Why Ca2NH works as an efficient and stable support of Ru catalyst in ammonia synthesis

Hydride-based materials have recently attracted attention because of their significant promotion effect on transition metal catalysts in ammonia synthesis under mild conditions. Here, we clarify the effect of hydride-nitride, Ca2NH, on the activity and stability of Ru catalyst as a catalyst support for ammonia synthesis. The anionic electrons formed at H‒ ion vacancy sites in Ca2NH effectively promote the N2 dissociation over Ru surface, which accounts for the high catalytic performance with a low apparent activation energy. The catalytic activity of Ru/Ca2NH is much superior to those of Ru/C12A7:e‒, Ru/Sr2NH, and Ru/CaNH. The simple metal hydride, CaH2, with Ru exhibits higher catalytic performance than Ru/Ca2NH, but its stability is poor because weak Ru-CaH2 interaction causes aggregation of Ru nanoparticles during the reaction. On the other hand, Ru nanoparticles are anchored on Ca2NH surface through a strong Ru–N interaction, which leads to excellent stability of Ru/Ca2NH catalyst.