Influence of NaOH and KOH on the synthesis of MCM-22 and MCM-49 zeolites

MCM-22 or MCM-49 zeolites were directly prepared using NaOH or KOH as mineralizing agents. The initial batch composition was 30SiO2–vAl(OH)3–xNaOH(or xKOH)–yHMI–zH2O, with v = 1, 1.5, 2, 3; x = 2.7, 5.4, 9, 10.5, 12, 15, 18; y = 10.6, 15; z = 1050, 1200, 1350; HMI = hexamethyleneimine. The products were obtained by hydrothermal synthesis at 150 °C in stirring conditions. For HMI/Na ratio greater than 2 MCM-22(P) is formed, while for a lower HMI/Na ratio MCM-49 is formed. In presence of K+ ions only MCM-22(P) could be obtained. In addition, the Al content of the MCM-22(P) samples is much lower (ca. 10 mol%) than those obtained with Na+ ions (ca. 20 mol%).The MCM-22(P) zeolites prepared in presence of Na+ ions are formed much faster than those prepared in presence of K+ ions. The formation of MCM-22(P) is more difficult with increasing Al-content in the gel.The 27Al NMR spectra show two lines at 55.5 ppm and 49.9 ppm. Both are due to framework tetrahedral species. No extraframework octahedral species were detected in any of the samples. The 29Si NMR spectra could be decomposed using eight crystallographically different sites.