Enhanced production of hydrogen via catalytic methane decomposition on a Pt_(7)-Ni(110) substrate:a reactive molecular dynamics investigation

Numerous researchers in the energy field are engaged in a competitive race to advance hydrogen as a clean and environmentally friendly fuel.Studies have been conducted on the different aspects of hydrogen,including its production,storage,transportation and utilization.The catalytic methane decomposition technique for hydrogen production is an environmentally friendly process that avoids generating carbon dioxide gas,which contributes to the greenhouse effect.Catalysts play a crucial role in facilitating rapid,cost-effective and efficient production of hydrogen using this technique.In this study,reactive molecular dynamics simulations were employed to examine the impact of Pt_(7) cluster decoration on the surface of a Ni(110)catalyst,referred to as Pt_(7)-Ni(110),on the rates of methane dissociation and molecular hydrogen production.The reactive force field was employed to model the atomic interactions that enabled the formation and dissociation of chemical bonds.Our reactive molecular dynamics simulations using the Pt_(7)-Ni(110)catalyst revealed a notable decrease in the number of methane molecules,specifically~11.89 molecules per picosecond.The rate was approximately four times higher than that of the simulation system utilizing a Ni(110)catalyst and approximately six times higher than that of the pure methane,no-catalyst system.The number of hydrogen molecules generated during a simulation period of 150000 fs was greater on the Pt_(7)-Ni(110)surface than in both the Ni(110)and pure methane systems.This was due to the presence of numerous dissociated hydrogen atoms on the Pt_(7)-Ni(110)surface.

Dynamic Modeling and Simulation of a Commercial Naphtha Catalytic Reforming Process

A first principles-based dynamic model for a continuous catalyst regeneration (CCR) platforming process, the UOP commercial naphtha catalytic reforming process, is developed in this paper. The lumping details of the naphtha feed and reaction scheme of the reaction model are given. The process model is composed of the reforming reaction model with catalyst deactivation, the furnace model and the separator model, which is capable of capturing the major dynamics that occurs in this process system. Dynamic simulations are performed based on Gear numerical algorithm and method of lines (MOL), a numerical technique dealing with partial differential equations (PDEs). The results of simulation are also presented. Dynamic responses caused by disturbances in the process system can be correctly predicted through simulations.

Dynamic model for predicting nitrogen oxide concentration at outlet of selective catalytic reduction denitrification system based on kernel extreme learning machine

To solve the increasing model complexity due to several input variables and large correlations under variable load conditions,a dynamic modeling method combining a kernel extreme learning machine(KELM)and principal component analysis(PCA)was proposed and applied to the prediction of nitrogen oxide(NO_(x))concentration at the outlet of a selective catalytic reduction(SCR)denitrification system.First,PCA is applied to the feature information extraction of input data,and the current and previous sequence values of the extracted information are used as the inputs of the KELM model to reflect the dynamic characteristics of the NO_(x)concentration at the SCR outlet.Then,the model takes the historical data of the NO_(x)concentration at the SCR outlet as the model input to improve its accuracy.Finally,an optimization algorithm is used to determine the optimal parameters of the model.Compared with the Gaussian process regression,long short-term memory,and convolutional neural network models,the prediction errors are reduced by approximately 78.4%,67.6%,and 59.3%,respectively.The results indicate that the proposed dynamic model structure is reliable and can accurately predict NO_(x)concentrations at the outlet of the SCR system.

The Role of Hydrogen Bond in Catalytic Triad of Serine Proteases

In order to investigate the origin of catalytic power for serine proteases,the role of the hydrogen bond in the catalytic triad was studied in the proteolysis process of the peptides chymotrypsin inhibitor 2(CI2),MCTI-A,and a hexapeptide(SUB),respectively.We first calculated the free energy profile of the proton transfer between His and Asp residues of the catalytic triad in the enzyme-substrate state and transition state by employing QM/MM molecular dynamics simulations.The results show that a low-barrier hydrogen bond(LBHB)only forms in the transition state of the acylation of CI2,while it is a normal hydrogen bond in the acylation of MCTI-A or SUB.In addition,the change of the hydrogen bond strength is much larger in CI2 and SUB systems than in MCTI-A system,which decreases the acylation energy barrier significantly for CI2 and SUB.Clearly,a LBHB formed in the transition state region helps accelerate the acylation reaction.But to our surprise,a normal hydrogen bond can also help to decrease the energy barrier.The key to reducing the reaction barrier is the increment of hydrogen bond strength in the transition state state,whether it is a LBHB or not.Our studies cast new light on the role of the hydrogen bond in the catalytic triad,and help to understand the catalytic triad of serine proteases.

Surface Photometry and Dynamical Properties of Lenticular Galaxies: NGC3245 as Case Study

In this paper, surface photometry and dynamical properties of Lenticular galaxies will be developed and applied to NGC3245. In this respect, we established new relation between the intensity distribution I and the semi-major axis a Moreover, some basic statistics of both independent and the dependent variables of the relation are also given. In addition to the I(a) relation , the Sérsic r1/n model is applied for the intensity profile I(r) resulting in an estimation of the effective radius, re, and the surface brightness it encloses, μe. Both relations (I(a) and I(r)) are accurate as judged by the precision criteria which are: the probable errors for the coefficients , the estimated variance of the fit and the Q value (the square distance between the exact solution and the least square estimated solution) where all very satisfactory. Correlation coefficients between some parameters of the isophotes are also computed. Finally as examples of applications of surface photometry we determined the dynamical properties: mass, density, potential distributions, as well as distributions of escape and circular speeds in terms of Sérsic model.

Suiting Dynamic Models of Fixed-Bed Catalytic Reactors for Computer-Based Applications

This work investigated the applicability of heterogeneous and pseudo-homogeneous models to predict the dynamic behavior of a fixed-bed catalytic reactor. Some issues concerning the dynamic behavior of the system were discussed, such as the prediction of the inverse response phenomenon. The proposed models (Het- erogeneous I and II and Pseudo-homogeneous) were able to predict with qualitative similarity the main characteristics of the dynamic behavior of a fixed-bed catalytic reactor, including the inverse response. The computational time demanded for the solution of the heterogeneous models was 10 to 50% longer than in the case of the pseudo-homogeneous model, making the use of the former suitable for applications where computational time is not the major restriction (off-line applications). On the other hand, when on-line applications are required, the simplified model (Pseudo-homogeneous model) showed to be a good alternative because this model was able to predict (qualitatively) the dynamics of the reactor using a faster and easier numerical solution.

化学链甲烷氧化偶联界面反应路径和晶格氧传递的分子动力学模拟

本研究采用分子动力学模拟的方法计算八种金属氧化物催化剂-载氧体CL-OCM反应性能,并对性能最优的Mn_(2)O_(3)开展反应时间和颗粒尺寸的研究。结果表明,适当延长反应时间有利于提高C_(2)H_(4)选择性;C/O=1是Mn_(2)O_(3)的理想尺寸。基于以上结果分析了Mn_(2)O_(3)CL-OCM界面反应路径和晶格氧传递问题,以揭示反应机理。CH_(3)^(*)气相二聚化生成C_(2)H6的是CL-OCM最主要的碳偶联路径。除此之外,还存在两条碳偶联路径,均由CH2^(*)引发。CH_(3)^(*)与OH^(*)表面结合生成甲醇是CL-OCM副反应的先决步骤,抑制甲醇生成是提高CL-OCM反应C_(2)选择性的关键。晶格氧存在转化,表面晶格氧是甲烷活化的活性氧。晶格氧数量差异及体相晶格氧迁移阻力差异是导致CH_(4)转化率和C_(2)选择性不同的主要原因。该研究为CL-OCM催化剂-载氧体的机理探究提供新的方法。

负压差斜管内催化剂颗粒流动特性的实验研究

在规格为Φ150 mm×3600 mm的负压差斜管-阀门实验装置上,通过测量和分析不同催化剂颗粒质量流率(G_(s))时斜管内轴向动态压力的特征参数,进行催化裂化装置斜管内催化剂颗粒的流动特性研究。结果表明:斜管蓄压能力随G_(s)的增大而增大,管内依次出现稀相分层流、密相分层流和填充流;斜管内的压力分布、主频、幅值、标准偏差与流态相对应,可用于流态的量化识别;当G_(s)=65.96 kg/(m^(2)·s)时,斜管内存在多流态,分别为过渡填充流、填充流、密相流;在斜管中部通入松动风,可以有效改善颗粒输送能力和斜管蓄压能力。

催化动力学光度法测定痕量亚硝酸根

在冰乙酸介质中,利用亚硝酸根催化条件下,溴酸钾氧化茜素红的褪色反应,建立催化动力学光度法,对痕量NO_(2)^(-)进行测定.通过单因素实验得到了各种成分的加入量、反应温度和反应时间等最佳条件.结果发现,在反应体系中,茜素红浓度与NO_(2)^(-)含量之间线性关系良好,在0.02~0.14μg/mL范围内,线性回归方程为ln(A_(0)/A)=1.43 c NO_(3)^(-)(μg/mL)+0.00859,相关系数r^(2)为0.9970,检出限为5.25×10^(-3)μg/mL.该方法操作简单、稳定性好.

基于定向进化技术提高呕吐毒素解毒酶DepA的催化活性

[目的]呕吐毒素(deoxynivalenol,DON)C3位羟基的异构化是生物脱毒的关键部位,其中DepA作为DON生物转化中第一步关键限速酶,存在催化活性低的问题,限制了其在食品及饲料加工领域中的应用。本文旨在通过定向进化技术对DepA进行分子改造,以期获得催化活性显著提高的突变酶,提高其工业化应用的潜力。[方法]通过易错PCR和DNA shuffling相结合的方法,构建突变文库,经高通量筛选后,对催化活性明显提高的突变体进行酶学性质表征。同时,采用分子动力学模拟和三维结构模拟分析,探究突变酶催化活性提高的分子机制。[结果]成功筛选到突变酶S2、S10和S12,与野生型相比,其比活力分别提高207%、293%和258%。动力学参数结果显示,突变酶S2、S10和S12的K m值分别为56.89、27.00和40.65μmol·L^(-1),是野生型的91.7%、43.5%和65.5%;k_(cat)/K_(m)值分别为327.30、576.67和380.07 L·mmol^(-1)·s^(-1),是野生型的1.25、2.20和1.45倍,相比野生型,突变酶亲和力和催化效率均显著提高。此外,分子动力学模拟和三维结构模拟分析结果表明,柔性增加、底物DON的进攻距离缩短、氢键增加、疏水性增加和远端效应是导致其催化活性提高的主要原因。[结论]本研究通过易错PCR和DNA shuffling相结合的定向进化策略有效提高了呕吐毒素解毒酶DepA的催化活性,为其工业化应用提供试验依据。

过氧化氢-耐尔蓝体系催化动力分光光度法测定冶炼废水中微量铜

随着水土环境的日益恶化,监控包括铜在内的重金属污染对水土环境的危害越来越受到重视,有的重金属通过食物链以有害浓度在人体内积累,严重危害人体健康。基于在柠檬酸缓冲溶液反应介质中,过氧化氢在Cu(Ⅱ)的催化下能氧化耐尔蓝褪色,其褪色程度与Cu(Ⅱ)含量成正比,从而建立了催化分光光度法测定微量Cu(Ⅱ)的新方法。选择的反应介质柠檬酸缓冲溶液具有某些表面活性剂的作用,浅析了柠檬酸缓冲溶液在工作中对耐尔蓝起增敏作用的原因,且柠檬酸作为植物提取物,具有无毒环保,易于分解,可调节酸度和化学性质稳定等优点。通过实验确定了方法的最大吸收波长为635 nm,柠檬酸缓冲溶液的最佳使用量为1.0 mL,耐尔蓝和过氧化氢的最佳用量分别为1.75和1.0 mL,反应时间和反应温度分别为11 min和90℃,Cu(Ⅱ)含量在0~0.32μg/mL内与吸光度的差值呈线性关系。对铜标准溶液和标准物质进行测定,测定结果的相对误差在2.8%~3.8%,相对标准偏差在3.8%~4.7%,表观摩尔吸光系数为5.0×10^(6)L/(mol•cm)。方法用于废水中微量Cu(Ⅱ)的测定,加标回收率在95.6%~102%。方法具有操作简便、选择性较好、有较灵敏度高、分析成本低、使用的试剂较为环保等优点。

钌催化剂在动态动力学拆分中的应用研究进展

手性化合物在有机合成中具有重要的作用,广泛应用于医药、农业、食品和材料等领域。获得单一手性化合物的方法一直是重要的研究课题,但是,一般的合成或提取方法得到的多是外消旋体。动态动力学拆分为外消旋体完全转化成单一对映体提供了一种强大的方法,该方法可以将一种构型的对映异构体选择性拆分,同时另一种构型的对映异构体外消旋化,从而获得单一构型的产物,且对映体过量值可达到>99%,理论产率可达到100%。研究者已经开发了一些钌-酶催化体系、钌-非酶催化体系和钌-手性配体络合物用于烯丙醇、二醇、含官能团的仲醇的动态动力学拆分,以及酮和酯的不对称转移氢化动态动力学拆分的有效方法。本文将对这些方法进行综述,并提供相关的示例,以期为这些方法的更进一步应用提供参考。

2,3-二氯吡啶催化加氢动力学研究

采用液相还原法制备了Pd/C催化剂,在压力0.6 MPa、温度303~323 K、转速800 r/min的条件下应用于2,3-二氯吡啶催化加氢反应动力学研究,建立了动力学反应模型,对动力学参数进行了估值。其中3-氯吡啶催化加氢反应为2.1级反应,反应速度方程为:r=1.18×10^(8)×M cat×e-5375.7/T C^(2.1)_(3cp),活化能44.14 kJ/mol,2-氯吡啶催化加氢反应为1级反应,反应速率方程为:r=4.696×10^(11)×M cat×e-8693.3/T C_(2cp),活化能72.28 kJ/mol,2,3-二氯吡啶催化剂加氢反应为3级反应,反应速度方程为:r=2.05×10^(15)×M cat×e-9758.6/T C^(3)_(2.3),活化能81.13 kJ/mol。

《饲料中碘的测定》硫氰酸铁-亚硝酸催化动力学法国家标准前处理方法修订解读

对修订的GB/T 13882—2023《饲料中碘的测定》第二法硫氰酸铁-亚硝酸催化动力学法的关于前处理的修订内容进行了解读。该方法相较之前更改了碘标准工作溶液的配制方式、干灰化法并删除了湿法。采用580℃灰化样品,使试样中的碘酸根转换为碘离子,同时使用580℃处理碘标准中间溶液,补偿样品前处理过程中碘的损失。相较于修订前,修订后的前处理样品方法和配制标准系列曲线方式能显著提高方法的准确性。

石油炼制催化重整工艺稳动态模型的构建及仿真分析

为进一步掌握石油炼制催化重整工艺的技术要点,为后续石油炼制的产量和质量提供支撑,在对催化重整工艺流程、影响因素以及优化方向进行简要概述的基础上,分别构建了催化重整稳态和动态模型并进行了验证,基于验证后的模型构建催化重整工艺仿真模型,对各反应器的温降情况进行分析,为今后参数的优化奠定基础。此外,基于验证过后的模型还可对催化重整其他反应进行研究。

催化裂化油浆动态与静态组合过滤技术工业实践

动态与静态二级组合过滤技术在某公司催化裂化装置油浆过滤单元进行了工业实践。该组合技术一级过滤系统采用动态过滤技术,二级过滤系统采用静态过滤技术。控制一级过滤系统净化油浆收率不大于85%,并辅以一级自清洗及二级反冲洗膜管再生技术,有利于系统的长周期运行。加工外购油浆试验期间,一级过滤器压差出现明显上升,为提高装置平稳运行水平,需加强对外购油浆性质的分析。工业标定数据表明,在进料量25 t/h、外购油浆掺炼比例为45%的条件下,该装置总净化油浆收率95.29%,净化油浆灰分小于100μg/g,灰分脱除率高达99.8%。长周期运行数据表明,在高负荷条件下连续运行,装置净化油浆产品质量与收率均可满足指标要求,两级过滤器压差平稳,管道未见明显磨损减薄,可以满足长周期工业运行的要求。

Design of process and control scheme for cyclohexanol production from cyclohexene using reactive distillation

Cyclohexanol is a commonly used organic compound.Currently,the most promising industrial process for synthesizing cyclohexanol,by cyclohexene hydration,suffers from a low conversion rate and difficult separation.In this paper,a three-column process for catalytic distillation applicable in the hydration of cyclohexene to cyclohexanol was established to solve these.Simulation with Aspen Plus shows that the process has good advantages,the conversion of cyclohexene reached 99.3%,and the product purity was>99.2%.The stable operation of the distillation system requires a good control scheme.The design of the control scheme is very important.However,at present,the reactive distillation process for cyclohexene hydration is under investigation experimentally and by steady-state simulation.Therefore,three different plant-wide control schemes were established(CS1,CS2,CS3) and the position of temperature sensitive stage was selected by using sensitivity analysis method and singular value decomposition method.The Tyreus-Luyben empirical tuning method was used to tune the controller parameters.Finally,Aspen Dynamics simulation software was used to evaluate the performance of the three control schemes.By introducing ΔF±20% and χ_(ENE)±5%,comparison the changes in product purity and yield of the three different control schemes.By comparison,we can see that the control scheme CS3 has the best performance.

Role of Residue 90 in Catalysis of Cytochrome P450 2C9

The cytochrome P450 mutant CYP2C9.13（L90P） shows a greatly impaired catalytic activity compared with the wild-type. We constructed the mutants by substitution at residue 90 of CYP2C9, expressed in COS-7 cells, assayed their thermal stability and catalysis activity and analyzed the mutants via molecular dynamic（MD） simulation and flexible docking. Mutant L90E exhibits a significantly lower catalytic activity than the wild-type for the hydroxylation of diclofenac, lornoxicam and luciferin and its molecular dynamics simulation results indicate that the size of the entrance of substrate access was reduced significantly. An increase or minor decrease of catalytic activity was observed for mutants L90Q, L90W, L90R, L90I and L90G, and the sizes of the entrances of substrate access and the active site cavities had a little change in those mutants. The thermal stability and the potential energy of the MD simulation of these mutants showed a similar tendency as the catalysis assays did. Flexible docking results show the fluctuation of interaction energy is due to the change of electrostatic potential distribution. All the above facts show that the changes in the catalysis activity of the mutants caused by the substitution at residue 90 are due to the changes in the size of entrance, the shape and size of active site cavity, electrostatic potential distribution and thermal stability. The residue 90 of CYP2C9 has an important effect on the enzyme catalytic activity.

Revisiting the dichotomy of early-type galaxies

We study the relationship between isophotal shapes, central light profiles and kinematic properties of early-type galaxies （ETGs） based on a compiled sample of 184 ETGs. These sample galaxies are included in Data Release 8 of the Sloan Digital Sky Survey and have central light profiles and kinematic properties available from the literature, which were compiled from observations by the Hubble Space Telescope and the ATLAS3D integral-field spectrograph, respectively. We find that there is only a weak correlation between the isophotal shape （a4/a） and the central light profile （within 1 kpc） of ETGs. About two-fifths of ＂core＂ galaxies have disky isophotes, and one-third of ＂power-law＂ galaxies are boxy. Our statistical results also show that there are weak correlations between galaxy luminosity and dynamical mass with a4/a, but such correlations are tighter with a central light profile. Moreover, no clear link has been found between the isophotal shape and the Sersic index. Comparisons show that there are similar correlations between a4/a and ellipticity, and between a4/a and specific angular momentum ARo/2 for ＂power-law＂ ETGs, but there are no such correlations for ＂core＂ ETGs. Therefore, we speculate that the bimodal classifications of ETGs are not as simple as previously thought, though we also find that the disky ETGs with highest a4/a are more elongated and fast rotators.

A generalized CFD model for evaluating catalytic separation process in structured porous materials

A hybrid multiphase model is developed to simulate the simultaneous momentum, heat and mass transfer and heterogeneous catalyzed reaction in structured catalytic porous materials. The approach relies on the combination of the volume of fluid(VOF) and Eulerian–Eulerian models, and several plug-in field functions. The VOF method is used to capture the gas–liquid interface motion, and the Eulerian–Eulerian framework solves the temperature and chemical species concentration equations for each phase.The self-defined field functions utilize a single-domain approach to overcome convergence difficulty when applying the hybrid multiphase for a multi-domain problem. The method is then applied to investigate selective removal of specific species in multicomponent reactive evaporation process. The results show that the coupling of catalytic reaction and interface species mass transfer at the phase interface is conditional, and the coupling of catalytic reaction and momentum transfer across fluid–porous interface significantly affects the conversion rate of reactants. Based on the numerical results, a strategy is proposed for matching solid catalyst with operating condition in catalytic distillation application.