2021
DOI: 10.1007/s11244-021-01432-1
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The Role of Composition and Phase upon the Lattice Nitrogen Reactivity of Ternary Molybdenum Nitrides

Abstract: The reactivity of the lattice nitrogen in the filled β-Mn structured Co2Mo3N and the η-carbide structured Co3Mo3N and Fe3Mo3N has been investigated under 3:1 H2/Ar at temperatures up to 900 °C. The lattice nitrogen in Co3Mo3N was found to be reactive, as reported previously, whereas Co2Mo3N was shown to be stable up to 800 °C. Upon H2/Ar treatment at 900 °C, the Co2Mo3N, Co3Mo3N and Fe3Mo3N phases decomposed. These results suggest that both metal composition and phase have an influence on the bulk lattice nitr… Show more

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Cited by 15 publications
(13 citation statements)
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“…In comparison with the vacancy formation energies for Co3Mo3N in the literature 15 , the corresponding Co3Mo3N(111) surface N vacancy formation energy was calculated to be 1.68 eV, only 0.21 eV less endothermic than for Fe3Mo3N. Whilst this is in agreement with the experimental findings that lattice N in Fe3Mo3N is generally less active compared to Co3Mo3N 38,39,59 , it is notable that the modest difference in the calculated vacancy formation energies for the two compounds suggests that formation of surface N vacancies on Fe3Mo3N is at the very least highly plausible, which is consistent with the experimental observation that bulk lattice N in Fe3Mo3N is inactive, if loss of lattice N is confined only to the surface layers, and therefore accounts for only a negligible loss of total lattice nitrogen from the experimental sample. Hence, this finding suggests that the experimentally observed resistance of Fe3Mo3N to loss of lattice N under high temperature hydrogenation conditions can be attributed to the diffusion of bulk and subsurface lattice nitrogen to the surface being kinetically, rather than thermodynamically, unfeasible.…”
Section: Surface Formation and Bulk Diffusion Of N Vacanciessupporting
confidence: 82%
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“…In comparison with the vacancy formation energies for Co3Mo3N in the literature 15 , the corresponding Co3Mo3N(111) surface N vacancy formation energy was calculated to be 1.68 eV, only 0.21 eV less endothermic than for Fe3Mo3N. Whilst this is in agreement with the experimental findings that lattice N in Fe3Mo3N is generally less active compared to Co3Mo3N 38,39,59 , it is notable that the modest difference in the calculated vacancy formation energies for the two compounds suggests that formation of surface N vacancies on Fe3Mo3N is at the very least highly plausible, which is consistent with the experimental observation that bulk lattice N in Fe3Mo3N is inactive, if loss of lattice N is confined only to the surface layers, and therefore accounts for only a negligible loss of total lattice nitrogen from the experimental sample. Hence, this finding suggests that the experimentally observed resistance of Fe3Mo3N to loss of lattice N under high temperature hydrogenation conditions can be attributed to the diffusion of bulk and subsurface lattice nitrogen to the surface being kinetically, rather than thermodynamically, unfeasible.…”
Section: Surface Formation and Bulk Diffusion Of N Vacanciessupporting
confidence: 82%
“…The Fe3Mo3N system, which is isostructural to Co3Mo3N, has also been found to be highly active for ammonia synthesis 37,38 . However, experimental studies show that, in contrast to the isostructural Co system, Fe3Mo3N appears to be highly resistant to reduction, with no appreciable loss of lattice N being observed even under harsh conditions 39 . Furthermore, experimental studies also show that the quaternary metal nitride system (Co3-xFexMo3N) is highly active towards ammonia synthesis 38 , opening the possibility to finely tune ammonia synthesis activity by determining the optimal Co:Fe ratio.…”
Section: Introductionmentioning
confidence: 98%
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“…The local environment for the lattice nitrogen in the -carbide structured or -Mn structured nitrides is similar with nitrogen coordinated to six metal species in each case [16]. It has been previously reported that metal composition appears to have an influence on the lattice nitrogen reactivity of -carbide structured or -Mn structured nitrides [17]. The possible influence the A metal has on activity has been investigated by comparing the ammonia synthesis activity of Co 3 CuN and Ni 3 CuN.…”
Section: Introductionmentioning
confidence: 62%
“…Initially, the role of nitrogen was believed to be limited to creating the right termination plan containing both Co and Mo. However, recent studies shed the light on the mobility and reactivity of nitrogen in Co3Mo3N via 15 N/ 14 N isotopic exchange studies and by DFT calculation pinpointing the potential role of the lattice nitrogen in ammonia synthesis via routes akin to the Mars-van Krevelen (MvK) mechanism [12][13][14]. Recently, the mobility and reactivity of lattice nitrogen, in binary and ternary nitrides, towards hydrogen has been the focus of several research activities [15][16][17].…”
Section: Introductionmentioning
confidence: 99%