甲烷部分氧化过程中强制振荡的动力学Monte Carlo模拟(英文)

为了有效控制动力学振荡行为以提高反应的转化率,利用Monte Carlo方法研究了甲烷催化部分氧化过程中的强制振荡行为,探讨了原料气周期性变化对振荡动力学和转化率的影响.研究表明原料气周期性变化不仅可以有效调控振荡的动力学行为,产生如短周期振荡和双峰振荡等特殊动力学过程,而且还可以提高反应的转化率.当强制过程的周期从T/3增大到2T(T为自发振荡过程的平均周期),振荡过程从短周期振荡变化为双峰振荡.对反应过程中CO的转化率进行了计算,结果表明原料气周期性变化可以有效提高反应的转化率.振荡动力学的改变和转化率的提高主要是因为强制振荡过程使得催化剂表面发生了从氧化态向还原态的转变.     

亚氯酸盐-硫代硫酸盐非缓冲体系的动力学

研究了亚氯酸盐-硫代硫酸盐反应体系在非缓冲条件下的复杂动力学行为.结果发现,在开放体系中反应的pH值和Pt电位存在准周期振荡分叉和混合模式振荡分叉通向混沌的过程，且pH峰与Pt电位峰反相位.当与起始浓度比相对较小时，随着流速的逐渐升高，体系的pH值和Pt电位从简单的小振幅振荡(S)经过准周期振荡分叉到混沌，最后回到简单大振幅振荡(L)；而当与起始浓度比相对较高时，随着流速的降低，体系的pH值和Pt电位出现LS1、LS2、LS3…LSn的混合模式振荡,并在每对(LSn、LSn＋1)振荡区间发现了LSn、LSn＋1随机出现的非周期振荡行为.运用硫价态变化的一般动力学模型，模拟出了反应体系的混合模式振荡及非周期振荡.     

过氧化氢氧化硫化钠反应体系的复杂振荡

研究了过氧化氢和硫化钠反应体系在连续流动搅拌反应器中的复杂振荡行为. 观察到11型振荡、12型振荡、非周期振荡以及衰减振荡; 在振荡周期内, 拐点附近区域H+扰动产生的延迟与振荡相位pH有关. 在完全基于硫价态变化的经验速率方程模型的基础上进行数值模拟, 得到的各种复杂振荡行为与实验现象基本一致, 证明了硫价态变化可驱动复杂非线性动力学行为.     

周期扰动位相对化学振荡的调制效应

由Rossler反应系统的理论模型出发,构造一种具有外部周期扰动的新动力学系统,并采用逆算符法和数值分析法研究该系统的振荡态在周期扰动调制下的动力学行为.结果表明,在周期扰动的调制下,系统的状态由单周期振荡态(1p)变为周期2(2p)、周期4(4p)等多周期振荡态以及混沌态.扰动位相是系统呈现上述多种演化模式的控制参数,在扰动位相不同的数值区间,系统呈现的演化模式不同,而且扰动位相数值的微小改变,还影响每种演化模式的内部结构.     

硫氰酸盐电化学氧化的动力学复杂性

本文利用多种电化学方法研究了多晶电极上硫氰酸盐电化学氧化的动力学和机理,观察到电流和电位振荡。循环伏安测量表明氧化动力学分为二步过程。除了振荡现象,系统也展示双稳态,利用时间电位扰动,氧化反应可在高电位和低电位稳态之间转换,而且强烈吸附的惰性离子也可诱导从振荡转化为稳态。     

异丁烷在钼酸锌上的催化氧化脱氢

研究了钼酸锌对异丁烷氧化脱氢反应的催化作用,考察了原料气中烷氧体积比、N₂及水蒸汽对反应结果的影响.提高反应原料气中的烷氧体积比能够提高异丁烯选择性,但也会降低异丁烷的转化率.原料气中加入N₂不利于反应;而加入水蒸汽可提高异丁烯选择性.催化剂表面主要是弱酸中心,对反应有利.     

以钌(Ⅱ)-联吡啶配合物为催化剂的B-Z化学发光振荡研究

报道了一种以钌(Ⅱ)-联吡啶[Ru(bpy)2+3]为催化剂的B-Z化学发光振荡新现象. 研究了B-Z化学发光振荡反应的影响因素, 并对体系的UV光吸收振荡进行了对比研究, 探讨了化学发光振荡反应的可能机理. 结果表明, 该体系的化学发光振荡是由于氧化态的钌(Ⅱ)-联吡啶被振荡反应过程中的强还原性中间体还原所引起的, 化学发光振荡随时间增加呈现周期性变化.     

甲醇在Pt表面电化学氧化过程中的化学振荡

基于甲醇电化学氧化的双途径机理,建立了能够表征甲醇电化学氧化过程电位振荡的非线性动力学模型.所建甲醇氧化系统动力学演化模型涉及三个主要的变量:电极电位(e),毒性中间体CO的表面覆盖度(x),含氧物种H2Oa的表面覆盖度(y).通过反应速率常数ki=exp(ai(e-ei))实现了化学反应与电极电位的耦合.研究发现,在不同的电流密度范围内甲醇电化学氧化呈现不同的动力学特征.甲醇电化学氧化时出现的电位振荡现象可以归因为:一是氧化过程中生成了毒性中间体CO,这是产生电化学振荡的诱因;二是强烈依赖于电极电位的非电化学反应,即,含氧物种H2Oa在Pt表面的生成与消失,则是维系振荡的直接原因.而甲醇电化学氧化体系复杂的动力学行为根源在于电极电位e对CO和含氧物种H2Oa所参与反应的耦合反馈作用.对所建模型的数值分析成功地解释了为什么甲醇电化学氧化时出现的电位振荡现象只发生在一定的电流密度范围.     

CoOx/CeO2催化剂上的CO低温氧化反应

 采用沉淀氧化法制备了CoOx/CeO2催化剂, 并分别在干燥和含有水汽的原料气中进行了CO的氧化反应. 结果发现, CoOx/CeO2复合氧化物催化剂具有良好的CO低温氧化活性和抗水性. 在干燥的原料气中和196 K的条件下,该催化剂催化氧化CO的转化率可连续400 min以上保持在99%; 当温度升高到298 K反应 2400 min后, CO的转化率可达到94%. 而当反应气中含有3.1%的水汽时, 在383 K下反应2400 min后, CO的转化率仍可保持在79%.     

钌基催化剂催化的气固相反应

催化剂被广泛应用于各种化学品的生产,从原子尺度了解整个催化反应体系有利于合理设计新型催化剂.参与气固相反应的催化剂主要有贵金属催化剂和过渡金属催化剂.近年来, Ru基催化剂由于在低温低压下表现出良好的催化活性而广泛应用于一些气固相反应.本文对 Ru的基本性质、氧化行为以及 Ru基催化剂的理论研究进行综述.介绍了钌基催化剂参与的气固相反应,包括挥发性有机物的催化氧化、一氧化碳优先氧化(PROX)、氨合成、氯化氢氧化以及甲烷部分氧化,分析了催化性能与理化性质之间的构效关系,提出了钌基催化剂在相关反应中存在的问题以及未来发展趋势. Ru具有多种氧化态,在 Ru基催化剂参与的气固相反应中,金属 Ru和/或 RuO2被认为是活性物种,通常反应温度在400oC以下. Ru (0001)晶面在 O2存在条件下,随着氧气含量的不同会从中间态过渡到氧化态,实验证明该晶面属于 RuO2.理论研究证实了在反应过程中 RuO2的存在,并提出了核壳结构,对于其它气固相反应的机理研究有一定启发.挥发性有机物(VOC)的催化氧化主要集中烷烃、烯烃、芳烃以及卤代烃的催化氧化,催化剂的理化性质包括颗粒粒径、价态和晶体结构等对催化活性有很大影响,并且 Ru基催化剂对卤代烃的催化氧化表现出良好的抗卤性,同时多卤代副产物低于其它贵金属体系. Ru基催化剂在低温条件下对 PROX具有高的活性和选择性,并且可以有效抑制 H2氧化、CO甲烷化和CO2甲烷化等副反应发生.氨合成的难点在于 N≡N具有很强的解离能,许多研究表明,氨合成使用的 Ru基催化剂的催化性能与载体性质密切相关, Ru与载体之间强的相互作用使得电子可以迅速地从载体转移到 Ru颗粒上,掺杂其它有效元素可能会提供更多的氧空位和有效防止高温焙烧导致催化剂烧结.对于 HCl氧化虽然研究较少,但是 Over等人对 HCl氧化机理进行了深入研究,并且日本住友化工设计的 Ru基催化剂已经商业化. Ru基催化剂可以有效降低甲烷部分氧化的反应温度和压力,并具有高的选择性和稳定性,避免副产物生成.现有催化系统以及新型催化剂开发仍面临诸多挑战,例如：对于单一 VOC氧化过程和多元 VOCs催化氧化的机理和动力学需要进一步研究;对于氨合成需要寻求具有高电导率的载体,从而将电子快速转移到 Ru颗粒表面,使得氨合成在更低温度下进行;为了避免副产物生成,需确保新型 Ru基催化剂上PROX和甲烷部分氧化在低温低压条件下进行; Ru基催化剂理化性质对活性的影响以及失活等问题需要进一步研究.     

催化剂对CaO固硫反应动力学的影响

提高CaO的固硫率是对煤炭燃烧污染防治的研究热点。本研究探索用催化剂提高CaO固硫率的可行性及其对固硫反应动力学的影响。用热天平测试了在CaO中添加不同催化剂的固硫反应的进程,并采用等效粒子模型处理实验数据,计算了表面化学反应控制阶段及产物层扩散控制阶段的动力学参数。实验表明,CaO固硫反应初期为表面化学反应控制阶段,后期转为产物层扩散控制阶段。以碱金属的盐类为催化剂,它们均能使固硫反应前期的化学反应控制阶段的反应活化能下降,并按Li,Na,K,Cs的顺序依次递减,而碱金属盐的负离子主要影响产物层扩散阶段的固硫反应。     

轻烃在改性ZSM－5催化剂上转化成芳烃与低碳烯烃的选择性控制

研究了Ｃ３－Ｃ９烷烃在不同的改性ＺＳＭ－５沸石上的反应规律．过渡金属离子改性的ＺＳＭ－５沸石显示了较高的芳烃选择性，芳烃的选择性还取决于改性金属离子的脱氧能力并可通过预硫化得到改进．钾、钡改性的沸石显示了较高的烯烃选择性，增加钾含量，烯烃选择性显著提高，但也明显抑制了催化剂的活性；提高Ｂａ含量，同样可提高烯烃选择性，但对活性影响不大．环己烯的模型反应结果表明，Ｋ，Ｂａ的作用在于抑制了双分子氢转移反应和提高了脱氢能力．红外表征结果表明，沸石表面的羟基，因不同金属改性而发生不同的变化．此外，气相氧对提高烯烃和芳烃的收率有明显作用     

Catalytic conversion of guaiacol to alcohols for bio-oil upgrading

Guaiacol was chosen to represent O-containing chemicals with lower effective hydrogen carbon ratio(H/Ceff factor) in bio-oil,and the hydrodeoxygenation of guaiacol was investigated over non-precious and nonsulfided catalysts. Effects of metal composition,reaction temperature,and hydrogen pressure on conversion and selectivity were investigated systematically. Among various compositions of catalysts,Ni Co/CNT exhibited best performance of guaiacol conversion with higher selectivity towards desired alcohols with higher H/Cefffactor. The reaction pathways of guaiacol in aqueous were proposed based on the product analyzed.Results show that metal composition and temperature have great effects on the conversion of guaiacol and the yields of desired products.     

Polyamide synthesis from 6-aminocapronitrile, part 2: heterogeneously catalyzed nitrile hydrolysis with consecutive amine amidation

To test the potential of heterogeneous catalysts for the nylon-6 synthesis from 6-aminocapronitrile, a number of zeolites, aluminum silicate, and metal oxides were tested as catalysts for the model reaction of pentanenitrile with water and hexylamine to N-hexylpentanamide. All zeolitic and aluminum silicate systems showed an insufficient performance, while the metal oxides (TiO(2), ZrO(2), Nb(2)O(5)) showed very promising results. The kinetic behavior of the metal oxides was further investigated. First the nitrile was catalytically hydrolyzed to the terminal amide and subsequently the amidation of the hexylamine occurred. To polymerize 6-aminocapronitrile into nylon-6, more than 99 % nitrile conversion was required to obtain a high-molecular-weight polymer. Pentanenitrile conversions larger than 99 % can be obtained within six hours, at 230 degrees C, by using ZrO(2) as the catalyst. A kinetic study (by using IR spectroscopy) on the behavior of the metal oxides demonstrated that the adsorbed nitrile was catalytically hydrolyzed at the surface, but remained tightly bound to the surface. Zirconia-catalyzed polymerizations of 6-amino-capronitrile demonstrated that high-molecular-weight nylon-6 is feasible by using this route.     

Deep oxidation of methane on granulated and monolith copper—manganese oxide catalysts

Deep oxidation of methane on the granulated Cu—Mn-mixed oxide catalyst and metallic monolith catalysts coated with the same oxide was studied. The experimental kinetic curves for both monolith and granulated catalysts are satisfactorily described by the first-order rate law. The values of activation energies, reaction rate constants, and feed flow rates for the specified conversion almost coincide for both types of the catalysts. The data obtained confirm the possibility of a quantitative comparison of the activities of the granulated and monolith catalysts. The activity of the monoliths is proportional to the concentration of the active component.     

Nanostructure Copper-exchanged ZSM-5 Catalytic Activity for Conversion of Volatile Organic Compounds (Toluene and Ethyl Acetate)

Gas phase catalytic oxidation of ethyl acetate and toluene was examined over copper modified ZSM‐5 catalysts under atmospheric pressure. Nanostructure of ZSM‐5 was characterized by XRD, SEM and TEM techniques. Elemental composition of ZSM‐5 was determined using EDX, ICP‐AES and XPS techniques. Results of catalytic studies showed better catalytic activity of Cu‐ZSM‐5 catalysts than those of parent ZSM‐5 and HZSM‐5, which revealed catalytic role of copper ions in the Cu‐ZSM‐5 catalysts. Effects of some parameters over catalytic conversion of these compounds were also studied. Ethyl acetate showed more reactivity than toluene over the Cu‐ZSM‐5 catalysts. Furthermore, the catalytic activity of Cu‐ZSM‐5 catalysts increased with increasing the copper loadings. The conversion behavior of a binary mixture of ethyl acetate and toluene was different from that of a single form. A promotive and inhibitive behavior was observed for conversion of ethyl acetate and toluene in the binary mixture, respectively. Water vapor as co‐feed had an inhibitive effect on conversion of organic compounds over the Cu‐ZSM‐5 catalysts.     

Durable and highly selective tungsten-substituted MFI metallosilicate catalysts for the methanol-to-propylene process by designing a novel feed-supply technique

For the catalytic reaction of methanol to propylene (MTP), conventional H-ZSM-5 and W-substituted MFI metallosilicate catalysts were successfully synthesized using a hydrothermal method. The catalysts were properly characterized by several techniques. For comparison of the catalytic lifetime, feedstock of MTP was provided by both a conventional system and a novel feed-supply technique. The novel technique used the piezoelectric ultrasonic effect. It was revealed that feed composition via novel feed-supply technique remained totally constant, whereas with conventional system it relatively changed. Complete methanol conversion, higher propylene yield of 54.3%, greater light olefin yield of 85.2%, and longer-term catalytic lifetime of 101 h were productively obtained for H-W(250)AlMFI catalyst using a novel method for provision of feed. The better performance of this catalyst can be attributed to adequate content of tungsten, appropriate mesoporosity, sufficient strength of acidic sites, and stable feed composition of the novel feed-supply technique. Furthermore, the MTP process was miniaturized by the piezoelectric ultrasonic device.     

Low-temperature activation of methane over rare earth metals promoted Zn/HZSM-5 zeolite catalysts in the presence of ethylene

At low temperature of 723 K, methane can be easily activated in the presence of ethylene in the feed, and converted to higher hydrocarbons (C2–C4) and aromatics (C6–C10), through its reaction over rare metals modified Zn/HZSM-5 zeolite catalysts without undesirable carbon oxides formation. Methane can get 37.3% conversion over the above catalysts under low temperature, and the catalysts show a longer lifetime than usual metal supported HZSM-5 zeolite catalysts without adding any rare earth metals. The effects of methane activation over various rare earth metal promoted Zn/HZSM-5 catalysts on the products and influences of several reaction conditions such as temperature, catalyst lifetime and molar ratio of CH4/C2H4 have been discussed.     

Statistical fluorinated copolymers from heterogeneous atom transfer radical copolymerization of styrene and 2,2,2‐trifluoroethyl methacrylate with similar reactivity ratios

Fluorinated copolymers with statistical structure of azeotropic or gradient composition were prepared from heterogeneous atom transfer radical copolymerizations of styrene (S) and 2,2,2‐trifluoroethyl methacrylate (T). The polymerization kinetic studies show that while the propagation rate constant of S increased with a decreasing S content in the comonomer feed ratio, the propagation rate of T decreased with decreases of the S content in the comonomer feed ratio. The polymerization rate and controllability of the heterogeneous ATRP of S and T were regulated by the solubility of Cu(II)/ligand in the reaction mixture, based on a mechanistic analysis and solubility tests of the Cu(II)/ligand system in the reaction media. The reactivity ratios of S and T were 0.22 and 0.35, as evaluated from kinetic analysis of monomer conversions higher than 35%. These statistical polymers self‐assembled in T to form giant vesicles GVs) with broad diameter distribution in the range of 1–10 μm. Unlike the methods normally used to prepare gradient copolymers by spontaneous controlling with feeding model or batch polymerization of comonomers with obvious differences in the reactivity ratio, in this contribution, we report a novel synthetic strategy for preparing gradient copolymers can also be prepared from both monomers with very similar reactivity ratio. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013