The effect of the H₂:N₂ pre-treatment and reactant ratio upon the ammonia synthesis performance of the Ni₂Mo₃N catalyst

The ammonia synthesis reaction over Ni2Mo3N was carried out at 400 degrees C and atmospheric pressure. The effects of the H-2:N-2 ratio on both nitridation and the ammonia synthesis reaction steps were investigated. Analysis of Ni2Mo3N samples nitrided at different H-2:N-2 ratios was performed using XRD and elemental analysis. The surface characteristics of Ni2Mo3N were determined using H-2-TPR. When Ni2Mo3N was nitrided under 3:1 H-2:N-2, it was observed that a lower hydrogen ratio of 0.5:1 H-2:N-2 during the catalytic test improved the performance slightly. It is believed that the H-2 poisoning effect decreases at lower H-2:N-2 ratios. The highest ammonia synthesis activity was observed over a Ni2Mo3N catalyst when nitrided under 0.5:1 H-2:N-2 when ammonia synthesis reaction was performed using a 3:1 H-2:N-2 reaction mixture. The reason can be the presence of metallic Ni in the catalyst structure, which is believed to facilitate H2 spillover to reaction medium.