Preparação, caracterização e aplicação de H3PW12O40 suportado em zircônia

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

12-tungstophosphoric acid (H3PW12O40 or HPW) is a heteropolyacid largely used for homogeneous and heterogeneous catalysis. In this work, HPW was supported on zirconia (ZrO2) by impregnation in acidic (HCl 0.1 mol/L) aqueous solution at different ratios (5, 10, 15, 20, 25, 40 and 60 mass %). The solids were characterized by FTIR, XRD, FT-Raman, and 31P MAS-NMR. The results demonstrated that under the experimental conditions, no decomposition of the Keggin structure was observed. XRD powder diffractions indicated high dispersion of HPW over the support, and only a monoclinic phase was present for ZrO2. The monolayer for supported HPW on zirconia was about 20%. The study of the thermal stability showed that Keggin anion starts to decompose at 500 C, when heated for 4 h, which is attested by its decrease of catalytic activity. Once prepared and characterized, the supported catalysts were used for kinetics studies of the transesterification of soybean oil with ethanol and esterification of oleic acid with ethanol. The experimental conditions tested were: different ratios of HPW/support, ethanol/acid, ethanol/oil and time, in order to optimize the catalytic performance of this material as well as to correlate with the chemical properties of the catalysts. The results showed a satisfactory conversion (88% for 4 h) for the esterification, but lower conversion (10.5% for 24 h) for the transesterification. In addition, the main advantages of these acidic catalysts are easy operation, transport and stocking because of the solid nature. For both reactions, the catalysts deactivated when reused directly (i.e., without any treatment) due to either leaching of HPW or adsorption of organic molecules on the active sites of the supported catalyst.

ASSUNTO(S)

catálise zircônia heteropoliácido quimica

ACESSO AO ARTIGO

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