Modified Fly Ash: An Eco‐Friendly, Cost‐Free, and Efficient Iron‐Based Catalyst for Ammonia Decomposition to CO_<i>x</i>‐Free Hydrogen

Abstract Fly ash (FA), an industrial waste produced in large amounts, is rich in metal oxides such as Al 2 O 3 , SiO 2 , and Fe 2 O 3 , making it an ideal candidate for use as a catalyst in ammonia decomposition. However, FA's surface area is very low (&lt;1.0 m 2 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 H 2 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 NH 3 h −1 g cat −1 , remaining stable for 140 h following an induction period of 30 h. Enhanced textural properties (18.5 m 2 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 H 2 were responsible for this performance.