Transforming coal fly ash into a high-performance catalyst for sustainable hydrogen generation: A circular-economy approach

Coal fly ash (CF), a major industrial by-product rich in metal oxides, offers significant potential for circular-economy applications when repurposed as a low-cost catalyst in clean-energy processes. However, naturally occurring CaSO 4 and the SiO 2 shell structure in CF limit its catalytic performance. This study introduces an acid–alkali modification strategy using HF and NaOH to enhance CF's catalytic activity for environmentally responsible hydrogen (H 2 ) production during coal steam gasification. The NaOH–HF treatment effectively removed CaSO 4 and disrupted the SiO 2 layer, releasing embedded iron species (α-Fe and α-Fe 2 O 3 ) and generating an active Fe-based phase (FeFy). These transformations strengthened surface functional groups, increased accessible C–H bonds, and significantly accelerated gasification reactions. The modified CF catalyst promoted stronger interactions with steam and coal, enabling more efficient cleavage of O–H and C–H bonds and resulting in higher H 2 yields. Hydrogen production increased from 915.99 mL/g for the E–A modification route to 1537.74 mL/g for the A–E route, achieving a carbon-conversion rate of 99.68 %. This work demonstrates how waste-derived catalysts advance both the hydrogen economy and environmental responsibility by transforming industrial waste into a high-performance material for sustainable coal gasification.