Phosphoric acid adsorbed on silica-ceria matrix obtained by sol-gel method: studies of local structure, texture and acid property

• Autor(a) principal: Pissetti,Fábio L.
• Data de Publicação: 2007
• Outros Autores: Francisco,Maria Suzana P., Landers,Richard, Gushikem,Yoshitaka
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Journal of the Brazilian Chemical Society (Online)
• Texto Completo: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532007000500015
• topic: silica-ceria; silica-ceria-phosphate; sol-gel method; acid sites

SiO2/CeO2 mixed oxide (designated as SC) with variable ceria contents, SC1 = 5.6, SC2 = 8.0 and SC3 = 13.0 wt%, prepared by the sol-gel processing method, were obtained as amorphous solids possessing specific surface areas of SC1 = 463, SC2 = 474 and SC3 = 460 m²g-1. Phosphate ions were immobilized onto the surface of these solids through Ce-O-P bonding by immersing SC into a phosphoric acid solution. Solids with the following P contents were obtained (in atom %): SCP1 = 0.60, SCP2 = 0.71 and SCP3 = 1.63. The binding energy peak P 2p3/2 at ca. 134.0 eV, observed by XPS, and the 31P MAS NMR single peak, observed at ca. -10 ppm, revealed that H2PO4- is the species present on the surface of the matrices. Using pyridine as a molecular probe, only Brønsted acid sites could be detected. The amount of these acid sites, determined by ammonia gas adsorption on the surface, reached the following values for each phosphate-treated solid: SCP1 = 0.37, SCP2 = 0.43 and SCP3 = 0.51 mmol g-1.