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1.
The electrochemical nitrogen reduction reaction (NRR) is a promising alternative to the energy‐intensive Haber–Bosch process for ammonia synthesis. Among the possible electrocatalysts, bismuth‐based materials have shown unique NRR properties due to their electronic structures and poor hydrogen evolution activity. However, identification of the active sites and reaction mechanism is still difficult due to structural and chemical changes under reaction potentials. Herein, in situ Raman spectroscopy, complemented by electron microscopy, is employed to investigate the structural and chemical transformation of the Bi species during the NRR. Nanorod‐like bismuth‐based metal–organic frameworks are reduced in situ and fragment into densely contacted Bi 0 nanoparticles under the applied potentials. The fragmented Bi 0 nanoparticles exhibit excellent NRR performance in both neutral and acidic electrolytes, with an ammonia yield of 3.25 ± 0 .08 µg cm ?2 h ?1 at ?0.7 V versus reversible hydrogen electrode and a Faradaic efficiency of 12.11 ± 0.84% at ?0.6 V in 0.10 m Na 2SO 4. Online differential electrochemical mass spectrometry detects the production of NH 3 and N 2H 2 during NRR, suggesting a possible pathway through two‐step reduction and decomposition. This work highlights the importance of monitoring and optimizing the electronic and geometric structures of the electrocatalysts under NRR conditions. 相似文献
2.
The production of ammonia (NH 3) from molecular dinitrogen (N 2) under mild conditions is one of the most attractive topics in the field of chemistry. Electrochemical reduction of N 2 is promising for achieving clean and sustainable NH 3 production with lower energy consumption using renewable energy sources. To date, emerging electrocatalysts for the electrochemical reduction of N 2 to NH 3 at room temperature and atmospheric pressure remain largely underexplored. The major challenge is to achieve both high catalytic activity and high selectivity. Here, the recent progress on the electrochemical nitrogen reduction reaction (NRR) at ambient temperature and pressure from both theoretical and experimental aspects is summarized, aiming at extracting instructive perceptions for future NRR research activities. The prevailing theories and mechanisms for NRR as well as computational screening of promising materials are presented. State‐of‐the‐art heterogeneous electrocatalysts as well as rational design of the whole electrochemical systems for NRR are involved. Importantly, promising strategies to enhance the activity, selectivity, efficiency, and stability of electrocatalysts toward NRR are proposed. Moreover, ammonia determination methods are compared and problems relating to possible ammonia contamination of the system are mentioned so as to shed fresh light on possible standard protocols for NRR measurements. 相似文献
3.
To enable an efficient and cost‐effective electrocatalytic N 2 reduction reaction (NRR) the development of an electrocatalyst with a high NH 3 yield and good selectivity is required. In this work, Ti 3C 2T x MXene‐derived quantum dots (Ti 3C 2T x QDs) with abundant active sites enable the development of efficient NRR electrocatalysts. Given surface functional groups play a key role on the electrocatalytic performance, density functional theory calculations are first conducted, clarifying that hydroxyl groups on Ti 3C 2T x offer excellent NRR activity. Accordingly, hydroxyl‐rich Ti 3C 2T x QDs (Ti 3C 2OH QDs) are synthesized as NRR catalysts by alkalization and intercalation. This material offers an NH 3 yield and Faradaic efficiency of 62.94 µg h ?1 mg ?1cat. and 13.30% at ?0.50 V, respectively, remarkably higher than reported MXene catalysts. This work demonstrates that MXene catalysts can be mediated through the optimization of both QDs sizes and functional groups for efficient ammonia production at room temperature. 相似文献
4.
To achieve the energy‐effective ammonia (NH 3) production via the ambient‐condition electrochemical N 2 reduction reaction (NRR), it is vital to ingeniously design an efficient electrocatalyst assembling the features of abundant surface deficiency, good dispersibility, high conductivity, and large surface specific area (SSA) via a simple way. Inspired by the fact that the MXene contains thermodynamically metastable marginal transition metal atoms, the oxygen‐vacancy‐rich TiO 2 nanoparticles (NPs) in situ grown on the Ti 3C 2T x nanosheets (TiO 2/Ti 3C 2T x) are prepared via a one‐step ethanol‐thermal treatment of the Ti 3C 2T x MXene. The oxygen vacancies act as the main active sites for the NH 3 synthesis. The highly conductive interior untreated Ti 3C 2T x nanosheets could not only facilitate the electron transport but also avoid the self‐aggregation of the TiO 2 NPs. Meanwhile, the TiO 2 NPs generation could enhance the SSA of the Ti 3C 2T x in return. Accordingly, the as‐prepared electrocatalyst exhibits an NH 3 yield of 32.17 µg h ?1 mg ?1cat. at ?0.55 V versus reversible hydrogen electrode (RHE) and a remarkable Faradaic efficiency of 16.07% at ?0.45 V versus RHE in 0.1 m HCl, placing it as one of the most promising NRR electrocatalysts. Moreover, the density functional theory calculations confirm the lowest NRR energy barrier (0.40 eV) of TiO 2 (101)/Ti 3C 2T x compared with Ti 3C 2T x or TiO 2 (101) alone. 相似文献
5.
The electrochemical nitrogen reduction reaction (NRR) process usually suffers extremely low Faradaic efficiency and ammonia yields due to sluggish N?N dissociation. Herein, single‐atomic ruthenium modified Mo 2CT X MXene nanosheets as an efficient electrocatalyst for nitrogen fixation at ambient conditions are reported. The catalyst achieves a Faradaic efficiency of 25.77% and ammonia yield rate of 40.57 µg h ?1 mg ?1 at ‐0.3 V versus the reversible hydrogen electrode in 0.5 m K 2SO 4 solution. Operando X‐ray absorption spectroscopy studies and density functional theory calculations reveal that single‐atomic Ru anchored on MXene nanosheets act as important electron back‐donation centers for N 2 activation, which can not only promote nitrogen adsorption and activation behavior of the catalyst, but also lower the thermodynamic energy barrier of the first hydrogenation step. This work opens up a promising avenue to manipulate catalytic performance of electrocatalysts utilizing an atomic‐level engineering strategy. 相似文献
6.
Methyl fluoride (CH 3F) and dimethyl ether (DME) inhibited nitrification in washed-cell suspensions of Nitrosomonas europaea and in a variety of oxygenated soils and sediments. Headspace additions of CH 3F (10% [vol/vol]) and DME (25% [vol/vol]) fully inhibited NO 2- and N 2O production from NH 4+ in incubations of N. europaea, while lower concentrations of these gases resulted in partial inhibition. Oxidation of hydroxylamine (NH 2OH) by N. europaea and oxidation of NO 2- by a Nitrobacter sp. were unaffected by CH 3F or DME. In nitrifying soils, CH 3F and DME inhibited N 2O production. In field experiments with surface flux chambers and intact cores, CH 3F reduced the release of N 2O from soils to the atmosphere by 20- to 30-fold. Inhibition by CH 3F also resulted in decreased NO 3- + NO 2- levels and increased NH 4+ levels in soils. CH 3F did not affect patterns of dissimilatory nitrate reduction to ammonia in cell suspensions of a nitrate-respiring bacterium, nor did it affect N 2O metabolism in denitrifying soils. CH 3F and DME will be useful in discriminating N 2O production via nitrification and denitrification when both processes occur and in decoupling these processes by blocking NO 2- and NO 3- production. 相似文献
7.
Conversion of air and water into valuable chemicals of ammonia (NH 3) by plasma activation and electrochemical reduction is a promising approach to achieve zero carbon-emission synthesis of NH 3. However, designing highly efficient electrochemical catalysts is one of the key challenges in accomplishing this strategy. Herein, a self-supported cobalt–tungsten alloy supported on cobalt foam (CoW/CF) is developed via a simple and efficient method at room temperature. Surprisingly, the catalyst exhibits ultra-high NH 3 partial current density (1559 mA cm −2), superior NH 3 yield rate (164.3 mg h −1 cm −2), and high Faradaic efficiency (98.1%) under the condition of 0.2 M nitrate/nitrite, outperforming most of the reported values of electrosynthesis of NH 3 to the knowledge. The introduction of W makes the Co atom surface electron deficient, which can enhance the adsorption of NO x− and mitigate the excessive bonding of hydroxyl radicals (OH *) generated during nitrite (NO 2*) hydrogenation, thereby reducing the energy barrier of the potential-determining step. More interestingly, a scale-up reaction system is established, achieving an NH 3 yield rate of 4.771 g h −1 and successfully converting the NH 3 in solution into solid NH 4Cl. The aforementioned progress significantly enhances the facilitation of NH 3 electrosynthesis industrialization. 相似文献
8.
The Haber‐Bosch process can be replaced by the ambient electrocatalytic N 2 reduction reaction (NRR) to produce NH 3 if suitable electrocatalysts can be developed. However, to develop high performance N 2 fixation electrocatalysts, a key issue to be resolved is to achieve efficient hydrogenation of N 2 without interference by the thermodynamically favored hydrogen evolution reaction (HER). Herein, in‐operando created strong Li–S interactions are reported to empower the S‐rich MoS 2 nanosheets with superior NRR catalytic activity and HER suppression ability. The Li + interactions with S‐edge sites of MoS 2 can effectively suppress hydrogen evolution reaction by reducing H* adsorption free energy from 0.03 to 0.47 eV, facilitate N 2 adsorption by increasing N 2 adsorption free energy from –0.32 to –0.70 eV and enhance electrocatalytic N 2 reduction activity by decreasing the activation energy barrier of the reaction control step (*N 2 → *N 2H) from 0.84 to 0.42 eV. A NH 3 yield rate of 43.4 μg h ?1 mg ?1 MoS 2 with a faradaic efficiency (FE) of 9.81% can be achieved in presence of strong Li–S interactions, more than 8 and 18 times by the same electrocatalyst in the absence of Li–S interactions. This report opens a new way to design and develop catalysts and catalysis systems. 相似文献
9.
A mutant of Rhodospirillum rubrum has been isolated, after mutagenesis with nitrosoguanidine, which is characterized by its inability to grow in the light on malate-minimal media with exogenous ammonia or alanine, poor growth on glutamine and vigorous growth on glutamate. This mutant produces low levels of a key NH +4 assimilation enzyme, glutamate synthase (NADPH-dependent). It also exhibits significant derepression of nitrogenase biosynthesis in the presence of ammonia or alanine, being 15% derepressed for the former and about 70% derepressed for the latter.Some of this mutant's fixed N 2 is excreted into the medium as NH +4 (1 μmol NH +4 per mg cell protein in 50 h). Nitrogenase-mediated H 2 production by this strain is considerable (42 μmol H 2 per mg cell protein in 50 h), approximately twice that of the wild type assayed under similar conditions.These results demonstrate that genetic alteration of the photosynthetic N 2-fixer's NH +4 assimilation system disrupts the tight coupling of N 2 fixation and NH +4 assimilation normally observed in these organisms, enabling photochemical conversion steps to be utilized for the photoproduction of NH +4 and H 2. 相似文献
10.
The electrochemical nitrogen reduction reaction (NRR), as an environmentally friendly method to convert nitrogen to ammonia at ambient temperature and pressure, has attracted the attention of numerous researchers. However, when compared with industrial production, electrochemical NRR often suffers from unsatisfactory yields and poor Faraday efficiency (FE). Recently, various structure engineering strategies have aimed to introduce extra active sites or enhance intrinsic activity to optimize the activation and hydrogenation of N 2. In this review, recent progress in atomic structure modification is summarized and discussed to design high‐efficiency NRR catalysts, with a focus on defect engineering (heteroatom doping and atom vacancy), surface orientation and amorphization, as well as heterostructure engineering. In addition, existing challenges and future development directions are proposed to obtain more credible NRR catalysts with high catalytic performance and selectivity. 相似文献
11.
Vanadium-based catalysts are used in many technological processes, among which the removal of nitrogen oxides (NO x) from waste gases is one of the most important. The chemical reaction responsible for this selective catalytic reaction (SCR) is based on the reduction of NO x molecules to N 2, and a possible reductant in this case is pre-adsorbed NH 3. In this paper, NH 3 adsorption on Brønsted OH acid centers on low-index surfaces of V 2O 5 (010, 100, 001) is studied using a theoretical DFT method with a gradient-corrected functional (RPBE) in the embedded cluster approximation model. The results of the calculations show that ammonia molecules are spontaneously stabilized on all low-index surfaces of the investigated catalyst, with adsorption energies ranging from ?0.34 to ?2 eV. Two different mechanisms of ammonia adsorption occur: the predominant mechanism involves the transfer of a proton from a surface OH group and the stabilization of ammonia as an NH 4 + cation bonded to surface O atom(s), while an alternative mechanism involves the hydrogen bonding of NH 3 to a surface OH moiety. The latter binding mode is present only in cases of stabilization over a doubly coordinated O(2) center at a (100) surface. The results of the calculations indicate that a nondirectional local electrostatic interaction with ammonia approaching a surface predetermines the mode of stabilization, whereas hydrogen-bonding interactions are the main force stabilizing the adsorbed ammonia. Utilizing the geometric features of the hydrogen bonds, the overall strength of these interactions was quantified and qualitatively correlated ( R?=?0.93) with the magnitude of the stabilization effect (i.e., the adsorption energy). Figure Two different modes (NH 3/NH 4 +) of ammonia adsorption on the (001)V 2O 5 net plane. 相似文献
12.
As an alternative approach for N 2 fixation under milder conditions, electrocatalytic nitrogen reduction reaction (NRR) represents a very attractive strategy for sustainable development and N 2 cycle to store and utilize energy from renewable sources. However, the research on NRR electrocatalysts still mainly focuses on noble metals, while, high costs and limited resources greatly restrict their large‐scale applications. Herein, as a proof‐of‐concept experiment, taking PdCu amorphous nanocluster anchored on reduced graphene oxide (rGO) as NRR catalysts, the optimum Pd 0.2Cu 0.8/rGO composite presents a synergistic effect and shows superior electrocatalytic performance toward NRR under ambient conditions (yield: 2.80 µg h ?1 mg cat.?1 at ?0.2 V vs reversible hydrogen electrode), which is much higher than that of monometallic, especially noble metal, counterparts. The superior catalytic performance of alloy catalysts with low noble metal loading would strongly spur interest toward more researches on NRR catalysts in the future. 相似文献
13.
Nitrous oxide (N 2O), a greenhouse gas, is emitted during autotrophic and heterotrophic ammonia oxidation. This emission may result from either
coupling to aerobic denitrification, or it may be formed in the oxidation of hydroxylamine (NH 2OH) to nitrite (NO 2
−). Therefore, the N 2O production during NH 2OH oxidation was studied with Alcaligenes faecalis strain TUD. Continuous cultures of A. faecalis showed increased N 2O production when supplemented with increasing NH 2OH concentrations. 15N-labeling experiments showed that this N 2O production was not due to aerobic denitrification of NO 2
−. Addition of 15N-labeled NH 2OH indicated that N 2O was a direct by-product of NH 2OH oxidation, which was subsequently reduced to N 2. These observations are sustained by the fact that NO 2
− production was low (0.23 mM maximum) and did not increase significantly with increasing NH 2OH concentration in the feed. The NH 2OH-oxidizing capacity increased with increasing NH 2OH concentrations. The apparent V
max and K
m were 31 nmol min −1 mg dry weight −1 and 1.5 mM respectively. The culture did not increase its growth yield and was not able to use NH 2OH as the sole N source. A non-haem hydroxylamine oxidoreductase was partially purified from A. faecalis strain TUD. The enzyme could only use K 3Fe(CN) 6 as an electron acceptor and reacted with antibodies raised against the hydroxylamine oxidoreductase of Thiosphaera pantotropha.
Received: 1 September 1998 / Received revision: 5 November 1998 / Accepted: 7 November 1998 相似文献
14.
In situ transesterification of wet microalgae is a promising, simplified alternative biodiesel production process that replaces multiple operations of cell drying, extraction, and transesterification reaction. This study addresses enhanced biodiesel production from Nannochloropsis gaditana at elevated temperatures. Compared with the previously reported in situ transesterification process of conducting the reaction at a temperature ranging from 95 to 125 °C, the present work employs higher temperatures of at least 150 °C. This relatively harsh condition allows much less acid catalyst with or without co-solvent to be used during this single extraction-conversion process. Without any co-solvent, 0.58% (v/v) of H2SO4 in the reaction medium can achieve 90 wt% of the total lipid conversion to biodiesel at 170 °C when the moisture content of wet algal paste is 80 wt%. Here, the effects of temperature, acid catalyst, and co-solvent on the FAEE yield and specification were scrutinized, and the reaction kinetic was investigated to understand the solvothermal in situ transesterification reaction at the high temperature. Having a biphasic system (water/chloroform) during the reaction also helped to meet biodiesel quality standard EN 14214, as Na+, K+, Ca2+, Mg2+ cations and phosphorus were detected only below 5 ppm. With highlights on the economic feasibility, wet in situ transesterification at the high temperature can contribute to sustainable production of biodiesel from microalgae by reducing the chemical input and relieve the burden of extensive post purification process, therefore a step towards green process. 相似文献
15.
The effect of ammonia on Chinese hamster ovary (CHO) cell growth and galactosylation of recombinant immunoglobulin (rIgG)
was investigated using shaking flasks with serum free media containing 0–15 mM NH 4Cl. The elevated ammonia inhibited cell growth and negatively affected the galactosylation of rIgG. At 15 mM NH 4Cl, the proportions of monogalactosylated glycan with fucosex (monogalactosylated glycan with fucose) and digalactosylated
glycan with fucose (G2F) were 23.9% and 6.3% lower than those at 0 mM NH 4Cl, respectively. To reduce ammonia formation by cells, glutamate was examined as a substitute for glutamine. The use of glutamate
reduced the accumulation of ammonia and enhanced the production of rIgG while depressing cell growth. At 6 mM glutamate, ammonia
level did not exceed 2 mM, which is only one third of that at 6 mM glutamine. Also, a 1.7-fold increase in the titer of rIgG
and specific rIgG productivity, q
rIgG, was achieved at 6 mM glutamate. The galactosylation of rIgG was favorable at 6 mM glutamate. The proportion of galactosylated
glycans, G1F and G2F, at 6 mM glutamate was 59.8%, but it was 50.4% at 6 mM glutamine. The use of glutamate also increased
complement-dependent cytotoxicity activity, one of the effector functions of rIgG. Taken together, substitution of glutamine
by glutamate can be considered relevant for the production of rIgG in CHO cells since glutamate not only enhances q
rIgG but also generates a higher galactosylation essential for the effector function of rIgG. 相似文献
16.
Ethyl levulinate (EL) is a versatile bio-based chemical with various applications such as fragrance and flavoring agents and also fuel blending component. EL can be produced through catalytic esterification of levulinic acid (LA) with ethanol. Herein, a series of zirconia (ZrO 2)-supported phosphotungstic acid (HPW) (HPW/Zr) catalyst, 15-HPW/Zr, 20-HPW/Zr, and 25-HPW/Zr, were prepared, characterized, and tested for EL production. The physicochemical properties of catalysts were characterized using Fourier-transformed infrared (FTIR) spectroscopy, x-ray diffraction (XRD), field emission scanning electron microscope (FESEM), N 2 physisorption, and ammonia temperature-programmed desorption (NH 3-TPD). The effect of reaction parameters: reaction time, temperature, catalyst loading, and molar ratio of LA to ethanol was inspected on LA conversion and EL yield. The catalyst with high surface area and high acidity seemed suitable for EL production. Among the catalysts tested, 20-HPW/Zr exhibited the highest EL yield of 97.3% at the following conditions: 150 °C, 3 h, 1.0 g of 20-HPW/Zr and 1:17 M ratio of LA to ethanol. The 20-HPW/Zr could be reused for at least four times with insignificant decrease in the EL yield. This study demonstrates the potential of ZrO 2-supported HPW for bio-based alkyl levulinate production at mild process conditions. 相似文献
17.
Metabolism of ammonia (NH 3) and hydroxylamine (NH 2OH) by wild-type and a nitrite reductase ( nirK) deficient mutant of Nitrosomonas europaea was investigated to clarify the role of NirK in the NH 3 oxidation pathway. NirK-deficient N. europaea grew more slowly, consumed less NH 3, had a lower rate of nitrite (NO 2
−) production, and a significantly higher rate of nitrous oxide (N 2O) production than the wild-type when incubated with NH 3 under high O 2 tension. In incubations with NH 3 under low O 2 tension, NirK-deficient N. europaea grew more slowly, but had only modest differences in NH 3 oxidation and product formation rates relative to the wild-type. In contrast, the nirK mutant oxidized NH 2OH to NO 2
− at consistently slower rates than the wild-type, especially under low O 2 tension, and lost a significant pool of NH 2OH–N to products other than NO 2
− and N 2O. The rate of N 2O production by the nirK mutant was ca. three times higher than the wild-type during hydrazine-dependent NO 2
− reduction under both high and low O 2 tension. Together, the results indicate that NirK activity supports growth of N. europaea by supporting the oxidation of NH 3 to NO 2
− via NH 2OH, and stimulation of hydrazine-dependent NO 2
− reduction by NirK-deficient N. europaea indicated the presence of an alternative, enzymatic pathway for N 2O production. 相似文献
18.
The photocatalytic reduction of nitrogen (N 2) with water (H 2O) as the reducing agent holds great promise as a sustainable future technology for the synthesis of ammonia (NH 3). Herein, the effect of oxygen vacancies and electron‐rich Cu δ+ on the performance of zinc‐aluminium layered double hydroxide (ZnAl‐LDH) nanosheet photocatalysts for N 2 reduction to NH 3 under UV–vis excitation is systematically explored. Results show that a 0.5%‐ZnAl‐LDH nanosheet photocatalyst (containing 0.5 mol% Cu by metal basis) affords a remarkable NH 3 production rate of 110 µmol g ?1 h ?1 and excellent stability in pure water. The X‐ray absorption spectroscopy, electron paramagnetic resonance, and density functional theory calculations reveal that Cu addition imparts oxygen vacancies and coordinatively unsaturated Cu δ+ (δ < 2) with electron‐rich property in the ZnAl‐LDH nanosheets, both of which readily contribute to efficient separation and transfer of photogenerated electrons and holes and promote N 2 adsorption, thereby both activating N 2 and facilitating its multielectrons reduction to NH 3. 相似文献
19.
As a microbial-environmental-control-type deodorizing system, we have developed a compact biotrickling filter system for small-scale livestock farms. The performance of the compact co-current biotrickling filter operated at high recycle liquid flow rates was systematically examined. In particular, we studied improvements in the nitrification ability of the system due to the resultant enhancement of absorption and dissolution of NH 3 and absorption of O 2 with the high flow rates of recycle liquid flowing downward co-currently with gas flow. At the empty bed residence time of 50 s, almost complete removal of NH 3 was obtained with recycle liquid flow rates of 103 and 205 L m −3 day −1 for 20 days while the inlet NH 3 concentration was increased from 200 to 500 ppm. With a recycle liquid flow rate of 411 L m −3 day −1 the removal efficiency remained above 95% for 57 days while the inlet NH 3 concentration was increased from 200 to 700 ppm. The biodegradation kinetics for NH 3 removal was successfully analyzed using the Haldane substrate inhibition kinetics. The present data and kinetic analyses showed that the substrate inhibition was suppressed and the biodegradation of ammonia in the compact biotrickling filter could be improved by the high recycle liquid flow rate. 相似文献
20.
A comparative study to produce the correct influent for Anammox process from anaerobic sludge reject water (700–800 mg NH 4+-N L −1) was considered here. The influent for the Anammox process must be composed of NH 4+-N and NO 2−-N in a ratio 1:1 and therefore only a partial nitrification of ammonium to nitrite is required. The modifications of parameters (temperature, ammonium concentration, pH and solid retention time) allows to achieve this partial nitrification with a final effluent only composed by NH 4+-N and NO 2−-N at the right stoichiometric ratio. The equal ratio of HCO 3−/NH 4+ in reject water results in a natural pH decrease when approximately 50% of NH 4+ is oxidised. A Sequencing batch reactor (SBR) and a chemostat type of reactor (single-reactor high activity ammonia removal over nitrite (SHARON) process) were studied to obtain the required Anammox influent. At steady state conditions, both systems had a specific conversion rate around 40 mg NH 4+-N g −1 volatile suspended solids (VSS) h −1, but in terms of absolute nitrogen removal the SBR conversion was 1.1 kg N day −1 m −3, whereas in the SHARON chemostat was 0.35 kg N day −1 m −3 due to the different hydraulic retention time (HRT) used. Both systems are compared from operational (including starvation experiments) and kinetic point of view and their advantages/disadvantages are discussed. 相似文献
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