Making Zeolites Without Templates

A template-free synthesis procedure can be used to prepare zeolites if the earliest stages of the crystallization process are carefully controlled, according to work reported in Science (DOI: 10.1126/science.1214798). Zeolites are a class of porous crystalline aluminosilicates that are widely used as catalysts in oil refining and petrochemical synthesis. Expensive organic compounds, such as the ether 18-crown-6, often serve the crucial role of structure-directing agents (templates) in zeolite preparation methods. Efforts to omit these costly compounds have until now met with little success. Svetlana Mintova of Caen University, in France, together with coworkers based in Malaysia and Germany, find that by fine-tuning the reactant ratios, nucleation temperatures and times, and heating procedures (conventional and microwave-driven), they can grow crystals of a zeolite known as EMT from a Na₂O–Al₂O₃–SiO₂–H₂O precursor system without using templates. The team reports that their low-temperature procedure (30 °C) yields ultrasmall and pure EMT zeolite crystals with diameters in the 6- to 15-nm range. And because the crystals are made without templates, the high-temperature treatment typically used to remove the templates is unnecessary, they note.