title: Temperature and high pressure effects on the structural features of catalytic nanocomposites oxides by Raman spectroscopy.
abstract: Structural characterizations of nanostructured oxides were studied by X-ray diffraction (XRD), Raman and infrared spectroscopy. The oxides catalysts namely, SnO2, ZrO2, CeO2, MnOx, Al2O3 and TiO2 were prepared by a nanocasting route and the effect of the temperature and pressure on the stability of the solids was evaluated. Raman spectra showed that ZrO2 and TiO2 exhibited phase transitions at moderate temperatures whereas CeO2, SnO2 and MnOx had an effective creation of defects in their structures upon annealing at elevated temperatures. The results suggested also that the effect of the temperature on the particles growth is related to the type of oxide. In this regard, phase transition by up to 600°C accelerated the sintering of ZrO2 and CeO2 grains compared to TiO2, SnO2 and MnOx counterparts. Under hydrostatic pressures lower than 10GPa, rutile TiO2 and tetragonal ZrO2 exhibited pressure induced phase transition whereas CeO2 and SnO2 were stable at pressures close to 15GPa. The experiments revealed that the nanostructured SnO2 oxide exhibited stable performance at relatively high temperatures without phase transition or sintering, being suitable to be used as catalysts in the range of temperature and pressure studied.
authors.affiliation: Universidade Federal do Ceará, Campus do Pici-Bloco 922, Departamento de Física, Fortaleza, Ceará, Brazil.
authors.forename: Antonio N
authors.initials: AN
authors.lastname: da Silva
authors.affiliation: Universidade Federal do Ceará, Campus do Pici-Bloco 922, Departamento de Física, Fortaleza, Ceará, Brazil.
authors.forename: Raffael C F
authors.initials: RC
authors.lastname: Pinto
authors.affiliation: Universidade Federal do Ceará, Campus do Pici-Bloco 922, Departamento de Física, Fortaleza, Ceará, Brazil.
authors.forename: Paulo T C
authors.initials: PT
authors.lastname: Freire
authors.affiliation: Universidade Federal do Ceará, Campus do Pici-Bloco 922, Departamento de Física, Fortaleza, Ceará, Brazil.
authors.forename: Jose Alves L
authors.initials: JA
authors.lastname: Junior
authors.affiliation: Universidade Federal do Ceará, Campus do Pici-Bloco 940, Departamento de Química Analítica e Físico-Química, Fortaleza, Ceará, Brazil. Electronic address: alcineia@ufc.br.
authors.forename: Alcineia C
authors.initials: AC
authors.lastname: Oliveira
authors.affiliation: Universidade Federal do Ceará, Campus do Pici-Bloco 922, Departamento de Física, Fortaleza, Ceará, Brazil.
authors.forename: Josué M
authors.initials: JM
authors.lastname: Filho
mesh_terms: D002384:Catalysis; D018360:Crystallography, X-Ray; D053761:Nanocomposites / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry; D010316:Particle Size; D011312:Pressure; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013696:Temperature
chemical_list: D010087:Oxides
keywords: Composite materials; Defects; Nanostructures; Oxides; Phase transitions; Raman spectroscopy