Catalytic Behavior of K‐doped Fe/MgO Catalysts for Ammonia Synthesis Under Mild Reaction Conditions
K. Era, Katsutoshi Sato, Shin‐ichiro Miyahara, T. Naito, K. Kanishka H. De Silva, Saeid Akrami, Hiroshi Yamada, Takaaki Toriyama, Tomokazu Yamamoto, Yasukazu Murakami, Ken‐ichi Aika, Koji Inazu, Katsutoshi Nagaoka
Abstract
Abstract An important part of realizing a carbon‐neutral society using ammonia will be the development of an inexpensive yet efficient catalyst for ammonia synthesis under mild reaction conditions (<400 °C, <10 MPa). Here, we report Fe/K(3)/MgO, fabricated via an impregnation method, as a highly active catalyst for ammonia synthesis under mild reaction conditions (350 °C, 1.0 MPa). At the mentioned conditions, the activity of Fe/K(3)/MgO (17.5 mmol h −1 g cat −1 ) was greater than that of a commercial fused iron catalyst (8.6 mmol h −1 g cat −1 ) currently used in the Haber‐Bosch process. K doping was found to increase the ratio of Fe 0 on the surface and turnover frequency of Fe in our Fe/K(3)/MgO catalyst. In addition, increasing the pressure to 3.0 MPa at the same temperature led to a significant improvement of the ammonia synthesis rate to 29.6 mmol h −1 g cat −1 , which was higher than that of two more expensive, benchmark Ru‐based catalysts, which are also potential alternative catalysts. A kinetics analysis revealed that the addition of K enhanced the ammonia synthesis activity at ≥300 °C by changing the main adsorbed species from NH to N which can accelerate dissociative adsorption of nitrogen as the rate limiting step in ammonia synthesis.