Deuterium Inverse Isotopic Effect in Ammonia Synthesis over Ru-Based and Fe-Based Catalysts

The deuterium inverse isotopic effect (DIIE) is important for the clarification of the ammonia synthesis mechanism over transition metal catalysts. We investigated the DIIE over Ru-based and Fe-based catalysts including pure Fe, multi-promoted fused Fe, pure Ru, Ru/γ-Al2O3, K-Ru/γ-Al2O3, Ru/MgO, K-Ru/MgO, and Ba-Ru/MgO under the reaction conditions of N2/H2 (or D2) volume ratio = 1/3, 0.2 MPa, 633–733 K, and GHSV = 24 000 and 12 000 h−1. A strong DIIE (rD/rH of about 2) was observed over the above catalysts. The trend of the DIIE with catalysts and temperature indicated a strong competition between the dynamic and thermodynamic factors.