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|Type:||Artigo de periódico|
|Title:||Silica-zirconia-phosphate composites: a study of their synthesis, proton exchange capacity and ammonia gas adsorption|
de Castro, SC
|Abstract:||Phosphoric acid was adsorbed on SiO2/ZrO2 mixed oxides prepared by a sol-gel processing method. The obtained composites, SiO2/ZrO2/phosphate with variable compositions, are very porous, having specific surface areas between 400 and 650 m(2)g(-1) and average pore volumes between 0.29 and 0.38 cm(3) g(-1). The binding energy P-2p = 134.5 eV and the atomic ratio P/Zr similar to 2, both determined by the X-ray photoelectron spectroscopy technique, and corroborated by the P-31 high power decoupling magic angle spinning and NMR techniques indicated that H2PO4- is the species present in the composites. The materials are all thermally very stable, and the phosphate entities show little thermal mobility. Under heat treatment up to 1273 K, the SiO2/ZrO2/phosphate samples did not show any phase transition corresponding to the transformation of phosphate to the pyrophosphate species. Large proton exchange capacities, between 1.22 and 2.90 mmol g(-1), were obtained. Ammonia gas was rapidly adsorbed by the materials with the formation of NH4+ on the solid surface; thermodesorption occurred above 949 K. (C) 2000 Elsevier Science B.V. All rights reserved.|
|Editor:||Elsevier Science Bv|
|Appears in Collections:||Artigos e Materiais de Revistas Científicas - Unicamp|
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