Realization of Ideal Ba Promoter State by Simultaneous Incorporation with Co into Carbon‐protective Framework for Ammonia Synthesis Catalyst

Extensive research is being conducted to fabricate non-noble metal catalysts for NH₃ synthesis under mild conditions toward a greener NH₃ synthesis process. Herein, a carbon (C)-based barium (Ba)-promoted cobalt (Co) catalyst with an NH₃ synthesis activity of 34 mmol g_cat ⁻¹ h⁻¹ at 350 °C/1 MPa is fabricated via a one-pot citric acid sol–gel method that can also be activated at mild conditions.

Abstract

Developing non-noble metal catalysts with excellent NH₃ synthesis activity under mild conditions is a long-term goal. The best catalysts reported to date often require laborious fabrication methods and controlled environments to fabricate the catalysts or high temperatures and long times to activate the catalysts. This work introduces a facile one-pot method to fabricate carbon (C)-based, barium (Ba)-promoted cobalt (Co) catalysts via the citric acid sol–gel method with metal nitrates as precursors and water as the solvent. This approach ensures the homogeneous incorporation of metal ions into the carbon framework. The resulting (Ba/Co)_0.3/C catalyst demonstrates an outstanding NH₃ synthesis activity of 34 mmol g_cat ⁻¹ h⁻¹ (350 °C, 1.0 MPa) with excellent stability. In-depth characterizations reveal that Ba exists as barium oxide (BaO), uniformly distributed on the carbon framework and around the Co nanoparticles. It is uncovered that retarding barium carbonate (BaCO₃) formation in the fresh catalyst significantly reduces the reduction temperature and time (485 °C/4 h), which is a fundamental advantage of this method. Density functional theory and molecular dynamics simulations indeed support the experimental observations. It is anticipated that this simple and economical strategy will resolve the issues in a broad field of heterogeneous catalyst research.