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1.
In this study, a new pressure drop method has been used to investigate the kinetics of carbon dioxide reaction with aqueous blend of 2-amino-2-ethyl-1,3-propanediol (AEPD) with piperazine (PZ). The blending of a small amount of PZ with AEPD has a significant effect on the observed rate constant, kobs. It was observed that kobs values of the blend increased more than twice than the summation of kobs values of individual alkanolamines. The reaction kinetics in this study were modeled by assuming a termolecular mechanism. The addition of 0.1 mol/L of PZ to 1 mol/L AEPD exhibited an observed rate constant, kobs of 8824.1 s−1, which is comparable to other alkanolamine mixtures. Hence, PZ/AEPD mixtures can be potentially used for rapid carbon dioxide capture.  相似文献   

2.
An apparatus is described for the measurement of oxygen uptake into a polymer sample at constant oxygen pressures in the range 20–1000 mm Hg. Measurements of the rate of oxygen uptake into poly-4-methylpentene-1 show that the rate is accurately first-order in oxygen pressure over the range 50–800 mm pressure for temperatures ranging from 122 to 154°C and film thickness in the range 0.001–0.025 cm. A theoretical treatment of the kinetics of a reaction in which oxygen diffuses into both faces of a thin film, in which it is consumed by a first-order reaction shows that the oxidation rate ρ per unit area of film surface is given by ρ = ρ tanh ßL/2 where ρ is the limiting oxidation rate for a thick film, L is the film thickness, and ß = (k/D)1/2, k being the oxidation rate constant and D the diffusion constant. Values of D and the activation energy for diffusion calculated from autoxidation data are in good agreement with values determined directly.  相似文献   

3.
It is shown that it is possible to obtain good data for the rate constant for the decomposition of alkoxy radicals [RO] by using nitric oxide as a radical trap. Two experimental systems have been used. The first system involves the use of dialkyl peroxides [(RO)2] as thermal sources of alkoxy radicals. The peroxide concentration was ~10?4M, nitric oxide ~2 × 10?4M, and the extent of reaction was ~10%. The total pressure was altered using carbon tetrafluoride as an inert gas. The mechanism is Hence R2/R3 = k2[N O]/k3. Our previous studies show that k2 lies in the range 1010.3±0.2M?1·sec?1. The second system employs alkyl nitrites [RONO] as a thermal source of alkoxy radicals. The experimental conditions are very similar, except that we chose to use an atmosphere of nitric oxide for initial experiments. If anything nitric oxide appears to be superior to carbon tetrafluoride as an energy transfer agent. The mechanism is Hence R3 = k1'k3[RO NO]/(k3 + k2 + k6 [N O]). Results are given for R = t-Am, s-Bu, t-Bu, i-Pr, Et, and Me. In addition the first unequivocal evidence is given for the pressure dependence of k3 when R = t-Bu. The implications for atmospheric chemistry and combustion are also discussed.  相似文献   

4.
Ozone, O3, reacts with a carbon sample at room temperature. Clean carbon samples show a half to one and a half order of magnitude increased initial rate constant (k0) for O3 loss relative to repetitively exposed carbon samples. The ozone loss rate and therefore the rate constant reaches steady state (kss) on the time scale of tens of minutes, upon exposure to a characteristic dose of 8 × 1017 molecules for a 30-mg carbon sample independent of the flow rate. This characteristic dose closely corresponds to a monolayer of adsorbed ozone molecules on the carbon sample. Both k0 and kss decrease with increasing flow rate of O3 into the reactor, and the loss rate is found to depend on [O3]. When the loss rate is plotted against the steady state concentration of O3, a saturation plot results which is proportional to the surface coverage, θ, at a given [O3].This interpretation rests upon a Langmuir type kinetics model with an assumed first-order dependence of the loss rate constant. The “sticking coefficients” track the rate constants and are on the order of 10?3 to 10?5 depending on the carbon sample, dose, and flow rate. Furthermore, ko depends on the length of the dark period (absence of O3 exposure) and is larger the longer time the sample has had to recuperate from previous O3 exposures up to a period of 150 s. This surface relaxation is thought of as a time-dependent change in surface coverage taking place in the dark period and is therefore an indication of a slow surface diffusion/reaction that can be separated from the adsorption-desorption kinetics. The mass balance shows that for every ozone molecule that is lost on the surface, an oxygen molecule is found. This adsorbed odd oxygen is then responsible for product formation, which comprises the volatile components CO and CO2 to an extent of 20 to 40% of the odd oxygen deposited on the surface. The difference is thought to be in a preoxidized state on the carbon sample, which evolves CO and CO2 upon heat treatment.  相似文献   

5.
The kinetic isotope effect (KIE) for carbon and oxygen in the reaction CO + OH has been measured over a range of pressures of air and at 0.2 and 1.0 atm of oxygen, argon, and helium. The reaction was carried out with 21–86% conversion under static conditions, utilizing the photolysis of H2O2 as a source of OH radicals. The value of the KIE for carbon varies with pressure and the kind of ambient gas; for air the ratio of the reaction rates 12k/13k has the value 1.007 at 1.00 atm and decreases to 0.997 at 0.2 atm; for oxygen and argon over the same pressure range the values are 1.002–0.994 and 1.000–0.991, respectively. The value of the KIE for the CO oxygen atom is 16k/18k = 0.990 over the pressure range 0.2–1.0 atm and is independent of the kind of ambient gas. No exchange of the oxygen atoms in the activated complex, followed by decomposition to the starting molecules, was observed. From the mechanistic standpoint the normal KIE observed for carbon at the high pressure is attributed to the initial formation of the activated HOCO radical, whereas the inverse KIE observed at low pressures is a result of the KIE for the reverse reaction HOCO? → CO + OH being greater than that for the forward reaction HOCO? → CO2 + H. The derived isotopic equilibrium constant for HOCO ?CO favors the enrichment of 13C in the more strongly bound HOCO.  相似文献   

6.
For the first time, the electrochemical oxygen reduction reaction (ORR), was investigated using cyclic voltammetry (CV) on the electrodeposited manganese oxide (MnO x )-modified glassy carbon (MnO x -GC) electrode in the room temperature ionic liquids (RTILs) of EMIBF4, i.e. 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4). The results demonstrated that, after being modified by MnO x on a GC electrode, the reduction peak current of oxygen was increased to some extent, while the oxidation peak current, corresponding to the oxidation of superoxide anion, i.e., O2 was attenuated in some degree, suggesting that MnO x could catalyze ORR in RTILs of EMIBF4, which is consistent with the results obtained in aqueous solution. To accelerate the electron transfer rate, multi-walled carbon nanotubes (MWCNTs) was modified the GC electrode, and then MnO x was electrodeposited onto the MWCNTs-modified GC electrode to give rise to a MnO x /MWCNTs-modified GC electrode, consequently, the improved standard rate constant, ks, originated from the modified MWCNTs, along with the modification of electrodeposited MnO x , showed us a satisfactory electrocatalysis for ORR in RTILs of EMIBF4. Published in Russian in Elektrokhimiya, 2009, Vol. 45, No. 3, pp. 340–345. The article is published in the original.  相似文献   

7.
We have studied the oxidation of benzyl alcohols by nitrous and nitric acid in sulfuric acid media. The oxidation by nitrous acid is rapid and has an activation energy of 10.6 ± 0.8 kcal mol?1. A Hammett plot of logk2 vs. σ+ is linear with a ρ value of ?1.4. The oxidation by nitric acid in sulfuric acid media is autocatalytic. From the kinetic and product analyses, it is concluded that a common oxidant, the nitrosonium ion is involved when either nitrous or nitric acid is used. A mechanism is proposed which involves the abstraction of hydride from the alcohols as the rate determining step. It is demonstrated that the autoxidation of the alcohols is catalyzed by nitrous acid or nitric oxide.  相似文献   

8.
The selective catalytic reduction rate of NO with N‐containing reducing agents can be enhanced considerably by converting a part of NO into NO2. The enhanced reaction rate is more pronounced at lower temperatures by using an equimolar mixture of NO and NO2. The kinetics of NO oxidation over Pt‐WO3/TiO2 catalyst has been determined in a fixed‐bed reactor with different concentrations of oxygen, nitric oxide, and nitrogen dioxide in the presence of 8% water. It has been found that the reaction is second order with respect to nitric oxide, first order for oxygen with a third‐order rate constant. Also, it is found that there is no effect on the reaction order with an addition of NO2, CO, or SO2. It follows the same second order but the reaction rate is found to be changed. It is observed that in the case of NO2 and SO2, the reaction rate tends to decrease, but it increases with the addition of CO into the feed. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 613–620, 2006  相似文献   

9.
The rate constant for the reaction of ground-state oxygen atoms with methanol has been determined between 297 and 544 K by a phase-shift technique using mercury photosensitized decomposition of N2O to generate oxygen atoms. The relative oxygen atom concentration was monitored by the chemiluminescence from the reaction of oxygen atoms with nitric oxide. The results are accommodated by the Arrhenius expression k1 = (9.79 ± 2.71) × 1012 exp[(?2267 ± 111)/T]cm3/mol·s, where the indicated uncertainties are 95% confidence limits for 10 degrees of freedom. As an incidental part of this work, the third-body efficiency of CH3OH relative to N2O for the reaction O + NO + M → NO2 + M (M = CH3OH) was determined to be 3.1 at 298 K.  相似文献   

10.
The catalysed ring opening copolymerizations (ROCOP) of carbon dioxide/epoxide or anhydride/epoxide are controlled polymerizations that access useful polycarbonates and polyesters. Here, a systematic investigation of a series of heterodinuclear Mg(II)M(II) complexes reveals which metal combinations are most effective. The complexes combine different first row transition metals (M(II)) from Cr(II) to Zn(II), with Mg(II); all complexes are coordinated by the same macrocyclic ancillary ligand and by two acetate co-ligands. The complex syntheses and characterization data, as well as the polymerization data, for both carbon dioxide/cyclohexene oxide (CHO) and endo-norbornene anhydride (NA)/cyclohexene oxide, are reported. The fastest catalyst for both polymerizations is Mg(II)Co(II) which shows propagation rate constants (kp) of 34.7 mM−1 s−1 (CO2) and 75.3 mM−1 s−1 (NA) (100 °C). The Mg(II)Fe(II) catalyst also shows excellent performances with equivalent rates for CO2/CHO ROCOP (kp=34.7 mM−1 s−1) and may be preferable in terms of metallic abundance, low cost and low toxicity. Polymerization kinetics analyses reveal that the two lead catalysts show overall second order rate laws, with zeroth order dependencies in CO2 or anhydride concentrations and first order dependencies in both catalyst and epoxide concentrations. Compared to the homodinuclear Mg(II)Mg(II) complex, nearly all the transition metal heterodinuclear complexes show synergic rate enhancements whilst maintaining high selectivity and polymerization control. These findings are relevant to the future design and optimization of copolymerization catalysts and should stimulate broader investigations of synergic heterodinuclear main group/transition metal catalysts.  相似文献   

11.
The consumption of nitric oxide in the shock-heated nitric oxide, hydrogen, and argon system had been studied and modeled as the chain-branching process containing the reaction H + NO ? N + OH (k3) as a slow-branching step. Through the computer simulation method the authors clarified the role of the initiation reaction H2 + NO ? HNO + H (k1) in the system and obtained the rate constants of k1 and k3 as k1 = 1013.5±0.15 exp (?55.2 kcal/RT) and k3 = 1013.7±0.15 exp (?48.7 kcal/RT) (cm3/mole·sec), respectively. k1 was one order larger than the value obtained in the flame experiment by Halstead and Jenkins.  相似文献   

12.
Characteristic features of naphthalene oxidation and the kinetics of naphthalene pyrolysis in supercritical water (SCW) were studied using a batch reactor under isobaric conditions at a pressure of 30 MPa, in the temperature range from 660 °C to 750 °C, and for different levels of oxygen supply, varying from 0 to 2.5 moles of O2 per mole of naphthalene. The pyrolysis produces benzene, toluene, methane, hydrogen, soot, and carbon oxides. The rate constant for naphthalene pyrolysis in SCW was found to be k = 1012.3±0.2exp(–E/T) s–1 where E = 35400±500 K. For T > 660 °C, water participates in the chemical reactions of naphthalene conversion, particularly, in the formation of carbon oxides. The conversion of naphthalene in pure SCW is accompanied by heat evolution. Molecular oxygen oxidizes a part of naphthalene completely, i.e., to CO2 and H2O, this reaction being so prompt that in some cases, self-heating of the mixture and thermal explosion in the reactor were observed.  相似文献   

13.
Progress in the photodynamic therapy (PDT) of cancer should benefit from a rationale to predict the most efficient of a series of photosensitizers that strongly absorb light in the phototherapeutic window (650–800 nm) and efficiently generate reactive oxygen species (ROS=singlet oxygen and oxygen‐centered radicals). We show that the ratios between the triplet photosensitizer–O2 interaction rate constant (kD) and the photosensitizer decomposition rate constant (kd), kD/kd, determine the relative photodynamic activities of photosensitizers against various cancer cells. The same efficacy trend is observed in vivo with DBA/2 mice bearing S91 melanoma tumors. The PDT efficacy intimately depends on the dynamics of photosensitizer–oxygen interactions: charge transfer to molecular oxygen with generation of both singlet oxygen and superoxide ion (high kD) must be tempered by photostability (low kd). These properties depend on the oxidation potential of the photosensitizer and are suitably combined in a new fluorinated sulfonamide bacteriochlorin, motivated by the rationale.  相似文献   

14.
The kinetics of iodine dioxide (OIO) reactions with nitric oxide (NO), nitrogen dioxide (NO2), and molecular chlorine (Cl2) are studied in the gas‐phase by cavity ring‐down spectroscopy. The absorption spectrum of OIO is monitored after the laser photodissociation, 266 or 355 nm, of the gaseous mixture, CH2I2/O2/N2, which generates OIO through a series of reactions. The second‐order rate constant of the reaction OIO + NO is determined to be (4.8 ± 0.9) × 10?12 cm3 molecule?1 s?1 under 30 Torr of N2 diluent at 298 K. We have also measured upper limits for the second‐order rate constants of OIO with NO2 and Cl2 to be k < 6 × 10?14 cm3 molecule?1 s?1 and k < 8 × 10?13 cm3 molecule?1 s?1, respectively. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 688–693, 2007  相似文献   

15.
Current researchers from environmental and industrial fields are focusing on advanced means of carbon dioxide (CO2) capture to limit its consequences in process industries. They also intend to enhance the mitigation of environmental impart by CO2 especially its greenhouse effect. In this study, the kinetics of CO2 reaction with an aqueous blend of piperazine (PZ) and 2‐amino‐2‐ethyl‐1,3‐propanediol (AEPD) were investigated. It was found that blending of AEPD with a little percentage of PZ generated the observed rate constant, ko, values that were more than twice the direct summation of the ko values of the aqueous pure amines at the corresponding concentration and temperature. The kinetic study of the system was modeled using a termolecular mechanism. Blending 0.05 kmol/m3 of PZ with 0.5 kmol/m3 of AEPD gives an observed rate constant ko value of 2397.9 s?1 at 298 K. This result is comparable to rate constants of other amine mixtures. Thus, the aqueous blend of AEPD with PZ is an attractive solvent for CO2 capture that has good advantages. The PZ that serves as the promoter in the reaction is needed in small fraction, whereas AEPD, which is a sterically hindered amine, increases CO2 absorption capacity of the system. AEPD can be produced from renewable materials. © 2013 Wiley Periodicals, Inc. Int J Chem Kinet 45: 161–167, 2013  相似文献   

16.
Utilization of carbon dioxide as a soft oxidant for the catalytic dehydrogenation of ethylbenzene (CO2-EBDH) has been recently attempted to explore a new technology for producing styrene selectively. This article summarizes the results of our recent attempts to develop effective catalyst systems for the CO2-EBDH on the basis of alumina-supported vanadium oxide catalysts. Its initial activity and on-stream stability were essentially improved by the introduction of antimony oxide as a promoter into the alumina-supported catalyst. Insertion of zirconium oxide into alumina support substantially increased the catalytic activity. Modification of alumina with magnesium oxide yielded an increase of catalyst stability of alumina-supported V–Sb oxide due to the coking suppression. Carbon dioxide has been confirmed to play a beneficial role of selective oxidant in improving the catalytic performance through the oxidative pathway, avoiding excessive reduction and maintaining desirable oxidation state of vanadium ion (V5+). The positive effect of carbon dioxide in dehydrogenation reactions of several alkylbenzenes such as 4-diethylbenzene, 4-ethyltoluene, and iso- and n-propylbenzenes was also observed. Along with the easier redox cycle between fully oxidized and partially reduced vanadium species, the optimal surface acidity of the catalyst is also responsible for achieving high activity and catalyst stability. It is highlighted that supra-equilibrium EBDH conversions were obtained over alumina-supported V–Sb oxide catalyst in CO2-EBDH as compared with those in steam-EBDH in the absence of carbon dioxide.  相似文献   

17.
The reaction of 1,3-cyclopentadiene (CPD) with ground-state atomic oxygen O(3P), produced by mercury photosensitized decomposition of nitrous oxide, was studied. The identified products were carbon monoxide and the following C4H6 isomers: 3-methylcyclopropene, 1,3-butadiene, 1,2-butadiene, and 1-butyne. The yield of carbon monoxide over oxygen atoms produced (?CO) was equal to the sum of the yields of C4H6 isomers in any experiment. ?CO was 0.43 at the total pressure of 6.5 torr and 0.20 at 500 torr. We did not succeed in detecting any addition products such as C5H6O isomers. It was found that 3-methylcyclopropene was produced with excess energy and was partly isomerized to other C4H6 isomers, especially to 1-butyne. The excess energy was estimated to be about 50 kcal/mol. The rate coefficient of the reaction was obtained relative to those for the reactions of atomic oxygen with trans-2-butene and 1-butene. The ratios kCPD+O/ktrans-2-butene+O= 2.34 and kCPD+O/k1-butene+O = 11.3 were obtained. Probable reaction mechanisms and intermediates are suggested.  相似文献   

18.
采用X射线光电子能谱(XPS)原位分析研究了298 K时烧结UC的清洁表面在O2气氛中的初始氧化过程. UC试样清洁表面通过氩离子束长时间溅射获取. 初始反应各阶段U4f, O1s和C1s芯能级谱的变化显示样品表面的氧化产物为UO2和自由碳. 当O2饱和吸附后, UC表面氧化膜的增长呈抛物线型, 氧透过氧化膜的扩散为UC进一步氧化的速率控制步骤. 定量分析表明, 反应过程中U, C原子均未出现明显的表面偏析.  相似文献   

19.
The rate constant for the reaction of CH3OCH2 radicals with O2 (reaction (1)) and the self reaction of CH3OCH2 radicals (reaction (5)) were measured using pulse radiolysis coupled with time resolved UV absorption spectroscopy. k1 was studied at 296K over the pressure range 0.025–1 bar and in the temperature range 296–473K at 18 bar total pressure. Reaction (1) is known to proceed through the following mechanism: CH3OCH2 + O2 ↔ CH3OCH2O2# → CH2OCH2O2H# → 2HCHO + OH (kprod) CH3OCH2 + O2 ↔ CH3OCH2O2# + M → CH3OCH2O2 + M (kRO2) k = kRO2 + kprod, where kRO2 is the rate constant for peroxy radical production and kprod is the rate constant for formaldehyde production. The k1 values obtained at 296K together with the available literature values for k1 determined at low pressures were fitted using a modified Lindemann mechanism and the following parameters were obtained: kRO2,0 = (9.4 ± 4.2) × 10−30 cm6 molecule−2 s−1, kRO2,∞ = (1.14 ± 0.04) × 10−11 cm3 molecule−1 s−1, and kprod,0 = (6.0 ± 0.5) × 10−12 cm3 molecule−1 s−1, where kRO2,0 and kRO2,∞ are the overall termolecular and bimolecular rate constants for formation of CH3OCH2O2 radicals and kprod,0 represents the bimolecular rate constant for the reaction of CH3OCH2 radicals with O2 to yield formaldehyde in the limit of low pressure. kRO2,∞ = (1.07 ± 0.08) × 10−11 exp(−(46 ± 27)/T) cm3 molecule−1 s−1 was determined at 18 bar total pressure over the temperature range 296–473K. At 1 bar total pressure and 296K, k5 = (4.1 ± 0.5) × 10−11 cm3 molecule−1 s−1 and at 18 bar total pressure over the temperature range 296–523K, k5 = (4.7 ± 0.6) × 10−11 cm3 molecule−1 s−1. As a part of this study the decay rate of CH3OCH2 radicals was used to study the thermal decomposition of CH3OCH2 radicals in the temperature range 573–666K at 18 bar total pressure. The observed decay rates of CH3OCH2 radicals were consistent with the literature value of k2 = 1.6 × 1013exp(−12800/T)s−1. The results are discussed in the context of dimethyl ether as an alternative diesel fuel. © 1997 John Wiley & Sons, Inc.  相似文献   

20.
The thermal decomposition of trifluoromethoxycarbonyl peroxy nitrate, CF3OC(O)O2NO2, has been studied between 278 and 306 K at 270 mbar total pressure using He as a diluent gas. The pressure dependence of the reaction was also studied at 292 K between 1.2 and 270 mbar total pressure. The rate constant reaches its high‐pressure limit at 70 mbar. The first step of the decomposition leads to CF3OC(O)O2 and NO2 formation, that is, CF3OC(O)O2NO2 + M ? CF3OC(O)O2 + NO2 + M (k1, k?1). Reaction (?1) was prevented by adding an excess of NO that reacts with the peroxy radical intermediate and leads to carbonyl fluoride (CF2O), carbon dioxide (CO2), nitrogen dioxide (NO2), and small quantities of CF3OC(O)O2C(O)OCF3. The kinetics of reaction (1) was determined by following the loss of CF3OC(O)O2NO2 via IR spectroscopy. The temperature dependence of the decomposition follows the equation k1(T) = 1.0 × 1016 e?((111±3)/(RT)) for the exponential term expressed in kJ mol?1. The values obtained for the kinetic parameters such as k1 at 298 K, the activation energy (Ea), and the preexponential factor (A) are compared with literature data for other acyl peroxy nitrates. The atmospheric thermal stability of CF3OC(O)O2NO2 and its dependence with altitude is discussed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 831–838, 2008  相似文献   

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