Citrate-gel preparation and ammonia synthesis activity of compounds in the quaternary (Ni,M)₂Mo₃N (M = Cu or Fe) systems

Abstract

Solid solutions based on copper and iron substitution into the nickel sites of Ni2Mo3N are produced using a citrate gel approach and used to catalyse ammonia synthesis.

Elucidating Catalytic Sites Governing the Performance toward the Hydrogen Evolution Reaction in Ternary Nitride Electrocatalysts

“…A minor N deficiency is common and has been noticed before. 14 In addition, Co, Ni, Fe, and Mo content values (determined by EDX analysis) were close to the expected values (Table S7). Therefore, the bulk character- ization showed that the compositions of nitrides were consistent with the targeted stoichiometries.…”

“…S2−S6). 14 Meanwhile, Mo and N (located on 12d and 4a positions) are always fully occupied and unaffected by Fe-substitution.…”

“…A recent study showed that Ni sites in Ni 2 Mo 3 N can be preferentially replaced by Fe atoms which leads to the formation of a series of homogeneous solid solutions (Fe x Ni 2−x Mo 3 N up to x ≈ 1.25). 14 Remarkably, 8c sites in Fe x Ni 2−x Mo 3 N can only be occupied by nickel and iron, whereas Mo and N do not take these sites. If the catalytic activity in Fe x Ni 2−x Mo 3 N decreases with the value of x, it could be served as evidence that Ni sites are catalytic, whereas if it remains the same, it will imply that either Mo or N sites are active.…”

“…A recent study showed that Ni sites in Ni 2 Mo 3 N can be preferentially replaced by Fe atoms which leads to the formation of a series of homogeneous solid solutions (Fe x Ni 2– x Mo 3 N up to x ≈ 1.25) . Remarkably, 8 c sites in Fe x Ni 2– x Mo 3 N can only be occupied by nickel and iron, whereas Mo and N do not take these sites.…”

Recent Advances in Heterogeneous Catalysis for Ammonia Synthesis

“…[84] (Table 3, Entry 5-6) Unlike Co 3 Mo 3 N (η-6 carbide structure), Ni 2 Mo 3 N crystallizes in β-Mn structure with low extent of lattice N exchange, hence lower activity in comparison to Co 3 Mo 3 N. [84] Additionally, partial substitution Co, Cu and Fe at the nickel sites in Ni 2 Mo 3 N has no major influence on the electronic properties hence no enhancement in NH 3 synthesis rate. [91] ( Table 3, Entry 7-10) Preliminary studies reported antiperovskite nitrides (Co 3 ZnN, Ni 3 ZnN, Co 3 InN, and Ni 3 InN) can produce NH 3 in H 2 /Ar atmosphere. Lattice N of these compounds are converted to into NH 3 , but further regeneration of lattice N was not realized and advanced research is necessary to efficiently produce NH 3 with long life.…”