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1.
Ultrasound can accelerate and change the reaction process and is widely used in the field of hydrogen production and storage. In this study, ultrasound (US) and AlOOH suspension (AH) are used to promote hydrogen production from Al hydrolysis. The results indicate that both US and AH greatly shorten the induction time and enhance the hydrogen production rate and yield. The promoting effect of US and AH on Al hydrolysis originates from the acoustic cavitation effect and catalytic effect, respectively. When AH is used in combination with US, Al hydrolysis has the best hydrogen production performance and the hydrogen yield can reach 96.6 % within 1.2 h, because there is a synergistic effect on Al hydrolysis between AH and US. Mechanism analyses reveal that the micro-jets and local high temperature environment arising from acoustic cavitation improve the catalytic activity of AlOOH, while the suspended AlOOH particles enhance the cavitation effect of US. This work provides a novel and feasible method to promote hydrogen production from Al hydrolysis.  相似文献   
2.
The reaction of N2 with trinuclear niobium and tungsten sulfide clusters Nb3Sn and W3Sn (n=0–3) was systematically studied by density functional theory calculations with TPSS functional and Def2-TZVP basis sets. Dissociations of N−N bonds on these clusters are all thermodynamically allowed but with different reactivity in kinetics. The reactivity of Nb3Sn is generally higher than that of W3Sn. In the favorite reaction pathways, the adsorbed N2 changes the adsorption sites from one metal atom to the bridge site of two metal atoms, then on the hollow site of three metal atoms, and at that place, the N−N bond dissociates. As the number of ligand S atoms increases, the reactivity of Nb3Sn decreases because of the hindering effect of S atoms, while W3S and W3S2 have the highest reactivity among four W3Sn clusters. The Mayer bond order, bond length, vibrational frequency, and electronic charges of the adsorbed N2 are analyzed along the reaction pathways to show the activation process of the N−N bond in reactions. The charge transfer from the clusters to the N2 antibonding orbitals plays an essential role in N−N bond activation, which is more significant in Nb3Sn than in W3Sn, leading to the higher reactivity of Nb3Sn. The reaction mechanisms found in this work may provide important theoretical guidance for the further rational design of related catalytic systems for nitrogen reduction reactions (NRR).  相似文献   
3.
A detailed study of the geometry, aromatic character, electronic and magnetic properties for a series of positively charged N-doped polycyclic aromatic hydrocarbons (PAHs) was performed. Magnetic properties of the examined molecules were analyzed by means of the magnetically induced current density calculated using the diamagnetic-zero version of the continuous transformation of origin of current density (CTOCD-DZ) method. The comparative study of the local aromaticity of the studied molecules was performed using several different indices: energy effect (ef), harmonic oscillator model of aromaticity (HOMA) index, six centre delocalization index (SCI) and nucleus independent chemical shifts (NICS). The presence of N-atoms in the inner rings was found to cause a planarity distortion in the studied N-doped systems. The geometric changes and charged nature of the studied N-doped systems do not significantly influence the current density and the local aromaticity distribution in comparison with the corresponding parent benzenoid hydrocarbons. The present study demonstrates how quantum chemical calculations can be used for rational design of novel PAHs and for fine tuning of their properties.  相似文献   
4.
Dehydrogenation of an organic compound is the first and the most fundamental elementary reaction in many organic reactions. In ethanol oxidation reaction (EOR) to form CO2, there are a total of 46 pathways in C2HxO (x=1–6) species leading to the removal of all six hydrogen atoms in five C−H bonds and one O−H bond. To investigate the degree of dehydrogenation in EOR under operando conditions, we performed density function theory (DFT) calculations to study 28 dehydrogenation steps of C2HxO on Ir(100). An activation energy surface was then constructed and compared with that of the C−C bond cleavages to understand the importance of the degree of dehydrogenation in EOR. The results show that there are likely 28 dehydrogenations in EOR under fuel cell temperatures and the last two hydrogens in C2H2O are less likely cleaved. On the other hand, deep dehydrogenation including 45 dehydrogenations can occur under ethanol steam reforming conditions.  相似文献   
5.
Supercapacitors (SCs) with high energy density and power density are a research hotspot. Herein, we report a flexible porous carbon membrane supercapacitor prepared by electrospinning polyacrylonitrile (PAN) with γ-cyclodextrin-MOF (γ-CD-MOF) and then carbonizing at 900 °C. BET results showed that the supercapacitor retained the skeleton of γ-CD, γ-CD-MOF and the pores formed by the spun-fibers, which were 0.73, 1.09 and 23–186 nm, respectively, showing a high specific surface area of 134.7 m2/g. The hierarchically porous structures ensure rapid charge transfer and ion diffusion, resulting in the PAN/γ-CD-MOF carbon electrode with a high capacity of 283.3 F/g. Moreover, the supercapacitor had a high energy density up to 17.5 Wh/kg and power density up to 6 kW/kg. Significantly, it showed excellent cycle stability with a capacitance retention of 97.5% after 6000 cycles. This work provides a supramolecular strategy to construct a flexible porous carbon membrane, which has potential for supercapacitor applications.  相似文献   
6.
针对属性权重未知,且属性值为毕达哥拉斯犹豫模糊数(PHFN)的风险型多属性决策问题,考虑到决策者的有限理性行为,提出基于累积前景理论(CPT)和多准则妥协优化解(VIKOR)的决策方法。首先,定义PHFN的分散率,并构建优化模型确定属性权重。其次,将CPT融入PHFN环境,定义PHFN的价值函数,并结合决策权重函数计算方案在各属性下的综合前景值。进一步,构建综合前景值矩阵,在此基础上运用VIKOR法确定方案排序。最后,通过风险投资项目选择的应用案例说明所提方法是可行、有效的。  相似文献   
7.
二维材料MXene纳米片由于具有较大的比表面积和较高的电子迁移率而受到广泛的关注。本文采用基于密度泛函理论的第一性原理计算,对单层MXene纳米片Ti2N电磁特性的过渡金属(Sc、V、Zr)掺杂效应进行了系统研究。结果表明,所有过渡金属掺杂体系结合能均为负值,结构均稳定;其中Ti2N-Sc体系的形成能为-2.242 eV,结构更易形成,且保持稳定;掺杂后Ti2N-Sc、Ti2N-Zr体系磁矩增大;此外,Ti2N-Sc体系中保留了较高的自旋极化率,达到84.9%,可预测该体系在自旋电子学中具有潜在的应用价值。  相似文献   
8.
9.
Having shown promising performance with high flexibility and efficiency in vehicular edge computing (VEC) network, the parked vehicles (PVs) received an increasing number of attentions in recent years. However, PVs’ residual battery power restricts their running time. In addition, there is still no alternate resource pool for the PVs to cope with the emergencies in the previous VEC framework. To alleviate these problems, we model a cloud-assisted parked vehicular edge computing (PVEC) framework, in which the PVs are classified based on their residual battery power. PVs corporate with the cloud servers (CSs) for the computational resources provision. In addition, we formulate the utilities of the service provider (SP) and PVs and design a contract-based resource allocation problem for the maximization of the SP’s utility. Considering that it is intractable to solve the optimization problem directly, the primal problem is simplified and decoupled into two sub-problems. To design the optimal contracts, we solve the sub-problems by Lagrangian multiplier method and dual function. Simulation results prove that the utilities of PVs can reach to the maximum when they choose the contract corresponding to their types. In addition, the simulation results illustrate the superiority of proposed scheme over previous schemes in improving the utilities of the SP and social welfare.  相似文献   
10.
分子构象的聚类是搜索分子动力学模拟轨迹中代表构象的主要方法。 它是分析复杂构象改变或分子间相互作用机制的关键步骤. 作为一种基于密度的聚类算法,密度峰值搜索算法因其聚类的准确度而被应用于分子聚类过程中. 但随着模拟时长的增长,密度峰值搜索算法较低的计算效率限制了其应用的可能. 本文提出K-means密度峰值搜索算法的聚类算法,它是密度峰值搜索算法在计算效率方面的一个扩展版本,用于解决密度峰值搜索算法中巨大的资源消耗问题. 在K-means密度峰值搜索算法中,首先,通过高效的聚类算法(例如K-means)进行初始聚类,得到的聚类中心被定义为具有权重的典型点. 然后,对加权的典型点通过密度峰值搜索算法实现二次聚类,并细化点为核心点、边界点、加细光晕点. 在与密度峰值搜索算法具有相似的精度的同时,计算复杂度由O(n2)降至O(n). 通过二面角,二级结构,关联图描述的分子构象,将KFDP用于多个模拟轨迹的聚类过程中. 并通过与K-means聚类算法,DBSCAN聚类算法的比较结果,验证了K-means密度峰值搜索算法的优势.  相似文献   
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