Synthesis of Embryonic Zeolites with Controlled Physicochemical Properties

Colloidal zeolite precursors with sharp particle size distributions (ca. 3–5 nm) and identical chemical compositions, so called embryonic zeolites (EZs), are prepared by strict control of aluminosilicate precursor polymerization in zeolite-yielding systems. The organic structure-directing agent (OSDA) acts as a sacrificial template and is eliminated by high-temperature combustion after the synthesis. Physicochemical properties of the EZs, such as the pore size and volume and specific surface area, are determined by the size of the OSDA and synthesis conditions employed, that is, the larger the OSDA, the higher the microporous volume and the specific surface area of the derived EZs. The EZs belong to the family of extra-large microporous (1–2.5 nm) materials. Upon calcination, EZs retain their structure/porosity, and most of their aluminum remains in a tetrahedral coordination to provide Bronsted acidity. Pyridine adsorption shows a lower acidic strength for embryonic zeolites with respect to their crystal...