Influence of zeolite acidity on CO₂ hydrogenation over iron-based ZSM-5 zeolite

Converting CO₂ into value-added chemicals is crucial for combating rising CO₂ levels and environmental impacts. Iron-based catalysts convert CO₂ to chemicals, but optimizing their fabrication strategy remains underexplored. Fe-impregnated nanosized ZSM-5 zeolite formulations with different preparation conditions (uncalcined UnC-, calcined C-, protonated CPC-series) and calcination temperatures (400, 600, and 800 °C) were prepared. Catalysts were characterized using XRD, FESEM, XRF, XPS, TPR, and TPD. Analysis showed Fe10%-ZSM-5 had higher XRD crystallinity for protonated sample compared to uncalcined and unprotonated zeolite, with sequential changes in chemical states and H₂ consumption as temperature rose to 900 °C·NH₃-TPD showed protonated zeolite enhanced overall acidity, generating major weak and strong acid sites. XRD and XPS revealed Fe mixed phases (Hematite/Maghemite) at low calcination temperature (<600 °C). This mixture creates synergistic effects enhancing thermal stability and reducibility for CO₂ hydrogenation. The 10 %-Fe-ZSM-5 (C-series) calcined at 600 °C achieved 19 % CO₂ conversion with 93 % CO selectivity and 6 % hydrocarbons, indicating Fe impregnation without zeolitic strong acidity favors CO generation. Protonation enhanced selectivity toward hydrocarbons, reaching 51 % using protonated zeolite (CPC-series) at 400 °C. The catalyst maintained activity and selectivity for 12 h in hydrogenation conditions.