X-ray diffraction when the sample was calcined at 1100°C, while segregation of CeO 2 was observed at such temperature in the CeO 2–Al 2O 3 preparation. The formation of Al V and Al VI coordinated aluminum was observed by MAS-NMR 27 Al spectra in La doped-alumina. In the Ce doped-sample only Al VI coordination was identified. Propene and acetone were the products in the iso-propanol decomposition over CeO 2–Al 2O 3, meanwhile, for the La 2O 3–Al 2O 3 support only propene was obtained. The platinum (0.5 wt.%) particle size distribution as determined by electron microscopy showed very small particles <1.0 nm. On the other hand, in the n-heptane dehydrocyclization the activity and selectivity to toluene of the Pt/La 2O 3–Al 2O 3 catalyst was found bigger than those of Pt/CeO 2–Al 2O 3 catalyst. It is proposed that doped-alumina prepared by the sol–gel method has structural defects which induce modification in the metal activity.