Highly loaded bimetallic iron-cobalt catalysts for hydrogen release from ammonia
Shilong Chen, Jelena Jelic, Denise Rein, Sharif Najafishirtari, Franz-Philipp Schmidt, Frank Girgsdies, Liqun Kang, Aleksandra Wandzilak, Anna Rabe, Dmitry E. Doronkin, Jihao Wang, Klaus Friedel Ortega, Serena DeBeer, Jan‐Dierk Grunwaldt, Robert Schlögl, Thomas Lunkenbein, Felix Studt, Malte Behrens
Abstract
Abstract Ammonia is a storage molecule for hydrogen, which can be released by catalytic decomposition. Inexpensive iron catalysts suffer from a low activity due to a too strong iron-nitrogen binding energy compared to more active metals such as ruthenium. Here, we show that this limitation can be overcome by combining iron with cobalt resulting in a Fe-Co bimetallic catalyst. Theoretical calculations confirm a lower metal-nitrogen binding energy for the bimetallic catalyst resulting in higher activity. Operando spectroscopy reveals that the role of cobalt in the bimetallic catalyst is to suppress the bulk-nitridation of iron and to stabilize this active state. Such catalysts are obtained from Mg(Fe,Co) 2 O 4 spinel pre-catalysts with variable Fe:Co ratios by facile co-precipitation, calcination and reduction. The resulting Fe-Co/MgO catalysts, characterized by an extraordinary high metal loading reaching 74 wt.%, combine the advantages of a ruthenium-like electronic structure with a bulk catalyst-like microstructure typical for base metal catalysts.