Mesopore generation by organosilane surfactant during LTA zeolite crystallization, investigated by high-resolution SEM and Monte Carlo simulation

The crystallization of LTA zeolite under a hydrothermal synthesis condition that contained a quaternary ammonium-type organosilane surfactant was studied with X-ray powder diffraction (XRD), high-resolution scanning electron microscopy (HRSEM) and Monte Carlo simulation of the crystal growth. The hydrothermal reaction products were collected at various crystallization times, and investigated with XRD and HRSEM. The HRSEM images of the final zeolite products were taken as synthesized and also after cross-sectioning with an argon ion beam. The HRSEM investigation revealed presence of a disordered network of mesoporous channels that penetrated the microporous zeolite crystal. Unless the loading of the surfactant was exceedingly high, the microporous zeolite particles exhibited truncated cubic morphologies that were almost like single crystals, despite penetration by the mesopores. The outline of the zeolite particle became progressively rounded as the mesoporosity was increased according to the surfactant loading. The mesoporosity in the zeolite crystals was well maintained against crystal-ripening processes for 6 d. This result supports the fact that the organosilane surfactant micelles became incorporated inside the zeolite crystal as a mesopore generator during the crystallization process. Data from Monte Carlo simulation agreed with these experimental results. (C) 2010 Elsevier Masson SAS. All tights reserved.