Green Synthesis of Hierarchical NaY Zeolite from Perlite for Enhanced Knoevenagel Condensation
Hierarchical aluminum-rich zeolites are promising catalysts for Knoevenagel condensation, but their synthesis is often costly and energy-intensive. This work reports a green route to hierarchical NaY zeolite using submolten salt (SMS) activated perlite as the sole silicon and aluminum source. The product exhibits high purity and crystallinity, with a framework SiO2/Al2O3 molar ratio of approximately 4.2, intercrystalline mesopores centered at about 20 nm, large external surface area, and abundant basic sites. Crystallization studies reveal that small crystals initially assemble on the activated perlite surface, then grow and aggregate to form a crystal-packed morphology with intercrystalline mesopores. In the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate, the hierarchical NaY zeolite achieves higher benzaldehyde conversion than conventional NaY zeolites, attributed to improved mass transfer and increased basic site accessibility. This work provides a cost-effective and sustainable catalyst while valorizing natural perlite.