Cs-modified iron nanoparticles encapsulated in microporous and mesoporous SiO2 for COx-free H2 production via ammonia decomposition

The stable core–shell Fe@SiO2 catalysts reported in this paper are highly efficient for the generation of COx-free H2 through ammonia decomposition. By tuning the porosity of SiO2 shells (using C18TMS agent) and with the introduction of an appropriate amount of Cs dopant (via pre-deposition as well as post-impregnation), the diffusion efficiency of the catalysts and the surface property of Fe cores can be modified for better performance. The Fe@SiO2 structures function as microcapsular-like reactors during ammonia decomposition. Naked nanoparticles of metallic iron tend to aggregate into bulk particles spontaneously. The role of the stable SiO2 shells is to prevent the enwrapped core particles from aggregation at high reaction temperatures.