Phosphotungstic acid

About: Phosphotungstic acid is a research topic. Over the lifetime, 1925 publications have been published within this topic receiving 38059 citations. The topic is also known as: Phosphowolframic acid.

Insight into Proton Transfer in Phosphotungstic Acid Functionalized Mesoporous Silica-Based Proton Exchange Membrane Fuel Cells

Abstract: We have developed for fuel cells a novel proton exchange membrane (PEM) using inorganic phosphotungstic acid (HPW) as proton carrier and mesoporous silica as matrix (HPW-meso-silica) . The proton conductivity measured by electrochemical impedance spectroscopy is 0.11 S cm^(–1) at 90 °C and 100% relative humidity (RH) with a low activation energy of 14 kJ mol^(–1). In order to determine the energetics associated with proton migration within the HPW-meso-silica PEM and to determine the mechanism of proton hopping, we report density functional theory (DFT) calculations using the generalized gradient approximation (GGA). These DFT calculations revealed that the proton transfer process involves both intramolecular and intermolecular proton transfer pathways. When the adjacent HPWs are close (less than 17.0 A apart), the calculated activation energy for intramolecular proton transfer within a HPW molecule is higher (29.1–18.8 kJ/mol) than the barrier for intermolecular proton transfer along the hydrogen bond. We find that the overall barrier for proton movement within the HPW-meso-silica membranes is determined by the intramolecular proton transfer pathway, which explains why the proton conductivity remains unchanged when the weight percentage of HPW on meso-silica is above 67 wt %. In contrast, the activation energy of proton transfer on a clean SiO_2 (111) surface is computed to be as high as 40 kJ mol^(–1), confirming the very low proton conductivity on clean silica surfaces observed experimentally.

Synthesis and characterization of mesoporous phosphotungstic acid/TiO2 nanocomposite as a novel oxidative desulfurization catalyst

Abstract: A series of mesoporous phosphotungstic acid/TiO 2 (HPW/TiO 2 ) nanocomposites with various HPW contents have been synthesized by evaporation-induced self-assembly method. These nanocomposites were used as catalysts for oxidative desulfurization of model fuel, which was composed of dibenzothiophene (DBT) and hydrocarbon, and used H 2 O 2 as oxidant. These catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption isotherm, transmission electron microscopy (TEM), FTIR and UV–vis. Characterization results suggest that these mesoporous HPW/TiO 2 possessed relatively uniform channel-like pores with Barrett–Joyner–Halenda (BJH) pore size of about 4 nm. The Brunauer–Emmett–Teller (BET) surface of the mesoporous HPW/TiO 2 slightly increases with the increase of HPW content and reach to a peak value of 176 m 2 /g and 0.25 cm 3 /g when the HPW content is 30 wt%. Keggin-type heteropolyacids (HPAs) has been encapsulated into anatase TiO 2 framework and the average size of TiO 2 nanoparticles is 8 nm. Catalytic oxidation results show that the catalysts are very active in refractory bulky molecule organosulfur compounds in fuel oil. The oxidative removal of DBT increases as the HPW content increases. The mesoporous HPW/TiO 2 also shows high selectivity for DBT oxidation in the DBT–petroleum ether–benzene system. The selective desulfurization ratio reach to 95.2% with mesoporous HPW/TiO 2 (20 wt%) catalyst under the reaction condition of 333 K, 2 h. In addition, the mesoporous HPW/TiO 2 catalyst shows excellent reusing ability, which makes it a promising catalyst in oxidative desulfurization process.

Location, acid strength, and mobility of the acidic protons in Keggin 12-H3PW12O40: a combined solid-state NMR spectroscopy and DFT quantum chemical calculation study.

Abstract: Solid-state C-13 NMR experiments and quantum chemical Density Functional Theory (DFT) calculations of acetone adsorption were used to study the location of protons in anhydrous 12-tungstophosphoric acid (HPW), the mobility of the isolated and hydrated acidic protons, and the acid strength heterogeneity of the anhydrous hydroxyl groups. This study presents the first direct NMR experimental evidence that there are two types of isolated protons with different acid strengths in the anhydrous Keggin HPW. Rotational Echo DOuble Resonance (REDOR) NMR experiments combined with quantum chemical DFT calculations demonstrated that acidic protons in anhydrous HPW are localized on both bridging (O-c) and terminal (O-d) atoms of the Keggin unit. The CP/MAS NMR experiments revealed that the isolated acidic protons are immobile, but hydrated acidic protons are highly mobile at room temperature. The isotropic chemical shift of the adsorbed acetone suggested that the acid strength of the H(H2O)(n)(+) species in partially hydrated HPW is comparable to that of a zeolite, while the acidity of an isolated proton is much stronger than that of a zeolite. Isolated protons on the bridging oxygen atoms of anhydrous HPW are nearly superacidic.