Modified fly ash: an eco-friendly, cost-free, and efficient iron-based catalyst for ammonia decomposition to COx-free hydrogen

Abstract

Fly ash (FA), an industrial waste produced in large amounts, is rich in metal oxides such as Al2O3, SiO2, and Fe2O3, making it an ideal candidate for use as a catalyst in ammonia decomposition. However, FA's surface area is very low (andlt;1.0 m2 g−1), limiting its potential. This study investigates the modification of FA by calcination at various temperatures (550, 700, and 1000 °C), HCl treatment, and HCl treatment followed by calcination at 500 °C to convert FA into a catalyst by utilizing its iron content as active sites. The catalyst obtained by treating FA with HCl at 220 °C, calcining at 500 °C, reducing in H2 at 700 °C, and activating in ammonia at 700 °C achieved 86.0% ammonia conversion at a reaction temperature of 700 °C and a space velocity of 30,000 mL NH3 h−1 gcat−1, remaining stable for 140 h following an induction period of 30 h. Enhanced textural properties (18.5 m2 g−1), elimination of S and Cl impurities, and the formation of relatively small Fe crystallites (23.8 nm determined by Scherrer equation and 24.0 nm measured by transmission electron microscopy (TEM)) when reduced in H2 were responsible for this performance. © 2024 Wiley-VCH GmbH.