Platinum supported on La2O3-Al2O3 and CeO2-Al2O3 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 gamma -Al2O3 in the La2O3-Al2O3 support was observed by X-ray diffraction when the sample was calcined at 1100 degreesC, while segregation of CeO2 was observed at such temperature in the CeO2-Al2O3 preparation. The formation of Al-V and Al-VI coordinated aluminum was observed by MAS-(NMRAl)-Al-27 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 CeO2-Al2O3, meanwhile, for the La2O3-Al2O3 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 Ptn/La2O3-Al2O3 catalyst was found bigger than those of Pt/CeO2-Al2O3 catalyst, It is proposed that doped-alumina prepared by the sol-gel method has structural defects which induce modification in the metal activity.