Computational Investigations of the Reactivity of Metalloporphyrins for Ammonia Oxidation

Barona, Melissa; Johnson, Samantha I.; Mbea, Margareth; Bullock, R. Morris; Raugei, Simone

doi:10.1007/s11244-021-01511-3

Cited by 7 publications

(7 citation statements)

References 58 publications

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“…For simplicity, we focused on Cr(TPP) as a proxy for Cr(TMP). Our prior studies on NH 3 oxidation by (TMP)Ru(NH 3 ) 2 and (TMP)Os(NH 3 ) 2 showed that the truncated (TPP)M(NH 3 ) 2 model has no significant effect on the spin-state ladder of each complex and reaction intermediates as well as on the BDFE values. ,, Additional computational details of the DFT calculations can be found in the Supporting Information.…”

Section: Resultsmentioning

confidence: 99%

“…Previous studies have demonstrated that Group VI metals tend to have very favorable HAA steps, while lacking a significant driving force to couple metal nitrido species. 19,21 This reactivity trend can be traced to the electropositive nature of these transition metals, with higher oxidation states (IV and V) accessible at mild oxidation potentials. Metal orbitals become accessible for increased M−N bonding, which further weakens subsequent N−H bonds.…”

Section: ■ Discussionmentioning

confidence: 99%

“…Our group has been utilizing 2,4,6-substituted phenoxyl radicals as H-atom-abstraction (HAA) reagents for the oxidation of NH 3 (Scheme ). ,− Abstraction of a H atom generates the substituted phenol, which ideally could be electrochemically oxidized to regenerate the phenoxyl radical . Ru(TMP)(NH 3 ) 2 (TMP = 5,10,15,20- meso -tetramesitylporphyrin), with a TON of 125, selectively yields N 2 when a bulky 4-(triphenylmethyl)-2,6-di- tert -butylphenoxyl radical is employed (Scheme , top). , …”

Section: Introductionmentioning

confidence: 99%

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Weakening the N–H Bonds of NH₃ Ligands: Triple Hydrogen-Atom Abstraction to Form a Chromium(V) Nitride

et al. 2022

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Weakening and cleaving N−H bonds is crucial for improving molecular ammonia (NH 3 ) oxidation catalysts. We report the synthesis and H-atom-abstraction reaction of bis(ammonia)chromium porphyrin complexes Cr(TPP)(NH 3 ) 2 and Cr(TMP)(NH 3 ) 2 (TPP = 5,10,15,10,15, using bulky aryloxyl radicals. The triple H-atom-abstraction reaction results in the formation of Cr V (por)(�N), with the nitride derived from NH 3 , as indicated by UV−vis and IR and single-crystal structural determination of Cr(TPP)(�N). Subsequent oxidation of this chromium(V) nitrido complex results in the formation of Cr III (por), with scission of the Cr�N bond. Computational analysis illustrates the progression from Cr II to Cr V and evaluates the energetics of abstracting H atoms from Cr II -NH 3 to generate Cr V �N. The formation and isolation of Cr V (por)(�N) illustrates the stability of these species and the need to chemically activate the nitride ligand for atom transfer or N−N coupling reactivity.

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Section: Resultsmentioning

confidence: 99%

Section: ■ Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Weakening the N–H Bonds of NH₃ Ligands: Triple Hydrogen-Atom Abstraction to Form a Chromium(V) Nitride

et al. 2022

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“…For the non‐noble metal systems, fabricating metal phosphides, sulfides, and nitrides as well as rationally manipulating their structure to obtain core–shell materials or multivacancy nanomaterials may be potentially beneficial for AOR applications (Figure 15). Currently, theoretical calculations have been carried out investigating the AOR process over metalloporphyrins, [ 107 ] and it has been found further tuning of their coordination structures and optimization of composition may provide new pathways for AOR electrocatalysis. In addition, AOR catalysts that are specifically designed for nonaqueous electrolyte systems should receive more attention as well.…”

Section: Discussionmentioning

confidence: 99%

Green Chemistry: Advanced Electrocatalysts and System Design for Ammonia Oxidation

et al. 2023

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Fossil fuels, including coal, petroleum, and natural gas, are still the main sources of energy supply in the world at present. [1,2] Their nonrenewable nature, however, determines that the total amount of these fossil fuels is limited, thus leading to the potential energy crisis. [3,4] This issue has given a strong impetus to the development of green, safe, and renewable energy supplies, such as wind, solar, and tide energy. [5][6][7][8] Although these novel energy sources are generally sustainable, their direct utilization is extremely difficult. For example, these green energy types, especially solar energy, commonly suffer high fluctuation, thus leading to the misalignment of electricity generation of these energies with the actual demand. [9] Therefore, it is very important to explore and exploit the optimal secondary energy carriers. Among the secondary energy carriers, hydrogen is one of the most economical and eco-friendly carriers due to its zero-carbon emission, abundance, high energy density (120 MJ kg À1 ), etc. [10][11][12] Due to the potential safety hazards in the storage and transportation of hydrogen gas, nevertheless, its practical utilization has great limitations. [13,14] To address these issues, it has been suggested to use methane or ammonia gas as the hydrogen carriers. [15][16][17][18] Methane has a wide range of resources and mature industrial processing technologies. Thermal catalytic decomposition of methane and steam reforming is the most mature technology of hydrogen generation in the industry currently. [19,20] However, the transportation and storage of methane remain problematic owing to its physical characteristics, which are similar to those of hydrogen. As a cost-effective hydrogen carrier, ammonia can turn into a liquid state at room temperature under moderate pressure (%8 bar), much milder than that hydrogen gas (690 bar and 15 °C). [10,21,22] Besides, the utilization of ammonia does not associate with greenhouse gas emissions. Moreover, the energy density of liquid ammonia (11.5 MJ kg À1 ) is also higher than that of liquid hydrogen (8.5 MJ kg À1 ). Moreover, the presence of ammonia can be easily detected even at a very low concentration of 1 ppm, allowing ammonia leaks to be assessed and dealt with in a timely manner. In addition, unlike hydrogen, ammonia is widely used and vastly produced (global production is 176 million tons a year) around the world in the pharmaceutical, fertilizer, and chemical industries. Consequently, the well-established and mature ammonia production-related infrastructure makes ammonia a viable energy source. [23][24][25][26] To utilize ammonia for energy applications, electrochemical ammonia oxidation reaction (AOR) is essential, either for hydrogen production via ammonia splitting or electricity generation via direct ammonia fuel cells (DAFCs), which are highly commercially promising. During operation, DAFCs just produce water and nitrogen gas. [22,[27][28][29] In addition, ammonia fuel cells are also theoretically superior to their hydrogen-based c...

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“…79 The rest of those reported span from 37–56 kcal mol −1 . For (TPP)Mo(NH 3 )(N–H), a close analogue of 3 , the BDFE calc was 56 kcal mol −1 , 40 though this is likely affected by the ligand trans to the nitride. Our experimentally estimated imido BDFE of 43 kcal mol −1 is similar to these computed values, though this may be inaccurate because the electrochemical reduction of the protonated nitride was irreversible, forcing us to estimate E 1/2 .…”

Section: Discussionmentioning

confidence: 99%

Catalytic reduction of dinitrogen to ammonia using molybdenum porphyrin complexes

et al. 2023

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Computational Investigations of the Reactivity of Metalloporphyrins for Ammonia Oxidation

Cited by 7 publications

References 58 publications

Weakening the N–H Bonds of NH₃ Ligands: Triple Hydrogen-Atom Abstraction to Form a Chromium(V) Nitride

Weakening the N–H Bonds of NH₃ Ligands: Triple Hydrogen-Atom Abstraction to Form a Chromium(V) Nitride

Green Chemistry: Advanced Electrocatalysts and System Design for Ammonia Oxidation

Catalytic reduction of dinitrogen to ammonia using molybdenum porphyrin complexes

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Computational Investigations of the Reactivity of Metalloporphyrins for Ammonia Oxidation

Cited by 7 publications

References 58 publications

Weakening the N–H Bonds of NH3 Ligands: Triple Hydrogen-Atom Abstraction to Form a Chromium(V) Nitride

Weakening the N–H Bonds of NH3 Ligands: Triple Hydrogen-Atom Abstraction to Form a Chromium(V) Nitride

Green Chemistry: Advanced Electrocatalysts and System Design for Ammonia Oxidation

Catalytic reduction of dinitrogen to ammonia using molybdenum porphyrin complexes

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Product

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Weakening the N–H Bonds of NH₃ Ligands: Triple Hydrogen-Atom Abstraction to Form a Chromium(V) Nitride

Weakening the N–H Bonds of NH₃ Ligands: Triple Hydrogen-Atom Abstraction to Form a Chromium(V) Nitride