Catalytic NH3synthesis and decomposition
offer a new
promising way to store and transport renewable energy in the form
of NH3from remote or offshore sites to industrial plants.
To use NH3as a hydrogen carrier, it is important to understand
the catalytic functionality of NH3decomposition reactions
at an atomic level. Here, we report for the first time that Ru species
confined in a 13X zeolite cavity display the highest specific catalytic
activity of over 4000 h–1for the NH3decomposition with a lower activation barrier, compared to most
reported catalytic materials in the literature. Mechanistic and modeling
studies clearly indicate that the N–H bond of NH3is ruptured heterolytically by the frustrated Lewis pair of Ruδ+–Oδ−in the zeolite
identified by synchrotron X-rays and neutron powder diffraction with
Rietveld refinement as well as other characterization techniques including
solid-state nuclear magnetic resonance spectroscopy, in situ diffuse
reflectance infrared transform spectroscopy, and temperature-programmed
analysis. This contrasts with the homolytic cleavage of N–H
displayed by metal nanoparticles. Our work reveals the unprecedented
unique behavior of cooperative frustrated Lewis pairs created by the
metal species on the internal zeolite surface, resulting in a dynamic
hydrogen shuttling from NH3to regenerate framework Brønsted
acid sites that eventually are converted to molecular hydrogen.