Effects of Fe Incorporation Strategies on the Coupled Catalytic and Transport Properties of Fe-Embedded Carbon Molecular Sieve Membranes

Abstract Catalytic membrane reactors offer a promising route to intensify chemical processes by integrating the reaction and selective product removal in a single unit. Carbon molecular sieve (CMS) membranes are attractive candidates for membrane reactors because of their strong molecular sieving capability, high thermal and pressure stability, and the presence of functional groups that enable metal incorporation. Although metal-containing CMS membranes have been reported for separation, their catalytic functions and the coupled effects of metal incorporation on transport and reactivity under harsh conditions remain largely unexplored. A key challenge is the limited understanding of how metal incorporation simultaneously influences the membrane microstructure, gas transport, and catalytic function under high-temperature reaction conditions. We prepared Fe-embedded CMS membranes derived from 6FDA-DAM-DABA (3:2) polyimide through cocasting (Fe_cc), dip-coating (Fe_dp), and post-pyrolysis incipient wetness impregnation (Fe_IWI) to directly examine how the Fe incorporation pathway governs membrane microstructure, NH3 transport, and catalytic behavior. We probe the catalytic performance for NH3 synthesis and observed that all Fe/CMS membranes are active for NH3 production: Fe_cc/CMS exhibiting the highest steady-state turnover frequency (2.48 min–1), followed by Fe_dp (1.59 min–1) and Fe_IWI (1.23 min–1). Permeation, sorption, and diffusion measurements were employed to directly measure NH3 transport in CMS membranes with and without metals. Fe incorporation reduced NH3 permeability from 1484 Barrer (metal-free CMS) to 201–450 Barrer (Fe-containing CMS), demonstrating that Fe incorporation significantly alters NH3 transport through CMS structure under ambient permeation conditions. Additionally, electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, and CO2 physisorption together revealed that the Fe incorporation pathway controls Fe particle size, oxidation state, and the extent of ultramicropore disruption within the CMS matrix. This work provides an integrated evaluation of gas transport and catalytic NH3 synthesis in Fe-CMS membranes and identifies the metal incorporation pathway as a critical design variable for catalytic membranes.