Synthesis of colloidal stable Linde Type J (LTJ) zeolite nanocrystals from rice husk silica and their catalytic performance in Knoevenagel reaction

Nanoscaled aluminosilicate zeolite Linde J (structure code LTJ) was synthesized from rice husk ash (RHA) under hydrothermal condition. Structural phases, morphologies, crystal size and chemical compositions of the nanocrystals were characterized by XRD, IR, FESEM, TEM, ICP-OES, TG/DTG and DLS/zeta potential analyses. The XRD and Rietveld refinement studies revealed that pure LTJ-type zeolite (Si/Al ratio = 1.86) can be obtained from the a precursor gel of 3.75SiO2:1Al2O3:15K2O:132H2O at 100 °C. The results also showed that co-crystallization of zeolite K-F could be avoided by extending the crystallization time to 30 h. The prepared zeolite nanocrystals (ca. 220 nm) exhibited long-term stability in colloidal form without adding any organic template. The zeolite framework structure was thermally stable up to 800 °C. The nanosized zeolite showed good catalytic performance in solvent-free Knoevenagel reaction, with ca. 88% reactant conversion and 100% product selectivity even after fourth cycle of reaction.