Ammonia cracking on single-atom catalysts: A mechanistic and microkinetic study
Xiuyuan Lu, Alberto Roldán
Abstract
Ammonia cracking has been identified as a crucial step to unlocking a sustainable H2 economy. Using the density functional theory, we modeled transition metal single-atom catalysts (SACs) supported on graphene and nitrogen-modified graphene to investigate the catalytic NH3 cracking process. The results showed that (i) N-modified graphene secures the transition metal atoms (M) stronger than C-matrixes, and (ii) structures with three anchoring nitrogens (MN3) are more reactive than MN4 ones. On IrN3 and RuN3 SAC models, the N2 evolution determines the total rate, while, on RhN3-SAC, it is the NH3 dehydrogenation. Temperature-programmed desorption simulations on SACs showed variations compared to extended metal surfaces. Batch reactor simulations were employed to balance the sequence of elementary steps as a function of the temperature, revealing the overall NH3 cracking activity. Results suggested IrN3 and RhN3 are strong candidates for NH3 cracking at temperatures as low as 230°C.