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 (NH3-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.