共查询到20条相似文献,搜索用时 31 毫秒
1.
Kinetics of isobutylene oxidation over a Mo-Sb-Te-O catalyst is studied in a flow-circulation system with the Korneichuk differential
reactor. The reaction orders of methacrolein, acetic acid, acetone, and CO2 formation, as well as the order of the overall reaction of isobutylene oxidation into methacrolein, with respect to oxygen
and isobutylene are determined at 613–703 K and oxygen concentrations of (0.33–13.05) x 10−3 mol/1 and isobutylene (3.2–121.9) × 10−4 mol/1. The activation energies of these reactions are determined. 相似文献
2.
Two oxidation stages of electrolytic ultradispersed iron powder at the temperature range of 90–450°C have been stated. The
contribution of increasing mass and evolving heat at the first oxidation stage due to changing Fe0 into Fe2O3 in the total oxidation effect is predominant. The thermal method of active metal determination in electrolytic iron powders
has been developed. The coarse-grained reduced iron powder was not oxidized completely just to 900°C because of local sintering
of big iron particles as a result of evolving heat at oxidation of high-dispersed iron particles.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
Hugo B. Suffredini Giancarlo R. Salazar-Banda Luis A. Avaca 《Journal of Sol-Gel Science and Technology》2009,49(2):131-136
One of the key objectives in fuel-cell technology is to improve the performance of the anode catalyst for the alcohol oxidation
and reduce Pt loading. Here, we show the use of six different electrocatalysts synthesized by the sol–gel method on carbon
powder to promote the oxidation of methanol in acid media. The catalysts Pt–PbO
x
and Pt–(RuO2–PbO
x
) with 10% of catalyst load exhibited significantly enhanced catalytic activity toward the methanol oxidation reaction as
compared to Pt–(RuO2)/C and Pt/C electrodes. Cyclic voltammetry studies showed that the electrocatalysts Pt–PbO
x
/C and Pt–(RuO2–PbO
x
)/C started the oxidation process at extremely low potentials and that they represent a good novelty to oxidize methanol.
Furthermore, quasi-stationary polarization experiments and cronoamperometry studies showed the good performance of the Pt–PbO
x
, Pt–(RuO2–PbO
x
)/C and Pt–(RuO2–IrO2)/C catalysts during the oxidation process. Thus, the addition of metallic Pt and PbO
x
onto high-area carbon powder, by the sol–gel route, constitutes an interesting way to prepare anodes with high catalytic
activity for further applications in direct methanol fuel cell systems. 相似文献
4.
Michael A. Beckett Martin P. Rugen-Hankey K. Sukumar Varma 《Journal of Sol-Gel Science and Technology》2006,39(2):95-101
The reaction of metaborate esters (RO)3B3O3 [R = Me, Et, ClCH2CH2–, Cl3CCH2–, ClCH2CH2CH2–, (ClCH2)2CH–] with Si(OR)4 (R = Me, Et), either neat or in dry propan-2-one or dry THF at room temperature, led to gels which when dried and heated
in air for 20 mins at 600°C afforded borosilicate glasses in high ceramic yields. The dried gels and glasses were characterized
by elemental analysis, TGA, IR, and powder XRD, and solid-state MAS 29Si and 11B NMR. The gelling reaction was investigated by solution 11B and 29Si NMR. These NMR studies indicated B–O–Si reaction intermediates and a mechanism involving alkoxy exchange and various condensation/elimination
reactions of the borosilicate esters have been proposed. 相似文献
5.
Zicheng Li Aiju Zhang Zhihong Li Yumei Zhu Liangjun Liu Huiqiang Xiang 《Journal of Sol-Gel Science and Technology》2011,57(1):24-30
The effect of ball milling process, co-doped seed and two step sintering technique on the properties of sol–gel derived alumina
abrasive sintered at low temperature was investigated. The results showed that ball milling time with 10 h can be effective
in enhancing the activity of the precursor and the microstructural uniformity of sintered alumina abrasive. A small amount
of Al2O3–(NH4)3AlF6 co-doped seed addition had potential synergistic effects for reducing α-Al2O3 phase transformation temperature and improving the mechanical property of alumina abrasive. A remarkable suppression of grain
growth was achieved by controlling sintering temperature with two-step sintering method. Therefore, by using ball milling
process, co-doping α-Al2O3–(NH4)3AlF6 seed and two-step sintering technique, the sol–gel derived uniform nanocrystalline alumina abrasive is easily achieved at
low temperature. Nanocrystalline alumina abrasive prepared at these conditions exhibited excellent mechanical properties and
wear resistance compared to fused corundum abrasive and those sol–gel derived corundum abrasive with conventional sintering
methods. 相似文献
6.
G. Czupińska 《Journal of Thermal Analysis and Calorimetry》2000,60(1):199-202
The phase equilibria in the part of the ternary system YPO4–K3PO4–Mg3(PO4)2 over the composition range YPO4–K3PO4–KMgPO4 were examined and determined by differential thermal analysis, X-ray powder diffraction and microscopic analysis in reflected
light.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
N. Achard J. J. Counioux G. Marichy A. Marchand 《Journal of Thermal Analysis and Calorimetry》2000,59(3):927-934
The electrical properties of ZnO varistors are induced by a sintering step. The phenomena occurring during this thermal treatment
have been studied through model systems whose nature and composition are well defined. The pure BiSbO4 and Bi3 Zn2 Sb3 O14 phases have been synthetised by Direct Oxidation of a Precursory Alloy (DOPA) and characterized using XRD method. Each one
of these phases can react with zinc monoxide through an invariant isobaric reaction in the ZnO–Bi2 O3 –Sb2 O3 system:
– at 998°C 17/3<ZnO>+2/3<Bi3 Zn2 Sb3 O14 > arrow <Zn7 Sb2 O12 > + ((Bi2 O3 ))
– at 1058°C 7<ZnO>+2<BiSbO4 > arrow <Zn7 Sb2 O12 >+((Bi2 O3 ))
These thermodynamic considerations can explain the thermal domain of the sintering reaction described in the literature.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Sharif Abdullah Al-Mamun Yasunori Tanaka Yoshihiko Uesugi 《Plasma Chemistry and Plasma Processing》2010,30(1):141-172
Here the authors developed a two-dimensional two-temperature chemical non-equilibrium (2T-NCE) model of Ar–CO2–H2 inductively coupled thermal plasmas (ICTP) around atmospheric pressure (760 torr). Assuming 22 different particles in this
model and by solving mass conservation equations for each particle, considering diffusion, convection and net production terms
resulting from 198 chemical reactions, chemical non-equilibrium effects were taken into account. Species density of each particle
or simply particle composition was also derived from the mass conservation equation of each one taking the non chemical equilibrium
effect into account. Transport and thermodynamic properties of Ar–CO2–H2 thermal plasmas were self-consistently calculated using the first order approximation of the Chapman–Enskog method at each
iteration point implementing the local particle composition and temperature. Calculations at reduced pressure (500 and 300 torr)
were also done to investigate the effect of pressure on non-equilibrium condition. Results obtained by the present model were
compared with results from one temperature chemical equilibrium (1T-CE) model, one-temperature chemically non equilibrium
(1T-NCE) model and finally with 2T-NCE model of Ar–N2–H2 plasmas. Investigation shows that consideration of non-chemical equilibrium causes the plasma volume radially wider than
CE model due to particle diffusion. At low pressure with same input power, presence of diffusion is relatively stronger than
at high pressure. Comparison of present reactive model with non-reactive Ar–N2–H2 plasmas shows that maximum temperature reaches higher in reactive C–H–O molecular system than non-reactive plasmas due to
extra contribution of reaction heat. 相似文献
9.
Ajaya Kumar Singh Bhawana Jain Reena Negi Yokraj Katre Surya P. Singh Virender K. Sharma 《Transition Metal Chemistry》2009,34(5):521-528
The kinetics of Ru(III) chloride-catalyzed oxidation of β-Alanine (NH3
+CH2CH2COOH, β-Ala) by N–bromophthalimide (NBP) in aqueous perchloric acid medium was studied at 35 °C. The rate law followed a first-order and zero-order
dependence with respect to [NBP] and [β-Ala], respectively. The reaction followed first-order kinetics with respect to [Ru(III)]
chloride at a range of low concentrations while the order changed from first- to zero-order at high concentration of [Ru(III)]
chloride; demonstrating the catalytic effect for the oxidation of β-Ala by NBP. The rate decreased with increase in acidity.
Chloride ions positively influenced the rate of the reaction. Neither phthalimide (NHP) nor Hg(II) influenced the reaction
rate. Ionic strength (I) and dielectric constant (D) of the medium had no significant effect on the rate. Activation parameters
of the reactions were determined by studying the reaction at different temperatures (30–50 °C). The colorimetric, FTIR, and
GC-MS techniques were used to identify methyl cyanide (CH3CN) and CO2 as products of the reaction. In the reaction, approximately 2.3 moles of NBP oxidized one mole of β-Ala. A reaction scheme
of the oxidation of β-Ala by NBP in the presence of Ru(III) chloride was found to be in consistent with the rate law and the
reaction stoichiometry. 相似文献
10.
Thi Ngoc Ha Le Mickaël Roffat Quoc Nghi Pham Stéphanie Kodjikian Odile Bohnke Claude Bohnke 《Journal of Sol-Gel Science and Technology》2008,46(2):137-145
The synthesis of the perovskite Li3xLa2/3–x□1/3–2xTiO3 by a chemical solution route, using a triblock copolymer surfactant, PEOn–PPOm–PEOn, is described. This titanate is a non-hygroscopic fast lithium conductor and therefore is a good candidate for electrochemical
applications. It is generally prepared by a conventional solid-state reaction (SSR) method. However this synthesis method
does not allow the preparation of nanopowders or the formation of thin films. For these special purposes, synthesis by a chemical
solution route, with the formation of a polymeric precursor during synthesis, has been investigated. By using the above-mentioned
non-ionic surfactant, the preparation of nanopowders of complex oxides can be done. Furthermore, this way of synthesis leads
to the formation of an intermediate polymeric precursor which can be easily spread on substrates to obtain films. We show
that the formation of a pure phase of the perovskite Li3xLa2/3–x□1/3–2xTiO3 is highly dependent on the synthesis conditions, namely the presence of water in the solvent, the EO/metal ratio, the Li+ content in the precursor and the calcination temperature. The influence of these parameters on the microstructure of the
oxide is studied by X-ray diffraction, scanning electron microscopy and granulometry. A powder of Li3xLa2/3–x□1/3–2xTiO3 (x = 0.10), with an average particles size of 200 nm, has been obtained. The ionic conductivity of this oxide is the same
as the one obtained with oxide prepared by SSR (a bulk conductivity of 1.4 × 10−3 S/cm at 37 °C). The ceramic obtained from this powder after sintering at 1,150 °C shows a good pH response. This material
can then be used as a sensitive membrane in a potentiometric pH sensor. The presence of hydrophobic PPO groups in the polymer
precursor allowed preparing films of Li3xLa2/3–x□1/3–2xTiO3 with a good adherence on Pt substrate. This kind of synthesis is then very promising to prepare micro pH sensors. 相似文献
11.
M. H. Pournaghi-Azar H. Dastangoo M. Ziaei 《Journal of Solid State Electrochemistry》2007,11(9):1221-1227
The electrocatalytic activity of a Prussian blue (PB) film on the aluminum electrode by taking advantage of the metallic palladium
characteristic as an electron-transfer bridge (PB/Pd–Al) for electrooxidation of 2-methyl-3-hydroxy-4,5-bis (hydroxyl–methyl)
pyridine (pyridoxine) is described. The catalytic activity of PB was explored in terms of FeIII [FeIII (CN)6]/FeIII [FeII (CN)6]1− system. The best mediated oxidation of pyridoxine (PN) on the PB/Pd–Al-modified electrode was achieved in 0.5 M KNO3 + 0.2 M potassium acetate of pH 6 at scan rate of 20 mV s−1. The mechanism and kinetics of the catalytic oxidation reaction of PN were monitored by cyclic voltammetry and chronoamperometry.
The results were explained using the theory of electrocatalytic reactions at chemically modified electrodes. The charge transfer-rate
limiting reaction step is found to be a one-electron abstraction, whereas a two-electron charge transfer reaction is the overall
oxidation reaction of PN by forming pyridoxal. The value of α, k, and D are 0.5, 1.2 × 102 M−1 s−1, and 1.4 × 10−5 cm2 s−1, respectively. Further examination of the modified electrodes shows that the modifying layers (PB) on the Pd–Al substrate
have reproducible behavior and a high level of stability after posing it in the electrolyte or Pyridoxine solutions for a
long time. 相似文献
12.
Nafise Modanlou Juibari Abbas Eslami 《Journal of Thermal Analysis and Calorimetry》2017,127(1):115-122
A new powder metallurgy technique was developed in order to increase the reinforcement proportion of aluminum with two different fractions of Al2O3. Aluminum powders were mixed with 20 % vol of alumina particles as primarily reinforcement, and additional alumina was produced in situ as a result of reaction between Al and additional 7.5 % vol of Fe2O3 powder. The three grades of powders were milled and hot-pressed into small preforms, and differential scanning analysis (DSC) was performed to determine the kinetics of microstructural transformations produced on heating. DSC curves were mathematically processed to separate the superposing effects of thermal reactions. Transformation points on resulting theoretical curves evidenced two distinct exothermal reaction peaks close to the melting point of aluminum that were correlated with formation of Fe–Al compounds and oxidation of aluminum. Microstructural investigations by means of SEM-EDX and XRD suggested that these exothermal reactions produced complete decomposition of iron (III) oxide and formation of Fe–Al compounds during sintering at 700 °C, and therefore, heating at higher temperatures would not be necessary. These results, along with calculation of activation energies, based on Kissinger’s method, could be used to optimize the fabrication of Al-Al2O3 composites by means of reactive sintering at moderate temperatures. 相似文献
13.
Specific features of the kinetics of alkane and alkylbenzene oxidation with HOONO formed in the H2O2-NaNO2 system (pH 4.27) are quantitatively explained assuming the simultaneous occurrence of reactions in the gas and liquid phases.
A model of the kinetic distribution method is developed and verified that accounts for the equilibrium distribution of a substrate
and a reagent between phases and their interaction in both phases. Relative rate constants for the oxidation ofn-alkanes (C3-C8), isobutane, cyclopentane, cyclohexane, benzene, and alkylbenzenes are measured over a wide range of the volume ratios of
the gas and liquid phases (λ = Vg/V1). Relative rate constants for the oxidation of alkanes in the gas phase and alkylbenzenes in gas and solution were determined.
Similarity in substrate selectivities and kinetic isotope effects of the gasphase reactions of alkanes and arenes with peroxynitrous
acid and•OH radicals suggest that hydroxyl radical or the ˙OH...NO2 radical pair is an active species in the gas phase. In solution, alkylbenzenes react nonselectively with HOONO, as well as
with ˙OH radicals. In contrast to the liquid-phase oxidation of arenes, the liquidphase oxidation of all alkanes under study
insignificantly contribute (5–15%) to the overall rate of the substrate consumption. 相似文献
14.
A kinetic model is presented which considers the catalytic reduction of NO to N2 by hydrocarbons in oxidizing atmosphere (NO−HC−O2) as the sum of two simultaneous competitive reactions: the red-ox reaction between NO and hydrocarbon (NO−HC) and the hydrocarbon
oxidation (O2−HC). The model is developed for alkenes employed as reductants and noble metal catalysts. The ratio of the kinetic constants
of the two reactions can be considered as a selectivity index in evaluating the ability of a catalyst to favor the desired
NO reduction with respect to the undesired O2−HC oxidation. 相似文献
15.
Kinetics and mechanism of oxidation of ferrocyanide by N-bromosuccinimide in aqueous acidic solution
Alaa Eldin M. Abdel-Hady 《Transition Metal Chemistry》2008,33(7):887-892
The kinetics of oxidation of ferrocyanide by N-bromosuccinimide (NBS) has been studied spectrophotometrically in aqueous acidic medium over temperature range 20–35 °C,
pH = 2.8–4.3, and ionic strength = 0.10–0.50 mol dm−3 over a range of [Fe2+] and [NBS]. The reaction exhibited first order dependence on both reactants and increased with increasing pH, [NBS], and
[Fe2+]. The rate of oxidation obeys the rate law: d[Fe3+]/dt = [Fe(CN)6]4–[HNBS+]/(k
2 + k
3/[H+]). An outer-sphere mechanism has been proposed for the oxidation pathway of both protonated and deprotonated ferrocyanide
species. Addition of both succinimide and mercuric acetate to the reaction mixture has no effect on the reaction rate under
the experimental conditions. Mercuric acetate was added to the reaction mixture to act as scavenger for any bromide formed
to ensure that the oxidation is entirely due to NBS oxidation. 相似文献
16.
V. I. Vedeneev L. B. Romanovich V. Ya. Basevich V. S. Arutyunov O. V. Sokolov Yu. V. Parfenov 《Russian Chemical Bulletin》1997,46(12):2006-2010
The phenomenon of the negative temperature coefficient (NTC) of the reaction rate of the oxidation of rich propane—oxygen
mixtures was experimentally studied. The NTC phenomenon is qualitatively described by a simple kinetic model containing a
minimum set of reactions related to the oxidation of the starting hydrocarbon, propane, and the propyl C3H7
. radical formed.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2120–2124, December, 1997. 相似文献
17.
Xiaojun Tan Weihua Wang Ping Li Xiuli Yang Gengxiu Zheng Yuxiang Ma Zhuangdong Yuan 《Theoretical chemistry accounts》2007,118(2):357-362
The formations of the phosphinidene derivative HPNaF and its insertion reactions with R–H (R=F, OH, NH2, CH3) have been systematically investigated employing the density functional theory (DFT), such as the B3LYP and MPW1PW91 methods.
A comparison with the results of MP2 calculations shows that MPW1PW91 underestimates the barrier heights for the four reactions
considered. Similarly, the same is also true for the B3LYP method depending on the selected reactions, but by much less than
MPW1PW91, where the barrier heights of the four reactions are 25.2, 85.7, 119.0, and 142.4 kJ/mol at the B3LYP/6-311+G* level
of theory, respectively. All the mechanisms of the four reactions are identical to each other, i.e., an intermediate has been
located during the insertion reaction. Then, the intermediate could dissociate to substituted phosphinidane(H2RP) and NaF with a barrier corresponding to their respective dissociation energies. Correspondingly, the reaction energies
for the four reactions are −92.2, −68.1, −57.2, and −44.3 kJ/mol at the B3LYP/6-311+G* level of theory, respectively, where
both the B3LYP and MPW1PW91 methods underestimate the reaction energies compared with the MP2 results. The linear correlations
between the calculated barrier heights and the reaction energies have also been observed. As a result, the relative reactivity
among the four insertion reactions should be as follows: H–F > H–OH > H–NH2 > H–CH3. 相似文献
18.
S. A. Hassanzadeh-Tabrizi E. Taheri-Nassaj 《Journal of Sol-Gel Science and Technology》2011,57(2):212-220
Response surface methodology (RSM) based on central composite design (CCD) was successfully applied to the optimization and
modeling of densification of nanocrystalline Al2O3 powder prepared by sol–gel method. The effects of three operating variables, sintering temperature, calcination temperature
and milling time on the densification of nanocrystalline Al2O3 were systematically evaluated. A quadratic model for densification was proposed. Analysis of variance (ANOVA) indicated that
the proposed quadratic model could be used to navigate the design space. The simulated values obtained from the statistical
model were in conformity with the experimental results within an average error of ±1.5%. The optimum operating conditions
for densification were found to be 1,579 °C of sintering temperature, 909 °C of calcination temperature and 117 min of milling
time. The obtained density under the optimum conditions determined by RSM was 98.5%. The results confirmed that RSM based
on central composite design was an accurate and reliable method to optimize the densification conditions of nanocrystalline
Al2O3 powder. 相似文献
19.
Nitrogenated nanocrystalline diamond films with controlled electrical conductivity are grown in electrical arc plasma in CH4/H2/Ar/N2 gas mixtures and characterized by scanning electron microscopy and spectroscopic measurements. Their electrochemical properties
are studied by electrochemical impedance spectroscopy. Transfer coefficients of reactions in the [Fe(CN)6]3−/4− redox system are determined. The electrochemical behavior of the material is controlled by its nitrogenation (3–20% N2 in the reaction gas mixture). The nitrogenated nanocrystalline diamond has higher differential capacitance in indifferent
electrolyte (1 M KCl) solution than not nitrogenated one; the nitrogenation also increases the reversibility of reactions
in the [Fe(CN)6]3−/4− redox system. By and large, with nitrogenation of diamond, its electrochemical behavior changes from the one characteristic
of a “poor conductor” to that characteristic of metallike conductor. In this respect the nanocrystalline diamond electrodes
grown in the electrical arc plasma are similar to those grown in microwave plasma. 相似文献
20.
Hugo R. Fernandes Dilshat U. Tulyaganov Ashutosh Goel José M. F. Ferreira 《Journal of Thermal Analysis and Calorimetry》2011,103(3):827-834
This article aims to shed some light on the structure and thermo-physical properties of lithium disilicate glasses in the
system Li2O–SiO2–Al2O3–K2O. A glass with nominal composition 23Li2O–77SiO2 (mol%) (labelled as L23S77) and glasses containing Al2O3 and K2O with SiO2/Li2O molar ratios (3.13–4.88) were produced by conventional melt-quenching technique in bulk and frit forms. The glass-ceramics
(GCs) were obtained from nucleation and crystallisation of monolithic bulk glasses as well as via sintering and crystallisation
of glass powder compacts. The structure of glasses as investigated by magic angle spinning-nuclear magnetic resonance (MAS-NMR)
depict the role of Al2O3 as glass network former with four-fold coordination, i.e., Al(IV) species while silicon exists predominantly as a mixture
of Q
3
and Q
4
(Si) structural units. The qualitative as well as quantitative crystalline phase evolution in glasses was followed by differential
thermal analysis (DTA), X-ray diffraction (XRD) adjoined with Rietveld-reference intensity ratio (R.I.R.) method, Fourier
transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The possible correlation amongst structural
features of glasses, phase composition and thermo-physical properties of GCs has been discussed. 相似文献