Engineering Ru–Co sites for promoted hydrogen spillover in ammonia synthesis

Abstract

To address the challenges of noble metal costs and the hydrogen poisoning of single-metal ruthenium (Ru)-based catalysts in ammonia synthesis, a RuCo bimetallic catalyst supported on CeO₂ nanorods was prepared in this work. First, a RuCoCe-BTC metal–organic framework precursor, where BTC denotes 1,3,5-benzenetricarboxylate, was obtained by partially substituting Ru with the non-noble metal cobalt (Co), followed by pyrolysis to yield the RuCo/CeO₂ catalyst. The formation of Co–Ru bonds, which provided enhanced metal support interactions in this bimetallic catalyst, was confirmed by the blue shift of the Ru–O–Ce vibration peaks in the Raman bands. Compared to a single-metal Ru/CeO₂ catalyst, Co doping enhanced the generation of more oxygen vacancies and the reduction of high-valence Ru, leading to promoted hydrogen transfer on the Ru sites. The hydrogen poisoning of Ru sites was suppressed due to H* spillover to the Co sites, which was explained by the higher H₂ adsorption energy on Co sites (−0.720 eV) compared to that on Ru sites (−0.367 eV). Consequently, the RuCo/CeO₂ catalyst achieved an NH₃ synthesis rate of 21.0 mmol/(g·h) at 5 MPa and 400 °C, demonstrating better performance than the Ru/CeO₂ catalyst (18.5 mmol/(g·h)).

Graphical Abstract

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