Photochemical Acceleration of Ammonia Production by Pt₁-Pt_n-TiN Reduction and N₂ 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 MN1-x is a necessary step to generate ammonia. However, encumbered by the formation of kinetically stable M-NH1-3 surface species, this reduction step remains challenging under mild conditions. Herein, we discovered that deleterious Ti-NH1-3 accumulation on TiN can be circumvented photochemically with supported single atoms and clusters of platinum (Pt-1-Pt-n) under N-2-H-2 conditions. The photochemistry of TiN selectively promoted Ti-NH formation, while Pt-1-Pt-n 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-2 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.