共查询到20条相似文献,搜索用时 125 毫秒
1.
Valentina M. Bondareva Valentina M. Bondareva Tamara V. Andrushkevich Tamara V. Andrushkevich Galina I. Aleshina Galina I. Aleshina Ludmila M. Plyasova Ludmila M. Plyasova Larisa S. Dovlitova Larisa S. Dovlitova Olga B. Lapina Olga B. Lapina Dzhalil F. Khabibulin Dzhalil F. Khabibulin Anatoliy A . Vlasov 《Reaction Kinetics and Catalysis Letters》2006,87(2):377-386
Summary Catalytic and physicochemical properties of V-Mo-Nb oxide catalysts (V0.3Mo1Nbx, where x = 0.05, 0.15, 0.22, and 0.27) have been studied in the ammoxidation of ethane. An increase in the Nb content in
the samples is accompanied by an increase in the catalytic activity and selectivity to acetonitrile. It was established that
a triple Mo5O14-like phase with a variable composition (V0.23 ±0.3Mo1Nbx, where х = 0.2?0.37) acts as an active component in the catalyst.</o:p> 相似文献
2.
M. D. Engelmann L. A. Metz N. E. Ballou 《Journal of Radioanalytical and Nuclear Chemistry》2006,268(2):201-204
Two
methods capable of near complete recovery of technetium adsorbed on charcoal
are presented. The first involves liquid extraction of the technetium from the
charcoal by hot 4M nitric acid. An average recovery of 98% (n=3) is
obtained after three rounds of extraction. The second method involves dry
ashing with air in a quartz combustion tube at 400-450 °C. This method yields
an average recovery of 96% (n=5). Other thermal methods were attempted, but
resulted in reduced recovery and incomplete material balance.</p>
</p> 相似文献
3.
Xuejun Xu Nelly M. Rodriguez Nelly M. Rodriguez R. Terry K. Baker R. Terry K. Baker 《Reaction Kinetics and Catalysis Letters》2006,87(2):305-312
Summary The potential of graphite nanofiber (GNF) supported silver catalysts to function as a catalyst system for the partial oxidation
of ethylene to ethylene oxide has been investigated at 220°C and atmospheric pressure. It was found that when the metal was
dispersed on “platelet”GNF that had been modified by pretreatment in argon at 2300°C the performance of the catalyst was superior
to that of the current commercial system Ag/a-alumina, when reacted under the same. It is suggested that the observed enhancement
in both activity and selectivity is related to electronic perturbations in the metal particles when dispersed on a highly
conductive support medium.</o:p> 相似文献
4.
Summary From extraction experiments and<span style='font-size:12.0pt;font-family:Symbol; mso-bidi-font-family:Symbol'>g-activity measurements,
the extraction constant corresponding to the equilibrium Ba2+(aq)+SrL2+(nb)?BaL2+(nb)+Sr2+(aq) taking place in the two-phase water-nitrobenzene system (L= valinomycin; aq= aqueous phase,</o:p>nb= nitrobenzene phase)
was evaluated as logKex(Ba2+, SrL2+)=1.3. Furthermore, the stability constant of the valinomycin-strontium complex in nitrobenzene saturated with water was calculated
for a temperature of 25 °C: logbnb(SrL2+)=5.4. 相似文献
5.
Ching Hsuan Lin Hung Tse Lin Yu Wei Tian Shenghong A. Dai Wen Chiung Su 《Journal of polymer science. Part A, Polymer chemistry》2011,49(22):4851-4860
We reveal a route for the preparation of phosphinated bisphenol, 1,1‐bis(4‐hydroxyphenyl)‐1‐(6‐oxido‐6H‐dibenz <c,e> <1,2> oxaphosphorin‐6‐yl)ethane (2) , via a one‐pot reaction of 1,1,1‐tris(4‐hydroxyphenyl)ethane and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide (DOPO) in the catalysis of p‐toluenesulfonic acid. A two‐step reaction mechanism, acid‐fragmentation of 1,1,1‐tris(4‐hydroxyphenyl)ethane followed by nucleophilic addition of DOPO, is proposed for the synthesis. Based on (2) , a dicyanate ester derivative, 1,1‐bis(4‐cyanatophenyl)‐1‐(6‐oxido‐6H‐dibenz <c,e> <1,2> oxaphosphorin‐6‐yl)ethane (3) was prepared and co‐cured with a commercially available dicyanate ester, the dicyanate ester of bisphenol A (BACY). Experimental data show that incorporating (3) into BACY enhances the flame retardancy and dielectric properties with little penalty to the thermal properties. A thermoset with Tg 274 °C, coefficient of thermal expansion (CTE) 49 ppm/°C, Dk 3.04 (1 GHz), Td (5%,) N2: 435 °C, air: 424 °C, and UL‐94 V‐0 rating can be achieved via this approach. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011. 相似文献
6.
Sh. Yu X. Li A. Ren D. Shao Ch. Chen X. Wang 《Journal of Radioanalytical and Nuclear Chemistry》2006,268(2):387-392
Summary The
removal of heavy metal ion Co(II) from aqueous solution was studied usingg-Al2O3
by batch technique. The experiments were performed at T=20±2 °C, in 0.01M
NaNO3 solutions and under aerobic conditions. The effect of pH,
ionic strength, fulvic acid (FA) and alumina amount on the sorption of Co(II)
on alumina were also investigated. The pH affected the sorption of Co(II)
significantly as compared with the effect of FA and ionic strength. The results
indicated that strong chemical bonds are formed between Co(II) and functional
groups of the bare or FA coated alumina, and a precipitation of Co(II) takes
place on the alumina surface, induced by a transition from the adsorption to
surface. The addition sequences of Co/FA on Co(II) sorption were also studied:
the sorption of Co(II) in the ternary system was found independent of addition
sequences.</p>
</p> 相似文献
7.
F. Granados Correa J. Serrano Gómez 《Journal of Radioanalytical and Nuclear Chemistry》2006,268(1):95-101
Summary Thermally treated hydrotalcite was synthesized and its ability to sorb 99Mo from aqueous solutions was studied under static conditions as a function of initial concentration, amount of sorbent and
pH. X-ray diffraction was used to characterize synthesized calcined hydrotalcite. The values of sorption data were fitted
to Freundlich, Langmuir and Dubinin-Radushkevich (D-R) sorption isotherms. The mean energy of sorption was calculated as 5.24
kJ. mol-1from D-R sorption isotherm. The Lagergren equation has been used for the study of the kinetic process. The rate constants
of 99Mo sorption on calcined hydrotalcite were calculated at various temperatures (293-323 K). The thermodynamic constans have
been calculated and the standard enthalpy of the system was found to be<span style='font-size:12.0pt; font-family:Symbol;mso-bidi-font-family:Symbol'>DH°=11.5±0.3 kJ. mol-1. The values of calculated<span style='font-size:12.0pt;font-family:Symbol;mso-bidi-font-family: Symbol'>DG° and<span style='font-size:12.0pt;font-family: Symbol;mso-bidi-font-family:Symbol'>DS° were</o:p>-13.9±2.0 kJ. mol-1and (8.7±0.2). 10-2kJ. K-1. mol-1, respectively. These results show that the sorption process is endothermic, spontaneous in nature and the degree of freedom
of ions is increased by sorption. 相似文献
8.
Chia Wei Chang Ching Hsuan Lin Po Wen Cheng Hann Jang Hwang Shenghong A. Dai 《Journal of polymer science. Part A, Polymer chemistry》2009,47(10):2486-2499
Two novel phosphorus‐functionalized aromatic diamines, 1,1‐bis(4‐aminophenyl)‐1‐(6‐oxido‐6H‐dibenz <c,e> <1,2> oxaphosphorin‐6‐yl)ethane ( 1 ) and bis(4‐aminophenyl)‐(6‐oxido‐6H‐dibenz <c,e> <1,2> oxaphosphorin‐6‐yl)phenylmethane ( 2 ), were prepared from 9,10‐dihydro‐oxa‐10‐phosphaphenanthrene‐10‐oxide, 4‐aminoacetophenone, or 4‐aminobenzophenone in excess aniline using p‐toluenesulfonic acid monohydrate as catalyst by an efficient, one‐pot procedure. The effect of electron withdrawing/donating groups on the stabilization of the resulting carbocation seems critical for the success of the process and was discussed in detail. Based on diamines ( 1–2 ), a series of new polyimides, (5a–5d) and (6a–6d) , were prepared, respectively. Polyimides (5a–5d) are flexible and creasable. In contrast, polyimides (6a–6d) are brittle because of the structure rigidity, according to the analysis based on the NMR temperature‐dependent spectra of ( 2 ). Polyimides 5 displaying high Tg (318–392 °C), high moduli (3.39–4.49 GPa), low coefficient of thermal expansion (42–50 ppm/°C), and moderate thermal stability (Td 5 wt % at 426–439 °C), are excellent high‐Tg and flame‐retardant materials. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2486–2499, 2009 相似文献
9.
Summary A
tail-made polymer matrix is proposed to remove strontium ions from aqueous
solutions. The removal behavior of strontium ions on a crosslinked copolymer
containing methacrylic acid as functional groups was investigated as a function
of sorptive concentration, time, temperature and pH. It was observed that an
increase of these parameters enhanced the removal of Sr(II) ions from aqueous
solution. It is found that a maximum adsorption of Sr(II) ions can be obtained
on the crosslinked copolymer after 30 minutes and at pH 8. The increase of
Sr(II) ion concentration in the solution resulted in an increase in the amount
of Sr(II) ions adsorbed on the crosslinked copolymer containing methacrylic
acid as functional groups. However, after a maximum of Sr(II) concentration in
the solution, the percentage of adsorbed Sr(II) ions decreased. The adsorption
data are well represented by the Freundlich, Langmuir and Dubinin-Radushkevich
(D-R) isotherms. The adsorption capacity of the copolymer and the free energy
change were calculated by using the D-R isotherm. For the adsorption of Sr(II)
ions on the crosslinked copolymer the thermodynamic parameters (DH°,DS° andDG°) were
calculated.</p>
</p> 相似文献
10.
Yoshiyuki Goh Takao Iijima Masao Tomoi 《Journal of polymer science. Part A, Polymer chemistry》2002,40(15):2689-2701
Novel tetrabutylammonium tetrakis(substituted benzoyloxy)borate salts ( 1a – 1d ) were synthesized by the reaction of tetrabutylammonium tetraphenylborate and corresponding substituted benzoic acids. Polyaddition reactions of diglycidyl ether of bisphenol A (DGEBA) and 4,4′‐bisphenol F (44BPF) or bisphenol F (BPF‐D) with the ammonium borates were investigated as model reactions of epoxy/phenol–novolac resin systems with respect to the thermal latency and storage stability of the catalyst. The polyaddition of DGEBA/44BPF with the ammonium borates in diglyme at 150 °C for 6 h proceeded up to 84–94% conversions and gave polymers with number‐average molecular weights of 3750–5750, whereas the polyaddition at 80 °C for 6 h gave less than 9% conversions. The catalytic activity of ammonium borates 1a – 1d depended on the substituent of the phenyl group of the borates, and the order of activity was 1b (p‐OMe) > 1a (? H) > 1c (p‐NO2) > 1d [3,5‐(NO2)2]. The ammonium borate catalyst with the substituent that yielded lower acidity of the corresponding substituted benzoic acid tended to reveal higher activity. In comparison with tetrabutylammonium bromide (TBAB) as a conventional ammonium salt, 1a – 1d revealed better thermal latency. The storage stability of DGEBA/BPF‐D with the ammonium borate catalysts in bulk at 40 °C was better than that with TBAB. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2689–2701, 2002 相似文献
11.
Sándor Gb?l?s József L. Margitfalvi József L. Margitfalvi Mihály Hegeds Yurii A. Ryndin Yurii A. Ryndin 《Reaction Kinetics and Catalysis Letters》2006,87(2):313-324
Summary Transformation of n-hexane over Al2O3and SiO2supported Pt, Pt+Ga and Ir+Pt+Ga catalysts was studied in a continuous-flow reactor operated under slug-pulse mode at 520°C.
Bimetallic catalysts were prepared by introducing first Ga(OEt)3and then diallylplatinum as precursor compounds. Iridium was then introduced viadecomposition of Ir4(CO)12adsorbed onto Pt+Ga catalysts. The addition of Ga to Pt/SiO2catalyst decreased hydrogenation, aromatization and hydrogenolysis selectivity. Over Pt/Al2O3catalyst Ga increased hydrogenolysis selectivity and decreased isomerization and C5-cyclization. The main effect of Ir was to increase hydrogenolysis selectivity and the stability of catalysts.</o:p> 相似文献
12.
D. Bontea C. Mita D. Humelnicu 《Journal of Radioanalytical and Nuclear Chemistry》2006,268(2):305-311
Summary Three
silylcellulosic derivatives with different substitution degree were examined as
sorbents for uranyl ions. The adsorption rate and capacity of cellulose and
modified cellulose were investigated in aqueous media, at various pH and
temperature values. The polymer - metal complexes of UO22+
were characterized by infrared and electronic spectra, and thermogravimetry.
The thermal behavior of cellulose (C), trimethylsilyl - cellulose (tmsc, SD=
2.85) and triphenylsilyl - cellulose (TPSC1, SD=2.89 and TPSC2, SD
=2.70) and their complexes with
uranyl ions in atmospheric air has been studied between room temperature and
600 °C. The Coats-Redfern method was applied to estimate the kinetic
parameters. The results revealed that the complexation of C and TMSC with UO22+
increases the thermal stability.</p>
</p> 相似文献
13.
A. S. Al-Hobaib K. M. Al-Sulaiman D. M. Al-Dhayan A. A. Al-Suhybani 《Journal of Radioanalytical and Nuclear Chemistry》2006,268(2):425-431
Summary Sand
filters are used in water treatment stations to remove particulate matter from
underground water, where iron and manganese are collected forming thin oxide
films. These oxides of iron and manganese adsorb radium from underground water.
Radium concentration increases in time on the filters, and consequently the
level of radioactivity increases in the station. The removal of adsorbed radium
on sand using inorganic acids was studied. Good efficiency of radium removal
was obtained by controlling different parameters like temperature, time, pH,
addition of competitive cations and anions. It was found that hydrochloric acid
is the best for radium removal from sand filters. Maximum removal obtained was
about 60% at 5M BaCl2 and 2M HCl at 50 °C for 180-minute contact
time. Kinetic parameters of the removal process were studied and compared with
literature data.</p>
</p> 相似文献
14.
S. R. Kayasth K. K. Swain T. Mukherjee 《Journal of Radioanalytical and Nuclear Chemistry》2006,268(2):393-395
Summary A
simple pre-irradiation separation approach has been worked out for the
determination of traces of tellurium in high purity selenium followed by
neutron activation analysis (NAA) for the end determination of the analyte/s.
The difference in volatilities of these elements has been utilized for the
separation of the analyte from the matrix. The complete volatility of selenium
at ~600 °C was established using neutron activation analysis and selenium
radiotracer. Standard addition was used to validate the results. The proposed
method of separation of selenium prior to irradiation could make the
determination of tellurium possible and also improved the detection limit by
several folds.</p>
</p> 相似文献
15.
Devon A. Shipp Xiang Yu 《Journal of polymer science. Part A, Polymer chemistry》2004,42(21):5548-5558
Kinetic studies of the atom transfer radical polymerization (ATRP) of styrene are reported, with the particular aim of determining radical‐radical termination rate coefficients (<kt>). The reactions are analyzed using the persistent radical effect (PRE) model. Using this model, average radical‐radical termination rate coefficients are evaluated. Under appropriate ATRP catalyst concentrations, <kt> values of approximately 2 × 108 L mol?1 s?1 at 110 °C in 50 vol % anisole were determined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5548–5558, 2004 相似文献
16.
R. Alexander A. Jefferson P. D. Lester 《Journal of polymer science. Part A, Polymer chemistry》1981,19(3):695-706
A comparative study was undertaken of the cationic oligomerization/polymerization of the natural propenylbenzene derivatives, anethole, isoeugenol, and isosafrole, together with synthetic o-methoxypropenylbenzene and N,N-dimethyl-p-propenylaniline using boron trifluoride diethyletherate as catalyst. Two (optimum) reaction temperatures were employed, ?12 and ?45°C, and only the (E) isomers of the monomers were studied. The order of reactivity of the monomers was found to be anethole > isoeugenol > isosafrole > o-methoxypronylbenzene as measured by following the rate of loss of monomer by proton magnetic resonance spectrometry at ?12°C. N,N-dimethyl-p-propenylaniline only appeared to form a complex with the catalyst. Low-molecularweight polymeric materials were prepared from anethole, isosafrole, and isoeugenol at ?45°C using the same catalyst while o-methoxypropenylbenzene formed oligomers. Isosafrole was recovered unchanged when treated with the boron trifluoride diethyl etherate initiator system at ?78°C in an attempt to increase the molecular weight of the polyisosafrole. 相似文献
17.
P. Mell J. Megyeri L. Riess Z. Máthé J. Csicsák K. Lázár 《Journal of Radioanalytical and Nuclear Chemistry》2006,268(2):405-410
Summary Sorption of60Co,85Sr, 137Cs and125I have been studied on samples
originated from Boda (siltstone-) claystone formation (BCF) (Hungary). The
distribution of Kdvalues have been determined in static batch
experiments using natural groundwater. The order of sorption of isotopes was
Co>Cs>Sr>I, where iodine exhibits sorption properties in a modest
extent. The sorption isotherm was determined for Cs from measurements carried
out in 10-5-10-1M initial concentration range. The
isotherm can be described with non-linear Freundlich approximation in the range
of</o:p></p>
10-7-10-4M equilibrium concentration. At
concentrations >10-2M the isotherm achieves saturation. Hence, it is suggested that sorption
of Cs on BCF is dominated by cation-exchange reactions on the illite mineral
component. In the case of Co and Sr, precipitation reactions occurred during
the experiments performed with carrier-containing solutions. This can be
attributed to the low values of solubility product constants of SrCO3, SrSO4and Co(OH)2, formed from anions present in the
natural groundwater.</p>
</p> 相似文献
18.
Ching Hsuan Lin Chen Ming Li Chin Kuang Hsu Hou Chien Chang Tzong Yuan Juang 《Journal of polymer science. Part A, Polymer chemistry》2013,51(12):2709-2715
High‐performance and flexible poly(pyrrolone imide)s (PPyIs) were firstly prepared by the reaction of dianhydrides with an unsymmetric phosphinated triamine, 1‐(3,4‐diaminophenyl)‐1‐(4‐aminophenyl)‐1‐(6‐oxido‐6H ‐dibenz <c,e> <1,2> oxaphosphorin‐6‐yl)ethane (1), which was prepared by a facile, one‐pot procedure from the reaction DOPO, 4‐aminoacetophenone in excess o‐phenylenediamine in the presence of p‐toluenesulfonic acid. Thermal properties of the resulting PPyIs were evaluated and compared with those of phosphinated polyimides with a similar structure. All of the prepared PPyIs films are tough and creasable. They display higher Tg (374–412 °C), lower coefficient of thermal expansion (34–46 ppm/°C), and better thermal stability (Td 5 wt %: 456–477 °C, 800 °C char yield: 59–63%) than analogous phosphinated polyimides. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2709–2715 相似文献
19.
Asymmetric Hydroalkoxylation of Non‐Activated Alkenes: Titanium‐Catalyzed Cycloisomerization of Allylphenols at High Temperatures
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M. Sc. Johannes Schlüter M. Sc. Max Blazejak Dr. Florian Boeck Prof. Dr. Lukas Hintermann 《Angewandte Chemie (International ed. in English)》2015,54(13):4014-4017
The asymmetric catalytic addition of alcohols (phenols) to non‐activated alkenes has been realized through the cycloisomerization of 2‐allylphenols to 2‐methyl‐2,3‐dihydrobenzofurans (2‐methylcoumarans). The reaction was catalyzed by a chiral titanium–carboxylate complex at uncommonly high temperatures for asymmetric catalytic reactions. The catalyst was generated by mixing titanium isopropoxide, the chiral ligand (aS)‐1‐(2‐methoxy‐1‐naphthyl)‐2‐naphthoic acid or its derivatives, and a co‐catalytic amount of water in a ratio of 1:1:1 (5 mol % each). This homogeneous thermal catalysis (HOT‐CAT) gave various (S)‐2‐methylcoumarans with yields of up to 90 % and in up to 85 % ee at 240 °C, and in 87 % ee at 220 °C. 相似文献
20.
Summary 0.5% Pt-supported on silica-basedpolydimethylsiloxane compositeswere preparedandcharacterized using BET surface area, FT-IR,
TGA, SEM and XRD. Hydrogenation ofCFC-22 over these catalysts produced mainly CH3F and CH4.</o:p> 相似文献