Bimetallic CuCo Research Articles

N‐Doped Hierarchical Porous Carbon Embedded Synergistic Bimetallic CoCu NPs with Unparalleled Catalytic Performance

AbstractBy virtue of the structural diversity, electronic tunability and synergetic effect, heterogeneous non‐noble bimetallic catalysts have demonstrated excellent catalytic performance in Fischer‐Tropsch synthesis, biomass conversion and fine chemicals synthesis community. However, the feature of synergetic effect and formation mechanism of bimetallic CoCu NPs under carbothermal conditions still remain to be explored. Herein we report an efficient protocol for fabrication of a representative N‐doped hierarchical porous carbon embedding bimetallic CoCu NPs catalyst. Particularly, the prepared Co0.7Cu0.3@NHPC‐800 catalyst demonstrates unprecedented catalytic activity and chemoselectivity for various nitroaromatics under extremely mild condition (1 atm H2, 30 °C), which is superior to the existing non‐noble metal‐based catalytic systems. It also exhibits excellent activity for hydrolysis of ammonia borane in pure water at room temperature. Furthermore, the possible formation process of bimetallic NPs is firstly brought to light, which could be the key to the nature of CoCu synergistic effect as well as the resultant high activity and selectivity.

Mechanistic Insights into the Synthesis of Higher Alcohols from Syngas on CuCo Alloys

Synthesis gas (CO + H2) conversion is an important process in the transformation of coal, natural gas, or biomass into higher-value products. The explicit conversion into C2+ oxygenates on transition-metal-based catalysts suffers from a low selectivity, being a consequence of an imperative integration of C–O bond splitting and C–C coupling reactions. Recently, it has been demonstrated that a bimetallic CuCo catalyst has high higher alcohol selectivity under mild reaction conditions, but the details of the reaction mechanism on the surface are still elusive. In this work, we studied the formation of methane, methanol, and ethanol from syngas on a close-packed (111) and a stepped (211) CuCo surface combining density functional theory (DFT) and microkinetic modeling. We found the CuCo alloy to be a promising candidate catalyst, displaying the required coverage of CO and CHx on the surface to facilitate C–C coupling. In addition, we found the selectivity to be very structure sensitive: the CuCo (211) surface ...

Bimetallic copper cobalt selenide nanowire-anchored woven carbon fiber-based structural supercapacitors

Structural supercapacitors provide a variety of opportunities for woven carbon fibers in portable electronics, hybrid automobiles and aerospace applications. We describe herein the synthesis of bimetallic Cu-Co selenide nanowires based on woven carbon fibers, and their use as electrodes in supercapacitors. Woven Kevlar fiber is used as separator for the electrodes and a polyester resin with an ionic liquid and lithium salt is used as solid polymer electrolyte. The supercapacitors exhibit efficient energy storage and significant enhancements in mechanical strength (89.38%) and modulus (70.41%) over those of bare woven carbon fiber base supercapacitors. The specific capacitance of these supercapacitors increases from 0.197 F g−1 to 28.63 F g−1 after the growth of nanowires, with accordingly high energy density (191.64 mW h kg−1) and power density (36.65 W kg−1). In situ mechano-electrochemical tests of these supercapacitors yield excellent capacitance retention (77.3%) at the mechanical failure point (481.29 MPa).

Structure of Copper-Cobalt Surface Alloys in Equilibrium with Carbon Monoxide Gas.

We studied the structure of the copper-cobalt (CuCo) surface alloy, formed by Co deposition on Cu(110), in dynamic equilibrium with CO. Using scanning tunneling microscopy (STM), we found that, in vacuum at room temperature and at low Co coverage, clusters of a few Co atoms substituting Cu atoms form at the surface. At CO pressures in the Torr range, we found that up to 2.5 CO molecules can bind on a single Co atom, in carbonyl-like configurations. Based on high-resolution STM images, together with density functional theory calculations, we determined the most stable CuCo cluster structures formed with bound CO. Such carbonyl-like formation manifests in shifts in the binding energy of the Co core-level peaks in X-ray photoelectron spectra, as well as shifts in the vibrational modes of adsorbed CO in infrared reflection absorption spectra. The multiple CO adsorption on a Co site weakens the Co-CO bond and thus reduces the C-O bond scission probability. Our results may explain the different product distribution, including higher selectivity toward alcohol formation, when bimetallic CuCo catalysts are used compared to pure Co.

Adsorption, hydrogenation and dehydrogenation of C2H on a CoCu bimetallic layer

In this paper, adsorption, hydrogenation and dehydrogenation of C2H on a single atomic layer of bimetallic CoCu were investigated using first-principles calculations. The CoCu bimetallic layer is formed by Cu replacement of partial Co atoms on the top layer of a Co(111) surface. Our adsorption and reaction results showed those sites, which have stronger adsorption energy of C2H, possess higher reactivity. The bimetallic layer possesses higher reactivity than either of the pure monometallic layer. A mechanism of higher reactivity of the bimetallic layer is proposed and identified, i.e. in the bimetallic catalyst, the catalytic performance of one component is promoted by the second component, and in our work, the catalytic performance of Co atoms in the bimetallic layer are improved by introducing Cu atoms, lowing the activation barrier of the reaction of C2H. The bimetallic layer could tune adsorption and reaction of C2H by modulating the ratio of Co and Cu. Results of adsorption energies and adsorption configurations reveal that C2H prefers to be adsorbed in parallel on both the pure Co metallic and CoCu bimetallic layers, and Co atoms in subsurface which support the metallic or bimetallic layer have little effect on C2H adsorption. For hydrogenation reactions, the products greatly depend on the concentration and initial positions of hydrogen atoms, and the C2H hydrogenation forming acetylene is more favorable than forming vinylidene in both thermodynamics and kinetics. This study would provide fundamental guidance for hydrocarbon reactions on Co-based and/or Cu-based bimetallic surface chemistry and for development of new bimetallic catalysts.

Silica-Supported Bimetallic Co-Cu Composite - An Efficient Catalyst for Ethanol Based Hydrogen Production by Steam Reforming Technique

Silica-Supported Bimetallic Co-Cu Composite - An Efficient Catalyst for Ethanol Based Hydrogen Production by Steam Reforming Technique

Synergetic Catalysis of Bimetallic CuCo Nanocomposites for Selective Hydrogenation of Bioderived Esters

Bimetallic catalysts based on nonprecious transition metals have attracted increasing attention because of their unique synergistic effects in catalytic reactions, but the understanding of the nature of synergistic effects and their roles in a specific hydrogenation reaction remains lacking. Herein, a series of bimetallic CuxCoy/Al2O3 (x/y = 5:1, 2:1, 1:1, 1:2, 1:5) nanocomposite catalysts were fabricated via the successive calcination and reductive activation process of layered double hydroxide precursors. Their catalytic performance in the selective hydrogenation of bioderived ethyl levulinate to 1,4-pentanediol (1,4-PeD) depended sensitively on the chemical composition of bimetallic CuCo catalysts. The optimal bimetallic Cu2Co1/Al2O3 catalyst exhibited markedly improved catalytic activity and selectivity compared to monometallic Cu/Al2O3, as confirmed by its lower apparent activation energy barrier of 65.1 kJ mol–1 of the rate-determining step and its high selectivity of 93% to 1,4-PeD. Detailed charac...

Metal-organic frameworks derived bimetallic Cu-Co catalyst for efficient and selective hydrogenation of biomass-derived furfural to furfuryl alcohol

In this study we report an efficient CuCo bimetallic catalyst with highly dispersed CuCo-based mixed metal/metal oxide on porous carbon matrix for the hydrogenation of furfural to furfuryl alcohol. The catalyst is derived from Co-doped Cu-BTC metal-organic frameworks (MOFs) by thermolysis in nitrogen atmosphere at temperatures ranging from 773K to 1073K. The best catalytic performance is achieved when cobalt to copper molar ratio is 0.4 and the precursor is calcined at 873K. The characterization of prepared catalytic materials is done by multi-techniques including XRD, XPD, SEM, TEM, TG and BET analysis. The sum of their results reveal that the doping of cobalt helps the dispersion of nanoparticles of copper and cobalt and thermolysis temperature has an impact on both the particle size and the chemical states. The resulting catalyst CuCo0.4/C-873 shows 98.7% furfural conversion and 97.7% furfuryl alcohol selectivity in ethanol solvent with good stability which is better than most reported catalysts.

Low temperature growth of fully covered single-layer graphene using a CoCu catalyst.

A bimetallic CoCu alloy thin-film catalyst is developed that enables the growth of uniform, high-quality graphene at 750 °C in 3 min by chemical vapour deposition. The growth outcome is found to vary significantly as the Cu concentration is varied, with ∼1 at% Cu added to Co yielding complete coverage single-layer graphene growth for the conditions used. The suppression of multilayer formation is attributable to Cu decoration of high reactivity sites on the Co surface which otherwise serve as preferential nucleation sites for multilayer graphene. X-ray photoemission spectroscopy shows that Co and Cu form an alloy at high temperatures, which has a drastically lower carbon solubility, as determined by using the calculated Co-Cu-C ternary phase diagram. Raman spectroscopy confirms the high quality (ID/IG < 0.05) and spatial uniformity of the single-layer graphene. The rational design of a bimetallic catalyst highlights the potential of catalyst alloying for producing two-dimensional materials with tailored properties.

Ambient Pressure X-ray Photoelectron Spectroscopy for Probing Monometallic, Bimetallic and Oxide-Metal Catalysts Under Reactive Atmospheres and Catalytic Reaction Conditions

Synchrotron-based ambient pressure X-ray photoelectron spectroscopy (APXPS) is an important in situ chemical probe in the toolbox of chemists and materials engineers. It uniquely aids in the investigation of the surfaces and interfaces of complex systems under dynamic environments, such as catalysts operating at the solid/gas interface. Nanoparticles (NPs) produced via colloidal chemistry offer the advantage of narrow particle distributions in APXPS studies of catalysts. They provide a narrow distribution in size, shape and composition of catalysts, which provide a closer correlation to actual catalysts than single crystal models for which APXPS is extensively employed. In this paper, some case studies of colloidaly-made uniform nanoparticles catalysts will be outlined. The examples will include monometallic, bimetallic and binary oxide-metal catalysts, where APXPS is used in different reactive atmospheres and during catalytic reactions. First, in situ CO oxidation studies of monometallic Rh NPs in the 2–7 nm range will be discussed. Next, APXPS studies of bimetallic NPs with size and composition control will be illustrated. NO-induced reversible core/shell restructuring of bimetallic PdRh NPs and gas-driven irreversible surface segregation of Cu in bimetallic CoCu NPs will be explained. To further illustrate the utility of the technique, APXPS and catalytic measurements carried out in parallel and under identical conditions will be described over bimetallic AuPd and CoPt NPs, during catalytic oxidation of CO. APXPS based structure–function correlations such as composition and ensemble dependence of catalytic activity will also be illustrated in this discussion. Finally, binary oxide-metal catalysts will be exemplified in APXPS studies of CeO2/Pt and TiO2/Co systems in hydrogen reducing atmospheres and/or during catalytic hydrogenation of CO2. Also, along with this idea, metal-support interactions in the forms of metal-induced reduction of oxide support, wetting and encapsulation of metal will be detailed in relation to catalytic properties.

RuCuCo nanoparticles supported on MIL-101 as a novel highly efficient catalysts for the hydrolysis of ammonia borane

The catalysts containing Ru, CuCo and trimetallic RuCuCo nanoparticles were successfully synthesized by in-situ reduction of Ru, Cu and Co salts into the highly porous and hydrothermally stable metal–organic framework MIL-101 via a simple liquid impregnation method, and then characterized the structure, size, composition and specific area of the catalysts with different metal nanoparticles loading by XRD, TEM, EDX, ICP-AES, XPS and BET techniques. Their catalytic activities had been examined in ammonia borane hydrolysis to generate hydrogen gas. The result shows that the as-synthesized RuCuCo@MIL-101 exhibits a higher catalytic activity than those of monometallic Ru and bimetallic CuCo counterparts loadings, owing to the strong trimetallic synergistic effects, uniform distribution of nanoparticles as well as bi-functional effects between RuCuCo nanoparticles and the host of MIL-101, with the turn over frequency (TOF) value of 241.2 mol H2 min−1 (mol Ru)−1 and the activation energy (Ea) is determined to be 48 kJ/mol. Moreover, this catalyst exhibits satisfied durability after five cycles for the hydrolytic dehydrogenation of ammonia borane.

Bimetallic CuCo nanoparticles derived from hydrotalcite supported on carbon fibers for higher alcohols synthesis from syngas

Higher alcohols synthesis (HAS) is a strong exothermal reaction which leads to the formation of hotspots on the catalysts and the hotspots result in poor selectivity, and Cu–Co based catalysts are one of the most promising to which the formation of Cu–Co alloy is critical. Therefore a new scheme was proposed, based on the excellent thermal conductivity of carbon fibers (CFs) and the uniform mixing of metal ions in layered double hydroxides (LDHs), the latter favors the formation of metallic alloy. Nanocomposites of LDHs and CFs were prepared by using co-precipitation method and used for HAS, and characterized by using FTIR, N2 adsorption–desorption, XRD, TPR, SEM and TEM techniques. In the composites, nanosheets with the typical LDHs morphology are perpendicularly grown on the surface of CFs while intersecting each other, creating a highly open and porous structure. After reduction, Cu–Co-alloy nanoparticles are formed from the LDHs. The resultant catalysts showed high activity and much high selectivity to higher alcohols. The reported methods can be expanded to prepare other LDHs/CFs composites.

Non-noble bimetallic CuCo nanoparticles encapsulated in the pores of metal–organic frameworks: synergetic catalysis in the hydrolysis of ammonia borane for hydrogen generation

Non-noble bimetallic CuCo alloy nanoparticles were successfully encapsulated in the pores of MIL-101 without aggregation on the external surfaces of the host framework, which exhibit excellent catalytic activity for hydrolytic dehydrogenation of ammonia borane.

Higher Alcohols through CO Hydrogenation over CoCu Catalysts: Influence of Precursor Activation

Bimetallic CoCu model catalysts were investigated for the synthesis of higher alcohols using catalytic CO hydrogenation according to the Fischer–Tropsch technology. Emphasis was placed on revealing the influence of the activation conditions. Accordingly, catalyst precursors were activated in argon, hydrogen, syngas (CO/H2), and CO under atmospheric conditions and at elevated temperatures (370 °C). All catalyst precursors were prepared via oxalate coprecipitation in the absence of a classic support. Alcohol selectivities between 30 and ∼40% (up to ∼50% for the sum of alcohols and alkenes) were obtained with an Anderson–Schulz–Flory (ASF) chain lengthening probability maximizing the slate up to C6. Detailed catalysis and characterization studies were performed using a Co2Cu1 catalyst composition. The catalytic performances of the H2- and syngas-activated Co2Cu1 catalyst were similar. While the CO-activated catalyst shows significantly higher catalytic activity and ASF chain lengthening probability, the alco...

Kinetic study of higher alcohol synthesis directly from syngas over CoCu/SiO2 catalysts

Higher alcohol synthesis (HAS) directly from syngas is one of the most promising approaches for utilizing nonoil resources cleanly and efficiently. A series of bimetallic CoCu catalysts with different Co/Cu ratios were prepared using a SiO2 support. The structure of Cu modified Co catalysts was characterized using HRTEM, in/ex situ X‐ray diffraction, and temperature‐programmed reduction. It was evidenced that nanoscale metal particles were formed and the reduction of Co oxide at above 673 K. Meanwhile, the interaction between Co and Cu on the surface was assumed to be responsible for the enhanced selectivity to HAS. The intrinsic kinetics for this reaction was performed over a CoCu/SiO2 catalyst under realistic conditions. The kinetic parameters, including apparent activation energies and reaction orders, were calculated through power‐law models. With the combination of chain growth probability and kinetics, the effect of temperatures on the reaction mechanism and the Cu promotional effects on Co catalysts were elaborated. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1797–1809, 2014

Surface Composition Changes of Redox Stabilized Bimetallic CoCu Nanoparticles Supported on Silica under H2 and O2 Atmospheres and During Reaction between CO2 and H2: In Situ X-ray Spectroscopic Characterization

In this paper, we report the colloidal synthesis and detailed characterization of 11 nm bimetallic CoCu nanoparticle catalysts. Presently Co and Cu is an attractive combination because of their respective properties for industrially important Fischer–Tropsch and methanol synthesis reactions of CO (and CO2) with H2. We report the preparation of catalysts by deposition of bimetallic metal nanoparticles, both within mesoporous silica (MCF-17) and on the native oxide surface of a silicon wafer. Subsequent phase separation into phase-segregated (i.e., dimer) particles is found to occur upon redox treatment. These nanoparticle catalysts have then been investigated using an array of techniques including synchrotron-based ambient pressure X-ray photoelectron spectroscopy (APXPS) and in situ near edge and extended X-ray absorption fine structure (NEXAFS/EXAFS) spectroscopies. CO2 hydrogenation is used as a probe reaction. All three techniques combine to show that an oxygen atmosphere segregates copper to the surface. In doing so the oxygen produces oxides of both Co and Cu metals. Significant hydrogen pressure and temperature are required to fully rereduce both metals to a metallic state as demonstrated by NEXAFS spectroscopy. Under the conditions of the CO2/H2 reaction monitored in situ using NEXAFS spectroscopy, both metals exist in a fully reduced state at 2.7 bar, 1:3 CO2:H2, and 260 °C.

Urchin-like CoCu Bimetallic Nanocomposites for Catalytic Hydrogenolysis of Glycerol to Propanediols

Bimetallic CoCu nanocomposites were synthesized in polyol by using Ru as heterogeneous nucleation agent and stearic acid as surfactant, and their catalytic properties were investigated by hydrogenolysis of glycerol to propanediols. It was found that the surfactant could induce Co nanocrystals to form nanowires as structure-directing agent, while it's ineffective for Cu because only spherical Cu particles were produced under the same condition. When Co2+ and Cu2+ coexist in polyol, Cu2+ is firstly reduced and forms the spherical particles, and then the Cu particles afford surface for the subsequential reduction of Co2+ and growth of Co nanocrystals to form the nanorods, obtaining the urchin-like CoCu nanocomposites. The catalytic performance in selective hydrogenolysis of glycerol to propanediols proposed that the CoCu urchin-like nanocomposites was superior to the Co nanowires possibly due to that the synergistic effect between Co and Cu component promoted conversion of glycerol and obtained the higher propanediol yields based on the specific surface areas of the catalysts.

First-Principles Study of the Structural, Electronic, and Magnetic Properties of Cu-Fe, Cu-Co, and Cu-Ni Linear and Zigzag Nanowires

By using first-principles calculations, we have systematically investigated the equilibrium structure, electronic, and magnetic properties of free-standing Cu-Fe, Cu-Co, and Cu-Ni bimetallic linear and zigzag nanowires, and a comparison was carried out with the corresponding monatomic chains. It was found that all the bimetallic linear and zigzag chains have stable ferromagnetic (FM) states, and the total energies of all the considered zigzag chains are lower than those of the corresponding linear chains. The equilibrium bond lengths of the bimetallic Cu-Fe, Cu-Co, and Cu-Ni nanowires lie in between the values of the corresponding monatomic systems. The magnetic moments in linear nanowires are generally larger than the ones of the corresponding zigzag nanowires, and the Fe, Co, and Ni atoms in bimetallic nanowires have quite high local magnetic moments. The calculations suggest that there is hybridization between the Cu-3d and Fe (Co or Ni) 3d states, which leads to lower cohesive energies of the bimetallic nanowires than those of the corresponding monatomic nanowires. The bimetallic Cu-Fe and Cu-Co nanowires also have high spin polarizations and may be good potential materials for spintronic devices.

Quantitative XPS Analysis of Bimetallic Cu-Co Catalysts

The surfaces of bimetallic Cu–Co/SiO2 catalyst with 1 Cu:2 Co atomic ratio has been studied focusing on the determination of bimetallic phase thickness and its distribution using a mathematical formalism from X-ray photoelectron spectroscopy (XPS) intensities. X-ray diffraction analysis indicated a Cu–Co alloy formation and XPS qualitative analysis showed that Cu0 and Co0 species were present on the surface. Atomic ratios of Cu/Si, Co/Si and Co/Cu from XPS and atomic absorption (A.A.) analyses suggested homogeneous particle formation with a slight Cu surface enrichment in the catalyst. A mathematical model was proposed from relative intensity ratios, which was able to determine the metallic particle thickness and its coverage fraction at the support. Considering that these values were comparable to those for the particle size obtained from transmission electron microscopy (TEM) measurements, it may be said that the model describes the evaluated system accurately.