Recrystallization of layered silicates to silicalite-1

Abstract

Three methods for the synthesis of silicalite-1 by recrystallization of layered silicates were investigated. The layered silicates included magadiite, kenyaite and octosilicate, which were made using poly(ethylene glycol) (PEG 200) as a template. Both as-synthesized and calcined forms of the layered silicates were used as the silica source. In the system of NaOH–TPABr–SiO 2–H 2O (Method 1), silicalite-1 as a single phase was synthesized using as-synthesized kenyaite, octosilicate, or calcined magadiite at 150 °C. Silicalite-1 with impurity was obtained from as-synthesized magadiite or calcined kenyaite. In the system of TPAOH–SiO 2–H 2O (Method 2), silicalite-1 could be obtained at temperatures of 135, 150 and 175 °C, using either the as-synthesized or calcined forms of the layered silicates. Compared to fumed silica, the layered silicates had a higher reactivity in the synthesis of silicalite-1. In the system of NaOH–TPAOH–SiO 2–H 2O (Method 3), pure silicalite-1 could be synthesized using as-synthesized magadiite, kenyaite and octosilicate as well as calcined kenyaite as the silica source at 150 °C. For each of the three methods, the degree of crystallinity and morphology of silicalite-1 were dependent upon the synthesis parameters, including the gel composition and the type of layered silicate as well as the reaction temperature and time.