Neutron diffraction and gravimetric study of the manganese nitriding reaction under ammonia decomposition conditions

Wood, Thomas J.; Makepeace, Joshua W.; David, William I. F.

doi:10.1039/c7cp07613d

Cited by 8 publications

(6 citation statements)

References 30 publications

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“…In contrast, MgO shows better synergy with amide–imide, allowing the formation of a ternary nitride instead of a ternary oxide, which is active for the decomposition of ammonia. However, there is no consensus in the literature about the role of ternary nitrides in the decomposition of ammonia. , Bramwell et al compared the catalytic activity of LiNH 2 alone or supported on carbon. In the case of the supported catalyst, no activity was recorded due to the formation of Li 2 NCN.…”

Section: Catalysts For the Thermal Decomposition Of Ammoniamentioning

confidence: 99%

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Review of the Decomposition of Ammonia to Generate Hydrogen

Lucentini

Garcia

Vendrell

et al. 2021

Ind. Eng. Chem. Res.

306

193

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Because of the problems associated with the generation and storage of hydrogen in portable applications, the use of ammonia has been proposed for on-site production of hydrogen through ammonia decomposition. First, an analysis of the existing systems for ammonia decomposition and the challenges for this technology are presented. Then, the state of the art of the catalysts used to date for ammonia decomposition is described considering the catalysts composed of noble and non-noble metals and their combinations, as well as novel materials such as alkali metal amides and imides. The effect of the supports and promoters used is analyzed in detail, and the catalytic activity obtained is compared. An analysis of the kinetics of the reaction obtained with different catalysts is also presented and discussed, including the reaction mechanism, the determining step of the reaction, and the apparent activation energy. Finally, the structured reactors used to date for the decomposition reaction of ammonia are explored, as well as the possibilities offered by catalytic membrane reactors, which allow the on-site simultaneous production and separation of hydrogen.

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Section: Catalysts For the Thermal Decomposition Of Ammoniamentioning

confidence: 99%

“…However, there is no consensus in the literature about the role of ternary nitrides in the decomposition of ammonia. 376,377 Bramwell et al 224 compared the catalytic activity of LiNH 2 alone or supported on carbon. In the case of the supported catalyst, no activity was recorded due to the formation of Li 2 NCN.…”

mentioning

confidence: 99%

Review of the Decomposition of Ammonia to Generate Hydrogen

Lucentini

Garcia

Vendrell

et al. 2021

Ind. Eng. Chem. Res.

306

193

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“…Manganese nitrides have also been studied as a looping catalyst in ammonia synthesis 10,11 and for the reverse reaction, ammonia decomposition, by thermogravimetric analysis and neutron diffraction. 12 Mn 6 N 5+x and lithium imide (Li 2 NH) when combined result in a larger rate of ammonia decomposition than for either of the separate parts. 13 Additionally, CaNH can exert a strong synergistic effect on Mn 6 N 5+x leading to greatly enhanced catalytic activity for ammonia decomposition.…”

Section: Introductionmentioning

confidence: 99%

On the possibility of an Eley–Rideal mechanism for ammonia synthesis on Mn₆N_5+x (x = 1)-(111) surfaces

Zeinalipour-Yazdi

2018

Phys. Chem. Chem. Phys.

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Recently we reported an Eley-Rideal/Mars-van Krevelen mechanism for ammonia synthesis on cobalt molybdenum nitride (Co3Mo3N). In this mechanism hydrogenation of activated dinitrogen occurs directly from the gas phase in a low barrier step forming a hydrazinylidene intermediate [double bond, length as m-dash]NNH2. In this paper we study whether such a mechanism of ammonia synthesis could occur on the (111) surface of another metal nitride, Mn6N5+x (x = 1), as this would explain the low-T ammonia synthesis activity of Co3Mo3N. We find that although N2 adsorbs more strongly than H2 on the (111) surface, having also examined the (110) and the (100) surface, N2 is not significantly activated when adsorbed in an end-on configuration. The hydrogenation reactions via an Eley-Rideal mechanism are all high barrier processes (>182 kJ mol-1) and therefore an Eley-Rideal mechanism for ammonia synthesis is predicted to not occur on this material unless there are high temperatures. Our study indicates that the fact that an Eley-Rideal/Mars-van Krevelen mechanism occurs on Co3Mo3N is a result of the stronger activation of dinitrogen at nitrogen vacancies when dinitrogen is adsorbed in an end-on configuration.

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“…Recent neutron powder diffraction studies of the reaction of manganese under flowing ammonia detected the slow transformation of manganese to Mn 4 N, Mn 2 N and Mn 3 N 2 in this temperature range. 26,27 The absence of any of these phases in this experiment is likely as a result of the higher hydrogen partial pressure and lower ammonia partial pressure due to the ammonia decomposition reaction, as described for the iron sample.…”

Section: Nd + Mnnmentioning

confidence: 83%

Bulk phase behavior of lithium imide–metal nitride ammonia decomposition catalysts

Makepeace

Wood

Marks

et al. 2018

Phys. Chem. Chem. Phys.

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Lithium imide is a promising new catalyst for the production of hydrogen from ammonia. Its catalytic activity has been reported to be significantly enhanced through its use as a composite with various transition metal nitrides. In this work, two of these composite catalysts (with manganese nitride and iron nitride) were examined using in situ neutron and X-ray powder diffraction experiments in order to explore the bulk phases present during ammonia decomposition. Under such conditions, the iron composite was found to be a mixture of lithium imide and iron metal, while the manganese composite contained lithium imide and manganese nitride at low temperatures, and a mixture of lithium imide and two ternary lithium-manganese nitrides (LixMn2-xN and a small proportion of Li7MnN4) at higher temperatures. The results indicate that the bulk formation of a ternary nitride is not necessary for ammonia decomposition in lithium imide-transition metal catalyst systems.

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Neutron diffraction and gravimetric study of the manganese nitriding reaction under ammonia decomposition conditions

Cited by 8 publications

References 30 publications

Review of the Decomposition of Ammonia to Generate Hydrogen

Review of the Decomposition of Ammonia to Generate Hydrogen

On the possibility of an Eley–Rideal mechanism for ammonia synthesis on Mn₆N_5+x (x = 1)-(111) surfaces

Bulk phase behavior of lithium imide–metal nitride ammonia decomposition catalysts

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Neutron diffraction and gravimetric study of the manganese nitriding reaction under ammonia decomposition conditions

Cited by 8 publications

References 30 publications

Review of the Decomposition of Ammonia to Generate Hydrogen

Review of the Decomposition of Ammonia to Generate Hydrogen

On the possibility of an Eley–Rideal mechanism for ammonia synthesis on Mn6N5+x (x = 1)-(111) surfaces

Bulk phase behavior of lithium imide–metal nitride ammonia decomposition catalysts

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Product

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On the possibility of an Eley–Rideal mechanism for ammonia synthesis on Mn₆N_5+x (x = 1)-(111) surfaces