Reduction Of Nitrate In Water Research Articles

Photocatalytic nitrate reduction over Pd–Cu/TiO2

Abstract The extension of photocatalytic nitrate reduction in water by a 1%Pd–1%Cu (%wt) catalyst supported on TiO 2 was evaluated under different reaction conditions. A series of electron sacrificial donors such as formic acid, oxalic acid, ethanol, methanol, and humic acid were used for inhibiting the mechanism of electron/hole recombination on the semiconductor by hole scavenging. In addition, the roles of H 2 as reducing agent and CO 2 as buffer are also discussed. The photocatalytic process is found to be more selective towards nitrogen than the dark catalytic process. Hole scavengers, or reducing H 2 increase significantly the photocatalytic reduction of nitrate. Complete (100%) conversion was obtained when both H 2 and CO 2 were used as reducing and buffer agent, respectively. Among the hole scavengers tested, 0.08 M formic acid solution represents the best compromise between nitrate conversion (84%) and nitrogen selectivity (83%).

나노 크기의 타이타니아 담체를 활용한 Pd-Cu 촉매의 수중 질산성 질소 저감 반응에의 적용

In this study, we synthesized TiO2 supports with nanosized crystalline structure by solvothermal method and prepared TiO2 supported Pd-Cu catalysts. It was shown that the crystalline size of TiO2 support in the catalyst influenced on the catalytic activity of nitrate reduction in water. The catalyst with the smaller crystalline size of TiO2 support presented faster nitrate reduction rate, but had low nitrogen selectivity due to high pH environment of reaction medium during the reaction. Through injection of carbon dioxide as a pH buffer, the nitrogen selectivity increased by about 60%. Furthermore, we investigated that the relationships between the catalytic performance and the physicochemical properties of the prepared catalysts characterized by N2 adsoprtion-desorption, X-ray diffraction (XRD), H2-temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS).

Simultaneous Bromate and Nitrate Reduction in Water Using Sulfur‐Utilizing Autotrophic and Mixotrophic Denitrification Processes in a Fixed Bed Column Reactor

Carcinogenic bromate (BrO3−) can be present in drinking water as a result of its formation from bromide (Br−) during ozonation. A fixed bed column reactor filled with elementel sulfur and limestone was operated for about six months under autotrophic and mixotrophic (autotrophic + heterotrophic) conditions at 30°C. The reactor was operated at the hydraulic retention time (HRT) ranging from 16.5 to 10.1 h at autotrophic conditions. Under mixotrophic conditions, 45 mg/L NO3‐N was removed completely at C/N ratio (mg CH3OH/mg NO3‐N) between 0.55 and 1.66 at HRT of 10.1 h. The average effluent pH was 7.8 and the sulfate concentration was lower than the Environmental Protection Agency limits at the mixotrophic stages. Efficient simultaneous BrO3− and nitrate removal was achieved at feed concentrations of 100–500 µg/L BrO3− and 45 mg/L nitrate under autotrophic and mixotrophic conditions. Effluent Br− measurements indicated that BrO3− was completely reduced without accumulation of by‐products.

Removal Techniques of Nitrate from Water

Nitrate pollution of water is a major environmental problem all over the world. Consequently, numerous techniques have been developed to remove or reduction of nitrate in water. A review of removal techniques of nitrate from water has been carried out in this paper. Recent literatures related to various techniques including reverse osmosis, ion exchange, electrodialysis, biological denitrification, chemical denitrification, adsorption methods using different adsorbents like carbon base, agricultural waste, natural materials are systematically review to assess their performance. The paper reveals that adsorption could be the most promising technique of removal of nitrate from water in near future.

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Nitrate contamination of groundwater limits it use as a drinking water supply unless the nitrate is removed. The aim of this study was to move toward implementing photocatalysis for nitrate treatment in drinking water systems by understanding the effects of experimental conditions and the mechanisms involved. Specifically, the photocatalytic reduction of nitrate in water was examined using titanium dioxide (Evonik P90) loaded with silver nanoparticles and formate as a hole scavenger (electron donor). Experimental conditions including pH, nitrate concentration, formate concentration, photocatalyst concentration, and silver loading were varied to demonstrate their effect on the rate of nitrate and formate removal as well as by-product selectivity. For drinking water applications, minimization of residual formate is essential to prevent adverse effects in potable water distribution systems (e.g., carbon source for biofilm growth). The experimental stoichiometric requirement for formate indicated that it acts as a two-hole scavenger, which suggests conduction band electrons, rather than radicals, are responsible for nitrate reduction. Using optimal operating conditions, nitrate and formate were efficiently removed at nearly a 1:1 ratio, showing that the residual hole scavenger concentration can be controlled while maintaining an acceptable rate. Compared to P90 alone, the addition of silver nanoparticles improved the rate of nitrate and formate removal significantly, reduced the overpotential for nitrate reduction, and provided a more positive surface charge. The removal rates decreased with increasing pH, which suggests that the reaction is a proton-coupled electron reaction and that adsorption of the constituents is necessary for effective charge transfer. Under acidic conditions (pH = 2.5), nitrogen gases (∼85%) and ammonium (∼15%) were the final by-products. Between pH 3.5 and 4, a sudden by-product switch occurred to nitrite, suggesting that, at higher pH, a co-catalyst that is efficient at localizing protons is required to move beyond nitrite.

Nitrate reduction of brines from water desalination plants by membrane electrolysis

The disposal of the saline effluent generated during membrane water desalination by electrodialysis (ED) or reverse osmosis (RO) is an increasing problem worldwide, especially for the desalination of inland brackish water. Electrolysis can be an alternative to the denitrification of brines by the reduction of nitrates to the desired product (N2). Nevertheless, in a paired electrolysis cell the reduced products could be re-oxidized in the anode by the reverse reactions; for example, nitrite could be again converted to nitrate. Membrane electrolysis can avoid these reactions. The aim of this study was to assess the efficacy of the membrane electrolysis technique in the reduction of nitrate in water. The experiments were performed in an electrochemical cell with two compartments separated by a cation-exchange membrane, the cathode being made of copper and the anode of titanium oxide and ruthenium oxide (70TiO2/30RuO2). Nitrite, ammonium and nitrogen containing gases (most of them N2) were the reaction products. The best value was achieved with a cell voltage of 9V and an initial concentration of 526mg/L of NO3−. Under these conditions, high conversion to nitrite and gaseous compounds was registered with the formation of just 7.8mg/L of ammonium.

Combinational effect of Pt/SrTiO3:Rh photocatalyst and SnPd/Al2O3 non-photocatalyst for photocatalytic reduction of nitrate to nitrogen in water under visible light irradiation

Photocatalytic reduction of nitrate in water in the co-presence of Pt/SrTiO3:Rh and SnPd/Al2O3 under visible light irradiation (λ>420nm) was investigated. This reaction system efficiently and selectively promoted the photocatalytic reduction of nitrate to nitrogen, whereas Pt/SrTiO3:Rh or SnPd/Al2O3 alone showed little activity under the reaction conditions. The selectivity to N2 was 94% under the optimum reaction conditions, where the amounts of Pt/SrTiO3:Rh and SnPd/Al2O3 loaded in the reaction system were 500mg and 150mg, respectively. This reaction system showed a superior nitrate decomposition rate and superior selectivity to nitrogen compared with SrTiO3:Rh directly modified with SnPd bimetal. From analysis of the reaction mechanism, hydrogen formed by photoreduction of water over Pt/SrTiO3:Rh acted as the reductant for a non-photocatalytic nitrate conversion reaction over SnPd/Al2O3. Moreover, the products, including formaldehyde and formic acid, formed by photo-oxidation of methanol over Pt/SrTiO3:Rh acted as reductants for nitrate over SnPd/Al2O3.

Catalytic reduction of nitrate in water over Pd–Cu/TiO2 catalyst: Effect of the strong metal-support interaction (SMSI) on the catalytic activity

In this study, we prepared TiO2-supported Pd–Cu catalysts of different anatase/rutile phase compositions, which were used in a nitrate reduction in water. It was shown that the catalysts containing a greater anatase phase composition had higher catalytic performance. Through characterization studies using H2-temperature programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS), the observed trend of the catalytic activity was correlated to the degree of the strong metal-support interaction (SMSI) over the catalysts. The SMSI occurred through pre-treatment of the catalysts by H2 reduction (at 200°C), which resulted in increased partially reduced TiO2−x and electron-rich active metal (Pd and Cu) states at the catalyst of higher composition of anatase phase. The relationships between the changes in the properties and activities of the catalysts as a result of the anatase phase composition are discussed.

중형 기공성 실리카 담체에 담지된 Pd-Cu 촉매를 활용한 수중 질산성 질소 저감 반응

본 연구에서는 중형 기공성 실리카 담체인 MCM-41과 SBA-15를 활용하여 팔라듐과 구리를 담지한 후, 제조 촉매의 수중 질산성 질소 저감 반응 활성을 평가하였다. 순수 수소 공급 반응 조건에서, 질산성 질소의 농도는 반응 시간에 따라 점차 저감되었지만, 반응기 내부에 높게 형성된 pH로 인해 질소의 선택도가 매우 낮은 문제점이 발견되었다. 이를 해결하기 위해 이산화탄소를 수소와 함께 공급하여 pH의 안정화를 도모하였고, 질소 선택도를 40% 가량 증가시켰다. 상기 두 반응 조건에서 모두 Pd-Cu/MCM-41가 Pd-Cu/SBA-15보다 높은 활성을 나타냈다. 이와 같이 수중 질산성 질소 저감 반응의 활성에 차이를 보이는 두 촉매에 대하여, 질소 흡-탈착, XRD, <TEX>$H_2$</TEX>-TPR, XPS 등과 같은 특성 분석을 수행하여 제조 촉매의 구조와 물성이 반응활성에 미치는 영향을 검토해보았다. In this study, we investigated the activity of Pd and Cu co-incorporated on mesoporous silica support such as MCM-41 and SBA-15 for catalytic nitrate reduction in water. In pure hydrogen flow, nitrate concentration was gradually decreased with the reaction time, but nitrogen selectivity was too low due to very high pH of reaction medium after the reaction. In order to acquire high nitrogen selectivity, we utilized carbon dioxide as a pH buffer, which resulted in higher nitrogen selectivity (about 40%). For the above reaction conditions, Pd-Cu/MCM-41 showed better performance than Pd-Cu/SBA-15. The physicochemical properties of both catalysts were investigated to figure out the relationship between the characteristics of the catalysts and the catalytic activity on the catalytic nitrate reduction by <TEX>$N_2$</TEX> adsoprtion-desorption, X-ray diffraction (XRD), <TEX>$H_2$</TEX>-temperature programmed reduction, X-ray photoelectron spectroscopy (XPS) techniques.

Activated carbon supported metal catalysts for reduction of nitrate in water with high selectivity towards N2

The catalytic removal of nitrate in water with hydrogen was investigated by using different activated carbon-supported metal catalysts. A commercial activated carbon (CAC) and one prepared by chemical activation of grape seeds with phosphoric acid (GS) were evaluated for the preparation of bimetallic catalysts (Pd–Cu, Pd–Sn and Pd–In). The support plays an important role in the catalytic performances for nitrate removal, affecting both activity and selectivity. Pd–Cu catalyst supported on GS showed the highest nitrate removal activity and nitrite was not found as by-product. The acidity of the reaction medium is associated with this behavior, attributing this effect to the chemical composition of the catalyst support. Control of pH through CO2 addition to the reaction medium was beneficial in the case of the Pd–Cu catalyst prepared with CAC. However, no significant influence was observed in the case of the GS-supported catalyst. The concentration of promoting metal affects more strongly the catalyst performance than that of Pd. Low Cu contents (0.5 and 1.5wt.%) within the range tested (0.5–5wt.%) led to the highest selectivity towards the undesired ammonium ion. The catalysts supported on GS with 2.5% Cu and 5% Pd allowed achieving the European Standards for drinking water when a 100mg/L nitrate starting solution was treated, in terms of nitrate, nitrite and ammonium concentrations. The Pd–based bimetallic catalysts containing Sn and In as promoting metal showed a lower catalytic activity and significantly higher selectivity towards ammonium.

Photocatalytic nitrate reduction in water: Managing the hole scavenger and reaction by-product selectivity

Nitrate contamination of groundwater limits it use as a drinking water supply unless the nitrate is removed. The aim of this study was to move toward implementing photocatalysis for nitrate treatment in drinking water systems by understanding the effects of experimental conditions and the mechanisms involved. Specifically, the photocatalytic reduction of nitrate in water was examined using titanium dioxide (Evonik P90) loaded with silver nanoparticles and formate as a hole scavenger (electron donor). Experimental conditions including pH, nitrate concentration, formate concentration, photocatalyst concentration, and silver loading were varied to demonstrate their effect on the rate of nitrate and formate removal as well as by-product selectivity. For drinking water applications, minimization of residual formate is essential to prevent adverse effects in potable water distribution systems (e.g., carbon source for biofilm growth). The experimental stoichiometric requirement for formate indicated that it acts as a two-hole scavenger, which suggests conduction band electrons, rather than radicals, are responsible for nitrate reduction. Using optimal operating conditions, nitrate and formate were efficiently removed at nearly a 1:1 ratio, showing that the residual hole scavenger concentration can be controlled while maintaining an acceptable rate. Compared to P90 alone, the addition of silver nanoparticles improved the rate of nitrate and formate removal significantly, reduced the overpotential for nitrate reduction, and provided a more positive surface charge. The removal rates decreased with increasing pH, which suggests that the reaction is a proton-coupled electron reaction and that adsorption of the constituents is necessary for effective charge transfer. Under acidic conditions (pH=2.5), nitrogen gases (∼85%) and ammonium (∼15%) were the final by-products. Between pH 3.5 and 4, a sudden by-product switch occurred to nitrite, suggesting that, at higher pH, a co-catalyst that is efficient at localizing protons is required to move beyond nitrite.

Poly[β-(1→4)-2-amino-2-deoxy-D-ghicopyranose] based zero valent nickel nanocomposite for efficient reduction of nitrate in water

Chemical reduction of nitrate using metal nanoparticles has received increasing interest due to over-dependence on groundwater and consequence health hazard of the nitrate ion. One major drawback of this technique is the agglomeration of nanoparticles leading to the formation of large flocs. A low cost biopolymeric material, poly [β-(1→4)-2-amino-2-deoxy-D-glucopyranose] (β-PADG) obtained from deacetylated chitin was used as stabilizer to synthesize zero valent nickel (ZVNi) nanoparticles. The β-PADG-ZVNi nanocomposite was characterized using infra red (IR), UV-Vis spectrophotometric techniques and Scanning Electron Microscope (SEM). The morphology of the composite showed that β-PADG stabilized-ZVNi nanoparticles were present as discrete particles. The mean particle size was estimated to be (7.76 ± 2.98) nm and surface area of 87.10 m2/g. The stabilized-ZVNi nanoparticles exhibited markedly greater reactivity for reduction of nitrate in water with 100% conversion within 2 hr contact owing to less agglomeration. Varying the β-PADG–to-ZVNi ratio and the ZVNi-to-nitrate molar ratio generally led to a faster nitrate reduction. About 3.4-fold difference in the specific reaction rate constant suggests that the application of the β-PADG-stabilizer not only increased the specific surface area of the resultant nanoparticles, but also greatly enhanced the surface reactivity of the nanoparticles per unit area.

Photocatalytic Synthesis of Urea from in situ Generated Ammonia and Carbon Dioxide

TiO(2) and Fe-titanate (different wt%) supported on zeolite were prepared by sol-gel and solid-state dispersion methods. The photocatalysts prepared were characterized by X-ray diffraction, scanning electron microscopy and ultraviolet (UV)-visible diffuse reflectance spectroscopy techniques. Photocatalytic reduction of nitrate in water and isopropanol/oxalic acid as hole scavengers are investigated in a batch reactor under UV illumination. The yield of urea increased notably when the catalysts were supported on zeolite. The Fe-titanate supported catalyst promotes the charge separation that contributes to an increase in selective formation of urea. The product formation is because of the high adsorption of in situ generated CO(2) and NH(3) over shape-selective property of the zeolite in the composite photocatalyst. The maximum yield of urea is found to be 18 ppm while 1% isopropanol containing solution over 10 wt% Fe-titanate/HZSM-5 photocatalyst was used.

Effect of support and pre-treatment conditions on Pt–Sn catalysts: Application to nitrate reduction in water

The effect of the support (activated carbon or titanium dioxide) on the catalytic activity and selectivity to nitrogen of Pt–Sn catalysts in nitrate reduction was studied. The effects of the preparation conditions and the Pt:Sn atomic ratio were also evaluated. It was observed that the support plays an important role in nitrate reduction and that different preparation conditions lead to different catalytic activities and selectivities. Generally, the catalysts supported on activated carbon were less active but more selective to nitrogen than those supported on titanium dioxide. The monometallic Pt catalyst is active for nitrate reduction only when supported on titanium dioxide, which is explained by the involvement of the support in the reaction mechanism. The catalysts were characterized by different techniques, and significant changes on metal chemical states were observed for the different preparation conditions used. Only metallic Pt and oxidized Sn were observed at low calcination and reduction temperatures, but some metallic Sn was also present when high temperatures were used, being also possible the formation of Pt–Sn alloys.

Reduction of nitrate on active carbon supported Pd-Cu catalysts

Bimetallic Pd-Cu catalysts supported on active carbon were tested for nitrate reduction in water. The catalysts were prepared either by successive incipient wetness impregnation or catalytic reduction and were characterized by HRTEM, XRD, TPR-H 2 and H 2-chemisorption. The method of preparation exerts an influence on the activity of Pd-Cu catalysts for nitrate reduction, but the effect on their selectivity to ammonia is negligible. The Cu/Pd atomic ratio and total metal content affect both activity and selectivity of the catalysts prepared by chemical reduction.

Catalytic reduction of nitrates in water on Pt promoted Cu hydrotalcite-derived catalysts: Effect of the Pt–Cu alloy formation

In this work, the role of the Pt–Cu interaction and the influence of the Pt metal loading in the catalytic reduction of nitrates in water have been studied, using Pt supported on CuMgAl mixed oxides catalysts in a continuous reactor. Following three Pt impregnation protocols different surface chemistries were obtained, as confirmed by BET, TPR, HRTEM, XRD and FTIR spectroscopy. In the first protocol, the presence of Cu and Pt–Cu alloy formation has been promoted, whereas the second protocol leads to separated Pt and Cu particles in close contact. The third protocol leads to the presence of Cu, Pt and Pt–Cu alloy particles. The different catalytic behaviors were related to the differences in the surface metal chemistry of the samples. Low ammonium formation was detected in all cases but nitrite concentrations need to be improved to fulfill the maximum admissible concentration of the EU legislation. It is concluded that: (i) the presence of Pt–Cu alloy particles leads to an increase in nitrogen selectivity, enhancing the nitrite reduction but showing lower nitrate conversion, and (ii) to maximize the nitrate conversion it is necessary to obtain mainly Pt particles interacting with Cu and Pt–Cu alloy particles.

Nitrate reduction in water catalysed by Pd–Cu on different supports

Screening tests were carried out in order to study the influence of the support in the performance of Pd monometallic and Pd–Cu bimetallic catalysts for the reduction of nitrate in water. Several metal oxides, as well as metal oxides and activated carbon or carbon nanotube composites were assessed as supports. The catalysts were prepared and tested under the same operation conditions. It was observed that supports play an important role in the catalytic performance and in some cases are directly involved in the reaction mechanism. The Pd–Cu catalysts supported on titanium dioxide and on the composite containing carbon nanotubes and titanium dioxide present the highest conversions, while those supported on ceria materials are the most selective to nitrogen.

Nitrate reduction in water: Influence of the addition of a second metal on the performances of the Pd/CeO 2 catalyst

An attempt is made to improve the catalytic nitrate reduction on Pd/CeO 2 catalysts by the addition of a second metal. The influence of the second metal such as Sn, In and Ag on the Pd/CeO 2 for nitrate reduction is explored. The second metal is introduced over monometallic Pd/CeO 2 by a redox reaction. Pd/CeO 2 is more active than the bimetallic catalysts under pure hydrogen flow. Whereas in presence of CO 2 the monometallic Pd/CeO 2 is inactive for nitrate reduction, bimetallic catalysts are found to be more active than under pure hydrogen flow and also than the monometallic catalyst with a low selectivity towards ammonium ions, undesired product of the reaction. The Pd–Sn/CeO 2 catalyst is comparatively the most suited for nitrate reduction.

Pd–Cu/AC and Pt–Cu/AC catalysts for nitrate reduction with hydrogen: Influence of calcination and reduction temperatures

The influence of calcination and reduction temperatures on the catalytic properties of Pd–Cu and Pt–Cu bimetallic catalysts supported on activated carbon for the reduction of nitrates was studied. The catalysts were prepared using different calcination and reduction temperatures, and the respective activities and selectivities for the reduction of nitrates in water with hydrogen were assessed. It was found that the different preparation conditions lead to different catalytic performances. For both catalysts, the activity decreases by increasing calcination and reduction temperatures, whereas the effect on the selectivity is not uniform. For the 1%Pd–0.3%Cu (wt.%) catalyst, the nitrate conversion after 5 h of reaction varies from 93% (sample calcined at 200 °C and not reduced) to 25% (sample calcined and reduced at 400 °C). The formation of alloys during the preparation of the catalysts is prejudicial for nitrate reduction. In all the preparation conditions tested the Pd–Cu pair is more selective for the transformation of nitrate into nitrogen. All the samples have been characterized by nitrogen adsorption at −196 °C, CO adsorption microcalorimetry, TPR, XRD, XPS and TEM.

Nitrate Reduction Catalyzed by Pd–Cu and Pt–Cu Supported on Different Carbon Materials

AbstractThe activities and selectivities of Pd-Cu and Pt-Cu bimetallic catalysts supported on different carbon materials (activated carbons with different surface chemistries, multiwalled carbon nanotubes and carbon xerogels) were studied in the catalytic reduction of nitrate in water. The surface chemistry of the support has an important role in the catalyst activity and selectivity, being its influence more pronounced when Pt-Cu catalysts are used. Generally, catalysts supported on basic carbon materials are more active and selective.Graphical AbstractNO 3 − concentrations during nitrate reduction in the presence of 2%Pt-1%Cu catalysts.[IMAGE]