Investigations Of Cu Research Articles

In Situ STM Investigations of Cu(100) and Bimetallic Ag/Cu(100) Model Catalysts for CO2 Electroreduction in Bicarbonate Solution

The electrochemical conversion of carbon dioxide (CO2RR) to valuable chemicals and fuels plays a crucial role in the sustainable energy economy as it represents a promising potential for the renewable energy storage as well as closing the carbon loop.[1,2] Thus, the design and development of a highly efficient and selective electrocatalyst for CO2RR has become a topic of great importance in recent years. Among elemental metals, copper exhibits unique catalytic behaviour to reduce CO2 towards multi-carbon products with reasonable Faradaic efficiency due to its moderate CO-binding energy.[3,4] However, the selectivity and activity of pure copper is still far away for a practical application. The integration of a secondary metal species provides a promising strategy to improve the catalytical performance of the copper catalyst. Combination with silver is particularly interesting for such bimetallic catalysts, since Ag is a highly efficient catalyst for CO2RR to CO, probably the most important intermediate in the CO2RR, and has been shown to promote the formation of multi-carbon products.[5]Here, we present in situ scanning tunnelling microscopy studies of well-defined Cu and AgCu electrodes in CO2-satured 0.1 M KHCO3, which is one of the most common electrolytes for CO2 electroreduction. For Cu(100) in the double layer potential range, coexistence of two ordered (bi)carbonate adlayer phases was observed (Fig. 1a,b, published in [6]). These adlayer phases have a highly complex structure, exhibit dynamic fluctuations, and undergo a potential dependent order-disorder transition at about 0 V vs. the reversible hydrogen electrode. Detailed density functional calculations reveal that the observed layer is composed of carbonate and water that coadsorb on the electrode surface, underlining the key role of water in the stabilization of the (bi)carbonate adlayers.[6]Upon decreasing the potential to the onset of CO2RR, the formation of Cu nanoclusters is observed on the Cu(100) surfaces by in situ STM. This surface restructuring can be assigned to the influence of CO intermediates formed in the CO2RR. Upon subsequent increase of the potential back into the double layer range, the clusters disperse, resulting in a highly disordered interface structure that contains Cu adatoms, (bi)carbonates, and further molecular adsorbates. This irreversible change of the molecular-scale electrode surface is supported by spectroscopic results.AgCu bimetallic model catalysts were prepared by electrodeposition of submonolayer Ag coverage on Cu(100) in 0.1 M H2SO4. Silver forms islands on Cu(100) with a hexagonal quasi-Ag(111) atomic lattice. After the preparation and characterization of the Ag-decorated Cu(100), the electrolyte was exchanged under potential control to 0.1 M KHCO3. The electrolyte exchange results in the distinct restructuring on the surface in the double layer potential range, in which the islands develop a strongly anisotropic shape. In addition, appearance of new islands and a reduced surface mobility are observed. Furthermore, in contrast to the Ag-free Cu(100), high-resolution STM images show a disordered molecular adlayer.Our results demonstrate the pronounced role of adsorbed (bi)carbonate at the catalyst/electrolyte interface and its impact on the surface morphology and dynamics already at potentials in the double layer regime. These adsorbate-induced structural changes need to be considered for a fundamental understanding and rational design of electrocatalysts for CO2RR.The Authors gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) via SPP 2080, project no. 327886311.

Structural, surface and optical investigations of Cu+ implanted NiO film prepared by reactive sputtering

Nickel oxide (NiO) films were deposited on silicon substrate using a DC magnetron sputtering system. The deposited films were annealed at 400 °C for 2 h and then irradiated by 500 keV copper ions (Cu+) in the dose range of 1 × 1011 to 1 × 1014 ions-cm−2 using Pelletron Accelerator. X-ray diffraction study revealed NiO and Ni phases in the films corresponding to (111) and (200) planes. The lattice parameter was increased with the increase of ion dose to 1 × 1012 ions-cm−2 and then decreased at the higher doses. Ion irradiation at 1 × 1011 ions-cm−2 improved the crystallinity of the film while at the higher doses, the crystallinity was decreased. The surface morphology of the films showed a decrease in the compactness of the granular structure with increasing the ion dose. Fourier Transform Infrared spectroscopy showed Cu–O and Ni–O stretching vibration peaks in the irradiated films. X-ray photoelectron spectroscopy (XPS) results revealed a decrease in NiO and increase in the Ni+3Ni+2 ratio with an increase of the ion dose to 1 × 1012 ions-cm−2, demonstrating an increase in the Ni vacancies in the film at lower doses. The depth-resolved XPS analysis displayed a change in the Ni and O atomic percentages in the film with the increase of the etching time from 50 to 250 s and validated the existence of metallic Ni in the NiO film. The photoluminescence (PL) spectra analysis showed a decreasing trend in the band gap of the NiO film irradiated up to 1 × 1012 ions-cm−2, then an increasing trend at the higher doses.

Sphingomyelin-based PEGylation Cu (DDC)2 liposomes prepared via the dual function of Cu2+ for cancer therapy: Facilitating DDC loading and exerting synergistic antitumor effects

The old alcohol-aversion drug disulfiram (DSF) has aroused wide attention as a drug repurposing strategy in terms of cancer therapy because of the high antitumor efficacy in combination with copper ion. However, numerous defects of DSF (e.g., the short half-life and acid instability) have limited the application in cancer treatment. Cu (DDC)2, the complex of diethyldithiocarbamate (DDC, DSF metabolite) and Cu2+, have been proven as the vital active component on cancer, which have aroused the attention of researchers from DSF to Cu (DDC)2. However, the poor water solubility of Cu (DDC)2 increase more difficulties to the treatment and in-depth investigations of Cu (DDC)2. In this study, sphingomyelin (SM)-based PEGylated liposomes (SM/Chol/DSPE-mPEG2000 (55:40:5, mole%)) were produced as the carriers for Cu (DDC)2 delivery to enhance the water solubility. DDC was added to Cu-containing liposomes with a higher encapsulation efficiency of more than 90%, and it reacted with Cu2+ to synthesize Cu (DDC)2. Due to the high phase transition temperature of SM and strong intermolecular hydrogen bonds with cholesterol, SM-based liposomes would be conducive to enhancing the stability of Cu (DDC)2 and preventing drug leakage during delivery. As proven by pharmacokinetic studies, loading Cu (DDC)2 into liposomes improve bioavailability, and the area under the curve (AUC0-t) and the mean elimination half-life (t1/2) increased 1.9-time and 1.3-time to those of free Cu (DDC)2, respectively. Furthermore, the anticancer effect of Cu (DDC)2 was enhanced by the liposomal encapsulation, thus resulting in remarkable cell apoptosis in vitro and a tumor-inhibiting rate of 77.88% in vivo. Thus, it was concluded that Cu (DDC)2 liposomes could be promising in cancer treatment.

Electrocatalytic Investigations of Cu(II) and Fe(III) Complexes of Salophen Derivative Schiff Bases on the Pencil Graphite Electrode

AbstractThis present study describes a pencil graphite electrode surface covered with Cu(II) and Fe(III) complexes based on Salophen derivative Schiff bases in acetonitrile solution containing LiClO4 as a supporting electrolyte. Cyclic voltammetry method was used for the surface modification procedure with 25 cycle at a sweep rate of 50 mV s−1. Some characterization methods were used to identify of the prepared modified surfaces including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Ultraviolet‐visible Spectroscopy (UV‐Vis), and Scanning Electron Microscopy/Energy Dispersive X‐ray Spectroscopy (SEM/SEM‐EDX). The catalytic activity of these modified surfaces on the electrochemical oxidation of catechol (CC) was investigated and they compared with each other. The results demonstrated that these modified electrodes showed perfect electrocatalytic activity on the catechol determination, however the modified electrode prepared with the Cu(II) complex has higher catalytic activity than this prepared with the Fe(III) complex thanks to its the lower detection limit.

Spatially resolved opto‐electrical performance investigations of Cu2ZnSnS3.2Se0.8 photovoltaic devices

AbstractA new statistical analysis of spatially resolved photocurrent and electroluminescence images has been developed and applied to Cu2ZnSn(SxSe1−x)4 (CZTSSe) monograin solar cells. CZTSSe as an absorber material has the potential to significantly reduce manufacturing costs and develop new application fields in photovoltaics. Deep understanding of the performance related parameters in various production steps is crucial for further development of the technology. In this paper we show that by a thorough investigation by means of a combination of opto‐electrical measurement methods such as light beam induced current mapping, scanning electron microscopy, optical microscopy, photoluminescence, and electroluminescence measurements a correlation with different current‐voltage (j/V) measurement parameters can be established. Hereby, we clearly identify barrier variations at the active interface as the main reason for current variations across the cell, which for record cells can largely be avoided. These variations show up clearly in the microscopic spatial analysis developed. The detailed analysis of the homogeneity of the solar cell photocurrent presented in this study is relevant for all kinds of solar cells including thin‐film and wafer‐based cells.

Synthesis and Structural Investigations of Cu, Mn doped Cd1-xZnxS Quantum Dots

Synthesis and Structural Investigations of Cu, Mn doped Cd1-xZnxS Quantum Dots

A Theoretical Insight into the Mechanism of Cu(I)‐Catalyzed CN Coupling between Aryl Halides and Aqueous Ammonia

AbstractComputational investigations of Cu(I)‐catalyzed CN coupling between aryl halides and aqueous ammonia without addition of any base or ligand were reported. Density functional theory calculations were performed to reveal the mechanism of the ligand‐free amination reaction for the preparation of primary aromatic amines. Through systematic evaluation of the relative concentrations of possible Cu species in solution, we propose that the active catalyst is the neutral Cu(I) complexes rather than the Cu(I) cations; oxidative addition of aryl bromide is a facile step of the catalytic cycle; reactant (NH3) and solvent molecule (NMP) can act as ligands of Cu species to help reduce the activation energy of the forward reaction and increase the activation energy of the reverse reaction; except for Pathway B, the deprotonation step is irreversible due to the extreme exothermic feature; the elimination of H2O is kinetically favored, while that of HBr is thermodynamically preferred. These findings should be valuable for the mechanism understandings of the ligand‐free Cu‐catalyzed CN cross‐coupling reactions and for the further development of highly efficient amination catalyst systems.

Synthesis and spectral investigations of Cu(II) ion-doped NaCaAlPO4 F3 phosphor.

Cu(II) ion-doped NaCaAlPO(4)F(3) phosphor has been synthesized using a solid state reaction method. The prepared sample is characterized by powder X-ray diffraction, scanning electron microscope, optical absorption, electron paramagnetic resonance photoluminescence and Fourier transform infrared spectroscopy techniques. The crystallite size evaluated from x-ray diffraction data is in nanometers. Scanning electron microscopy micrographs showed the presence of several irregular shaped particles. From optical absorption and electron paramagnetic resonance spectral data the doped Cu(II) ions are ascribed to distorted octahedral site symmetry. The synthesized phosphor exhibits emission bands in ultraviolet, blue and green regions under the excitation wavelength of 335 nm. The CIE chromaticity coordinates (x = 0.159, y = 0.204) also calculated for the prepared sample from the emission spectrum. The Fourier transform infrared spectroscopy spectrum revealed the characteristic vibrational bands of the prepared phosphor material.

Bending Strength and Fracture Investigations of Cu Based Composite Materials Strengthened with δ-Alumina Fibres

Abstract Bending strength, thermal and electric conductivity and microstructure examinations of Cu based composite materials reinforced with Saffil alumina fibres are presented. Materials were produced by squeeze casting method applying the designed device and specially elaborated production parameters. Applying infiltration pressure of 90MPa and suitable temperature parameters provided manufacturing of copper based composite materials strengthened with Saffil alumina fibres characterized by the low rest porosity and good fibre-matrix interface. Three point bending tests at temperatures of 25, 100 and 300ºC were performed on specimens reinforced with 10, 15 and 20% of Saffil fibres. Introduced reinforcement effected on the relatively high bending strengths at elevated temperatures. In relation to unreinforced Cu casting strength of composite material Cu - 15vol.% Saffil fibres increase by about 25%, whereas at the highest applied test temperature of 300oC the improvement was almost 100%. Fibres by strengthening of the copper matrix and by transferring loads from the matrix reduce its plastic deformation and hinder the micro-crack developed during bending tests. Decreasing of thermal and electrical conductivity of Cu after incorporating fibres in the matrix are relatively small and these properties can be acceptable for electric and thermal applications.

Copper and xanthate adsorption onto pyrite surfaces: Implications for mineral separation through flotation

The findings of synchrotron based spectromicroscopic investigations of Cu and xanthate adsorption onto pyrite surfaces are reported. Synchrotron based photoemission electron microscopy measurements have revealed that Cu adsorbs only onto specific surface sites on pyrite. The Cu 2p X-ray absorption near edge structure and position (2p3/2 peak at 934.3eV) confirms the presence of Cu+ with transitions from 2p to 4s states being apparent. Moreover, the peak position is typical of Cu+ bonded to S, Cu(I)S. This is confirmed by S 2p X-ray photoelectron spectroscopy with oxidised S2− species (S−), most likely resulting from electrochemical interaction of solution Cu2+ and surface S2− species, being observed. Fe 2p X-ray absorption spectroscopy shows that surface Fe does not take part in the Cu adsorption or subsequent restructuring processes.Synchrotron FTIR microscopy analysis of xanthate (potassium ethyl xanthate, KEX) adsorbed onto Cu activated surfaces also shows a heterogeneous distribution on pyrite. The use of a dilute (10−5M) KEX concentration shows Cu(I)–xanthate as the only surface xanthate containing species. This species may have formed through a chemical process involving previously adsorbed Cu+ and the xanthate from solution. When a greater (10−3M) concentration of KEX is used significant concentrations of Cu(I)–xanthate precipitate from solution onto the pyrite surfaces and cannot be easily removed. Under this condition, the predominant surface species remains Cu(I)–xanthate with smaller concentrations of diethyl dixanthogen also being present. The latter species may form in solution although some previous studies also suggest direct surface formation.

Thermal, morphological and optical investigations of Cu(DAB)2 thin films produced by matrix-assisted pulsed laser evaporation and laser-induced forward transfer for sensor development

Many hybrid metal–organic complex materials which exhibit crystalline nature, nonlinear optical properties and chemoselective behavior generate interest as choice materials in various applications. In this paper we report results on Cu(II) 2,2′-dihydroxyazobenzene thin films deposited on silicon and quartz substrates by matrix assisted pulsed laser evaporation using a Nd:YAG laser, at 266 and 355nm laser wavelengths. Thermal analysis, atomic force microscopy, scanning electron microscopy and spectroscopic ellipsometry were performed in order to investigate thin film properties. Micrometric pixels of the compound have been transferred on glass plates by laser-induced forward transfer for chemoselective sensor development purposes.

ReaxFF molecular dynamics simulation of thermal stability of a Cu3(BTC)2 metal–organic framework

The thermal stability of a dehydrated Cu(3)(BTC)(2) (copper(II) benzene 1,3,5-tricarboxylate) metal-organic framework was studied by molecular dynamics simulation with a ReaxFF reactive force field. The results show that Cu(3)(BTC)(2) is thermally stable up to 565 K. When the temperature increases between 600 K and 700 K, the framework starts to partially collapse. The RDF analysis shows that the long range correlations between Cu dimers disappear, indicating the loss of the main channels of Cu(3)(BTC)(2). When the temperature is above 800 K, we find the decomposition of the Cu(3)(BTC)(2) framework. CO is the major product, and we also observe the release of CO(2), O(2), 1,3,5-benzenetricarboxylate (C(6)H(3)(CO(2))(3), BTC) and glassy carbon. The Cu dimer is stable up to 1100 K, but we find the formation of new copper oxide clusters at 1100 K. These results are consistent with experimental findings, and provide valuable information for future theoretical investigations of Cu(3)(BTC)(2) and its application in adsorption, separation and catalytic processes.

Investigations of Cu, Pb and Zn partitioning by sequential extraction in harbour sediments after electrodialytic remediation

Electrodialytic remediation was used to remove Cu, Zn and Pb from three different contaminated harbour sediments. Electrodialytic experiments lasting 2 and 4 weeks were performed and 48–86% Cu, 74–90% Zn and 62–88% Pb were removed from the different sediments and the removal increased with longer remediation time. A three step sequential extraction scheme (BCR), with an extra residual step, was used to evaluate the heavy metal distribution in the sediments before and after electrodialytic remediation. Cu was mainly associated with the oxidisable phase of the sediment, both before and after remediation. Zn and Pb were found in the exchangeable and reducible phases before remediation. Zn was still found in the exchangeable and reducible phases after remediation, whereas most Pb was removed from these phases during electrodialytic remediation.

Photoluminescence and XPS investigations of Cu2+‐doped ZnS quantum dots capped with polyvinylpyrrolidone

AbstractCu2+‐doped ZnS quantum dots were synthesized by a chemical precipitation method in water/ethanol solution. The quantum dots obtained were characterized by X‐ray diffraction, transmission electron microscopy and spectroscopy techniques including X‐ray photoelectron spectroscopy. The [S2−]/[Zn2+] ratios have an effect on the photoluminescence of both aqueous solutions and powders of Cu2+‐doped ZnS quantum dots. For aqueous samples, a green luminescence centre is observed in the spectrum of sample 1 with [S2−]/[Zn2+] = 1:2 and a blue one for sample 2 with [S2−]/[Zn2+] = 1:1. For powders, only the green emission is the main luminescence centre, and the integrated intensity in the blue emission region of sample 1 is stronger than that of sample 2. Compared with the spectrum of CuS powders, the X‐ray‐induced Auger electron spectrum of Cu L3M45M45 in ZnS quantum dots shows a unique spectral characteristic. The 3d level of the Cu2+ ion is split into two different energy levels at 334.0 and 347.2 eV, respectively.

Raman investigations of Cu(In,Ga)Se 2 thin films with various copper contents

CuIn 1 − x Ga x Se 2 (CIGS) thin films with a Ga/(Ga + In) ratio x = 0.3 with various Cu contents were characterized by micro-Raman spectroscopy. All samples were investigated with a frequency-doubled Nd:YAG laser (532 nm) in the back-scattering geometry. The frequency of the CIGS Raman A 1 mode decreases with increasing Cu content and reaches a minimum at a composition near stoichiometry. Furthermore, the full width at half maximum of the A 1 mode decreases with increasing Cu content of the CIGS thin films due to better crystallinity and reduced disorder in the films. In addition to the CIGS A 1 mode, CIGS with Cu/(Ga + In) <0.8 showed a broad shoulder at around 150 cm − 1 which is a result of ordered defect compounds like Cu(In,Ga) 3Se 5 or Cu 2(In,Ga) 4Se 7. Cu-rich films with Cu/(Ga + In) > 1 exhibit a non-chalcopyrite mode at 260 cm − 1 which is assigned to Cu 2 − x Se. Mappings of Cu-rich samples revealed a lateral distribution of the Cu 2 − x Se compound in domains of 1–2 μm.

Synthesis and Spectroscopic Investigations of Cu- and Pb-Doped Colloidal ZnS Nanocrystals

A novel organometallic synthesis method for the preparation of colloidal ZnS nanoparticles is presented. This method enables the synthesis of undoped ZnS nanocrystals as well as doping with Cu, Pb, or both. The particles can be covered with an undoped layer of ZnS, forming core/shell-type particles with the ZnS:Pb, ZnS:Cu, or ZnS:Cu,Pb cores. The particles were characterized via TEM, XRD, dynamic light scattering, and optical spectroscopy. We investigated the extrinsic surface defects and their coverage with an additional ZnS layer in detail by temperature-dependent luminescence and luminescence lifetime spectroscopy.

2,4,5-Trihydroxyphenylalanine Quinone Biogenesis in the Copper Amine Oxidase from Hansenula polymorpha with the Alternate Metal Nickel

Copper amine oxidase (CAO) is a dual-functioning enzyme that catalyzes the biosynthesis of a self-derived coenzyme and subsequent oxidative deamination of primary amines. The organic cofactor, 2,4,5-trihydroxyphenylalanine quinone (TPQ), is generated from the post-translational modification of an active site tyrosine (Y405) in a reaction shown to be dependent on both molecular oxygen and a mononuclear copper center. Previous investigations of Cu(II)-dependent cofactor formation in the Hansenula polymorpha amine oxidase (HPAO) provided evidence for the coordination of the precursor tyrosine in forming a ligand-to-metal charge transfer complex as a means of activating the tyrosyl ring for direct attack by triplet-state dioxygen. To further delineate the role of the metal in facilitating this complex series of reactions, apo-HPAO was reconstituted with alternate metals of varying reduction potentials and Lewis acidities [Ni(II), Co(II), Mn(II), Fe(II), and Fe(III)] and the consequence of each substitution on TPQ biogenesis examined. Ni(II) was found to support the transformation of the precursor tyrosine to the quinone cofactor to yield a mature enzyme competent for methylamine oxidation. Detailed kinetic analysis of the mechanism of TPQ biogenesis for the Ni(II)-substituted enzyme has led to the proposal of a direct electron transfer from the metal-coordinated tyrosinate to dioxygen as the dominant rate-limiting step.

Dendrimer Enhanced Ultrafiltration. 1. Recovery of Cu(II) from Aqueous Solutions Using PAMAM Dendrimers with Ethylene Diamine Core and Terminal NH2 Groups

This article discusses the feasibility of using dendrimer enhanced ultrafiltration (DEUF)to recover Cu(II) from aqueous solutions. Building upon the results of fundamental investigations of Cu(II) binding to PAMAM dendrimers with ethylenediamine (EDA) core and terminal NH2 groups, we combine (i) dead-end ultrafiltration (UF) experiments with (ii) atomic force microscopy (AFM) characterization of membrane fouling to assess the feasibility of using DEUF to recover Cu(II) from aqueous solutions. On a mass basis, the Cu(II) binding capacities of the EDA core PAMAM dendrimers are much larger and more sensitive to solution pH than those of linear polymers with amine groups. The dendrimer-Cu(II) complexes can be efficiently separated from aqueous solutions by ultrafiltration. The metal ion laden dendrimers can be regenerated by decreasing the solution pH to 4.0; thus enabling the recovery of the bound Cu(II) ions and recycling of the dendrimers. The UF measurements and AFM characterization studies show that EDA core PAMAM dendrimers with terminal NH2 groups have very lowtendency to foul the commercially available regenerated cellulose (RC) membranes evaluated in this study. The overall results of these experiments suggest that DEUF is a promising process for recovering metal ions such as Cu(II) from aqueous solutions.

Correlation between UV-VIS spectra and the structure of Cu(II) complexes with hydrogenated dextran in alkaline solutions

UV-VIS spectrophotometric investigations of Cu(II) complexes with hydroge-nated dextran showed that the complexation of Cu(II)-ions began at pH &gt; 7. The formation of Cu(II) complexes with dextran monomer units was observed at pH 7-12. With further increase in solution pH &gt; 12, the Cu(II)-dextran complex decomposed to Cu(OH)42~-ions and dextran. With increasing solution pH the absorption maximum of complex solutions increased and shifted to shorter wavelength (hypsochromic shift) compared with uncomplexed Cu(II). The UV spectra displayed bathochromic shifts. The changes of UV-VIS spectra with increasing in solution pH confirmed the formation of different kinds of complex species. The correlation between the results of UV-VIS spectrophotometry and the central metal ionligand coordination predicted that the copper binding within the complex depended on the pH and participation H2O molecules. Dextran complexes with Cu(II) were formed by the displacement of water molecules from the coordination sphere of copper by OH groups. The analysis indicated that the Cu(II) center was coordinated to two glucopyranose units of dextran. The spectrophotometric parameters of the investigated complexes were characteristic of a Cu(II)-ion in a square-planar or tetragon ally distorted octahedral coordination.

In situ XPS investigations of Cu1−xNixZnAl-mixed metal oxide catalysts used in the oxidative steam reforming of bio-ethanol

A series of CuNiZnAl-multicomponent mixed metal oxide catalysts with various Cu/Ni ratios were prepared by the thermal decomposition of Cu1−xNixZnAl-hydrotalcite-like precursors and tested for oxidative steam reforming of bio-ethanol. Dehydrogenation of EtOH to CH3CHO is favored by Cu-rich catalyst. Introduction of Ni leads to CC bond rupture and producing CO, CO2 and CH4. H2 yield (selectivity) varied between 2.6–3.0mol/mol of ethanol converted (50–55%) for all catalysts at 300°C. The above catalysts were subjected to in situ XPS studies to understand the nature of active species involved in the catalytic reaction. Core level and valence band XPS as well as Auger electron spectroscopy revealed the existence of Cu2+, Ni2+ and Zn2+ ions on calcined materials. Upon in situ reduction at reactions temperatures, the Cu2+ was fully reduced to Cu0, while Ni2+ and Zn2+ were partially reduced to Ni0 and Zn0, respectively. On reduction, the nature of ZnO on Cu-rich catalyst changes from crystalline to amorphous, relatively inert and highly stabilized electronically. Relative concentration of the Ni0 and Zn0 increases upon reduction with decreasing Cu-content. Valence band results demonstrated that the overlap between 3d bands of Cu and Ni was marginal on calcined materials, and no overlap due to metallic clusters formation after reduction. Nonetheless, the density of states at Fermi level increases dramatically for Ni-rich catalysts and likely this influences the product selectivity.