沸石咪唑骨架N_2吸附的分子模拟与BET分析

采用分子模拟的方法模拟77 K下N2在沸石咪唑骨架材料(ZIFs)上的吸附等温线,并与实验结果比较,确定合适的力场参数,提供用BET方法分析ZIFs材料比表面积的吸附等温线。通过BET吸附方程中的参数c与单层吸附压力(p/p0)m之间的关系为(p/p0)m=(槡c+1)-1,确定应用BET方程分析时的压力区间。采用这样的方法计算5种ZIF材料的比表面积并与根据一致性原则(Rouquerol,2007)的结果进行比较,结果表明方法是可靠的,这说明采用合适的压力区间时,BET方法同样适用于分析微孔ZIF材料的比表面积。计算得到的5种ZIF材料比表面积均在1 000 m2/g以上,说明ZIF材料是一种具有高比表面积、有应用前景的吸附材料。     

Highly active and selective Co‐based Fischer–Tropsch catalysts derived from metal–organic frameworks

The design of supported Co‐based Fischer–Tropsch (F–T) catalysts with suitable reducibility, dispersion, loading, and nanoparticle structure is necessary so that high catalytic activity and selectivity for C₅₊ hydrocarbons can be achieved. Herein, we report that pyrolyzing a Co‐metal–organic framework‐71 precursor can provide porous carbon‐supported Co catalysts with completely reduced, well‐dispersed face‐centered cubic (FCC) Co nanoparticles (～10 nm in average size). The catalysts can be further tailored dimensionally by doping with Si species, and the FCC Co nanoparticles can be partially transformed into hexagonal close‐packed Co via a Co₂C intermediate. All the as‐prepared catalysts had extremely high Co site density (>3.5 × 10^?4 mol/g‐cat.) because they had a high number of Co active sites and low mass. Aside from having high F–T activity and C₅₊ selectivity, with diesel fuels being the main constituents, they showed unprecedentedly high C₅₊ space time yields (up to 1.45 g/(g‐cat. h)) as compared to conventional Co catalysts. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2935–2944, 2017     

Formation of macroporous styrene–divinylbenzene copolymer networks: Theory vs. experiments

A kinetic–thermodynamic model is presented to predict the total porosities of macroporous copolymer networks formed by free‐radical crosslinking copolymerization of styrene (S) and commercial divinylbenzene (DVB, a mixture of meta and para DVB isomers and ethylstyrene). The kinetic part of the model predicts, based upon the method of moments, the concentration of the reacting species, the gel, and sol properties as a function of the monomer conversion. The thermodynamic part of the model describes the phase equilibria between the gel and separated phases during the S–DVB copolymerization and predicts the volume of the separated phase, which is the pore volume of the crosslinked material, as a function of the monomer conversion. Calculation results show that the porosity of S–DVB networks increases as the polymer–diluent interaction parameter increases, or as the initial monomer concentration decreases. Porosity also increases on increasing the DVB content of the monomer mixture. Both the polymerization temperature and the initiator concentration affect significantly the kinetics of S–DVB copolymerization. However, the final porosity of S–DVB copolymers is largely insensitive to the amount of the initiator and to the polymerization temperature. All calculation results are in accord with the experimental data published previously. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2181–2195, 1999     

Phase behavior and molecular mobility in polyurethane/styrene–acrylonitrile blends

Differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC) techniques, dielectric relaxation spectroscopy (DRS), and dynamic mechanical thermal analysis (DMTA), covering together a wide range of temperatures and frequencies, were employed to investigate molecular mobility and microphase separation in blends of crosslinked polyurethane (PUR) and styrene–acrylonitrile (SAN) copolymer, prepared by reactive blending with polymer polyols. The results by each technique indicate that the degree of microphase separation of PUR into hard‐segment (HS) microdomains and soft‐segment (SS) microphase increases on addition of SAN. The various techniques were critically compared to each other, with respect to their characteristic time and length scales, on the basis of activation diagrams (Arrhenius plots). The results show that for the dynamic glass transition of the PUR SS microphase the characteristic time scales at the same temperature are similar for DMTA, DSC, and TSDC and shorter for DRS. In terms of fragility, the PUR/SAN blends are classified as fragile systems. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1071–1084, 2001     

Kinetics modeling of a modified epoxy–amine formulation cured by thermal and microwave energy

The reaction kinetics of a rubber-modified epoxy formulation cured by microwave or thermal energy were investigated. Two phenomenological models were developed to predict the time and temperature dependence of the conversion for the neat and the modified systems. Good agreement was observed between the kinetic models and experimental results generated by chromatographic and calorimetric techniques. The same kinetic behavior was observed whatever the curing process (conventional or microwave heating). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 543–552, 1998     

Separation of gold(III) ions from copper(II) and zinc(II) ions using thiourea–formaldehyde or urea–formaldehyde chelating resins

Thiourea–formaldehyde (TF) and urea–formaldehyde (UF) chelating resins were synthesized and these resins were used in the separation of gold(III) ions from copper(II) and zinc(II) base metal ions. In the experimental studies, the effect of acidity on gold(III) uptake and gold(III) adsorption capacities by batch method, and loading and elution profiles of gold(III) ions, gold(III), copper(II), and zinc(II), dynamic adsorption capacities and the stability tests of TF and UF resins by column method were examined. By batch method, the optimum acidities were found as pH 2 and 0.5M HCl, and gold(III) adsorption capacities in the solutions including copper(II) and zinc(II) ions were obtained as 0.088 and 0.151 meq Au(III)/g for UF and TF resins, respectively. On the other hand, by column method, the dynamic adsorption capacities were calculated as 0.109 meq Au(III)/g with TF, 0.023 meq Au(III)/g with UF, 0.015 meq Cu(II)/g with TF, 0.0057 meq Cu(II)/g with UF, and under 6.1 × 10^?5 meq Zn(II)/g with TF or UF. TF resin was more effective in the separation and the concentration of gold(III) ions from copper(II) and zinc(II) ions than UF resin. It was seen that sulfur atoms contributed the gold(III) adsorption comparing with oxygen atoms. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

From Structure–Activity to Structure–Selectivity Relationships: Quantitative Assessment,Selectivity Cliffs,and Key Compounds

The exploration of structure–activity relationships (SARs) in chemical lead optimization is mostly focused on activity against single targets. Because many active compounds have the potential to act against multiple targets, achieving a sufficient degree of target selectivity often becomes a major issue during optimization. Herein we report a data analysis approach to explore compound selectivity in a systematic and quantitative manner. Sets of compounds that are active against multiple targets provide a basis for exploring structure–selectivity relationships (SSRs). Compound similarity and selectivity data are analyzed with the aid of network‐like similarity graphs (NSGs), which organize molecular networks on the basis of similarity relationships and SAR index (SARI) values. For this purpose, the SARI framework has been adapted to quantify SSRs. Using sets of compounds with differential activity against four cathepsin thiol proteases, we show that SSRs can be quantitatively described and categorized. Furthermore, local SSR environments are identified, the analysis of which provides insight into compound selectivity determinants at the molecular level. These environments often contain “selectivity cliffs” formed by pairs or groups of similar compounds with significantly different selectivity. Moreover, key compounds are identified that determine characteristic features of single‐target SARs and dual‐target SSRs. The comparison of compounds involved in the formation of selectivity cliffs often reveals chemical modifications that render compounds target selective.     

A soft computing approach to model the structure–property relations of nonwoven fabrics

A soft computing approach to model the structure–property relations of nonwoven fabrics for filtration use is developed. Because the number of samples is very limited, the artificial neural network model to be established must be a small‐scale one. Consequently, this soft computing approach includes two stages. In the first stage, the structural parameters are selected by using a ranking method, to find the most relevant parameters as the input variables to fit the small‐scale artificial neural network model. The first part of this method takes the human knowledge on the nonwoven products into account. The second part uses a data sensitivity criterion based on a distance method that analyzes the measured data of nonwoven properties. In the second stage, the artificial neural network model of the structure–property relations of nonwoven fabrics is established. The results show that the artificial neural network model yields accurate prediction and a reasonably good artificial neural network model can be achieved with relatively few data points by integrated with the input variable selecting method developed in this research. The results also show that there is great potential for this research in the field of computer‐assisted design in nonwoven technology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 442–450, 2007     

Viscoelastic properties of polyaniline–emeraldine base nanostructured films: Experimental results and molecular dynamics simulations

Comprehensive exploration of the viscoelastic properties of polyaniline–emeraldine base (PANI–EB) nanostructured films is presented from two viewpoints of experimental study associated with dynamic mechanical thermal analysis and thermogravimetric measurements and of computational simulations by molecular dynamics (MD) approach. The results are expressed in storage and loss modulus components (E′ and E″). The role of drying temperature, time, and residual solvent content were studied on the E′ and E″ of prepared PANI–EB films. Using the principle of time–temperature superposition, E′ and E″ at different temperatures and frequencies can be plotted on master curves. The relationship between the modulus components with the solvation level of PANI–EB film is also studied. MD simulation is applied to study the viscoelasticity of simulated PANI structures with different monomeric aniline chains. The temperature dependence of viscoelastic properties provides good information for fractional free volume, cavity size distribution, and activation energy of PANI structures. Simulation outcomes provide a fairly good compatibility with the experimental results. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41858.     

Ceria in catalysis: From automotive applications to the water–gas shift reaction

Ceria is a crucial component of automotive catalysts, where its ability to be reduced and re‐oxidized provides oxygen storage capacity. Because of these redox properties, ceria can greatly enhance catalytic activities for a number of important reactions when it is used as a support for transition metals. For reactions that use steam as an oxidant (e.g., the water–gas‐shift reaction and steam reforming of hydrocarbons), rates for ceria‐supported metals can be several orders of magnitude higher than that for ceria or the transition metal alone. Because the redox properties of ceria are strongly dependent on treatment history and the presence of additives, there are significant opportunities for modifying catalysts based on ceria to further improve their performance. This article will review some of the contributions from my laboratory on understanding and using ceria in these applications. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

The role of interfacial interactions on the crystallinity and nanomechanical properties of clay–polymer nanocomposites: A molecular dynamics study

Polymer clay nanocomposites (PCN) show enhanced mechanical, thermal, liquid or gas barrier properties in comparison to pure polymer. However, the mechanisms for enhancement of these physical properties of PCN are not well understood. This knowledge is important for tailoring the properties of PCN to desired specifications. Our earlier study showed that organic modifiers have significant influence on the crystallinity and nanomechanical properties of PCN. For quantitative evaluation of the influence of organic modifiers on the crystallinity and nanomechanical properties of PCN, molecular models of three intercalated PCNs containing same polymer and clay but with three different organic modifiers are constructed in this work. Using molecular dynamics simulations, the interaction energies among the different constituents of PCNs are evaluated. This study reveals that the interactions between polymer, organic modifiers, and intercalated clay are critical factors in controlling the crystallinity and enhancement of nanomechanical properties of PCN. We have described the possible mechanisms leading to change in crystallinity and nanomechanical properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Probing cooperative jump-diffusion in zeolites: Neutron spin–echo measurements and molecular dynamics simulations of benzene in NaX

We report neutron spin–echo measurements of transport diffusivities for perdeuterated benzene in NaX zeolite. Corrected diffusivities from these neutron measurements were obtained for comparison with recently reported molecular dynamics simulations. Experimental diffusivities were measured with benzene loadings of 1, 2, 3 and 4.5 molecules per NaX cage, and at 300, 350 and 400 K. Both corrected and transport diffusivities increase from 1 to 3 molecules per cage, then decrease sharply to 4.5 molecules per cage. The comparison between experiment and simulation shows remarkably good agreement in both the loading dependence and in the overall magnitudes of the corrected diffusivities, with values mostly in the range 10⁻¹²–10⁻¹¹ m² s⁻¹.     

Biochar soil amendments for increased crop yields: How to design a “designer” biochar

The development and testing of a transient adsorption/desorption model that describes the response of biochar particles to nutrient pulses simulating the application of fertilizer is presented in this study. Intraparticle nutrient transfer occurs both by diffusion through liquid‐filled pores and by surface diffusion, and nutrient adsorption is described by Langmuir–Freundlich (Sips) isotherms. Simulation results show that the ability of a biochar to adsorb and then slowly release the nutrient is modulated by a complex interplay of external mass transfer, intraparticle diffusion (both pore and surface diffusion), and adsorption dynamics. The nutrient retention potential of biochar‐amended soils is quantified and is shown to depend on multiple factors that include chemical and physical biochar properties, soil permeability, water flow, and the method of fertilizer application. These findings may explain why biochars with similar properties can potentially have widely different impacts on crop yields, as has been repeatedly reported in the literature. © 2017 American Institute of Chemical Engineers AIChE J, 63: 5425–5437, 2017     

Finite element solution for gas–solid reactions: Application to the moving boundary problems

Gas–solid reactions are very important in the chemical and metallurgical process industries. Several models described these reactions such as volume reaction model, grain model, and nucleation model. These models give two coupled partial differential equations (CPDEs). In this work an integral transformation and subsequent finite element method is used for solving the coupled partial differential equations of these reactions. In each mesh the Rayleigh–Ritz method is applied. Finally the results of this work are compared with the existing numerical solutions and experimental data successfully.     

Adsorption characteristics of reduced Mo and Ni–Mo catalysts in the hydrodeoxygenation of benzofuran

The promotional effect of Ni on the hydrodeoxygenation (HDO) of benzofuran (BF) over reduced Ni–Mo/γ-Al₂O₃ catalysts was studied. The adsorption characteristics of Al₂O₃ support, mono-metallic Mo, and bi-metallic Ni–Mo catalysts that were pre-reduced were investigated using the feed molecule (BF) and a probe molecule (NO) as adsorbates. NO was used to probe the coordinatively unsaturated sites (CUS). Three adsorption modes for benzofuran over reduced Al₂O₃ support, Mo, and Ni–Mo catalysts were proposed that involved OH groups, Brønsted acid sites, and CUS, respectively. Benzofuran molecule adsorbed more strongly on B acid sites and CUS than on OH groups and was activated with weakening of the C–O bond. With increasing catalytic hydrogenation activity (increasing CUS) and/or decreasing hydrogenolysis activity (decreasing acidity), the reaction pathway for benzofuran HDO changes from a hydrogenolysis route to a route that involves saturation of the benzene ring before any heteroatom removal takes place.     

Effect of interface on the mechanical behavior of polybutadiene–silica composites: An experimental and simulation study

The effect of interface property on the mechanical behavior of silica–polybutadiene composites is systematically investigated via combined experimental and dynamics simulation. In experiment, the interface property is controlled by SiO₂ particle size, silane coupling agents, and silane grafting density. The effects of these control parameters on the vulcanization kinetics, tensile strength, and dynamic mechanic properties are investigated and discussed. Both the experimental and simulation studies reveal the pivot role of filler–polymer interface on the mechanical reinforcement. Simulation study reveals that the constrained polymer layer (～12 nm) surrounding the silica particles shows increased stress from 30 to 230 MPa, which is identified as the major reason for the overall enhancement of 100% modulus from 0.8 to 1.6 MPa. The molecular mechanics of interface from simulation is well correlated to the experimental results in this study, which provides a molecular level understanding of the relationship between interfacial interaction and mechanical reinforcement. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46089.     

Phase separation and crystallization behavior in extruded polypropylene/ethylene–propylene rubber blends

Liquid–liquid (L–L) phase separation and its effects on crystallization in polypropylene (PP)/ethylene–propylene rubber (EPR) blends obtained by melt extrusion were investigated by time‐resolved light scattering (TRLS) and optical microscopy. L–L phase separation via spinodal decomposition (SD) was confirmed by TRLS data. After L–L phase separation at 250°C for various durations, blend samples were subjected to a temperature drop to 130°C for isothermal crystallization, and the effects of L–L phase separation on crystallization were investigated. Memory of the L–L phase separation via SD remained for crystallization. The crystallization rate decreased with increasing L–L phase‐separated time at 250°C. Slow crystallization for the long L–L phase‐separated time could be ascribed to decreasing chain mobility of PP with a decrease in the EPR component in the PP‐rich region. The propylene‐rich EPR exhibited good affinity with PP, leading to a slow growth of a concentration fluctuation during annealing. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 695–700, 2001     

Novel phenomenological discrete bubble model of freely bubbling dense gas–solid fluidized beds: Application to two‐dimensional beds

A phenomenological discrete bubble model has been developed for freely bubbling dense gas–solid fluidized beds and validated for a pseudo‐two‐dimensional fluidized bed. In this model, bubbles are treated as distinct elements and their trajectories are tracked by integrating Newton's equation of motion. The effect of bubble–bubble interactions was taken into account via a modification of the bubble velocity. The emulsion phase velocity was obtained as a superposition of the motion induced by individual bubbles, taking into account bubble–bubble interaction. This novel model predicts the bubble size evolution and the pattern of emulsion phase circulation satisfactorily. Moreover, the effects of the superficial gas velocity, bubble–bubble interactions, initial bubble diameter, and the bed aspect ratio have been carefully investigated. The simulation results indicate that bubble–bubble interactions have profound influence on both the bubble and emulsion phase characteristics. Furthermore, this novel model may become a valuable tool in the design and optimization of fluidized‐bed reactors. © 2012 American Institute of Chemical Engineers AIChE J, 2012