Remarkably high stability of relatively small iron amount exchanged into HZSM-5 catalysts toward ethanol conversion into ethylene: Experimental and computational studies

Abstract

The sustainable production of green ethylene from bioethanol provides a realistic pathway to lowering the carbon footprint of conventional petrochemical routes. In this study, Fe exchanged H-ZSM-5 catalysts with a Si/Al ratio of 26 and different iron contents were synthesized and characterised using Powdered X ray Diffraction (PXRD), Fourier Transform Infrared Spectroscopy (FT-IR), Pyridine Infrared Spectroscopy (Py-IR), Ammonia Temperature Programmed Desorption (NH 3 -TPD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Atomic Absorption Spectroscopy (AAS), and Thermogravimetric Analysis (TGA). Catalytic tests were performed in a fixed bed reactor by varying temperature between 200 and 300 °C and weight hourly space velocity (WHSV) from 2 to 19 h −1 . The 3Fe ZSM-5 catalyst containing 2.3 wt% Fe achieved 98% bioethanol conversion and more than 95% ethylene selectivity at 280 °C and WHSV of 9 h −1 , while remaining stable for 56 h on stream. Acidity characterization revealed that Fe incorporation weakens strong Brønsted sites and generates Lewis acid sites, limiting secondary reactions and coke formation. Consistently, TGA showed around 11% less coke compared to the parent zeolite. Density Functional Theory (DFT) calculations using DMol3 identified Fe-O-Si motifs with Fe-O distances of 1.99 to 2.02 Å. • Fe exchanged ZSM 5 catalysts convert bioethanol to green ethylene efficiently under mild and practical conditions. • Tuning Fe loading adjusts Brønsted and Lewis acidity, thereby boosting ethylene selectivity and limiting the formation of diethyl ether. • Optimized Fe-ZSM-5 delivers near-complete bioethanol conversion and high ethylene selectivity for 56 h on stream. • Multi-technique characterization links structure, texture, and acidity to catalytic activity and coke resistance. • DFT calculations on Fe-O-Si sites reveal favorable pathways for ethanol activation and dehydration that align with experimental trends.