The Solid Acidity of 12-Tungstophosphoric Acid

Solvent effect on the preparation of H3PW12O40 supported on alumina

“…For low concentration of H 3 PW (20 wt.%) there is a wide single peak (line-width of 330 Hz) centered at À13.5 ppm, while hydrated H 3 PW shows a peak at À15.5 ppm (both referenced to 85 wt.% H 3 PO 4 ). It has been discussed that 31 P MAS-NMR signal of H 3 PW depends upon the hydration degree and can be varied from À10.0 to À16 ppm [10]. For the 40 wt.% H 3 PW/ Al 2 O 3 sample, two peaks were observed: a higher one centered at À13.4 ppm and a smaller at À15.5 ppm.…”

“…The Cal-ad method has been applied together with spectroscopic data to analyze acidity of various heteropolyacids such as H 3 PW 12 O 40 [10], supported H 3 PW 12 O 40 on silica [15] and cesium derivatives of H 3 PW [25]. In addition, other solids such as silica gel [26], mordenite [27], Y zeolite [28], ZSM-5 [29], TS-1 [30], sulfated zirconia [31], etc., are among the variety of important solid acids characterized by this method.…”

“…Heteropoly compounds with Keggin structure are the most studied class within POMs, because they possess relatively high thermal stability [8,9] and acidity [10]. A wide range of acid strength can be obtained by substitution of the cation and the addenda atoms, which allow them to be used in several reactions in homogeneous and heterogeneous media [11][12][13].…”

Methacrylic Acid: Not a Mere Product But Activator in the Catalytic Oxidation of Methacrolein?

“…It is well known that cesium salts of Keggin HPAs can hold considerable amount of water in the secondary structure, and some small organic polar molecules can be stabilized within the lattice of HPA [8,9]. However, no data have been reported on the structural aspect of the interaction of MAA with Cs x H 4-x PVMo 11 O 40 .…”

Silica Supported Tungstosilicic Acid as an Efficient and Reusable Catalyst for the One-Pot Synthesis of β-Acetamido Ketones via a Four-Component Condensation Reaction

“…HPAs with Keggin structure are the most studied class within polyoxometalates, because they possess relatively high thermal stability 4 and acidity, 5 and, 12-tungstophosphoric acid and 12-tungstosilicic acid are the usual catalysts of choice because of their high acidic strength, relatively high thermal stability, and lower oxidation potential. HPAs can be used either directly as a bulk material or in supported form in both homogeneous and heterogeneous systems.…”