Synthesis of long zeolite-L crystals with flat facets

Abstract

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 Al 2O 3:SiO 2:K 2O:H 2O = a: b: c: d, where a = 1.3–2.0, b = 20–24, c = 10.2–10.5, and d = 1000–1400 and with Al 2(SO 4) 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 SiO 2, H 2O, or Al 2O 3 content, but with decreasing the K 2O content. While the length increased, the width decreased upon increasing both Al 2(SO 4) 3 and H 2O 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 Al 2(SO 4) 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 MgCl 2 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 Al 2O 3 content. The addition of CaCl 2 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.