Ta₂⁺-mediated ammonia synthesis from N₂and H₂at ambient temperature

Abstract

In a full catalytic cycle, bare Ta2+ in the highly diluted gas phase is able to mediate the formation of ammonia in a Haber–Bosch-like process starting from N2 and H2 at ambient temperature. This finding is the result of extensive quantum chemical calculations supported by experiments using Fourier transform ion cyclotron resonance MS. The planar Ta2N2+, consisting of a four-membered ring of alternating Ta and N atoms, proved to be a key intermediate. It is formed in a highly exothermic process either by the reaction of Ta2+ with N2 from the educt side or with two molecules of NH3 from the product side. In the thermal reaction of Ta2+ with N2, the N≡N triple bond of dinitrogen is entirely broken. A detailed analysis of the frontier orbitals involved in the rate-determining step shows that this unexpected reaction is accomplished by the interplay of vacant and doubly occupied d-orbitals, which serve as both electron acceptors and electron donors during the cleavage of the triple bond of N≡N by the ditantalum center. The ability of Ta2+ to serve as a multipurpose tool is further shown by splitting the single bond of H2 in a less exothermic reaction as well. The insight into the microscopic mechanisms obtained may provide guidance for the rational design of polymetallic catalysts to bring about ammonia formation by the activation of molecular nitrogen and hydrogen at ambient conditions.

Single vs double atom catalyst for N2 activation in nitrogen reduction reaction: A DFT perspective

“…Bader charge analysis was also carried out to demonstrate the charge transfer (CT) between metal and ligand (Table ). In the DAC case, the metal ligand charge transfer was around , which is similar to the previous report of . But in the SAC case, IIIB series elements showed slightly stronger CT than IVB series counterparts, and they were almost TM 2 + , except for the magnetic case of Mn anchored system.…”

“…In the DAC case, the metal ligand charge transfer was around TM + 2 , which is similar to the previous report of Ta + 2 . 46 But in the SAC case, IIIB series elements showed slightly stronger CT than IVB series counterparts, T A B L E 1 Geometric and the other parameters of the SAC and DAC: coordination number (CN), metal-N (d TM-N ) and metal-metal bond length (d TM ) and the average metal ligand charge transfer (MLCT) between the metal and substrate C 2 N, overpotential of NRR (η) and potential limiting step (PLS) Mn Sc Y La Ti Zr Hf TM NC 3 3 2 2 2 6 2 F I G U R E 5 N 2 molecule activation mechanism for the DAC, A, and SAC, B and C. The π (left) and σ (right) splitting of LOL for N 2 adsorption on the double anchored V, D, single anchored Sc, E, and Ti, F, respectively and they were almost TM 2+ , except for the magnetic case of Mn anchored system. The occupation of the split d orbital was the main difference in both SAC and DAC systems.…”

Complete cleavage of the N≡N triple bond by Ta2N+via degenerate ligand exchange at ambient temperature: A perfect catalytic cycle

“…In this context, metal clusters that bring about scission of the N≡N bond have served as prototypical systems to probe the active sites in heterogeneous catalysis (9,20,21). Indeed, recent combined experimental/ theoretical gas-phase studies provided a conceptual understanding of dinitrogen activation and conversion (22)(23)(24)(25).…”

“…However, examples of structurally well-defined complexes rendering a complete cleavage of the N≡N triple bond are rather limited so far (22)(23)(24)(25)(26)(27)(28)(29)(30)(31). Experiments using matrix isolation have shown that dimers of transition metals can split completely the triple bond of N 2 and form M 2 N 2 molecules consisting of a 4-membered, mostly planar ring; in the latter, the 2 nitrogen atoms are connected to both metal atoms but no longer to each other (30).…”

Analisis Molekular dan Transpor Ion Amonium Clorida

“…Banyak senyawa yang paling penting pada bidang industry, seperti amonia (42)(43)(44)(45)(46) , asam nitrat (47) , nitrat organik (propelan dan bahan peledak), serta sianida, mengandung nitrogen. Nitrogen banyak ditemukan dalam bentuk ikatan rangkap dua dan tiga, namun ada juga yang membentuk ikatan tunggal(single bond) (48)(49)(50)(51)(52)(53) .…”