Direct Conversion of Syngas into Methyl Acetate,Ethanol, and Ethylene by Relay Catalysis via the Intermediate Dimethyl Ether

Selective conversion of syngas (CO/H₂) into C₂₊ oxygenates is a highly attractive but challenging target. Herein, we report the direct conversion of syngas into methyl acetate (MA) by relay catalysis. MA can be formed at a lower temperature (ca. 473 K) using Cu‐Zn‐Al oxide/H‐ZSM‐5 and zeolite mordenite (H‐MOR) catalysts separated by quartz wool (denoted as Cu‐Zn‐Al/H‐ZSM‐5|H‐MOR) and also at higher temperatures (603–643 K) without significant deactivation using spinel‐structured ZnAl₂O₄|H‐MOR. The selectivity of MA and acetic acid (AA) reaches 87 % at a CO conversion of 11 % at 643 K. Dimethyl ether (DME) is the key intermediate and the carbonylation of DME results in MA with high selectivity. We found that the relay catalysis using ZnAl₂O₄|H‐MOR|ZnAl₂O₄ gives ethanol as the major product, while ethylene is formed with a layer‐by‐layer ZnAl₂O₄|H‐MOR|ZnAl₂O₄|H‐MOR combination. Close proximity between ZnAl₂O₄ and H‐MOR increases ethylene selectivity to 65 %.     

Reductive hydrothermal synthesis of La(OH)<Subscript>3</Subscript>:Tb<Superscript>3+</Superscript> nanorods as a new green emitting phosphor

A reductive hydrothermal process with use of hydrazine hydrate as a protecting agent is proposed to synthesize La(OH)₃:Tb³⁺ (Tb mol% = 0, 1, 5, 10, and 20) nanorods. The oxidation of Tb³⁺−Tb⁴⁺ was effectively prevented in the presence of hydrazine hydrate; hence the La(OH)₃:Tb³⁺ nanorods exhibited much stronger green photoluminescence than the product prepared by the normal hydrothermal process. X-ray diffraction and transmission electron microscopy were employed to characterize the products, the results of which revealed that all the products were one-dimensional rod-like nanostructures of hexagonal structure (∼20 nm in diameter). The reductive hydrothermal process is desirable for the synthesis of other efficient Tb³⁺ doped nanophosphers.     

对称正则长波方程的拟紧致守恒差分逼近

该文对称正则长波方程的初边值问题进行了数值研究, 提出了一个两层隐式拟紧差分格式,格式很好地模拟了初值问题的守恒性质. 得到了差分解的存在唯一性, 并在先验估计基础上运用能量方法分析了格式的稳定性及二阶收敛性.     

Two-dimensional multi-channel acousto-optic diffraction

In this paper, we have investigated the interaction between acoustic waves generated by an incident light beam propagating through two-dimensional transducers. A set of coupled mode equations for two-dimensional multi-channel acousto-optic inter-modulation are derived, and the solutions are obtained. A new type of two-dimensional multi-channel Bragg acousto-optic modulator is designed by analyzing two-dimensional multi-channel acousto-optic inter-modulation based on the coupled mode theory, and its performance has also been experimentally characterized. The experimental results are in accordance with our theoretical analysis.     

Vector dissipative solitons in graphene mode locked fiber lasers

Vector soliton operation of erbium-doped fiber lasers mode locked with atomic layer graphene was experimentally investigated. Either the polarization rotation or polarization locked vector dissipative solitons were experimentally obtained in a dispersion-managed cavity fiber laser with large net cavity dispersion, while in the anomalous dispersion cavity fiber laser, the phase locked nonlinear Schrödinger equation (NLSE) solitons and induced NLSE soliton were experimentally observed. The vector soliton operation of the fiber lasers unambiguously confirms the polarization insensitive saturable absorption of the atomic layer graphene when the light is incident perpendicular to its 2-dimentional (2D) atomic layer.     

带补偿C^0非协调板元的多重网格法

本文考虑重调和方程的Ｃ０非协调元逼近．通过双线性型ｃｋ（ｕ，ｖ）引入的补偿和将多重网格法应用到Ｃ０非协调板元，给出了更精确的逼近．     

A study of mechanical properties of pure and nitrogen-doped ultrananocrystalline diamond films under various loading conditions

To better understand the mechanical responses of ultrananocrystalline diamond (UNCD) under various loading conditions, a numerical study is performed to investigate the size, loading rate and temperature effects on the material properties of pure and nitrogen-doped UNCD films. Since the UNCD growth mechanism is not completely understood yet, a simple procedure by combining kinetic Monte Carlo and molecular dynamics (MD) methods is developed to form a polycrystalline UNCD block with an artificial grain boundary (GB). By randomly inserting different numbers of nitrogen (N) atoms into the GB of the resulting polycrystalline UNCD films, N-doped UNCD films can be formed. The responses of the simulated pure and N-doped UNCD films with various grain sizes are then investigated by applying displacement-controlled tensile loading under different rates and temperatures in the MD simulations. The simulation results presented in this paper provide a better understanding of the combined size, rate and thermal effects on the material responses of pure and N-doped UNCD films.     

Convergence of iterates with errors of semicontractive mappings

In this paper, we are concerned with the study of an iterative scheme with errors involving two hemicontractive mappings. We approximate the common fixed points of these two mappings by weak and strong convergence of the iteration process in Hilbert space.     

铁氧化物催化类Fenton反应

高级氧化技术是当今水处理技术领域研究的热点,Fenton试剂因操作简单、反应条件温和及氧化效率高等优势而备受关注。铁氧化物催化类Fenton反应能有效地解决催化剂回收利用难等问题,并且能够在较为广泛的pH范围内使用,从而成为Fenton氧化领域一个新的研究方向,但反应过程和机制往往更为复杂。本文评述了铁氧化物催化类Fenton反应中可能存在的多种机理,主要是羟基自由基理论、氧空位机理和高价态铁络合物机制。类Fenton反应速率的限速步骤是Fe(Ⅲ)/Fe(Ⅱ)循环过程,从提高反应速率的机理出发,本文探讨了类Fenton反应中铁氧化物催化剂的制备和发展,催化剂中多种价态的铁元素,通过相互间发生电子转移以加速Fe(Ⅱ)的再生,提高反应效率。铁氧化物掺杂过渡金属能显著提高催化H2O2有效分解的活性。阐明了多金属掺杂铁氧化物中多金属组分的催化机制和铁氧化物结构形态对反应性能的影响。研究表明催化剂中铁的结构形态、催化剂比表面积、催化剂与H2O2之间电子转移速率等都是决定催化剂性能的重要因素。最后讨论了继续研究方向,为开展非均相类Fenton反应提供参考。