Layered La-Ba-Cu mixed oxides with perovskite structure as catalyst for NO reduction by CO

The mixed oxides, including LaBa2Cu3O7, LaBaCu2O5, La4BaCu5O12 with perovskite structure, were prepared. The catalysts were characterized by means of chemical analysis, XRD, H-2-TPR. It was found that their structures were layered ABO(3) perovskite structure and they were the active catalysts for the NO reduction by CO. The existence of Cu3+ is an important factor to give the catalysts a high activity for the NO reduction by CO.

Catalysis of hydrotalcite-like compounds in liquid phase oxidation: (I) phenol hydroxylation

Hydrotalcite-like compounds (HTLcs): (CuMAlCO3)-Al-II-HTLcs, where M-II=Co2+, Ni2+, Cu2+, Zn2+ and Fe2+, were synthesized by coprecipitation and characterized with XRD and IR. The catalysis of these HTLcs was studied in the phenol hydroxylation by H2O2 in liquid phase; then the effects of the ratio of Cu/Al, reaction temperature, solvent and pH of medium were investigated. It has been found that the uncalcined HTLcs have higher activities than those of calcined samples in this reaction. The catalyst CuAlCO3-HTLcs having Cu/Al=3 efficiently oxidized phenol and gave high yields of the corresponding diphenols in appropriate reaction conditions. A tentative reaction mechanism is also proposed. (C) 1998 Elsevier Science B.V.

Perovskite-like mixed oxides La2-x(Sr,Th)(x)CuO4+/-lambda

Two groups of mixed oxides La2-xThxCuO4+/-lambda (0.0 less than or equal to x less than or equal to 0.4) and La2-xSrxCuO4+/-lambda (0.0 less than or equal to x less than or equal to 1.0) were prepared. Their crystal structures were studied with XRD and IR spectra, etc. Meanwhile, the average valence of Cu ions and nonstoichiometric oxygen (lambda) was measured through chemical analyses. Catalysis of the abovementioned mixed oxides was investigated in phenol hydroxylation, good results were obtained for some mixed oxides, and found that the catalysis of these mixed oxides have close relation with their defect structure and composition. A radical substitution mechanism was also proposed for this catalytic reaction.

Influences of acid treatments of active carbons on no reduction over carbon-supported copper oxides

Active carbon supported copper oxides were used in NO reduction. The conversions of NO reduction depends strongly on surface oxygen-containing groups on the active carbons, among them the carboxyls and lactones favored remarkably the NO reduction. However, hydrochloric acid treatment led to the decomposition of the carboxyls and lactones on C2 and C3, decreasing their reactivities for NO reduction. Concentrated HNO3 treatment of active carbon produced higher conversions of NO reduction at relatively low temperatures due to the marked increase in the amounts of the carboxyls and lactones.

Y-Ba-Cu-O mixed oxides for production of diphenols in liquid-solid phase

Superconductor mixed oxides were often used as catalysts at higher temperature in gas phase oxidations, and considered not suitable for lower temperature reactions in the liquid-solid phase; here the catalysis of YBa2Cu3O7+/-x and Y2BaCuO5+/-x in the phenol hydroxylation at lower temperature with H2O2 as oxygen donor was studied, and found that the superconductor YBa2Cu3O7+/-x, has no catalytic activity for phenol hydroxylation, but Y2BaCuO5+/-x does, even has better catalytic activity and stability than most previously reported ones. With the studies of catalysis of other simple metal oxides and perovskite-like mixed oxides, a radical substitution mechanism is proposed and the experimental facts are explained clearly, and draw a conclusion that the perovskite-like mixed oxides with (AO)(ABO(3)) and (AO)2(ABO(3)) structure have better catalytic activity than the simple perovskite oxides with (ABO(3))(3) structure alone, and (AO) structure unit is the key for the mixed oxides to have the phenol hydroxylation activity. No pollution of this process is very important for its further industrial application.

ESR STUDY OF SUPERHYPERFINE INTERACTION OF I-127 IN [CU(IO5OH)(2)](5-) ION COMPLEX

ESR method has been used to study superhyperfine. interaction of I-127 in [Cu (IO5OH)(2)](5-) ion for Na4KCu(IO5OH)(2) . 12H(2)O single crystal. The main purpose of this paper is to confirm the existence of unpaired electron spin on iodine atom and to find a reasonable explanation for the spin delocalization of CU2+ ions. Based on the ESR parameters of paramagnetic [Cu(IO5OH)(2)](5-) ions, the calculated results show that about 0.77% of the unpaired eletron spin is located on each iodine atom.

EFFECT OF HYDROPHOBIC OXIDES ON RADIATION CROSS-LINKING OF LOW-DENSITY POLYETHYLENE

Effect of hydrophobic oxide, containing =Si-CH=CH2 groups, on the radiation crosslinking of low density polyethylene (LDPE) has been studied. It was found that mechanical stability of irradiated LDPE containing improved SiO2 is higher than that of samples containing unimproved SiO2.

ELECTROCHEMICAL CATALYSIS AT AN ULTRAMICROELECTRODE MODIFIED WITH REDOX SPECIES

General equations of the electrocatalytic reaction at an ultramicroelectrode modified with redox species have been described according to the Andrieux Saveant model. The electrocatalytic kinetic process has been discussed for the whole set of cases, ie (R), (R + S), (SR) (SR + E), (E), (R + E), (ER), (S), (ER + S) and (S + E) limiting situations. The effect of gamma on the catalytic steady state current shows that the higher the value of gamma, the lower the catalytic current. The kinetic process shifts rapidly from R to E with increasing values of gamma. It is favorable for catalysis only when gamma is very low. Therefore, the redox species modified ultramicroelectrode with thin film is utilized for electrocatalysis, and the larger the radius of ultramicroelectrode, the higher the catalytic efficiency.

STUDY ON THE ACTIVE-CENTERS OF METHANE COUPLING CATALYSTS BY MEANS OF FLUORESCENCE EMISSION OF EU3+

Eu3+ ion was adopted as a probe to detect the probability of entrance of alkali elements into the crystal lattice of MgO, CaO and La2O3 by means of its characteristic emission. Based on the experimental data it is concluded that Li+ and Na+ ions can substitute Mg2+ and Ca2+ ions and only a small amount of K+ ion can enter into the lattice of CaO. Whilst Li+ ion can not enter into the lattice of lanthana. The conclusion of this investigation is in good agreement with that obtained by Lunsford by ESR studies.

LIQUID-CHROMATOGRAPHY AMPEROMETRIC DETECTION OF CATECHOL, RESORCINOL, AND HYDROQUINONE WITH A COPPER-BASED CHEMICALLY MODIFIED ELECTRODE

A copper-based chemically modified electrode (CME) has been constructed and characterized for flow-through amperometric detection of catechol, resorcinol, and hydroquinone. Novel potential dependence of the detector response was first obtained for these analytes at the Cu CME, where negative peaks together with positive ones were observed in one definite chromatogram using amperometric detection. Its advantages in chromatographic applications were demonstrated. From these observations it is proposed that the detector response was governed by formation of copper complexes with the solutes. A dynamic linear range over two orders of magnitude was obtained, when operating the detector at +0.10 V vs. SCE, from which ng detection limits were achieved.

CYCLIC VOLTAMMETRIC AND SPECTROELECTROCHEMICAL STUDIES OF COPPER IN ALKALINE-SOLUTION

The behaviour of the electroplated copper film electrode on tin oxide/glass or glassy carbon surface was studied in potassium hydroxide medium by cyclic voltammetry and in situ transmission spectroelectrochemistry. The results indicate that the electroplated copper film electrode is similar to a copper electrode and cyclic voltammetry with this electrode affords more resolution. The anodic peaks were found to correspond successively to the adsorption of oxygen, the formation of a surface layer of Cu2O, the formation of a surface layer of Cu(OH)2 or CuO and formation of a thick multilayer film of CuO. This is the first time it has been proposed that a surface layer of Cu(OH)2 or CuO is formed from the oxidation of the surface layer of Cu2O. Similarly, a clear interpretation is presented that the cathodic peaks correspond successively to the reduction of CuO to Cu2O, the reductions of Cu2O to Cu and the soluble Cu(II) species to Cu. On the other hand, a shoulder peak related to the chemical transformation of Cu(OH)2 to CuO was first observed.

THE ACTIVE OXYGEN ON THE LI/LA2O3 CATALYST SURFACE AND ITS CATALYTIC BEHAVIOR IN THE OXIDATIVE COUPLING OF METHANE

The coupling selectivity was greatly enhanced by adding Li to La2O3, compared with the single La2O3. The O2- species was found on the Li/La2O3 but not on the single La2O3. In low-temperature desorption, ethane desorbed from the Li/La2O3 but was not detected with the single La2O3. It is considered that the addition of Li gave rise to some basic sites which are favorable for the coupling reaction.

LIQUID-CHROMATOGRAPHY AMPEROMETRIC DETECTION OF CARBOXYLIC-ACIDS AND PHENOLIC-ACIDS WITH A COPPER-BASED CHEMICALLY-MODIFIED ELECTRODE

A copper-based chemically-modified electrode has been constructed and characterized by various experimental parameters in flow-through amperometric detection of carboxylic acids and phenolic acids. Novel hydrodynamic voltamperograms were first obtained in flow-through amperometric detection with the Cu-based CME and subsequently negative and positive peaks were observed in a single chromatogram. This unique and flexible potential dependence could be of great benefit in chromatographic speciation and quantification. These observations suggest that the detector response was governed by the complexation reaction of copper ions with the solutes.

Analysis of the effect of copper on the virulence of a pathogenic Edwardsiella tarda strain

Aim: To investigate the effect of copper on the virulence of Edwardsiella tarda. Methods and Results: The pathogenic Edw. tarda strain TX5 was cultured under copper-stressed conditions and examined for any potential alteration in capacities that are associated with pathogenicity. The results showed that compared to untreated TX5, Cu-treated TX5 exhibits reduced planktonic and biofilm growth, an impaired ability to adhere to host mucus, modulation of host immune response, and dissemination in host blood and liver. Consistent with these observations, the overall bacterial virulence of Cu-treated TX5 is significantly attenuated. SDS-PAGE analyses of whole cell protein production showed that Cu-treated TX5 differs from the untreated TX5 in its production of at least one protein. Quantitative real time reverse transcriptase PCR analyses showed that copper treatment decreased the expression of virulence-associated genes encoding components of the type III and type VI secretion systems, the Eth haemolysin system, and the LuxS/AI-2 quorum-sensing system. Conclusions: Prolonged exposure to copper has multiple effects on TX5 and results in significant attenuation of bacterial virulence. Significance and Impact of the Study: The results of this study demonstrate that copper treatment has a broad and profound effect on the virulence-associated capacities of TX5, which is exerted at least in part at the transcription level. These findings provide new insights to the antimicrobial mechanism of copper.

Molecular analysis of the copper-responsive CopRSCD of a pathogenic Pseudomonas fluorescens strain

CopRS/CopABCD is one of the known systems that control copper homeostasis in bacteria. Although CopRS/CopABCD homologues are found to exist in Pseudomonas fluorescens, the potential role of this system in P. fluorescens has not been investigated. In this study a genetic cluster, consisting of copR, S, C, and D but lacking copAB, was identified in a pathogenic P. fluorescens strain (TSS) isolated from diseased fish. The copRSCD cluster was demonstrated to be required for full copper resistance and regulated at the transcription level by Cu. Expression of copCD is regulated directly by the two-component response regulator CopR, which also regulates its own expression. Interruption of the regulated expression of copR affected bacterial growth, biofilm formation, and tissue dissemination and survival. A mutant CopR, which lacks the N-terminal signal receiver domain and is constitutively active, was found to have an attenuating effect on bacterial virulence when expressed in TSS. To our knowledge, this is the first report that suggests a link between CopR and bacterial pathogenicity in P. fluorescens.