Superconducting properties of binary rare-earth HoREBCO thin films prepared by pulsed layer deposition

The superconducting properties of REBa₂Cu₃O_y (REBCO or RE123, RE = rare earth elements) coated conductors could essentially depend on the rare earth elements, which could be the premise of all potential superconducting applications. In this paper, Ho_0.75RE_0.25Ba₂Cu₃O_7-σ (HoREBCO, RE = Dy, Er, Yb) high temperature superconducting films were fabricated successfully by a reel-to-reel pulsed laser deposition (PLD) system for the first time. By replacing Ho elements with heavy rare earth elements in a certain mole ratio, the critical currents of the HoREBCO superconducting films were improved significantly compared with pure HoBCO films. The lattice distortions are considered as the determinative factors of the changes. The replacement of Ho atoms by Dy, Er or Yb also influenced the structure and the surface morphology of the superconducting films. The decrease of the lattice constant in HoREBCO superconducting film and the variation of the interatomic force play the decisive role in the improvement of the superconducting property.     

Catalytic combustion of volatile aromatic compounds over CuO-CeO<Subscript>2</Subscript> catalyst

Ce_1?x Cu _x O₂ oxide solid solution catalysts with different Ce/Cu mole ratios were synthesized by the one-pot complex method. The prepared Ce_1?x Cu _x O₂ catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and H₂ temperature-programmed reduction (H₂-TPR). Their catalytic properties were also investigated by catalytic combustion of phenyl volatile organic compounds (PVOCs: benzene, toluene, xylene, and ethylbenzene) in air. XRD analysis confirmed that the CuO species can fully dissolve into the CeO₂ lattice to form CeCu oxide solid solutions. XPS and H²-TPR results indicated that the prepared Ce_1?x Cu _x O₂ catalysts contain abundant reactive oxygen species and superior reducibility. Furthermore, the physicochemical properties of the prepared Ce_1?x Cu _x O₂ catalysts are affected by the Ce/Cu mole ratio. The CeCu₃ catalyst with Ce/Cu mole ratio of 3.0 contains abundant reactive oxygen species and exhibits superior catalytic combustion activity of PVOCs. Moreover, the ignitability of PVOCs is also affected by the respective physicochemical properties. The catalytic combustion conversions of ethylbenzene, xylene, toluene, and benzene are 99%, 98.9%, 94.3%, and 62.8% at 205, 220, 225, and 225 °C, respectively.     

Effect of Pretreatment Atmosphere on CuO/TiO2 Activities in NO + CO Reaction

Using TiO₂ as carrier, CuO/TiO₂ catalysts with different CuO loading were prepared by the impregnation method. The catalytic activities in NO+CO reaction were examined with a micro-reactor gas chromatography reaction system and the methods of TPR, XPS and NO-TPD. It was found that the catalytic activities were affected by pretreatment atmosphere, i.e. H₂ atmosphere > reduction–reoxidation > 10%CO/He > reaction gas (fresh sample). NO decomposition was better by low-valence Cu species than by high-valence Cu species, i.e. Cu⁰>Cu⁺>Cu²⁺. The XPS results indicated that Cu species on CuO/TiO₂ were Cu⁰, Cu⁺, normal Cu²⁺(Cu²⁺(I)) and chain-structured Cu²⁺(Cu²⁺(II)) as –Cu–O–Ti–O–. The activities of Cu²⁺(II) were much higher than that of Cu²⁺(I), but both species were very unstable in the reaction atmosphere and easily reduced by CO, which accounted for the variable activities of fresh catalysts with increasing reaction temperature. In NO+CO reaction, the redox process was a cycle of Cu⁺–Cu²⁺(I) at low reaction temperature but was a cycle of Cu⁰–Cu⁺ at high reaction temperature. As shown by NO-TPD, high catalytic activities could be attributed to the following factors, e.g. oxygen caves on the catalyst’s surface after pretreatment with H₂ and reduction–reoxidation, formation of Cu⁰ after pretreatment with H₂, and increment of Cu species dispersion and formation of Cu²⁺(II) after pretreatment with reduction–reoxidation.     

Comparative Study on Catalytic Performances for Low-temperature CO Oxidation of Cu–Ce–O and Cu–Co–Ce–O Catalysts

Two series of Cu–Ce–O and Cu–Co–Ce–O catalysts were prepared by co-precipitation method. The prepared catalysts were characterized by XRD, IR, TPR, XPS, BET and ICP-AES. The catalytic activities of the catalysts for low-temperature CO oxidation were evaluated through a microreactor-GC system. TPR results indicate that the addition of cobalt to the Cu–Ce–O can increase the dispersion of copper oxide, and the interaction between cobalt and copper can enhance the reducibility of each other. XPS analysis show that Ce⁴⁺, Cu²⁺, along with Co₃O₄, are present on the surface of Cu_0.4Co_0.6Ce₄ catalyst. The Co/Cu atomic ratio and the calcination temperature have significant effect on the activities of the catalysts. Compared with Cu₁Ce₄ catalyst, the Cu_0.4Co_0.6Ce₄ catalyst has better activity and thermal stability.     

Cobalt(II), Copper(II) and Zinc (II) complexes of 2-methyl benzimidazole encapsulated in zeolite as catalysts for the hydroxylation of phenol

Cobalt(II), Copper(II) and Zinc (II) complexes of 2-methylbenzimidazole (Mebzlh) encapsulated in the super cages of zeolite-Y and ZSM-5 have been synthesized by flexible ligand method and characterized by various physico-chemical measurements. The catalytic activity of encapsulated complexes was investigated for the decomposition of H₂O₂ and for the hydroxylation of phenol using H₂O₂ as an oxidant. The hydroxylation of phenol yielded catechol and hydroquinone as the major products. All catalysts show good selectivity for diphenol products. The results showed that conversion of phenol varies in the order [Cu(Mebzlh)]-Y > [Cu(Mebzlh)]-ZSM-5 > [Zn(Mebzlh)]-Y > [Co(Mebzlh)]-Y > [Zn(Mebzlh)]-ZSM-5 > [Co(Mebzlh)]-ZSM-5 after 6 h of reaction time.     

Hydroxylation of phenol with H2O2 over transition metal containing nano-sized hollow core mesoporous shell carbon catalyst

The catalytic performance of transition metal (Fe²⁺ or Cu²⁺) containing nano-sized hol low core mesoporous shell carbon (HCMSC) heterogeneous catalysts for the hydroxylation of phenol with hydrogen peroxide (H₂O₂) in water was investigated in a batch reactor. The metal-containing HCMSC catalyst showed higher activity than the same metal ion-exchanged zeolites. The nature of the metal and its content in the HCMSC had remarkable influence on the reaction results under the typical reaction conditions (PhOH/H₂O₂=3, reaction temperature=60 ‡C). Fe²⁺ containing HCMSC catalyst showed high catalytic activity with phenol conversion of 29%, selectivity to catechol (CAT) and hydroquinone (HQ) about 85%, H₂O₂ effective conversion about 70% and selectivity to benzoquinone (BQ) below 1% in the batch system.     

Comparison of the surface and catalytic properties of rare earth‐promoted CaO catalysts in the oxidative coupling of methane

Rare earth (viz. La, Ce, Sm, Nd and Yb) promoted CaO catalysts have been investigated, comparing their surface properties (viz. surface area and basicity/base strength distribution) and catalytic activity/selectivity in the oxidative coupling of methane at different reaction conditions (temperatures, 650–800 °C, CH₄/O₂ ratios, 2.0–8.0 and space velocity, 51 360 cm³ g^?1 h^?1). The surface properties and catalytic activity/selectivity are strongly influenced by the rare earth promoter and its concentration. Apart from the Sm‐promoted CaO catalyst, both the total and strong basic sites (measured in terms of CO₂ chemisorbed at 50° and 500 °C respectively) are decreased due to the promotion of CaO by rare earth metals (viz. La, Ce, Nd and Yb). The catalytic activity/selectivity is strongly influenced by the temperature, particularly below ?700 °C, whereas at higher temperature no further effect is seen. The La₂O₃? CaO, Nd₂O₃? CaO and Yb₂O₃? CaO catalysts showed high activity and selectivity, and also their results are comparable. Among the catalysts, Nd‐promoted CaO (with Nd/Ca = 0.05) showed the best performance (19.5% CH₄ conversion with 70.8% C₂₊ selectivity) in the oxidative coupling of methane. A close relationship between the surface density of total and strong basic sites (measured in terms of CO₂ chemisorbed at 50° and 500 °C respectively) and the C₂₊ selectivity and/or C₂₊ yield has been observed. Copyright © 2005 Society of Chemical Industry     

π‐Complexation Studied by Fluorescence Technique: Application in Desulfurization of Petroleum Product using Magnetic π‐Complexation Sorbents

Abstract

Magnetic π‐complexation sorbents were studied for petroleum product desulfurization by fluorescent technique. The ability of metal cation to form π‐complexation decreases in the order following: Cu⁺>Ni²⁺>Co²⁺>Al³⁺. The order is consistent with that of desulfurization performance of their corresponding magnetic sorbents (γ‐Al₂O₃‐Cu(I)>γ‐Al₂O₃‐Ni(II)>γ‐Al₂O₃‐Co(II)>γ‐Al₂O₃). Both π‐complexation strength and desulfurization performance of the sorbents increase with temperature. The adsorptive performances of magnetic γ‐Al₂O₃‐Cu(I) sorbent to different compounds have the following orders: DBT>fluorene, and pyrene>naphthalene>benzene, respectively. In this study, dibenzothiophene (DBT) was used as a model sulphur‐containing compound for desulfurization. The maximal adsorption amount of magnetic γ‐Al₂O₃‐Cu(I), was 0.362 mmol DBT g^?1.     

Rare‐Earth Free Phosphors with Ultra‐Broad Band Emission Application for High Color Rendering Index Lighting Source

Rare‐earth containing phosphors have been widely applied in lighting and display fields in the past century. Lower cost rare‐earth free phosphors with high performance are highly desired driven by the exhaustion of rare earth resources and the requirement of cheaper production. Herein, Cu⁺ ions doped tetracalcium phosphate (TTCP) yellow emitting phosphors with quantum yield of 21% are exploited. Particularly, ultra‐broad band emission with a full width at half maximum (FWHM) about 200 nm throughout almost entire visible light region is observed for TTCP: Cu⁺ phosphors, evidencing its promising application in high color rendering index (CRI) lighting source. White light emission with CRI value about 94.3 is generated by combining this TTCP: Cu⁺ phosphor with commercial BaMgAl₁₀O₁₇: Eu²⁺ blue phosphor, exhibiting superiority over the traditional trichromatic phosphors. Therefore, we predict great potential application for this cheaper rare‐earth free TTCP: Cu⁺ phosphor in high CRI lighting sources.     

CuO and CuO-ZnO catalysts supported on CeO2 and CeO2-LaO3 for low temperature water-gas shift reaction

This paper describes an investigation on CuO and CuO-ZnO catalysts supported on CeO₂ and CeO₂-La₂O₃ oxides, which were designed for the low temperature water-gas shift reaction (WGSR). Bulk catalysts were prepared by co-precipitation of metal nitrates and characterized by energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), surface area (by the BET method), X-ray photoelectron spectroscopy (XPS), and in situ X-ray absorption near edge structure (XANES). The catalysts' activities were tested in the forward WGSR, and the CuO/CeO₂ catalyst presented the best catalytic performance. The reasons for this are twofold: (1) the presence of Zn inhibits the interaction between Cu and Ce ions, and (2) lanthanum oxide forms a solid solution with cerium oxide, which will cause a decrease in the surface area of the catalysts. Also the CuO/CeO₂ catalyst presented the highest Cu content on the surface, which could influence its catalytic behavior. Additionally, the Cu⁰ and Cu¹⁺ species could influence the catalytic activity via a reduction-oxidation mechanism, corroborating to the best catalytic performance of the Cu/Ce catalyst.     

High‐performance HTLcs‐derived CuZnAl catalysts for hydrogen production via methanol steam reforming

A series of CuZnAl oxide‐composite catalysts were prepared via decomposition of CuZnAl hydrotalcite‐like compounds (HTLcs). The catalysts derived from CuZnAl HTLcs (Cu: 37%, Zn: 15%, Al: 48% mol; using metal nitrate or acetate precursors) at 600°C provided excellent activity and stability for the methanol steam reforming. CuZnAl HTLcs were almost decomposed completely at 600°C to form highly dispersed CuO with large specific surface area while forming CuAl₂O₄ spinel that played a key role in separating and stabilizing the nano‐sized Cu and ZnO during the reaction. The CuZnAl catalyst prepared from metal acetates could highly convert H₂O/MeOH (1.3/1, mol/mol) mixture into hydrogen with only ～0.05% CO at 250°C or ～0.005% at 210°C. It is evidenced that the former afforded stronger Cu‐ZnO interaction, which might be the intrinsic reason for the significant promotion of catalyst selectivity. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Catalytic combustion of SOFC stack flue gas over CuO and Mn2O3 supported by La0.8Sr0.2Mn0.67Cu0.33O3 perovskite

An efficient oxidation catalyst was developed to increase the combustion efficiency of unreacted CO, H₂, and CH₄ in flue gas of solid oxide fuel cell (SOFC) stack. Amorphous Cu‐Mn oxide catalyst (CuMnLa/Alumina) showed high catalytic activity, but significant degradation occurred due to phase transition to spinel structure at high temperatures (T > 650°C). La_0.8Sr_0.2Mn_0.67Cu_0.33O₃ perovskite (LSMC(p)) supported CuO or Mn₂O₃ exhibited improved thermal stability than CuMnLa/Alumina catalyst. Especially in case of 50Mn/LSMC(p), after the catalyst was exposed to 800°C for 24 h, T₅₀ of CO, H₂ and CH₄ was achieved at 170, 230, and 600°C, respectively. This result is much lower than that of CuMnLa/Alumina, which was exposed to the same condition. The high combustion efficiency is due to retention of the Cu²⁺‐Mn³⁺ redox couple, and supply of lattice oxygen from LSMC(p), especially at high temperature. © 2017 American Institute of Chemical Engineers AIChE J, 64: 940–949, 2018     

Cobalt and Copper Composite Oxides as Efficient Catalysts for Preferential Oxidation of CO in H2-Rich Stream

A series of Co–Cu composite oxides with different Co/Cu atomic ratios were prepared by a co-precipitation method. XRD, N₂ sorption, TEM, XPS, H₂-TPR, CO-TPR, CO-TPD and O₂-TPD were used to characterize the structure and redox properties of the composite oxides. Only spinel structure of Co₃O₄ phase was confirmed for the Co–Cu composite oxides with Co/Cu ratios of 4/1 and 2/1, but the particle sizes of these composite oxides decreased evidently compared with Co₃O₄. These composite oxides could be reduced at lower temperatures than Co₃O₄ by either H₂ or CO. CO and O₂ adsorption amounts over the composite oxides were significantly higher than those over Co₃O₄. These results indicated a strong interaction between cobalt and copper species in the composite samples, possibly suggesting the formation of Cu _x Co_3?x O₄ solid solution. For the preferential oxidation of CO in a H₂-rich stream, the Co–Cu composite oxides (Co/Cu = 4/1–1/1) showed distinctly higher catalytic activities than both Co₃O₄ and CuO, and the formation of Cu _x Co_3?x O₄ solid solution was proposed to contribute to the high catalytic activity of the composite catalysts. The Co–Cu composite oxide was found to exhibit higher catalytic activity than several other Co₃O₄-based binary oxides including Co–Ce, Co–Ni, Co–Fe and Co–Zn oxides.     

Gas‐Phase Hydrogenolysis of Glycerol Catalyzed by Cu/MOx Catalysts

The catalytic activities of Cu/MO_x (MO_x = Al₂O₃, TiO₂, and ZnO) catalysts in the gas‐phase hydrogenolysis of glycerol were studied at 180–300 °C under 0.1 MPa of H₂. Cu/MO_x (MO_x = Al₂O₃, TiO₂, and ZnO) catalysts were prepared by the incipient wetness impregnation method. After reduction, CuO species were converted to metallic copper (Cu⁰). Cu/Al₂O₃ catalysts with high acidity, high specific surface areas and small metallic copper size favored the formation of 1,2‐propanediol with a maximum selectivity of 87.9 % at complete conversion of glycerol and a low reaction temperature of 180 °C, and favored the formation of ethylene glycol and monohydric alcohols at high reaction temperature of 300 °C. Cu/TiO₂ and Cu/ZnO catalysts exhibited high catalytic activity toward the formation of hydroxyacetone with a selectivity of approx. 90 % in a wide range of reaction temperature.     

Oxidation of carbon monoxide over barium cuprate catalysts

Catalytic activities of BaCuO₂, Ba₂Cu₃O₅ and CuO for CO oxidation were investigated. At 250 ° C, BaCuO₂ was found to be about 7 times more active than CuO, while Ba₂Cu₃O₅ was found to be only slightly more active than CuO. This result also demonstrates that expensive rare earth elements such as La and Y are not necessary for a cuprate to have good activity for CO oxidation. After sintering at 940 ° C in air, the conversion substantially decreased for CuO. At steady state, both barium cuprates exhibited higher activity than in the fresh state. Based on the absence of significant changes in the XRD spectra, the change in catalytic activity is attributed to changes at the surface and possibly slight reduction of Cu²⁺. Reaction orders of CO were found to be 1.2 and 0.3, and reaction orders of O₂ were found to be 0 and 0.3 for BaCuO₂ and Ba₂Cu₃O₅, respectively.     

Influence of rare-earth elements (La,Ce, Nd and Pr) on the performance of Cu/Zn/Zr catalyst for CH3OH synthesis from CO2

A series of Cu/Zn/Zr (CZZ) catalysts with different rare earth elements (La, Ce, Nd and Pr) were prepared by co-precipitation method and tested for CO₂ hydrogenation to methanol. The influence of modifier (La, Ce, Nd and Pr) on the physicochemical properties of CZZ catalysts was studied. The results of catalytic test reveal that CO₂ conversion was correlated to the introduction of different promoters. The introduction of La and Ce favors the production of methanol, and Nd and Pr modified CZZ catalysts show relative low activity compared with the reference CZZ catalyst.     

Liquid‐phase hydrogenation of cinnamaldehyde over Cu‐Au/SiO2 catalysts

The synthesis, characterization, and application of silica‐supported Cu‐Au bimetallic catalysts in selective hydrogenation of cinnamaldehyde are described. The results showed that Cu‐Au/SiO₂ bimetallic catalysts were superior to monometallic Cu/SiO₂ and Au/SiO₂ catalysts under identical conditions. Adding a small amount of gold (6Cu‐1.4Au/SiO₂ catalyst) afforded eightfold higher catalytic reaction rate compared to Cu/SiO₂ along with the high selectivity (53%, at 55% of conversion) toward cinnamyl alcohol. Characterization techniques such as x‐ray diffraction, H₂ temperature‐programmed reduction, ultraviolet‐visible spectroscopy, transmission electron microscopy, Fourier‐transform infrared spectra of chemisorbed CO, and x‐ray photoelectron spectroscopy were employed to understand the origin of the catalytic activity. A key genesis of the high activity of the Cu‐Au/SiO₂ catalyst was ascribed to the synergistic effect of Cu and Au species: the Au sites were responsible for the dissociative activation of H₂ molecules, and Cu⁰ and Cu⁺ sites contributed to the adsorption‐activation of C?C and C?O bond, respectively. A combined tuning of particle dispersion and its surface electronic structure was shown as a consequence of the formation of Au‐Cu alloy nanoparticles, which led to the significantly enhanced synergy. A plausible reaction pathway was proposed based on our results and the literature. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3300–3311, 2014     

Preparation of CuxCe1?xO2?x/SBA-15 catalysts and the catalytic properties of CO oxidation

Cu_xCe_1?xO_2?x/SBA-15 (x?=?0?C1) catalysts were prepared using the mesoporous silica material SBA-15 as the support. The catalysts were characterized by N₂ adsorption?Cdesorption, X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction. The catalytic activity of the catalysts for the oxidation of CO was evaluated and the activation energies were obtained by avoiding internal and external diffusions. The results indicated that highly dispersed CuO was formed in the obtained catalysts when the Cu content was low. Co-impregnation with Cu and Ce salt solutions does not destroy the SBA-15 mesoporous structure. Both Cu²⁺ and Cu⁺ existed on the surface of the obtained catalysts, while the Ce⁴⁺ was the main Ce species. All the obtained catalysts showed excellent activities for the combustion of CO. CO could be totally oxidized at 187?°C at the space velocity of 48,000?mL/(g?h).     

Synergistic extraction of rare earths(III) from chloride medium with mixtures of 1‐phenyl‐3‐methyl‐4‐benzoyl‐pyrazalone‐5 and di‐(2‐ethylhexyl)‐2‐ethylhexylphosphonate

The synergistic effect of 1‐phenyl‐3‐methyl‐4‐benzoyl‐pyrazalone‐5 (HPMBP, HA) and di‐(2‐ethylhexyl)‐2‐ethylhexylphosphonate (DEHEHP, B) in the extraction of rare earths (RE) from chloride solutions has been investigated. Under the experimental conditions used, there was no detectable extraction when DEHEHP was used as a single extractant while the amount of RE(III) extracted by HPMBP alone was also low. But mixtures of the two extractants at a certain ratio had very high extractability for all the RE(III). For example, the synergistic enhancement coefficient was calculated to be 9.35 for Y³⁺, and taking Yb³⁺ and Y³⁺ as examples, RE³⁺ is extracted as RE(OH)A₂.B. The stoichiometry, extraction constants and thermodynamic functions such as Gibbs free energy change ΔG (?17.06 kJ mol^?1), enthalpy change ΔH (?35.08 kJ mol^?1) and entropy change ΔS (?60.47 J K^?1 mol^?1) for Y³⁺ at 298 K were determined. The separation factors (SF) for adjacent pairs of rare earths were calculated. Studies show that the binary extraction system not only enhances the extraction efficiency of RE(III) but also improves the selectivity, especially between La(III) and the other rare earth elements. Copyright © 2006 Society of Chemical Industry     

Powellite‐Rich Glass‐Ceramics: A Spectroscopic Study by EPR and Raman Spectroscopy

The aim of this study was to better understand the incorporation of rare‐earth elements in glass‐ceramics of nuclear interest. We synthesized glass‐ceramics from glasses in the system SiO₂–B₂O₃–Na₂O–CaO–Al₂O₃–MoO₃–Gd₂O₃ by various heat treatments. Gadolinium is used both as a spectroscopic probe and as a minor actinide surrogate. Glass‐ceramics contain only one crystalline phase in the bulk: powellite (CaMoO₄). This phase can incorporate Gd³⁺ and Na⁺ ions by substitutions on the Ca site. We demonstrated that the charge compensation by Na⁺ favors the incorporation of rare‐earth elements. Moreover, the incorporated elements do not seem to be randomly distributed into the powellite structure.