Diffusion process in enzyme–metal hybrid catalysts

Enzyme–metal hybrid catalysts bridge the gap between enzymatic and heterogeneous catalysis, which is significant for expanding biocatalysis to a broader scope. Previous studies have demonstrated that the enzyme–metal hybrid catalysts exhibited considerably higher catalytic efficiency in cascade reactions, compared with that of the combination of separated enzyme and metal catalysts. However, the precise mechanism of this phenomenon remains unclear. Here, we investigated the diffusion process in enzyme–metal hybrid catalysts using Pd/lipase-Pluronic conjugates and the combination of immobilized lipase (Novozyme 435) and Pd/C as models. With reference to experimental data in previous studies, the Weisz–Prater parameter and efficiency factor of internal diffusion were calculated to evaluate the internal diffusion limitations in these catalysts. Thereafter, a kinetic model was developed and fitted to describe the proximity effect in hybrid catalysts. Results indicated that the enhanced catalytic efficiency of hybrid catalysts may arise from the decreased internal diffusion limitation, size effect of Pd clusters and proximity of the enzyme and metal active sites, which provides a theoretical foundation for the rational design of enzyme–metal hybrid catalysts.     

Nickel-based metal−organic framework-derived whisker-shaped nickel phyllosilicate toward efficiently enhanced mechanical,flammable and tribological properties of epoxy nanocomposites

Metal−organic framework-derived materials have attracted significant attention in the applications of functional materials. In this work, the rod-like nickel-based metal−organic frameworks were first synthesized and subsequently employed as the hard templates and nickel sources to prepare the whisker-shaped nickel phyllosilicate using a facile hydrothermal technology. Then, the nickel phyllosilicate whiskers were evaluated to enhance the mechanical, thermal, flammable, and tribological properties of epoxy resin. The results show that adequate nickel phyllosilicate whiskers can disperse well in the matrix, improving the tensile strength and elastic modulus by 13.6% and 56.4%, respectively. Although the addition of nickel phyllosilicate whiskers could not obtain any UL-94 ratings, it enhanced the difficulty in burning the resulted epoxy resin nanocomposites and considerably enhanced thermal stabilities. Additionally, it was demonstrated that such nickel phyllosilicate whiskers preferred to improve the wear resistance instead of the antifriction feature. Moreover, the wear rate of epoxy resin nanocomposites was reduced significantly by 80% for pure epoxy resin by adding 1 phr whiskers. The as-prepared nickel phyllosilicate whiskers proved to be promising reinforcements in preparing of high-performance epoxy resin nanocomposites.     

A density functional theory study of methane activation on MgO supported Ni9M1 cluster: role of M on C–H activation

Methane activation is a pivotal step in the application of natural gas converting into high-value added chemicals via methane steam/dry reforming reactions. Ni element was found to be the most widely used catalyst. In present work, methane activation on MgO supported Ni–M (M = Fe, Co, Cu, Pd, Pt) cluster was explored through detailed density functional theory calculations, compared to pure Ni cluster. CH₄ adsorption on Cu promoted Ni cluster requires overcoming an energy of 0.07 eV, indicating that it is slightly endothermic and unfavored to occur, while the adsorption energies of other promoters M (M = Fe, Co, Pd and Pt) are all higher than that of pure Ni cluster. The role of M on the first C–H bond cleavage of CH₄ was investigated. Doping elements of the same period in Ni cluster, such as Fe, Co and Cu, for C–H bond activation follows the trend of the decrease of metal atom radius. As a result, Ni–Fe shows the best ability for C–H bond cleavage. In addition, doping the elements of the same family, like Pd and Pt, for CH₄ activation is according to the increase of metal atom radius. Consequently, C–H bond activation demands a lower energy barrier on Ni–Pt cluster. To illustrate the adsorptive dissociation behaviors of CH₄ at different Ni–M clusters, the Mulliken atomic charge was analyzed. In general, the electron gain of CH₄ binding at different Ni–M clusters follows the sequence of Ni–Cu (–0.02 e) < Ni (–0.04 e) < Ni–Pd (–0.08 e) < Ni–Pt (–0.09 e) < Ni–Co (–0.10 e) < Ni–Fe (–0.12 e), and the binding strength between catalysts and CH ₄ raises with the CH₄ electron gain increasing. This work provides insights into understanding the role of promoter metal M on thermal-catalytic activation of CH₄ over Ni/MgO catalysts, and is useful to interpret the reaction at an atomic scale.     

Carbon-coated Ni-Co alloy catalysts: preparation and performance for in-situ aqueous phase hydrodeoxygenation of methyl palmitate to hydrocarbons using methanol as the hydrogen donor

Carbon-coated Ni, Co and Ni-Co alloy catalysts were prepared by the carbonization of the metal doped resorcinol-formaldehyde resins synthesized by the one-pot extended Stöber method. It was found that the introduction of Co remarkably reduced the carbon microsphere size. The metallic Ni, Co, and Ni-Co alloy particles (mainly 10–12 nm) were uniformly distributed in carbon microspheres. A charge transfer from Ni to Co appeared in the Ni-Co alloy. Compared with those of metallic Ni and Co, the d-band center of the Ni-Co alloy shifted away from and toward the Fermi level, respectively. In the in-situ aqueous phase hydrodeoxygenation of methyl palmitate with methanol as the hydrogen donor at 330 °C, the decarbonylation/decarboxylation pathway dominated on all catalysts. The Ni-Co@C catalysts gave higher activity than the Ni@C and Co@C catalysts, and the yields of n-pentadecane and n-C₆–n-C₁₆ reached 71.6% and 92.6%, respectively. The excellent performance of Ni-Co@C is attributed to the electronic interactions between Ni and Co and the small carbon microspheres. Due to the confinement effect of carbon, the metal particles showed high resistance to sintering under harsh hydrothermal conditions. Catalyst deactivation is due to the carbonaceous deposition, and the regeneration with CO₂ recovered the catalyst reactivity.     

A ternary mechanism for the facilitated transfer of metal ions onto metal–organic frameworks: implications for the ‘‘versatility’’ of these materials as solid sorbents

Although metal–organic frameworks offer a new platform for developing versatile sorption materials, yet coordinating the functionality, structure and component of these materials remains a great challenge. It depends on a comprehensive knowledge of a “real sorption mechanism”. Herein, a ternary mechanism for U(VI) uptake in metal–organic frameworks was reported. Analogous MIL-100s (Al, Fe, Cr) were prepared and studied for their ability to sequestrate U(VI) from aqueous solutions. As a result, MIL-100(Al) performed the best among the tested materials, and MIL-100(Cr) performed the worst. The nuclear magnetic resonance technique combined with energy-dispersive X-ray spectroscopy and zeta potential measurement reveal that U(VI) uptake in the three metal–organic frameworks involves different mechanisms. Specifically, hydrated uranyl ions form outer-sphere complexes in the surface of MIL-100s (Al, Fe) by exchanging with hydrogen ions of terminal hydroxyl groups (Al-OH₂, Fe-OH₂), and/or, hydrated uranyl ions are bound directly to Al(III) center in MIL-100(Al) through a strong inner-sphere coordination. For MIL-100(Cr), however, the U(VI) uptake is attributed to electrostatic attraction. Besides, the sorption mechanism is also pH and ionic strength dependent. The present study suggests that changing metal center of metal–organic frameworks and sorption conditions alters sorption mechanism, which helps to construct effective metal–organic frameworks-based sorbents for water purification.     

双层桥面大跨钢管拱面内极限承载力分析

通过建立空间复合梁单元,将钢管拱根据不同的材料划分为纵向的纤维,每根纤维在纵向分段,纵向的分段通过取若干积分点来实现,采用这样的方法可以更加全面地追踪结构极限承载力的发展过程,并把这种方法用于分析大跨径钢管混凝土拱桥,取得了较好的效果。     

由昆明理工大学白龙校区评析校园户外空间

从“以人为本”的角度通过实例分析和问卷调查对昆明理工大学白龙校区的户外空间做了深入的评析，探讨高校户外开放空间对大学生交流的促进作用，寻求适合高校户外开放空间的设计方法。     

探析节点对城市空间秩序的规范性

城市作为人类社会的外化产物,其空间内或显性或隐性地存在着秩序.节点是城市空间的重要组成要素之一,节点根据功能关系形成不同的结构,通过场力的作用规范城市空间.在规划设计中,可通过建构节点来达到规范城市空间秩序的目的.     

智能空间——智能建筑的延伸

智能建筑在全球范围广泛兴起,其主要实现形式是集成现有的各种智能化子系统。普适计算的发展推动信息技术革命,同时也给建筑带来深刻变化,智能空间就是普适计算与建筑结合的产物,其特点包括空间的伸缩性、信息技术的广泛应用、信息空间与物理空间的融合,同时也是智能建筑的延伸(从静态到动态的延伸、从有形到无形的延伸、从被动到主动的延伸)。