超临界甲烷在氯化锆层柱纳米材料中吸附的分子模拟

用巨正则MonteCarlo(GCMC)方法模拟了甲烷在氯化锆层柱材料中的吸附。模拟中,氯化锆层柱材料模型化为柱子均匀分布在层板间的层柱孔,非极性分子甲烷采用Lennard-Jones分子模型,层板墙采用Steele的10-4-3模型,流体分子与柱子的相互作用采用点-点(sitetosite)的方法计算。在高度理想化模型的基础上,引入交互作用参数kfw,建立了有效势能模型。通过实验数据确定交互作用参数kfw,从而使该模型能有效地表征流体与层板墙的相互作用。根据77K温度下氮气的实验吸附数据,确定了流体和层板墙间的交互相作用参数。然后用这个有效的参数kfw=0.65模拟了三个超临界温度下氯化锆层柱材料中甲烷的吸附情形,得到了它位的吸附等温线,局部密度分布以有流体分子在层柱微孔中的瞬时构象,并分析了温度对材料吸附性能的影响。结果表明GCMC方法是预测材料吸附性能的一种强有力的工具。     

巨正则系综Monte Carlo模拟方法确定活性炭的微孔尺寸

根据299K下甲烷在活性炭中的吸附实验数据,通过调节狭缝微孔的孔宽参数,利用巨正则系综MonteCarlo(GCEMC)方法得到不同孔宽下流体的微观结构以及吸附等温线.比较并拟合模拟结果和实验数据,确定了活性炭微孔的平均孔宽,为下一步求解微孔尺寸分布以及为预测吸附剂在不同温度下吸附不同吸附质分子时的吸附性能提供了基础与指导.模拟中,甲烷分子采用单点Lennard-Jones球型分子模型,活性炭用狭缝孔来近似表征,流体分子与单个狭缝墙的相互作用采用著名的Steele的10－4-3势能模型.模拟表明,此方法为考察介孔材料的微孔分布以及微孔平均孔宽提供了新的思路.     

超临界甲烷在氯化锆层柱纳米材料中吸附的分子模拟

用巨正则MonteCarlo(GCMC)方法模拟了甲烷在氯化锆层柱材料中的吸附。模拟中,氯化锆层柱材料模型化为柱子均匀分布在层板间的层柱孔,非极性分子甲烷采用Lennard-Jones分子模型,层板墙采用Steele的10-4-3模型,流体分子与柱子的相互作用采用点-点(sitetosite)的方法计算。在高度理想化模型的基础上,引入交互作用参数kfw,建立了有效势能模型。通过实验数据确定交互作用参数kfw,从而使该模型能有效地表征流体与层板墙的相互作用。根据77K温度下氮气的实验吸附数据,确定了流体和层板墙间的交互相作用参数。然后用这个有效的参数kfw=0.65模拟了三个超临界温度下氯化锆层柱材料中甲烷的吸附情形,得到了它位的吸附等温线,局部密度分布以有流体分子在层柱微孔中的瞬时构象,并分析了温度对材料吸附性能的影响。结果表明GCMC方法是预测材料吸附性能的一种强有力的工具。     

ZrO2助剂对Ni/SiO2催化剂CO甲烷化催化活性及其吸附性能的影响

采用连续流动微反装置和原位漫反射红外光谱法考察了Ni/SiO₂及添加ZrO₂助剂的Ni/ZrO₂-SiO₂催化剂CO甲烷化催化活性和吸附性能。结果表明,在CO体积分数 1%、空速 5000h^-1、常压的反应条件下,200℃时Ni/ZrO₂-SiO₂催化剂可将CO完全转化。而相同反应条件下Ni/SiO₂催化剂上CO的转化率仅为35%,直至270℃时方可将CO完全转化。由此可见,ZrO₂助剂的添加明显提高了Ni/ZrO₂-SiO₂催化剂的CO甲烷化催化活性。同时,ZrO₂助剂的添加显著提高了Ni/ZrO₂-SiO₂催化剂对CO的吸附能力,H₂存在时可通过在较低温度时形成较多的桥式羰基氢化物来提高Ni/ZrO₂-SiO₂催化剂的CO甲烷化催化活性;CO甲烷化反应条件下,Ni/SiO₂和Ni/ZrO₂-SiO₂催化剂上C-O键的削弱和断裂是经由羰基氢化物 多氢羰基氢化物的途径,而不是经由C-O键的直接断裂途径。     

制备条件对Ni/ZrO2-SiO2催化剂煤气甲烷化的影响

采用浸渍法制备了ZrO₂-SiO₂复合载体和Ni质量分数为6%的Ni/ZrO₂-SiO₂催化剂,考察了载体制备时浸渍溶液pH值、焙烧温度和催化剂制备时的焙烧温度对Ni/ZrO₂-SiO₂催化剂煤气甲烷化反应性能的影响。采用X射线衍射、程序升温还原和扫描电子显微镜等方法对催化剂进行了表征。结果表明,载体浸渍溶液pH值为8.0～9.0, 载体焙烧温度为550 ℃,催化剂焙烧温度为450 ℃时,Ni/ZrO₂-SiO₂催化剂在煤气甲烷化反应中显示了最优的催化性能,CO转化率100%,CO₂转化率1.8%,CH₄生成速率16.6 mmol/(h·g)。进一步表征发现,制备ZrO₂-SiO₂复合载体时,增大浸渍溶液的pH值有利于形成粒径较小的亚稳态四方晶相ZrO₂,可见四方晶相ZrO₂更有利于甲烷化反应;载体焙烧温度会影响到NiO粒径的大小和其在催化剂表面的分散,温度过高和过低都会导致NiO粒径大小的不适宜以及分散性的降低;催化剂焙烧温度过高则会导致NiO与载体间的相互作用减弱,NiO分散性降低。     

介电失配度对沸石电流变液界面极化的影响

利用介电谱方法研究了NaA沸石/硅油和NaA沸石/煤油两种电流变液的介电行为, 测量发现两体系在10⁵ Hz处均出现明显的弛豫现象. 采用单弛豫Cole-Cole函数拟合各体系的介电参数, 结果表明在相同体积分数条件下硅油体系具有较大的介电增量(?ε), 且两体系的介电增量与体积分数(φ)均服从?ε＝4ε_mφ的函数关系. 通过计算和分析粒子与介质间介电失配程度, 阐明了油介质的介电常数(ε_m)对于沸石电流变液界面极化强度的贡献. 此外研究了吸附水对沸石电流变液界面极化的影响, 结果发现水的吸附对于体系的?ε值没有影响, 但明显降低了弛豫时间, 证明吸附水对沸石电流变液的界面极化率具有增强作用.     

巨正则系综Monte Carlo模拟方法研究活性炭的微孔尺寸

根据299K下甲烷在活性炭中的吸附实验数据，通过调节狭缝微孔的孔宽参数，利用巨正则系综Monte Carlo（GCEMC）方法得到不同也宽下流体的微观结构以及吸附等温线，比较并拟合模拟结果和实验数据，确定了活性炭微孔的平均孔宽，为下一步求解微孔尺寸分布以及为预测吸附剂在不同温度下吸附不同吸附质分子的吸附性能提供了基础与指导，模拟，甲烷分子采用单点Lennard-Jones球型分子模型，活性炭用狭缝孔来近似表征，流体分子与单个狭缝墙的相互作用采用著名的Steele的10－4－3势能模型，模拟表明，此方法为考察介孔材料的微孔分布以及微孔平均孔宽提供了新的思路。     

层柱状微孔材料吸附存储天然气的Monte Carlo模拟

采用巨正则系综MonteCarlo方法模拟了天然气中主要成分甲烷在层柱状微孔材料中T=300K下的吸附存储,在模拟中层柱状微孔采用Yi等人建立的柱子均匀分布在两炭孔墙之间的模型来表征。甲烷分子采用Lennard-Jones球型分子模型,炭孔墙采用Steele的10-4-3模型,对孔宽为1.36nm的层柱微孔,模拟了四个不同孔率的层柱材料吸附甲烷的情形。得到了孔中流体的局部密度分布以及吸附等温线,对比不同孔率下甲烷的吸附量,得到了此情形吸附甲烷的较佳孔率为0.94。     

H2,CO和H2/CO在ZrO2催化剂上吸附行为研究

用insituFTIR法研究了H₂、CO及CO/H₂在ZrO₂表面的吸附行为.结果表明,H₂在ZrO₂表面吸附存在两种形态的羟基(即ZrOH和ZrOHZr),吸附温度增加,羟基数量增加.CO在200℃易与ZrO₂表面羟基作用形成甲酸盐物种,吸附温度升高时,该物种逐渐分解生成CO和ZrOH.当CO和H₂共存时,表面甲酸盐的量明显增加,并随温度增加,逐渐加氢形成甲氧基,最后生成甲烷.甲氧基的加氢过程较慢,所需反应温度也较高,被认为是CO加氢合成醇的速控步骤.     

NOx在担载CeO2的纳米ZrO2上的吸附研究

通过反相微乳液法制备了纳米级高比表面积ZrO₂粉体材料,用TEM,XRD和氮气吸附BET比表面积等手段对其进行了表征,研究了Ce(NO₃)₃溶液浸渍的ZrO₂粉体对氮氧化物的吸附活性.实验结果表明,5%Ce/ZrO₂样品室温时可吸附NO_x的最大值为34.5mg;100℃时为17.5mg;200℃时可达9.5mg.对比表明,同样条件下微乳液法制备的ZrO₂对NO_x的最大吸附量是一般沉淀法制备的ZrO₂样品的2.5倍.纳米级ZrO₂的特殊孔结构可能是导致微乳液法制备的ZrO₂样品吸附量较高的主要原因.     

Grand canonical Monte Carlo simulation for determination of optimum parameters for adsorption of supercritical methane in pillared layered pores

A grand canonical Monte Carlo (GCMC) method is carried out to determine optimum adsorptive storage pressures of supercritical methane in pillared layered pores. In the simulation, the pillared layered pore is modeled by a uniform distribution of pillars between two solid walls. Methane is described as a spherical Lennard-Jones molecule, and Steele's 10-4-3 potential is used for representing the interaction between the fluid and a layered wall. The site-site interaction is also used for calculating the interaction energy between methane molecules and pillars. An effective potential model that reflects the characteristics of a real pillared layered material is proposed here. In the model, a binary interaction parameter, k(fw), is introduced into the combining rule for the cross-energy parameter for the interaction between the fluid and a layered wall. Based on the experimental results for the Zr-pillared material synthesized and characterized by Boksh, Kikkinides, and Yang, the binary interaction parameter, k(fw), is determined by fitting the simulation results to the experimental adsorption data of nitrogen at 77 K. Then, by taking it as a model of pillared layered material, a series of GCMC simulations have been carried out. The excess adsorption isotherms of methane in a pillared layered pore with three different pore widths and porosities are obtained at three supercritical temperatures T=207.3, 237.0, and 266.6 K. Based on the simulation results at different porosities, various pore widths and different supercritical temperatures, the pillared layered pore with porosity psi=0.94 and pore width hsigma(p)=1.02 nm is recommended as adsorption storage material of supercritical methane. Moreover, the optimum adsorption pressure is determined at a given temperature and a fixed width of the pillared layered pore. For example, at temperature T=207.3 K, the optimum adsorption pressures are 3.1, 3.7, and 4.5 M Pa at H=1.02, 1.70, and 2.38 nm, respectively. In summary, the GCMC method is a useful tool for optimizing adsorption storage of supercritical methane in pillared layered material.     

Liquid-liquid phase separation of binary Lennard-Jones fluid in slit nanopores

The capillary phase separation of a binary mixture of two truncated and shifted Lennard-Jones (LJ) Ar liquids in slit-shaped oxygen nanopores is examined. The LJ parameters—ε(Ar(A)–Ar(A))=ε(Ar(B)–Ar(B))=0.8ε(Ar(A)–Ar(B)) and 0.5ε(Ar(A)–O)?=?ε(Ar(B)–O)—were used to distinguish the two Ar liquids. The cut off distance for Ar was 3.5σ. We employed a molecular dynamics (MD) technique in which a pore space was connected with a bulk solution to easily determine the equilibrium bulk concentration. Liquid phase isotherms were obtained for pores with widths ranging from 5.5σ to 9.5σ, and the relation between the pore width and the phase separation concentration was determined. Each simulation was run until the bulk concentration attained equilibrium (1–2 μs). The MD results show that the Patrick model overestimates the bulk concentration for a given pore size. We proposed a modified Patrick model in which the pore wall potential is considered. In our model, the Gibbs-Tolman-Koenig-Buff effect is not considered for the interfacial tension since two surfaces of tension exist on both sides of the equimolar dividing surface of the two-Ar liquid phase. The two surfaces of tension neutralized Gibbs-Tolman-Koenig-Buff effect each other. The present simple model successfully describes the relation to prove its reliability.     

Molecular simulation of adsorption and separation of mixtures of short linear alkanes in pillared layered materials at ambient temperature

Grand canonical Monte Carlo and configurational-bias Monte Carlo techniques are carried out to simulate the adsorption of ternary and quaternary mixtures of short linear alkanes, involving methane, ethane, propane, and n-butane, in pillared layered materials at ambient temperature, T=300 K. In the simulation, a pillared layered pore is modeled by a uniform distribution of pillars between two layered walls built by making two separate talc lamellas parallel each other with a given size of interlayer distance. The interaction between fluid molecules and two layered walls is measured by storing potentials calculated in advance at a series of grid points. The interaction between fluid molecules and pillars is also calculated by a site-to-site method. The potential model proposed in this work is proved to be effective because of the simulation result being good agreement with the experimental data for the adsorption of nitrogen at 77 K. Then, the adsorption isotherms of mixtures of short linear alkanes in pillared layered pores with three different porosities psi=0.98, 0.93 and 0.85, and three pore widths H=1.02, 1.70 and 2.38 nm at 300 K are obtained by taking advantage of the model. The simulation results tell us that the longer chain component is preferentially adsorbed at low pressures, and its adsorption increases and then decreases as the pressure increases while the shorter chain component is still adsorbed at high pressures. Moreover, the sorption selectivity of pillared layered materials for the longest chain component in alkane mixtures increases as the mole fraction of methane in the gas phase increases. The selectivity of pillared layered materials for the longest chain component in alkane mixtures also increases as the pore width decreases and the porosity increases.     

超临界甲烷在纳米材料中最适吸附压力的确定

用巨正则Monte Carlo (GCMC)方法模拟了超临界甲烷在层柱纳米材料中的吸附.模拟中,层柱纳米材料采用了柱子均匀分布在层板间的模型, 非极性分子甲烷采用Lennard Jones分子模型, 层板墙采用Steele的10 4 3模型, 流体分子与柱子的相互作用采用点 点 (site to site) 的方法计算.得到了甲烷的随着压力先增大后减小的超额吸附等温线.在T=207.3 K时,1.02、1.70和2.38 nm孔宽对应的最适操作压力 (即对应于最大吸附量时的操作压力) 分别为2.4、3.1和3.7 MPa.然而,在T=237.0 K时,1.02、1.70和2.38 nm孔宽对应的最适操作压力分别为2.9、3.6和4.9 MPa,分别比T=207.3 K时相同孔宽下对应的最适操作压力至少高0.5 MPa. 模拟结果表明, GCMC方法是研究材料吸附性能的一种强有力的工具.     

New combining rules for well parameters and shapes of the van der Waals potential of mixed rare gas systems

New combining rules are presented for calculating the van der Waals well parametersε andσ as well asC ₆,C ₈ andC ₁₀ for the mixed rare gas systems from the corresponding values of the homogeneous dimers. The combining rules forε andσ are tested by comparison with the recent compilation of Aziz and found to be superior to the best previous combining rules selected by Aziz. Effective Born-Mayer repulsive potential parameters are determined from the model potential of Tang and Toennies and make possible the calculations of accurate potential curves for all combinations of rare gas atoms.     

Structure and properties of polymer modified TiO2 pillared montmorillonite

With the aim of improving the microstructures and properties of TiO₂ pillared montmorillonite (MMT), a long-chain polymer (polyoxypropylenediamine, PPO-D 2000) was used as a template to synthesize composite pillared MMT. The materials were characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectrophotometer, Fourier Raman (FT-Raman) spectrophotometer, thermo-gravimeter/differential thermogravimeter (TG/DSC), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) methods. The results show that as compared to low-molecular weight surfactant, this polymer significantly expanded the interlayer spacing and thus more TiO₂ could be intercalated into MMT. The specific surface area of polymer/TiO₂ pillared MMT was increased by 13% with comparison to TiO₂ pillared MMT and rose to 241.52 m²/g. Both the pore diameter and volume are doubled, and thus the pore structure is optimized markedly. The investigation on the photo-catalytic degradation of methyl orange in aqueous solution show that the modulation of polymer molecules raise the adsorption content of montmorillonite and improve the photo-catalytic activity. Therefore, this process provides a novel alternative to design and prepare the advanced eco-catalytic materials with high adsorption capacity and photo-catalytic activity. __________ Translated from Huaxue Tongbao, 2007, 12: 936–941 [译自: 化学通报]