Mo-Bi系丙烯氨氧化催化剂上氨分解反应动力学的Monte Carlo模拟

Monte Carlo method is applied to investigate the kinetics of ammonia oxidative decomposition over the commercial propylene ammoxidation catalyst(Mo-Bi).The simulation is quite in agreement with experimetal results.Monte Carlo simulation proves that the process of ammonia oxidation decomposition is a two-step reaction.     

晶粒正常生长的Monte Carlo模拟

本文建立了晶界能各向同性情况下晶粒生长的二维Monte Carlo模型,并对等温情况下的晶粒生长过程进行了模拟。在模拟过程中,对传统Monte Carlo方法中能量与概率统计方法进行了改进。为了更加直观地显示出晶粒生长过程中系统能量的变化,统计了在整个晶粒生长过程中能量的变化趋势,结果与晶粒尺寸变化相符合。模拟得到的晶粒生长指数在0.35~0.45之间,与理论值相符,证明了改进方法的可靠性。     

气溶胶在毛细管中输运Monte Carlo模拟

气溶胶在管道中的输运广泛应用于气溶胶采样、监测和气溶胶的危害评价中,前人基于对流扩散方程、流体速度分布规律,结合初始条件和边界条件,对气溶胶粒子在管道中的扩散特性进行了理论分析,取得了一定成功．Monte Carlo方法作为一种统计实验方法,在模拟中子或光子在介质中的Markoff输运过程中取得了巨大成功．另外,Monte Carlo方法也成功用于吸附质在多孔介质中的吸附和解吸特征研究．气溶胶粒子在气体介质中,由于受到气体分子的随机碰撞,     

高分子构象模拟研究中的Monte Carlo方法

介绍了Monte Carlo方法及其特点,进而分析了Monte Carlo用于高分子模拟的优势,并描述了两类模拟模型。论文重点综述了近年来Monte Carlo方法在高分子构象模拟中的一些研究与应用,并展望了Monte Carlo方法在高分子构象模拟中的发展趋势和前景。     

水力旋流器分离过程的 Monte Carlo 模拟

根据颗粒在水力旋流器中的运动特点,提出了颗粒运动状态的交换构成三角马尔可夫链的观点,建立了水力旋流器分离过程的随机数学模型,并利用ＭｏｎｔｅＣａｒ┐ｌｏ方法进行了数值模拟,模拟程序中采用变参数设计,在输入一定的结构和工艺参数下,由计算机自动生成水力旋流器分离过程的级效率曲线,并给出总效率值;并计算了在不同容量下的模拟精度,结果表明样本容量越大,模拟精度越高     

加速Monte Carlo分子模拟收敛的能量选择取样法

为提高Monte Carlo分子模拟的取样效率,加速模拟过程的收敛,本文提出了根据粒子能量进行取样的方法。通过对凝固点附近的L-J流体的模拟,将能量选择取样法与Metropolis取样法以及力偏倚取样法的收敛性和模拟结果作了比较,表明能量选择取样法的收敛速度显著高于Metropolis取样法,与力偏倚取样法相当,而计算量比力偏倚取样法小。     

无规共聚高分子溶液相平衡的Monte Carlo模拟

引　言近年来 ,随着计算机硬件能力的不断提高和新的模拟方法的不断涌现 ,对于高分子溶液的相平衡问题的计算机模拟研究取得了很大的进展 ,但大多将注意力放在如何改进模拟方法以获得更长的均聚高分子溶液的相平衡数据 ,以检验Ｆｌｏｒｙ -Ｈｕｇｇｉｎｓ理论、修正Ｆｒｅｅｄ理论等的有效性 .如Ｍａｄｄｅｎ等[1]曾利用蛇行法 (ｒｅｐｔａｔｉｏｎ)和伪动态模拟算法( ｐｓｅｕｄｏｋｉｎｅｔｉｃｓｉｍｕｌａｔｉｏｎａｌｇｏｒｉｔｈｍ)、Ｍａｃｋｉｅ等[2 ]在邻位数Ｚｎ=2 6的格子模型上用Ｇｉｂｂｓ系综法、Ｗｉｌｄｉｎｇ等[3]用键长涨…     

NPT系综Monte Carlo分子模拟方法的改进

通过调节体系密度使得体系的瞬时压力保持恒定,从而实现 NPT 系综的 Monte Carlo 分子模拟。对 Lennard-Jones 流体的模拟结果表明,该方法与现行的 NPT 系综模拟方法相比具有更快的收敛速度。本文应用改进的方法对 Ar-Kr 混合物的热力学性质进行了模拟。     

高分子抑制蛋白质聚集的动态Monte Carlo模拟

抑制聚集是蛋白质产品下游加工特别是制剂过程中的重要问题。本文采用动态Monte Carlo方法和二维晶格HP蛋白质模型,通过建立高分子-蛋白质复合物微观结构和蛋白质构象概率分布来研究高分子对蛋白质聚集行为的影响。结果表明,高分子的疏水性、分子量及其浓度对于蛋白质的聚集行为有显著的影响。当其疏水性适宜时,高分子可富集在蛋白表面疏水位点,强化蛋白质分子在水溶液中的分散,从而抑制聚集。高分子还可缠绕在蛋白质分子表面形成限制性空间从而稳定蛋白质的天然结构。     

丙烯腈共聚物序列分布的Monte Carlo模拟

通过Monte Carlo方法，对不同共聚单体的聚丙烯腈组成进行了模拟。通过比较．与文献中提供的实验结果基本一致。同时模拟了衣康酸(1A)、丙烯酸(AA)、甲基丙烯酸(MAA)分别与丙烯腈(AN)在不同配比下共聚物的序列分布，结果表明：在Monte Carlo模型中，可以通过控制单体的配比来控制序列分布，而在实际的合成中，要获得均匀的序列结构，就可以通过降低第二单体投料比法或滴加单体法来实现。     

Monte Carlo simulation studies of the catalytic combustion of methane

A Monte Carlo (MC) simulation is carried out of the catalytic oxidation of methane based on the pseudo-Langmuir-Hinshelwood (LH) mechanism proposed by Iglesia et al., that attempts to interpret the behavior of this reaction, which from experiments is assumed to be of the Mars-van Krevelen type. The results interpret reasonably some experimental findings (reaction order with respect to H₂O, CH₄, activity and structural sensitivity) if certain criteria based on the experiment and some laboratory data for the kinetic and thermodynamic parameters from the literature are considered.     

Local forcing of a nonlinear surface reaction: CO oxidation on Pt(100)

A novel spatiotemporal perturbation method for nonlinear surface reactions is reported, thus allowing the creation of new spatially localized structures. Forcing was achieved by dosing reactant gases through a capillary positioned near the catalyst surface, providing control over the local surface coverage and reaction rate. The emergence of localized concentration patterns and oscillations in an otherwise stable system is attributed to a local modification of the catalytic properties of the surface due to external forcing. Based on the spatial orientation, the temporal and thermal stability of the modified surface, as well as the affinity of CO toward the perturbed surface, subsurface O is proposed as a possible source of the observed localized patterning and surface memory effect. © 2008 American Institute of Chemical Engineers AIChE J, 2009     

Monte Carlo simulation of polyampholyte-nanoparticle complexation

The complexation between a polyampholyte and a charged particle was investigated via Monte Carlo simulations on an off-lattice. The simulations revealed that there are three regions for the conformation of the complex formed between a positively charged particle and a polyampholyte chain. When the charge density and the size of the particle were small, the chain adsorbed on the particle surface maintained to a large extent its configuration from the bulk (spherical, dumb-bell, necklace or rod-like). By increasing the charge density and the particle size, the polyampholyte chain has collapsed on the surface. Further increases of the charge density and size of the particle caused a segregation of the beads of the sub-chains with mostly positive charges from those with mostly negative charges, those richer in positive charges being repelled by the particle. The simulation results are compared with some analytical results.     

Experimental evidence for an oxidation/reduction mechanism in rate oscillations of catalytic CO oxidation on Pt/SiO2

In situ X-ray diffraction experiments have been conducted during rate oscillations of catalytic CO oxidation on a supported Pt catalyst, EuroPt-1. The measurements which were carried out at atmospheric pressure with flow rates of 200 ml/min showed that the non-isothermal oscillations in the reaction rate were accompanied by periodic intensity variations of a Bragg peak. A Debye function analysis of beam profiles recorded at the two extrema of the oscillations revealed that the Pt catalyst undergoes a periodic oxidation and reduction during rate oscillations. The diffraction experiments are therefore considered to be the first experimental proof that the oxide model proposed originally by Sales, Turner and Maple to explain rate oscillations in the CO + O₂ reaction at atmospheric pressure is in fact correct.     

Monte Carlo simulation of nano-particle sintering

This paper uses a multi-state Potts model to simulate the sintering of nano-particles by boundary migration and evaporation-condensation. The variables in this simulation are the reduced temperature, a next-nearest neighbour weighting and the ratio of interfacial to surface energy. The effect of these parameters on simulation of sintering of two and three-particle clusters is systematically explored as a basis for the study of more complex aggregates.     

Monte Carlo simulation of sequence distributions of acrylonitrile copolymers

A Monte Carlo simulation examining the effect of monomer ratios on the composition and sequence distribution of acrylonitrile(AN) copolymers with N‐vinyl pyrrolidone (NVP), itaconic acid (IA), and acrylic acid (AA) as comonomers has been developed. The Kelen–Tudos method was used to estimate monomer reactivity ratios. The results of the simulation are consistent with the academic conclusion and are as foreseen by the experimental data. The average number of NVP identical monomers in a sequence length of AN/NVP copolymer chain increases continuously and the average number of AN identical monomers in a sequence length shows a prominent decrease with an increase of NVP concentration in the feed. Changes in the monomer average number of AN/IA and AN/AA copolymers in a sequence length were the same as those of AN/NVP copolymer with an increase of comonomer concentration in the feed. The optimum weight ratio of AN with comonomers for manufacturing carbon fibers is 98/2. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 483–488, 2005     

Monte Carlo simulations combined with UHV-atmospheric pressure reaction studies on CO hydrogenation on cobalt

We show that useful information on catalytic reactions can be obtained using Monte Carlo simulations combined with experimental data from model catalysts. The experimental rate dependencies of CO hydrogenation on the partial pressures were used to guide the selection of different parameter values used in the simulations. The results give the following picture of the reaction conditions on the surface: hydrogen and carbon monoxide occupy different adsorption sites, the diffusion of hydrogen and the growth of hydrocarbon chains are fast processes, and the rate-limiting elementary reaction step is the termination of the hydrocarbon chains (-hydrogenation). The formation of longer chain hydrocarbons falls onto the line defined by the Anderson-Flory-Schulz distribution but the value of the chain growth parameter , obtained in the simulations, is higher than the experimental value.     

Monte Carlo simulation of particle breakage process during grinding

The Monte Carlo method is quite useful in the modeling of particulate systems. It is used here to simulate the particle brekage process during grinding that can be represented by a population balance equation. The simulation technique is free from discretization of time or size. The results of simulation under restricted conditions of grinding compare very well with the available analytical solution of the population balance equation. The procedure is extended to simulate the grinding process in its entirety. This method provides an alternative to the modeling of the grinding process where the governing population balance equation cannot be readily solved.     

Monte Carlo simulation of the PEMFC catalyst layer

The performance of the polymer electrolyte membrane fuel cell (PEMFC) is greatly controlled by the structure of the catalyst layer. Low catalyst utilization is still a significant obstacle to the commercialization of the PEMFC. In order to get a fundamental understanding of the electrode structure and to find the limiting factor in the low catalyst utilization, it is necessary to develop the mechanical model on the effect of catalyst layer structure on the catalyst utilization and the performance of the PEMFC. In this work, the structure of the catalyst layer is studied based on the lattice model with the Monte Carlo simulation. The model can predict the effects of some catalyst layer components, such as Pt/C catalyst, electrolyte and gas pores, on the utilization of the catalyst and the cell performance. The simulation result shows that the aggregation of conduction grains can greatly affect the degree of catalyst utilization. The better the dispersion of the conduction grains, the larger the total effective area of the catalyst is. To achieve higher utilization, catalyst layer components must be distributed by means of engineered design, which can prevent aggregation.