Ammonium Metatungstate Modified Borated Zirconium
Samples of tungsten-modified borated zirconia are often prepared to be used as catalyst in 2-phenoxyethanol acetylation. The borated zirconium were obtained by impregnation of zirconium dioxide (S2 and S4) obtained by the micellar method using different zirconium precursor concentrations with boric acid solution containing 0.3 moles B/dm3. These solids and the zirconium dioxide were impregnated with two concentration levels of ammonium metatungstate solutions (0.11 and 0.22 moles W/dm3). The solids containing boron mainly have amorphous characteristics and strong acidity, while those that contain only tungsten showed stronger acidity and evidence of the presence of a crystalline phase.
The specific surface area and the pore volume slightly decreased in the solids obtained by adding tungsten to borated zirconia, and more markedly in those that contain only tungsten, and the mean pore size increased with respect to the parent support. It was observed that in the 2-phenoxyethanol acetylation using acetic acid as acylating agent and tungsten-modified borated zirconia as catalyst, the yield to acetylated product was high and it is correlated with the acid strength of the catalysts. In turn, the solids that contain only tungsten have a correlation with the acidity, but lead to low yield values due to a poorer dispersion of the tungsten species. The best yield was obtained with the catalyst prepared with the borated S4 zirconia containing 15% g B2O3/100 g support and 12.5% g W/100 g support. Using this catalyst and the same reaction conditions, the acetylation of different alcohols and phenols was studied, the reactivity order being as follows: primary alcohols > secondary alcohols > phenols.
Ammonium metatungstate (AMT) is an important intermediate compound of tungsten hydrometallurgical process, the yellowish white crystal. The solubility of ammonium metatungstate is the largest in the tungsten compounds, which is greater than 300g WO3/100ml H2O (in 25 ℃).
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