Pd-Cu负载型催化剂催化还原水中硝酸盐的研究进展

综述了Pd-Cu负载型催化剂催化还原水中硝酸盐的研究进展。总结了Pd-Cu负载型催化剂的催化特征及其催化活性。重点介绍了Pd-Cu/陶瓷膜催化剂催化还原水中硝酸盐的活性及其作用机理。提供了一种新的方法用来提高催化还原硝酸盐过程中的催化性能。     

Catalytic reduction of nitrates and nitrites in water solution on pumice-supported Pd–Cu catalysts

Two series of pumice-supported palladium and palladium–copper catalysts, prepared by impregnation with different palladium and copper precursors, were tested for the hydrogenation of aqueous nitrate and nitrite solutions. Measurements were performed in a stirred tank reactor, operating in batch conditions, in buffered water solution at atmospheric pressure and at 293 K. The activities of the catalysts were calculated in terms of nitrate and/or nitrite removal. With the monometallic Pd/pumice, the reduction of nitrite is highly selective; only 0.2% of the initial nitrite content is converted to ammonium ions. The activity in terms of turn over frequency (TOF) is higher as compared to a catalyst of Pd on silica. Addition of copper to the palladium catalyst is essential for the reduction of nitrates, although it decreases the nitrite reduction activity and increases the production of ammonium ions. Nitrate reduction appears to be structure-insensitive and a volcano-type dependence of the activity versus the overall Cu atomic weight percentage is observed for the two series of catalysts.     

TiO_2光催化还原去除饮用水中硝酸盐的实验研究

在间歇式反应器中,以TiO2为催化剂,进行了光催化还原去除饮用水中硝酸盐的实验,考察了空穴清除剂种类、甲酸用量、催化剂用量和硝酸盐浓度对去除硝酸盐效率的影响。结果表明,在TiO2作用下,硝酸盐能被有效地还原去除,去除率可达35.16%;与甲醇、甲酸钠和EDTA相比,甲酸作空穴清除剂时硝酸盐去除效果最佳;甲酸和硝酸盐的浓度对光催化反应的影响显著,催化剂最佳用量为100 mg。探讨了反应机理,认为光催化还原硝酸盐是一分步反应。     

Adsorption of phosphate and nitrate anions on ammonium-functionnalized mesoporous silicas

Surface modified mesostructured silica materials represent potential adsorbents offering an opportunity to remediate several important water pollutants. In the present work, ammonium-functionnalized MCM-41, MCM-48 and SBA-15 mesoporous silica materials were synthesized via post-synthesis grafting and co-condensation. Their efficiency to remove nitrate and phosphate anions in aqueous solutions was investigated. The adsorbent materials showed high adsorption capacities reaching 46.5 mg NO₃⁻/g and 55.9 mg H₂PO₄⁻/g under the operating conditions explored. The mesoporous silica materials functionalized via post-synthesis grafting method exhibited higher performances in terms of percentage pollutant removal and adsorption capacities if compared to their analogs synthesized according to the co-condensation strategy.     

Al-pillared clay supported CuPd catalysts for nitrate reduction

PdCu catalysts on clay and Al-pillared clay supports were prepared by wet impregnation procedure and characterized by powder x-ray diffraction (PXRD), Scanning Electron Microscope Dispersive x-ray analysis (SEM-EDAX) and Transmission Electron Microscopy (TEM). The incorporation of [Al₁₃O₄(OH)₂₄(H₂O) ₁₂]⁷⁺ clusters in the clay interlayers and subsequent formation of Al-pillared clays was confirmed from PXRD patterns. The EDAX analysis indicated good homogeneous mix of metallic components, in the form of monometallic or inhomogeneous bimetallic particles, on the clay and pillared clay surfaces. TEM pictures showed striking particle size differences upon Al₂O₃-pillaring. The metallic particles were much smaller in size on Al-pillared clay than those formed on parent clay. The clay supported PdCu catalysts were tested for nitrate ion reduction in aqueous phase under hydrogen atmosphere. Preliminary results show that the catalysts with Pd and Cu components together exhibit superior performance in activity and selectivity to nitrogen compared to their monometallic particles supported on both clay samples. This study indicates the possibility of using PdCu catalysts supported on pillared clays as environmental friendly and efficient catalysts for nitrate reduction reactions.     

Influence of nitrate concentration on its electrochemical reduction on tin cathode: Identification of reaction intermediates

The influence of the concentration of nitrate in the range between 100 and 62,000 mg L⁻¹ NaNO₃ in NaCl solutions was studied under constant potential electrolysis at −2.8 V vs. Ag/AgCl. The rate of the reduction follows Langmuir-Hinshelwood kinetics, according to which zero order kinetics is followed at concentrations higher than 0.3 M whereas first order at lower concentrations.The selectivity to nitrogen increases from 70 to 83% as the concentration of nitrate increases from 100 to 1500 mg L⁻¹ and it remains almost constant for higher nitrate concentrations, whereas that of ammonia exhibits the opposite trend decreasing from 25 to 11%. The % Faradaic Efficiency (%FE) increased with the increase of the concentration of nitrate from 25% at 0.1 M to 78% at 1 M when 95% of nitrate was reduced in both cases. At high concentrations of nitrate, hyponitrite and hydroxylamine were detected as intermediates of the reduction and a reaction scheme which is in agreement with the experimental results has been proposed.The hydrogen evolution in our conditions probably takes place through the discharge of the cation of the supporting electrolyte instead of the Volmer-Tafel mechanism and the reduction of nitrate proceeds through electrochemical hydrogenation.     

催化还原法去除饮用水中硝酸盐氮研究进展

综述了催化还原法去除饮用水中硝酸盐氮的研究进展,介绍了反应机理,总结了促进组分、载体、制备方法对催化剂催化性能的影响以及还原剂的新发展,阐明了溶液pH值、水质因素和传质条件对硝酸盐去除效果的制约。     

Pyridine-N-rich Cu single-atom catalyst boosts nitrate electroreduction to ammonia

Nitrate-to-ammonia electroreduction (NO₃RR) offers a sustainable alternative to the energy-extensive Haber–Bosch process. Previous studies have reported nitrogen-coordinated copper single-atom catalysts with impressive activity and selectivity. However, regulating the nitrogen coordination structure at the atomic scale and its impact on the catalytic mechanism are not yet clear. This work demonstrates a pyridinic-N-rich copper single-atom catalyst (PR-CuNC) derived from semi-interpenetrating polypyrrole-polyethyleneimine hydrogels for the NO₃RR. By contrast to the catalyst with insufficient pyridinic nitrogen, PR-CuNC exhibits a maximum NH₃ Faraday efficiency of 94.61 % and a yield rate of 130.71 mg_NH3 mg_Cu⁻¹ h⁻¹ (3.74 mg_NH3 h⁻¹ cm⁻²). Theoretical evidence reveals that different N coordination types significantly affect the electronic structures of CuN₄ sites, resulting in the enhanced intrinsic activity. Our results show that the nitrogen structure is highly relevant to the performance of NO₃RR, underlining the importance of directly regulating the local coordination environment at the molecular level.     

Rhodium deposits on pyrolytic graphite substrate: Physico-chemical properties and electrocatalytic activity towards nitrate reduction in neutral medium

The electrodeposition of metallic rhodium on pyrolytic graphite from 10 mM Na₃RhCl₆ + 0.5 M NaCl aqueous solution was studied by potentiostatic method with the use of a double-pulse technique involving nucleation and growth pulses. Physico-chemical properties of Rh deposits were investigated by electrochemical methods and scanning electron microscopy. The activity of Rh-modified graphite electrodes towards nitrate reduction in neutral medium was demonstrated, the activation energy of nitrate reduction and NO₃⁻ Langmuir adsorption constant on Rh deposits were determined.

The use of double-pulse technique resulted in enhanced surface coverage in comparison with usual potentiostatic deposition and in decreasing the mean particle size down to 30 nm, while the specific catalyst surface area attains 32 m² g⁻¹. The increase in the nucleation pulse duration from 20 to 100 ms enhances the mass catalytic activity towards NO₃⁻ reduction, which reaches 175 A g⁻¹ for the best samples. Irrespectively of electrodeposition parameters, only NH₃ and NO₂⁻ were detected as nitrate reduction products. The rate of NO₃⁻ destruction was equal to which is much higher than that of most of Pd/Cu-based nitrate hydrogenation systems and Ag/TiO₂ photocatalysts.     

Platinization of Ti for the fabrication of a Sn-modified Pt/Ti electrode for reduction of nitrate

This work investigated the fabrication characteristics of platinized-Ti for use in the preparation of a Sn-modified platinized-Ti electrode to reduce nitrate. A Pt electro-plating method to form special open clearances within a Pt coating layer on an etched Ti substrate was important to effectively remove the residual contaminate due to the plating solution at the fabricated electrode surface and to maximize the electrode’s actual surface area. The electro-cleaning caused a morphologic change of the platinized-Ti electrode surface through a place-exchange process of Pt atoms, with many of the downy hair-like polyps formed on the surface disappearing, resulting in a decrease in the electrode area. The platinized-Ti electrode itself had some electro-activity to the reduction of nitrate even though its surface was not Sn-modified. The Sn-modified platinized-Ti electrode significantly increased electro-activity to the reduction of nitrate compared with the Pt metal electrode.     

Efficient electrochemical reduction of nitrate to nitrogen using Ti/IrO2-Pt anode and different cathodes

Electrochemical reduction of nitrate using Fe, Cu, and Ti as cathodes and Ti/IrO₂-Pt as anode in an undivided and unbuffered cell was studied. In the presence of appropriate amount of NaCl, both cathodic reduction of nitrate and anodic oxidation of the by-products of ammonia and nitrite were achieved by all cathodes under a proper condition. Both in the absence and presence of NaCl, the order of nitrate removal rate was Fe > Cu > Ti. The nitrate removal was 87% and selectivity to nitrogen was 100% in 3 h with Fe cathode in the presence of NaCl. Ti/IrO₂-Pt anode played an important role during nitrate reduction, especially in the presence of NaCl, at which by-products could efficiently be oxidized. Moreover, atomic force microscopy (AFM) investigation shown Ti/IrO₂-Pt anode was suitable for nitration reduction and the surface roughness of all cathodes increased. The concentrations of Fe, Cu, and Ti in the electrolyte were less than 0.15, 0.12 and 0.09 mg/L after 3 h electrolysis, respectively.     

Influence of the concentration and the nature of the supporting electrolyte on the electrochemical reduction of nitrate on tin cathode

The influences of the potential, the concentration and the nature of the supporting electrolyte on the rate of the reduction of nitrate on tin were studied by both voltammetry and constant potential electrolytic experiments.Both the rate of the reduction of nitrate and the yield of nitrogen increase as the negative potential increases from −1.8 to −2.8 V versus Ag/AgCl, while the yield of nitrite decreases. The yield of ammonia displays a maximum at −2.4 V and consequently decreases.The rate of the reduction at −1.8 V versus Ag/AgCl increases significantly as the concentration of NaCl increases. The cation of the supporting electrolyte increases the rate of the reduction along the series Li⁺ < Na⁺ < K⁺ < Cs⁺. Higher rates than that of the alkalimetals have been obtained in the presence of ammonium as well as of multivalent cations such as Ca²⁺ and La³⁺. The anion of the supporting electrolyte decreases the rate of the reduction in the order I⁻ > Br⁻ > Cl⁻ > F⁻ at −1.8 V.The experimental results were qualitatively explained by the Frumkin theory and additionally by the theory of the formation of ion pairs between the cation of the supporting electrolyte and the reacting nitrate.     

Electrodeposition of macroporous silver films from ionic liquids and assessment of these films in the electrocatalytic reduction of nitrate

Macroporous silver films, ordered or fragmented, were fabricated by electrodeposition of silver into the interstitial spaces of templates formed by polystyrene (PS) latex spheres that had been self-assembled onto bare indium tin oxide (ITO) electrodes or onto gold-coated ITO (ITO/Au) electrodes (in which the electrode had been coated by gold sputtering deposition) from two room-temperature ionic liquids (ILs): N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (BMP-TFSI) and N-butyl-N-methylpyrrolidinium dicyanamide (BMP-DCA), respectively, under normal atmospheric conditions. After electrodeposition of silver, the PS spheres were removed by dissolution in tetrahydrofuran (THF) to leave a macroporous silver structure. The higher wettability of ILs onto PS spheres leads to improved penetration of the ILs into the cavities of the PS templates. Electrodeposition is easier if an electrolyte that has a good penetration into the interstitial spaces between the PS spheres. The macroporous silver electrode exhibited much better electrocatalytic performance with respect to nitrate reduction than a regular silver wire electrode. Quantitative determination of nitrate was also examined.     

水滑石负载型PdCu催化剂的制备及性能

以掺杂Cu的类水滑石(Cu-HTs)作为载体,Cu-HTs中高分散的构晶离子Cu~(2+)作为定位剂,利用Cu和Pd间的强相互作用,诱导Pd原子定位分散在载体表面,得到小尺寸和高分散的PdCu双金属纳米催化剂。采用XRD、STEM、XPS、HRTEM等对催化剂结构、物相及组成进行表征。结果表明,PdCu/HTs的纳米颗粒尺寸约为2.4 nm,分散度达36.7%,形成PdCu合金。在苯甲醇氧化反应中考察PdCu/HTs催化剂的性能,苯甲醇可实现完全转化,苯甲醛产率达97%。     

Electrocatalytic reduction of nitrate on copper electrode in alkaline solution

This work is devoted to the study of the kinetics and reaction mechanism of nitrate reduction on a copper electrode in 0.1 M NaOH, which acts as the supporting electrolyte. The experimental methods include cyclic voltammetry (CV), cronoamperometry (CA), controlled-potential electrolysis (CPE), and coulometry. In CV, there are three potential regions where charge transfer reactions take place, reactions which are associated with NO₃⁻ and/or intermediates reduction. Two isopotential points observed in CV indicate the existence of some competitive adsorption processes at the electrode surface.The three charge transfer steps were also made evident in the CA, CPE and coulometry studies. The correlation of the experimental results with the literature data led to the conclusion that NO₃⁻ reduction on a copper electrode in 0.1 M NaOH has an intermediate (N₂O₂²⁻) species, which reduces to N₂ at a potential of about −1.3 V and to NH₄OH at potential values lower than −1.4 V (both values are vs. SCE).     

Adsorption of carbon dioxide on hydrotalcite-like compounds of different compositions

The adsorption of carbon dioxide on hydrotalcite-like compounds was investigated. Two different powdered hydrotalcites were used containing the cations nickel and iron. The powdered materials were screened for carbon dioxide adsorption using a thermogravimetric method and it was found that NiMgAl (Sample 1) hydrotalcite has the largest capacity for CO₂, adsorbing 1.58 mmol g⁻¹ at 20 °C, and highest rate of adsorption of up to 0.17 mmol g⁻¹ min⁻¹. This represented an increase of 53% in adsorption capacity, compared with NiMgAlFe (Sample 2). In order to improve the rheological behaviour of hydrotalcite paste for extrusion, hydrotalcite powders were combined with boehmite alumina (70:30 and 50:50 ratios of hydrotalcite:boehmite) before extrusion into pellets suitable for use in a fixed bed adsorber. These pellets were then re-crushed and further tested by thermogravimetric methods. The effects of temperature, composition and pre-treatment of the hydrotalcites on the adsorption of carbon dioxide and nitrogen are reported. At 20 °C, the amount of carbon dioxide adsorbed was between 2.0 and 2.5 mmol g⁻¹ for all the hydrotalcite/alumina samples in this study, although this decayed rapidly with increasing temperature. The results are compared with silica gel as a common sorbent reference, and with literature values. Hydrotalcite/alumina samples have thermal stability and a high adsorption capacity for carbon dioxide over a wide range of temperatures. The composition of the hydrotalcite/alumina pellets investigated in this study has less effect upon the adsorption behaviour compared with the non-calcined hydrotalcite powder, thus allowing a wide choice of pellet compositions to be used.     

Optimization of the N2 generation selectivity in aqueous nitrate reduction using internal circulation micro-electrolysis

The reduction of nitrate using internal circulation micro-electrolysis technology (ICE) was investigated. The effect of the reaction time, initial pH, Fe/C ratio, and aeration rate on the nitrate reduction was investigated using a single factor experiment. Based on the results of the single factor experiment, a response surface methodology (RSM) was applied to optimize the N₂ generation selectivity. The effects and interactions of three independent variables were estimated using a Box-Behnken design. Using the RSM analysis, a quadratic polynomial model with optimal conditions at pH=8.8, Fe/C=1:1, and an aeration rate of 30 L·min^-1 was developed by means of the regression analysis of the experimental data. Using the RSM optimization, the optimal conditions yielded a N₂ generation selectivity of 72.0%, which is in good agreement with experimental result (73.2%±0.5%) and falls within the 95% confidence interval (IC:66.8%-77.3%) of the model results. This indicates that the model obtained in this study effectively predicts the N₂ generation selectivity for nitrate reduction by the ICE process, thus providing a theoretical basis for process design.     

The electrochemical reduction of nitrate in acidic nitrate solutions

Cathodic regeneration of nitrous acid by electrochemical reduction of nitrates could yield a catholyte which is useful in the processing of manganiferous ores. The purpose of the present investigations was to study the cathodic reaction in an electrolytic cell with an acidic nitrate electrolyte. Electrochemical reduction of nitrate has been investigated in the ranges 0.45–2.70m H+, 0.0–0.1m HNO2, 0.5–2.0m NO3– and 20–80°C at several cathode materials. Potentiodynamic scanning experiments with a platinized titanium cathode showed limiting current densities of 0–300Am–2 at cathode potentials of +950–+700mV vs SHE. At cathode potentials less than +700mV vs SHE, cathodic reduction of nitrous acid to nitric oxide took place. A linear relation between the nitrous acid concentration and the limiting current density was found in this experimental range. Nitrous acid can be produced by cathodic reduction of nitric acid in a membrane cell. However, the maximum concentration of nitrous acid that can be produced is limited by two reactions; decay of nitrous acid to nitric acid and nitric oxide and cathodic reduction of nitrous acid to nitric oxide.     

Promoting effect of electroactive polymer supports on the catalytic performances of palladium-based catalysts for nitrite reduction in water

Conducting polymers, polypyrrole and polyaniline, were used as supports for Pd in order to obtain catalysts with higher performances than a classical Pd/Al₂O₃ catalyst for application in water treatment. The supports and the catalysts were characterized by elemental analysis, Fourier transformed infra-red spectroscopy (FTIR), transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD) and by their activity in nitrite reduction. It was demonstrated that these conducting polymers can be advantageously used as support for noble metals such as palladium. Indeed, the redox properties of these supports allow the deposition of a part of palladium directly in the reduced state and also a direct reduction of nitrite, even if this reduction is not complete. The Pd/polyaniline and Pd/polypyrrole catalysts are much more active than the classical Pd/Al₂O₃ catalyst with less ammonium ions. These better performances were explained by the redox and ion-exchange properties of the conducting polymers allowing the exchange between the hydroxides produced and the dopant anion of the conducting polymer. The ion-exchange property of the polymer depends on its oxidation state which is directly linked to the polymerization conditions and then can be easily modulated.