Pt/WC催化剂甲醇脱氢反应机理的研究

采用密度泛函理论(DFT)和周期平板模型,研究了甲醇在PtML/WC(0001)催化剂表面上的脱氢反应机理。通过对甲醇分解过程中反应物、中间体及产物的结构优化和对可能基元反应的过渡态搜索,得到了各吸附物种在最稳定吸附构型下的吸附能和各基元反应的活化能垒。通过对三条可能反应路径的比较,即甲醇分子中O—H键断裂生成甲氧基(CH_3O~*)和氢(H~*)、C—H键断裂生成羟甲基(CH_2OH~*)和氢(H~*)、C—O键断裂生成甲基(CH_3~*)和羟基(OH~*),发现O—H键的断裂所需活化能最低。因此,在PtML/WC(0001)表面上,甲醇分子中的O—H键断裂生成CH_3O~*为整个反应的速控步骤。     

从抽余油中分离甲基环戊烷

研究了从芳烃抽余油中分离甲基环戊烷的方法和流程,首先用Aspen Plus软件模拟了精馏法提取甲基环戊烷的分离结果。通过模拟计算得到了最优的设计参数、操作条件、各塔冷凝器、再沸器的热负荷。在此基础上,还模拟了用甲醇作共沸剂共沸精馏分离得到甲基环戊烷的结果,获得了最优的设计参数和操作条件。     

改性活性炭对亚甲基蓝与Cd~(2+)复合污染物的吸附性能研究

探究改性活性炭对模拟的阳离子染料印染废水亚甲基蓝/Cd⁽²⁺⁾混合溶液的吸附效果及其吸附机理。结果表明,改性活性炭对亚甲基蓝/Cd(2+)混合溶液的吸附效果及其吸附机理。结果表明,改性活性炭对亚甲基蓝/Cd⁽²⁺⁾混合溶液的吸附过程中,亚甲基蓝和Cd(2+)混合溶液的吸附过程中,亚甲基蓝和Cd⁽²⁺⁾存在竞争吸附与静电排斥作用,造成改性活性炭对Cd(2+)存在竞争吸附与静电排斥作用,造成改性活性炭对Cd⁽²⁺⁾的吸附性能降低。改性活性炭对模拟的阳离子染料溶液中两种污染物的吸附符合Langmuir模型,吸附动力学属于准二级动力学模型。对亚甲基蓝和Cd(2+)的吸附性能降低。改性活性炭对模拟的阳离子染料溶液中两种污染物的吸附符合Langmuir模型,吸附动力学属于准二级动力学模型。对亚甲基蓝和Cd⁽²⁺⁾的吸附分别为物理吸附和物理与化学吸附共同作用的单分子层吸附。     

甲基环戊烷及正己烷的抽提分离

测定了正己烷和甲基环戊烷在邻苯二甲酸二丁酯的无限稀释活度系数;采用单参数法确定Ｗｉｌｓｏｎ方程中的模型参数;以Ｗｉｌｓｏｎ方程为汽液平衡模型,模拟不同温度下,正己烷的净化和甲基环戊烷回收的分离结果。     

瓜环的固载化过程及其对甲基橙的吸附动力学

研究了羟基瓜环在氯甲基化聚苯乙烯株（氯球）上的固载动力学及固载影响因素,并研究了固载化瓜环对甲基橙染料的吸附动力学.结果表明,羟基瓜环通过亲核取代反应固载到氯球上,提高固载温度和提高羟基瓜环的投加量有利于瓜环的固载.羟基瓜环在氯球上的固载动力学符合准二级动力学方程.固载化瓜环对甲基橙的吸附动力学符合准二级动力学模型,而准一级动力学模型适合吸附过程的初始阶段,吸附过程受颗粒内扩散控制,但不是吸附速率的唯一控制因素,整个吸附过程是多种动力学机理共同作用的结果.     

Raney镍上α-蒎烯催化加氢本征动力学

测定在不同类型搅拌器下高压釜的持气量和反应效果，认识到α－蒎烯在雷尼镍上催化加氢反应严重受到外扩散的影响，利用改造搅拌器类型和提高搅拌转速的方法消除外扩散；改变Raney镍的粒度，消除内扩散影响，使反应处于化学动力学控制区，然后采集动力学数据，经对17种可能的反应机理模型进行筛选，认为最可几的反应机理为：催化剂表面上被吸附的氢原子和α蒎烯分子间的表面反应为控制步骤，据此推导其本征动力学方程。     

一种高沸点差三元体系气液平衡数据的测量

利用改进型Gillespie循环式平衡釜测定了不同压力下，正己烷－甲基环戊烷－邻苯二甲酸二丁酯三元体系的气液平衡数据，提出了在高沸点差三元体系气液平衡数据的测量中，采用色谱分析结合精密称重法确定液相组成的方案，结果是令人满意的。所测数据为正己烷和甲基环戊烷的萃取精馏分离小试工作提供了依据。     

异丁烷热裂解反应机理的分子模拟

用分子模拟方法对异丁烷的热裂解反应机理进行了研究,建立了可能的反应路径,为了确定每个反应发生的可能性和难易程度,对各个基元反应做了热力学和动力学的计算。结果表明,其热裂解反应的速率控制步骤为异丁烷分子中C-C键断裂生成CH₃自由基和em-C₃H₇自由基的反应,动力学上最支持生成丙烯的反应路径,目的产物中丙烯与异丁烯的比例为1.40:1,与实验值较接近。     

4—甲基—2—环戊基苯腈和1—氰基—4—甲基—1,4—二环戊基—2,5—环己二烯的合成

本文在进行甲基苯腈与溴化环戊烷的烷基化反应同时，发现有特殊的烷基加成反应发生，得到两种新化合物４－甲基－２－环戊基苯腈和１－氰基－４－甲基－１，４－二环戊基－２，５－环己二烯，并对其结构进行了鉴定。     

抽提甲基环戊烷及精制正己烷的分离研究

测定了正己烷和甲基环戊烷在七种溶剂中的无限稀释活度系数,比较溶剂的选择性和溶解性的差别。分析温度对邻苯二甲酸二丁酯分离能力等参数的影响;以Ｗｉｓｏｎ方程为汽液平衡模型,模拟不同温度下,正己烷的化和甲基环戊烷回收的分离结果。     

Characteristics of adsorbed intermediates in the hydrogenative ring opening of methylcyclobutane and methylcyclopentane over silica-supported Pt and Pd catalysts

The hydrogenative ring opening of methylcyclobutane and methylcyclopentane was studied over silica-supported Pt and Pd catalysts by kinetic and infrared (IR) spectroscopic measurements. First, the temperature (473-673 K) and hydrogen pressure (3.3-73.2 kPa) dependences of the ring-opening reactions were determined. The reaction rates were determined over the initial and the working catalysts for both compounds. According to the type of product formation vs. hydrogen pressure dependence curves either dissociative or associative adsorption was suggested for methylcyclobutane and methylcyclopentane. The geometry of adsorbed intermediates was proposed on the basis of the regioselectivity of ring opening. The regioselectivity data show close to statistical ring opening for both compounds, which indicate flat-lying adsorbed intermediates. The structure of adsorbed intermediates was also studied by transmission IR spectroscopy. The H-D exchange reactions between the surface hydroxyl groups and adsorbed species in most cases confirmed the type of adsorption suggested by kinetic measurements. This revised version was published online in July 2006 with corrections to the Cover Date.     

Catalytic reactions of methylcyclopentane on HY zeolite

Catalytic reactions of methylcyclopentane have been studied on HY Zeolite at 500°C. Initial reactions include ring cleavage, the formation of paraffins and the formation of methylcyclopentane. Aromatic species are formed as both primary and secondary products. In contrast to the reaction of methylcyclopentane under reforming conditions, benzene is not a dominant initial aromatic product formed under cracking conditions. Unlike the reaction of cyclopentane on HY, the cracking of methylcyclopentane produces molecular hydrogen as an initial product. This we attribute to the presence of a hydrogen atom bonded to a tertiary carbon in the methylcyclopentane molecule.     

Towards understanding the mechanism for the selective hydrogenation of maleic anhydride to tetrahydrofuran over palladium

First-principles density functional (DFT) quantum chemical calculations were carried out to understand the overall energetics for the hydrogenation of maleic anhydride to tetrahydrofuran (THF), over a Pd(1 1 1) cluster model. The calculated vapor phase structures and vibrational frequencies for maleic anhydride, succinic anhydride, γ-butyrolactone and THF compare well with the reported experimental X-ray crystal structure data and infrared (IR) frequency measurements. The overall reaction energies for vapor phase maleic anhydride hydrogenation to THF, determined using DFT, are within 5 kcal/mol of the enthalpies of reaction, based on standard heats of formation. The adsorption structures for maleic anhydride, succinic anhydride, γ-butyrolactone, THF, water and atomic hydrogen were completely optimized on a fixed Pd(12,7) cluster model of the Pd(1 1 1) surface. The binding energies for maleic anhydride on the Pd₁₉ cluster in the di-σ, π and η¹ adsorption modes were −83, −34 and −28 kJ/mol, respectively. The computed adsorption energy and vibrational frequencies for di-σ bound maleic anhydride on Pd(1 1 1) are in good agreement with temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) measurements of Xu and Goodman [Langmuir 12 (1996) 1807-1816]. Preliminary calculations indicate that the most favorable adsorption mode for succinic anhydride, γ-butyrolactone, THF and water on Pd(1 1 1) is η¹, with binding energies of −28, −38, −45 and −30 kJ/mol, respectively. The energetically most stable adsorption site for atomic hydrogen on the Pd(1 1 1) surface is the 3-fold fcc site, with a binding energy of −257 kJ/mol. Towards understanding the detailed reaction mechanism on Pd(1 1 1), we have postulated elementary reaction pathways for C–H bond formation in maleic anhydride hydrogenation and the ring opening reaction of maleic anhydride on Pd(1 1 1). The DFT-computed activation barrier for C–H bond formation in maleic anhydride hydrogenation to maleic anhydryl on a Pd₁₉ cluster is +82 kJ/mol and the energy of reaction is −9 kJ/mol. The ring opening reaction of maleic anhydride on Pd(1 1 1) has an activation barrier of +163 kJ/mol and is endothermic by 90 kJ/mol. The activation barrier on Re(0 0 0 1), however, is only +80 kJ/mol, whereas the reaction is exothermic by −96 kJ/mol. These results are consistent with the observations from UHV experiments.     

Kinetic Studies on Karlıova Coal

In this study, reaction kinetics of the liquefaction of Karlova coal in a process development unit having three reactors in series have been studied at temperatures of 530–570°C and pressures of 15–25 MPa. It is shown that the rate of hydrogen consumption can be expressed as a function of the concentrations of coal and catalyst, hydrogen partial pressure, reaction temperature, and residence time, and is controlled by the rates of hydrogenation of polynuclear aromatic components and the rates of formation and stabilization of radicals. The relative contribution of these reactions, at any temperature, determines the influence of the hydrogen partial pressure on the rate of the hydrogen consumption. The kinetics of the decomposition reactions of coal to preasphaltene, asphaltene, and oil also have been studied. The apparent activation energies determined are 20 kJ/mol for coal to preasphaltene, 40 kJ/mol for preasphaltene, 66 kJ/mol for asphaltene to oil, and 174 kJ/mol for oil to gases.     

Multiple steady states in reaction controlled surface catalysed reactions

Even when gas composition and pressure above an isothermal catalyst surface are constant and rate parameters are independent of coverage, the reaction rate may not be unique. Necessary and sufficient conditions for reaction rate multiplicity are obtained here for uni- and bimolecular reactions when mo than one vacant site is required for reaction. The work of Eigenberger is extended and generalized for this situation. Bimolecular reaction with compet or noncompetitive chemisorption of at least two species may lead to multiple reaction rates.The presence of a precursor (noncompetitively adsorbed intermediate state) may also lead to multiple steady states, even when less than two vacant site are required for reaction. Conditions for steady state multiplicity are also considered for the Eley-Rideal reaction mechanism.     

The adsorption of methyl nitrite on the Au(111) surface

The interaction of the methyl nitrite molecule (CH₃ONO) with the gold(111) surface has been studied by means of density functional calculations. The perfect Au(111) surface has been represented by a rather large cluster model, Au₂₂, that was in turn used to extract information about the preferred adsorption geometry of the CH₃ONO species. Vibrational frequencies and adsorption energy are also reported. The calculated adsorption energies are 31.2 kJ/mol with respect to gas phase cis-conformer and 35.1 kJ/mol with respect to trans-methyl nitrite, very close to the experimental adsorption energy of 33.5 kJ/mol. From the analysis of vibrational frequencies of gas phase and adsorbed species it is concluded that only the cis-conformer is present at the Au(111) surface.     

Modeling thermal and catalytic conversion of decalin under industrial FCC operating conditions

The processability of decalin, a two-fused ring cycloparaffin, in the absence and presence of USY catalysts of different zeolite crystallite sizes is investigated under actual FCC conditions. Thermal and catalytic cracking experiments using decalin are carried out in the mini-fluidized CREC riser simulator. This novel unit operates under relevant FCC process conditions in terms of partial pressures of decalin, temperatures (450–550 °C), contact times (3–7 s), catalyst–decalin mass ratios (5) and using well-fluidized catalysts. Decalin overall conversions ranged between 8–19wt% at low reaction temperatures and 14–27 wt% at high temperatures. It is found that decalin undergoes reactions such as ring opening, protolytic cracking, isomerization, hydrogen transfer and transalkylation. A heterogeneous kinetic model for decalin conversion including thermal effects, adsorption and intrinsic catalytic reaction phenomena is established. Adsorption and kinetic parameters are determined, including the heat of adsorption (?61 kJ/mol) as well as thermal and primary catalytic intrinsic activation energies, which are in the range of 56–59 kJ/mol and 74–91 kJ/mol, respectively. It is determined that hydrogen transfer reactions are more pronounced and selectively favored against other reactions at lower reaction temperatures, while ring-opening and cracking reactions predominate at higher reaction temperatures.     

离子交换树脂吸附苯酚的性能研究

研究了717强碱阴离子交换树脂对苯酚的吸附性能。结果表明,在pH=10~13时,吸附能力最好。等温吸附符合Freundlich和Langmuir经验式。在293~313 K条件下,苯酚吸附量为220~260 mg/g的吸附焓变为-13.69~-12.02 kJ/mol,吸附自由能变为-7.02~-7.21 kJ/mol,吸附熵变为-22.76~-15.37 J/(K.mol)。吸附动力学符合Lagergren准二级速率方程,吸附速率常数为8.5×10-4~2.74×10-3g/(mg.min),吸附活化能为44.1 kJ/mol。303 K下其静态累积饱和吸附容量为399.8 mg/g(4.253 mmol/g)。用0.05 mol/L HCl溶液能定量洗脱苯酚,洗脱率达99%。     

在工业镍催化剂上苯气相加氢反应动力学

在常压下,应用内循环式无梯度反应器,研究了在国产工业镍催化剂上苯气相加氢的本征动力学.假设催化剂表面上存在两类不同的活性中心,氢及苯各自吸附在相邻的不同类型的活性中心上,设第一个氢原子加入苯环的步骤为反应速率控制步骤,据此以导出反应的动力学方程,与实验数据颇相符合,平均偏差6.1%.测得的本征反应活化能为13.1kcal/mol.苯的吸附热为9.84kcal/mol,与不存在化学反应时的测定结果相接近.     

Brönsted方程动力学模型研究ZSM-5催化乙烯齐聚及芳构化活性和酸强度分布之间的定量关系

乙烯催化齐聚和芳构化是烯烃高值化和合成液体燃料的关键过程,采用NH₃-TPD谱图分析计算方法得到的探针分子脱附活化能作为催化剂的酸位点强度分布的参数,结合线性自由能理论在Br?nsted方程中引入酸强度对反应的影响因子γ作为动力学方程参数关联探针分子脱附活化能与反应活化能,明确固体酸酸强度的基准在催化动力学方程中的物理意义。建立同为MFI拓扑结构 Si /Al摩尔比为12.5、19、25、60、70的ZSM-5分子筛催化剂上不同酸强度位和乙烯齐聚及芳构化中氢转移、齐聚、芳构化各单元步骤以及对应的烷烃、低碳烯烃和芳烃产物分布的定量关系。根据拟合得到动力学参数γ可以发现不同强度的酸位点对乙烯齐聚及芳构化具有不同的作用系数。氨脱附活化能(DAE)为90 kJ·mol^-1的酸位点是氢转移反应的主要活性位点,而对于乙烯齐聚反应中主要的活性酸位点为DAE 90 kJ·mol^-1和124 kJ·mol^-1,DAE为150 kJ·mol^-1的酸位点是芳构化反应的主要活性位点。