Synthesis and characterization of tungstophosphoric acid-modified mesoporous sponge-like TUD-1 materials

Mesoporous sponge-like siliceous materials (TUD-1) were synthesized using TEOS (tetraethylorthosilicate) as a precursor of silica and TEA (triethanolamine) as a mesostructure-directing agent. Different TEOS/TEA molar ratios and hydrotreatment times were used, and their influence on the textural and morphological properties of the solids was evaluated. They were characterized by transmission electron microscopy (TEM), X-ray diffraction, and N₂ adsorption/desorption isotherm analysis. By changing the TEOS/TEA molar ratio, micro-mesoporous and mesoporous (with a narrow or wide pore size distribution) materials were obtained. The increment of hydrotreatment times increased the average pore size of TUD-1 and significantly reduced the specific surface area. TEM images showed that the solids were formed by agglomerates of rather spherical particles whose size increased with the increment of the TEA amount used. The structure and morphology of TUD-1 solids modified with tungstophosphoric acid (TPA) were similar to those of the mesoporous silica used as support. Their diffraction patterns did not display any of the characteristic peaks of TPA or its more common hydrates, suggesting that TPA was well dispersed on the support as a noncrystalline phase. In addition, the characterization of all the solids impregnated with TPA by FT-IR and ³¹P NMR indicated the presence of undegraded [PW₁₂O₄₀]^3? and [H_3?XPW₁₂O₄₀]^X? species interacting electrostatically with the ≡Si–OH₂⁺ groups, and by potentiometric titration it was estimated that the solids presented very strong acid sites. The TUD-1 solids modified with TPA gave excellent yield in the solvent-free synthesis of 2,4,5-triphenyl-1H-imidazole, without formation of by-products resulting from competitive reactions or decomposition products. In summary, they are good candidates to be used in multicomponent reactions catalyzed by acids.

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Quantum macroscopic equations from Bohm potential and propagation of waves

Bohm’s interpretation of Quantum Mechanics leads to the derivation of a Quantum Kinetic Equation. In the present work, moments of this kinetic equation are taken, thus deriving conservation equations. These macroscopic equations are then applied to study the propagation of longitudinal density perturbations in neutral gases and plasmas, of either fermions or bosons. The dispersion relation is derived and the effect of the Bohm potential shown; the speed of propagation calculated and the difference between fermions and bosons investigated. Pseudosonic waves in quantum plasmas are obtained including the effect of the Bohm potential.     

Direct modification with tungstophosphoric acid of mesoporous titania synthesized by urea-templated sol-gel reactions

A series of mesoporous titania materials modified with tungstophosphoric acid (TPA) were successfully synthesized by using urea as low-cost template via sol-gel reactions, followed by removing the urea by extraction with water. They were characterized by FT-IR, 31P MAS-NMR, XRD, DTA-TGA, DRS, TEM and BET. The samples presented mesopores with a diameter higher than 3.0 nm. The S(BET) of the solids decreases with the increase of the TPA content and with the increase of the calcination temperature. According to FT-IR and 31P MAS-NMR studies the main species present in the samples is [PW12O40]3- anions, which was partially transformed into [P2W21O71]6- and [PW11O39]7- anion during the synthesis and drying step. The XRD patterns of the modified samples only exhibited the characteristic peaks of anatase phase. The presence of TPA retarded the crystallization of the anatase phase and its transformation into rutile phase. The point of zero charge decreased in parallel with the increment of tungstophosphoric acid in the samples and with the increase of the calcination temperature. The band gap energy decreased as a result of the introduction of TPA into the TiO2 matrix, but remained practically constant with the increase of the calcination temperature.