Selective Catalytic Reduction at Quasi-Perfect Pt(100) Domains: A Universal Low-Temperature Pathway from Nitrite to N 2 (original) (raw)
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Applied Catalysis A: General, 2014
The electrocatalytic reduction of NO 3 − and its intermediate NO 2 − in neutral medium was performed at a Cu-immobilized Pt surface. The voltammetric investigations showed that the bare Cu electrode has little effect on nitrate reduction reactions (NRR) whereas an enhanced catalytic effect (i.e. a positive shift of the peak potential and an increased reduction current) was observed when Cu particles were immobilized onto Pt surface. At the Cu-Pt electrode surface, the NRR process was observed to occur via a two-step reduction mechanism with a transfer of 2 and 6 electrons in the first and second steps, respectively. Similar results were obtained by chronoamperometric (CA) studies. Closer NRR mechanistic studies at the as prepared Cu-Pt electrode revealed concentration-dependent kinetics with a "critical" nitrate ion concentration of ca. 0.02 M. Moreover, NRR proceeded via a simple adsorption-desorption mechanism following a Langmuir isotherm with an adsorption Gibbs free-energy of ca. −10.16 kJ mol −1 (1st step) and ca. −10.05 kJ mol −1 (2nd step). By means of a Pt|Nafion|Cu-Pt type reactor without any supporting electrolyte, bulk electrolysis was performed to identify nitrate reduction products. It was found that after 180 min of electrolysis, 51% of NO 3 − was converted into NO 2 − intermediate. This percentage decreased to 30% in CO 2 buffered conditions. However, when a tri-metallic Pt-Pd-Cu electrode was employed as a cathode, all of the NO 2 − produced could be successfully converted into NH 3 and N 2 . The electrocatalysis of nitrate ion on Cu-Pt electrode surface showed no apparent surface poisoning as confirmed by its stability after excessive CV runs. This was further supported by surface analysis and morphology of the as-prepared catalyst with scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis.
Electro-reduction of Nitrate and Nitrite Ions on Carbon-Supported Pt Nanoparticles
ECS Transactions, 2008
Synthesized carbon-supported Pt nanoparticles (10 wt% Pt/C) and their commercial counterpart (40 wt% Pt-Etek/C) have been used to study the electrochemical reduction of NO x ions at different concentrations in alkaline and acid pH. A comparative study between nanostructured and massif platinum was evaluated. Cycling Voltammetry (CV), Rotating Disc Electrode (RDE) and Differential Mass Spectrometry (DEMS) were used for this purpose. Stationary current-potential curves indicate that the adsorption-desorption phenomena take place in two different regions of potential: the electrochemical reduction of NO x ions for potentials ranging from -0.60 to -0.95 V/SCE, and the hydrogen evolution reaction (HER) at potential lower than -0.95 V/SCE. These results confirmed that the reduction of NO x ions follows the order Pt/C > Pt-Etek/C > Pt-massif. DEMS demonstrated the formation of nitrogen species such as N 2 , NO, N 2 O and NO 2 .
Process Safety and Environmental Protection, 2021
This study reports an electrochemical reduction of the NO 3 − along with oxidation of the in-situ generated NH 4 + with maximum selectivity of the N 2 gas as the final-product. The use of aluminum as a cathode and Ti/RuO 2 as an anode showed enhanced electrochemical nitrate reduction at the cathode and oxidation of the ammonium ion at the anode. Effects of various parameters like initial NO 3 − concentration (C o = 100−400 mg L −1), a dose of the Cl − as NaCl (NaCl = 100−400 mg L −1), current density applied (j = 83.3-333.3 A m −2), solution pH (pH = 4-10) and electrolysis time (t = 0−120 min) were studied in terms of NO 3 − reduction and total nitrogen (TN) removal efficiencies. Current efficiency (CE) was elaborated with respect to end products like N 2 , NO 2 − and NH 4 +. Specific electrical energy consumption (SEC) was calculated in kWh kg −1 NO 3 − removed for the electrochemical process. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were utilized for understanding the oxidation/reduction mechanism over electrodes and the characteristics of the electrodes in a different solution. The studied mechanism suggested a circular conversion of NO 3 − through complex processes into the N 2 gas as the final product. The ultimate nitrate and TN degradation efficiency of ≈95 % with N 2 selectivity of ≈100 % were achieved at the optimum condition of C o = 100 mg L −1 , NaCl = 300 mg L −1 , j = 333.3 A m −2 , pH = 6 and time = 120 min with SEC = 927.4 kW h kg −1 NO 3 − removed. The 1 st , 2 nd , and n th-order kinetic models were used for the reaction kinetics. FE-SEM, XRD, and AFM techniques were used for the characterization of the electrodes before and after all the electrochemical runs. The operating cost was calculated for lab-scale treatment along with a comparison with previous studies. No sludge or scum got produced for each electrochemical run. Finally, this study delivers a superior perceptive for electrochemical characteristics of Al at the cathode side and Ti/RuO 2 at anode side as well as electrochemical NO 3 − reduction and oxidation of the generated NH 4 + , simultaneously.
Modern research in catalysis, 2024
Nitrate pollution is of great importance in both the environmental and health contexts, necessitating the development of efficient mitigation strategies. This review provides a comprehensive analysis of the many catalysts employed in the electrochemical reduction of nitrate to ammonia, and presents a viable environmentally friendly approach to address the issue of nitrate pollution. Hence, the electrochemical transformation of nitrate to ammonia serves the dual purpose of addressing nitrate pollution in water bodies, and is a useful agricultural resource. This review examines a range of catalyst materials such as noble and non-noble metals, metal oxides, carbon-based materials, nitrogen-doped carbon species, metal complexes, and semiconductor photocatalysts. It evaluates catalytic efficiency, selectivity, stability, and overall process optimization. The performance of catalysts is influenced by various factors, including reaction conditions, catalyst structure, loading techniques, and electrode interfaces. Comparative analysis was performed to evaluate the catalytic activity, selectivity, Faradaic efficiency, current density, stability, and durability of the catalysts. This assessment offers significant perspectives on the structural, compositional, and electrochemical characteristics that affect the efficacy of these catalysts, thus informing future investigations and advancements in this domain. In addition to mitigating nitrate pollution, the electrochemical reduction of nitrate to ammonia is in line with sustainable agricultural methods, resource conservation, and the utilization of renewable energy resources. This study explores the factors that affect the catalytic efficiency, provides new opportunities to address nitrate pollution, and promotes the development of sustainable environmental solutions.
In Situ Electrochemical Promotion by Sodium of the Platinum-Catalyzed Reduction of NO by Propene
Journal of Physical Chemistry B, 1997
The Pt-catalyzed reduction of NO by propene exhibits strong electrochemical promotion by spillover Na supplied from a ′′-alumina solid electrolyte. In the promoted regime, rate increases by an order of magnitude are achievable. At sufficiently high loadings of Na the system exhibits poisoning, and excursions between the promoted and poisoned regimes are fully reversible. Reaction kinetic data obtained as a function of catalyst potential, temperature, and gas composition indicate that Na increases the strength of NO chemisorption relative to propene. This is accompanied by weakening of the N-O bond, thus facilitating NO dissociation, which is proposed as the critical reaction-initiating step. The dependence of N 2 /N 2 O selectivity on catalyst potential is in accord with this view: Na pumping to the Pt catalyst favors N 2 production at the expense of N 2 O. X-ray photoelectron spectroscopic (XPS) data confirm that electrochemical promotion of the Pt film does indeed involve reversible pumping of Na to or from the solid electrolyte. They also show that under reaction conditions the promoter phase consists of a mixture of sodium nitrite and sodium nitrate and that the promoted and poisoned conditions of the catalyst correspond to low and very high loadings of these sodium compounds. Under all reaction conditions, a substantial fraction of the promoter phase is present as 3D crystallites.
Electroreduction of nitrate ions on Pt(111) electrodes modified by copper adatoms
Electrochimica Acta, 2010
Kinetics and mechanism of nitrate ion reduction on Pt(1 1 1) and Cu-modified Pt(1 1 1) electrodes have been studied by means of cyclic voltammetry, potentiostatic current transient technique and in situ FTIRS in solutions of perchloric and sulphuric acids to elucidate the role of the background anion. Modification of platinum surface with copper adatoms or small amount of 3D-Cu crystallites was performed using potential cycling between 0.05 and 0.3 V in solutions with low concentration of copper ions, this allowed us to vary coverage  Cu smoothly. Following desorption of copper during the potential sweep from 0.3 to 1.0 V allowed us to estimate actual coverage of Pt surface with Cu adatoms. Another manner of the modification was also applied: copper was electrochemically deposited at several constant potentials in solutions containing 10 −5 or 10 −4 M Cu 2+ and 5 mM NaNO 3 with registration of current transients of copper deposition and nitrate reduction.
Atomic Structure Modification for Electrochemical Nitrogen Reduction to Ammonia
Advanced Energy Materials, 2019
The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/aenm.201903172\. and high pressure (15-30 MPa), [1,2] which consumes more than 1% of the energy generated in the world each year. [3] This is due to the high bond energy of NN bond (941 kJ mol −1), especially the first step cleavage that requires thermodynamically strong energy barrier of 410 kJ mol −1. To maintain the reaction, it is necessary to artificially input massive energy to activate the strong bonding. Therefore, an efficient ammonia preparation process with relatively low energy consumption, low pollution, and mild conditions is urgently needed. Methods based on electrochemical catalytic reactions such as hydrogen evolution reaction (HER), oxygen evolution reaction (OER), carbon dioxide reduction reaction (CO 2 RR), and oxygen reduction reaction (ORR) have achieved great progress in the preparation of hydrogen, [4-8] hydrocarbons, [9] and oxygenates, [10] which also meet the basic requirements for establishing an emerging ammonia production process. Therefore, the study on electrochemical nitrogen reduction reaction, including reaction mechanism and electrocatalyst design, has become a top priority. In nature, the biological nitrogenase can convert N 2 into NH 3 under normal temperature and pressure. The iron-molybdenum cofactor based on the nitrogenase C@Fe 6 MoS 9 cluster with complexation and reduction active sites is considered to be the intrinsic complex for the nitrogen fixation. [11] Therefore, a large number of electrocatalysts with similar mechanisms such as transition metal sulfides and nitrides are successively analyzed and optimized, exhibiting good nitrogen-fixing properties. [12-15] In addition, some studies further developed materials like B 4 C, Bi, and black phosphorus for electrocatalytic nitrogen fixation due to the similarities in the properties of elemental electron orbital structures when compared with transition metals. [16-19] In spite of the great progress on the catalysts for NRR, regrettably, almost all electrocatalysts developed have not been exhibiting significant yields and Faraday efficiency (FE) for industrialization, mainly due to the competition between NRR and HER. In general, electrocatalysts with abundant active sites exposed at the interface between electrolyte and materials facilitate the adsorption and activation of N 2. The electrolyte, however, a natural proton source, can enable more protons during reaction due to the lower activation energy when compared with that for N 2 , that is, active sites on the interface are preferentially
The Journal of Physical Chemistry Letters, 2010
An electrode incorporating two distinct heterogeneous electrocatalysts acting in series was specifically designed to promote the reduction of nitrate beyond the nitrite stage in weakly buffered aqueous solutions (pH = 3) containing Cd 2þ. This novel interface consists of Au nanoparticles, Au(np), on which underpotentially deposited Cd reduces nitrate predominantly to nitrite, dispersed on a hemin-modified glassy carbon (GC) surface, Hm|GC, where nitrite is further reduced to yield hydroxylamine as the only product detected using a rotating Au(ring)|Hm|Au(np)|GC (disk) electrode. Additional evidence in support of this series mechanism was obtained from numerical simulations in which the bifunctional electrode was regarded as a hexagonal, closed-packed array of coplanar concentric Cd|Au(np) disks and Hm|GC rings (with no insulating gap), using rate constants determined independently from rotating Au and Hm|GC disk electrodes in solutions containing either nitrate or nitrite, respectively.
Journal of Molecular Catalysis A: Chemical, 2014
Cathodic reduction of nitrate ions has been carried out using a sandwich type membrane reactor having a configuration of Pt|Nafion|Pt-Cu in absence of any supporting electrolyte. Both Pt and Cu metals are in polycrystalline form on the cathodic surface immobilized on Nafion membrane. The globular Cu particles have a wide range of sizes (70-120 nm). During the course of electrolysis in the reactor, the bimetallic Pt-Cu surface reduces NO 3 − into NH 3 and N 2 by means of electrochemical and catalytic hydrogenation reactions, respectively. The electrochemical contribution of nitrate reduction has been investigated in details by using voltammetric and electrolysis techniques. The NO 3 − ions are electrochemically reduced using a consecutive reaction. On the consecutive way of reduction, the intermediate NO 2