Untersuchung an Nickel-Zeolith-Trägerkatalysatoren. II. Benzolhydrierung in der Gasphase an Nickel-Zeolith-Träger-katalysatoren

NI-exchanged zeolite catalysts were studied, by means of the benzene hydrogenation at 100–150°C. Catalysts of zeolite type A proved to be more active than those of the X type. Catalytic activity (related to the amount of Ni) decreases with increasing Ni content in the catalysts. The effective energy of activation is 13.5 kcal/mole; it does not depend on the Xi content and the kind of support. It could be shown by adsorption of benzene on Ni zeolite catalysts that in case of A-type catalysts benzene is adsorbed only on the external surface. In ease of X-type catalysts, however, benzene molecules are able to reach the internal surface, too. Hydrogenation of benzene proceeds only on the external surface for both types of catalysts.     

PHOTOPHYSICAL BEHAVIOUR OF NEW PYRROLOCOUMARIN DERIVATIVES

Abstract— The photophysical behaviour of new pyrrolocoumarins with different substituents on the nitrogen are reported. The photophysical properties of these pyrrolocoumarins are generally in agreement with those of the psoralens: a strong absorption (240–400 nm), a weak fluorescence (400–680 nm) characterized by a short singlet lifetime, and a rather strong phosphorescence at 77 K (480–600 nm). The absorption and fluorescence properties were investigated in several solvents. The shift of the fluorescence maximum is interpreted on the basis of the solvatochromic parameters π*, α and β. The triplet-triplet absorption spectra also depend on the nature of the solvent, while the triplet excited state has a lifetime of a few microseconds at room temperature (concentration 2.5 × 10⁻⁴ M ). Some absorption and fluorescence characteristics of the 4',5'-dihydropyrrolocoumarins, which are suitable models for the 4',5'-monoadducts to pyrrolocoumarins are reported.     

Saturated long linear aliphatic chain sodium monocarboxylates for the corrosion inhibition of lead objects—an initiative towards the conservation of our lead cultural heritage

In this study, sodium salts of saturated linear carboxylic acids with the general formula CH₃(CH₂) _n?2COONa (n = 14, 18)—labeled NaC₁₄ and NaC₁₈—were used to inhibit the corrosion of metallic lead via the development of protective coatings for lead heritage objects. The salts were dissolved in water/ethanol 1:1 (V/V) mixture at 50 °C to increase their solubility, and the coatings were formed by immersing lead samples in the resulted solutions for 24 h. The coatings were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. A hydrophobic layer of lead carboxylates appeared to form on the metal surface, and its corrosion inhibition properties were examined by linear sweep voltammetry and electrochemical impedance spectroscopy in a corrosive solution simulating the environment of museums with uncontrolled conditions. The lead carboxylates formed a protective barrier that inhibited further lead corrosion.

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Immobilization of cytochrome c on cysteamine-modified gold electrodes with EDC as coupling agent

Cyclic voltammetry has been applied for the characterization of cross-linked horse heart cytochrome c (HHC) on cysteamine-modified gold electrodes. The cross-linking, i.e. amide bond formation, between the proteins was achieved by using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) as coupling reagent. The optimal conditions for the formation of the HHC film were determined by varying the HHC concentration. In addition the reproducibility, stability and the influence of the scan rate upon these films were investigated with cyclic voltammetry. The protein film stability in a 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer solution was tested by UV/vis absorption spectroscopy.     

Ozonization and cyclic voltammetry as efficient methods for the regeneration of gelatin-coated SPR chips

The application of ozonization and cyclic voltammetry for the regeneration of gold chips containing a chemisorbed gelatin layer is reported. The efficiency of the regeneration process was analyzed using various surface analysis techniques indicating a complete removal of the biopolymer layer. The current findings open up perspectives for regeneration and multiple application of gold chips for SPR measurements.     

Electrochemical deposition of dodecanoate on lead in view of an environmentally safe corrosion inhibition

Non-toxic linear sodium monocarboxylates can be successfully used as inhibitors for the corrosion of many metals. The adsorption of these molecules onto a metal is usually achieved by immersing the metal in the carboxylate solution for a few hours. This paper describes the strength of cyclic voltammetry in forming a sodium dodecanoate coating on a lead electrode. We show that this approach is much less time-consuming compared with the immersion method and enables one to control and to characterize the layer formed by following the potential and current during the process. Additional ATR-IR and X-ray diffraction spectroscopic analyses were performed to qualitatively characterize the newly formed coating.     

Electrochemical quantification of copper-based alloys using voltammetry of microparticles: optimization of the experimental conditions

Voltammetry of microparticles has been used in this work for the qualitative and quantitative analyses of zinc, tin, lead and copper in binary, ternary or quaternary alloy samples. The analyses were carried out by spiking small amounts of the metals into a carbon paste electrode, after which they were anodically stripped off using differential pulse voltammetry. The work involved four separate experiments. The first one examined the type of electrolyte, which is suitable to identify the four elements. More specifically, the aim was to examine in which electrolyte all elements can be measured simultaneously–as would be the case in a quaternary copper alloy–without seeing any overlap in their current peaks. The second experiment focused on optimizing the measurement conditions with the aim of having the current peaks of each element well separated from the others. For this part, we made use of the central composite design. The aims were to: (i) maximize the separation between current peaks, (ii) determine which variable has a higher impact on the response, (iii) give an insight in the robustness of the method close to the optimum conditions and (iv) eventually show interactions between variables. In the third experiment, the four elements were quantified in their binary mixtures. Here, the percentage of the oxidation current for each metal, which is directly related to the ratio of the metal in the binary matrices, was employed for the calibration. Finally, in the last experiment, the elements were quantified in two real quaternary samples: a brass and a lead bronze.     

Electrochemical study of gelatin as a matrix for the immobilization of horse heart cytochrome c

The aim of this paper is to emphasize the strength of gelatin as a stable matrix for redox enzymes. Cyclic voltammetry has been applied for a detailed electrochemical study of horse heart cytochrome c (HHC) entrapped in a gelatin matrix immobilized on a gold electrode. The influence of the HHC concentration, the mass percentage of the gelatin and the nature of the gelatin on the electrochemical behaviour of HHC have been described in detail. In addition, attenuated total reflection infrared (ATR-IR) spectroscopy was used to prove the immobilization on a qualitative and conformational level. The thickness of the gelatin film was determined using a non-contact optical profiler. These results open up new perspectives in the development of stable, biocompatible matrices for redox enzymes. The latter has its relevance in the field of biosensor development.     

Self assembled films of porphyrins with amine groups at different positions: influence of their orientation on the corrosion inhibition and the electrocatalytic activity

Self-assembled molecular films of two cobalt porphyrins with amine groups at different positions-(5,10,15,20-tetrakis-(2-aminophenyl) porphyrin-cobalt(II), [Co(II) (T(o-NH(2))PP)] and (5,10,15,20-tetrakis-(4-aminophenyl) porphyrin-cobalt(II), [Co(II)(T(p-NH(2))PP)]-were formed on a gold substrate. The functionalized surfaces were characterized using Raman spectroscopy, atomic force microscopy and electrochemical methods. Both modified gold surfaces completely mask the charge transfer of a [Fe(CN)(6)](3-/4-) redox couple in solution, indicating the layer is highly resistive in behavior. Electrochemical impedance spectroscopy analyses revealed that the porphyrin film with amine groups at ortho positions shows a higher charge-transfer resistance with a better protective behavior compared to the para position modified surface. Raman, AFM and EIS data suggests that an ortho amine positioned molecule forms a more compact layer compared to the para-positioned molecule. This can be explained in terms of their orientation on the gold surface. [Co(II)(T(o-NH(2))PP)] adopted a saddle shape orientation whereas [Co(II)(T(p-NH(2))PP)] adopted a flat orientation on the gold surface. The porphyrin modified gold electrode catalyzes the oxygen reduction at lower potentials compared to the bare gold electrode. The shift in the overvoltage was higher in case of molecules with flat orientation compared to the saddle shaped oriented porphyrin molecules on the surface.     

Electrochemical deposition of a copper carboxylate layer on copper as potential corrosion inhibitor

Carboxylic acids and sodium carboxylates are used to protect metals against aqueous and atmospheric corrosion. In this paper, we describe the application of a layer of copper carboxylate on the surface of a copper electrode by means of cyclic voltammetry technique and tests which measure the corresponding resistance to aqueous corrosion. Unlike the soaking process, which also forms a film on the surface, the use of cyclic voltammetry allows one to follow the deposition process of the copper carboxylates onto the electrode. The modified electrodes have been characterised with infrared spectroscopy. In addition, the corrosion resistance of the film has been investigated using polarisation resistance and Tafel plot measurements.