Papers by Keyword: 12-Tungstophosphoric Acid

Abstract: 12-tungstophosphoric acid was supported on amine-modified SBA-15 by impregnation. The structure and properties of the catalyst were characterized by FT-IR spectroscopy, X-ray diffraction, N2 adsorption-desorption, TEM,Raman spectra and NH3–TPD technology.the result confirmed the mesostructure for SBA-15 and the Keggin structure of the heteropolyanions was preserved. The tungstophosphoric acid can disperse in the pore of the support SBA-15/NH2, but the acidity of the catalyst reduced. The catalytic activities of the catalysts were evaluated for the esterification reaction of ethyl acetoacetate and ethylene glycol .and the catalysts supported on amine-modified SBA-15 show excellent reusability and selectivity.

Abstract: The K3PW12O40, K2.5H0.5PW12O40, K2HPW12O40, KH2PW12O40, Ag3PW12O40 and Tl3PW12O40 salts were synthesized and characterized by thermal analysis, IR and impedance spectroscopy, and SEM. The physicochemical characterization of acid alkaline salts revealed the presence of biphasic mixtures of unreacted heteropoly acid and its neutral salt. The unreacted heteroply acid could be washed away by treating the acid salt with water.

Abstract: On the basis of previously recorded Raman and IR spectral data on different crystallohydrates of alkaline-earth 12-tungstophosphoric acid salts (obtained from mother solution and those kept under constant relative humidity (RH) of 35%), an effort was made to determine the position of cations in the Keggin unit. Shifts or band splitting in vibrational spectra of the salts, as well as the changes in band intensities were found to be connected to the cation properties. The spectral data also demonstrated a great influence of cation properties on the secondary structure of Keggin anions and dynamics of protonic species.

Abstract: In our previous work we investigated the conductivity and dielectric relaxation phenomena in heteropoly acids and their salts. In this work, we have studied the conductivity of grains and grain boundaries in compressed powders of 12-tungstophosphoric acid (WPA) salts with univalent and bivalent ions. The method of impedance spectroscopy has been employed in the frequency range from 5 Hz to 500 kHz. We obtained grains and grain boundaries conductivities as well as corresponding activation energies. Grain conductivity in all investigated salts is always higher than the grain boundary conductivity.