Synthesis of iron-loaded MFI-type (Fe/ZSM-5) zeolite using Philippine natural zeolites (PNZ) for potential adsorption and catalytic applications

Abstract Philippine natural zeolites (PNZ) are locally abundant aluminosilicates used in different applications such as filtration and purification. However, the presence of impurities limits their usability. Structure modification of PNZ into a new framework was conducted in the study to address this issue. This study used PNZ as a precursor in the sustainable synthesis of iron-loaded MFI-type (Fe/ZSM-5) zeolite, a synthetic zeolite extensively studied for its excellent catalytic activity and high adsorption capacity. PNZ was depolymerized into active silica and alumina, then recrystallized via hydrothermal synthesis. Ammonium iron citrate (AIC) and TPAOH were used as the iron source and structure-directing agent, respectively. The disappearance and appearance of FTIR peaks in the depolymerized PNZ spectra deduced the successful destruction of the initial zeolite framework of the PNZ. The synthesized material was characterized using FTIR, XRD, SEM-EDS, TGA, and BET analyses. FTIR showed the crystallinity peak of MFI-type zeolite, while XRD confirmed its successful synthesis. SEM images show hierarchical aggregated particles suggesting the presence of intercrystalline and intracrystalline mesopores. The BET surface area of the synthesized zeolite increased by 168% compared to the raw PNZ, and TGA results show its high thermal stability. EDS analysis confirmed the presence of iron in the sample.