Transition‐Metal–Boron Intermetallics with Strong Interatomic d–sp Orbital Hybridization for High‐Performance Electrocatalysis

A theoretical and experimental study gives insights into the nature of the metal–boron electronic interaction in boron‐bearing intermetallics and its effects on surface hydrogen adsorption and hydrogen‐evolving catalytic activity. Strong hybridization between the d orbitals of transition metal (T_M) and the sp orbitals of boron exists in a family of fifteen T_M–boron intermatallics (T_M:B=1:1), and hydrogen atoms adsorb more weakly to the metal‐terminated intermetallic surfaces than to the corresponding pure metal surfaces. This modulation of electronic structure makes several intermetallics (e.g., PdB, RuB, ReB) prospective, efficient hydrogen‐evolving materials with catalytic activity close to Pt. A general reaction pathway towards the synthesis of such T_MB intermetallics is provided; a class of seven phase‐pure T_MB intermetallics, containing V, Nb, Ta, Cr, Mo, W, and Ru, are thus synthesized. RuB is a high‐performing, non‐platinum electrocatalyst for the hydrogen evolution reaction.     

Isolation of the Copper Redox Steps in the Standard Selective Catalytic Reduction on Cu‐SSZ‐13

Operando X‐ray absorption experiments and density functional theory (DFT) calculations are reported that elucidate the role of copper redox chemistry in the selective catalytic reduction (SCR) of NO over Cu‐exchanged SSZ‐13. Catalysts prepared to contain only isolated, exchanged Cu^II ions evidence both Cu^II and Cu^I ions under standard SCR conditions at 473 K. Reactant cutoff experiments show that NO and NH₃ together are necessary for Cu^II reduction to Cu^I. DFT calculations show that NO‐assisted NH₃ dissociation is both energetically favorable and accounts for the observed Cu^II reduction. The calculations predict in situ generation of Brønsted sites proximal to Cu^I upon reduction, which we quantify in separate titration experiments. Both NO and O₂ are necessary for oxidation of Cu^I to Cu^II, which DFT suggests to occur by a NO₂ intermediate. Reaction of Cu‐bound NO₂ with proximal NH₄⁺ completes the catalytic cycle. N₂ is produced in both reduction and oxidation half‐cycles.     

Furfural Hydrogenation on Nickel‐promoted Cu‐containing Catalysts Prepared from Hydrotalcite‐Like Precursors

The nickel‐promoted Cu‐containing catalysts (Cu_xNi_y‐MgAlO) for furfural (FFR) hydrogenation were prepared from the hydrotalcite‐like precursors, and characterized by X‐ray powder diffraction, inductively‐coupled plasma atomic emission spectroscopy, N₂ adsorption‐desorption, UV‐Vis diffuse reflectance spectra and temperature‐programmed reduction with H₂ in the present work. The obtained catalysts were observed to exhibit a better catalytic property than the corresponding Cu‐MgAlO or Ni‐MgAlO samples in FFR hydrogenation, and the CuNi‐MgAlO catalyst with the actual Cu and Ni loadings of 12.5 wt% and 4.5 wt%, respectively, could give the highest FFR conversion (93.2%) and furfuryl alcohol selectivity (89.2%). At the same time, Cu⁰ species from the reduction of Cu²⁺ ions in spinel phases were deduced to be more active for FFR hydrogenation.     

Dispersion‐Force‐Assisted Disproportionation: A Stable Two‐Coordinate Copper(II) Complex

The synthesis of the first linear coordinated Cu^II complex Cu{N(SiMe₃)Dipp}₂ ( 1 Dipp=C₆H₅‐2,6Prⁱ₂) and its Cu^I counterpart [Cu{N(SiMe₃)Dipp}₂]^? ( 2 ) is described. The formation of 1 proceeds through a dispersion force‐driven disproportionation, and is the reaction product of a Cu^I halide and LiN(SiMe₃)Dipp in a non‐donor solvent. The synthesis of 2 is accomplished by preventing the disproportionation into 1 by using the complexing agent 15‐crown‐5. EPR spectroscopy of 1 provides the first detailed study of a two‐coordinate transition‐metal complex indicating strong covalency in the Cu?N bonds.     

Conversion of CuO Nanoplates into Porous Hybrid Cu2O/Polypyrrole Nanoflakes through a Pyrrole‐Induced Reductive Transformation Reaction

Porous hybrid Cu₂O/polypyrrole nanoflakes have been synthesized from solid CuO nanoplate templates through the pyrrole‐induced reductive transformation reaction at elevated temperature. The conversion mechanism involves the reductive transformation of CuO to Cu₂O and the in situ oxidative polymerization of pyrrole to polypyrrole. In addition, the morphology of the as‐converted nanohybrids depends on the shape of the CuO precursors. The strategy enables us to transform single‐crystalline CuO nanosheets into hollow hybrid Cu₂O/polypyrrole nanoframes. The ability to transform CuO and an organic monomer into porous hybrid materials of conducting polymer and Cu₂O with macrosized morphological retention opens up interesting possibilities to create novel nanostructures. Electrochemical examinations show that these porous hybrid Cu₂O/polypyrrole nanostructures exhibit efficient catalytic activity towards oxygen reduction reaction (ORR), excellent methanol tolerance ability, and catalytic stability in alkaline solution, thus making them promising nonprecious‐metal‐based catalysts for ORR in alkaline fuel cells and metal–air batteries.     

Synthesis of Cu3Sn Alloy Nanocrystals through Sequential Reduction Induced by Gradual Increase of the Reaction Temperature

Cu₃Sn alloy nanocrystals are synthesized by sequential reduction of Cu and Sn precursors through a gradual increase of the reaction temperature. By transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDS), UV/Vis spectroscopy, and X‐ray diffraction (XRD) analyses, the alloy formation mechanism of Cu₃Sn nanocrystals has been studied. The incremental increase of the reaction temperature sequentially induces the reduction of Sn, the diffusion of Sn into the preformed Cu nanocrystals, resulting in the intermediate phase of Cu–Sn alloy nanocrystals, and then the formation of Cu₃Sn alloy nanocrystals. We anticipate that the synthesis of Cu₃Sn alloy nanocrystals encourages studies toward the synthesis of various alloy nanomaterials.     

An unusual coordination polymer containing Cu+ ions and featuring possible Cu...Cu `cuprophilic' interactions: poly[di‐μ‐chlorido‐(μ4‐3,5‐diaminobenzoato‐κ4O:O′:N:N′)tricopper(I)(3 Cu—Cu)]

Compounds containing copper(I) are of interest for their role in biological processes. The nature of short (< ∼3.2 Å) Cu...Cu contacts within these compounds has been debated, being either described as weakly attractive (bonding) `cuprophilic' interactions, or simply as short metal–metal distances constrained by ligand geometry or largely ionic in nature. The title three‐dimensional Cu<sup>+</sup>‐containing coordination polymer, [Cu<sub>3</sub>(C<sub>7</sub>H<sub>7</sub>N<sub>2</sub>O<sub>2</sub>)Cl<sub>2</sub>]<sub>n</sub>, was formed from the in situ reduction of CuCl<sub>2</sub> in the presence of 3,5‐diaminobenzoic acid and KOH under hydrothermal conditions. Its complex crystal structure contains ten distinct Cu<sup>I</sup> atoms, two of which lie on crystallographic inversion centres. The copper coordination geometries include near‐linear CuOCl and CuN<sub>2</sub>, T‐shaped CuOCl<sub>2</sub> and distorted tetrahedral CuOCl<sub>3</sub> groups. Each Cu<sup>I</sup> atom is also associated with two adjacent metal atoms, with Cu...Cu distances varying from 2.7350 (14) to 3.2142 (13) Å; if all these are regarded as `cuprophilic' interactions, then infinite [01] zigzag chains of Cu^I atoms occur in the crystal. The structure is consolidated by N—H...Cl hydrogen bonds.     

A Highly Stable Copper‐Based Catalyst for Clarifying the Catalytic Roles of Cu0 and Cu+ Species in Methanol Dehydrogenation

Identification of the active copper species, and further illustration of the catalytic mechanism of Cu‐based catalysts is still a challenge because of the mobility and evolution of Cu⁰ and Cu⁺ species in the reaction process. Thus, an unprecedentedly stable Cu‐based catalyst was prepared by uniformly embedding Cu nanoparticles in a mesoporous silica shell allowing clarification of the catalytic roles of Cu⁰ and Cu⁺ in the dehydrogenation of methanol to methyl formate by combining isotope‐labeling experiment, in situ spectroscopy, and DFT calculations. It is shown that Cu⁰ sites promote the cleavage of the O?H bond in methanol and of the C?H bond in the reaction intermediates CH₃O and H₂COOCH₃ which is formed from CH₃O and HCHO, whereas Cu⁺ sites cause rapid decomposition of formaldehyde generated on the Cu⁰ sites into CO and H₂.     

Thermally Triggered Solid‐State Single‐Crystal‐to‐Single‐Crystal Structural Transformation Accompanies Property Changes

The 1D complex [(CuL_0.5H₂O) ? H₂O]_n ( 1 ) (H₄L=2,2′‐bipyridine‐3,3′,6,6′‐tetracarboxylic acid) undergoes an irreversible thermally triggered single‐crystal‐to‐single‐crystal (SCSC) transformation to produce the 3D anhydrous complex [CuL_0.5]_n ( 2 ). This SCSC structural transformation was confirmed by single‐crystal X‐ray diffraction analysis, thermogravimetric (TG) analysis, powder X‐ray diffraction (PXRD) patterns, variable‐temperature powder X‐ray diffraction (VT–PXRD) patterns, and IR spectroscopy. Structural analyses reveal that in complex 2 , though the initial 1D chain is still retained as in complex 1 , accompanied with the Cu‐bound H₂O removed and new O(carboxyl)?Cu bond forming, the coordination geometries around the Cu^II ions vary from a distorted trigonal bipyramid to a distorted square pyramid. With the drastic structural transition, significant property changes are observed. Magnetic analyses show prominent changes from antiferromagnetism to weak ferromagnetism due to the new formed Cu1‐O‐C‐O‐Cu4 bridge. The catalytic results demonstrate that, even though both solid‐state materials present high catalytic activity for the synthesis of 2‐imidazolines derivatives and can be reused, the activation temperature of complex 1 is higher than that of complex 2 . In addition, a possible pathway for the SCSC structural transformations is proposed.     

Facet‐Dependent Catalytic Activity of Cu2O Nanocrystals in the One‐Pot Synthesis of 1,2,3‐Triazoles by Multicomponent Click Reactions

We report the highly facet‐dependent catalytic activity of Cu₂O nanocubes, octahedra, and rhombic dodecahedra for the multicomponent direct synthesis of 1,2,3‐triazoles from the reaction of alkynes, organic halides, and NaN₃. The catalytic activities of clean surfactant‐removed Cu₂O nanocrystals with the same total surface area were compared. Rhombic dodecahedral Cu₂O nanocrystals bounded by {110} facets were much more catalytically active than Cu₂O octahedra exposing {111} facets, whereas Cu₂O nanocubes displayed the slowest catalytic activity. The superior catalytic activity of Cu₂O rhombic dodecahedra is attributed to the fully exposed surface Cu atoms on the {110} facet. A large series of 1,4‐disubstituted 1,2,3‐triazoles have been synthesized in excellent yields with high regioselectivity under green conditions by using these rhombic dodecahedral Cu₂O catalysts, including the synthesis of rufinamide, an antiepileptic drug, demonstrating the potential of these nanocrystals as promising heterogeneous catalysts for other important coupling reactions.     

Cu‐Based Catalyst Resulting from a Cu,Zn,Al Hydrotalcite‐Like Compound: A Microstructural,Thermoanalytical, and In Situ XAS Study

A Cu‐based methanol synthesis catalyst was obtained from a phase pure Cu,Zn,Al hydrotalcite‐like precursor, which was prepared by co‐precipitation. This sample was intrinsically more active than a conventionally prepared Cu/ZnO/Al₂O₃ catalyst. Upon thermal decomposition in air, the [(Cu_0.5Zn_0.17Al_0.33)(OH)₂(CO₃)_0.17] ? mH₂O precursor is transferred into a carbonate‐modified, amorphous mixed oxide. The calcined catalyst can be described as well‐dispersed “CuO” within ZnAl₂O₄ still containing stabilizing carbonate with a strong interaction of Cu²⁺ ions with the Zn–Al matrix. The reduction of this material was carefully analyzed by complementary temperature‐programmed reduction (TPR) and near‐edge X‐ray absorption fine structure (NEXAFS) measurements. The results fully describe the reduction mechanism with a kinetic model that can be used to predict the oxidation state of Cu at given reduction conditions. The reaction proceeds in two steps through a kinetically stabilized Cu^I intermediate. With reduction, a nanostructured catalyst evolves with metallic Cu particles dispersed in a ZnAl₂O₄ spinel‐like matrix. Due to the strong interaction of Cu and the oxide matrix, the small Cu particles (7 nm) of this catalyst are partially embedded leading to lower absolute activity in comparison with a catalyst comprised of less‐embedded particles. Interestingly, the exposed Cu surface area exhibits a superior intrinsic activity, which is related to a positive effect of the interface contact of Cu and its surroundings.     

A one‐pot method for synthesis of reduced graphene oxide‐supported Cu–Cu2O and catalytic application in tandem reaction of halides and sodium azide with terminal alkynes

Reduced graphene oxide (RGO)‐supported Cu–Cu₂O nanocomposite material (Cu‐Cu₂O@RGO) was prepared through a one‐pot reflux synthesis method. The morphology, crystal structure and composition of the prepared Cu‐Cu₂O@RGO were characterized using transmission electron microscopy, X‐ray diffraction, and X‐ray photoelectron, infrared and Raman spectroscopies. Cu‐Cu₂O@RGO as a heterogeneous catalyst was applied to tandem reactions of halides and sodium azide with terminal alkynes to synthesize effectively 1,4‐disubstituted 1,2,3‐triazoles. Moreover, the catalyst showed excellent recyclability performance with very little leaching of the metal. Compared with homogeneous catalysts, Cu‐Cu₂O@RGO as a green and efficient catalyst was recoverable, easy to separate and highly stable in the tandem method for the synthesis of 1,2,3‐triazole compounds.     

Catalytic CO Oxidation by O2 Mediated by Noble‐Metal‐Free Cluster Anions Cu2VO3–5−

Catalytic CO oxidation by molecular O₂ is an important model reaction in both the condensed phase and gas‐phase studies. Available gas‐phase studies indicate that noble metal is indispensable in catalytic CO oxidation by O₂ under thermal collision conditions. Herein, we identified the first example of noble‐metal‐free heteronuclear oxide cluster catalysts, the copper–vanadium bimetallic oxide clusters Cu₂VO_3–5^? for CO oxidation by O₂. The reactions were characterized by mass spectrometry, photoelectron spectroscopy, and density functional calculations. The dynamic nature of the Cu?Cu unit in terms of the electron storage and release is the driving force to promote CO oxidation and O₂ activation during the catalysis.     

Silica‐Protection‐Assisted Encapsulation of Cu2O Nanocubes into a Metal–Organic Framework (ZIF‐8) To Provide a Composite Catalyst

The integration of metal/metal oxide nanoparticles (NPs) into metal–organic frameworks (MOFs) to form composite materials has attracted great interest due to the broad range of applications. However, to date, it has not been possible to encapsulate metastable NPs with high catalytic activity into MOFs, due to their instability during the preparation process. For the first time, we have successfully developed a template protection–sacrifice (TPS) method to encapsulate metastable NPs such as Cu₂O into MOFs. SiO₂ was used as both a protective shell for Cu₂O nanocubes and a sacrificial template for forming a yolk–shell structure. The obtained Cu₂O@ZIF‐8 composite exhibits excellent cycle stability in the catalytic hydrogenation of 4‐nitrophenol with high activity. This is the first report of a Cu₂O@MOF‐type composite material. The TPS method provides an efficient strategy for encapsulating unstable active metal/metal oxide NPs into MOFs or maybe other porous materials.     

In Situ Fabrication of Inorganic/Organic Hybrid Based on Cu/Co‐ZIF and Cu2O

We successfully fabricate a well‐defined inorganic/organic hybrid Cu₂O@Cu/Co‐ZIF (ZIF=zeolitic imidazolate frameworks) by use of growth of dual‐metal Cu/Co‐ZIF on the obtained Cu₂O hollow spheres. The key point of the strategy is coupling the in situ self‐sacrificing template. Cu₂O and the coordination of metal ions (Cu⁺ and Co²⁺) with 2‐methylimidazole. This new hybrid was characterized by powder X‐ray diffraction, (scanning) transmission electron microscopy, energy‐dispersive spectroscopy mapping, in situ FT‐IR spectroscopy, UV/Vis diffuse reflection spectroscopy, N₂ sorption measurements, and electron spin resonance. It was evidenced that Cu/Co‐ZIF nanocrystals have been assembled to continuous shells surrounding the Cu₂O cores as well as in the voids between layers and inner pores. Cu₂O@Cu/Co‐ZIF exhibits visible light responsiveness and holds potential as narrow band gap semiconductor and visible photocatalyst.     

A Four‐Electron Sulfur Electrode Hosting a Cu2+/Cu+ Redox Charge Carrier

The elemental sulfur electrode with Cu²⁺ as the charge carrier gives a four‐electron sulfur electrode reaction through the sequential conversion of S?CuS?Cu₂S. The Cu‐S redox‐ion electrode delivers a high specific capacity of 3044 mAh g^?1 based on the sulfur mass or 609 mAh g^?1 based on the mass of Cu₂S, the completely discharged product, and displays an unprecedently high potential of sulfur/metal sulfide reduction at 0.5 V vs. SHE. The Cu‐S electrode also exhibits an extremely low extent of polarization of 0.05 V and an outstanding cycle number of 1200 cycles retaining 72 % of the initial capacity at 12.5 A g^?1. The remarkable utility of this Cu‐S cathode is further demonstrated in a hybrid cell that employs an Zn metal anode and an anion‐exchange membrane as the separator, which yields an average cell discharge voltage of 1.15 V, the half‐cell specific energy of 547 Wh kg^?1 based on the mass of the Cu₂S/carbon composite cathode, and stable cycling over 110 cycles.     

Redox‐Driven Migration of Copper Ions in the Cu‐CHA Zeolite as Shown by the In Situ PXRD/XANES Technique

Using quasi‐simultaneous in situ PXRD and XANES, the direct correlation between the oxidation state of Cu ions in the commercially relevant deNO_x NH₃‐SCR zeolite catalyst Cu‐CHA and the Cu ion migration in the zeolitic pores was revealed during catalytic activation experiments. A comparison with recent reports further reveals the high sensitivity of the redox‐active centers concerning heating rates, temperature, and gas environment during catalytic activation. Previously, Cu⁺ was confirmed present only in the 6R. Results verify a novel 8R monovalent Cu site, an eventually large Cu⁺ presence upon heating to high temperatures in oxidative conditions, and demonstrate the unique potential in combining in situ PXRD and XANES techniques, with which both oxidation state and structural location of the redox‐active centers in the zeolite framework could be tracked.     

Deactivation of Cu‐Exchanged Automotive‐Emission NH3‐SCR Catalysts Elucidated with Nanoscale Resolution Using Scanning Transmission X‐ray Microscopy

To gain insight into the underlying mechanisms of catalyst durability for the selective catalytic reduction (SCR) of NO_x with an ammonia reductant, we employed scanning transmission X‐ray microscopy (STXM) to study Cu‐exchanged zeolites with the CHA and MFI framework structures before and after simulated 135 000‐mile aging. X‐ray absorption near‐edge structure (XANES) measurements were performed at the Al K‐ and Cu L‐edges. The local environment of framework Al, the oxidation state of Cu, and geometric changes were analyzed, showing a multi‐factor‐induced catalytic deactivation. In Cu‐exchanged MFI, a transformation of Cu^II to Cu^I and Cu_xO_y was observed. We also found a spatial correlation between extra‐framework Al and deactivated Cu species near the surface of the zeolite as well as a weak positive correlation between the amount of Cu^I and tri‐coordinated Al. By inspecting both Al and Cu in fresh and aged Cu‐exchanged zeolites, we conclude that the importance of the preservation of isolated Cu^II sites trumps that of Brønsted acid sites for NH₃‐SCR activity.     

Antibacterial and physicochemical properties of co‐sputtered CuSn thin films

Copper‐tin thin films (CT TFs) were deposited on p‐type Si(100) by radio frequency (RF) magnetron co‐sputtering method. The atomic ratio of Cu and Sn showed complementary tendency with various RF powers on metal targets. Antibacterial test was conducted with Gram‐negative Escherichia coli. The ratio of Cu and Sn ions and the contact time with E. coli affected the antibacterial efficiency. Increasing the ratio of Cu ions and contact time showed higher antibacterial activity. Cu₂₀Sn₆ called as bronze structure, metallic Cu, and copper oxide phases were identified from X‐ray diffraction data after sterilization. The lattice strain that was changed due to the substitution of Cu and Sn was also calculated. The surface morphology of CT TFs was entirely grown to round shape when the dominant element was Sn. But, as the content of Cu increased, the surface morphology was changed from ball shape to sharp column shape. When fixed contact time, the intensities of Cu 2p increased but the intensities of Sn 3d decreased as increasing the atomic ratio of Cu. The oxidation of Cu was more sharply progressed as the RF power on Cu target increased. When fixed CT TFs, the intensities of Cu 2p were consistent but the intensities of Sn 3d_3/2 decreased as increasing contact time between CT TF and E. coli.     

An All‐Alkynyl Protected 74‐Nuclei Silver(I)–Copper(I)‐Oxo Nanocluster: Oxo‐Induced Hierarchical Bimetal Aggregation and Anisotropic Surface Ligand Orientation

The hardness of oxo ions (O^2?) means that coinage‐metal (Cu, Ag, Au) clusters supported by oxo ions (O^2?) are rare. Herein, a novel μ₄‐oxo supported all‐alkynyl‐protected silver(I)–copper(I) nanocluster [Ag_74?xCu_xO₁₂(PhC≡C)₅₀] ( NC‐1 , avg. x=37.9) is characterized. NC‐1 is the highest nuclearity silver–copper heterometallic cluster and contains an unprecedented twelve interstitial μ₄‐oxo ions. The oxo ions originate from the reduction of nitrate ions by NaBH₄. The oxo ions induce the hierarchical aggregation of Cu^I and Ag^I ions in the cluster, forming the unique regioselective distribution of two different metal ions. The anisotropic ligand coverage on the surface is caused by the jigsaw‐puzzle‐like cluster packing incorporating rare intermolecular C?H???metal agostic interactions and solvent molecules. This work not only reveals a new category of high‐nuclearity coinage‐metal clusters but shows the special clustering effect of oxo ions in the assembly of coinage‐metal clusters.