Effect of Pore Confinement of LiNH₂ on Ammonia Decomposition Catalysis and the Storage of Hydrogen and Ammonia

Abstract

LiNH2 is of interest to several aspects of energy storage such as reversible hydrogen storage, battery technology, catalysis, and ammonia capture/storage. We investigated the impact of nanoconfinement in carbon scaffolds on the hydrogen and ammonia release properties of LiNH2 and its catalytic activity in NH3 decomposition. Ammonia release from macrocrystalline LiNH2 begins at 350 °C, while confined LiNH2 releases ammonia from below 100 °C under helium flow. This ammonia release consisted of 30.5 wt % ammonia in the first cycle and was found to be partially reversible. Above 300 °C, hydrogen is also released due to an irreversible reaction between LiNH2 and the carbon support to form Li2NCN. Ni-doped LiNH2/C nanocomposites were active in the catalytic decomposition of ammonia into N2 and H2 with 53% conversion at 400 °C and a gas hourly space velocity of 13000 h–1. This is comparable to the performance of a commercial-type Ru-based catalyst where 79% conversion is observed under the same conditions. This work demonstrates that nanoconfinement is effective for improving the functionality of LiNH2. The versatility of this system offers promise in a number of different areas including hydrogen/ammonia storage and ammonia decomposition catalysis.

Complex Hydrides for Energy Storage, Conversion, and Utilization

“…Further studies showed that other alkali and alkaline earth metal amides/imides could also synergize with 3d TM(N) or Ru to exhibit superior catalytic activities . Confining LiNH 2 and Ni in carbon scaffolds leads to enhance catalytic activity in ammonia decomposition that is comparable to that of the commercial Ru‐based catalyst …”

Emerging Materials and Methods toward Ammonia‐Based Energy Storage and Conversion

“…[105a,108a] de Jongh et al, on the other hand, used a melt infiltration method to stabilize/confine alkali metal amides (LiNH 2 , NaNH 2 , or KNH 2 ) within the pores of carbon matrix. [109] The interaction of amide and carbon support may prevent the loss of amide from the catalyst and mitigate the stability issue to a certain extent. However, the formation of side product (cyanamide) may lower the catalytic activity.…”

Making more with less: confinement effects for more sustainable chemical transformations

“…The Jongh group used confinement inside porous carbon structures to tackle the H 2 storage challenge. 56 LiNH 2 is a strong H 2 carrier candidate, but it has the drawback of only releasing H 2 at temperatures above 300 °C. Ammonia is another H 2 carrier option, but the current commercial catalyst for NH 3 conversion to H 2 is based on Ru, an expensive metal.…”