Synthesis of large mordenite crystals with different aspect ratios

Abstract

Large mordenite crystals hold interest for fundamental research on separation and catalysis as well as emerging applications such as functional devices. A number of methods are now available to obtain large mordenite crystals. However, it still remains a challenge to synthesize large and uniform crystals with a desired aspect ratio. Moreover, a detailed description of a reproducible synthesis method is still lacking. We report here large and uniform mordenite crystals (27 × 36 × 30 μm 3) with an accessible micropore volume of 0.17 cm 3/g that can be reproducibly synthesized. The synthesis procedure is described in detail. The effects of synthesis parameters on mordenite morphology (size and aspect ratio of the crystals), such as silicon precursors, H 2O content, Na 2O/SiO 2/Al 2O 3 ratios, alcohol additives, have been systematically studied. Large mordenite crystals (up to 85 μm) with prismatic shape were formed from a dense synthesis gel with high SiO 2/Al 2O 3 and Na 2O/SiO 2 ratios, or by adding alcohol additives. Moreover, the aspect ratio of the large crystals was controlled by finely altering the above synthesis parameters. In the presence of an excess amount of alcohol, hollow and core–shell mordenite crystals were formed.