Antimony (V) Oxide Adsorbed on a Silica-Zirconia Mixed Oxide Obtained by the Sol-Gel Processing Method: Preparation and Acid Properties (original) (raw)

2002, Journal of the Brazilian Chemical Society

A preparação, o grau de dispersão, estabilidade térmica e a acidez de Lewis e de Brφnsted do óxido de antimônio (V) adsorvido sobre SiO 2 /ZrO 2 , preparado previamente pelo processo sol-gel, são descritas neste trabalho. Amostras de SiO 2 /ZrO 2 /Sb 2 O 5 de composições (% em massa): (a) Zr= 8,1 e Sb= 6,3; (b) Zr= 11,4 e Sb= 11,4, foram preparadas. As imagens de microscopia eletrônica de varredura conectada a um espectrômetro de energia dispersiva de raios X mostraram que os metais, Zr e Sb, estão homogeneamente dispersos em ambas as matrizes. Os padrões de difração de raios X de SiO 2 /ZrO 2 /Sb 2 O 5 aquecido a diversas temperaturas mostraram que até 1023 K a amostra apresentou-se amorfa. Em 1273 K a formação da fase cristalina ZrO 2 (baddeleita) foi observada e elevando-se a temperatura a 1573 K, as fases cristalinas de SiO 2 (cristobalita) e possivelmente de ZrO 2 /Sb 2 O 5 foram observadas. Utilizando a piridina como sonda molecular, sítios ácidos de Brφnsted do sólido SiO 2 /ZrO 2 /Sb 2 O 5 , aquecido até 523 K, mostraram ser bastante estáveis. The preparation, degree of dispersion, thermal stability and Lewis and Brfnsted acidity of antimony (V) oxide adsorbed on SiO 2 /ZrO 2 mixed oxide, previously prepared by the sol-gel processing method, are described herein. The samples SiO 2 /ZrO 2 /Sb 2 O 5 , with compositions (in wt %): (a) Zr= 8.1 and Sb= 6.3; (b) Zr= 14.9 and Sb= 11.4, were prepared. Scanning electron microscopy images connected to a X-ray energy dispersive spectrometer showed that both metals, Zr and Sb, were highly dispersed in the matrices. The X-ray diffraction patterns of SiO 2 /ZrO 2 /Sb 2 O 5 heated at different temperatures showed that, up to 1023 K, the matrix was amorphous. At 1273 K a crystalline phase of ZrO 2 (baddeleyite) was observed and raising the temperature to 1573 K, crystalline phases of SiO 2 (cristobalite) and presumably of ZrO 2 /Sb 2 O 5 were observed. Using pyridine as a molecular probe, Brφnsted acid sites on the SiO 2 /ZrO 2 /Sb 2 O 5 matrix, heat treated up to 523 K, were shown to be very stable.