Monometallic Copper Research Articles

Effect of monometallic copper on zeolitic imidazolate framework-8 synthesized by hydrothermal method

Metal-organic frameworks (MOFs), which are self-assembled and can be synthesized by the coordination of metal cation/clusters with organics linkers. Copper/zeolitic imidazolate framework-8 (Cu/ZIF-8) MOF catalyst was successfully synthesized by reaction of metal sulfates of Cu with ZIF-8 via hydrothermal method. Thermogravimetric analysis (TGA) exhibits the excellent thermal stability up to 450°C of the Cu/ZIF-8 catalyst. Fourier transform infrared spectroscopy (FTIR) confirmed the ZIF-8 structure and the addition of copper metal. Field emission scanning electron microscopy (FESEM) images exhibit great morphologies which confirms the synthesis of Cu/ZIF-8 catalyst. UV-Vis (Ultraviolet-visible) spectroscopy and DRS (diffuse reflectance spectroscopy) show more absorbance in the visible region of Cu/ZIF-8 and lower band gap energy respectively, which leads to photocatalytic support. Our discoveries investigated a basic and intense approach to photocatalyst without losing their properties.

Novel Rh(Pd)-Cu(Ni) supported catalysts for oxy-steam reforming of methanol

Monometallic copper, nickel and bimetallic Pd(Rh)-Cu(Ni) catalysts supported on a binary oxide containing various content of ZrO2 and Al2O3 were prepared by impregnation method. Their physicochemical and catalytic properties in oxy-steam reforming of methanol reaction (OSRM) were extensively investigated. Selecting an optimal composition of the catalyst for the OSRM process was the main goal of this work. The influence of zirconia content on the reactivity and physicochemical properties of supported copper catalysts in OSRM was also studied. The reactivity measurements showed that the supported copper catalyst was more active than the nickel catalyst. The catalytic measurements showed that the catalyst properties depend on their surface composition, acidity and adsorption properties. High selectivity of supported copper catalyst with composition 20%Cu/ZrO2·Al2O3 (Zr:Al = 1:2) towards carbon dioxide and hydrogen was confirmed. In addition, the promotion effect of palladium and rhodium on the activity of monometallic supported copper and nickel catalysts in OSRM was confirmed. The most active system in the OSRM process was 0.5%Rh-20%Cu/ZrO2·Al2O3.

Cu-Based Nanoparticles as Emerging Environmental Catalysts.

This account provides an overview of current research activities on nanoparticles containing the earth-abundant and inexpensive element copper (Cu) and Cu-based nanoparticles, especially in the field of environmental catalysis. The different synthetic strategies with possible modification of the chemical/ physical properties of these nanoparticles using such strategies and/or conditions to improve catalytic activity are presented. The design and development of support and/or bimetallic systems (e. g., alloys, intermetallic, etc.) are also included. Herein, we report synthetic approaches of Cu and Cu-based nanoparticles (monometallic copper, bimetallic copper and copper (II) oxide nanoparticles/nanostructures) and impregnation of such nanoparticles onto support material (e. g., Co3 O4 nanostructure), along with their applications as environmental catalyst for various oxidation and reduction reactions. Finally, this account provides necessary advances and perspectives of Cu-based nanoparticles in the environmental catalysis.

NiCu single atom alloys catalyze the C[sbnd]H bond activation in the selective non- oxidative ethanol dehydrogenation reaction

NiCu single atom alloy (SAA) nanoparticles supported on silica are reported to catalyze the non-oxidative dehydrogenation of ethanol, selectively to acetaldehyde and hydrogen products by facilitating the CH bond cleavage. The activity and selectivity of the NiCu SAA catalysts were compared to monometallic copper and to PtCu and PdCu single atom alloys, in a flow reactor at moderate temperatures. In-situ DRIFTS showed that the silica support facilitates the OH bond cleavage of ethanol to form ethoxy intermediates over all the supported alloy catalysts. However, these remain unreactive up to 250 °C for the Cu/SiO2 monometallic nanoparticles, while in the NiCu SAA, acetaldehyde is formed at much lower temperatures, below 150 °C. In situ DRIFTS was also used to identify the CH activation step as the rate determining step of this reaction on all the copper catalysts we examined. The presence of atomically dispersed Ni in Cu significantly lowers the CH bond activation barrier, whereas Pt and Pd atoms were found less effective. This work provides direct evidence that the CH bond cleavage is the rate determining step in ethanol dehydrogenation over this type catalyst.

Photocatalytic Degradation of an Azo Dye over Novel Monometallic Copper Catalysts Supported on Fibreglass

The monometallic copper catalysts were synthesized by impregnation of fibreglass material covered by TiO2 using magnetron sputtering method at a low temperature plasma technique in vacuum camera. Their physicochemical properties were extensively studied by BET, TPR-H2 and XRD techniques. The photocatalytic properties in degradation of an azo dye were controlled by determination of chemical oxygen demand, total organic carbon and using UV–VIS technique. Fibreglass covered with TiO2 and copper oxides has shown remarkable photocatalytic properties in degradation of Reactive Violet 2 dye. Its stability was increased by its preliminary treatment in HCl. The optimal content of Cu appeared to be 5% in the oxide layer of the catalyst digested in HCl. Kinetic constants determined for the process of the dye photodegradation over Cu2O (5%)/TiO2/fibreglass catalyst were one order higher than for TiO2/fibreglass.

Bimetallic Pd–Cu/ZnO–Al2O3 and Pd–Cu/ZrO2–Al2O3 catalysts for methanol synthesis

Monometallic copper and bimetallic palladium-copper catalysts supported on ZnO–Al2O3 and ZrO2–Al2O3 were prepared by conventional impregnation method and tested in methanol synthesis reaction under elevated pressure (3.5 MPa) in gradientless reactor at 220°C. The physicochemical properties of prepared catalytic systems were studied using BET, X-ray, TPR-H2, TPD-NH3 techniques. The promotion effect of palladium on catalytic activity and selectivity of copper supported catalyst in methanol synthesis reaction was proven. The highest activity of this system is explained by the Pd–Cu alloy formation.

Metal Nanoparticles Based Inkjet Ink for Advanced Circuit Board Application

This study investigates the synthesis of mono metallic (copper and silver) and bi-metallic (copper/silver core/shell) conductive nanopigments for inkjet printing. Polyethylene glycol (PEG) was used as a main reducing agent followed by polyvinylpyrrolidone (PVP) as a capping and dispersing agent. From the XRD, TEM, and SEM analyses, the synthesized mono and bi metallic particles were con?rmed to be in a nano scale with particle size 7, 8.5 and 15.5 nm for copper, silver and copper/silver core/shell, respectively. The prepared nanopigments were included in inkjet ink formulation and printed on flexible polyethylene terephthalate (PET) films. The printed ink films were sintered at various temperatures (110, 150, 200). The results revealed that the resistivity of these particles was reduced by sintering and the resistivity of Cu, Ag and Cu/Ag patterns sintered in air at 200 ºC for 30 min were 3.1, 2.99 and 4.14 µ?-cm, respectively. The obtained results were in a good agreement with the published ones and insured the promising using of our products in metal-based inkjet printed circuit boards (PCB).

Bimetallic Pd-Cu/ZnO-Al2O3 and Pd-Cu/ZrO2-Al2O3 Catalysts for Methanol Synthesis

Monometallic copper and bimetallic palladium-copper catalysts supported on ZnO-Al 2 O 3 and ZrO 2 -Al 2 O 3 were prepared by conventional impregnation method and tested in methanol synthesis reaction under elevated pressure (3.5 MPa) in gradientless reactor at 220 °C. The physicochemical properties of prepared catalytic systems were studied using BET, X-Ray, TPR-H 2 , TPD-NH 3 techniques. The promotion effect of palladium on catalytic activity and selectivity of copper supported catalyst in methanol synthesis reaction was proven. The highest activity of this system is explained by the Pd-Cu alloy formation.

MCM-41 modified with transition metals by template ion-exchange method as catalysts for selective catalytic oxidation of ammonia to dinitrogen

Copper, iron and manganese were deposited on MCM-41 using template ion-exchange (TIE) method. Methanol solutions of CuCl2, FeCl2 and MnCl2 were used as precursors of deposited transition metal species. It was shown that introduction of transition metals into MCM-41 by TIE method resulted in deposition of iron and manganese in the form of highly dispersed species (mainly monomeric cations), while in case of copper also CuO crystallites were formed. Such aggregated copper oxide species were not detected in the samples of MCM-41 containing both copper and iron as well as copper and manganese. MCM-41 modified with transition metals by TIE method were found to be active catalysts for the process of the selective oxidation of NH3 to N2 (NH3-SCO), however catalytic performance of the studied samples strongly depended on the type of deposited metal. The samples modified with iron and manganese effectively catalyzed ammonia oxidation to dinitrogen only in the high temperature range. On the other side MCM-41 modified with copper was catalytically active at significantly lower temperatures, however selectivity to dinitrogen decreased at elevated temperatures. It was shown that simultaneous incorporation of copper and iron as well as copper and manganese resulted in the catalysts for the low-temperature NH3-SCO with significantly increased selectivity to dinitrogen in comparison to the monometallic copper containing catalyst.

Comparative Studies of Bimetallic Ru–Cu, Rh–Cu, Ag–Cu, Ir–Cu Catalysts Supported on ZnO–Al2O3, ZrO2–Al2O3 Systems

This paper interrogates the catalytic properties of monometallic copper and various bimetallic Ru–Cu, Rh–Cu, Ag–Cu, Ir–Cu catalysts supported on binary oxide ZrO2–Al2O3 or ZnO–Al2O3 in oxy-steam reforming of methanol reaction. X-ray diffraction, specific surface area and porosity, temperature programmed reduction and temperature programmed desorption were used to characterize monometallic and bimetallic copper supported catalysts. The promoting effect of noble metals on reducibility and catalytic properties of copper catalyst was proven. The activity results showed that rhodium doped copper catalysts supported on ZnO–Al2O3 exhibited the highest conversion of methanol and a high selectivity towards main products of the reaction demonstrating its potential application in fuel cell technology.

A new approach to 4-chlorophenol dechlorination on monometallic copper compared to its Cu/Fe bimetallic system

In this work, with very different mechanism from Cu/Fe bimetallic system, monometallic Cu0 showed an unusually high reductive dechlorination reactivity for 4-chlorophenol (4-CP) in aqueous media. The Cu/Fe bimetallic system showed a typical indirect hydrogenation dechlorination with the main product of phenol, while the monometallic Cu0 showed a direct electron reduction with the main product of cyclohexanone. Cu0 exhibited higher dechlorination activity. The aim of this work was to explore the reasons for the mechanism. Based on our experiments, the high degradation efficiency of monometallic Cu0 should result from the conjugation between electron orbits of Cu0 and large pi bond of the benzene ring of 4-CP. With this mechanism, phenol was also efficiently transformed to cyclohexanone by monometallic Cu0. Although aliphatic chlorinated organic compounds are less chemically stable than aromatic chlorinated organics, Cu0 cannot degrade aliphatic chlorinated organics, such as monochloroacetic acid (MCA) and dichloroacetic acid (DCA). Because no conjugation is existed between them. The conjugation reaction also depends on the purity of the copper surface, a clean, reactive surface of the metal was found to be very important. That is the reason of anions such as AcO−, SO42− inhibited the degradation.

Monometallic copper catalysts supported on multi-walled carbon nanotubes for the oxy-steam reforming of methanol

This paper presents the catalytic properties of monometallic copper catalysts supported on multi-walled carbon nanotubes in the oxy-steam reforming of methanol. Catalytic systems were prepared by the impregnation method and their physicochemical properties were examined using X-ray diffraction (XRD), specific surface area and porosity, temperature programmed reduction and chemisorption methods. The catalytic activity measurements showed that the activity of copper supported catalysts depends on the copper loading, dispersion of metallic copper and reducibility of the investigated catalysts. The most suitable catalytic system for the oxy-steam reforming of methanol was the 20 %Cu/MWCNT catalyst, which exhibited 75 % of methanol conversion at 300 °C and the lowest concentration of CO in the effluent gas. The high activity of 20 %Cu/MWCNT catalyst is explained by the dispersion of the metallic copper and its reducibility.

Cu/MnOx–CeO2 and Ni/MnOx–CeO2 catalysts for the water–gas shift reaction: Metal–support interaction

Monometallic copper and nickel catalysts supported on cerium-manganese mixed oxides are prepared, characterized and evaluated for the Water–Gas Shift (WGS) reaction. Active metal loading of 2.5 wt% and 7.5 wt% are used to impregnate MnOx–CeO2 supports with 30% and 50% Mn:Ce molar ratio. The structure of the samples strongly depends on both the active metal employed and the manganese content in the mixed support. For both Cu and Ni samples, the best catalytic behavior is found in samples supported on the MnOx–CeO2 oxides with 30% Mn:Ce molar ratio, as a result of the presence of CuxMnyO4 spinel-type phases in the case of copper catalysts and the presence of a NiMnO3 mixed oxide with defect ilmenite structure in the case of nickel catalysts.

Identification of synergistic Cu/V redox pair in VCu:AlPO-5; a comparison with VCu:ZSM-5.

Vanadium(V) and copper(II) were co-deposited into AlPO-5 and H-ZSM-5 three-dimensional microporous carriers to yield VCu:AlPO-5 and VCu:ZSM-5. The materials, along with copper analogues were tested for the selective oxidation of propene, and the catalysts perform in the following order: VCu:AlPO-5 > Cu:AlPO-5 > VCu:ZSM-5 > Cu:ZSM-5. Acrolein was selectively formed over VCu:AlPO-5 and Cu:AlPO-5 over a very wide range from 300 to 450 °C, whereas VCu:ZSM-5 displays a limited temperature window for acrolein formation (300-350 °C). Hence, the choice of carrier and presence of vanadium as a co-cation greatly affects the acrolein selectivity and activity window. The vanadium and copper reduction events were monitored by in situ X-ray Absorption Spectroscopy (XAS) during C3H6-TPR (1.11%) to 450 °C. The Cu(II)/(I) redox pair initiates reduction of V(V) → V(IV) in VCu:AlPO-5 and VCu:ZSM-5 at 375 °C. Metallic copper is the major valence fraction above 400 °C in both samples while vanadium is present as V(IV)/V(III) species. In the monometallic copper analogues Cu(I) is the major valence fraction above 350 °C, hence synergistic effects between the Cu/V pair causes hyper-reduction of copper. EXAFS shows that copper and vanadium are in close proximity in VCu:AlPO-5 only, being linked by bridging oxygens (Cu-O-V) believed to interact with propene. By contrast, propene adsorbs on Brønsted sites in VCu:ZSM-5 inhibiting acrolein formation at elevated temperatures, as confirmed by DRIFTS. We believe the reactive Cu/V pair in neutral AlPO-5 generates extralattice oxygens favouring acrolein formation over a wide temperature range.

Catalytic properties of monometallic copper and bimetallic copper-nickel systems combined with ceria and Ce-X (X = Gd, Tb) mixed oxides applicable as SOFC anodes for direct oxidation of methane

The present contribution analyses the possibilities of both Cu and bimetallic Cu-Ni formulations combined with CeO 2-based oxides for their use as anodes of solid-oxide fuel cells (SOFC) for direct oxidation of methane. The main objective is related to examining how the metals combination and the presence of dopants like Gd and Tb into the ceria structure could affect the catalytic activity of this type of materials towards reaction with methane. For this purpose, cermets of Cu alone as well as bimetallic Cu-Ni (with 20 and 40 wt.%) have been synthesised in combination with various supports composed by oxides of Ce, Ce-Tb and Ce-Gd. The behaviour of such systems towards interaction with dry methane up to 900 °C was analysed by means of CH 4-TPR tests. Appreciable differences in the catalytic activity are revealed as a function of the presence of nickel as well as Gd or Tb dopants in the systems. The characteristics of carbonaceous deposits formed upon such interaction was analysed by means of TPO and XPS.

Dehydrogenation of isopropyl alcohol on carbon-supported Pt and Cu–Pt catalysts

The kinetics of isopropyl alcohol (IPA) dehydrogenation over carbon-supported Pt and three bimetallic Cu Pt catalysts were examined and compared with previous results for carbon-supported Cu. Adsorption of H 2 and CO, dissociative chemisorption of N 2O, and the titration of adsorbed O atoms by H 2 and CO were used to determine surface compositions and metal dispersion. Monometallic platinum catalysts had a higher specific activity than monometallic Cu catalysts and the bimetallic catalysts; for example, at 448 K and 14 Torr IPA, for an activated carbon heat treated at 1223 K as the support, the turnover frequency (TOF) on the Pt catalyst was 0.11 s −1, the TOF on the Cu catalyst was 0.020 s −1, and the TOFs on the three bimetallic catalysts were between 0.006 and 0.043 s −1. Reaction orders were typically between 0 and 1 2 for IPA and slightly negative for acetone and H 2. Increasing the Cu loading reduced the number of surface Pt atoms, and the kinetic behavior became similar to that of monometallic copper catalysts. The apparent activation energy for acetone production from IPA on Pt/C was 6.8 kcal mol −1, compared with 21 kcal mol −1 for the monometallic Cu/C catalysts. Apparent activation energies for the Cu Pt/C catalysts (7–9 kcal mol −1) were comparable to those of Pt/C at lower temperatures and decreased further to ∼ 3 kcal mol −1 above 443 K. This decrease is not due to diffusional limitations and can be explained by a decrease in the surface coverage of IPA. A Langmuir–Hinshelwood model invoking cleavage of the alcohol O H bond to form a surface isopropoxide species as the rate-determining step fit the data well and accounted for the shift in the apparent activation energy. Physically meaningful values of enthalpies and entropies of adsorption were obtained from the fitting parameters contained in the L-H rate expression. Additional evidence for adsorbed IPA and acetone was provided by infrared spectra of the catalysts obtained under reaction conditions.

Distinct roles of copper in bimetallic copper–rhodium three-way catalysts deposited on redox supports

Copper (4.7%)–rhodium (0–2000ppm) catalysts deposited on three supports with different oxygen storage capacity (OSC) were tested under three-way catalytic cycling conditions using a low frequency and large composition fluctuations. The reducibility by hydrogen was also studied for all the catalysts in order to assess their OSC. Alumina (Al), ceria–alumina (CeAl) and ceria–zirconia (CeZr) were selected as supports. Both copper and rhodium metals favour the reduction of CeAl and CeZr at low temperature. The catalytic activity of rhodium in CO, NO and C3H6 conversion in presence of oxygen is less influenced by the oxygen mobility of the support. However the OSC of the supports allow to attenuate or even suppress the effects of the composition fluctuations and thus improves the conversion at high temperatures. For monometallic copper catalysts, copper participates in the regulation of the oxidant/reducer ratio and is determinant if the support OSC is insufficient. Moreover, the interaction between copper and the mobile oxygen of the support greatly favours the CO oxidation at low temperature, whereas it has less influence on C3H6 oxidation and disfavours the NO reduction at low temperature. No synergetic effect was observed for the bimetallic CuRh catalysts. In this case, the activity is ruled by the metal or the association metal-support, which is the most active in each temperature range. The association “copper-support exhibiting mobile oxygen” is the most active for CO conversion. NO reduction depends mainly on the rhodium content, especially at low temperature, and C3H6 conversion is a little improved by rhodium addition.

Formation of a Cu II complex through metal-assisted alcoholysis reaction of an oxadiazole-containing dipyridyl ligand: mechanism, characterization and crystal structure

The reaction of 2,5-bis(2-pyridyl)-1,3,4-oxadiazole ( L 1 ) with Cu(OAc) 2·H 2O salt in a CH 3OH/CH 3CN medium produces a new monometallic copper(II) complex 1 [Cu( L 4 )(OAc)(H 2O)](H 2O) 2(CH 3CN), where H L 4 = N-(α-hydroxyl-2-pyridyl)- N′-(α-methoxy-2-pyridyl)ketazine (C 13H 12N 4O 2), which was characterized by IR, UV–vis and elemental analysis, and established by X-ray diffraction technique. The results reveal that metal-assisted alcoholysis of L 1 leads to the open of the central oxadiazole ring to give a new ligand H L 4 during this course. In the crystal structure of complex 1, L 4 acts as a tridentate chelating anionic ligand to coordinate to the Cu II center, which lies in a square-pyramid coordination environment. Additionally, hydrogen-bonding interactions also play an important role in the self-assembly process. The mechanism of the metal-assisted alcoholysis of L 1 in formation of complex 1 was discussed in detail and the spectral properties of 1 were also investigated.

Bimetallic reactivity. On the use of oxadiazoles as binucleating ligands.

Two (1,3,4)-oxadiazole ligands have been prepared. In one case the oxadiazole ring is flanked by two o-aniline groups, and in the other case it is an extension of the first where the amines are condensed with 2-picolyl groups. A monometallic copper(II) complex of the former has been prepared, and its crystal structure was determined. A number of bimetallic copper(II), cobalt(II), and nickel(II) complexes of the di-deprotonated latter ligand were prepared and isolated. The crystal structure of the cobalt(II) complex bearing two acetate bridges is reported. The work demonstrates that the seldom-employed oxadiazole ring can be used effectively for generating bimetallic complexes.

Tetracopper Assembly Complexes Comprised of One Dimetallic Core and Two Monometallic Auxiliaries: Intramolecular Electron-Transfer Relevant to Multicopper Oxidases.

Two tetracopper assembly complexes, comprised of one dimetallic di(3-iminomethylsalicylato)dicopper(II) core and two monometallic copper(II) auxiliaries attached to the imino nitrogens of the dinuclear core through an alkane chain, have been prepared. [Cu(4)(L(1))](PF(6))(4).2CH(3)CN.3H(2)O (1) has di(2-pyridylmethyl)aminecopper(II) as the monometallic auxiliary, and [Cu(4)(L(2))](ClO(4))(4).CH(3)OH (2) has 1,4,8,11-tetraazacyclotetradecanecopper(II) as the auxiliary. Assembly 1 in acetonitrile shows a two-electron reduction at -0.08 V (vs SCE) followed by a one-electron reduction at -0.42 V. Together with EPR studies for electrolyzed solutions, it is shown that the two monometallic auxiliaries are reduced at -0.08 V, followed by an intramolecular electron transfer from one of the reduced auxiliaries to the dimetallic core and by the second reduction at the resulting monometallic Cu(II) center at -0.42 V: {Cu(II)-Cu(2)(II,II)-Cu(II)}/{Cu(I)-Cu(2)(II,II)-Cu(I)} --> {Cu(I)-Cu(2)(I,II)-Cu(II)}/{Cu(I)-Cu(2)(I,II)-Cu(I)}. The CV of 2 in DMSO shows two couples at -0.68 and -0.99 V attributable to the stepwise reductions: {Cu(II)-Cu(2)(II,II)-Cu(II)}/{Cu(II)-Cu(2)(I,II)-Cu(II)}/{Cu(I)-Cu(2)(I,II)-Cu(II)}. Assembly 1 is reduced with ascorbic acid to the {Cu(I)-Cu(2)(I,II)-Cu(I)} species, whereas 2 is not reduced with ascorbic acid. The relevance of the intramolecular electron transfer observed for 1 to multicopper oxidases is discussed.