C3链烃的热解/气化机理及速率常数计算

针对C₃链烃化合物在热处置过程中反应时间短、反应路径多且反应过程难以通过试验的方式进行准确检测和分析的问题，基于密度泛函理论和过渡态理论，对丙烷、丙烯和丙炔在H₂O以及O/H/OH/CH₃自由基作用下的热解/气化机理进行研究。通过Gaussian及其配套软件逐一分析了潜在的反应路径，并通过反应速率常数确定主要的反应路径和演化规律。结果表明，H₂O和这些自由基主要是通过攻击丙烷端链上的甲基进行反应，丙烯和丙炔则主要是在双键或三键位置与自由基加成后再进行脱碳反应。其中，H自由基与C₃链烃进行脱碳反应的速率常数最快，且与不饱和度成正比。     

可燃工质氨的燃烧及阻燃机理的研究

当前环境问题日益突出,天然工质氨作为环保性制冷剂再次引起科学界的广泛重视。但NH₃存在可燃可爆性问题,在实际应用中存在着一定的安全隐患。采用量子化学密度泛函理论计算方法,在M06-2X/6-311+G（d,p）的计算水平上,对NH₃的燃烧及阻燃机理开展研究,得到反应过程的微观反应路径。研究表明,NH₃可通过三种方式发生燃烧微观反应,一是发生自身裂解反应,生成H自由基;二是与氧气发生碰撞反应,生成OOH自由基;三是与活性自由基发生碰撞反应,生成新的活性自由基,NH₃可与H、O、OH自由基反应,反应能垒较低。此外,还计算了两种典型的阻燃基团F和CF₃对可燃分子NH₃的微观阻燃路径,验证其阻燃效果。本文从微观分子的角度考察了可燃工质氨的燃烧及阻燃机理,为新一代低温室效应工质的燃烧及阻燃机制提供了参考。     

MOCVD生长InN气相反应路径的量子化学研究

利用量子化学的密度泛函理论,对MOCVD生长InN的气相反应路径进行较全面的计算分析,通过计算不同温度下各反应的Gibbs能差和反应能垒,分别从热力学和动力学角度确定从TMIn/NH₃生长InN的主要气相反应路径。研究发现：当载气为N₂时,InN生长的气相反应路径主要为热解路径与加合路径的竞争。在高温(T>873.0 K)时以TMIn的热解为主,在低温(T<602.4 K)时以TMIn与NH₃的加合反应为主,在中温(602.4 K3的分解反应为主。当载气为H₂时,由于气相热解和表面反应将产生H和NH₂自由基,H自由基将加速TMIn的热解,NH₂自由基将与TMIn、DMIn等反应生成氨基物DMInNH₂。H自由基还会与氨基物反应,在高温衬底附近生成InNH₂,从而使表面反应前体由传统的MMIn和In变为InNH_2<...     

C_4烷烃混合热裂解反应机理的数值模拟

通过对蒸汽热裂解反应机理实验研究困难的分析,提出了将Materials studio模拟和Aspen Plus模拟计算相结合的烃类热裂解自由基反应机理的理论研究方法。并用该理论方法对正丁烷和异丁烷及其混合物的相互作用机理进行了研究。结果表明:正丁烷热裂解主要是1-C4H9·中β-C—C键发生的断裂生成乙烯,由2-C4H9·断β-C—C键生成丙烯;异丁烷热裂解主要是i-C4H9·中β-C—C键的断裂生成丙烯。采用与文献[1]同样的原料数据进行模拟,并与该文献中混合C4烷烃热裂解的实验数据进行了对比,说明该理论方法计算得到的结果与实验结果吻合较好。     

1-丁烯热裂解自由基反应模型的建立及验证

基于自由基链式反应机理,将Materials Studio(MS)模拟和Aspen Plus模拟计算相结合研究了1-丁烯热裂解自由基反应机理,运用MS软件对1-丁烯的结构进行优化、分析,建立了初步的、可能发生的12个自由基反应网络和2个可能反应路径;对1-丁烯可能发生的热裂解自由基反应进行模拟计算,得到1-丁烯裂解自由基反应相关动力学参数如活化能(Ea)及速率常数(k)等;用Aspen模拟软件建立裂解反应器模拟实验过程,预测1-丁烯热裂解自由基反应产物分布情况。结果表明,1-丁烯热裂解自由基反应机理模型与一维热裂解工艺模型软件模拟1-丁烯热裂解的主要产物的种类一致,预测的产物分布也吻合,1-丁烯热裂解的主要目的产物是丁二烯、丙烯及少许乙烯,与已有的实验结论相符。     

铁基载氧体纤维素化学链解聚试验及分子模拟

为探索纤维素在铁基载氧体作用下的化学链解聚机理及过程。通过热重分析试验研究不同升温速率下纤维素的化学链燃烧特性；通过化学反应动力学计算纤维素化学链燃烧过程中的活化能并揭示其动力学机制；利用ReaxFF MD模拟综合技术从微观原子尺度阐释纤维素化学链燃烧过程微观反应网络。热分析结果表明，铁基载氧体的加入可降低纤维素化学链解聚的起始温度，其释放的晶格氧有助于促进纤维素的化学链解聚。纤维素化学链燃烧过程分为3个阶段：挥发分析出燃烧、半焦转化燃烧和焦炭燃烧阶段。反应动力学研究显示，纤维素在热转化过程中不同转化率下的活化能为220～405 kJ/mol,其中第3个阶段的反应活化能最高。ReaxFF MD模拟结果显示，纤维素化学链燃烧过程整体遵循自由基链反应理论。纤维素裂解产生的活性自由基与载氧体释放的晶格氧反应生成2-羟基丙酮等中间体，然后进一步发生自由基反应生成CO₂。最终获得了载氧体作用下纤维素化学链解聚过程中CO₂生成释放的复杂反应网络。     

微型流化床中焦油热裂解和水蒸气重整的反应特性及动力学对比

采用微型流化床反应分析仪(MFBRA)考察了不同温度(T,750~950℃)和水蒸气分压(SP,10%~30%)下生物质焦油水蒸气重整过程中的气体生成、气体产物中总碳转化和焦油转化等反应特性,求算反应动力学,并与焦油热裂解特性进行比较。在热裂解过程中,随温度增加,各气体(H₂、CH₄、CO、CO₂)产率和气体产物中的总碳转化率增加,反应时间缩短。而在焦油水蒸气重整过程中,等温下的反应时间明显延长,且H₂、CH₄、CO产率和气体产物中的总碳转化率显著提升,而CO₂产率在850℃时有最大值。在焦油水蒸气重整过程中,不仅有焦油裂解,还有裂解产物与水蒸气的反应,促进碳转化。在950℃、SP=30%条件下,气体产物中的总碳转化率达到92.34%。水蒸气作用下,气体组分的产率和气体产物中的总碳转化率增加,而等温条件下的反应速率下降。水蒸气分压对各气体组分的影响具有差异性。随分压增加,CO、CH₄的生成速率和气体产物中的总碳转化的反应速率增加;H₂生成速率逐渐下降,速率稳定段扩大;CO₂生成速率在850℃时有最大值。采用均相模型求取焦油水蒸气重整反应过程中的活化能,气体产物的生成活化能(H₂、CO、CO₂和CH₄)、气体产物中的总碳转化及焦油转化的活化能明显偏低,分别为90.10、42.01、58.56、64.92、61.44和63.26 kJ/mol,对应数值明显小于焦油热裂解,说明水蒸气对焦油重整反应的促进作用。最后,将焦油热裂解动力学数据与文献数据对比,验证了MFBRA对焦油水蒸气重整反应测试的可行性和分析结果的准确性。     

微型流化床中萘裂解生成小分子气体的反应动力学研究

气化是煤、生物质以及其他含碳燃料高值化利用的有效途径之一。为了考察气化过程中焦油的反应转化特性,选取萘作为焦油模型化合物,以流化催化裂化（fluid catalytic cracking,FCC）催化剂及褐煤热解焦作为接触裂解载体,利用微型流化床考察流化条件下萘催化裂解反应规律,并采用Friedman法和积分法计算萘裂解生成CH₄和H₂等典型气体组分的动力学参数。结果表明,FCC催化剂与褐煤焦均对萘裂解有明显的催化效果,褐煤焦用于萘裂解的反应活化能整体数值低于FCC催化剂。FCC催化剂裂解萘生成H₂符合三维扩散（球形对称）模型,生成CH₄符合成核与生长（n=2/3）模型。相应地,褐煤焦裂解萘反应生成H₂和CH₄分别采用收缩几何形状（圆柱形对称）和三维扩散（圆柱形对称）具有较好的拟合度。     

全氟三乙胺热解机理的实验与理论研究

氟胺类物质是最有希望作为哈龙替代品的含氮化合物之一,全氟三乙胺作为典型的氟胺类物质具有良好的灭火效果。为研究全氟三乙胺热解机理,在管式加热炉内对全氟三乙胺进行热分解,通过GC-MS分析全氟三乙胺在不同温度条件下的热解产物,并用Gaussian软件对其热解反应路径进行理论计算。结果表明：保持停留时间为10 s,全氟三乙胺的初始热解温度为600℃,750℃完全热解,热解产物有C₄F₉N、C₃F₇N、C₂F₆和C₃F₈,热解温度较低时C₄F₉N体积分数最大,热解温度较高时C₃F₇N体积分数最大。在全氟三乙胺热解反应路径计算中,全氟三乙胺分子中的C—C键断裂后存在1条反应路径,可生成实验产物中的C₃F₈;全氟三乙胺分子的C—N键断裂后存在3条反应路径,可生成实验产物中的C₃F₇N、 C₄F₉N和C₂F₆。全氟三乙胺热解后产生的CF₃自由基可与H、OH自由基发生反应,从而产生灭火作用。此外,其热解产物C₄F₉N和C₃F₇N具有CN双键,更容易与燃烧活泼自由基·OH、·H发生化学作用,对研究全氟三乙胺的灭火机理具有十分重要的意义。     

AP在氟化石墨烯表面分解机理的密度泛函理论研究

为了探讨氟化石墨烯(FG)用于AP燃烧催化的可行性，采用密度泛函理论(DFT)计算方法研究了HClO₄和NH₃在FG表面的分解行为，阐述了AP在FG表面分解的反应机理；对HClO₄分子在FG表面分解反应的反应网络中各个基元反应的活化能和反应热进行了分析。结果表明，HClO₄分子的主要分解路径为HClO₄→ClO^-₃→HClO₃→ClO^-₂→HClO₂→ClO^-→Cl^-。高氯酸分解生成氯酸根的反应为该路径的速控步骤，反应活化能为1.675 eV;HClO₄分子分解产生的吸附在FG表面的O^*原子会抑制HClO₄分子在FG表面的进一步分解，但这些O^*原子能够促进NH₃分子在FG表面的脱氢反应并生成OH<...     

Surface-Initiated Gas-Phase Epoxidation of Propylene with Molecular Oxygen by Silica-Supported Molybdenum Oxide: Effects of Addition of C3H8 or NO and Reactor Design

The gas-phase epoxidation of propylene was studied over MoO _x /SiO₂ catalysts in a reaction system with a post-catalytic bed volume. In the reaction of a mixture of propylene and propane with oxygen below 578 K, propylene oxide (PO) was mainly formed from the oxidation of propylene. It was found that the oxidation reaction was very sensitive to the temperature of the post-catalytic space more than the temperature of the catalyst bed, strongly indicating that radical reactions occurring in the post-catalytic bed free space were responsible for the PO formation. The addition of NO increased propylene conversions and PO selectivity at low conversions, confirming that radical reactions were involved in the propylene reactions.     

Epoxidation of Propylene on a [Ag<Subscript>14</Subscript>O<Subscript>9</Subscript>] Cluster Representing Ag<Subscript>2</Subscript>O (001) Surface: A Density Functional Theory Study

Abstract  

Density functional theory calculations were employed to study partial oxidation of propylene on a [Ag₁₄O₉] cluster representing Ag₂O (001) surface for which positive effect for ethylene oxide formation has been reported in our earlier work at the same level of theory (Fellah et al., Catal Lett 141:762, 2011). Propylene oxide (PO), propanal, acetone and П-allyl radical formation reaction mechanisms were investigated. Π-allyl formation path and two propylene adsorption paths resulting in PO formation are competing reactions on silver oxide (001) surface because of their comparable activation barriers (9, 8 and 9 kcal/mol, respectively) while Π-allyl formation path is generally a more favorable path on Ag (111) surface as reported in previous theoretical literature. SO₂ adsorption calculations indicate that silver oxide has lower Lewis basicity relative to oxygen atom adsorbed on silver. Calculations also showed that surface oxygen atom of Ag₂O (001) has a higher spin density compared to that of oxygen atom adsorbed on Ag (111), which indicates that oxygen atom on Ag₂O (001) cluster has a more radical character.     

The kinetics modeling and reactor simulation of propylene chlorination reaction process

The kinetics experiments of fast reaction process of propylene chlorination at low temperature (30–90°C) and high temperature (420–480°C) are respectively conducted, and the corresponding reaction mechanisms and kinetics models are proposed. The radical mechanism at high temperature and the molecular mechanism at low temperature are found to be most likely with the experimental results. Specifically, the kinetics model, firstly considering the reversible reaction step of forming C₃H₆Cl · and direct hydrogen abstraction of forming C₃H₅ · , shows better agreement with the experimental data. Furthermore, the critical reaction temperature T_critical is firstly proposed to determine the dominant reaction mechanism in different conditions, and correspondingly the combination method of the high-temperature and low-temperature kinetics models has been adopted for tubular reactor simulation, which can reasonably reflect the influence of wide variation range of temperature in the reactor and guide the industrial reactor design in the further work.     

Heterogeneous photocatalytic degradation of ethylene glycol and propylene glycol

The photocatalytic decomposition of ethylene glycol and propylene glycol was investigated by using UV-illuminated TiO₂ and metal-loaded TiO₂ catalysts. The effects of pH, initial concentration, and wavelength of light on the decomposition rate of the glycols were explored. Platinum-and palladium-loaded TiO₂ catalysts enhanced the rates of photodecomposition compared to unloaded TiO₂. The glycols were oxidized primarily to carbon dioxide and water. Formaldehyde was found to be an important reaction intermediate. A detailed chemical reaction mechanism for the destruction of ethylene glycol and propylene glycol in water via free radical pathway and trapped hole reactions at the particle surface is proposed.     

Oxidative dehydrogenation of isobutane over pyrophosphates catalytic systems

The catalytic effect of metal pyrophosphates (i.e., Mn₂P₂O₇, Ni₂P₂O₇, CeP₂O₇, Mg₂P₂O₇, ZrP₂O₇, Ba₂P₂O₇, V₄(P₂O₇)₃ and Cr₄(P₂O₇)₃) on the oxidative dehydrogenation of isobutane to isobutene in the reaction temperature range of 400–600 °C has been investigated. CeP₂O₇ gives the highest isobutene yield and selectivity (71%), however, V₄(P₂O₇)₃ is the most active catalyst with an isobutane conversion of 33.5% at 500 °C. Increasing the reaction temperature results in higher isobutane conversions and lower isobutene selectivity. Reaction by-products are propylene, CO, CO₂ and traces of methane and ethylene. No oxygenate products are formed under the used reaction conditions. The sum of selectivities of CO, CO₂ and methane is approximately equal to that of propylene, indicating their formation from total oxidation of C₁ species accompanying the isobutane crack reactions. Working at temperatures higher than 550 °C, the homogeneous gas phase reactions become significant and the oxygen conversion reaches 100%. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of MCM-41 nanoparticles on the kinetics of free radical and RAFT polymerization of styrene

To examine the effect of mobil composition of matter 41 (MCM-41) nanoparticles on the kinetics of free radical and 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT)-mediated reversible addition fragmentation chain transfer (RAFT) polymerization, the polymerization reaction using various amounts of as-synthesized MCM-41 were performed. To study the reaction kinetics, conversion, molecular weight and polydispersity index (PDI) were obtained during the polymerization. Also, differential scanning calorimetry (DSC) was used to determine the glass transition temperature (T _g) values of samples. According to the results, in free radical polymerization, conversion was increased by adding nanoparticles but the reverse trend was observed in RAFT polymerization. The same results were obtained for molecular weight values. In free radical polymerization, increasing the MCM-41 content led to higher PDI value, while in RAFT polymerization it did not appreciably affect the PDI value. In RAFT polymerization, no induction time was observed which indicates that DDMAT is an appropriate RAFT agent for styrene polymerization. Also in free radical polymerization, the addition of MCM-41 particles reduced T _g values in comparison to neat PS. On the other hand, there was an increase in T _g value up to 5 wt% of MCM-41 loading and a drastic reduction was observed in 7 wt% MCM-41 loading in the RAFT polymerization. Finally, the T _g values of nanocomposites produced by RAFT method were higher than those in the nanocomposites synthesized using the free radical method.     

Comparison of physically mixed and separated MgO and WO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript> catalyst for propylene production via 1-butene metathesis

We examined the catalyst bed design of MgO and WO₃/SiO₂ for production of propylene via metathesis of 1-butene. WO₃/SiO₂ was used as a bi-functional catalyst for isomerization and metathesis reactions. Addition of MgO was proposed to help improve the isomerization activity and hence the propylene yield. Experimental studies were carried out to determine activity and reaction kinetics of 1-butene isomerization over MgO isomerization catalyst and 1-butene metathesis over WO₃/SiO₂ bi-functional catalyst for designing a suitable catalyst bed. Two types of catalyst bed arrangement—physically mixed bed and separated bed—were considered and compared by computer simulation. The simulations reveal that adding MgO in the separated bed by packing MgO before WO₃/SiO₂ offers superior propylene yield to the physically mixed bed. The appropriate %MgO loading in catalyst bed which offers a maximum propylene yield was found to vary (3 and 23%), depending on operating condition.     

Direct evidence of intramolecular rearrangement in skeletal isomerization of n-butane over bifunctional catalysts

Mechanisms of skeletal isomerization of n-butane over bifunctional catalysts, Pt–Cs_2.5H_0.5PW₁₂O₄₀ and Pt-sulfated ZrO₂, as well as the corresponding solid acids were studied using 1,4-¹³C₂-n-butane. The isotopic distributions of the reactant and product were analyzed with field ionization mass spectrometry, by which the parent peak patterns were obtained. It was found that 1,4-¹³C₂-n-butane was selectively isomerized to ¹³C₂-isobutane over these catalysts in the presence of H₂ at 423–523 K, while the corresponding solid acids gave isobutane with binomial distributions of ¹³C. These results clearly demonstrate that the skeletal isomerization of n-butane proceeded mainly via a monomolecular path with intramolecular rearrangement on both the bifunctional catalysts, while it occurred through a bimolecular path with intermolecular rearrangement on the solid acids. This difference in reaction mechanism is reflected on that in the selectivity to isobutane.     

Selective oxidation of isobutane to methacrolein over MoVTe mixed oxide supported on SBA-3 and SiO2

SBA-3 and SiO₂-supported MoVTe mixed oxide catalysts have been prepared by impregnation and/or direct synthesis methods and tested for selective oxidation of isobutane to methacrolein (MAL). It was found that the supported catalysts showed much higher activity than the bulk MoVTe mixed oxide for the reaction. Among the supported catalysts, better isobutane conversion and MAL yield were achieved on the 3% MoV_0.8Te_0.23O_x/SBA-3 catalyst prepared by the impregnation method. The catalysts were characterized with BET, XRD, Raman, H₂-TPR, XPS and FT-IR of pyridine adsorption. The good performance of the SiO₂ and SBA-3 supported MoV_0.8Te_0.23O_x catalysts was attributed to a combination of different properties: (i) formation of well dispersed active phases on large surface areas of SiO₂ and SBA-3 supports, which is beneficial for the isolation of active site and preventing the further oxidation of unstable reaction intermediate as well as product; (ii) improved activity for hydrogen abstraction of C-H bond of isobutane due to the formation of isolated pseudotetrahedral VO₄ species.     

Kinetic Study of the Steam Reforming of Isobutane Using a Pt–CeO2–Gd2O3 Catalyst

Steam reforming of isobutane on a 0.5% Pt–Ce_0.8Gd_0.2O_1.9 catalyst was carried out from 300 to 700 °C under integral conditions with a gas hourly space velocity (GHSV) of 12,000 h⁻¹. The major products were H₂, CO₂, CO and CH₄. The other products produced were ethane, ethylene, propane and propylene with a total molar composition of less than 1.5%. A complete conversion of isobutane was achieved at 700 °C, Kinetic data was obtained by changing the partial pressure of the reactants and the temperature under differential conditions with a GHSV of 55,400 h⁻¹. This was done after observing stable isobutane steam reforming for 160 h and under conditions where the mass transfer limitations were insignificant. An empirical Langmuir–Hinshelwood type model that best fit the kinetic data available was developed.