Intermetallic Electride Catalyst as a Platform for Ammonia Synthesis

Abstract

Electrides loaded with transition‐metal (TM) nanoparticles have recently attracted attention as emerging materials for catalytic NH3 synthesis. However, they suffer from disadvantages associated with the growth and aggregation of nanoparticles. TM‐containing intermetallic electrides appear to be promising catalysts with the advantages of both electrides and transition metals in a single phase. LaRuSi is reported here to be an intermetallic electride with superior activity for NH3 synthesis, and direct evidence is provided supporting its electride‐character‐induced catalytic performance. The discussion is made mainly based on the contrasting synthesis rates over the isostructural compounds LaRuSi, CaRuSi, and LaRu2Si2, and the N2 isotope‐exchange reactions over these compounds. Lattice hydride ions, which can reversibly exchange with anionic electrons, are shown to be indispensable in the promotion of NHx formation. The mechanism derived from the present findings provides new guidelines for NH3 synthesis.

The Journey toward Low Temperature, Low Pressure Catalytic Nitrogen Fixation

“…[ 23 ] For Ru‐based catalysts, recent attention has been given to the nature of the support and the use of promoters to modify the morphology and electron structure of Ru. The introduction of inorganic electrides (ionic compounds whose anions are simply electrons) such as C12A7:e − , [ 24 ] Ca 2 N:e − , [ 25 ] Y 5 Si 3 , [ 26 ] and LaRuSi [ 27 ] to enhance the catalytic activity of ammonia synthesis. Electrides have excess electrons which can arrange themselves periodically at crystallographic sites and serve as anions.…”

“…Electrides have excess electrons which can arrange themselves periodically at crystallographic sites and serve as anions. [ 27 ] Take dodecacalcium hepta‐aluminate (C 12 A 7 :e − ) as an example. The compound has a low work function (2.4 eV), meaning that electrons are easily transferred from it to supported Ru nanoparticles, shifting the Fermi level of Ru upward and thus facilitating the transfer of electrons into the antibonding π*‐orbitals of adsorbed nitrogen molecules.…”

Recent progress towards mild-condition ammonia synthesis

“…Other electrides were also reported to promote Ru for ammonia synthesis, e.g., the Ca 2 N:e − deposited with Ru nanoparticles (NPs) could catalyze ammonia formation at ca. 200 °C [44][45][46] . Similarly, oxyhydride (BaTiO 2.5 H 0.5 ), partially reduced metal oxide (La 0.5 Ce 0.5 O 1.75 ), etc.…”

Simple Chemical Synthesis of Ternary Intermetallic RENi₂Si₂ (RE = Y, La) Nanoparticles in Molten LiCl–CaH₂ System

“…Nickel silicide is an attractive catalyst to show high performances in CO methanation, 1,2) hydrogenation, 39) hydrodesulfurization, 1012) photocatalytic decomposition of nitrogen monoxide 13) and electro-chemical hydrogen evolution. 14) In addition, rare earth metal doped intermetallic silicide catalysts have been reported to exhibit tremendous improvement in the catalytic activity of transition metals, such as LaCu 0.67 Si 1.33 , 15) LaCoSi, 16) LnRuSi (Ln = La Nd) 17,18) and LnNiSi, 19) due to the electron donation from the rare earth metals. The metal silicide catalysts are so fascinating that they are inexpensive and chemically stable.…”