Recent Advances of Single-atom Catalysts for Electro-catalysis

Single-atom catalysis is the “hot spot” in the field of catalysis due to the special geometries, electronic states, and their unique catalytic performance. Single-atom catalysts(SACs), isolated metal atoms dispersed on the support, show the highest atom efficiency, cutting down the potential cost in the industrial process. Consequently, this “homo-hetero” catalyst could be a promising candidate for the next-generation catalysts. The applications for the SACs are widely reported, like gas-solid reactions, organic reactions, and electro-catalysis. In this mini- review, we will focus on the recent work of SACs on electro-catalysis, including hydrogen evolution reaction(HER), oxygen reduction reaction(ORR), oxygen evolution reaction(OER), CO₂ reduction reaction(CO₂ RR), and nitrogen reduction reaction(NRR).     

Encapsulation of Palladium Carbide Subnanometric Species in Zeolite Boosts Highly Selective Semihydrogenation of Alkynes

The selective hydrogenation of alkynes to alkenes is a crucial step in the synthesis of fine chemicals. However, the widely utilized palladium (Pd)-based catalysts often suffer from poor selectivity. In this work, we demonstrate a carbonization-reduction method to create palladium carbide subnanometric species within pure silicate MFI zeolite. The carbon species can modify the electronic and steric characteristics of Pd species by forming the predominant Pd−C₄ structure and, meanwhile, facilitate the desorption of alkenes by forming the Si−O−C structure with zeolite framework, as validated by the state-of-the-art characterizations and theoretical calculations. The developed catalyst shows superior performance in the selective hydrogenation of alkynes over mild conditions (298 K, 2 bar H₂), with 99 % selectivity to styrene at a complete conversion of phenylacetylene. In contrast, the zeolite-encapsulated carbon-free Pd catalyst and the commercial Lindlar catalyst show only 15 % and 14 % selectivity to styrene, respectively, under identical reaction conditions. The zeolite-confined Pd-carbide subnanoclusters promise their superior properties in semihydrogenation of alkynes.     

关于Cahn-Ingold-Prelog 顺序规则的讨论

简述了使用Cahn-Ingold-Prelog顺序规则时学生易出的错误,Cahn-Ingold-Prelog顺序规则的修改补充规定及Cahn-Ingold-Prelog顺序规则的不足之处,提出了用氧化数法弥补这一不足的新方法。     

含环氧侧基酚酞聚芳醚酮的合成及其自固化

由3,3′-双(4-羟基苯基)苯并吡咯酮(HPP)和4,4′-二氟二苯酮经亲核缩聚合成聚芳醚酮(PEK-H),再经与环氧氯丙烷(ECH)的亲核取代反应,制得了一种含量可控的环氧侧基酚酞聚芳醚酮(PEK-HE)。 改变ECH的投料量,可调控环氧侧基在聚合物中的含量。 采用FTIR、1H NMR和TGA等技术对聚合物进行了结构表征与性能测试,并考察了经自固化后聚合物涂膜的性能。 涂膜热稳定性较固化前明显提高,5%热失重温度均在450 ℃以上。 涂膜具有优异的热性能和机械性能：耐温(350±20) ℃;冲击强度高于100 kg·cm。     

基于HI-13串列加速器的中子俘获反应截面测量方法

利用BaF₂晶体对γ射线探测效率高、时间分辨率好的特点,研制了国内首套由40个BaF₂探测器单元组成的γ全吸收型探测装置,用于在线测量中子俘获反应截面。在HI-13串列加速器上建立250～850 keV的中子源,其0°角的源强约为5.09×10⁶ n/（Sr·s）,使用γ全吸收型探测装置,通过瞬发γ射线法测量了⁹³Nb、¹⁹⁷Au、^natC和空样品的实验数据。根据BaF₂探测器信号的特征,采用了基线补偿、软件阈值设置、时间窗限定、脉冲幅度积分增长率设置和快慢成分比设置等多种数字化波形分析方法,剔除噪声信号以提高效应本底比。以¹⁹⁷Au样品数据为标准,^natC样品数据为样品相关性本底,空样品数据为样品无关性本底,采用相对测量法得到了⁹³Nb的中子俘获反应截面实验数据。通过与ENDF评价库数据的比较,验证了测量装置和技术方法的可行性。     

Quality factor enhancement of plasmonic surface lattice resonance by using asymmetric periods

We report that using asymmetric lattice periods can enhance the quality factor of plasmonic surface lattice resonances(SLRs)in two-dimensional array of metal-insulator-metal nanopillars in asymmetric dielectric environment.Simulation results show that by adopting appropriate asymmetric lattice periods,the SLR quality factor can be enhanced by 24%compared with the scenario of symmetric periods.We find that the SLR quality factor is optimized when the resonance wavelength is closest to the Rayleigh cutoff wavelength.We also find that the SLRs effect is polarization sensitive in the proposed structure.We expect this work will advance the engineering of SLRs especially in asymmetric dielectric environments,and will promote their applications in sensing.     

关于型III对称空间的热核构造

引进了第III类典型域上的内切超圆坐标;计算出了矩阵极坐标下相应于不变度量的体积元素;利用积分变换构造出了不变度量的Laplace-Beltrami算子的热核.     

Regulating the Synergistic Effect in Bimetallic Two-Dimensional Polymer Oxygen Evolution Reaction Catalysts by Adjusting the Coupling Strength Between Metal Centers

Bimetallic electrocatalysts with its superior performance has a broad application prospect in oxygen evolution reaction (OER), but the fundamental understanding of the mechanism of synergistic effect is still limited since there lacks a practical way to decouple the influence factors on the intrinsic activity of active sites from others. Herein, a series of bimetallic Co−Ni two-dimensional polymer (2DP) model OER catalysts with well-defined architecture, monolayer characteristic, were designed and synthesized to explore the influence of the coupling strength between metal centers on OER performance. The coupling strength was regulated by adjusting the spacing between metal centers or the conjugation degree of bridge skeleton. Among the examined 2DPs, CoTAPP-Ni-MF-2DP, which has the strongest coupling strength between metal centers exhibited the best OER performance. These model systems can help to explore the precise structure-performance relationships, which is important for the rational catalyst design at the atomic/molecular levels.     

Gamma全吸收型BaF2探测装置中子屏蔽体与吸收体的研究

中国原子能科学研究院已经建造完成了我国第一套全吸收型BaF₂探测装置,采用瞬发γ测量法,精确测量中子俘获反应截面。中子源是利用HI-13串列加速器产生的脉冲化质子束,通过7Li(p, n)7Be反应建立。为了有效降低周围环境材料和探测器产生的散射中子本底,约束中子束流的形状,使用MCNP程序模拟设计了屏蔽体,采用含硼聚乙烯(B₄C质量分数为5%)包裹5 cm铅的方案,以及准直器采用平行孔的方案。该设计使样品处的中子束斑平整均匀,直径约为2 cm,束斑外的中子注量降低5个数量级,γ注量降低3个数量级。同时设计了中子吸收体(外半径为10 cm,厚度为7 cm)用于吸收待测样品产生的散射中子。MCNP和GEANT4程序的模拟结果表明:选择含硼聚乙烯(10B₄C质量分数为10%)作为中子吸收体的加工材料,其中子吸收率达到了80%,并设置1 MeV的能量加和阈,能够满足在线测量中子俘获反应截面的实验要求。     

A series of furan‐aromatic polyesters synthesized via direct esterification method based on renewable resources

A series of furan‐aromatic polyesters were successfully synthesized via direct esterification method starting from 2,5‐furandicarboxylic acid, ethylene glycol, 1,3‐propanediol, 1,4‐butanediol, 1,6‐hexanediol, and 1,8‐octanediol and characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (¹H NMR), X‐ray diffraction (XRD), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), tensile tests, and so on. The preliminary evidence clearly showed that direct esterification method was rewarding and worthy to synthesize these furan‐aromatic polyesters. The densities of furan‐aromatic polyesters were ranging from 1.19 to 1.38 kg/m³. The FTIR and ¹H NMR confirmed their expected structures in detail. The results of XRD showed that these furan‐aromatic polyesters were crystalline polyesters. The results of DSC, TGA, DMA, and tensile tests showed that they behaved as thermoplastic polyester, had satisfactory thermal and mechanical properties, and their thermal stabilities were quite similar to that of corresponding benzene‐aromatic polyesters. The results of contact angle measurement showed that they were hydrophilic. The properties above showed that furan‐aromatic polyesters based on renewable resources could be a viable alternative to their successful petrochemical benzene‐aromatic counterpart. Furthermore, they could be used as biopolymer materials according their satisfactory thermal and mechanical properties and hydrophilicity in the future. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012