Étude par RMN MAS liquide de³¹P de l'évolution des solutions d'acide 12-tungstophosphorique (ion de Keggin) en fonction du pH, de la dilution et du temps

\nHeteropoly acids of the Keggin type H$_{\\rm 8-x}$XM$_{12}$O$_{40}$, where X is the central atom (Si, P,...), x its\noxidation state and M, a transition metal (Mo, W,...) are well known as oxidation and acid catalysts. The\nchief disadvantage of heteropoly acids is their weak thermal stability, resulting in a degradation of the active\nphase. Therefore, several attempts were taken on to stabilize them by supporting on various carriers. Silica is\nan excellent support for the heteropoly acids. Generally, the solid is prepared by impregnation of the active\nphase by a solution. In this paper, we proposed to determine and quantify the different tungstophosphate\nspecies by choosing the optimal conditions to incorporate one of such species. Results obtained by $^{31}$P NMR\nin aqueous medium of tungstophosphate species were discussed by varying the pH, the dilution and the evolution duration.\n