Fabrication of BaO-promoted Cobalt Catalyst Incorporated into Carbon Framework by Citric Acid Sol-gel Method for Ammonia Synthesis

Developing non-noble metal catalysts with excellent NH3 synthesis activity at mild conditions is a long-term objective. The reported best catalysts require either laborious multiple steps and controlled environments to fabricate the catalysts or high temperatures and long times to activate the catalysts. This work reports a facile one-pot method to fabricate carbon-based Ba-promoted Co catalysts via the citric acid sol-gel method using metal nitrates as precursors and water as the solvent, which allows the metal ions to be incorporated into the carbon framework homogeneously. The obtained (Ba/Co)0.3/C catalyst shows an outstanding NH3 synthesis activity of 34 mmol gcat−1 h−1 (350 oC, 1.0 MPa) with excellent stability. In-depth characterizations reveal that Ba exists as BaO, which is homogeneously distributed on the carbon framework and around the Co metal nanoparticles. We uncover that by retarding the BaCO3 formation in the fresh catalyst, the reduction temperature and time can be greatly decreased (485 oC/4 h), which is a fundamental advantage in this method. Density functional theory and molecular dynamics simulations indeed support the experimental observations. We anticipate that this facile and economical strategy will resolve the issues in a broad field of heterogeneous catalyst research.