Insights into structure–function relationships of mesoporous H-ZSM-5 zeolite catalysts for direct amination of cyclohexene with NH3

Abstract

Developing a 100% atom economic direct amination reaction of bulky cycloolefins with NH₃ is important but challenging for CN bond formation. This work describes a novel strategy of employing H-mZSM-5 zeolites with meso–microporous architecture as a solid acid catalyst for highly selective preparation of cyclohexylamine by vapor-phase acid-catalyzed amination of cyclohexene with NH₃. The mesoporous H-mZSM-5 compared to the referenced microporous H-ZSM-5 delivers outstanding catalytic activity, providing a cyclohexylamine selectivity of 95.6% and 4.9% conversion at 9 MPa and 300 °C. The relationship of zeolite structure and catalytic activity is established by using multiple techniques, such as N₂ adsorption–desorption, XRD, SEM, TEM, Py-FTIR and NH₃-TPD. The pore structure and Brønsted-acid sites of the zeolites played crucial roles in the cyclohexene amination reaction. Based on in situ FT-IR spectroscopy and DFT simulations, the reactant adsorption and product desorption, and molecular diffusion on the mesoporous HZSM-5 suggested that the accessible Brønsted-acid sites in the 10-MR micropores are the key factors controlling the catalytic process.