Synthesis and characterization of mordenite-type zeolites with varying Si/Al ratio

Abstract

One factor that makes mordenite-type zeolites attractive in adsorption applications is its high cation exchange capacity (CEC) that can further be improved by controlling its Si/Al ratio (SAR). Mordenite-type zeolites with SAR of 25, 20, 15, 10 and 5 were attempted to synthesize via hydrothermal method using silica gel and sodium aluminate as Si and Al sources respectively. The SAR was varied by changing the molar composition of the starting gel solution. The starting solution with theoretical SAR of 15 and 10 successfully produced mordenite with high degree of crystallinity and purity. At high SAR equal to 20, the product was found to be amorphous with significant peaks indexed to mordenite. Amorphous materials were mostly formed from the starting solution with theoretical SAR of 25. On the other hand, the starting solution with theoretical SAR of 5 yielded analcime-type zeolites. FTIR confirms the presence of vibrational bands that are typical to zeolites and/or aluminosilicates for all samples. The synthesized crystalline mordenites have prismatic, hexagonal shapes while others have fibrous or needle-like structures. XRF analysis shows that the synthetic mordenites indeed have varying actual SAR, though the values are lower than expected.