A study of the decomposition behaviour of 12-tungstophosphate heteropolyacid in solution

Abstract

In this paper, the decomposition of H3PW12O40 in aqueous solution or in mixed solutions of water–ethanol or water–acetone is investigated by potentiometric titration and 31P NMR. Identification of the products from H3PW12O40 decomposition over a pH range of 1–12 was achieved using preparation high performance liquid chromatography (Pre-HPLC) combined with IR, UV–vis spectroscopy, and inductively coupled plasma atomic emission spectroscopy (ICP). It is found that H3PW12O40 in aqueous solution decomposes in a stepwise fashion with increasing pH, with the following solution compositions: [PW12O40]3– (at pH ~ 1) [Formula: see text] [PW12O40]3– + [P2W21O71]6– + [PW11O39]7– (at pH 2.2) [Formula: see text] [PW12O40]3– + [P2W21O71]6– + [PW11O39]7– + [P2W18O62]6– + [P2W19O67]10– (at pH 3.5) [Formula: see text] [P2W21O71]6– + [PW11O39]7– + [P2W18O62]6– (at pH 5.4) [Formula: see text] [PW9O34]9– (at pH 7.3) [Formula: see text] PO43– + WO42– (pH > 8.3). In the first stages at pH < 8, H3PW12O40 decomposes partially with removal of W=O units. In the second stage at pH > 8, tungstophosphoric completely decomposes to PO43–. In contrast, the decomposition of H3PW12O40 is reduced, or the stability of the [PW12O40]3– anion is enhanced, in ethanol–water or acetone solution at pH < 8. Key words: 12-tungstophosphate heteropolyacid, decomposition behaviour, potentiometric titration, 31P NMR, preparation high performance liquid chromatography.

Influence of synthesis conditions on the performance of chitosan–Heteropolyacid complexes as membranes for low temperature H2–O2 fuel cell

“…(PW 12 O 40 ) 3À released by PTA impregnated AAM. In the employed concentrated PTA aqueous solution (0.38 M) only (PW 12 O 40 ) 3À anions are present, while lacunary or defective Keggin ions concentration is negligible [21]. When the two electrolytes come in contact, the ionic crosslinking brings to the formation of CS/PTA composite membrane through the following chemical reaction:…”

A study of 12-tungstosilicic and 12-molybdophosphoric acids in solution

“…The same system was investigated over a wide pH range (1-12) using preparative high performance liquid chromatography combined with IR, UV-Vis and ICP spectroscopy. 20,21 Smith and Patrick applied 31 P-and 183 W-NMR spectroscopy in a detailed study of tungstophosphoric and tungstosilicic acids in aqueous solutions. 22−24 The species present in these systems were identified and quantified as a function of pH.…”

A Comparison of Catalytic Properties of Cs x H3−x PW12O40 Salts of Various Cesium Contents in Gas Phase and Liquid Phase Reactions

“…In fact the pH values increases from Cs2 up to Cs3 salt ( Table 2). Literature data show that in homogeneous solution of HPW the Keggin anions are stable at strong acidic conditions (pH *1) because of their transformation to lacunary forms at higher pH [25]. However, owing to very low solubility of Cs2.5 salt in water or methanol determined by Kozhevnikov et al [26] to be 3.7 and 2.7%, respectively, this transformation seems to be neglected in our experiments.…”