Hydrogen Spillover to Oxygen Vacancy of TiO<sub>2–<i>x</i></sub>H<sub><i>y</i></sub>/Fe: Breaking the Scaling Relationship of Ammonia Synthesis
Chengliang Mao, Jiaxian Wang, Yunjie Zou, Guodong Qi, Joel Y. Y. Loh, Tianhua Zhang, Meikun Xia, Jun Xu, Feng Deng, Mireille Ghoussoub, Nazir P. Kherani, Lu Wang, Huan Shang, Meiqi Li, Jie Li, Xiao Liu, Zhihui Ai, Geoffrey A. Ozin, Jincai Zhao, Lizhi Zhang
Abstract
Optimizing kinetic barriers of ammonia synthesis to reduce the energy intensity has recently attracted significant research interest. The motivation for the research is to discover means by which activation barriers of N2 dissociation and NHz (z = 1–2, surface intermediates) destabilization can be reduced simultaneously, that is, breaking the “scaling relationship”. However, by far only a single success has been reported in 2016 based on the discovery of a strong–weak N-bonding pair: transition metals (nitrides)-LiH. Described herein is a second example that is counterintuitively founded upon a strong–strong N-bonding pair unveiled in a bifunctional nanoscale catalyst TiO2–xHy/Fe (where 0.02 ≤ x ≤ 0.03 and 0 < y < 0.03), in which hydrogen spillover (H) from Fe to cascade oxygen vacancies (OV–OV) results in the trapped form of OV-H on the TiO2–xHy component. The Fe component thus enables facile activation of N2, while the OV-H in TiO2–xHy hydrogenates the N or NHz to NH3 easily.