Effect of the Al content in the precursor on the crystallization of OSDA-free Beta zeolite

To date, many types of zeolites have been successfully synthesized without using any organic structure directing agent (OSDA). However, so-called "OSDA-free synthesis of zeolites" including Beta often gives a low product yield. The present study shows that hydrothermal synthesis using precursor suspension with a high-aluminum content substantially improved the yield in the OSDA-free synthesis of Beta zeolite. By means of monitoring time course changes of solid products in detail, it was found that the crystallization proceeded through the "solution-mediated mechanism" in which the amount of aluminosilicate species (not silicate species alone) in the mother solution determined the product yield. Synthesis parameters such as silica raw material, alkalinity, and seed crystal were optimized, achieving similar to 80% yield based on SiO2. (C) 2015 Elsevier Inc. All rights reserved.