Reduction Of Nitrite In Water Research Articles

Uniformly Distributed Palladium Nanoparticles on NH2‐MIL‐53 Fabricated by an Equilibrium Adsorption Method for Reduction of Nitrite in Water

Metal particle on a support material should be small and homogeneous in size, which is desirable when using it as a catalyst. In this study, we investigated to introduce Pd nanoparticles (NPs) with narrow size distribution into NH2‐MIL‐53, which was prepared by the reaction of aluminum(III) nitrate with 2‐aminoterephthalic acid. Only by immersing it in an aqueous PdCl2 solution, followed by the reduction with NaBH4, Pd NPs of about 2 nm with unform distribution were formed in NH2‐MIL‐53 up to 3.5 wt.% Pd loadings. Amino group on the linkers in NH2‐MIL‐53 played a critical role for the introduction of (PdCl3)– as a precursor for Pd NPs, while no Pd was introduced into MIL‐53 without amino group. The obtained catalysts (Pd@NH2‐MIL‐53) showed high catalytic performance for reduction of nitrite in water. The specific activity per Pd site exposed on the surface changed greatly depending on the Pd loadings despite the size of Pd NPs unchanged. Pd@NH2‐MIL‐53 with low Pd loadings showed higher specific activity (TOF = 2.9×102 h‐1), which might be due to the preferential exposure of Pd(111) facet on Pd NPs.

Electrocatalytic Multielectron Nitrite Reduction in Water by an Iron Complex

Catalytic reduction of nitrite by an iron complex in water near neutral pH to form hydroxylamine and ammonium is reported. The catalyst is an iron center coordinated by the pentadentate macrocycle ...

Insight into the size effect of Pd nanoparticles on the catalytic reduction of nitrite in water over Pd/C catalysts

Nitrite catalytic reduction over Pd nanocatalyst is a size sensitive reaction in terms of both activity and selectivity.

Selective Reduction of Nitrite to Nitrogen with Carbon-Supported Pd–AOT Nanoparticles

The catalytic reduction of nitrite in water with hydrogen has been studied using a new strategy to control selectivity. The catalysts used are based on size-controlled Pd–AOT nanoparticles, synthesized via sodium bis[2-ethylhexyl] sulfosuccinate (AOT)/isooctane reverse microemulsion, supported on activated carbon. The most remarkable feature of the catalysts is the negligible selectivity toward ammonium, which is attributed to shielding of Pd NPs by AOT and blockage of the active centers related to ammonium generation. The shielding by AOT also reduces the activity of Pd–AOT NPs, which can be overcome by immobilization on carbon and thermal treatment at mild conditions (473 K, N2 atmosphere), although excessive removal of AOT results in higher ammonium production. Complete nitrite conversion with total selectivity to N2 was achieved at room temperature for the Pd–AOT/C catalysts at controlled pH media using CO2 as buffer agent. Moreover, the catalytic activity results at controlled pH show that the nitrit...

PdAu Alloy Nanoparticle Catalysts: Effective Candidates for Nitrite Reduction in Water

Well-defined palladium–gold nanoparticles (PdAuNPs) with randomly alloyed structures and broadly tunable compositions were studied in catalytic nitrite (NO2–) reduction. The catalysts were synthesized using a microwave-assisted polyol coreduction method. PdxAu100–xNPs with systematically varied compositions (x = 18–83) were supported on amorphous silica (SiO2) and studied as model catalysts for aqueous NO2– reduction in a batch reactor, using H2 as the electron donor. The reactions followed pseudo-first-order kinetics for ≥80% NO2– conversion. The PdxAu100–xNP-SiO2 catalysts showed a volcano-like correlation between NO2– reduction activity and x; the highest activity was observed for Pd53Au47, with an associated first-order rate constant of 5.12 L min–1 gmetal–1. Alloy NPs with greater proportions of Au were found to reduce the loss in catalytic activity due to sulfide fouling. Density functional theory calculations indicate that this is because Au weakens sulfur binding at PdAuNP surfaces due to atomic e...

Catalytic reduction of nitrite in water over ceria- and ceria–zirconia-supported Pd catalysts

In this study, we tested Pd/Ce1−xZrxO2 catalysts (x=0, 0.3, 0.5 and 0.7) for nitrite reduction in water. The Ce1−xZrxO2 was synthesized by the co-precipitation method, and Pd was impregnated on the support using the deposition–precipitation method. The introduction of Zr into the ceria lattice of the catalyst with x=0.3 and 0.5 distorted the lattice structure, accordingly, both the catalysts easily reduced nitrite than the pure CeO2 supported Pd catalyst. In contrast, the Pd/Ce0.3Zr0.7O2 (x=0.7) catalyst became difficult to reduce as the tetragonal ZrO2 phase was dominant in the catalyst structure. These phenomena led to the difference in the amount of oxygen vacancies on the surface of the catalyst. In the nitrite reduction test, the catalyst containing more oxygen vacancies showed higher activity. The relationships between the catalytic activities and the surface properties with composition of the support over Pd/Ce1−xZrxO2 catalysts were investigated by X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses.

Controlled Pd deposition on fibers by electroless plating. The effects of the support on the reduction of nitrite in water

Pd catalysts supported on activated silica–alumina fibers (CFs) and activated carbon felts (ACFs) were prepared and evaluated for the reduction of nitrite in water in a batch reactor. The electroless plating (ELP) method was used in order to deposit small Pd particles on the surface of the fibers. While a homogeneous distribution of Pd nanoparticles was obtained for carbon fibers, this was not the case for ceramic ones in which non-homogeneous patches of Pd films were formed. This fact resulted in a higher activity for nitrite reduction when carbon fibers were used. However, the selectivity toward the undesired product ammonia, measured at the end of the reaction, was slightly higher for Pd/ACFs catalysts.

Synthesis of Pd/Al2O3 coating onto a cordierite monolith and its application to nitrite reduction in water

The catalytic properties of Pd/Al2O3 coating onto cordierite monolith channels for the nitrite reduction in water were studied. This coating was synthesized producing an alumina layer via washcoat and adding the palladium species to this layer by immersion into a PdCl2 solution. Different characterization techniques, XRD, XPS, SEM and EDX were used to study the physicochemical and morphological properties of the catalytic coatings. The comparison of these results along with the catalytic behaviors allowed comprehension of Pd active sites and their way of acting. The structured catalyst so obtained was active and stable in the nitrite reduction.

Nitrite reduction over Pd supported CNFs: Metal particle size effect on selectivity

Pd catalysts supported on carbon-nano-fibers (CNFs) were synthesized via Pd colloids stabilized with polyvinyl-alcohol (PVA). Pd catalysts with narrow particle size distributions and mean Pd sizes between 2.6 and 30nm were immobilized on CNFs. Characterization with CO-chemisorption and transmission electron microscopy (TEM) revealed that a significant part of the Pd surface is blocked by the polymer layer on the Pd particles. The prepared catalysts were tested for nitrite reduction in water, resulting in formation of nitrogen and ammonia. Turn over frequencies were found to be independent of Pd particle size while selectivity to ammonia clearly decreased with increasing Pd particle size.

Controlled Pd deposition on carbon fibers by electroless plating for the reduction of nitrite in water

Abstract Pd catalysts supported on activated carbon felts (ACFs) with different metallic loadings were prepared by electroless plating and evaluated for the reduction of nitrite in water in a batch reactor. Homogeneous Pd dispersions were obtained, the plating solution concentration and the seeding step being the key variables that determine particle size and morphology. The formation of Pd crystals of 96 ± 22 nm situated at the external surface of the carbon fibers was obtained for 0.14 wt.% of metal loading, while an incipient formation of a Pd thin layer was detected for 1.9 wt.%. The fresh and used catalysts were characterized by SEM, EDS, XRD and XPS.

Effect of supports on Pd–Cu bimetallic catalysts for nitrate and nitrite reduction in water

The activities of the Pd–Cu catalysts supported on various metal oxides for the reduction of nitrate and nitrite ions were compared at a constant pH. Among them, the catalysts supported on titania xerogel prepared by a glycothermal method showed the highest performance for nitrate reduction. For the reduction of nitrite ions, Pd–Cu/CeO2 showed the highest catalytic activity; however, significant dissolution of the components of the catalyst was observed during the reaction at a relatively low pH range. On the other hand, a single-component Pd catalyst supported on titania xerogel showed excellent activity for the reduction of nitrite ion and could be used at a wide range of pH. For these catalysts, the product selectivity for N2 from nitrite ions was markedly improved by decreasing the partial pressure of H2 in the feed.

Carbon nanofibers in catalytic membrane microreactors

Abstract In this study, we report on the fabrication and operation of new hybrid membrane microreactors for gas–liquid–solid (G–L–S) reactions. The presented reactors consist of porous stainless steel tubes onto which carbon nanofibers (CNFs) are grown as catalyst support, all encapsulated by a gas permeable coating. Such reactors benefit from a controlled G–L–S interface of a membrane reactor and high surface area of carbon nanofibers as catalyst support. Preparation steps such as porous stainless steel hollow fiber fabrication, CNF growth on the stainless steel surface, palladium catalyst immobilization and an outer gas permeable polymeric coating steps are presented. The fabricated microreactors have high surface area, mechanical strength and catalytic activity for nitrite reduction in water. Results proved high nitrite reduction performance of these reactors, even without the presence of palladium (Pd) or additional hydrogen (H 2) supply. Our results suggest intrinsic reductant properties and catalytic activity of the reactors, which make them very suitable for hydrogenation reactions.

Support effect on selectivity of nitrite reduction in water

Palladium catalysts on various supports were studied for the hydrogenation of aqueous nitrite solution. The effects of reaction parameters such as nitrite and hydrogen concentration, pH and reaction temperature on the selectivity were discussed. Internal concentration gradients are influencing the selectivity significantly. Gradients of protons and nitrite are responsible for increasing ammonia selectivity. Carbon based catalysts were more selective towards ammonia as compared to oxidic supports. We propose that electron conductivity of carbon supports influences internal concentration gradients of both hydrogen and protons, favouring ammonia selectivity.

Activated Carbon Supported Metal Catalysts for Nitrate and Nitrite Reduction in Water

Ten monometallic and 13 bimetallic catalysts supported on activated carbon were assessed, the former in the reduction of nitrate or nitrite and the latter in the nitrate reduction. Under the conditions used, nitrite was shown to be reduced by monometallic catalysts. With exception of Ru, only some of the bimetallic catalysts were able to reduce nitrate. Rh–Cu shows the highest conversion, but Pd–Cu is the most promising catalyst if selectivity into nitrogen is also considered.

Metallocenyl Dendrimers and Their Applications in Molecular Electronics, Sensing, and Catalysis

We have investigated the movement of electrons around the peripheries of dendrimers and between their redox termini and electrodes through studies of the electrochemistry of dendrimers presenting metallocenes (and other transition metal sandwich complexes) as terminal groups. Because these compounds can be stabilized in both their oxidized and their reduced forms, their electrochemical and chemical redox processes proceed without decomposition (chemical reversibility). Most interestingly, electrochemical studies reveal that electron transfer within the dendrimers and between the dendrimers and electrodes are both very fast processes when the branches are flexible (electrochemical reversibility). When the dendrimer branches are sufficiently long, the redox events at the many termini of the metallodendrimer are independent, appearing as a single wave in the cyclic voltammogram, because of very weak electrostatic effects. As a result, these metallodendrimers have applications in the molecular recognition, sensing, and titration of anions (e.g., ATP(2-)) and cations (e.g., transition metal complexes). When the recognition properties are coupled with catalysis, the metallodendrimers function in an enzyme-like manner. For example, Pd(II) can be recognized and titrated using the dendrimer's terminal redox centers and internal coordinate ligands. Redox control over the number of Pd(II) species located within a dendrimer allows us to predetermine the number of metal atoms that end up in the form of a dendrimer-encapsulated Pd nanoparticle (PdNP). For hydrogenation of olefins, the efficiency (turnover frequency, TOF) and stability (turnover number, TON) depend on the size of the dendrimer-encapsulated PdNP catalysts, similar to the behavior of polymer-supported PdNP catalysts, suggesting a classic mechanism in which all of the steps proceed on the PdNP surface. On the other hand, Miyaura-Suzuki carbon-carbon bond-forming reactions catalyzed by dendrimer-encapsulated PdNPs proceed with TOFs and TONs that do not depend on the size of the PdNPs. Moreover these catalysts are more efficient when employed in lower (down to "homeopathic") amounts, presumably because of a leaching mechanism whereby Pd atoms escape from the PdNP surface subsequent to oxidative addition of the aryl halide. Under these conditions, the "mother" PdNPs have greater difficulty quenching the extremely active leached Pd atoms because of their low concentration. Although dendrimers presenting catalysts at their branch termini can be recovered and reused readily, their inner-sphere components can lead to steric inhibition of substrate approach. In contrast, star-shaped catalysts do not suffer from such steric problems, as has been demonstrated for water-soluble dendrimers bearing cationic iron-sandwich termini, which are redox catalysts of cathodic nitrate and nitrite reduction in water.

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.

Water-soluble mono- and star-shaped hexanuclear functional organo-iron catalysts for nitrate and nitrite reduction in water: syntheses and electroanalytical study

Ten functional sandwich complexes [Fe II(η 5-C 5H 4CO 2H)(η 6-(arene)][PF 6] and [Fe +(η 5-C 5H 5)(η 6-(C 6(CH 2CH 2C 6H 4OH) 6)][PF 6] have been synthesized to provide water-soluble redox catalysts with a range of redox potentials for the Fe II–Fe I redox couple. The CpFe + induced CH benzylic activation and the carboxylation of hexamethylbenzene, the CpFe + induced one-pot polymethylation of mesitylene and hexamethylbenzene, and the one-pot CpFe + induced hexa- p-methoxybenzylation of hexamethylbenzene have led to the desired functionalized complexes. These compounds catalyze the cathodic reduction of nitrate and nitrite in a basic aqueous medium on a Hg cathode. The rates of the rate-limiting steps of the redox-catalytic processes involving the homogeneous reduction of nitrate and nitrite by the ‘19-electron’ states of the redox catalysts have been measured using enhancement of the intensity of the monoelectronic cathodic wave Fe II→Fe I in the presence of the substrate by cyclic voltammetry, polarography and chronoamperometry. For six iron sandwich complexes without excessive bulk around the iron center, a linear Marcus-type correlation between the kinetics and the thermodynamics was found by plotting the logarithm of this rate constant versus the redox potential, which indicates that the homogeneous electron-transfer from the 19-electron catalyst to the substrate is rate-limiting. With four complexes in which chains of the arene ligand introduced more bulk around the iron center, the rates were found to be an order of magnitude lower, showing the crucial effect of the distance on the outer-sphere electron transfer. A small inner-sphere contribution cannot be discarded, however. When the redox catalysts are attached to the termini of the branches of hexa-branch star-shaped cores, the rate constants are close to those of unencumbered catalysts, i.e. no significant loss of activity is observed.

Effect of ph on the reduction of nitrite in water by metallic iron

Chemical reduction is an alternative technique to remove nitrogen oxides from contaminated groundwater and closed-surface water body. Metallic iron was employed as a reductant for the reduction of nitrite in water in this study. The effect of pH on the rate and products of nitrite reduction was investigated with a fixed dosage of metallic iron powder (12 mol-Fe/mol-N, size of the powder: 80 mesh). The reduction of nitrite by metallic iron was a pseudo-zero-order reaction under the experimental conditions. The reduction rate of nitrite was increased with decreasing the pH of reaction solution, and the pseudo-zero-order reaction rate constants were 180, 130, 60, 15, 10, and 1 mM/h at pH=2, 3, 4, 5, 6, and 7, respectively. The reduction products of nitrite were nitrogen gas and ammonium. The yields of nitrogen gas from nitrite reduction were 0.63, 0.74, 0.81, 0.87, 0.92, and 0.98 as molar ratios of nitrogen atom at pH=2, 3, 4, 5, 6, and 7, respectively. Neutral condition enhanced the formation of nitrogen gas from nitrite reduction.