Influence of composition of heteropolyphosphatotungstate catalyst on epoxidation of propylene

A series of heteropolyphosphatotungstate catalysts with different W/P ratio were prepared by different means. P-31 MAS NMR spectra show every heteropolyphosphatotungstate contains several species with different W/P ratio. Combined with propylene epoxidation results, it is shown that the band at chemical shift ca. delta = 5 ppm maybe corresponds to a catalyst precursor which can be the most efficiently converted to the structure {PO4 [WO(O-2)(2)](4)}(3-). Characterization results of ICP show, the catalysts with low W/P ratio show a good reactivity for propylene epoxidation. (C) 2004 Elsevier B.V. All rights reserved.

Retention modeling and optimization of pH value and solvent composition in HPLC using back-propagation neural networks and uniform design

A novel method for the optimization of pH value and composition of mobile phase in HPLC using artificial neural networks and uniform design is proposed. As the first step. seven initial experiments were arranged and run according to uniform design. Then the retention behavior of the solutes is modeled using back-propagation neural networks. A trial method is used to ensure the predicting capability of neural networks. Finally, the optimal separation conditions can be found according to a global resolution function. The effectiveness of this method is validated by optimization of separation conditions for both basic and acidic samples.

Influence of the deposition energy on the composition and thermal cycling behavior of La-2(Zr0.7Ce0.3)(2)O-7 coatings

Lanthanum-zirconium-cerium composite oxide (La-2(Zr0.7Ce0.3)(2)O-7, LZ7C3) coatings were prepared under different conditions by electron beam-physical vapor deposition (EB-PVD). The composition, crystal structure, surface and cross-sectional morphologies, cyclic oxidation behavior of these coatings were studied. Elemental analysis indicates that the coating composition has partially deviated from the stoichiometry of the ingot, and the existence of excess La2O3 is also observed.

Synthesis of Cu-In-S ternary nanocrystals with tunable structure and composition

Nearly monodisperse Cu-In-S ternary nanocrystals with tunable composition, crystalline structure, and size were synthesized by a hot-injection method using mixed generic precursors. Such ternary nanocrystals with zincblende and wurtzite structure were reported for the first time.