Confined Ru Sites in a 13X Zeolite for Ultrahigh H₂ Production from NH₃ Decomposition

Abstract

Catalytic NH₃ synthesis and decomposition offer a new promising way to store and transport renewable energy in the form of NH₃ from remote or offshore sites to industrial plants. To use NH₃ as a hydrogen carrier, it is important to understand the catalytic functionality of NH₃ decomposition 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^-1 for the NH₃ decomposition 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 NH₃ is ruptured heterolytically by the frustrated Lewis pair of Ru^δ+-O^δ- 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 NH₃ to regenerate framework Brønsted acid sites that eventually are converted to molecular hydrogen.