Exploring the Interactions of Atomic Oxygen on Silver Clusters with Hydrogen

The interactions between Ag_nO^-(n=1-8) and H₂ (or D₂) were explored by combination of the mass spectroscopy experiments and density function theory (DFT) calculations. The experiments found that all oxygen atoms in Ag_nO^-(n=1-8) are inert in the interactions with H₂ or D₂ at the low temperature of 150 K, which is in contrast to their high reactivity with CO under the same condition. These observations are parallel with the preferential oxidation (PROX) of CO in excess hydrogen catalyzed by dispersed silver species in the condensed phase. Possible reaction paths between Ag_nO^-(n=1-8) and H₂ were explored using DFT calculations. The results indicated that adsorption of H₂ on any site of Ag_nO^-(n=1-8) is extremely weak, and oxidation of H₂ by any kind of oxygen in Ag_nO^-(n=1-8) has an apparent barrier strongly dependent on the adsorption style of the "O". These experiments and theoretical results about cluster reactions provided molecule-level insights into the activity of atomic oxygen on real silver catalysts.     

Effects of some nucleating agents on the supercooling of erythritol to be applied as phase change material

Nine nucleating agents, calcium pimelate (CaPi), bicyclic [1, 2, 2]heptane di-carboxylate (HPN-68), a commercially obtained aryl amide nucleating agent (TMB-5), calcium salt of hexahydrophthalic acid (HPN-20E), 1,3:2,4-di-p-methylbenzylidene sorbitol (MDBS) and sodium, potassium, magnesium and calcium salt of benzene-1, 3, 5-tricarboxylic acid (Na₃BTC, K₃BTC, Mg₃BTC₂ and Ca₃BTC₂, respectively), were applied to reduce the supercooling of erythritol, and their effects were investigated by cyclic differential scanning calorimetry (DSC). The results revealed that Na₃BTC and K₃BTC could not induce erythritol to crystallize under the experiment condition. MDBS could only make erythritol to crystallize at a temperature slightly higher than that of pure erythritol, and the effect was unstable. Mg₃BTC₂, Ca₃BTC₂ and HPN-68 could induce erythritol to crystallize at relatively high temperature, but the peak temperature of crystallizing (T _{p, cr}) and the phase change enthalpy of crystallizing (Δ_cr H) decreased greatly as the melting–crystallizing cycles increased. HPN-20E-doped erythritol crystallized at a high temperature with the T _{p, cr} of 69.3 °C at the first cycle, but the T _{p, cr} and Δ_cr H varied greatly during the melting–crystallizing cycles. CaPi and TMB-5 could induce erythritol to crystallize at a stable temperature with the T _{p, cr} of about 69 °C and 64 °C, respectively, and with a stable Δ_cr H of about 204 and 185 J g^?1, respectively, in all melting–crystallizing cycles. Hence, CaPi- and TMB-5-doped erythritol could be used as PCMs and applied in thermal energy storage in which the energy was absorbed at a high temperature and released at a lower but stable temperature.     

Thermal properties characterization of two promising phase change material candidates

Solar absorption cooling is a wonderful method to provide cold energy by exploiting solar energy. Phase change materials (PCMs) that store latent thermal energy are indispensible in solar absorption cooling system. It is worthwhile to find new PCMs due to the demanding on the temperature of the stored thermal energy which in turn would power the absorption chiller. In this paper, two compounds: 1-bromo-2-methoxynaphthalene (compound 1) and 2,2′-diphenyl-4,4′-bi(1,3-dioxane)-5,5′-diol (compound 2), were selected as potential PCMs. Their thermal energy storage properties and thermal stability were characterized by differential scanning calorimetry and thermogravimetric analysis. The results showed that both compounds could be applied as good PCMs in solar absorption cooling systems. Compound 1 melted at 356.82 K with the ΔH of 98.81 J g^?1, while compound 2 melted in a broad temperature range with the melting point of 466.26 K and the ΔH of 101.4 J g^?1. Both compounds exhibited good thermal stability. Furthermore, the molar specific heat capacities of these two compounds were measured by temperature-modulated differential scanning calorimetry from 198.15 K to the temperature that they started to decompose, and the thermodynamic functions of [H _T–H _298.15] and [S _T–S _298.15] were calculated based on the specific heat capacities data.     

Accurate Theoretical Study of LiS Radical and Its Singly Charged Cation and Anion in their Ground Electronic State

Potential energies of LiS(²Π), LiS^-(¹Σ⁺) and LiS⁺(³Σ^-) are calculated by using the multireference configuration interaction method including Davidson correction and the augmented correlation-consistent basis sets aug-cc-PV(X+d)Z (X=T, Q). Such obtained potential energies are subsequently extrapolated to the complete basis set limit. Both the core-valence correction and the relativistic effect are also considered. The analytical potential energy functions are then obtained by fitting such accurate energies utilizing a least-squares fitting procedure. By using such analytical potential energy functions, we obtain the accurate spectroscopic parameters, complete set of vibrational levels and classical turning points. The present results are compared well with the experimental and other theoretical work.     

Superconvergence of the direct discontinuous Galerkin method for convection‐diffusion equations

This paper is concerned with superconvergence properties of the direct discontinuous Galerkin (DDG) method for one‐dimensional linear convection‐diffusion equations. We prove, under some suitable choice of numerical fluxes and initial discretization, a 2k‐th and ‐th order superconvergence rate of the DDG approximation at nodes and Lobatto points, respectively, and a ‐th order of the derivative approximation at Gauss points, where k is the polynomial degree. Moreover, we also prove that the DDG solution is superconvergent with an order k + 2 to a particular projection of the exact solution. Numerical experiments are presented to validate the theoretical results. © 2016 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 33: 290–317, 2017     

关于上三角矩阵代数之间经典伴随交换单射

令F是一个域,且|F|n+1,m,n为整数且m,n≥3.Tn(T_m)(F)是F上所有n×n(m×m)上三角矩阵的集合.本文中,刻画了从T_n(F)到T_m(F)的保经典伴随交换的单映射,给出了映射的表达式,对相应的方阵的工作是一个新的补充,所用方法是将其化归为相应的线性保持问题.     

A Complete Solution to the Existence of ‐Cycle Frames of Type

The existence problem of a ‐cycle frame of type is now solved for any quadruple .     

The Hamilton–Waterloo Problem for ‐Factors and ‐Factors

The Hamilton–Waterloo problem asks for a 2‐factorization of (for v odd) or minus a 1‐factor (for v even) into ‐factors and ‐factors. We completely solve the Hamilton–Waterloo problem in the case of C₃‐factors and ‐factors for .     

A general extension theorem for cohomology classes on non reduced analytic subspaces

The main purpose of this paper is to generalize the celebrated L~2 extension theorem of Ohsawa and Takegoshi in several directions: The holomorphic sections to extend are taken in a possibly singular hermitian line bundle, the subvariety from which the extension is performed may be non reduced, the ambient manifold is K¨ahler and holomorphically convex, but not necessarily compact.     

钾改性氧化铝基羰基硫水解催化剂及其失活机理

天然气、油田伴生气、高炉煤气等化工生产过程中伴生COS气体,不仅会腐蚀管道和毒害催化剂,还会严重污染环境并危害人类健康。COS催化水解反应可在温和条件下高效的将COS脱除,是最具应用前景的COS脱除技术之一。碱金属元素因其具有独特的电子供体性质、表面碱性和静电吸附等特性,常被用作助催化剂以提高Al₂O₃的COS催化水解性能。近年来,以钾为助剂改性的Al₂O₃催化剂(K₂CO₃/Al₂O₃)在COS催化水解反应中得到广泛的应用,但由于负载在Al₂O₃上的K物种的组成复杂,目前研究者对K₂CO₃/Al₂O₃催化剂上COS水解机理的理解仍存在一定的困惑和争议。本论文通过湿法浸渍法合成出一系列钾盐和钠盐改性的Al₂O₃催化剂,并利用各类先进的表征技术对这些催化剂进行分析。活性测试表明,以K₂CO₃、K₂C₂O₄、NaHCO₃、Na₂CO₃和NaC₂O₄改性Al₂O₃催化剂均有助于COS的水解。其中K₂CO₃/Al₂O₃拥有最佳的COS水解性能,连续运行20 h后其COS转化率仍高于~93%,远远优于未改性的Al₂O₃ (~58%)。我们利用原位红外光谱和X射线光电子能谱探明了反应过程中催化剂的化学结构特征,阐明了H₂O分子在K₂CO₃/Al₂O₃上的水解作用机制。原位红外表明COS在K₂CO₃/Al₂O₃上的水解过程中形成了硫代碳酸氢盐中间产物。X射线光电子能谱表征证明催化剂的失活主要是因为催化剂表面积累了硫酸盐和单质硫。此外,我们还研究了水蒸气含量对COS水解性能的影响,研究发现,由于H₂O和COS分子在催化剂表面存在竞争吸附,过量的H₂O会引起催化活性的下降。上述研究表明,K₂CO₃/Al₂O₃催化剂上COS水解性能的提高主要是形成了HO-Al-O-K界面活性位。更为重要的是,所制备的催化剂都是在模拟工业工况条件下进行的,这为后续的工业应用提供了宝贵理论指导。本工作为理解助剂钾在Al₂O₃催化剂上COS水解活性的增强提供了新的见解,这为未来设计稳定高效的COS水解催化剂打开了新的发展方向。