AB5-type intermetallic compounds as catalysts for ammonia synthesis

Abstract

Ammonia synthesis via the Haber–Bosch process is an energy-intensive process. Consequently, developing innovative strategies to enhance the catalytic performance of ammonia synthesis catalysts remains a critical focus in the fields of catalysis and hydrogen storage. Herein, we employ a straightforward mechanical milling technique to treat LaNi₅ alloy powders, significantly reducing their particle size through violent impact and exposing more active surfaces within a short time. Remarkably, the catalytic ammonia synthesis rate of the alloy increases from 77.38 μmol_NH3 g⁻¹ h⁻¹ to an astonishing 1660 μmol_NH3 g⁻¹ h⁻¹ under ambient pressure, and escalates to 2080 μmol_NH3 g⁻¹ h⁻¹ with an H₂/N₂ ratio of 2. Experimental results reveal that the synergism of surface nitrides, surface-active hydrogen (H*) and interstitial hydrogen is conducive to ammonia synthesis. This mechanism not only overcomes the bottleneck of N₂ dissociation but also endows the LaNi₅ alloy with robust catalytic performance for ammonia synthesis under hydrogen-rich conditions, effectively overcoming the hydrogen poisoning effect typically observed in conventional catalysts. These findings highlight the potential for AB₅-type intermetallic compounds to serve as effective catalysts for ammonia synthesis, bringing them closer to industrial application.