Histidine-Stabilized Cobalt Nanoparticles on Silica for Efficient Ammonia Cracking

Ammonia cracking is a key reaction for hydrogen storage and release, offering a promising route toward a hydrogen economy. Herein, a robust silica-supported cobalt (Co) catalyst is developed using a histidine-assisted dispersion strategy to mitigate sintering. Histidine (His), a naturally occurring amino acid, is codissolved with the Co(II) precursor to produce uniformly dispersed Co nanoparticles on silica via incipient wetness impregnation (2, 6, and 10 wt %). The resulting particles exhibit sizes of ∼2−3 nm, significantly smaller than those prepared without histidine. Thermogravimetric analysis confirms complete removal of histidine after treatment at 250 °C for 48 h. Synchrotron powder X-ray diffraction reveals that the histidine-assisted method suppresses Co 3 O 4 formation, favoring smaller CoO species during the initial synthesis stage. H 2 temperature-programmed reduction confirms the corresponding differences of Co 3 O 4 and CoO in reducibility and further shows that histidine-assisted samples possess smaller nanoparticles. The 10 wt % Co-His/SiO 2 catalyst demonstrates superior activity and stability in ammonia cracking at 500 °C, achieving 30.5% NH 3 conversion compared to 13.5% for the nonhistidine-assisted counterpart. These findings confirm the use of histidine as a biodegradable ligand to conveniently prepare supported metal catalysts that are less prone to sintering and remain catalytically active in reactions critical to sustainability.