多晶钯表面上CO脱附动力学的探讨

本文研究了多晶钯表面上CO脱附动力学,对各种覆盖度的脱附谱图进了划分温区的分析,对低温区首次提出恒定脱附速度的动力学解析.对于多晶钯面上CO的脱附,随脱附温度的升高,脱附反应级数减小而视活化能增加.为解释这种现象提出了活性集团假设,深入研究活性集团的动力学性能将有助于了解脱附过程的动力学特性.     

热重分析测定脱附活化能分布研究

以脱附过程本征动力学模型为基础,提出了一种采用热重分析技术测定脱附活化能随吸附质分子表面覆盖率分布的方法。该方法通过一条热重分析曲线就可以得到清晰的脱附活化能关于覆盖率的函数表达式。采用所提出的方法,通过不同升温速率下的热重分析实验测定了芴和蒽在活性炭上脱附活化能的线性分布,结果表明覆盖率越高,脱附活化能越低。对芴和蒽,由于覆盖率上升,脱附活化能最大降幅达18.5%和15.1%。     

最小二乘法计算苯、噻吩和正辛烷在NaY上程序升温脱附活化能

采用程序升温脱附(TPD)技术测定了苯、噻吩和正辛烷在NaY上以不同升温速率升温时的TPD谱图. 利用TPD谱图的峰形和其微分曲线判断了程序升温脱附过程中的脱附级数. 提出了一种利用最小二乘法计算吸附剂/催化剂的脱附活化能及其动力学参数的方法. 以这些TPD谱图为基础, 分别采用传统TPD计算模型、最小二乘法以及一阶微分曲线法计算了苯、噻吩和正辛烷在NaY上的脱附活化能和动力学参数. 结果表明, 最小二乘法对在不同线性升温速率时的程序升温脱附活化能的计算结果是一致的.     

功函数、AES和TDS研究CO在Ag-Pd合金上的吸附

在超高真空条件下,用功函数测量、俄歇电子能谱(AES)、程序升温热脱附(TDS)等方法,分别研究了CO在富银和富钯合金表面上的吸附与脱附。结果表明,CO的吸附导致了合金表面功函数的增加。室温时,CO在Ag—Pd合金上仅存在一种吸附态,对应的脱附发生在410K附近,脱附活化能为104kJ/mol。研究结果还表明,CO在富银合金表面的吸附导致了体相钯原子向表面的迁移。     

添加Ag或Ag,Ni的V2O5表面氧性质及催化性能研究

用ＴＰＤ－ＭＳ及甲苯选择氧化活性测定等方法研究了Ｖ２Ｏ５和添加Ａｇ或Ａｇ，Ｎｉ的３种样品的表面氧和晶格氧的热脱附性能及催化活性。结果表明，在Ｖ２Ｏ５中加入Ｎｇ或Ａｇ，Ｎｉ后，样品表面上的Ｏ＾－和Ｏ＾２－氧物种的脱附活化能明显降低。添加Ａｇ，Ｎｉ样品表面氧的脱附活化能最低，而苯甲醛生成的选择性最高，在Ｖ２Ｏ５和含有Ａｇ，Ｎｉ的样品中，温度为９６８和７３４℃时，均依次出现以晶格氧（Ｏ＾２－）脱附为主的     

红外光谱法测定CO在Ni/AL2O3催化剂上的吸附热和脱附活化能

本文介绍了用红外光谱(IR)和程序升温脱附原位红外(TPD-IR)技术测定吸附热(Q_a)和脱附活化能(E_d)的实验方法,并测定了CO在Ni/Al_2O_3催化剂上弱吸附线式态的吸附热和强吸附线式态的脱附活化能。结果表明弱吸附线式态的吸附热约为21kJ/mol,强吸附线式态的脱附活化能在10%Ni/Al_2O_3上约为84kJ/mol,在20%Ni/Al_2O_3上约为100kJ/mol。对本方法及实验结果进行了讨论。     

铁钼氧化物TPD-MS及催化性能的研究

制备了一系列不同配比的Ｆｅ－Ｍｏ氧化物催化剂,采用比表面积,ＸＲＤ,ＦＴ－ＩＲ和ＬＲＳ等方法,考察了催化剂的有关物化性质,测定了对甲苯选择性氧化生成苯甲醛的催化活性。用ＴＰＤ－ＭＳ技术研究了催化剂表面氧物种的脱附。结果表明,随着样品中Ｆｅ／Ｍｏ含量的改变,表面氧物种的脱附峰的峰温,氧脱附量和脱附活化能Ｅｄ也发生变化。３＃样品的氧脱附峰峰温较低,表面氧物种Ｏ＾－和Ｏ＾２－脱附量最大,Ｅｄ值最小,生成     

磷脂微乳电动色谱的定量结构保留关系研究

以大豆磷脂为主要的表面活性剂,制备适合毛细管电动色谱使用的不同构成比的微乳体系, 应用溶剂化参数模型研究了中性溶质在其中的定量结构保留关系.使用动态涂层毛细管, 以二甲基亚砜和十二烷基苯分别作为电渗流和微乳液滴迁移的标记物, 测定了26个具有不同结构小分子中性化合物在17种微乳电动色谱体系下的保留因子, 建立了线性溶剂化能量关系(LSER)方程.通过比较两体系的LSER方程系数比较体系相似性.结果表明, 本研究建立的磷脂微乳电动色谱体系在线性溶剂化特征上和其它构成的微乳电动色谱体系相似.对溶质保留贡献较大的是溶质体积和有效氢键碱度, 油相种类及浓度对溶质的保留选择性无明显影响.     

氧在Co3O4催化剂上的化学吸附

测定了氧在氨氧化催化剂Co_3O_4上于100—400℃下的吸附动力学和室温-600℃的热脱附谱,并与离子探针质谱测定的结果进行了比较。动力学曲线指出氧具有快速和慢速不同类型的吸附,热脱附谱显示有相应的脱附曲线。快速吸附对应于两个脱附峰,峰的极大值温度各为165℃,380—420℃;相应的吸附氧粒子可指定为O_2~-,O~-;脱附活化能分别为13.3千卡/克分子,26.7千卡/克分子。慢速吸附服从Elovich吸附规律,吸附过程可能是快速吸附的氧粒子在催化剂表面上迁移生成O~(2-)并入氧化物表面晶格,脱附温度高于500℃时可由表面晶格中逸出。吸附中心可能是表面Co~(2+)离子。讨论了氧吸附与氨催化氧化反应之间的关系。     

程序升温热脱附法研究HZSM-5和HM分子筛的酸性质

程序升温热脱附法测定HZSM-5和HM分子筛吸附氨的程脱谱均有两个峰。HZSM-5的峰Ⅰ和峰Ⅱ的T_M分别为199和418℃,HM的为207和526℃,它们代表了两种强弱不同的吸附中心。通过分析脱附的氨量,计算了强弱两种吸附中心数,并与两种分子筛中所含的理论酸中心数作了比较,得到了与两个峰相应的酸中心性质的信息。 另外用电子计算机模拟热脱附曲线的方法,测定了HZSM-5和HM分子筛上氨的脱附活化能E_d与覆盖度θ的函数关系,提出用E_d和E_d～θ表征酸强度和酸强度分布。结果表明:HM的强酸中心的强度较HZSM-5强,而且酸强度分布更不均匀。但两种分子筛的弱酸中心的性质从能量上看很相似,也较强酸中心均匀。     

Analysis of Affinity Energy Between Biphenyl Dioxygenase and Polychlorinated Biphenyls Using Molecular Docking

Molecular docking was used to calculate the affinity energy between biphenyl dioxygenases(BphA),including 1ULJ,1WQL,2YFJ,2YFL,2GBX,2XSH,2B4P,3GZX,and 3GZY(selected from the Protein Data Bank)and 209 polychlorinated biphenyl(PCB)congeners.The relationships between the calculated affinity energy and the persistent organic pollutant characteristics(migration,octanol-air partition coefficients,lgKOA;persistence,half-life,lgt1/2;toxicity,half-maximal inhibitory concentration,IgIC50;bioaccumulation,bioconcentration factor,lgBCF)of the PCBs were studied to mderstand the BphA mediated degradation of PCBs.The effect of substituent characteristics on the affinity energy was explored through full factorial experimental design.The affinities of nine kinds of BphA proteins on PCBs ranked as follows:2GBX>2YFJ>2YFL>3GZX>2XSH>3GZY>2E4P>1 WQL>1ULJ.The relationships between the calculated affinity energy and the molecular weight,lgKOA,lgBCF,and lgt1/2 of the PCBs were statistically signiflcant(p<0.01),whereas the relationship with the lgIC50 of PCBs was not statistically significant(p>0.05).PCBs were more difficult to degrade following an increase in the free energy of binding.Correlation analysis showed that the average affinity energy values of PCBs gradually increased as the number of chlorine atoms increased,regardless of the substituent position.The substituents at the ortho-positions interacted mainly through a second-order interaction,whereas those at the para-positions did not participate via a second-order interaction.     

Apolar chromatography on Sephadex LH-20 combined with high-speed counter-current chromatography. High yield strategy for structurally closely related analytes-Destruxin derivatives from Metarhizium anisopliae as a case study

A novel high yield isolation procedure for lipophilic cyclic peptide derivatives is presented. Destruxin (dtx) A, B, D, E, and E-diol retrieval from Metarhizium anisopliae culture broth was achieved with a three-step purification protocol. After liquid-liquid extraction column chromatography over Sephadex LH-20 served as enrichment step. High-speed counter-current chromatography (HSCCC) was used for the final purification. Within the first chromatographic step dtx D and dtx E-diol were separated in purities exceeding 90%. The separation of dtx A, B, and E was achieved from an enriched Sephadex LH-20 fraction by a HSCCC protocol using light petroleum-ethyl acetate-methanol-water = 2:5:2:5 (v/v) as eluent system. These derivatives were obtained in purities above 98% and total yields exceeding 40%.     

Molecular Exchanging Energy of Anionic／Cationic Surfactants System on the Surface of Solution

In order to study synergism of the mixed surfactants system with molecular exchanging energy ( ε ), the Lennard-Jones formula has been firstly introduced to evaluate the ε of the mixed system, CH3(CH2)nOSO 3^- /CH3(CH2)nN^ (CH3)3, directly from their molecular structure. The comparison of the calculated and the observed results showed that this method is practical.     

生物质空气－水蒸气气化制取合成气热力学分析

基于Gibbs自由能最小化原理，计算了包括H2O(l)和C(s)在内的，生物质空气 水蒸气气化体系热力学平衡，对比分析了常压气化和加压气化的特点，通过回归分析得到了不同压力下，气化产物中可燃气体分率最高时的水蒸气/生物质质量比（S/B，Steam to Biomass Ratio）与空气当量比（ER，Equivalence Ratio）的关系曲线，为探讨适于制取合成气的气化工艺和条件提供初步的理论指导。研究表明，相对于常压气化，加压气化体系的平衡温度较高，平衡状态下可燃气体分数较低，但CH4含量明显增加；一定温度和当量比下，加压气化使得气化产物中可燃气体分数达到最高所对应的S/B比增大，即需要消耗更多水蒸气；通过调节S/B比，可以比较方便地控制产物中H2和CO的比例。以常压为例，T=1173K，S/B=0.17时，气化产物中H2/CO约为1.1∶1，而S/B=1.02时，气化产物中H2/CO约为2∶1；不同压力下最佳S/B比和ER有很好的线性关系，温度为1173K时，最佳S/B比与压力及ER〖的关系为S/B=－1.48×ER－4.49 E×10－5×p2 + 5.83 E×10－3×p + 0.32。     

电场和温度对含水电流变液性能的影响

测试了聚甲基丙烯酸锂（Li－PMAA）粒子含水量（Q）不同时的Li－PMAA／硅油电流变（ER）液的静态屈服应力（τs）和电流密度（J）随电场强度（E）和温度（T）的变化，同时分别用幂函数和Ar－rheniu方程拟合了τs、J与E、T的关系，并计算了与τs、J有关的两种活化能（Ea、Eb）．发现ER液在低电场下，τs∝E2；而在高电场下，τs∝Eb，b与Q有关，随Q增加而增加．当Q较小时，ER液的τs、J随温度的升高而增加，且Ea＝0．15eV，Eb＝0．70eV．作者认为该体系的ER效应主要是由粒子中的可移动离子如Li＋在电场作用下产生粒子内迁移所致．     

Microcanonical unimolecular rate theory at surfaces. II. Vibrational state resolved dissociative chemisorption of methane on Ni(100)

A three-parameter microcanonical theory of gas-surface reactivity is used to investigate the dissociative chemisorption of methane impinging on a Ni(100) surface. Assuming an apparent threshold energy for dissociative chemisorption of E(0)=65 kJ/mol, contributions to the dissociative sticking coefficient from individual methane vibrational states are calculated: (i) as a function of molecular translational energy to model nonequilibrium molecular beam experiments and (ii) as a function of temperature to model thermal equilibrium mbar pressure bulb experiments. Under fairly typical molecular beam conditions (e.g., E(t)>/=25 kJ mol(-1), T(s)>/=475 K, T(n)/=100 K the dissociative sticking is dominated by methane in vibrationally excited states, particularly those involving excitation of the nu(4) bending mode. Fractional energy uptakes f(j) defined as the fraction of the mean energy of the reacting gas-surface collision complexes that derives from specific degrees of freedom of the reactants (i.e., molecular translation, rotation, vibration, and surface) are calculated for thermal dissociative chemisorption. At 500 K, the fractional energy uptakes are calculated to be f(t)=14%, f(r)=21%, f(v)=40%, and f(s)=25%. Over the temperature range from 500 K to 1500 K relevant to thermal catalysis, the incident gas-phase molecules supply the preponderance of energy used to surmount the barrier to dissociative chemisorption, f(g)=f(t)+f(r)+f(v) approximately 75%, with the highest energy uptake always coming from the molecular vibrational degrees of freedom. The predictions of the statistical, mode-nonspecific microcanonical theory are compared to those of other dynamical theories and to recent experimental data.     

Electron energy distribution functions and rate and transport coefficients of H2/H/CH4 reactive plasmas for diamond film deposition

Electron energy distribution functions (eedf) and rate and transport coefficients for H₂/H/CH₄ mixtures have been calculated by solving a stationary Boltzmann equation as a function of reduced electric field E/N, of molar fraction, and of different concentrations of electronically excited states. Superelastic electronic collisions superimpose structures to eedf especially for E/N values < 40 Td.     

Brillouin scattering in liquid mixtures: CCl4/CHCl3

The Brillouin light scattering spectra of mixtures of liquid CCl₄ and CHCl₃ have been obtained. The resulting relaxation rates and the relaxing energy reservoir were studied as a function of the mole fraction over the entire concentration range. The energy exchange between the pertinent degrees of freedom are discussed in terms of the relaxation rates of homomolecular and heteromolecular collisions. We came to the conclusion that the resonance energy transfer between vibrational levels play a significant role in determining the vibration—translation energy migration observed by Brillouin scattering'     

In silico prediction of drug solubility: 2. Free energy of solvation in pure melts

The solubility of drugs in water is investigated in a series of papers and in the current work. The free energy of solvation, DeltaG*(vl), of a drug molecule in its pure drug melt at 673.15 K (400 degrees C) has been obtained for 46 drug molecules using the free energy perturbation method. The simulations were performed in two steps where first the Coulomb and then the Lennard-Jones interactions were scaled down from full to no interaction. The results have been interpreted using a theory assuming that DeltaG*(vl) = DeltaG(cav) + E(LJ) + E(C)/2 where the free energy of cavity formation, DeltaG(cav), in these pure drug systems was obtained using hard body theories, and E(LJ) and E(C) are the Lennard-Jones and Coulomb interaction energies, respectively, of one molecule with the other ones. Since the main parameter in hard body theories is the volume fraction, an equation of state approach was used to estimate the molecular volume. Promising results were obtained using a theory for hard oblates, in which the oblate axial ratio was calculated from the molecular surface area and volume obtained from simulations. The Coulomb term, E(C)/2, is half of the Coulomb energy in accord with linear response, which showed good agreement with our simulation results. In comparison with our previous results on free energy of hydration, the Coulomb interactions in pure drug systems are weaker, and the van der Waals interactions play a more important role.     

Microcanonical transition state theory for activated gas-surface reaction dynamics: application to H2/CU(111) with rotation as a spectator

A microcanonical unimolecular rate theory (MURT) model incorporating quantized surface vibrations and Rice-Ramsperger-Kassel-Marcus rate constants is applied to a benchmark system for gas-surface reaction dynamics, the activated dissociative chemisorption and associative desorption of hydrogen on Cu(111). Both molecular translation parallel to the surface and rotation are treated as spectator degrees of freedom. MURT analysis of diverse experiments indicates that one surface oscillator participates in the dissociative transition state and that the threshold energy for H2 dissociation on Cu(111) is E0 = 62 kJ/mol. The spectator approximation for rotation holds well at thermally accessible rotational energies (i.e., for Er less than approximately 40 kJ/mol). Over the temperature range from 300 to 1000 K, the calculated thermal dissociative sticking coefficient is ST = S0 exp(-Ea/kBT) where S0 = 1.57 and Ea = 62.9 kJ/mol. The sigmoid shape of rovibrational eigenstate-resolved dissociative sticking coefficients as a function of normal translational energy is shown to derive from an averaging of the microcanonical sticking coefficient, with threshold energy E0, over the thermal surface oscillator distribution of the gas-surface collision complexes. Given that H2/Cu(111) is one of the most dynamically biased of gas-surface reactive systems, the simple statistical MURT model simulates and broadly rationalizes the H2/Cu(111) reactive behavior with remarkable fidelity.