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The vanadium phosphorous oxide (VPO) catalysts, supported on Santa Barbara amorphous molecular sieve (SBA-15) with different vanadium loadings, were prepared by the precipitation method in an organic phase. Techniques such as X-ray diffraction, Bruner–Emmett–Teller method, scanning electron micrograph (SEM), and transmission electron micrograph (TEM) were used for characterization of the catalysts. The high surface area, large pore volume, and pore size of SBA-15 provide an excellent dispersion of (VO)2P2O7species on the support surface. Oxidation of various alcohols was studied in the liquid phase over the VPO/SBA-15 catalyst, usingtert-butylhydroperoxide as an oxidant. The activities of VPO/SBA-15 samples were considerably higher than that of the bulk VPO catalyst. At 90°C, the obtained activities were 0.567 andover the bulk VPO and 15 wt.% VPO/SBA-15 catalysts, respectively. The effects of substrates, oxidants, reaction time, oxidant/alcohol molar ratio, solvents, amount of catalyst, catalyst recycling, and leaching of VPO in the liquid phase were also investigated. [ABSTRACT FROM PUBLISHER]

Vanadium phosphorus oxide (VPO) catalysts synthesized via hydrothermal method were introduced with some different dopants, Cr, Ni, Fe, and Mn during the preparation of the precursors, VOHPO4 · 0.5H2O. All modified precursors were subsequently transformed under reaction conditions to give the active phase, (VO)2P2O7. Several techniques were used to characterize the physicochemical properties of the catalysts, such as X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), H2-temperature programmed reduction (TPR), laser Raman spectroscopy (LRS), and chemical analysis. The catalytic performance of the catalysts for selective oxidation of n-butane to maleic anhydride has been carried out by using a fixed bed microreactor (673 K, gas hourly space velocity [GHSV] = 2,400 hr-1). The results show that the addition of dopants into the VPO catalysts increased the surface area of the catalysts and induced the formation of V5+ phases as shown in XRD and LRS spectra that promoted the catalytic performance. A further water reflux treatment to all the precursors gave catalysts with only (VO)2P2O7 phase. However, the activity and selectivity of these catalysts were reduced markedly. [ABSTRACT FROM AUTHOR]

The molecular organization of N,N'-dimethyl-N,N'-dioctylhexylethoxymalonamide (DMDOHEMA), the current reference extractant for the DIAMEX (DIAMide EXtraction) process, is correlated with its water extraction properties from neutral media. The aggregation of DMDOHEMA in n-heptane was investigated by vapor pressure osmometry (VPO) and the aggregate speciation characterized by combined small-angle neutron and X-ray scattering (SANS and SAXS, respectively). Two approaches were taken to model the aggregation of the diamide and the water extraction as a function of the diamide concentration by taking into account a single aggregation equilibrium with an average aggregation number N equal to 4.28 ± 0.05; and a competition between two types of aggregates in the organic phase, namely, aggregates of the reverse micelle type with 4 diamides per aggregate, and an oligomeric structure composed of about 10 diamide molecules which appears at high extractant concentration (>1 mol/L). In both cases, the supramolecular speciation representing the monomers/aggregates distribution was determined, and for each supramolecular organization, a solubilization parameter was calculated using the Sergievskii-Dannus relationship. Thus, the correlation between the two types of micellization of the diamide and the extraction of water into the organic phase was demonstrated. The larger aggregates can extract about five times more water than monomers. [ABSTRACT FROM AUTHOR]