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排序方式: 共有134条查询结果,搜索用时 31 毫秒
1.
Anne M. Garrido Pedrosa M. J. B. Souza A. O. S. Silva Dulce M. A. Melo A. S. Araujo 《Journal of Thermal Analysis and Calorimetry》2006,84(2):503-509
The study of the incorporation
of rare earth elements as additives in Y zeolites is a very interesting field
of research, mainly by its potential application as additives in catalytic
cracking process. In this work was studied the thermal and structural properties
of cerium, holmium and samarium supported on HZSM-12 zeolite. The obtained
materials were characterized by X-ray diffraction (XRD), infrared spectroscopy
(FTIR), nitrogen adsorption, thermogravimetry (TG/DTG), differential scanning
calorimetry (DSC) and differential thermal analysis (DTA). TG/DSC/DTA analyses
showed that the dehydration temperatures of RE/HZSM-12 zeolites (RE=Ce, Ho, Sm) increase in relation to pure HZSM-12.
The acid properties were investigated by pyridine thermo desorption via TG.
The results showed two events of mass loss attributed to elimination of pyridine
adsorbed on the weak+medium acid sites and on the strong acid sites. 相似文献
2.
A correction of a recent work on the dependence of the DC conductivity of diluted colloidal suspensions on the size, zeta potential, and state of motion of dispersed particles (C. Grosse, S. Pedrosa, V.N. Shilov, J. Colloid Interface Sci. 251 (2002) 304) is presented. It is shown that the procedure used in that work to calculate the contribution of the particles to the conductivity of the suspension leads to a result that includes the variation of the conductivity of the dispersion medium. Revised analytical and numerical calculations are presented, which strongly reinforce the conclusions reached in the original work: The expression for the conductivity increment based on the value of the dipolar coefficient of the suspended particles (calculated taking into account their electrophoretic motion) appears to be valid over the whole range of particle sizes. 相似文献
3.
Chiral 1,3-perhydrobenzoxazines 1, 2, and 9-14, prepared by condensation of 8-(benzylamino)menthol with different aldehydes, react with alkylmagnesium bromides and trimethylaluminum leading to the open amino alcohols 3a-d, 4a-d, and 15-20 in excellent chemical yields and good to excellent diastereomeric excess. The sequential elimination of the menthol appendage by heating with P(2)O(5) and the benzyl group by hydrogenolysis lead to primary amines 7a-d, 8a-d, and 27-30 in excellent chemical yields and ee. The addition of the alkyl group from the Grignard derivatives and the methyl group from the trimethylaluminum occurs from opposite sides of the heterocycle, yielding the final primary amines with the same stereochemistry. 相似文献
4.
[reaction: see text] Condensation of N-substituted glycines with chiral 3-allyl-2-formyl perhydro-1,3-benzoxazines forms an azomethine ylide that cyclizes to give octahydropyrrolo[3,4-b]pyrrole derivatives. The [3 + 2] dipolar cycloadditions are stereoespecific leading to a single diastereoisomer. The chemical yields are dependent on the reaction temperature and the presence or absence of a base. 相似文献
5.
S. M. Bardavid G. C. Pedrosa M. Katz M. A. Postigo P. García 《Journal of solution chemistry》1996,25(11):1125-1135
Exces molar volumes, and excess viscosities of then-hexane+dichloromethane+tetrahydrofuran system have been determined at 25°C by measuring densities and viscosities. Different expressions exist in the literature to predict these excess properties from binary data. The empirical correlation of Cibulka is shown to be the best in this system. 相似文献
6.
Angel Alberola Celia Andrs Alfonso Gonzlez Ortega Rafael Pedrosa Martina Vicente 《Journal of heterocyclic chemistry》1987,24(3):709-713
Unsymmetrically substituted β-aminoenones react with malononitrile, cyanomethylphenylsulfone, benzoyl-acetonitrile and ethyl cyanoacetate, in very mild conditions, to yield regiospecifically 3-functionalized 2(1H)-pyridones in high yields. 相似文献
7.
The dependence of the DC conductivity of diluted colloidal suspensions on the size, zeta potential, and state of motion of the dispersed particles is analyzed both theoretically and numerically. It is shown that the simple formula that represents the conductivity as a sum of products: charge times mobility, taken over all the carriers present in the suspension, is only valid for exceedingly low values of the product kappaa. In contrast, the formulation based on the value of the dipolar coefficient of the suspended particles seems to be valid for all the range of particle sizes. This assertion is only true if the dipolar coefficient is calculated taking into account the electrophoretic motion of the particles. For very low values of the product kappaa, the dipolar coefficient of particles free to move can be several orders of magnitude larger than that of immobile particles. 相似文献
8.
A simple rapid, accurate, and reliable method of simultaneous determination of arsenic, germanium, phosphorus, and silicon is reported. The method involves first, the determination of germanium as its phenlfluorone complex and its selective extraction with isoamyl alcohol. Phosphorus is next determined as its heteropoly blue after selective extraction of phosphomolybdic acid by isobutyl acetate at pH 1.0-0.8 and its direct reduction in this solvent. Silicon is then determined after its extraction as silicomolybdic acid by isooctyl alcohol at pH < 0.4 and direct reduction in the solvent phase. Finally, arsenic is determined in the remaining aqueous phase after reduction to its heteropoly blue. 相似文献
9.
A. M. Garrido Pedrosa M. J. B. Souza D. M. A. Melo A. S. Araujo 《Journal of Thermal Analysis and Calorimetry》2007,87(2):351-355
The thermo-programmed reduction study of
Pt/WOx–ZrO2 materials
prepared with different tungsten loading were performed by thermogravimetry.
The samples were synthesized by impregnation method and calcined at 600, 700
and 800°C. The characterizations of both un-calcined and calcined materials
were carried out using different techniques: thermal analysis (TG and DTA),
X-ray diffraction (XRD) and thermo-programmed reduction (TPR). TG and DTA
analysis of un-calcined were used to determination of calcination temperatures
of the samples. XRD diffractograms were useful to help us in the determination
of phase presents. TPR profiles showed between three and four events at different
temperatures attributed to platinum reduction and the different stages of
tungsten specie reduction. 相似文献
10.
Sodiun borohydride reacts with oxazolidinium methiodides derived from ephedrine and pseudoephedrine, in ethereal solvents, cleaving regioselectively the C-N bond of the ring and leading, in good yields, to chiral amine-borane adducts of know absolute configuration. The 1HNMR data allow to predict the most stable conformation. 相似文献