KINETIC STUDY OF ETHYLENE OXIDATION OVER AG CATALYST

This paper deals with the kinetics of ethylene oxidation under higher pressures. The detailed kinetics and the mechanism of this reaction have been studied under 21 atm.According to the experimental results, we summarize two kinetic equations. The mechanism of reaction is also discussed     

A Study of the Reaction Dynamics for the H+BrCH_3 System Using Quasi-classical Trajectory Theory

In the present paper, scattering probabilities and rate constants of different channels for the H + BrCH_3 reaction system have been calculated by means of quasiclassical trajectory (QCT) method. Several important kinetic effects such as vibrational enhancement, channel competition, vibrational adiabaticity, mass combination, coupling of angular momenta and the relation between the kinetic effects and the feature of the potential energy surface have been discussed. Based on these analyses, a direct-type rebonded mechanism for this reaction has been inferred and used to explain the nonsymmetric angular distribution of the products crossed-molecular beam experiment. The agreement of calculation with experimental results is satisfactory.     

Theoretical Study of the AlCl Disproportionation Reaction Mechanism on the Al(100) Surface

The surface disproportionation reaction mechanism of aluminum subchloride on the aluminum (100) surfaces has been investigated by the plane-wave density functional theory (DFT).Three kinds of possible reaction mechanism of AlCl disproportionation reaction on the aluminum (100) surfaces have been taken into account.The structures of reactants and products have been optimized,transition states have been confirmed and activation energies have been calculated.The adsorption energy of reactants and desorption energy of products have been determined.All of these have been employed to confirm the reaction mechanism and the rate determining step of AlCl disproportionation reaction on the aluminum (100) surfaces.     

Addition Mechanisms of Phenol toward Formaldehyde under Acidic Condition： a Theoretical Investigation

The reaction mechanisms of phenol with formaldehyde in the first and second addition at the ortho- and para-position in acid solution were theoretically investigated at the PW91/DNP level with solvent effects included. The reaction of phenol with protonated methanediol firstly forms an adduct intermediate, via a SN2 mechanism with a water molecule as the leaving group. From the adduct intermediate, there are two reaction channels involving a proton transfer to form the addition products. One is that a proton directly transfers via a four-membered ring transition state with a notable energy barrier (Four-member mechanism). Another mechanism involving a water molecule as catalyst to mediate the proton transfer (WCP mechanism), is a barrierless process, indicating that the formation of the adduct intermediate, the first reaction step, is rate-limiting. The reaction products are free hydroxymethyl phenols and/or hydroxybenzy carbocation (HOC6H4CH2+) which plays an important role in the following formation of methylene and methylene ether linkages. The second addition reactions between formaldehyde and hydroxymethyl phenol at all possible reaction sites of the phenol ring in acid solution were also investigated and discussed.     

X-Ray Photoelectron Spectroscopic Study on the Synthesis of Copper Sulphide in LB Films( Ⅱ )

The present paper covers the formation process of copper sulphide in copper stearate Langmuir-Blodgett films studied carefully by XPS. The further identification of sulfur species and the examination of its change in the reaction have been made. Also the formation mechanism of sulfur species in the special microenvironment-LB films is discussed.     

The Thermal Decomposition of Calcium Carbonate

The thermal decomposition reaction of calcium carbonate is a typical thermal decompo- sition reaction of the solid state. A great deal of studies on this reaction have been performed by previous investigators. This paper reports a procedure for estimating the non-isothermal kinetic parameters and the reaction mechanism of calcium carbonate.TG-DTG experiments were carried out on a LCT-1 model thermobalance and a WF-1 model differentiator with a TG-DTA-DTG simultaneous device. The size of…     

(Et_4N)_2[Fe_4(SPh)_10] Stimulated S_(RN)1 Reactions of α-Bromonaphth-alene with Pinacolone Carbanion

The studies of the radical chain nucleophilic substitution reaction (SRN1) have been active field in both mechanism and organic synthesis research1-4. The mechanism is a well known process by which a nucleophilic substitution is produced on a non-actived adequated substituted substrate. It is a chain process which involves radicals and radical anions as intermediates. The main steps of this mechanism are sketched in scheme 1. As stimulated methods of initiation step, the photostimulated5-7, …     

纳米氧化钕的制备及其催化性能的研究

Nanometer-sized neodymium oxide has been synthesized by humid solid state reaction at room temperature， and characterized by scanning electron microscope， laser light scattering and X-ray diffraction. The effects of nanometer -sized neodymium oxide on catalyzing thermal decomposition reaction of hexogen (cyclotrimethylenetriamine， RDX) and absorbent powder (nitrocellulose absorbed nitroglycerin， NC/NG) have been investigated by DSC method. The mechanism of these catalytic reactions has also been proposed. The experimental results show that nanometer-sized neodymium oxide can catalyze the decomposition reaction of RDX and NC/NG effectively. The experimental results further suggest that nanometer-sized neodymium oxide is a potentially useful combustion catalyst of nitroamine propellant.     

ORGANIC SOLVATION EFFECTS ON COLOUR REACTIONS OF MULTICOMPONENT COMPLEXES——GALLIUM (Ⅲ)-CHROMAZUROL S-CETYLTRIMETHYLAMMONIUM BROMIDE-ALCOHOL (AQUEOUS) SYSTEM

In this paper, the organic solvation effects on chromazurol S (CAS) and colour reactions of the multicomponent complexes (MCC, Ga-CAS-CTAB-Alcohols) have been investigated. The organic solvent, eontaining oxygen, could vigorously intensify the sensitivity and selectivity of the colour reaction of sensitized MCC. The composition, salvation number, solvation constant and stability constant of MCC were determined. The mechanism of organic solvation was explored.     

水热法制备氢氧化镍纳米线

Nickel hydroxide nanowires were prepared by hydrothermal method. The products were characterized by powder X-ray diffraction(XRD) and transmission electron microscopy(TEM). The results show that the morphology of nickel hydroxide nanowire is mainly straight. The diameters of the nanowires are about 20～30 nm and the lengths reach several micronmeters. The effects of hydrothermal reaction time and filling factor on the morphologies and structure of the products were studied. The formation mechanism for nickel hydroxide nanowires is also discussed.     

Kinetics of aquation of chloropentamminecobalt(III) perchlorate in ethylene glycol-water media

Summary The aquation of chloropentamminecobalt(III) ion has been studied in ethylene glycol-water mixtures up to 80% by weight at five temperatures from 35 to 55°C. Specific solvent effects on the reaction rate and mechanism have been investigated and discussed. The validity of our previously proposed equations, correlating the specific reaction rate with the dielectric constant of the medium has been examined. The thermodynamic parameters of activation have been calculated and presented as evidence for the solvation effects and in support of the proposed reaction mechanism.     

A density functional theory study on mechanism and substituent effects of a base-free and catalyst-free synthesis of functionalized dihydrobenzoxazoles

The reaction mechanism and the substituent effects of a base-free and catalyst-free synthesis of functionalized dihydrobenzoxazole have been investigated in detail by using the density functional theory (DFT) method. The calculated results reveal that the whole reaction should occur through three processes, and the initial intramolecular nucleophilic attack reaction is the rate-determining step. The possibility to afford crossover reaction products has been carefully excluded based on the extremely high barrier, which is well-consistent with the experimental results that the crossover products cannot be observed. The substituent effects have been studied through exploring the correlation of the experimental yields and the theoretically predicted barriers, which proves that the more electron-donating substituents of the imine should be more beneficial to the occurrence of the reaction.     

Solvent effects on binuclear complex formation between aquopentacyanoferrate(II) and tetraamminepyrazinecarboxylatocobalt(III) in binary aqueous mixtures

The substitution reaction between aquopentacyanoferrate(II) and tetraamminepirazynecarboxylatocobalt(III) to form a binuclear species is studied in various binary aqueous mixtures at different temperatures. Values of activation parameters seem to indicate no change in the mechanism of the reaction in the different mixtures. Medium effects have been rationalized by using a multiparameter regression of solvent parameters. Results show that the reaction follows a dissociative mechanism. © 1993 John Wiley & Sons, Inc.     

Relativistic DFT study on the reaction mechanism of second-row transition metal Ru with CO2

To estimate the importance of relativistic effects on the reaction mechanisms between Ru and CO2, the potential energy surfaces have been performed in the triplet and quintet electronic states using quasi-relativistic (Pauli), zero-order regularly approximated (ZORA), and nonrelativistic (NR) density functional theory (DFT) at the PW91/TZP level. The results demonstrate that there are two rival reaction mechanisms: one is an addition mechanism and the other is an insertion mechanism in the triplet state. The only mechanism in the quintet state is the insertion mechanism. The most favored reaction mechanism in Ru + CO2 is that the Ru atom in its ground state first attacks the CO bond of CO2, forming q-Ru(CO)O (5A') with the insertion mechanism, and then undergoes an intersystem crossing to t-Ru(CO)O (3A'). Then it crosses t-TS3 to produce t-ORuCO molecule. The relativistic effects are important for reactivity of the second-row transition metal to CO2. In the key step of t-Ru(CO)O via t-TS3 to t-ORuCO, relativistic effects reduce the barrier energy by 10.3 kcal/mol, which is nearly half the nonrelativistic barrier energy.     

Electrochemical Oxidation of Catechols in the Presence of Triethyl Phosphite

The mechanism of electrochemical oxidation of catechol and some of its derivatives have been studied in the presence of triethyl phosphite as a nucleophile in aqueous solution. Voltammetric studies indicate that the quinones derived from catechol, and its derivatives, participate in Michael addition reaction with triethyl phosphite. The reaction mechanism consists of electron transfer followed by a chemical reaction which is named as an EC mechanism. The homogeneous rate constants (k_obs) were estimated by comparing the experimental cyclic voltammograms with the digitally simulated voltammograms based on EC mechanism. Also the effects of nucleophile concentration and substituted group of catechols on voltammetric behavior and the rate constants of chemical reactions were examined.     

Mechanistic investigation of the 2,5-diphenylpyrrolidine-catalyzed enantioselective alpha-chlorination of aldehydes

The mechanism for the 2,5-diphenylpyrrolidine-catalyzed enantioselective alpha-chlorination of aldehydes with electrophilic halogenation reagents has been investigated by using experimental and computational methods. These studies have led us to propose a mechanism for the reaction that proceeds through an initial N-chlorination of the chiral catalyst-substrate complex, followed by a 1,3-sigmatropic shift of the chlorine atom to the enamine carbon atom. The suggested reaction course is different from previously proposed mechanisms for organocatalytic enamine reactions, in which the carbon-electrophile bond is formed directly. Furthermore, the rate-determining step in the overall reaction was determined and the presence of nonlinear effects was probed.     

Intrinsic oxidation kinetics of sulfite catalyzed by peracetic acid under different water quality and light conditions

Oxidation of sulfite is an important process in wet flue gas desulfurization. Using highly purified water or distilled water as a reaction medium and a transparent or an opaque intermittent reaction apparatus, the intrinsic oxidation kinetics of sulfite catalyzed by peracetic acid was investigated under four different conditions. The reaction order of the reagents and the activation energy were obtained. The results indicate that water quality and light have no obvious effects on the reaction order and activation energy, but have an influence on the reaction rate constant. The mechanism of the intrinsic reaction is proposed. The results derived with this mechanism are in good agreement with the experimental results. Supported by the National Basic Research Program of China (Grant No. JK00020), the Doctor Research Fund from North China Electric Power University (Grant No. 200612008), and the National High Technology Research and Development Program of China (Grant No. 2007AA061703)     

Transformation of 1,1-Dichloro-2,2-bis(4-nitrophenyl)ethene in the Reaction with Nitrite Ion in Polar Aprotic Solvents

The reaction of 1,1-dichloro-2,2-bis(4-nitrophenyl)ethene with sodium nitrite in polar aprotic solvents has been studied. Products of the reaction have been identified, and effects of different factors, including reactant dissociation and solvation, on the reaction rate constants have been analyzed. Thermodynamic parameters of the reaction have been determined, the multistep process has been simulated by quantum chemical calculations, and a plausible mechanism has been proposed.     

高分子载钯催化剂对有机锡烷偶联反应的催化性能及结构表征

制备了几种负载型钯催化剂，用于有机锡烷与有机卤化物的偶联反应中，考察了催化剂的使用寿命及载体对催化剂催化活性的影响，通过XPS、XRD、电镜等技术对催化剂进行了表征。结果表明，催化活性中心的质点钯是金属态钯，即催化剂中的钯可以看成是两配位不饱和的，经过氧化加成、金属转换、还原消除过程完成催化反应。     

高分子共混物中Friedel-Crafts烷基化反应原位增容与催化降解机理

采用GPC方法对共混组分的分子量、接枝率和降解度等数据进行分析, 发现AlCl₃催化剂对PS/POE共混物的作用表现在原位增容和催化降解两个方面. 结合Friedel-Crafts烷基化反应的特点细化反应过程, 发现PS/POE共混物在AlCl₃作用下发生接枝反应时, 有大量碳正离子出现, 而碳正离子周围的电子重排会导致分子链断裂, 从而引起共混组分出现大幅度降解. PS/POE/AlCl₃共混物中原位接枝与催化降解是一对竞争性反应, 同时存在, 并相互竞争.