Zirconia-supported Copper Research Articles

Oxidative dehydrogenation of cyclohexene on atomically precise subnanometer Cu4-nPdn (0 ≤ n ≤ 4) tetramer clusters: the effect of cluster composition and support on performance.

The pronounced effects of the composition of four-atom monometallic Cu and Pd and bimetallic CuPd clusters and the support on the catalytic activity and selectivity in the oxidative dehydrogenation of cyclohexene are reported. The ultra-nanocrystalline diamond supported clusters are highly active and dominantly produce benzene; some of the mixed clusters also produce cyclohexadiene, which are all clusters with a much suppressed combustion channel. The also highly active TiO2-supported tetramers solely produce benzene, without any combustion to CO2. The selectivity of the zirconia-supported mixed CuPd clusters and the monometallic Cu cluster is entirely different; though they are less active in comparison to clusters with other supports, these clusters produce significant fractions of cyclohexadiene, with their selectivity towards cyclohexadiene gradually increasing with the increasing number of copper atoms in the cluster, reaching about 50% for Cu3Pd1. The zirconia-supported copper tetramer stands out from among all the other tetramers in this reaction, with a selectivity towards cyclohexadiene of 70%, which far exceeds those of all the other cluster-support combinations. The findings from this study indicate a positive effect of copper on the stability of the mixed tetramers and potential new ways of fine-tuning catalyst performance by controlling the composition of the active site and via cluster-support interactions in complex oxidative reactions under the suppression of the undesired combustion of the feed.

Glycerol Valorization over ZrO2-Supported Copper Nanoparticles Catalysts Prepared by Chemical Reduction Method

Copper nanoparticles (NPs) and ZrO2-supported copper NPs (Cu NPs/ZrO2) were synthesized via a chemical reduction method applying different pH (4, 7 and 9) and evaluated in a glycerol dehydration reaction. Copper NPs were characterized with transmission electron microscopy (TEM) and UV–vis spectroscopy. Transmission electron microcopy (TEM) results revealed a homogeneous distribution of copper NPs. A hypsochromic shift was identified with UV–vis spectroscopy as the pH of the synthesis increased from pH = 4 to pH = 9. Zirconia-supported copper NPs catalysts were characterized using N2 physisorption, X-ray diffraction (XRD), TEM, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia (NH3-TPD) and N2O chemisorption. The presence of ZrO2 in the chemical reduction method confirmed the dispersion of the copper nanoparticles. X-ray diffraction indicated only the presence of tetragonal zirconia patterns in the catalysts. XPS identified the Cu/Zr surface atomic ratio of the catalysts. TPR patterns showed two main peaks for the Cu NPS/ZrO2 pH = 9 catalyst; the first peak between 125 and 180 °C (region I) was ascribed to more dispersed copper species, and the second one between 180 and 250 °C (region II) was assigned to bulk CuO. The catalysts prepared at pH = 4 and pH = 7 only revealed reduction at lower temperatures (region I). Copper dispersion was determined by N2O chemisorption. With NH3-TPD it was found that Cu NPs/ZrO2 pH = 9 exhibited the highest total quantity of acidic sites and the highest apparent kinetic constant, with a value of 0.004 min−1. The different pH applied to the synthesis media of the copper nanoparticles determined the resultant copper dispersion on the ZrO2 support, providing active domains for glycerol conversion.

Reduction of carbon dioxide via catalytic hydrogenation over copper-based catalysts modified by oyster shell-derived calcium oxide

This research aims to investigate the effects of CaO and modified CaO on copper-based catalysts for methanol synthesis. The CaO and modified CaO were derived from oyster shell and employed as an additive in a zirconia-supported copper catalyst (Cu/ZrO2). The physical and chemical properties of the catalysts were characterized by XRD, BET, CO2-TPD, H2-TPD and XANES. The addition of oyster shell-derived calcium oxide promoters to the catalysts significantly improved their chemical properties and methanol synthesis possibly owing to impurities and defects in the crystal structure of natural calcium oxide.

Thermal and plasmochemical activation of the zirconia-supported copper catalyst for ethanol dehydrogenation

It was shown that copper-containing nanocomposites based on t-zirconium dioxide 5% Cu/t-ZrO2 can be activated using preliminary treatments in high-frequency (HF) hydrogen plasma and critical low-temperature treatments. The increased activity was explained by the formation of many active centers due to the creation of additional t-zirconia defects as a result of the redistribution of copper ions on its surface before the reductive treatment.

The conversion of glycerol to lactic acid catalyzed by ZrO2-supported CuO catalysts

Zirconia-supported copper oxide catalysts with various compositions were prepared and characterized by atomic absorption spectroscopy, N2 physical adsorption, temperature programmed reduction, powder X-ray diffraction and X-ray photoelectron spectroscopy. These catalysts were evaluated for the conversion of glycerol to lactic acid in aqueous solution in the presence of a base and under an inert atmosphere. The results showed that CuO/ZrO2 with ∼30% Cu loading exhibited the highest activity for the conversion of glycerol. Under optimum conditions, 100% glycerol conversion and 94.6% selectivity for lactic acid were obtained over 30%CuO/ZrO2 when reacting 10mL of glycerol solution (1.4M), using 0.2g catalyst in the presence of NaOH (1:1 NaOH/glycerol molar ratio) at 453K and 1.4MPaN2 for 8h. Moreover, the reusability of 30%CuO/ZrO2 was investigated, and a reaction mechanism for the conversion of glycerol is proposed.

Zirconia-Supported Copper and KNO3 Catalysts for Diesel Soot Combustion. Deactivation by Hydrotreatment and SO2

In this study, the sulfur tolerance and hydrothermal stability of Cu-KNO3/ZrO2 catalysts in catalytic diesel soot oxidation were investigated. Supported alkaline nitrate catalysts have shown excellent activity for soot oxidation in the presence of O2 or NO/O2. High-temperature water vapor treatments do not affect the catalytic activity, suggesting a good hydrothermal stability of the catalysts. Treatments performed at high SO2 concentration lead to a partial deactivation of the catalysts for the combustion reaction in the presence of O2. The presence of copper improves the sulfur tolerance of the KNO3/ZrO2 catalyst for the combustion of soot in the presence of NOx. NO/O2 present in the feed flow of the reactor can regenerate in situ nitrate anions that provide the redox cycles required for the reaction. Keywords: Diesel soot, Combustion, Hydrothermal stability, SO2.

Structure and State of Copper Oxide Species Supported on Yttria-Stabilized Zirconia

The structure and state of the active component-copper species in zirconia-supported copper catalysts with yttria-stabilized zirconia as a support were investigated. Catalysts with different copper contents (2−10 wt % of Cu) prepared by an impregnation technique were characterized by X-ray diffraction (XRD) analysis, radial distribution function (RDF) of electronic density method, X-ray absorption fine structure (XAFS) analysis, UV−visible diffuse reflectance spectroscopy (UV−vis DRS), and X-ray photoelectron spectroscopy (XPS). It was established that a small amount of copper could be incorporated in the zirconia fluorite lattice, while the main portion of the copper was situated on the support surface as finely dispersed copper oxide chain clusters.

Structural Evolution and Catalytic Properties of Nanostructured Cu/ZrO2 Catalysts Prepared by Oxalate Gel-Coprecipitation Technique

A series of zirconia-supported copper oxide catalysts synthesized by decomposition of the oxalate precursors formed by oxalate gel-coprecipitation in alcoholic solution were extensively investigated in relation to their performance in methanol steam reforming. The combination of different techniques (N2 adsorption, X-ray diffraction (XRD), N2O titration, H2-TPR, diffuse reflectance Fourier transform infrared, Raman, and X-ray photoelectron spectroscopy) in the characterization of Cu/ZrO2 catalysts shows that the surface and structural characteristics of the zirconia phase as well as the dispersion and nature of the copper species depend strongly on the calcination temperature. Temperature-programmed reduction patterns reveal the presence of three types of copper species on the ZrO2 support. XRD results indicate that, depending on the calcination temperature, a substantial incorporation of Cu species into the zirconia lattice leading to a strong Cu−ZrO2 metal−support interaction may occur. The N2O titration reveals that the 550 °C calcined material exhibits the highest metallic copper surface area as compared to other samples, as opposed to in situ XRD analysis showing that the lower the calcination temperature the higher the copper dispersion. Spectroscopic measurements reveal that the phase transformation of zirconia from tetragonal to monoclinic takes place initially at the surface regions of the Cu−ZrO2 sample, as evidenced from the fact that the monoclinic phase can be detected first by Raman spectroscopies for the samples calcined at a lower temperature than by XRD. The highest activity was achieved for the 550 °C calcined material, illustrating that the creation of monoclinic phase enriched on the surface of tetragonal zirconia in Cu/ZrO2 are beneficial for the generation of copper catalyst with enhanced activities.

Zirconia-Supported Copper Oxide—A Catalyst for Removal of Vehicular Exhaust Gas Pollutants

Copper oxide and zirconia-supported copper oxide catalysts were tested for their catalytic activity for carbon monoxide and propylene oxidation reactions. The synthesized catalyst was supported by wet impregnation on zirconia. The higher activity of zirconia-supported catalyst compared to unsupported catalyst may be attributed to homogeneous and higher dispersion on zirconia, ionic oxygen carrying capacity of zirconia. Catalyst 10% CuO∕Zr O2 showed a best conversion efficiency of 90% at a temperature as low as 265°C for CO oxidation. T50 and T100 for propylene oxidation on zirconia-supported copper oxide were 392 and 450°C , respectively.

Effect of zirconia phase on the reduction behaviour of highly dispersed zirconia-supported copper oxide

Reduction processes of copper oxide supported both on tetragonal and on monoclinic zirconia were investigated by means of hydrogen temperature-programmed reduction (H 2-TPR). Results show that there exists apparent difference between the reduction behaviour of highly dispersed CuO supported on these two-phase zirconia; while two reduction peaks appear in the H 2-TPR profile of monoclinic zirconia-supported monolayer CuO, only one reduction peak at low temperature is developed for tetragonal zirconia-supported counterpart.

FT-IR spectroscopic investigation of the reactivity of NOx species adsorbed on Cu2+/ZrO2 and CuSO4/ZrO2 catalysts toward decane

The nature of the NOx species produced on NO adsorption and its co-adsorption with O2 at room temperature on zirconia-supported copper(II) catalysts has been studied by means of in situ FT-IR spectroscopy. The samples were prepared by impregnation of zirconia with aqueous solutions of copper(II) nitrate and sulfate. The structural identification of the surface NOx complexes exhibiting absorptions in the fundamental nitro–nitrato region was performed by analyzing the combination bands of the nitrate species. In order to understand which factors control the selectivity of the catalysts in the catalytic reduction of NO by longer chain hydrocarbons, the stability of surface nitro–nitrato species and their reactivity toward adsorbed decane at various temperatures was investigated. The nitrates on the CuSO4/ZrO2 catalyst are characterized by significantly lower thermal stability than the nitro–nitrato species on the Cu2+/ZrO2 sample. The difference in the thermal stability of the NOx− species (x is 2 and 3) parallels their reactivity toward the adsorbed decane. The sulfate-free catalyst contains bidentate nitro species that are inert toward the hydrocarbon. The bidentate nitro species start to decompose to NO at temperatures higher than 523K. In contrast, the nitrate species formed on the CuSO4/ZrO2 catalyst are able to oxidize the adsorbed decane completely at 523K producing acetates, formates, adsorbed CO and isocyanate species. It is proposed that the presence of stable nitro species on the sulfate-free copper(II)-zirconia catalyst is associated with its non-selective behavior above 573K in the reduction of NO with decane in an excess of oxygen reported in the literature.

Effects of Zirconia Phase on the Synthesis of Methanol over Zirconia-Supported Copper

A study has been conducted to identify the influence of zirconia phase and copper to zirconia surface area on the activity of Cu/ZrO2 catalysts for the synthesis of methanol from either CO/H2 or CO2/H2. To determine the effects of zirconia phase, a pair of Cu/ZrO2 catalysts was prepared on tetragonal (t-) and monoclinic (m-) zirconia. The zirconia surface area and the Cu dispersion were essentially identical for these two catalysts. At 548 K, 0.65 MPa, and H2/COx= 3 (x = 1, 2), the catalyst prepared on m-ZrO2 was 4.5 times more active for methanol synthesis from CO2/H2 than that prepared on t-ZrO2, and 7.5 times more active when CO/H2 was used as the feed. Increasing the surface area of m-ZrO2 and the ratio of Cu to ZrO2 surface areas further increased the methanol synthesis activity. In situ infrared spectroscopy and transient-response experiments indicate that the higher rate of methanol synthesis from CO2/H2 over Cu/m-ZrO2 is due solely to the higher concentration of active intermediates. By contrast, the higher rate of methanol synthesis from CO/H2 is due to both a higher concentration of surface intermediates and the more rapid dynamics of their transformation over Cu/ZrO2.

First principles study of carbon monoxide adsorption on zirconia-supported copper

We have calculated the adsorption energy of carbon monoxide on a monolayer of copper adsorbed on the (1 1 1) face of cubic zirconia. For the bulk oxide, we compute the structural parameters of cubic, tetragonal, and monoclinic ZrO 2 and obtain good agreement with experimental parameters. We also analyze the structural relaxation of the stoichiometric, oxidized and reduced (1 1 1) surfaces of cubic zirconia (c-ZrO 2). For adsorption of copper on stoichiometric c-ZrO 2, we find that the preferred binding site is atop the terminal oxygen atom, favored by 0.4 eV over other high symmetry sites. Charge density rearrangement reveals that adsorption on the oxide support causes a depletion of charge from the Cu d z 2 orbitals. Consequently, CO adsorption on zirconia-supported copper is significantly stronger than CO adsorption on clean c-ZrO 2 or clean Cu(1 0 0).

XAFS study of zirconia-supported copper catalysts for the NO–CO reaction: Deactivation, rejuvenation and stabilization of Cu species

A Cu/ZrO2 (1 wt.% Cu) catalyst shows high activity for the NO–CO reaction, even at low temperature (100–200 °C). However, the low-temperature activity is easily lost during prolonged reaction at 250 °C. The activity of the deactivated Cu/ZrO2 catalyst is completely restored by NO treatment (1% in He) at >250 °C or O2 treatment (5% in He) at 500 °C. The addition of iron (2 wt.%) to Cu/ZrO2 causes not only a dramatic increase in the low-temperature activity but also high stability against deactivation. An X-ray absorption fine structure (XAFS) study has been conducted to reveal the local structure and chemical state of the Cu species in Cu/ZrO2 and Cu–Fe/ZrO2 during the reaction and rejuvenation. X-ray absorption near-edge structure (XANES) spectra and, in particular, their first derivatives are shown to be very effective for characterization of the Cu species. It is revealed that the deactivation of Cu/ZrO2 is a consequence of reduction and sintering of highly dispersed Cu+ species, derived from Cu2+(Oct) species in an octahedral symmetry, to Cu metal particles. The Cu metal particles in a deactivated Cu/ZrO2 catalyst are transformed into the original Cu2+(Oct) species by the NO treatment at 250 °C via highly dispersed Cu+ species. On the other hand, O2 treatments bring about successive formation of Cu2O at 150 °C and CuO at 250 °C. The Cu2+(Oct) species are reformed at >400 °C. The XAFS study of Cu–Fe/ZrO2 suggests that the high stability of highly dispersed Cu+ species is a consequence of direct interaction of Cu species with iron oxide clusters. On the basis of kinetics and XAFS results, the catalytic synergies between Cu and Fe are inferred to be two-fold: stabilization of highly dispersed and catalytically active Cu+ species during the reaction and simultaneous participation of both Cu and Fe in the reaction.

Effect of Oxygen Vacancy on CO−NO−O2 Reaction over Yttria-Stabilized Zirconia-Supported Copper Oxide Catalyst

The effect of oxygen vacancy on the enhancement of activity of CO−NO−O2 reaction over yttria-stabilized zirconia (YSZ)-supported CuO catalyst was investigated in the present study. The catalysts were prepared by the impregnation method, and their characteristics were studied by temperature-programmed reduction. The catalyst was placed in a flow reactor for performing the temperature-programmed reaction, and the effluent gas was analyzed by an on-line NOx analyzer, consisting of a chemiluminescence unit and two gas chromatographs in series. The present results indicate that copper oxide supported by YSZ exhibits a higher catalytic activity than that supported by α-Al2O3, for the CO−NO−O2 reaction. The enhanced activity is inferred to result from the formation of interfacial Cu2O and the oxygen-ion transfer. Additionally, the probable effect of oxygen vacancy in promoting the CO−O2 or CO−NO2 reaction has been elucidated by a mechanism involving oxygen-ion transfer via surface oxygen vacancies of YSZ, which are located at the interface between CuO and YSZ. It was found that the CuO/YSZ catalyst is a promising substitute for the conventional Rh/alumina catalyst.

Zirconia-supported copper catalysts for NO[ndash ]CO reactions Surface copper species on zirconia

Download options Please wait... Article information DOI https://doi.org/10.1039/A704625A Article type Paper Download Citation J. Chem. Soc., Faraday Trans., 1997,93, 3879-3885 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Zirconia-supported copper catalysts for NO[ndash ]CO reactions Surface copper species on zirconia Y. Okamoto, H. Gotoh, H. Aritani, T. Tanaka and S. Yoshida, J. Chem. Soc., Faraday Trans., 1997, 93, 3879 DOI: 10.1039/A704625A To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Yasuaki Okamoto Hideki Gotoh Hirofumi Aritani Tsunehiro Tanaka Satohiro Yoshida