Infrared Spectra of N–H Compounds in LiCl-KCl-CsCl Molten Salts Using the Diffuse Reflectance Optical System

Serizawa, Nobuyuki; Takei, Katsuhito; Nishikiori, Tokujiro; Ito, Yasuhiko

doi:10.5796/electrochemistry.17-00084

“…Additional evidence for Equation (4a)–(4c) is provided by IR spectroscopy of the melt frozen midway through reaction, where peaks are observed in the region expected for both LiNH 2 and Li 2 NH (Figure D) . This is also supported by recent in situ infrared experiments in which N−H stretches were observed when H 2 was bubbled through Li 3 N …”

Section: Resultssupporting

confidence: 65%

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl–KCl Eutectics

McPherson

¹

,

Sudmeier

²

,

Fellowes

³

et al. 2019

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Molten LiCl and related eutectic electrolytes are known to permit direct electrochemical reduction of N2 to N3− with high efficiency. It had been proposed that this could be coupled with H2 oxidation in an electrolytic cell to produce NH3 at ambient pressure. Here, this proposal is tested in a LiCl–KCl–Li3N cell and is found not to be the case, as the previous assumption of the direct electrochemical oxidation of N3− to NH3 is grossly over‐simplified. We find that Li3N added to the molten electrolyte promotes the spontaneous and simultaneous chemical disproportionation of H2 (H oxidation state 0) into H− (H oxidation state −1) and H+ in the form of NH2−/NH2−/NH3 (H oxidation state +1) in the absence of applied current, resulting in non‐Faradaic release of NH3. It is further observed that NH2− and NH2− possess their own redox chemistry. However, these spontaneous reactions allow us to propose an alternative, truly catalytic cycle. By adding LiH, rather than Li3N, N2 can be reduced to N3− while stoichiometric amounts of H− are oxidised to H2. The H2 can then react spontaneously with N3− to form NH3, regenerating H− and closing the catalytic cycle. Initial tests show a peak NH3 synthesis rate of 2.4×10−8 mol cm−2 s−1 at a maximum current efficiency of 4.2 %. Isotopic labelling with 15N2 confirms the resulting NH3 is from catalytic N2 reduction.

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“…Additional evidence for Equation (4a)-(4c) is provided by IR spectroscopy of the melt frozen midway through reaction, where peaks are observed in the region expected for both LiNH 2 and Li 2 NH ( Figure 2D). [26] This is also supported by recent in situ infrared experiments in which NÀHs tretches were observed when H 2 was bubbled through Li 3 N. [27] Thes tepwise change in equilibrium potential of the H 2 electrode observed during the open circuit control measurement, and its change in polarity during the constant potential 0.7 Ve xperiment, further suggest that the intermediates formed are themselves redox active.T he redox properties of all proposed components of the electrolyte were therefore characterized to understand their interactions and determine if atruly catalytic path to ammonia synthesis in this system is indeed possible.…”

Section: Angewandte Chemiementioning

confidence: 99%

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl–KCl Eutectics

McPherson

¹

,

Sudmeier

²

,

Fellowes

³

et al. 2019

View full text Add to dashboard Cite

Molten LiCl and related eutectic electrolytes are known to permit direct electrochemical reduction of N2 to N3− with high efficiency. It had been proposed that this could be coupled with H2 oxidation in an electrolytic cell to produce NH3 at ambient pressure. Here, this proposal is tested in a LiCl–KCl–Li3N cell and is found not to be the case, as the previous assumption of the direct electrochemical oxidation of N3− to NH3 is grossly over‐simplified. We find that Li3N added to the molten electrolyte promotes the spontaneous and simultaneous chemical disproportionation of H2 (H oxidation state 0) into H− (H oxidation state −1) and H+ in the form of NH2−/NH2−/NH3 (H oxidation state +1) in the absence of applied current, resulting in non‐Faradaic release of NH3. It is further observed that NH2− and NH2− possess their own redox chemistry. However, these spontaneous reactions allow us to propose an alternative, truly catalytic cycle. By adding LiH, rather than Li3N, N2 can be reduced to N3− while stoichiometric amounts of H− are oxidised to H2. The H2 can then react spontaneously with N3− to form NH3, regenerating H− and closing the catalytic cycle. Initial tests show a peak NH3 synthesis rate of 2.4×10−8 mol cm−2 s−1 at a maximum current efficiency of 4.2 %. Isotopic labelling with 15N2 confirms the resulting NH3 is from catalytic N2 reduction.

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“…Concerning the IR spectrum of 2 , which we obtained in reflection mode from a crystal put on a gold surface, we found within the 3000–3500 cm –1 region a broader signal at 3335 and a sharper and bigger one at 3175 cm –1 (there are also signals around 3700 cm –1 , which we ascribe to O–H obtained by partial hydrolysis of 2 ). We tentatively assign the two signals to NH and NH 2 (partial hydrolysis) by comparison with a salt melt of Li 2 NH (see also references herein). In this article the signal at 3160 cm –1 is believed to belong to the stretching of NH 2– .…”

Section: Resultsmentioning

confidence: 96%

“…We tentatively assign the two signals to NH and NH 2 (partial hydrolysis) by comparison with a salt melt of Li 2 NH (see also references herein). In this article the signal at 3160 cm –1 is believed to belong to the stretching of NH 2– . In the 14 N NMR spectra of 1 and 2 the signal for the H–N group is hampered because of the quadrupole moment of N(H), whereas the other nitrogen atoms show a single signal with satellite couplings to 117/119 Sn and 29 Si.…”

Section: Resultsmentioning

confidence: 96%

The Imino Stannylene SnNH Incorporated in a Molecular Tin‐Nitrogen Cage and other Tin(II)‐Nitrogen Derivatives

Veith

¹

,

Opsölder

²

,

Hüch

³

2018

Zeitschrift anorg allge chemie

0

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The iminostannylene HNSn was successfully incorporated in a molecular cage of composition (Me2RSi–NSn)3(HNSn) with group R either being a methyl (1) or vinyl (2) substituent. An X‐ray structure analysis reveals that 2 consists of a distorted Sn4N4 cube. The Sn–N(H) bond lengths [2.189(2) Å] are in the range for Sn4N4 hetero cubanes. When stored in a toluene solution the clusters 1 and 2 decompose slowly into the symmetric cubanes (Me2RSi–NSn)4 [R = Me (3), CHCH2 (4)] and an amorphous and insoluble powder of composition HNSn. The decomposition follows a first order rate law as established for 2 with a half life time t1/2 = 320 d at 20 °C. The compounds 1 and 2 can thus be regarded as a result of interaction between three entities {Me2RSi–NSn} and one entity {HNSn}. We also isolated the twistane‐like Me2Si(NtBu)2Sn2NtBu (5) in a crystalline form. The central structure of this molecule, which has almost C2v symmetry, has a trigonal bipyramid Sn2N3 unit with the nitrogen atoms occupying the equatorial plane. Each nitrogen atom has a tert‐butyl ligand and two of the N atoms are further connected by the dimethylsilyl group. There is one nitrogen atom in an almost planar environment (only bonding to tert‐butyl and two tin atoms) with a remarkable short Sn–N bond length of 2.048(5) Å. Both tin atoms in cage 5 can bond to Cr(CO)5 to form [Me2Si(NtBu)2Sn2NtBu][Cr(CO)5]2 (6) with an almost linear Cr–Sn···Sn–Cr arrangement and Sn–Cr bond lengths of 2.581(1) Å (X‐ray diffraction).

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Infrared Spectra of N–H Compounds in LiCl-KCl-CsCl Molten Salts Using the Diffuse Reflectance Optical System

Cited by 8 publications

References 16 publications

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl–KCl Eutectics

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl–KCl Eutectics

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl–KCl Eutectics

The Imino Stannylene SnNH Incorporated in a Molecular Tin‐Nitrogen Cage and other Tin(II)‐Nitrogen Derivatives

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