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31.
32.
Garcia EM Sanchez MD Tonetto G Volpe MA 《Journal of colloid and interface science》2005,292(1):179-185
The preparation of different samples of vanadia supported on ultrastable zeolite (VO(x)/USY) is discussed. The samples were prepared in order to obtain highly dispersed V-species, avoiding the formation of crystalline vanadia and the destruction of the zeolite framework. Two methods were employed for preparing VO(x)/USY samples: an organic route using V(AcAc)3 and an inorganic route using NH4VO3. The characterization of the samples was performed with XRD, TPR, NH3-TPD, and N2 isotherms. From these results it is concluded that when VO(x) is supported on the surface of USY from acidic aqueous solution of ammonium metavanadate, the destruction of the zeolite framework is accomplished. For higher pH values in the impregnating solution, undesired V2O5 is formed on the USY surface. On the other hand, VO(x)/USY prepared from the organic precursor shows no destruction of the USY structure. In addition, highly dispersed VO(x) are formed, though for relatively high V loadings (6%) an obstruction of the zeolite windows takes place. The samples are tested as catalysts for gas phase dehydrogenation of n-butane to olefins. The catalysts prepared from NH4VO3 are almost inactive for the reaction. On the other hand, both samples prepared from V(AcAc)3 present initial conversion levels in the 8-12% range. However, the selectivity depends on the V loading, the catalysts with 6% loading being the most selective (75%). The catalytic patterns of the samples (activity and selectivity) are in agreement with the physicochemical features of the VO(x)/USY surface. 相似文献
33.
Sánchez-Moreno MJ Gómez-Coca RB Fernández-Botello A Ochocki J Kotynski A Griesser R Sigel H 《Organic & biomolecular chemistry》2003,1(10):1819-1826
The synthesis of (1H-benzimidazol-2-yl-methyl)phosphonic acid, H2(Bimp)+/-, is described: 2-chloromethylbenzimidazole was reacted with ethylchloroformate to give 1-carboethoxy-2-chloromethylbenzimidazole which was treated with trimethyl phosphite and after hydrolysis with aqueous HBr H2(Bimp)+/- was obtained. In H2(Bimp)+/- one proton is at the N-3 site and the other at the phosphonate group; both acidity constants were determined in aqueous solution by potentiometric pH titrations (25 degrees C; I = 0.1 M, NaNO3) and this furnished the pKa values of 5.37 +/- 0.02 and 7.41 +/- 0.02, respectively. The acidity constant for the release of the primary proton from the P(O)(OH)2 group of H3(Bimp)+ was estimated: pKa = 1.5 +/- 0.2. Moreover, Bimp2- can be further deprotonated at its neutral (N-1/N-3)H site to give the benzimidazolate residue, but this reaction occurs only in strongly alkaline solution (KOH); application of the H_ scale developed by G. Yagil (J. Phys. Chem., 1967, 71, 1034) together with UV spectrophotometric measurements gave pKa = 14.65 +/- 0.12. Comparisons with acidity constants taken from the literature show that this latter pKa value is far too large and this allows the conclusion that an intramolecular hydrogen bond is formed between the (N-1/N-3)H site and the phosphonate group of Bimp2-; the formation degree of this hydrogen-bonded isomer is estimated to be 98 +/- 2%. The general relevance of this and the other results are shortly discussed and the species distribution for the Bimp system in dependence on pH is provided. 相似文献
34.
Solid solutions of GeO2 in Fe2O3 were prepared by mechanically mixing the solids and firing at 1000°C in air, and from a gel obtained by the addition of an alcohol solution of germanium ethoxide to iron dissolved in HNO3. The dried gel was then heated at 1000°C. The solubility limit is 5 mole% GeO2, Fe1.95Ge0.05O3. Similar procedures were used to prepare solid solutions with Si and the solubility limit is greater than 4 mole% SiO2. Firing of mixtures or gels of Fe2O3 containing Mg produces a spinel phase even at the lowest detectable concentrations. The resistivity of pressed pellets of Fe2?xGexO3 varies from about 106 ohm-cm for x = 0 to about 10?1 ohm-cm for x = 0.05. The photoassisted electrolysis of water at Ge-doped Fe2O3 electrodes is demonstrated. The photoelectrochemical cell showed a 0.29-V open-circuit voltage, 1.2-mA/cm2 short-circuit current, 0.31 fill factor, and 0.06% power efficiency. 相似文献
35.
Seghezzo L Trupiano AP Liberal V Todd PG Figueroa ME Gutiérrez MA Da Silva Wilches AC Iribarnegaray M Guerra RG Arena A Cuevas CM Zeeman G Lettinga G 《Applied biochemistry and biotechnology》2003,109(1-3):167-180
A pilot-scale sewage treatment system consisting of two upflow anaerobic sludge bed (UASB) reactors followed by five waste stabilization ponds (WSPs) in series was studied under subtropical conditions. The first UASB reactor started up in only 1 mo (stable operation, high chemical oxygen demand [COD] removal efficiency, low volatile fatty acids concentration in the effluent, alkalinity ratio above 0.7, biogas production above 0.1 Nm3/kg of CODremoved). Removal efficiencies up to 90% were obtained in the anaerobic steps at a hydraulic retention time of 6 + 4 h (80% removal in the first step). Fecal coliform removal in the whole system was 99.9999% (99.94% in anaerobic steps and 99.98% in WSPs). COD balances over UASB reactors are provided. A minimum set of data necessary to build COD balances is proposed. Intermittent sludge washout was detected in the reactors with the COD balances. Sludge washout from single-step UASB reactors should be monitored and minimized in order to ensure constant compliance with discharge standards, especially when no posttreatment is provided. The system combined high COD and fecal coliform removal efficiency with an extremely low effluent concentration, complying with discharge standards, and making it an attractive option for sewage treatment in subtropical regions. 相似文献
36.
37.
M. Chatry M. Henry M. In C. Sanchez J. Livage 《Journal of Sol-Gel Science and Technology》1994,1(3):233-240
The hydrolysis and condensation of zirconium n-propoxide in n-propanol have been chemically controlled via the complexation of the zirconium precursor with acetylacetone. The size of the zirconium oxide-based particles is mainly controlled by the complexation ratio x=[acac]/[Zr]. the mean size increases from nanometric to submicronic range when x decreases from 1 to 0.1. Amorphous colloidal particles are obtained at room temperature. They result from a competitive growth/termination mechanism of zirconium-oxo species in the presence of acac surface capping agents. However non-aggregated nanocrystalline particles of tetragonal zirconia, about 2 nm in diameter are formed upon aging at 60°C when hydrolysis is performed in the presence of paratoluene sulfonic acid (PTSA). 相似文献
38.
A multiresidue, automated and rapid method for the determination of pesticide residues in olive oil is presented. The method employs the through oven transfer adsorption-desorption interface for the on-line coupling of reversed-phase liquid chromatography and gas chromatography. In this fully automated system, olive oil is directly injected with no sample pre-treatment step other than filtration. Methanol-water is used as eluent in the liquid chromatography pre-separation step. The selected liquid chromatography fraction containing the pesticides is automatically transferred to the gas chromatography. The liquid chromatography column flow during elution is different from the flow during the transfer. Using a flame ionisation detector, pesticide detection limits varied from 0.1 to 0.3 mg/l. 相似文献
39.
Wege HA Aguilar JA Rodríguez-Valverde MA Toledano M Osorio R Cabrerizo-Vílchez MA 《Journal of colloid and interface science》2003,263(1):162-169
A new methodology capable of providing reliable and reproducible contact angle (theta) data has been employed to study the effect of clinical treatments grinding, acid etching, and deproteinization on medial dentin tissue. It is based on the application of the ADSA-CD algorithm to the determination of low-rate dynamic contact angles, obtained from slowly growing drops, and on contact angle measurement, as well as spreading behavior analysis, during the relaxation of the system (water on treated dentin) after initial drop growth. The theta data obtained were substantially more reproducible than those obtained with classical methods. A net effect of the treatment on theta was found, increasing dentin wettability: theta (polished) >theta (etched) >theta (deproteinized). The spreading rates correlate with the angles and are adequate for the dentin surface characterization. ANOVA and SNK tests show that for advancing contact angles the means corresponding to all treatments are significantly different. In the relaxing phase, mean angle and spreading rates on polished dentin differ significantly from those on etched and deproteinized dentin, but the latter do not differ significantly from each other. 相似文献
40.
Determination of triclosan in foodstuffs 总被引:1,自引:0,他引:1
Sanches-Silva A Sendón-García R López-Hernández J Paseiro-Losada P 《Journal of separation science》2005,28(1):65-72
A reverse-phase high-performance liquid chromatographic (RP-HPLC) method coupled with an ultraviolet detector was developed to determine triclosan which had migrated into foodstuffs from packaging materials. The method includes extraction with hexane, followed by evaporation to dryness and residue re-dissolution in ACN 90%. Chromatographic separation was performed with a Kromasil 100 C18 column (15 cm x 0.4 cm ID, 5 microm particle size) at 30 degrees C and using ACN and water as mobile phases. Regarding recoveries, good results (higher than 83% and lower than 112%) were obtained for the three representative food matrixes selected (orange juice, chicken breast meat, and Gouda cheese). 相似文献