Photochemical Acceleration of Ammonia Production by Pt-Pt-TiN Reduction and N Activation.

Stable metal nitrides (MN) are promising materials to fit the future "green" ammonia-hydrogen nexus. Either through catalysis or chemical looping, the reductive hydrogenation of MN to MN is a necessary step to generate ammonia. However, encumbered by the formation of kinetically stable M-NH surface species, this reduction step remains challenging under mild conditions. Herein, we discovered that deleterious Ti-NH accumulation on TiN can be circumvented photochemically with supported single atoms and clusters of platinum (Pt-Pt) under N-H conditions. The photochemistry of TiN selectively promoted Ti-NH formation, while Pt-Pt effectively transformed any formed Ti-NH into free ammonia. The generated ammonia was found to originate mainly from TiN reduction with a minor contribution from N activation. The knowledge accrued from this fundamental study could serve as a springboard for the development of MN materials for more efficient ammonia production to potentially disrupt the century-old fossil-powered Haber-Bosch process.