A dual-site Fe-based catalyst for efficient ammonia synthesis under mild conditions

Abstract

Achieving green ammonia (NH₃) synthesis requires developing effective catalysts under mild conditions. However, the competitive adsorption of N₂ and H₂, as well as the strong binding of N-containing intermediates on the catalyst, greatly inhibits the active sites for efficient NH₃ synthesis. Here, we constructed a series of ZrH₂-modified Fe catalysts with dual active sites to address these issues and realized efficient NH₃ synthesis under mild conditions. Our study shows that ZrH₂ can not only provide active sites for H₂ activation but also transfer electrons to Fe sites for accelerating N₂ activation. The interaction between Fe and ZrH₂ over 40ZrH₂-Fe leads to a decrease in work function and a downward shift of the d-band center, which is conducive to N₂ activation and NH₃ desorption, respectively. The utilization of distinct sites for activating different reactants can avoid the competitive adsorption of N₂ and H₂, leading to excellent NH₃ synthesis activity of the 40 wt.% ZrH₂-mediated Fe catalyst. As a result, 40ZrH₂-Fe exhibits a high NH₃ synthesis rate of 23.3 mmol g_cat⁻¹ h⁻¹ at 400 °C and 1 MPa and robust stability during 100 h time-on-stream.