Active nitrogen sites on nitrogen doped carbon for highly efficient associative ammonia decomposition

Nitrogen doped carbon materials have been studied as catalyst support for ammonia decomposition. There are 4 different types of nitrogen environments (graphitic, pyrrolic, pyridinic and nitrogen oxide) on the amorphous support identified. In this paper, we report a 5%Ru on MgCO₃ pre-treated nitrogen doped carbon catalyst with high content of edge nitrogen-containing sites which displays an ammonia conversion rate of over 90% at 500°C and WHSV = 30,000 mL g_cat ^-1 h^-1. It also gives an impressive hydrogen production rate of 31.3 mmol/(min g_cat) with low apparent activation energy of 43 kJ mol^-1. Fundamental studies indicate that the distinct average Ru-N₄ coordination site on edge regions is responsible for such high catalytic activity. Ammonia is stepwise decomposed via a Ru-N(H)-N(H)-Ru intermediate. This associative mechanism circumvents the direct cleavage of energetic surface nitrogen from metal to form N₂ hence lowering the activation barrier for the decomposition over this catalyst.