Self-Polarization Triggered Multiple Polar Units Toward Electrochemical Reduction of CO2 to Ethanol with High Selectivity

Electrochemical conversion of CO₂ to highly valuable ethanol has been considered a intriguring strategy for carbon neutruality. However, the slow kinetics of coupling carbon-carbon (C−C) bonds, especially the low selectivity ethanol than ethylene in neutral conditions, is a significant challenge. Herein, the asymmetrical refinement structure with enhanced charge polarization is built in the vertically oriented bimetallic organic frameworks (NiCu-MOF) nanorod array with encapsulated Cu₂O (Cu₂O@MOF/CF), which can induce an intensive internal electric field to increase the C−C coupling for producing ethanol in neutral electrolyte. Particularly, when directly employed Cu₂O@MOF/CF as the self-supporting electrode, the ethanol faradaic efficiency (FE_ethanol) could reach maximum 44.3 % with an energy efficiency of 27 % at a low working-potential of −0.615 V versus the reversible hydrogen electrode (vs. RHE) using CO₂-saturated 0.5 M KHCO₃ as the electrolyte. Experimental and theoretical studies suggest that the polarization of atomically localized electric fields derived from the asymmetric electron distribution can tune the moderate adsorption of *CO to assist the C−C coupling and reduce the formation energy of H₂CCHO*-to-*OCHCH₃ for the generation of ethanol. Our research offers a reference for the design of highly active and selective electrocatalysts for reducing CO₂ to multicarbon chemicals.     

Ni,Ru掺杂CePO4纳米材料的合成与仿酶性质

通过水热方法合成了具有高比表面积的Ni, Ru掺杂CePO₄纳米粒子(NiRu-CePO₄). 结合纳米粒子的X射线衍射(XRD)、 扫描电子显微镜(SEM)、 透射电子显微镜(TEM)和X射线能谱(EDX)的表征结果发现, NiRu-CePO₄符合六方相磷酸铈, 纳米粒子长轴尺寸约为20 nm, Ni和Ru均匀分布于纳米CePO₄中; 样品的BET表面积高达178.4 m²/g, ζ电势为-18.2 mV. 以3,3',5,5'-四甲基联苯胺(TMB)作为电子供体和显色剂, 通过分光光度法监测652 nm处的吸光度值对产物浓度进行分析, 结果表明, NiRu-CePO₄催化剂在宽泛的pH范围内表现出类过氧化物酶和类氧化酶活性. 对催化后的催化剂进行表征, 发现样品形貌、 元素分散性和表面Ce的价态均未显著变化, 表明NiRu-CePO₄具有较高的稳定性.     

双金属在掺硼金刚石表面电化学共沉积-共溶出模型

采用微分脉冲阳极溶出伏安法, 研究了Ag+、Cu2+、Pb2+、Sn2+、Cd2+等多种共存金属离子在掺硼金刚石(BDD)表面双金属共沉积-共溶出电化学行为. 结果表明, 双金属在掺硼金刚石膜表面的共沉积-共溶出模型是由金属本身的析出电位, 金属之间的相互作用, 金属离子和溶液间的相互作用等多种因素决定的. 微分阳极溶出法的研究结果表明, 双金属在掺硼金刚石电极上的共沉积-共溶出过程表现出金属1溶出-金属2溶出、金属1溶出-析氢-金属2溶出、金属1溶出-金属合金溶出-金属2溶出、金属1溶出-析氢-金属2络合物形成-金属2溶出等四种模型.     

Unsymmetric bimetal(II) complexes: Synthesis, structures and catalytic behaviors toward ethylene

A series of unsymmetric bimetal(II) (Fe, Co and Ni) complexes ligated by 2-methyl-2,4-bis(6-iminopyridin-2-yl)-1H-1,5-benzodiazepines were synthesized and characterized by IR spectra and elemental analysis, while a representative nickel(II) complex (5a) was determined by single-crystal X-ray crystallography. These iron(II) complexes were found to exhibit good activities for ethylene oligomerization and polymerization in the presence of MMAO and afforded α-olefins in high selectivity, and the composition of oligomers followed the Schluz-Flory distribution. The nickel(II) complexes mainly dimerize ethylene with considerable activity. The influences of coordinative ligands and reaction parameters were fully investigated on the catalytic activity and properties of these complexes.     

Strain field and extrusion load in ECAE process of bi-metal circular cross section

In this paper the previous velocity field proposed by the authors for the prediction of strain field and deformation load of circular cross section billet in ECAE process has been extended to take into account the deformation behavior of bimetal circular billet in the same process. Accordingly, using Bezier method, as a robust method for determining the geometry of the streamlines, the strain field developed in the circular bimetal billet is calculated. Then, based on the kinematically admissible velocity and strain fields and using the upper bound theorem the ECAE load is predicted. It was found that at constant inner corner angle of ECAE die, with decreasing of outer curve corner the inhemogenity of strain distribution is decreased and the ECAE force is increased. Also, at a constant outer curve corner, by decreasing the inner corner angle, the extrusion load is increased. A good agreement was found between the predicted and experimental results.     

Sonochemical synthesis of graphitic carbon nitrides‐wrapped bimetal oxide nanoparticles hybrid materials and their electrocatalytic activity for xanthine electro-oxidation

A novel network-like magnetic nanoparticle was fabricated on a graphitic carbon nitride through a facile sonochemical route at frequency 20 kHz and power 70 W. To enhance the electrocatalytic activity of the modified materials, the graphitic carbon nitrides (g-C₃N₄) was prepared from melamine. Monitoring of xanthine concentration level in biological fluids is more important for clinical diagnosis and medical applications. As modified CuFe₂O₄/g-C₃N₄ nanocomposite exhibits better electrochemical activity towards the oxidation of xanthine with higher anodic current compared to other modified and unmodified electrode for the detection of xanthine with larger linear range (0.03–695 µM) and lower limit of detection (13.2 nM). To compare with these methods, the electrochemical techniques may be an alternative high sensitive method due to their simplicity and rapid detection time. In addition, the practical feasibility of the sensor was inspected with biological samples, reveals the acceptable recovery of the sensor in real samples.     

A practical procedure of propargylation of aldehydes

An operationally simple procedure of propargylation of aldehydes in moist solvent (distilled THF) has been developed through direct addition of propargyl bromide to aldehyde substrates mediated with low valent iron or tin. The metals were spontaneously prepared in situ employing bimetal redox strategy. Using different aldehydes as substrates (3a-k) both these metal mediated reactions took place producing homopropargyl alcohols (4a-k) in good yields in all cases and with high chemoselectivity in most of the cases (Table 1). Due to its efficacy, operational simplicity, performance in moist solvent, and being comprised of the use of inexpensive metal/metal salts, the procedure is practically viable and potentially scalable.     

In situ FT-IR study on CO2 hydrogenation over SiO2-supported PtM (M = Cr, Mo, W) complex catalysts

The in situ FT-IR spectra were used to study the CO₂ hydrogenation reaction over the SiO₂-supported heterobinuclear metal complex catalysts, PtM (M=Cr, Mo, W). The bands, which correspond to the formate species absorbed on the catalysts, were observed. During the hydrogenation reactions, the adsorbed linear and bridging CO was not observed. The experimental results suggest that for the CO₂ and CO hydrogenation reaction over the same catalysts, their catalytic active intermediate species and the reaction mechanisms should be different.     

准原位XPS和HS-LEIS研究载体对PtCu合金纳米催化剂表面组成的影响

Pt是一类高效、稳定的催化剂,但Pt资源短缺且价格昂贵,限制了其广泛商业化应用.合金化可以使Pt的用量大为减少,且往往能显著提高其催化性能,因而广泛应用于多相催化和电催化.其中PtCu合金是一类很有前景的催化剂,Cu资源丰富、价格低廉,不仅降低了成本,而且由于合金效应提高了催化剂的活性和稳定性.由于合金的粒径、形状、组成及结构是影响其催化性能的重要因素,目前研究大多关注这些特征的可控合成.然而,大多工业金属催化剂都是负载于氧化物上以提高催化性能,合金纳米粒子的形貌以及表面组成因与载体作用而发生改变,也就是所谓的载体效应.这体现在金属/氧化物界面处,能够促进金属粒子分散、改变其形貌甚至化学态、进而改变其催化性能,其中最具代表性的金属-载体强相互作用.因此,研究不同氧化物载体上合金催化剂的分散度、表面组成、化学态,特别是不同气氛的影响,对明确影响催化剂性能的关键控制因素非常重要.但是由于多相催化剂的复杂性,且表面灵敏的测试手段很少,目前相关报道还不多.近年发展起来的高灵敏度低能离子散射谱(HS-LEIS)是表面层灵敏的测试技术,可以测定最表面层的组成和含量.本文采用溶剂热共还原法成功制备了均一单相、粒径分布较窄的PtCux合金纳米颗粒,并运用浸渍法将其负载在TiO2载体上,以保证载体上纳米粒子组成的均一性.应用准原位X-射线光电子能谱(XPS)和高HS-LEIS对负载的PtCu合金纳米催化剂在不同条件处理后的表面组成和化学状态进行表征,发现催化剂的表面组成、分布、形貌和化学状态显著受到载体和处理条件的影响,同时得到负载和未负载的催化剂表面组成与体相组成关系的相图.结果表明,PtCux/TiO2催化剂在连续氧化过程中,Cu被氧化并较好在载体表面铺展,Pt-Cu合金状态被破坏,Pt可能主要形成单一金属的纳米粒子,并在界面处形成Ptδ+.在连续还原过程中,部分被还原的Cu,与Pt形成富Pt合金粒子.催化剂表面层主要是Cu,Pt很少,与体相组成有很大差别,说明载体对Cu的分散起到重要作用.     

Pd/Co双金属纳米颗粒的制备及催化制氢性能

采用聚乙烯吡咯烷酮(PVP)保护的化学共还原法制备了Pd/Co双金属纳米颗粒, 研究了PVP及还原剂(NaBH₄)的用量、金属盐浓度、金属比例等对Pd/Co双金属纳米颗粒催化NaBH₄制氢性能的影响. 透射电子显微镜(TEM)的结果表明, 所制备的Pd/Co双金属纳米颗粒的平均粒径在1.5-2.8 nm之间. Pd/Co双金属纳米颗粒(BNPs)的催化活性远高于Pd与Co单金属纳米颗粒的活性; 当Pd/Co的理论原子比为1/9时, 双金属纳米颗粒的催化活性最高可达15570 mol·mol^-1·h^-1 (文中纳米颗粒的催化活性均为每摩尔Pd的活性). 密度泛函理论(DFT)的计算结果表明, Pd原子与Co原子之间发生电荷转移, 使得Pd原子带负电而Co原子带正电, 荷电的Pd和Co原子进而成为催化反应的活性中心. 所制备的Pd/Co双金属纳米颗粒具有很好的催化耐久性, 即使重复使用5次后, 该催化剂仍具有较高的催化活性, 且使用后的纳米颗粒催化剂也没有出现团聚现象. 双金属纳米颗粒催化NaBH₄水解反应的活化能约为54 kJ·mol^-1.