Estudos Raman emcatalisadores nanoestruturados: Efeitos de temperatura e potência do laser.

Abstract

In this work, the Raman spectroscopy technique was used to investigate the vibrational properties of the nanostructured catalyst oxides CeZr, CeMn and ZrMn and correlate them with structural characteristics and thermal stability. The solids were prepared using the nanocastingtechnique. The effects of temperature on CeZr were studied by varying the temperature from 22 to 650 ° C. Were evaluated the effects of laser induced heating in CeMn, CeZr and ZrMn solids by varying the incident power from 0.017 mW to 4.0 mW. The vibrational properties of the catalysts were investigated and suggested changes in their physical and chemical properties, varying the temperature and the laser power. With the variation of the temperature from 22 to 650 ° C in the CeZr catalyst oxide, there were changes in the size of the particles and the appearance of defects due to oxygen vacancies. No phase transition was observed. The particle sizes of the nanostructured oxides CeMn and CeZr were influenced by the effects of local heating induced by the laser with consequent sintering of the catalysts. Defects due to oxygen vacancies appeared in the CeMn and CeZr solids, and oxidation of the MnO2-related phases was observed with the laser power ranging from 0.017 mW to 4.0 mW. The catalyst oxide ZrMn showed transformation from the MnO2 phases to the α-Mn2O3 phase in about 1.1 mW. The results bring new perspectives for the application of nanostructured oxides in catalysis and indicate that the structural properties of CeZr, CeMn and ZrMn solids can be investigated, in order to monitor them, aiming at catalytic applications in thetemperature and power range of the laser in which they were analyzed.