Studies on the crystallization of a novel, large-pore, high-silica molecular sieve, NCL-1

Abstract

The synthesis of a novel, large-pore, high-silica molecular sieve, NCL-1, is described in detail. A comparison of the XRD powder patterns of NCL-1 and other known structures revealed that zeolite NCL-1 is a new phase. However, zeolite SSZ-31, a Chevron material, and NCL-1 have some common features and may belong to a common family. Adsorption measurements (o-xylene = 7.4 and mesitylene = 4.8 wt% at P/Po = 0.5, T = 298 K) rank NCL-1 as a large-pore zeolite. The synthesis has been carried out using fumed silica, aluminum sulfate (optional), and hexamethylene bis(triethylammonium bromide) (R 2.) as an organic template under hydrothermal conditions in alkaline medium. The kinetics of crystallization has been studied using X-ray powder diffraction, scanning electron microscopy (SEM), and framework i.r. spectroscopy. The influence of various synthesis parameters such as the Si/AI and Na+/Si molar ratios, alkalinity (OH-/Si), concentration of the organic template (R2+/Si), the H20/Si ratio, and the temperature on the crystallization time, phase purity, and yield of crystalline product has been investigated.