Synthesis of NiO Crystals Exposing Stable High‐Index Facets

Metal oxides exposing high‐index facets are potentially impactful in catalysis and adsorption processes owing to under‐coordinated ions and polarities that alter their interfacial properties compared to low‐index facets. Here, we report molten‐salt syntheses of NiO particles exposing a variety of crystal facets. We show that for a given anion (nitrate or chloride), the alkali cation has a notable impact on the formation of crystals exposing {311}, {611}, {100}, and {111} faces. Based on a parametric analysis of synthesis conditions, we postulate that the crystallization mechanism is governed by the formation of growth units consisting of Ni^II complexes whose coordination numbers are determined by temperature and the selection of anion (associated to the coordination sphere) and alkali cation (associated with the outer coordination sphere). Notably, our findings reveal that high‐index facets are particularly favored in chloride media and are stable under prolonged periods of catalysis and steaming.     

Amine-assisted synthesis of concave polyhedral platinum nanocrystals having {411} high-index facets

High-index surfaces of a face-centered cubic metal (e.g., Pd, Pt) have a high density of low-coordinated surface atoms and therefore possess enhanced catalysis activity in comparison with low-index faces. However, because of their high surface energy, the challenge of chemically preparing metal nanocrystals having high-index facets remains. We demonstrate in this work that introducing amines as the surface controller allows concave Pt nanocrystals having {411} high-index facets to be prepared through a facile wet-chemical route. The as-prepared Pt nanocrystals display a unique octapod morphology with {411} facets. The presence of high-index {411} exposed facets endows the concave Pt nanocrystals with excellent electrocatalytic activity in the oxidation of both formic acid and ethanol.     

Electroreduction of CO2 on Au(310)@Cu High-index Facets

The chemical selectivity and faradaic efficiency of high-index Cu facets for the CO₂ reduction reaction (CO₂RR) is investigated. More specifically, shape-controlled nanoparticles enclosed by Cu {hk0} facets are fabricated using Cu multilayer deposition at three distinct layer thicknesses on the surface facets of Au truncated ditetragonal nanoprisms (Au DTPs). Au DTPs are shapes enclosed by 12 high-index {310} facets. Facet angle analysis confirms DTP geometry. Elemental mapping analysis shows Cu surface layers are uniformly distributed on the Au {310} facets of the DTPs. The 7 nm Au@Cu DTPs high-index {hk0} facets exhibit a CH₄ : CO product ratio of almost 10 : 1 compared to a 1 : 1 ratio for the reference 7 nm Au@Cu nanoparticles (NPs). Operando Fourier transform infrared spectroscopy spectra disclose reactive adsorbed *CO as the main intermediate, whereas CO stripping experiments reveal the high-index facets enhance the *CO formation followed by rapid desorption or hydrogenation.     

Structure of concentrated aqueous solutions of scandium chloride

It is shown via X-ray diffraction that aqueous solutions of scandium chloride form ionic associates in a wide range of concentrations. It is established that the Sc³⁺ ion coordination number increases upon dilution to 8.2 at an unchanged Sc³⁺–OH² distance of 0.215 nm. The second coordination sphere of the cation forms at an average distance of 0.420 nm. The number of solvent molecules in the sphere logically increases during dilution. It is concluded that the anion does not form its own sphere in highly concentrated solutions. This coordination sphere begins to form only in solutions with moderate concentrations at a distance of 0.315 nm, and it contains six water molecules in diluted solutions.     

Synthesis of nanocrystals with variable high-index Pd facets through the controlled heteroepitaxial growth of trisoctahedral Au templates

The shape-controlled synthesis of noble metal nanocrystals (NCs) bounded by high-index facets is a current research interest because the products have the potential of significantly improving the catalytic performance of NCs in industrially important reactions. This study reports a versatile method for synthesizing polyhedral NCs enclosed by a variety of high-index Pd facets. The method is based on the heteroepitaxial growth of Pd layers on concave trisoctahedral (TOH) gold NC seeds under careful control of the growth kinetics. Polyhedral Au@Pd NCs with three different classes of high-index facets, including concave TOH NCs with {hhl} facets, concave hexoctahedral (HOH) NCs with {hkl} facets, and tetrahexahedral (THH) NCs with {hk0} facets, can be formed in high yield. The Miller indices of NCs are also modifiable, and we have used the THH NCs as a demonstrative example. The catalytic activities of these NCs were evaluated by the structure-sensitive reaction of formic acid electro-oxidation. The results showed that the high-index facets are generally more active than the low-index facets. In summary, a seeded growth process based on concave high-index faceted monometallic TOH NC templates and careful control of the growth kinetics is a simple and effective strategy for the synthesis of noble metal NCs with high-index facets. It also offers tailorability of the surface structure in shape-controlled synthesis.     

A 3D AgCl Hierarchical Superstructure Synthesized by a Wet Chemical Oxidation Method

A novel 3D AgCl hierarchical superstructure, with fast growth along the 〈111〉 directions of cubic seeds, is synthesized by using a wet chemical oxidation method. The morphological structures and the growth process are investigated by scanning electron microscopy and X‐ray diffraction. The crystal structures are analyzed by their crystallographic orientations. The surface energy of AgCl facets {100}, {110}, and {111} with absorbance of Cl^? ions is studied by density functional theory calculations. Based on the experimental and computational results, a plausible mechanism is proposed to illustrate the formation of the 3D AgCl hierarchical superstructures. With more active sites, the photocatalytic activity of the 3D AgCl hierarchical superstructures is better than those of concave and cubic ones in oxygen evolution under irradiation by visible light.     

Formation of paramagnetic intermediates under the conditions of Brookhart-type catalyst activation and operation

The formation of two types of paramagnetic species in the catalytic system NiBr₂(DAB)/ MAO under real catalytic conditions was found. These are Ni^II are Ni^I complexes with the diimine ligand and complexes with the radical anion ligand in the coordination sphere. Under catalysis conditions, these forms are in equilibrium with each other, the equilibrium being shifted towards the radical anion form upon substrate addition.     

高指数晶面纳米催化剂的电化学制备及应用

催化剂的性能与其表面结构及组成密切相关,高指数晶面纳米晶的表面含有高密度的台阶原子等活性位点而表现出较高的催化活性. 本文综述了电化学方波电位方法用于Pt、Pd、Rh等贵金属高指数晶面结构纳米晶催化剂的制备、形成机理及其电催化性能的研究. 针对贵金属利用率问题,还着重介绍了具有较高质量活性的小粒径Pt二十四面体的制备. 在此基础上,还介绍了电化学方波电位方法用于低共熔溶剂中制备高指数晶面纳米晶,以及高指数晶面纳米催化剂的表面修饰及应用;最后对高指数晶面纳米催化剂的发展做出了展望.     

Enhancing Effects of Salt Formation on Catalytic Activity and Enantioselectivity for Asymmetric Hydrogenation of Isoquinolinium Salts by Dinuclear Halide‐Bridged Iridium Complexes Bearing Chiral Diphosphine Ligands

Asymmetric hydrogenation of 1‐ and 3‐substituted and 1,3‐disubstituted isoquinolinium chlorides using triply halide‐bridged dinuclear iridium complexes [{Ir(H)(diphosphine)}₂(μ‐Cl)₃]Cl has been achieved by the strategy of HCl salt formation of isoquinolines to afford the corresponding chiral 1,2,3,4‐tetrahydroisoquinolines (THIQs) in high yields and with excellent enantioselectivities after simple basic work‐up. The effects of salt formation have been investigated by time‐course experiments, which revealed that the generation of isoquinolinium chlorides clearly prevented formation of the catalytically inactive dinuclear trihydride complex, which was readily generated in the catalytic reduction of salt‐free isoquinoline substrates. Based on mechanistic investigations, including by ¹H and ³¹P{¹H} NMR studies and the isolation and characterization of several intermediates, the function of the chloride anion of the isoquinolinium chlorides has been elucidated, allowing us to propose a new outer‐sphere mechanism involving coordination of the chloride anion of the substrates to an iridium dihydride species along with a hydrogen bond between the chloride ligand and the N‐H proton of the substrate salt.     

从头开始理解形貌依赖的CuOx-CeO2相互作用

CuOx/CeO2催化剂在CO氧化反应中表现出高催化活性和显著结构敏感性.文献报道中CuOx/CeO2催化剂体系的合成条件差异较大,从而导致观察到的CuOx-CeO2相互作用存在较大争议.因此,系统研究并阐明CuOx/CeO2催化剂中CuOx-CeO2相互作用对于理解复杂的CuOx-CeO2界面催化作用具有重要的研究意义.近期发现,氧化物纳米晶的形貌可作为一种新的结构参数,在不改变氧化物催化剂组成的条件下实现其结构和性能的调控.本文以不同形貌CeO2纳米晶为载体,包括优先暴露{110}+{100}晶面的CeO2纳米棒、优先暴露{100}晶面的CeO2纳米立方体和优先暴露{111}晶面的CeO2纳米多面体,采用等体积浸渍方法合成了Cu担载量为0.025%~5%的CuOx/CeO2纳米晶催化剂,结合谱学和电镜表征方法,以及CO吸附原位红外光谱,系统研究了CuOx物种在不同形貌CeO2纳米晶上的结构演化及其催化CO氧化的构-效关系.结构表征结果表明, CuOx物种结构不仅依赖于Cu的担载量,也依赖于载体CeO2的形貌.随着Cu担载量的增加, CuOx物种优先沉积在CeO2的表面缺陷位,然后聚集和长大;同时伴随着CuOx物种从孤立Cu离子到与载体强/弱相互作用的CuOx团簇,高分散Cu O颗粒和大尺寸Cu O颗粒.孤立Cu^+离子和与载体弱相互作用CuOx团簇主要形成于CeO2纳米立方体的表面,这可能与CeO2纳米立方体暴露的氧终止CeO2{100}晶面相关.CO吸附原位红外结果表明, CuOx团簇与不同CeO2表面相互作用的强度顺序为:CeO2纳米棒暴露的{110}面>CeO2纳米多面体暴露的{111}面>CeO2纳米立方体暴露的{100}面.CeO2纳米立方体与Cu2+离子间相互作用弱于与Cu^+之间的,因此CeO2纳米立方体负载的CuOx物种在CO还原过程中容易停留在稳定的Cu^+中间物种;而CeO2纳米棒与Cu2+离子之间的相互作用强于与Cu^+之间的相互作用,因此CeO2纳米棒负载的CuOx物种在CO还原过程中容易形成金属铜.因此CO吸附原位红外光谱观察到CeO2纳米立方体负载CuOx催化剂中吸附在Cu^+的CO物种远远多于CeO2纳米棒负载CuOx催化剂.CO氧化反应结果表明, CuOx/CeO2催化剂表现出同时依赖于CuOx物种结构和CeO2形貌的结构敏感性.CuOx/CeO2催化剂活性表现出与CuOx/CeO2催化剂的CO还原性能的正相关性,说明中CuOx/CeO2催化CO氧化反应遵循Mv K反应机理.这些结果系统地关联了CeO2形貌, CuOx-CeO2相互作用, CuOx物种结构和CeO2还原性能, CuOx/CeO2催化CO氧化反应活性.     

The Effects of Exposed Specific Facets and Sulfation on the Surface Acidity of Cu2O Solids

Cuprous oxide microcrystals with {111}, {111}/{100}, and {100} exposed facets were synthesized. ³¹P MAS NMR using trimethylphosphine as the probe molecule was employed to study the acidic properties of samples. It was found that the total acidic density of samples increases evidently after sulfation compared with the pristine cuprous oxide microcrystals. During sulfation, new {100} facets are formed at the expense of {111} facets and lead to the generation of two Lewis acid sites due to the different binding states of SO₄²⁻ on {111} and {100} facets. Moreover, DFT calculation was used to illustrate the binding models of SO₄²⁻ on {111} and {100} facets. Also, a Pechmann condensation reaction was applied to study the acidic catalytic activity of these samples. It was found that the sulfated {111} facet has better activity due to its higher Lewis acid density compared with the sulfated {100} facet.     

X-ray structure of a novel histidine-copper(II) complex

A new crystal structure of the dichloro(L-histidine)copper(II) half-hydrate is reported. In this complex, histidine acts as a bidentate ligand to the copper(II) cation. The coordination sphere of the copper cation is created by the carboxyl oxygen and the amine nitrogen from main chain group of histidine. Two additional chloride anions complete the square coordination of the central Cu⁺² cation. In the crystal, the copper cations are additionally surrounded by two chloride anions from neighboring complex molecules, which are located in the distant axial position and fill up the stretched octahedral coordination sphere Cu⁺². In the presented complex, the histidine molecule exists as a zwitter ion with an unprotonated negatively charged carboxyl group and with double protonated positively charged imidazole ring. Crystallographic study was supported by IR measurements confirming the presence of water in the crystal structure.     

Nucleophilic addition of methanol and methanethiol to acetylene in the superbasic system KOH-DMSO: a quantum chemical model

Cluster-continuum models (KOH·nDMSO, n = 1, 5) were used to model the superbasic system “alkali metal hydroxide-dimethyl sulfoxide” within the framework of MP2/6-311++G**/ and B3LYP/6-31G* methods. The KOH molecule surrounded by five DMSO molecules exists as “solvate-loosened” ion pair with elongated K-O distance. It is proposed to consider the “solvate-loosened” ion pair of potassium cation with hydroxide anion in the surroundings of five solvent molecules as the catalytic coordination sphere of the superbasic system KOH-DMSO. Methanol and methanethiol molecules can be incorporated with ease into the first coordination sphere of potassium cation to form methoxide and methanethiolate ions. The possibility of nucleophilic attack of methoxide and methanethiolate ions on acetylene molecule in the first coordination sphere of potassium cation was studied. The model reaction system C₂H₂-CH₃OK-H₂O with one DMSO molecule included explicitly to maintain the “solvate-loosened” [CH₃O]^?...K⁺ ion pair and additional inclusion of solvent effects within the framework of the IEFPCM continuum model is the most preferable for serial calculations.     

Atomic‐Scale Determination of Active Facets on the MoVTeNb Oxide M1 Phase and Their Intrinsic Catalytic Activity for Ethane Oxidative Dehydrogenation

Aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) has been used to image the basal {001} plane of the catalytically relevant M1 phase in MoVTeNb complex oxides. Facets {010}, {120}, and {210} are identified as the most frequent lateral termination planes of the crystals. Combination of STEM with He ion microscopy (HIM) images, Rietveld analysis, and kinetic tests reveals that the activation of ethane is correlated to the availability of facets {001}, {120}, and {210} at the surface of M1 crystals. The lateral facets {120} and {210} expose crystalline positions related to the typical active centers described for propane oxidation. Conversely, the low activity of the facet {010} is attributed to its configuration, consisting of only stable M₆O₂₁ units connected by a single octahedron. Thus, we quantitatively demonstrated that differences in catalytic activity among M1 samples of equal chemical composition depend primarily on the morphology of the particles, which determines the predominant terminating facets.     

Controlled Synthesis and Enhanced Catalytic and Gas‐Sensing Properties of Tin Dioxide Nanoparticles with Exposed High‐Energy Facets

A morphology evolution of SnO₂ nanoparticles from low‐energy facets (i.e., {101} and {110}) to high‐energy facets (i.e., {111}) was achieved in a basic environment. In the proposed synthetic method, octahedral SnO₂ nanoparticles enclosed by high‐energy {111} facets were successfully synthesized for the first time, and tetramethylammonium hydroxide was found to be crucial for the control of exposed facets. Furthermore, our experiments demonstrated that the SnO₂ nanoparticles with exposed high‐energy facets, such as {221} or {111}, exhibited enhanced catalytic activity for the oxidation of CO and enhanced gas‐sensing properties due to their high chemical activity, which results from unsaturated coordination of surface atoms, superior to that of low‐energy facets. These results effectively demonstrate the significance of research into improving the physical and chemical properties of materials by tailoring exposed facets of nanomaterials.     

Synthesis of polyhedral iron oxide nanocrystals bound by high-index facets

High surface energy of high-index facets endows nanocrystals with high activities and thus promotes potential applications such as highly efficient catalysts,special optical,electrical and magnetic devices.But the high surface energy of the high-index facets usually drives them to grow faster than the other facets and finally disappear during the crystal growth,which leads the synthesis of nanocrystals with high-indexed facets exposed to be a great challenge.Herein,we introduced two routes to control the synthesis of-Fe2O3polyhedrons with different sets of high-index facets,one using different metal ions(Ni2+,Cu2+or Zn2+)as structure-directing agents and the other applying polymer surfactant sodium carboxymethyl cellulose(CMC)as additive.The growth process of high-index-Fe2O3polyhedrons was also discussed and possible growth mechanism was proposed.     

Crystal‐Facet Engineering of Ferric Giniite by Using Ionic‐Liquid Precursors and Their Enhanced Photocatalytic Performances under Visible‐Light Irradiation

In the work presented here, well‐dispersed ferric giniite microcrystals with controlled sizes and shapes are solvothermally synthesized from ionic‐liquid precursors by using 1‐n‐butyl‐3‐methylimidazolium dihydrogenphosphate ([Bmim][H₂PO₄]) as phosphate source. The success of this synthesis relies on the concentration and composition of the ionic‐liquid precursors. By adjusting the molar ratios of Fe(NO₃)₃ ? 9H₂O to [Bmim][H₂PO₄] as well as the composition of ionic‐liquid precursors, we obtained uniform microstructures such as bipyramids exposing {111} facets, plates exposing {001} facets, hollow spheres, tetragonal hexadecahedron exposing {441} and {111} facets, and truncated bipyamids with carved {001} facets. The crystalline structure of the ferric giniite microcrystals is disclosed by various characterization techniques. It was revealed that [Bmim][H₂PO₄] played an important role in stabilizing the {111} facets of ferric giniite crystals, leading to the different morphologies in the presence of ionic‐liquid precursors with different compositions. Furthermore, since these ferric giniite crystals were characterized by different facets, they could serve as model Fenton‐like catalysts to uncover the correlation between the surface and the catalytic performance for the photodegradation of organic dyes under visible‐light irradiation. Our measurements indicate that the photocatalytic activity of as‐prepared Fenton‐like catalysts is highly dependent on the exposed facets, and the surface area has essentially no obvious effect on the photocatalytic degradation of organic dyes in the present study. It is highly expected that these findings are useful in understanding the photocatalytic activity of Fenton‐like catalysts with different morphologies, and suggest a promising new strategy for crystal‐facet engineering of photocatalysts for wastewater treatment based on heterogeneous Fenton‐like process.     

Bis{tris[(1H‐benzimidazol‐3‐ium‐2‐yl)methyl]amine} tetraaquaocta‐μ2‐chlorido‐octachloridopentacadmate(II) monohydrate

The title compound, (C₂₄H₂₄N₇)₂[Cd₅Cl₁₆(H₂O)₄]·H₂O, contains a [Cd₅Cl₁₆(H₂O)₄]⁶⁻ anion, two triply protonated tris[(1H‐benzimidazol‐3‐ium‐2‐yl)methyl]amine cations and one solvent water molecule. The structure of the anion is a novel chloride‐bridged pentanuclear cluster. The five unique Cd^II centres have quite different coordination environments. Two of the central hexacoordinated Cd^II cations have a CdOCl₅ chromophore, in which each Cd^II cation is ligated by four bridging chloride ligands, one terminal chloride ligand and one water molecule, adopting a distorted octahedral environment. The third central Cd^II cation is octahedrally coordinated by four bridging chloride ligands and two water molecules. Finally, the two terminal Cd^II cations are pentacoordinated by two bridging and three terminal chloride ligands and adopt a trigonal–bipyramidal geometry. A three‐dimensional supramolecular network is formed through intra‐ and intermolecular O—H...O, O—H...Cl, N—H...Cl and N—H...O hydrogen bonds and π–π interactions between the cations and anions.<!?tpb=20.6pt>     

Truncated ditetragonal gold prisms as nanofacet activators of catalytic platinum

We report a facile, seed-mediated method to synthesize nanoscale gold truncated ditetragonal nanoprisms (TDPs) enclosed by 12 high-index {310} facets. The method leads to the formation of nanoparticles with high size and shape monodispersity and allows for easy surfactant removal. The dependence of particle shape on the synergetic contribution of metallic ions, halide ions, and surfactant adsorbates during synthesis is described. The resulting high-index nanoparticle facets were demonstrated as efficient activators of a supported catalytic material (platinum). A Pt monolayer deposited onto the Au TDP nanofacets with sharp electrochemical signatures exhibits an enhanced catalytic activity.     

Interactions of the ethanolamino groups of nanofilms with Co(II), Ni(II), Cu(II), Zn(II), and Cr(III) ammoniates at the surface of PVC plates

Interactions of nanofilms containing ethanolamino groups with cobalt(II), nickel(II), copper(II), and zinc(II) ammoniates at the surface of polyvinylchloride plates and with chromium(III) ammoniate in a solution of ammonium chloride were studied. It was found that the groups of the film, together with chloride ions, displace all ammonia molecules from the inner coordination sphere of the metal. The average number of the ethanolamino N atoms of the film participating in formation of the metal ion coordination sphere is 3.35, 3.47, 3.67, 3.42, and 3.37 for Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Cr³⁺ complexes, respectively. The average number of chloride ions is 2 for Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ and 3 for Cr³⁺. The coordination number of the central atoms is 6. The Cr³⁺ ion forms a coordination sphere composed of three N atoms and three chloride ions and a coordination sphere (charged 1+) made up of four N atoms and two chloride ions, with the third chloride ion being in the outer sphere. The Co²⁺, Ni²⁺, and Cu²⁺ ions form uncharged coordination spheres of two types: (1) with four N atoms and two chloride ions and (2) with three N atoms, two chloride ions, and the O atom of the ethanol hydroxyl group.