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1.
Ahmed A. Abd El-Raady Nasr E. Fouad Mohamed A. Mohamed Samih A. Halawy 《Monatshefte für Chemie / Chemical Monthly》2002,133(10):1351-1361
Summary. Selective decomposition of ethanol was used as a test reaction at 350°C to evaluate the catalytic activity of two Al–Mg–O
mixed oxides prepared by two different methods (wet impregnation and coprecipitation). The catalyst precursors were examined
by TG and DTA and were calcined between 500–900°C for 5 h in air. The surface area of all catalysts was measured by N2 sorption using the BET method. The total acidity and basicity were determined by TPD using pyridine and formic acid. The
catalysts were characterized by XRD analysis. It was found that the preparation method of Al–Mg–O catalyst has a great effect
on the selective decomposition of ethanol. Al–Mg–O (I) catalysts, prepared by wet impregnation, were more selective towards
ethene formation during dehydration of ethanol. This is ascribed to their high total surface acidity. On the other hand, Al–Mg–O
(II) catalysts, prepared by coprecipitation, were highly selective in the oxidative dehydrogenation of ethanol to yield acetaldehyde.
This could be attributed to their high concentration of basic sites. In addition, the production of traces of diethyl ether
was also observed (three times more for Al–Mg–O (II) than for Al–Mg–O (I)).
Corresponding author. E-mail: shalawy99@yahoo.com
Received October 12, 2001. Accepted (revised) January 7, 2002 相似文献
2.
Iron-nickel mixed oxides containing up to 10 mole% of NiO have been prepared by hydroxide coprecipitation technique. The oxide samples have been heated to different temperatures ranging from 300 to 1300°C and studied by infrared spectroscopy, magnetic susceptibility, and X-ray diffraction measurements. The maximum solubility of NiO in Fe2O3 under the present experimental conditions is found to be 2 mole% when the samples are heated to 550°C. The solubility decreases with increase of sintering temperature and also as the total NiO content of the sample increases. Formation of nickel ferrite phase at concentrations higher than 2 mole% of NiO is clearly indicated. 相似文献
3.
Hongbo Guan Pei Wang Biying Zhao Yuexiang Zhu Youchang Xie 《Frontiers of Chemistry in China》2007,2(2):204-208
Nanometer MgO samples with high surface area, small crystal size and mesoporous texture were synthesized by thermal decomposition
of MgC2O4 · 2H2O prepared from solid-state chemical reaction between H2C2O4 · 2H2O and Mg (CH3COO)2 · 4H2O. Steam produced during the decomposition process accelerated the sintering of MgO, and MgO with surface area as high as
412 m2 · g−1 was obtained through calcining its precursor in flowing dry nitrogen at 520°C for 4 h. The samples were characterized by
X-ray diffraction, N2 adsorption, transmission electron microscopy, thermogravimetry, and differential thermal analysis. The as-prepared MgO was
composed of nanocrystals with a size of about 4–5 nm and formed a wormhole-like porous structure. The MgO also had good thermal
stability, and its surface areas remained at 357 and 153 m2·g−1 after calcination at 600 and 800°C for 2 h, respectively. Compared with the MgO sample prepared by the precipitation method,
MgO prepared by solid-state chemical reaction has uniform pore size distribution, surface area, and crystal size. The solid-state
chemical method has the advantages of low cost, low pollution, and high yield, therefore it appears to be a promising method
in the industrial manufacture of nanometer MgO.
Translated from Chinese Journal of Catalysis, 2006, 27(9): 793–798 (in Chinese) 相似文献
4.
(100-x) mole% SiO2-x mole% P2O5-glasses withx=1–9 have been prepared by the sol-gel process using tetraethylorthosilicate and triethylphosphate as precursors. The gels
were fired at various temperatures up to 950°C and then exposed to γ-ray irradiation to induce paramagnetic centers. CW-EPR
and FT-EPR Spectroscopies were employed at temperatures between 4 and 300 K in order to determine the resulting structures.
The dried gels exhibited four types of O
2
−
-ions trapped in pores of different sizes. The gels fired atT=670°C exhibited theE’
1-center and non-bridging oxygen as a results of the fracture of the Si-O-Si bonds. At higher temperatures, the spectra of
the POHC, POHC
b
,E’, and CH
3
−
-centers have been detected that are a function ofx andT. 相似文献
5.
Elena N. Konyushenko Miroslava Trchová Jaroslav Stejskal Irina Sapurina 《Chemical Papers》2010,64(1):56-64
Conditions of polyaniline (PANI) nanotubes preparation were analyzed. Aniline was oxidized with ammonium peroxydisulfate in
0.4 M acetic acid. There are two subsequent oxidation steps and the products were collected after each of them. At pH > 3,
neutral aniline molecules are oxidized to non-conducting aniline oligomers. These produce templates for the subsequent growth
of PANI nanotubes, which takes place preferably at pH 2–3. At pH < 2, granular morphology of the conducting PANI is obtained.
High final acidity of the medium should be avoided in the preparation of nanotubes, e.g., by reducing the amount of sulfuric
acid which is a by-product. Reduction of the peroxydisulfate-to-aniline mole ratio was tested for this purpose in the present
study. Lowering of the reaction temperature from 20°C to −4°C had a positive effect on the formation of nanotubes. 相似文献
6.
Fábio A. Silva Cilene C. F. Padilha Gustavo Rocha de Castro Paulo dos Santos Roldan Ana R. de Araujo Nogueira Paula M. Moraes Pedro M. Padilha 《Central European Journal of Chemistry》2011,9(1):119-125
This paper proposes a method to determine selenium in samples of fish muscle and liver tissue using ultrasound assisted extraction
process, and analysed by graphite furnace atomic absorption spectrometry (GFAAS). The selenium content was extracted by 0.10
M HCl at the optimal extraction conditions which were established as follows: sample mass of 100 mg; granulometry of the sample
<60 μm; sonication time of five 40 s cycles; and sonication power of 136 W. The selenium determinations were performed by
GFAAS, at a drying temperature of 120°C/250°C, pyrolysis temperature of 1300°C, atomization temperature of 2300°C, and cleaning
temperature of 2800°C. Palladium nitrate was used as a chemical modifier coinjected with the samples, and tungsten as a permanent
modifier. The concentration of selenium determined in the pool of fish muscle and liver tissue were 280.4±4.2 e 592.3±6.7
μg kg−1, respectively. The accuracy and precision of the proposed extraction method were evaluated using certified standard Bovine
Muscle — NIST 8414. The results obtained by the ultrasonic extraction method were equivalent to those obtained by the method
of acid mineralization of samples in a microwave oven 相似文献
7.
Nano-crystalline sulfated zirconia catalyst, prepared by two-step sol–gel method, has been studied for the solvent free self
condensation of acetophenone to dypnone. The influence of calcination temperature on the structural, textural and catalytic
activity of sulfated zirconia has been analyzed. The surface acidity along with the structural and textural features of the
catalyst influenced its activity. The conversion of acetophenone was found to be effected by the variation in the reaction
and calcination temperature, however, the dypnone selectivity was not affected much. The catalyst calcined at 650 °C, showed
maximum dypnone selectivity of 92% with 68.2% acetophenone conversion at 170 °C after 7 h. The catalyst was reused up to five
cycles with marginal decrease in acetophenone conversion, however, without losing its selectivity for dypnone. 相似文献
8.
An ultra-low hydrolysis sol-gel route for titanosilicate xerogels and their characterization 总被引:1,自引:0,他引:1
Toney Fernandez Gijo Jose Siby Mathew Rejikumar PR Unnikrishnan NV 《Journal of Sol-Gel Science and Technology》2007,41(2):163-168
In this work TiO2-SiO2 xerogels were prepared through an ultra low hydrolysis method using titanium and silicon alkoxide. The samples were heat
treated to 500°C. The xerogels were characterized using TGA/DTA, FTIR, XRD and TEM. The samples showed the formation of Si–O–Ti
bridges by its characteristic vibration within 925–960 cm−1 range. Si–O–Si bond angles were calculated using the central force network model. The TiO2 in all the samples crystallized on heat treatment to 500°C. The crystallite size calculated using the Scherer formula from
the XRD was verified from the Transmission Electron Micrograph. Samples heat treated to 350°C remained amorphous and hence
could be used as hosts for biomaterials and organic optical materials. 相似文献
9.
The kinetics of the acid hydrolysis of chromatopenta-amminecobalt(III) ion has been studied using a stopped-flow method over
the acidity range 0.01≤[H+]<-1.0 mol dm−3 and 20.0°C<-ϕ<-30.0°C at ionic strengths 0.5 and 1.0 mol dm−3 (LiNO3). These studies reveal that the complex is first protonated and subsequently hydrolysed to the aquapentaammine cobalt(III)
ion. The rate constants for the hydrolysis of the mono and diprotonated species at 25°C are 0.83±0.01 s−1 and (1.60±0.02)×104 mol−1 dm−3 s−1, respectively.
TMC 2664 相似文献
10.
Xin Zhang Xiaogang Li Junsheng Wu Renchun Yang Limin Tian Zhihua Zhang 《Journal of Sol-Gel Science and Technology》2009,51(1):1-3
Mesoporous TiO2 with a high specific surface area was prepared from titanium sulfate solution in a simple sol–gel route, where formamide
was used as pH adjusting agent. TiO2 had a high resistance to phase transformation, and maintained monophasic anatase after calcinating at 600 °C. The highest
specific surface area achieved on the prepared samples is 231.90 m2 g−1 after calcinating at 450 °C. 相似文献
11.
H. Zhao S. Bennici J. Shen A. Auroux 《Journal of Thermal Analysis and Calorimetry》2010,99(3):843-847
The surface acidic properties of sulfated vanadia–titania catalysts prepared by various methods were investigated by adsorption
microcalorimetry, using ammonia as probe molecule. The acidic characteristics of the samples were shown to be strongly affected
by the preparation method, calcination temperature, and sulfur content. The samples prepared by sol–gel and mechanical grinding
exhibited higher acidity than co-precipitated samples. Moreover, increasing the calcination temperature of co-precipitated
samples resulted in a decrease in surface area from 402 to 57 m2 g−1 and sulfur content from around 4 to 0.2 mass%, but up to a certain point generated a stronger acidity. The optimal calcination
temperature appeared to be around 673 K. 相似文献
12.
The gelling behaviour of an aqueous sodium silicate solution with boric acid was investigated for different initial compositions
and solid sodium borosilicate samples were obtained by drying the gels at 100°C, 225°C and 450°C. The chemical composition,
dissolution, pH, loose-packed bulk density, B.E.T. surface area, moisture, size distribution and XRD/IR patterns of the sodium
borosilicate particles were determined. The minimum gelling times were observed at pH values between 9–10 and although no
gels were obtained using HCl at pH = 11, the silicate solution was gelled with boric acid suggesting borate ions promote the
formation of siloxane network and behave as a crosslinking agent. 相似文献
13.
The effect of the melting of the collagen-like acid and alkaline gelatin aggregates on the stability against aggregation
of bovine casein micelles was investigated by turbidimetry, DSC and circular dichroism in the wide range of biopolymers concentrations,
gelatin/casein ratio (R) in initial mixture (R=0.03–20), pH (4.9–6.7), ionic strength (I=10−3 to 1.0/NaCl/), and temperature (10°–70 °C), using glucono-δ-lactone (GL) as acidifier. At low ionic strength (10−3/milk salts/) and neutral pH interaction between gelatin molecules and casein micelles is suppressed significantly above 36 °C.
The melting of the collagen-like acidic gelatin above this temperature shifts the pH at which the complex formation is maximal
to the acidic range. The cause may be that some of the functional ionized groups of gelatin molecules are inaccessible due
to the conformational changes. The presence of gelatin B molecules had no effect on the aggregation stability of micellar
casein in the range 0.03<R<20. At very high total protein concentration (above 10%) depletion flocculation of casein micelles
was observed. The reason for the very high stability of casein micelles in this case cannot be explained by volume exclusion.
Received: 28 March 2000 Accepted: 5 October 2000 相似文献
14.
Jingqi Guan ShuBo Jing Shujie Wu Haiyan Xu Zhenlv Wang Qiubin Kan 《Reaction Kinetics and Catalysis Letters》2007,90(1):27-33
A series of MoV0.3Tex (x = 0−0.3) mixed oxides were prepared and investigated for the selective oxidation of isobutane. Among them, MoV0.3Te0.23 showed the best methacrolein and methacrylic acid selectivity (as high as 17% and 16%, respectively), and the yield to methacrolein
and methacrylic acid reached 3.6% and 3.5%, respectively, at 21.3% isobutane conversion at 440°C. 相似文献
15.
A novel lidocaine ion-selective electrode is prepared, characterized and used in pharmaceutical analysis. The electrode incorporates
PVC-membrane with lidocaine-sulfathiazole ion pair complex. The influences of membrane composition, temperature, pH of the
test solution, and foreign ions on the electrode performance were investigated. The electrode showed a Nernstian response
over a lidocaine concentration range from 1.0 ×10−5 to 1.0 × 10−1 mol L−1 with a slope of 60.1 ± 0.2 mV per decade at 25°C and was found to be very selective, precise, and usable within the pH range
5–9.5. The standard electrode potentials, E
o, were determined at 10, 15, 20, 25, 30, 35 and 40°C, and used to calculate the isothermal temperature coefficient (dE
o/dT=−0.0003 V °C−1) of the electrode. However, the electrode performance is significantly decreased at temperatures higher than 45°C. The electrode
was successfully used for potentiometric determination of lidocaine hydrochloride in pharmaceutical products.
The article is published in the original. 相似文献
16.
Shaobin Wang K. Murata T. Hayakawa S. Hamakawa K. Suzuki 《Reaction Kinetics and Catalysis Letters》1999,67(2):219-224
The oxidative dehydrogenation of ethane into ethylene has been investigated on metal oxide-based sulfated zirconia catalysts
at temperatures of 400–600°C. It is found that the activity and selectivity toward ethylene depend on the nature of metal
oxide and temperature and that Ni and V oxides supported on sulfated zirconia exhibited higher ethylene yields. 相似文献
17.
N. T. Silva N. F. Nascimento L. S. Cividanes C. A. Bertran G. P. Thim 《Journal of Sol-Gel Science and Technology》2008,47(2):140-147
Diphasic cordierite gels were prepared from colloidal silica, aluminum and magnesium nitrates and citric acid. The mechanism
of xerogel decomposition was studied by infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA). The thermal
decomposition of the xerogel forms a solid mixture of MgO, Al2O3 and SiO2 at around 250 °C. Cordierite crystallization was studied by X-ray diffraction (XRD) and differential thermal analysis (DTA).
Xerogels were initially thermally treated, and this sample crystallized to μ-cordierite at 850 °C, at 900 °C α-cordierite
crystallizes and at 1150 °C α-cordierite is the major phase and μ-cordierite is totally consumed. The apparent activation
energy for cordierite crystallization process was determined based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory, Ligero
methods and the Arrhenius law for dependence of activation energy with temperature. The apparent activation energy was (466.8 ± 34.3) kJ/mol,
the exponent of Avrami was (1.9 ± 0.2) and the frequency factor was (1.55 × 1020) s−1. The Avrami value indicates a nucleation controlled process, which can be a consequence of the high xerogel homogeneity,
a consequence of the early and simultaneous formation of the MgO, Al2O3 and SiO2 mixture. 相似文献
18.
M. M. Portela Marques I. M. Miranda Salvado F. M. A. Margaça L. M. Ferreira 《Journal of Thermal Analysis and Calorimetry》2010,100(2):557-561
Hybrid materials were prepared by sol–gel method using Tetraethylortosilicate and Polydimethylsiloxane silanol terminated
with the addition of small contents of Zirconium Propoxide ≤5 wt%. The thermal stability of the prepared samples was studied
by Infra-red spectroscopy, 29Si Nuclear Magnetic Resonance, Thermal Analysis and Scanning Electron Microscopy. All samples were monolithic after drying
at 120 °C. After heat treatment at 400 °C the samples prepared with 0 wt% in Zirconium Propoxide present high porosity. It
was found that the content in Zirconium Propoxide is directly related with the thermal stability of the hybrid materials prepared
in this study. 相似文献
19.
Venkataraman Vishwanathan Gajula Balakrishna Balraj Rajesh Venkatreddy Jayasri Lucky Sikhwivhilu Neil J. Coville 《Reaction Kinetics and Catalysis Letters》2007,92(2):311-317
A series of sulphate-promoted ZrO2 solid acid catalysts with different contents of SO4
2− were calcined at 450°C in air for 4 h and tested for the liquid-phase alkylation of catechol to guaiacol in a fixed-bed down-flow
reactor. The 5 wt.% SO4
2− on ZrO2 showed the best conversion (82%) and selectivity for guaiacol (84%) at 200°C and 1 bar pressure. A smooth correlation was
observed between the catalytical activity and surface acidity of sulphated zirconia. Based on our results, a surface mechanism
is proposed. 相似文献
20.
H. G. El-Shobaky 《Journal of Thermal Analysis and Calorimetry》2006,85(2):321-327
The solid–solid interactions in pure and MoO3-doped
CuO/MgO system were investigated using TG, DTA and XRD. The composition of
pure mixed solids were 0.1CuO/MgO, 0.2CuO/MgO and 0.3CuO/MgO and the concentrations
of MoO3 were 2.5 and 5 mol%. These solids were prepared
by wet impregnation of finely powdered basic magnesium carbonate with solutions
containing calculated amounts of copper nitrate and ammonium molybdate followed
by heating at 400–1000°C.
The results revealed that
ammonium molybdate doping of the system investigated enhanced the thermal
decomposition of copper nitrate and magnesium hydroxide which decomposed at
temperatures lower than those observed in case of the undoped mixed solids
by 70 and 100°C, respectively. A portion of CuO present dissolved in the
lattice of MgO forming CuO–MgO solid solution with subsequent limited
increase in its lattice parameter. The other portion interacted readily with
a portion of MoO3 at temperatures starting from 400°C
yielding CuMoO4 which remained stable up to 1000°C.
The other portion of MoO3 interacted with MgO producing
MgMoO4 at temperatures starting from 400°C and
remained also stable at 1000°C. The diffraction peaks of Cu2MgO3
phase were detected in the diffractograms of pure and MoO3-doped
0.3CuO/MgO precalcined at 1000°C. The formation of this phase was accompanied
by an endothermic peak at 930°C. 相似文献