Síntese e caracterização de óxidos mistos CeO2-Nb2O5 para aplicação em catálise heterogênea

Abstract

Cerium and niobium mixed oxides (CeO2-Nb2O5) were synthesized by the Pechini method and calcined in a two heating steps' procedure (300 and 550 oC). Oxides were characterized by Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TG-DTA) and X-Ray Diffraction (XRD) with Rietveld's refinment. The purpose of the characterization was the understanding of the effects of niobium incorporation on the crystalline structure of cerium oxide. Some of the observed changes consisted in decreasing crystallite size and increasing the concentration of oxygen vacancies. The incorporation of niobium atoms in the cerium oxide's unit cell also caused contraction of the same, as can be observed in the displacement of the peaks for CeNb25 and CeNb50 on the X-ray diffractograms. These two samples were characterized as solid solutions, probably substitucionals. For the incorporation of 75% of niobium atoms into the cerium oxide's structure, it is possible to observe the formation of two segregated phases, which allows us to observe that the maximum amount of niobium atoms that can be inserted into the crystalline structure of cerium oxide to form a solid solution, using the Pechini method, is comprised between 50 and 75%.