Application of ultramicroelectrodes in studies of homogeneous catalytic reactions—part III. The condition for quasi-first and second order homogeneous catalytic reactions at ultramicrodisk electrodes in the steady state

The conditions for quasi-first and second order homogeneous catalytic reactions and their variation with each other at an ultramicrodisk electrode in the steady state are discussed in this paper. The order of reaction can be controlled by changing the dimension of the ultramicroelectrode: the second order reaction can be changed to quasi-first by decreasing the dimension of the ultramicroelectrode. An example of this is given. The main factor effect on the reaction order is the dimension of the ultramicroelectrode. The K₄Fe(CN)₆-aminopyrine system is selected to confirm the theory, the experiments showing that the system is a second order reaction at a 432 μm microelectrode, and a quasi-first order reaction at a 19 μm ultramicroelectrode. The kinetic constant of the system can be determined by applying the previous theory of homogeneous catalytic reaction.     

茂金属/有机硼化物催化1-癸烯均相聚合反应动力学

以茂金属体系rac-Et（1-Ind）₂ZrCl₂/C₆H₅NH（CH₃）₂B（C₆H₅）₄/Al（i-Bu）₃催化1-癸烯聚合,对不同反应条件下（如温度,铝锆摩尔比）聚合反应动力学进行了研究。通过中间取样并利用GC测定单体浓度、GPC测定聚合物相对分子质量,获取动态的变化数据;结合聚合反应机理和物料平衡,对烯烃聚合反应做了一些假设,建立了聚合反应的动力学模型,该模型包括链引发、链增长、链转移至单体、链转移至活性中心和链终止几个反应。借助Levenberg-Marquardt算法对模型参数进行优化,通过该模型可以预测聚合反应速率、数均分子量和重均分子量等参数,验证实验结果表明模型预测值与实验数据相接近。模型显示链引发过程在几秒内完成,链增长反应相对于链转移反应具有较低的活化能,温度升高有利于链转移反应的进行。     

Dynamics of irreversible uncoiling of a polymer chain

Using a simple dynamic model, the growth of rigidity and of the mean size of the polymer chain induced by a chemical reaction irreversibly fixing extended conformations of units has been investigated. When the reaction rate is controlled by the rotational diffusion of segments, the change in the mean length of a rigid segment and mean radius of gyration of the chain with time are described by power dependencies. For a macromolecule in a constant viscosity medium, the time needed to complete the reaction (i.e. to transform the coil into an extended rigid rod) is t_comp N³, where N is the initial number of segments in the chain. The cases of a kinetically controlled reaction and a mixed type of reaction have also been considered. The slowing down of the reaction caused by increasing the viscosity of the reaction medium has been evaluated, giving t_comp N⁷.     

Ag/MIL-101催化剂还原对硝基苯酚反应动力学

采用双溶剂浸渍法制备得到了粒径为1.9nm±0.6nm高分散性的Ag/MIL-101催化剂。考察了该催化剂在过量NaBH₄存在下,还原对硝基苯酚生成对氨基苯酚反应中的催化性能。本文通过研究催化剂浓度、底物浓度和温度对催化活性的影响,获得不同条件下的表观反应速率常数k_app,采用Langmuir-Hinshelwood吸附反应模型对所得动力学数据进行拟合,获得本征反应速率常数k,底物吸附常数K_4-NP和K_BH4,底物吸附焓、熵以及真实活化能E_A,k等热力学参数。研究表明,诱导时间t₀直接与该反应速率控制步骤的反应速率常数k有关。     

有机激发三重态参与的光化学反应研究进展

光化学反应包括直接光解和间接氧化反应,其中间接氧化反应主要通过活性氧化性物种（reactive oxygen species, ROS）包括单线态氧（¹O₂）、过氧自由基（{\mathrm{O}}_{\mathrm{2}}^{-}）和羟基自由基（·OH）等进行。近年来,有机激发三重态（³C^*）作为一种特殊的氧化剂参与光化学反应引起了广泛关注。本文主要综述了有机三重态光敏剂的形成和光化学反应机制、³C^*参与的环境光化学反应、³C^*自由基寿命、反应速率及稳态浓度测定和激发三重态的应用5个方面,并对未来有机分子激发三重态的研究方向进行了展望,指出³C^*是很多挥发性有机化合物（VOCs）或半/中等挥发性有机化合物（S/IVOCs）在大气中重要的汇,自然水体中溶解性有机质（dissolved organic matter,DOM）的激发三重态（³DOM^*）是污染物降解的主要氧化剂。今后应扩大³C^*与有机物反应的研究范畴,测定不同体系中³C^*的稳态浓度、产生速率（量子产率）等,为污染物治理提供理论依据。     

微通道下费托合成催化剂层涂覆厚度的数值研究

采用COMSOL-Multiphysics软件, 针对Fe基催化剂费托合成反应动力学特性, 建立了耦合流动、传热、传质、化学反应多物理场的二维数值计算单元模型, 研究微通道内的费托合成反应。重点研究了催化剂涂层厚度、冷却介质流速对微通道内传热传质、费托反应产物分布的影响规律。模拟结果表明:沿反应通道轴向方向, 催化剂涂层温度呈先升高后降低的趋势;随着催化剂涂层厚度的增加, 温度峰值出现的位置逐渐远离出口, CO转化率提高, CH₄的选择性增大, 而C₅₊的选择性逐渐减小;提高冷却介质流速有利于实现较好的温度控制, 显著降低CH₄的选择性, 提高C₅₊选择性;对于截面尺寸为0.6×0.6mm²、长度为200mm的微通道结构, 较佳的催化剂涂层厚度为0.1mm, 随着冷却侧冷却能力的增强, 较佳的催化剂涂层厚度变大。     

Interaction of ciprofloxacin hydrochloride with sodium dodecyl sulfate in aqueous/electrolytes solution at different temperatures and compositions

Interactions of ciprofloxacin hydrochloride(CPFH) with sodium dodecyl sulfate(SDS) were investigated by conductivity measurement in H_2O/electrolyte solutions(NaCl, Na_2SO_4 Na_3PO_4) over 298.15–318.15 K temperature range(with 5 K interval) considering the human body temperature. In all cases, two critical micelle concentrations(c~*) were observed which are increased in the presence of drug and decreased in the presence of salts enunciating the presence of interaction amongst the studied components. For(CPFH + SDS) system in the presence of salt, the c~*values at 303.15 K and I = 0.50 mmol·kg~(-1) followed the order: C_(NaCl)C_(Na_2SO_4)C_(Na_3PO_4). The ΔG_(1,m)~0 and Δ G_(2,m)~0values are found to be negative for all systems that show that the micellization process is thermodynamically spontaneous. For(CPFH + SDS) system in water, the Δ H_m~0 Δ S_m~0 values reveal that the micellization processes is both entropy dominated in almost all cases. In the occurrence of electrolytes, Δ H_m~0 and Δ S_m~0 values indicate that micellization processes are both entropy enthalpy restricted at upper temperature but it becomes totally entropy dependent at higher temperature. The higher positive Δ S_m~0 values indicate the enhanced hydrophobic interaction in presence of salts. The enthalpy-entropy compensation was determined from the linear relationship betweenΔ H_m~0 and Δ S_m~0 values in every state. Different transfer energies as well as compensation temperature and intrinsic enthalpy were also evaluated and the behaviors were comparable to other biological system.     

MONOLITHIC CATALYSTS: DIFFUSIONAL MASS TRANSFER OF CO THROUGH Y-ALUMINA SUBSTRATES UNDER REACTING CONDITIONS

Experimental kinetic data have been obtained for the CO oxidation reaction over laboratory made platina-rhodium monolithic catalyst. Inert layers of y-yalumina were deposited over the active layer in order to elucidate the diffusional effects on the monolithic catalyst. A synthetic gas mixture consisting of CO₁, O₂ and N₂ was the feed of an integral tubular reactor between 180 and 370°C. A first order kinetic rate expression with respect to CO concentration, which includes an inhibition term of second order was found to fit the experimental data via a model which also accounts for diffusional resistances. The obtained kinetic and diffusional data can be used in the design of a catalytic converter with improved efficiency. The results can also be used to interpret the diffusion mechanism inside the catalyst itself and it was concluded that Knudsen diffusion mechanism prevails.     

Dynamics of catalytic reactions on microdesigned surfaces

We report experimental and computational studies of reaction dynamics on Pt/Rh and Pt/TiO₂ microcomposite catalytic surfaces. Reaction fronts initiated at the material interface dominate both steady and dynamic behavior of the composite catalytic material. Our analysis links the transient phenomenon of front initiation to the bifurcations of reaction–diffusion systems with active boundaries.     

Determination of water uptake and diffusion of Cl ion in epoxy primer on aluminum alloys in NaCl solution by electrochemical impedance spectroscopy

The electrochemical impedance spectroscopy (EIS) of epoxy-coated aluminum alloy LY12 has been investigated during exposure to 3.5% NaCl solution. Using the continuous simulation of EIS by expanded general electrical model, the time-dependent impedance model of the alloy/coating/solution system was deduced. The results shown that the composite electrode displayed a barrier behavior before water and oxygen penetrated to alloy base. After water and oxygen reached the base, the impedance associated with corrosion of alloy base changed with the immersion time as following: (i) active corrosion period at the beginning (double-layer capacitance, C_dl, in parallel to the charge transfer resistance of electrochemical corrosion R_ct), (ii) impeding of the diffusion of corrosion production at the intermediate period as a result of the presence of coated film (a constant phase element Z_diff was additionally in series with R_ct), and (iii) appearance of the characteristic impedance related to Cl⁻ ion-participating reaction with alloy base at the later stage. From the linear part of ln C_c–t^0.5 curve in the early immersion stage, the apparent diffusion coefficient of water was obtained. The diffusion coefficient of water and Cl⁻ ion through the coating was also calculated by the required time for diffusion of permeation species through the coating to the metal interface obtained from the simulation of EIS data by which the occurrence of characteristic impedance element(s) corresponding to special species arrival can be determined.     

The highly selective catalytic hydrogenation of CO2 to CO over transition metal nitrides

Three transition metal-like facet centered cubic structured transition metal nitrides, γ-Mo₂N, β-W₂N and δ-NbN, are synthesized and applied in the reaction of CO₂ hydrogenation to CO. Among the three nitride catalysts, the γ-Mo₂N exhibits superior activity to target product CO, which is 4.6 and 76 times higher than the other two counterparts of β-W₂N and δ-NbN at 600 ℃, respectively. Additionally, γ-Mo₂N exhibits excellent stability on both cyclic heating–cooling and high space velocity steady state operation. The deactivation degree of cyclic heating–cooling evaluation after 5 cycles and long-term stability performance at 773 and 873 K in 50 h are all less than 10%. In-situ XRD and kinetic studies suggest that the γ-Mo₂N itself is able to activate both of the reactants CO₂ and H₂. Below 400 ℃, the reaction mainly occurs at the surface of γ-Mo₂N catalyst. CO₂ and H₂ competitively adsorbe on the surface of catalyst and CO₂ is the relatively stronger surface adsorbate. At a higher temperature, the interstitial vacancies of the γ-Mo₂N can be reversibly filled with the oxygen from CO₂ dissociation. Both of the surface and bulk phase sites of γ-Mo₂N participate in the high temperature CO₂ hydrogenation pathway.     

Kinetics of the Graphite-Uranium Dioxide Reaction from 1400° to 1756°C

The reaction of microspheres of UO_z with graphite was studied from 1400° to 1756°C. When a spherically symmetrical layer of carbide was produced around the UO₂ core, only UC₂ was formed, and the diffusion of oxygen through this layer was rate-controlling. The Arrhenius relation for this system is k_D= 21.0 exp(−90, 000/ RT ) cm²/s
The reaction of a geometrically nonsymmetrical configuration of UO₂ and UC₂ was also studied. Comparison of the reactions in the symmetrical and nonsymmetrical systems demonstrated that the kinetic behavior of the two systems is quite different and that the conversion in the nonsymmetrical system was 2 to 5 times faster. The importance of these observations to kinetic results reported in the literature for analogous systems is discussed.     

芳烃催化加氢反应机理的研究进展

对萘、菲、蒽及芘根据不同计算方法所得的反应活性位进行总结,对苯在金属表面的催化加氢机理-芳烃交换机理进行概括,对菲在MoS₂/Al₂O₃催化剂表面生成二氢菲的基元反应步骤和在Ni-MoS₂/Al₂O₃催化剂表面加氢生成四氢菲的过程进行总结,还给出了蒽的催化加氢反应网络图,分析了在不同催化条件下蒽是否有中环断裂情况的发生,给出了芘在RaneyNickel（W-7）催化剂表面生成二氢芘、四氢芘和六氢芘的催化加氢机理反应图,以及根据能量最低理论,判断芘发生加氢反应的优先位置情况,分别计算了芘加氢生成二氢芘、四氢芘、六氢芘和十氢芘可能存在的加氢路径。并总结了蒽、菲等多环芳烃发生催化加氢反应的规律。加深对多环芳烃催化加氢机理的研究将更好地指导重质油轻质化的进行,因此对多环芳烃催化加氢机理的研究具有重要意义。     

铁、钴、镍、铜和锌催化剂催化氨硼烷水解产氢性能研究

采用浸渍-还原法制备了铁、钴、镍、铜和锌催化剂,考察了其催化氨硼烷水解产氢性能,并优化了钴催化剂的制备条件和反应条件。结果发现,铁催化剂中铁以Fe₂B合金相存在,钴催化剂中钴以金属钴存在,镍催化剂中镍以金属镍和Ni（OH）₂·2H₂O存在,铜催化剂中铜以金属铜和氧化亚铜存在,锌催化剂中锌以Zn₄SO₄（OH）₆·4H₂O存在。铁、钴、镍、铜和锌催化剂催化氨硼烷水解产氢活性由大到小顺序为钴催化剂、镍催化剂、铜催化剂、铁催化剂、锌催化剂。显然,具有金属钴相的钴催化剂、金属镍相的镍催化剂和金属铜相的铜催化剂催化氨硼烷产氢活性高于具有Fe₂B合金相的铁催化剂。锌催化剂在制备条件下不能被还原为金属相,它几乎没有催化氨硼烷产氢活性。氯化钴与还原剂硼氢化钠的物质的量比为1∶1.3、还原温度为303 K时制备的钴催化剂催化BH₃NH₃水解产氢性能最佳。反应动力学计算表明钴催化剂催化BH₃NH₃水解产氢反应对氨硼烷浓度的反应级数为零级,对钴催化剂浓度的反应级数为一级,活化能为58 kJ/mol。     

甲烷直接催化氧化制甲醇催化剂及反应机理

研究甲烷合成甲醇的催化剂及催化机理是甲烷直接催化氧化制甲醇的关键。本文综述了甲烷合成甲醇的Pt系催化剂、Pd系催化剂、Rh系催化剂、Fe改性沸石催化剂、Cu改性沸石催化剂、改性金属有机框架材料催化剂以及相应的催化机理。结果表明,Pt系催化剂中K₂PtCl₄、Pt(bpym)Cl₂、Pt(bipy)Cl₂催化甲烷制甲醇机理为亲电取代反应。Pd系催化剂中Pd(OAc)₂在CF₃COOH水溶液中通过多步电子传递链将甲烷转化为甲醇;Pd/C在乙酸水溶液中催化甲烷合成甲醇是亲电取代和活性氧物种氧化两种机理共同作用的结果。Rh系催化剂中的Rh/ZSM-5、Rh/TiO₂通过锚定在载体孔道内的一价Rh与CO、H₂O和O₂作用将甲烷转化为甲醇。Fe、Cu改性沸石催化剂及改性金属有机框架材料催化剂通过均裂、异裂等自由基反应转化甲烷得到甲醇。指出研究高效活化甲烷分子和抑制甲醇深度氧化催化剂的设计、制备及深入探究其催化机理仍然是今后的研究重点。     

二维AuP2材料电催化固氮性能的理论研究

通过电化学反应将氮气（N₂）和水（H₂O）在常温常压的条件下转化为氨气（NH₃）是一种绿色环保的合成氨方法。但由于N₂具有非常高的化学惰性,必须借助电催化剂来加速反应的动力学过程。通过密度泛函理论计算揭示出新型二维无机材料AuP₂对N₂电化学还原制NH₃具有很好的催化活性。在二维AuP₂材料中,Au与P之间由于电负性差异发生显著的电荷转移,使带有正电荷的P可作为活性位点促进氮还原。计算表明整个反应的速控步是N₂生成^*NNH的过程,限制电压为1.2 V,催化活性可以跟部分金属催化剂相媲美。为设计高效氮还原电催化剂提供了新的思路。     

Some kinetic aspects of unsteady-state partial oxidation reactions. Dynamic processes on metal oxide surfaces

It is shown that steady-state kinetic data do not allow the discrimination between the redox and associated mechanisms of the partial oxidation reactions. A discrimination between these mechanisms was performed using transient experiments. The obtained rate expressions are in agreement with experimental kinetic data for catalytic partial oxidation of o-xylene.

An influence of the conjugate oxidation of a catalyst surface on dynamics and kinetics of the heterogeneous catalytic oxidative reactions is considered. Computing simulation of methane oxidative coupling of methane reaction at lowered temperature and elevated pressure has been performed. It showed that the reaction order with respect to oxygen exceeding unity is consistent with the chain branching mechanism of the reaction in the presence of TiSi₂ and TiB₂ and showed the important role of the branching chain cycles in the low-temperature OCM reaction at elevated pressure.     

循环流化床锅炉内石灰石同时煅烧/硫化反应模型研究

循环流化床锅炉内石灰石分解、脱硫发生的是同时煅烧/硫化反应。建立了石灰石同时煅烧/硫化反应的随机孔模型,综合考虑石灰石的分解、烧结和硫化,且CaO硫化反应基于CaSO₄产物层固态离子扩散模式。模型计算结果与实验测试结果吻合良好,并采用该模型研究了同时煅烧/硫化反应的特性。石灰石的同时煅烧/硫化反应包含连续的质量下降阶段和质量上升阶段,且质量最低点随着SO₂浓度的增加而升高。石灰石颗粒的煅烧反应发生在颗粒的壳层内,煅烧反应更符合区域反应模型而不是均相反应或缩核反应模型。煅烧环境中的SO₂与CaO层反应生成CaSO₄,导致CaO层内孔径和孔隙率减小,CO₂外扩散阻力增大,从而导致煅烧反应减慢。颗粒硫化反应速度随时间减慢,主要是颗粒内SO₂耗尽导致的,颗粒外层不断积累的CaSO₄减小了SO₂扩散通道,增加了SO₂孔内扩散阻力,使颗粒内SO₂耗尽区不断增大,颗粒的硫化反应速度不断下降。     

乙酸正戊酯酯化反应动力学探讨与催化精馏模拟

在间歇釜式反应器中,以NKC-9阳离子交换树脂为催化剂,对乙酸和正戊醇催化合成乙酸正戊酯的酯化过程进行了研究。实验考察了不同催化剂用量及反应温度对乙酸转化率的影响,同时测定了实验条件下乙酸正戊酯酯化反应的反应动力学数据。采用拟均相模型对实验数据进行关联,得到了平衡常数和反应速率常数的计算式。在本实验条件下,该酯化反应为吸热反应,反应热及正、逆反应活化能分别为8.339kJ/mol、50.191kJ/mol和41.852kJ/mol,平衡常数及正、逆反应速率常数与温度的关系式分别为：K=54.2173e^-8338.8/RT,k₁=95402.5e^50191/RT,k₂=1759.6e^41852.2/RT。结合测定的动力学方程,建立了基于严格数学模型的过程模拟计算方法,对乙酸正戊酯催化精馏酯化过程进行过程模拟优化。优化后的操作条件为精馏段板数3、反应段板数9、提馏段板数14、进料位置7、混合进料酸醇摩尔比1.1∶1,此时塔釜乙酸正戊酯摩尔分数与正戊醇转化率达到99%以上。     

微反应器内甲苯气固催化氧化反应动力学

微通道反应器具有优良的传热、传质性能，能有效避免催化剂床层内热点的形成，为研究强放热反应动力学提供有利条件。开展了微反应器内的V2O5/TiO2催化剂上的甲苯气相选择氧化动力学研究，在简化反应网络的基础上建立了动力学模型，并给出动力学参数。该模型能较好地反映和预测较宽的反应条件范围内的甲苯气固相催化氧化反应转化率及产物分布，为优化操作条件提供依据。