Synthesis of long zeolite-L crystals with flat facets

Synthetic conditions that produce long zeolite-L crystals in hexagonal columnar structures with flat basal and side planes were investigated. The gels with the molar compositions of Al2O3:SiO2:K2O:H2O = a:b:c:d, where a = 1.3-2.0, b = 20-24, c = 10.2-10.5, and d = 1000-1400 and with Al2(SO4)3 as the Al source produced zeolite-L with sharp edged hexagonal columnar structures and flat basal and side planes upon heating at 180 °C for 3 d. The crystal size, in particular the length, increased with increasing the SiO2, H2O, or Al2O3 content, but with decreasing the K2O content. While the length increased, the width decreased upon increasing both Al2(SO4)3 and H2O contents, leading to the production of sharp-edged hexagonal columnar crystals. In the case where a = 1.7, b = 20, c = 10.9, and d = 1030, sharp edged hexagonal columnar crystals with the length up to 20 μm and the width of 2.3 μm were produced. When Al(OH)3, a more commonly used Al source, was used instead of Al2(SO4)3, crystals with blunt edges and round planes were produced. Furthermore, the size decreased with increasing the Al(OH)3 content. While KCl and NaCl had a negligible effect on the morphology change, LiCl and MgCl2 led to a dramatic decrease in size by 96% and 91%, respectively, even with in the presence of 0.2 and 0.001 equivalents, respectively, with respect to the amount of Al2O3 content. The addition of CaCl2 led to the production of an unknown phase. The use of mixed base, i.e., the KOH and NaOH mixture in the mole ratio of 6:4.9, led to the formation of crystals whose one end was connected to a bundle of narrow and long crystals.