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1.
Barbara Pacewska Olga Kluk-Płoskońska D. Szychowski 《Journal of Thermal Analysis and Calorimetry》2006,86(3):751-760
Aluminium hydroxide was precipitated
during a hydrolysis of aluminium perchlorate in ammonia medium. The materials
were studied with the following methods: thermal analysis, IR spectroscopy,
X-ray diffraction, low-temperature nitrogen adsorption and adsorption–desorption
of benzene vapours.
Freshly precipitated boehmite had a high value
of SBET=211 m2 g–1
determined from nitrogen adsorption, good sorption capacity for benzene vapours,
developed mesoporous structure and hydrophobic character. After prolonged
refluxing at elevated temperature its crystallinity increased which was accompanied
by an increase of specific surface determined from nitrogen adsorption up
to 262m2g–1 ,
decrease of sorption capacity for benzene vapours and stronger hydrophobic
character. The calcinations of all boehmites at temperature up to 1200°C
resulted in formation of à-Al2O3
via transition form of γ-, δ- and θ-Al2O3.
The samples of aluminium oxides obtained after calcination at 550 and 900°C
were characterised with high values of specific surface area of 205–220
and 138–153 m2 g–1
, respectively. The SBET values calculated for the oxide samples derived from
aged hydroxides and calcined at 1200°C are higher than for the analogous
sample prepared without the ageing step. It was concluded that the process
of ageing at elevated temperature developed thermal stability of aluminium
oxides. 相似文献
2.
The effect of ferric and manganese oxides dopants on thermal and physicochemical properties of Mn-oxide/Al2O3 and Fe2O3/Al2O3 systems has been studied separately. The pure and doped mixed solids were thermally treated at 400–1000°C. Pyrolysis of pure
and doped mixed solids was investigated via thermal analysis (TG-DTG) techniques. The thermal products were characterized
using XRD-analysis. The results revealed that pure ferric nitrate decomposes into Fe2O3 at 350°C and shows thermal stability up to1000°C. Crystalline Fe3O4 and Mn3O4phases were detected for some doped solids precalcined at 1000°C. Crystalline γ-Al2O3 phase was detected for all solids preheated up to 800°C. Ferric and manganese oxides enhanced the formation of α-Al2O3 phase at1000°C. Crystalline MnAl2O4 and MnFe2O4 phases were formed at 1000°C as a result of solid–solid interaction processes. The catalytic behavior of the thermal products
was tested using the decomposition of H2O2 reaction.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
O. V. Matrosova Yu. N. Rufov M. V. Vishnetskaya 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(12):2187-2189
Low-temperature emission of the singlet form of dioxygen 1O2 from the surface of the individual and mixed V and Mo oxides was detected by thermal desorption at 20–350°C. The amount of
the desorbing 1O2 and the temperature range of 1O2 emission were found to depend on the composition of the catalyst; the low-temperature 1O2 form can be regenerated after its contact with oxygen. 相似文献
4.
O. V. Mokhnachuk S. A. Solov’ev V. G. Il’in P. S. Yaremov 《Theoretical and Experimental Chemistry》2006,42(5):327-333
It has been established that addition of oxides of the rare earth elements (La2O3, CeO2, and their mixtures) increases the thermal stability of the porous structure of highly dispersed aluminum oxide-a secondary
carrier of structured catalysts. The greatest stabilizing effect was noted with La2O3. The reason for this effect is the formation of a solid solution of La2O3 in Al2O3 which prevents the diffusion of aluminum ions and slows the transition of low temperature modifications of Al2O3 into high temperature α-Al2O3.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 5, pp. 318–323, September–October, 2006. 相似文献
5.
The synthesis of new pigments based on Bi2O3
is investigated because they give interesting orange hues and can substitute
the pigments problematic from the environmental point of view. Chemical compounds
of the Bi2–xZr3x/4O3
type were synthesized. The host lattice of these pigments is Bi2O3
that is doped by Zr4+ ions. The area of ZrO2
solubility in Bi2O3 at 800°C
forming solid solution of both oxides was studied. The incorporation of doped
ions provides interesting colours and contributes to a growth of the thermal
stability of these compounds. The simultaneous TG-DTA measurements were used
for determination of the temperature region of the pigment formation and thermal
stability of pigments. 相似文献
6.
Aleksey A. Yaremchenko Vladislav V. Kharton Evgeny N. Naumovich Alim A. Vecher 《Journal of Solid State Electrochemistry》1998,2(3):146-149
The minimum concentration of niobium to stabilize the fluorite-type f.c.c. phase in the Bi2O3–Nb2O5 oxide system at temperatures below 996 K was ascertained to be about 10 mol%. Thermal expansion, electrical conductivity
and crystal lattice parameters of the Bi(Nb)O1.5+δ solid solutions decrease with increasing niobium content. Thermal expansion coefficients were calculated from the dilatometric
data to be (10.314.5)×10−6 K−1 at temperatures in the range 300–700 K and (17.526.0)×10−6 K−1 at 700–1100 K. The conductivity of the Bi1−
x
Nb
x
O1.5+δ ceramics is predominantly ionic. The p-type electronic transference numbers of the Bi(Nb)O1.5+δ solid solutions in air were determined to be less than 0.1. Annealing at temperatures below 900 K results in a sharp decrease
in conductivity of the Bi1−
x
Nb
x
O1.5+δ ceramics.
Received: 18 August 1997 / Accepted: 20 October 1997 相似文献
7.
Iron and its binary oxides are meticulously exploited for environmental remediations. However, only limited studies have been carried out on the degradation of industrial organics by advanced oxidation process. In this study, iron oxide, cobalt oxide, and iron–cobalt binary oxides were synthesized by a modified hydrothermal method as heterogeneous Fenton-like catalysts for the removal of methylene blue (MB) from wastewaters. The oxide nanostructures were characterized by different analytical techniques. Studying the effects of various parameters such as catalyst dose, MB concentration, and H2O2 concentration, the reaction conditions were optimized to enhance the removal of MB dye. The results revealed that α-Fe2O3–Co3O4 shows much higher activity than both Co3O4 and α-Fe2O3 for the degradation of MB at room temperature and beyond. The binary α-Fe2O3–Co3O4 shows degradation efficiency of 96.4% at 65 °C within 60 min. Furthermore, the binary α-Fe2O3–Co3O4 catalyst retains its activity for up to four successive cycles. A probable mechanism is also proposed, involving the generation of ‧OH radical as well as Fe2+/Fe3+ or Co2+/Co3+ redox couple of the binary α-Fe2O3–Co3O4 catalyst. 相似文献
8.
S. A. Solov’ev E. V. Gubareni Ya. P. Kurilets 《Theoretical and Experimental Chemistry》2008,44(6):368-373
It has been established that oxides of the rare-earth elements with moderate redox potentials (La2O3, CeO2) increased the activity and working stability of Ni-Al2O3/cordierite catalysts in the reactions of deep and partial oxidation of methane. In the presence of the (NiO + La2O3 + Al2O3)/cordierite catalyst the process of carbon dioxide conversion of methane can be intensified by introduction of oxygen into
the reaction gas mixture which decreases the temperature to achieve high conversion to 75–100 °C and has practically no effect
on selectivity with respect to H2.
Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 6, pp. 359–364, November–December, 2008. 相似文献
9.
一步水热合成Y-CoO复合氧化物催化剂及催化分解NO 《燃料化学学报》2019,47(4):446-454
用一步水热、分步水热、浸渍等方法分别制备Y-Co3O4复合氧化物,用于催化分解N2O的反应,其中,一步水热法制备的催化剂活性较高。再用一步水热法制备了不同Y/Co物质的量比的Y-Co3O4复合氧化物,在优化出的催化剂(0.03Y-Co3O4)表面浸渍K2CO3溶液,制备K改性催化剂(0.02K/0.03Y-Co3O4)。用X射线衍射(XRD)、N2物理吸附、H2程序升温还原(H2-TPR)、O2程序升温脱附(O2-TPD)、扫描电镜(SEM)、X射线光电子谱(XPS)等技术表征催化剂结构。研究发现,Co3O4和Y-Co3O4同为尖晶石结构,但Y-Co3O4的催化活性显著高于Co3O4。K改性增加了催化剂表面的活性位(Co2+),还有利于吸附氧的脱除,从而提高了催化剂活性。在无氧无水、有氧无水、有氧有水气氛中,K改性催化剂上的N2O全分解温度分别为325、350、375 ℃,催化剂活性较高。有氧有水气氛350 ℃连续反应50 h,K改性催化剂上N2O分解率保持90%以上,稳定性较高。研究发现,Y-Co3O4及K改性催化剂上N2O分解反应的Ea和lnA之间存在动力学补偿效应。 相似文献
10.
Aigars Vītiņš Ģirts Vītiņš Jānis Krastiņš Ints Šteins Ilmārs Zālīte Andrejs Lūsis 《Journal of Solid State Electrochemistry》1998,2(5):299-307
Ceramic specimens have been obtained from the powder of ZrO2-7.5 mol% Y2O3 having a specific surface area of 30 m2/g synthesized in air plasma. The novelty of this research lies in the fact that the plasma process makes it possible to prepare
so-called nanopowders with a particle size less than 100 nm, possessing specific physical, chemical and technological properties.
The sintered density of the specimens was 94–96% of the theoretical value, 6.001 g/cm3. The X-ray diffraction pattern of the specimens corresponded to a face-centered cubic lattice. Impedance in the frequency
range of 100 Hz–15 MHz and d.c. polarization curves in a potential range of −10 to 10 mV were measured in the temperature
range 200–850 °C in heating and cooling cycles. The intragrain, the grain boundary and the total bulk conductivities, the
electrode polarization resistance and their activation energies were determined. The thermal stability of the studied system
was proved in three measurement series up to 600–850 °C in heating and cooling cycles. The results obtained have shown that
the conductivity of ZrO2-7.5 mol% Y2O3 ceramics is not solely a function of temperature, but also depends on the previous thermal state of the ceramics.
Received: 16 October 1997 / Accepted: 19 January 1998 相似文献
11.
12.
The Er3+-doped Al2O3 nanopowders have been prepared by the sol-gel method, using the aluminium isopropoxide [Al(OC3H7)3]-derived γ-AlOOH sols with addition of the erbium nitrate [Er(NO3)3·5H2O]. The five phases of γ-(Al,Er)2O3, θ-(Al,Er)2O3, α-(Al,Er)2O3, ErAlO3, and Al10Er6O24 were detected with the 0–20 mol% Er3+-doped Al2O3 nanopowders at the different sintering temperature of 600–1200°C. The average grain size was increased from about 5 to 62 nm
for phase transformation of undoped γ-Al2O3→α-Al2O3 at the sintering temperature from 600 to 1200°C. At the same sintering temperature, average grain size was decreased with
increase of the Er3+ doping concentration. Infrared absorption spectra of γ-Al2O3 and θ-Al2O3 nanopowders showed the two broad bands of 830–870 and 550–600 cm−1, the three broad bands of 830–870, 750–760, and 550–600 cm−1, respectively. The infrared absorption spectra for the α-Al2O3 nanopowder showed three characteristic bands, 640, 602, and 453 cm−1. The two characteristic bands of 669 and 418 cm−1 for Er2O3 clusters were observed for the Er3+-doped Al2O3 nanopowders when Er3+ doping concentration was increased up to 2 mol%. The 796, 788, 725, 692, 688, 669, 586, 509, 459, and 418 cm−1 are the characteristic bands of Al10Er6O24 phase. 相似文献
13.
Barbara Pacewska Olga Kluk-Płoskońska D. Szychowski 《Journal of Thermal Analysis and Calorimetry》2006,85(2):351-359
An attempt
to obtain aluminium hydroxide that could give aluminium oxides of increased
thermal stability was made. Aluminium hydroxide was precipitated during a
hydrolysis of aluminium chloride in ammonia medium. The influence of preparative
conditions, such as a dosing rate of aluminium precursor, pH, duration of
the precipitate refluxing and temperature of calcination, on the properties
of obtained hydroxides and oxides was investigated. The materials were studied
with the following methods: thermal analysis, IR spectroscopy, low-temperature
nitrogen adsorption and adsorption–desorption of benzene vapours.
Precipitated boehmites had high values of S
BET
determined from nitrogen adsorption (220–300 m2g–1),
good sorption capacity for benzene vapours, developed mesoporous structure
and hydrophilic character. It has been proved that a high pH value during
the precipitation of aluminium hydroxide favoured better crystallisation of
boehmite structure, higher temperature of its dehydroxylation into γ-Al2O3,
and delayed transformation of γ phase into α-Al2O3.
Aluminium oxides derived from the hydroxides precipitated at a high pH were
the most stable at high temperatures, and were characterised with the best
surface properties.
The online version of the original
article can be found
at 相似文献
14.
Iordanova R. Lefterova E. Uzunov I. Dimitriev Y. Klissurski D. 《Journal of Thermal Analysis and Calorimetry》2002,70(2):393-404
Characteristic temperatures, such as T
g (glass transition), T
x (crystallization temperature) and T
l (liquidus temperature) of glasses from the V2O5-MoO3-Bi2O3 system were determined by means of differential thermal analysis (DTA). The higher content of MoO3 improved the thermal stability of the glasses as well as the glass forming ability. The non-isothermal crystallization was
investigated and following energies of the crystal growth were obtained: glass #1 (80V2O5·20Bi2O3) E
G=280 kJ mol-1, glass #2 (40V2O5·30MoO3·30Bi2O3) E
G=422 kJ mol-1 and glass #3 (80MoO3·10V2O5·10Bi2O3) E
G=305 kJ mol-1. The crystallization mechanism of glass #1 (n=3) is bulk, of glass #3 (n=1) is surface. Bulk and surface crystallization was supposed in glass #2. The presence of high content of a vanadium oxide
acts as a nucleation agent and facilitates bulk crystallization.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
Dong Ju Moon 《Catalysis Surveys from Asia》2009,13(3):191-204
Generally, water gas shift (WGS) reaction is a very important step in the industrial production of hydrogen, ammonia and other
bulk chemicals utilizing synthesis gases. In this paper, we are reporting WGS reaction carried out in our research group for
the application of hydrogen station and fuel processor. We prepared various Mo2C, Pt–Ni-based and Cu-based catalysts for low temperature WGS reaction. The characteristics of the prepared catalyst were
analyzed by N2 physisorption, CO chemisorptions, XRD, SEM and TEM technologies, and compared with that of commercial Cu-Zn/Al2O3 catalyst. It was found that prepared catalysts displayed reasonably good activity and thermal cycling stability than commercial
LTS (Cu–Zn/Al2O3) catalyst. It was found that the deactivation of commercial LTS catalyst during the thermal cycling run at 250 °C was caused
by the sintering of active metal even though it shows high activity at less than 250 °C. The deactivation of Mo2C catalyst during the thermal cycling run was caused by the transition of Moδ+, MoIV and Mo2C on the surface of Mo2C catalyst to MoVI(MoO3) with the reaction of H2O in reactants. However, they showed higher stability than the commercial LTS catalyst during thermal cycling test. The Pt–Ni/CeO2 catalyst after the thermal cycling shows slightly deactivation due to the sintering of Ni metal. Among Cu-based catalysts,
it was found that Cu–Mo/Ce0.5Zr0.5O2 catalyst has higher WGS activity and stability over commercial LTS catalyst. The results suggested that Pt–Ni/CeO2 and Cu–Mo/Ce0.5Zr0.5O2 catalysts are desirable candidates for application in hydrogen station and fuel processor system even though all other catalysts
deactivated slowly during the thermal cycling run. 相似文献
16.
I. V. Vasilenko K. S. Gavrilenko I. E. Kotenko O. Kador L. Ouahab V. V. Pavlishchuk 《Theoretical and Experimental Chemistry》2007,43(5):353-360
A study was carried out on the conditions of formation of highly crystalline, superparamagnetic, nanosized oxides, MII Fe
2
III
O4 and γ-Fe2O3 (4.9–11.7 nm) by the thermal decomposition of complexes [MFe2O(CH3CO2)6(H2O)3] (M = Mn, Fe, Co, Ni) in tetraethylene glycol. The presence of surfactants leads to a decrease in the size and size distribution
of the nanoparticles formed, while the use of microwave radiation significantly reduces the time for formation of the nanocrystalline
oxides. The magnetic measurements showed ferrimagnetic ordering in the nanoparticles studied and their superparamagnetic behavior.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 5, pp. 323–329, September–October, 2007. 相似文献
17.
R. P. Gura V. M. Vlasenko V. A. Kuznetsov V. V. Raksha 《Theoretical and Experimental Chemistry》1985,21(3):324-329
Weight-space and IR spectroscopic methods have been used to investigate the reaction of NO and N2O with the surface of a copper-chromium oxide catalyst in the form of copper chromite with a 20% excess of Cr2O3. Comparisons have been made between the relative reactivities of the different oxides (NO, N2O, O2) in oxidation of the Cu+ and Cuo surface centers. The role of these centers in oxidation of CO by oxygen and by nitrogen oxides is discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 3, pp. 338–343, May–June, 1985. 相似文献
18.
M. G. Kotur 《Theoretical and Experimental Chemistry》1998,34(5):297-300
We have studied the correlation between the crystal structure and the catalytic activity of manganese oxides MnO, MnO2, Mn3O4, and Mn2O3 in liquid-phase oxidation of 1-octene by molecular oxygen. The catalytic activity decreases in the series of oxides with
octahedral coordination environment for the manganese atoms MnO−Mn2O3−MnO2. The oxide Mn3O4 (with mixed tetrahedral and octahedral environment for the Mn atoms) catalyzes the process according to a different mechanism.
L'vov Polytechnic State University, 12 S. Bandery ul., L'vov-13 290646, Ukraine. Translated from Teoreticheskaya i éksperimental'naya
Khimiya, Vol. 34, No. 5, pp. 324–327, September–October, 1998. 相似文献
19.
Małecki A. Prochowska-Klisch B. Gajerski R. 《Journal of Thermal Analysis and Calorimetry》1998,54(1):25-34
It has been found that the modified Zhuravlev equation, [(1−α)−1/3−1]2=ktn, which describes the kinetics of oxidation of V2O4 and V6O13 in the temperature range 820–900 K and in the oxygen pressure range 1.0–20 kPa, can be derived via the assumption that the
changes in the observed activation energy result from the changing contributions of the two diffusion processes controlling
the reaction rate. The values of the observed activation energy are in the range 160–175 kJ mol−1 for V2O4 and 188–201 kJ mol−1 for V6O13 in the scope of the experimental oxygen pressures and temperatures and conversion degrees of 0.1–0.9.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
El-Shobaky G. A. Radwan N. R. E. Radwan F. M. 《Journal of Thermal Analysis and Calorimetry》2002,68(1):275-287
The results obtained showed that the addition of small amounts of LiNO3 to the reacting mixed solids, consisting of equimolar proportion of Fe2O3 and basic MgCO3 much enhanced the thermal decomposition of magnesium carbonate. The addition of 12 mol% LiNO3 (6 mol% Li2O) decreased the decomposition temperature of MgCO3 from 525.5 to362°C. MgO underwent solid–solid interaction with Fe2O3 at temperatures starting from800°C yielding MgFe2O4. The amount of ferrite produced increased by increasing the precalcination temperature of the mixed solids. However, the
completion of this reaction required prolonged heating at elevated temperature above 1100°C. Doping with Li2O much enhanced the solid–solid interaction between the mixed oxides leading to the formation of MgFe2O4 phase at temperatures starting from 700°C. The addition of 6 mol% Li2O to the mixed solids followed by precalcination at 1050°C for 4 h resulted in complete conversion of the reacting oxides
into magnesium ferrite. The heat treatment of pure and doped solids at 900–1050°C effected the disappearance of most of IR
transmission bands of the free oxides with subsequent appearance of new bands characteristic for MgFe2O4 structure. The promotion effect of Li2O towards the ferrite formation was attributed to an effective increase in the mobility
of the various reacting cations. The activation energy of formation (ΔE) of magnesium ferrite was determined for pure and variously doped solids and the values obtained were 203, 126, 95 and 61
kJ mol−1 for pure mixed solids and those treated with 1.5, 3.0 and 6.0 mol% Li2O, respectively.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献