On the Role of Ferromagnetic Interactions in Highly Active Mo‐Based Catalysts for Ammonia Synthesis

Abstract

Reactions involving nitrogen fixation and transfer are of great industrial interest. In this regard, unveiling all the physical principles that determine their activity would be enormously beneficial for the rational design of novel catalysts with improved performance. Within this context, this work explores the activity of bulk molybdenum-based transition metal nitrides in ammonia synthesis. Our results highlight that the most active compositions show increasing ferromagnetism in the metal-nitrogen bonds, which constitute the active sites. We observe that the total spin accumulated in the bonds at the active sites is a physically meaningful descriptor to discriminate optimum catalysts. Higher activities are associated with ferromagnetic phases, and the underlying reason is an enhanced overlapping of the electronic wavefunctions; which also make the reaction steps spin-sensitive. These finding provides strong evidence of the general influence of electrons magnetic moment in catalysis, being part of the specific field of spintro-catalysis.

Ferromagnetic ligand holes in cobalt perovskite electrocatalysts as an essential factor for high activity towards oxygen evolution

“…By looking carefully, we can see examples where magnetic structures associate overall with active heterogeneous catalysis. FM oxides show better activity than Pt in the oxidation of nitrous oxide (NO has doublet ground state) 15,16 , FM nitrides improve ammonia synthesis 17 , or Co doping in MoS 2 induces FM 18 and enhances the activity in various reactions. In addition of particular interest for electrocatalysis, interatomic FM orderings leads to favourable spin-charge transport, avoiding antiferromagnetic (AFM) electronic localization.…”

Reaction on a Rink: Kondo-Enhanced Heterogeneous Single-atom Catalysis

“…( 1), it is obvious that the speedup is more prominent with a more negative ∆∆ r G . The speedup gained via the ROAR is somewhat analogous to that achieved by harnessing the QSEI, [16][17][18] since in both mechanisms the acceleration of the RDS originates from the reduced activation barrier due to generalized spin-exchange interactions. 15,17 Nevertheless, a notable difference is that the QSEI involved in most of the previous works is ferromagnetic, while the Kondo spin-screening is antiferromagnetic in the ROAR.…”

“…In recent years, Gracia et al [15][16][17][18] have explored the quantum spin exchange interaction (QSEI) between the electrons in the catalytic species and those in the reactant molecule and analyzed its nontrivial impact on the catalytic reactions. Physical and chemical means have been employed to modulate the QSEI, 16,19,20 leading to enhanced electrocatalytic activity of certain magnetic materials, such as CoFe 2 O 4 19 and magnetized Co 3−x Fe x O 4 /Co(Fe)O x H y . 20 Apart from this, various strategies have been proposed to optimize the atomic microenvironment of SACs, 21 e.g.…”

The trend of chemisorption of hydrogen and oxygen atoms on pure transition metals: Magnetism justifies unexpected behaviour of Mn and Cr

“…1 are being particularly useful to rationalize oxygen electrocatalysis, 14,21,22 relevant in clean energy technologies. The statements presented here are necessarily general and have broad applicability since there are multiple crucial reactions in heterogenous catalysis where the most active compositions are magnetic, like CO hydrogenation towards hydrocarbons, 23,24 ammonia synthesis, 25 oxidation of organic molecules, 26 hydrodesulfurization, 27 etc. 28 Conclusions.…”