Microwave-assisted synthesis of ZSM-5 from blast furnace slag

Abstract

A rapid hydrothermal synthesis method was employed to prepare a novel Zeolite Socony Mobil-5 (ZSM-5) material impregnated with intrinsic metal alloys (Fe₂O₃, MnO, TiO₂, Cr₂O₃, and NiO). Green chemistry was paired with the synthesis method as a sustainable approach to valorize blast furnace slag (BFS) while addressing the growing demand for high-performance zeolites. This study investigated the role of acid-leached BFS as a precursor and explored the advantages of microwave-assisted hydrothermal synthesis over conventional methods. The synthesis temperature and time were varied to explore their effects on the physicochemical, textural, and structural properties of the synthesized ZSM-5 products, with commercial ZSM-5 serving as a reference material for comparison. The favourable synthesis conditions were found to be 180 °C and 13 h, yielding a crystalline ZSM-5 product characterized by well-defined cubic prism shapes with microsized intergrown rectangular crystals. Furthermore, the synthesized ZSM-5 had a mesoporous structure with an average crystallinity of 52.4 % and a low specific surface area (108.4 m²/g) compared to the reference sample (436.4 m²/g). The use of microwave irradiation significantly reduced the synthesis time and energy consumption while preserving the structural integrity of the zeolite framework. Moreover, the synthesis temperature strongly affected the crystal size, while the synthesis time affected the morphology. However, neither the synthesis temperature nor the synthesis time affected the chemical composition of the products. This study highlighted the potential of BFS as a low-cost, sustainable feedstock for zeolite synthesis and the effectiveness of microwave-assisted methods in improving process efficiency. Further work has been proposed to evaluate the potential use of the synthesized ZSM-5 in industrial applications such as catalysis or adsorption processes.