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1.
The reduction of nitrate has gained renewed attention due to environmental problems like overfertilization and the increasing costs of purification of drinking water. The usual techniques (e.g. ion-exchange and biofiltration) have some disadvantages1. So … 相似文献
2.
A simple method for the modification of carbon powder with copper oxides is presented. Carbon powder is impregnated with copper(II) nitrate by stirring carbon powder in copper(II) nitrate solution for 1 hour and subsequently thermally treated at 823 K. The modified carbon powder was characterized using electrochemical and spectroscopic techniques. The existence of both copper(I) and copper(II) oxides have been established. The copper oxide modified carbon powder was used for preparation of composite electrodes, and the electrochemical and electrocatalytic behavior of the resulting composite electrodes was studied. The copper oxide modified carbon powder – epoxy composite electrodes showed a high electrocatalytic activity for the nitrite detection in aqueous media, with the detection limit comparable or lower than detection limits obtained with other electrochemical sensors. 相似文献
3.
ABSTRACT Significant catalytic activity towards the reduction of nitrite at unmodified Cu - 30% Ni alloy electrodes was found within the concentration ranges 16 – 200 μM nitrite. The reduction of nitrite was found to occur at potentials significantly less negative than the reduction of nitrate thereby providing clear resolution and the possibility of reliable nitrite / nitrate speciation. The results are contrasted with those found at a bare copper electrode where the spatial resolution of the nitrate and nitrite reduction processes is severely limited with significant overlap of the reduction processes. The procedure represents an inexpensive and facile method for nitrite determination in a number of applications. 相似文献
4.
Electrochemical reduction of nitrate was studied using a Cu/Zn cathode and Ti/Pt, Ti/IrO 2–Pt and Ti/RuO 2–Pt anodes in an undivided and unbuffered cell. A novel condition for performing both cathodic reduction of nitrate and anodic oxidation of the ammonia and nitrite by-products was achieved using Ti/Pt and Ti/IrO 2–Pt anodes in the presence of NaCl, especially with Ti/IrO 2–Pt anode. Nitrate could be completely removed using the Ti/IrO 2–Pt and Ti/Pt anode, with neither ammonia nor nitrite detected in the treated solution. A low nitrate reduction rate was observed when using a Ti/RuO 2–Pt anode in the presence of NaCl. However, in the absence of NaCl, all anodes showed good performance for nitrate reduction, with the Ti/Pt anode having the highest selectivity for reducing nitrate to nitrogen. 相似文献
5.
The paper reports on the electrocatalytic activity of boron-doped diamond (BDD) electrodes electrochemically modified with palladium (Pd) or gold nanoparticles (Au NPs) towards oxygen reduction reaction (ORR) in alkaline medium. The BDD/Pd NP interface shows a well-defined diffusion-controlled voltammetric oxygen reduction peak at −0.25 V vs. Ag/AgCl. This is more positive than the ORR peak at −0.59 V vs. Ag/AgCl observed on BDD/Au-NP composite electrodes. The ORR proceeds via a four-electron process in both cases. 相似文献
6.
Pt-based metals are very effective catalysts widely adopted in many fields. But the high cost prevents its further industrial application. One of the effective ways to solve the problem is to replace platinum with relatively cheap palladium and its alloy with copper. However, producing Pd/Cu bimetallic catalysts efficiently and economically with controllable particle size and uniform distribution is still challenging, especially when trying to reduce the consumption of precious metals. In this paper, ultrasmall palladium/copper (Pd/Cu) bimetallic catalysts with even dispersion were prepared on multi-walled carbon nanotubes (MWCNTs) by adding polyethylene glycol 400 (PEG 400) as a reducing agent and stabilizer under visible light irradiation at room temperature. The catalytic performance was studied in the catalysis of p-nitrophenol ( p-NP) reduction. Of all the bimetallic catalysts produced in different conditions, the best one was obtained under the reaction condition of pH = 7 and violet light irradiation (wavelength 380–435 nm). The average particle size of 0.85 nm, and the apparent rate constant in the catalysis is 1.47 min ?1. This research probes the role of visible light as a key kinetic controlling method in the formation of ultrasmall particles (UPs). It proves the effectiveness of using visible light irradiation as an effective and more “green chemistry” approach to get precious metal UPs as catalysts beyond the traditional ultraviolet or laser photochemistry methods. 相似文献
7.
A method has been developed for obtaining Cu–Pd hydrosols via catalytic reduction of copper ions by hydrogen on seed palladium nanoparticles 2.5 ± 0.3 nm in size. It has been found that reduction of Cu 2+ to metal proceeds stage-by-stage through the formation of an intermediate Cu + ion. Cu–Pd hydrosol remains stable with respect to sedimentation and aggregation for several weeks. The hydrodynamic size of Cu–Pd nanoparticles increases proportionally to the copper content in particles. It has been shown that this is due to an acidification of the solution as a result of H + ions formation via the reaction of reduction of Cu 2+ ions by hydrogen. 相似文献
8.
The effects of palladium precursors (PdCl 2, (NH 4) 2PdCl 4, Pd(NH 3) 2Cl 2, Pd(NO 3) 2 and Pd(CH 3COO) 2) on the catalytic properties in the selective oxidation of ethylene to acetic acid have been investigated for 1.0 wt% Pd–30 wt% H 4SiW 12O 40/SiO 2. The structures of the catalysts were characterized using X-ray diffraction, N 2 adsorption, H 2-pulse chemical adsorption, infrared spectrometry of the adsorbed pyridine, H 2 temperature-programmed reduction and X-ray photoelectron spectroscopy. The present study demonstrates that the different palladium precursors can lead to the significant changes in the dispersion of palladium. It is found that Pd dispersion decreases as follows: PdCl 2 > (NH 4) 2PdCl 4 > Pd(NO 3) 2 > Pd(NH 3) 2Cl 2 > Pd(C 2H 3O 2) 2, which is nearly identical to the catalytic activity. This indicates that the dispersion of palladium plays an important role in the catalytic activity. Furthermore, density of Lewis ( L) and Brönsted ( B) acid sites are also strongly dependent on the palladium precursors. It is also demonstrated that an effective catalyst should possess a well combination of Brönsted acid sites with dispersion of palladium. 相似文献
9.
High-precision X-ray powder diffraction and differential dissolution methods are used to show that copper chromite with a structure of tetragonal spinel is recovered under certain conditions upon the reoxidation of the system of phases formed by the reduction of the initial copper chromite, cation-deficient spinel stabilized by hydrogen and Cu 0 particles epitaxially bound to its surface at 250–350°C. However, because of destruction of the initial surface layer at the initial moment of reduction, equilibrium cannot be complete: reoxidized spinel is nonstoichiometric and contains some lattice oxygen-bound protons, and the copper oxide is formed on the surface in some amount. The difference in the phase transition of copper chromite during reduction–reoxidation from the reversible polymorphic transitions characteristic of copper chromite during temperature variations is analyzed. 相似文献
10.
Summary 1-(o-Carboxyphenyl)-3-hydroxy-3-phenyltriazene was found to be an excellent spectrophotometric reagent for the determination of nickel(II), palladium(II) and copper(II). At pH 6.8–8.3, 2.4–3.5 and 2.2–3.8, nickel, palladium and copper form greenish yellow, yellowish orange and light green complexes with maximum absorption at 410, 410, 400 nm, respectively. The systems obey Beer's law with optimum ranges from 0.25 to 2.0 ppm for Ni(II), 0.5–4.0 for Pd(II) and 0.5–4.0 for Cu(II); the elements form 11 complexes with the instability constants 2.1×10 –5, 1.5×10 –5 and 2.0×10 –5, resepctively. Effects of other anions and cations on the colour systems have been studied and procedures for the determination of Ni(II), Pd(II) and Cu(II) in presence of each other are described.
Spektrophotometrische Bestimmung von Nickel(II), Palladium(II) und Kupfer(II) nebeneinander und in Gegenwart anderer Ionen mit Hilfe von 1-(o-Carboxyphenyl)-3-hydroxy-3-phenyltriazen Zusammenfassung Ni, Pd und Cu bilden mit dem Reagens bei pH 6,8–8,3, 2,4–3,5 bzw. 2,2–3,8 grünlich-gelbe, gelblich-orange bzw. hellgrüne Komplexe mit Absorptionsmaxima bei 410, 410 bzw. 400 nm. Das Beersche Gesetz wird in den Bereichen 0,25–2,0, 0,5–4,0 bzw. 0,5–4,0 ppm befolgt. Die Elemente bilden 11-Komplexe mit den Instabilitätskonstanten 2,1 · 10–5, 1,5 · 10–5 bzw. 2,0 · 10–5. Der Einfluß anderer Kationen und Anionen wurde untersucht und Arbeitsvorschriften werden angegeben. 相似文献
11.
Cu-ZSM-5 catalysts for the selective reduction of NO with propane were obtained by ion exchange between H-ZSM-5 zeolite and an aqueous or aqueous ammonia solution of a copper salt (acetate or nitrate). Their Cu/Al values (%) defined as 2 × 100 (Cu : Al), where Cu : Al is the copper-to-aluminum atomic ratio, were determined as a function of ion exchange pH, which was varied by changing the copper salt and solution concentration. Cu/Al is primarily determined by the chemical nature of the starting copper salt. For a given salt, it is governed by the salt concentration in the solution. At a fixed salt concentration, Cu/Al is always larger for copper acetate than for copper nitrate. It can be raised to ≫100% by using an aqueous ammonia solution of a copper salt. Furthermore, it increases with increasing Si/Al in the starting zeolite if the other ion exchange conditions are equal. Irrespective of preparation conditions, the catalytic activity of Cu-ZSM-5 grows in proportion to Cu/Al. It peaks at Cu/Al ∼ 100% and then remains constant up to Cu/Al ∼ 400%. In order to achieve Cu/Al ∼ 100%, it is most appropriate to use a copper acetate solution.__________Translated from Kinetika i Kataliz, Vol. 46, No. 4, 2005, pp. 652–656.Original Russian Text Copyright © 2005 by Tsikoza, Matus, Ismagilov, Sazonov, Kuznetsov. 相似文献
12.
A rapid technique for determination of nitrate by acid reduction and diazotization at elevated temperature has been standardized. The technique is based on quantitative diazotization of sulfanilamide by nitrate on incubation in boiling water bath for 3, 5 or 10 min in presence of high concentration of HCl, ca. 64.5%. The diazotized sulfanilamide is coupled at room temperature to N-1-(naphthyl)-ethylenediamine dihydrochloride, and the chromophore evaluated spectrophotometrically at 540 nm. The technique provides linear estimate of nitrate over the test range of 0.5 through 10 μg N mL −1 sample with all test incubation time periods using alkali nitrate and nitric acid as sources of nitrate anion. Urea treatment enables selective determination of nitrate in presence of nitrite with overall 99 ± 1% recovery, and without affecting nitrate determination ( P > 0.1) or its regression coefficient. The technique has obvious advantages over metal-reduction technique. It is simple, rapid, selective in presence of nitrite, and an inexpensive method for routine determination of nitrate with detection range 0.5–10 μg N mL −1 sample. Besides, the technique provides opportunity to detect nitric acid as low as 35 μM even in presence of other acids. 相似文献
13.
We synthesized Pt monolayer electrocatalysts for oxygen-reduction using a new method to obtain the supporting core–shell nanoparticles. They consist of a Pt monolayer deposited on carbon-supported Co–Pd core–shell nanoparticles with the diameter of 3–4 nm. The nanoparticles were made using a redox-transmetalation (electroless deposition) method involving the oxidation of Co by Pd cations, yielding a Pd shell around the Co core. The quality of the thus-formed core–shell structure was verified using transmission electron microscopy and X-ray absorption spectroscopy, while cyclic voltammetry was employed to confirm the lack of Co oxidation (dissolution). A Pt monolayer was deposited on the Co–Pd core–shell nanoparticles by the galvanic displacement of a Cu monolayer obtained by underpotential deposition. The total noble metal mass-specific activity of this Pt monolayer electrocatalyst was ca. 3-fold higher than that of commercial Pt/C electrocatalysts. 相似文献
14.
Sols containing Pd(0) clusters with polyoxo anions are prepared by the reduction of colloidal solutions of polyhydroxo complexes of Pd(II) in the presence of Mo(VI), W(VI), V(V), and Nb(V) polyoxo anions. The cluster sizes varied within the limits of 1–10 nm depending on the nature of the polyoxo anion. The stability of sols toward coagulation depends on the ratio between the palladium and polyoxo anion amounts in solution and on the composition of the solvent. Supported Pd catalysts are obtained by the adsorption of particles from sols; Pd can exist in these catalysts as individual particles or associates or form filamentary structures. 相似文献
15.
Radiolysis of aqueous sodium nitrate solution was studied as a function of concentration in the range 10 –4M to 1M NaNO 3. The radiolytic yield of nitrite was found to be linear with dose and concentration. The effect of transition metal chloride additives on the radiolysis of 0.01M NaNO 3 resulted in higher and lower yields of nitrite in the presence of cobalt and nickel chlorides, respectively, than that obtained in the pure nitrate system. The reduction of nitrate to nitrite is totally quenched even at very low concentration of copper chloride in the binary mixture. The results are explained on the basis of oxidizing and reducing properties of transition metal ions. 相似文献
16.
The state of highly dispersed palladium particles supported on filamentous carbon was studied using high-resolution electron microscopy, XPS, and X-ray diffraction analysis. Three types of filamentous carbon were used, in which the basal planes of graphite were arranged along, across, and at an angle to the nanofiber axis. The amount of supported palladium was 0.25–5.8 wt %. The structure of the carbon support was found to affect the properties of the active component. Highly dispersed palladium particles exhibited the strongest interaction with a carbon surface formed by the butt ends of graphite (002) layers. This interaction resulted in electron transfer from the metal to the support and in the stabilization of palladium in the most dispersed state. A change in the properties of palladium particles caused a change in the catalytic properties of Pd/C catalysts in the reaction of selective 1,3-butadiene hydrogenation to butenes. The strong interaction of Pd 2+ with the butt ends of graphite resulted in the stabilization of palladium in an ionic state. An increase in the fraction of Pd 2+ in the catalysts was responsible for a decrease in both the overall activity and selectivity of Pd/C catalysts in the reaction of 1,3-butadiene hydrogenation to butenes. 相似文献
17.
Colloidal palladium was prepared by -irradiation or by H 2 reduction of Pd(NH 3) 4l 2 in aqueous solutions containing sodium polyacrylate as a stabilizer. The sots contain spherical particles 2–4 nm in diameter. Their optical spectra contain a band at 230 nm ( = 6.1 · 10 3 L mol –1 cm –1) smoothly descending toward the visible range. The sots reversibly absorb chemically from 0.35 to 0.15 g-mol of H 2 per g-atom of Pd. The spectra of ultrafine metal particles saturated with molecular hydrogen exhibit an absorption band at 265 nm ( = 4.5 · 10 3 L mol –1 cm –1). One-electron reduction of methylviologen by hydrogen is catalyzed by the colloidal palladium prepared.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 313–316, February, 1996. 相似文献
18.
Aiming the selective recovery of palladium from high level radioactive liquid waste (HLW), a chelating thiamide type sorbent,
CWP–TU, was prepared by the modification of Japanese cedar wood powder (CWP). Convection oven and microwave heating were separately
used for modification purpose and found that microwave heating is more effective over oven heating. CWP–TU was extensively
studied for the adsorption of Pd(II) from nitric acid medium. The batch test showed that nitric acid concentration of 3 M
or higher is favorable for Pd(II) loading. Consistent adsorption of Pd(II) under gamma irradiation condition demonstrated
the feasibility of using CWP–TU in real HLW. Also, Pd(II) only adsorption from simulated HLW solution verified the palladium
only selectivity of the sorbent as well as the lack of influence of coexisting metal ions on its affinity toward Pd(II). CWP–TU
holds maximum Pd(II) loading capacities of 0.98 mol/kg at 30 °C and 1.04 mol/kg under gamma irradiation. A comparative study
using some ion exchange resins revealed that the resins are either ineffective in nitrate medium or lack stability under irradiation. 相似文献
19.
A mixture of Ta and 25 mass% Cu elemental powders was subjected to mechanical alloying in a high-energy ball mill up to 60 h. The results are composite particles formed by nanocrystalline Cu and amorphous Ta phases. Thermal stability of amorphous was investigated by DSC. The XRD, FTIR and EDX analyses of Ta–25 mass% Cu powder milled for 60 h performed after DSC at 800 and 900 °C have revealed large amounts of Ta nitride and Ta oxides even though the milling process was done in Ar atmosphere. This is due to high reactivity of Ta fine particles with oxygen and nitrogen from air. During manipulations of the powder (taking samples from vials and its investigation), the adsorption phenomena on its surface occur, and both surface-adsorbed N2 and O2 are processed with powder and embedded in it. While heating of Ta–25% Cu milled powder in DSC, nitrogen and oxygen diffusion into tantalum is activated, and Ta2N and TaO2/Ta2O5 compound forms. 相似文献
20.
Moscow University Chemistry Bulletin - In this study, copper oxide (Cu2O) particles were synthesized by octahedral shape and then were loaded with palladium (Pd). Photocatalysis, which was prepared... 相似文献
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