Influence of Si species on intergrowth and anisotropic crystal growth of silicalite-1

Silicalite-1 crystals were hydrothermally synthesized from silica gels prepared under different conditions. The influence of the state of Si species in the silica gels and the concentrations of silicate ions and a template agent in the reaction sols on crystal growth of silicalite-1 was examined. The use of silica gels with a high degree of condensation of Si species resulted in the intergrowth of silicalite-1 crystals, whereas a low degree of condensation of Si species led to coffin-shaped crystals. Thus, the degree of condensation of Si species had significant influence on the intergrowth of silicalite-1 crystals. Moreover, at a low silicate concentration, silicalite-1 crystals elongated along the c-axis were obtained. With increasing silicate concentration in the reaction sols, the aspect ratio of silicalite-1 decreased. Furthermore, with decreasing the amount of N(C3H7)4+ used as a template agent, the silicalite-1 crystals became larger isotropically. Thus, the growth direction of silicalite-1 crystals was dependent on silicate ion concentration in the reaction sols, but not on N(C3H7)4+ concentration.