Low temperature ethanol dehydration performed by MOR catalysts obtained from 2D–3D transformation

Abstract

The silanol groups present on the surface of lamellar silicates are excellent reaction sites for a varied number of chemical modifications. The conversion of these solids into zeolitic structures has shown to be an interesting synthetic alternative, once avoiding hard templating methods and producing materials with particular characteristics. In this work, a post-synthesis OSDA-free procedure was employed for the 2D–3D transformation of Na-RUB-18 lamellar silicate into mordenite zeolite. The conversion was performed at 140 °C and produced small zeolitic crystals (300–500 nm) after 12 and 24 h of crystallization. The reaction presented 65% yield (mol/mol SiO2), producing materials with a similar Si/Al molar ratio (around 6). The 27Al MAS NMR spectra showed signals related to tetrahedrally coordinated aluminum. The N2 adsorption/desorption isotherms confirmed the solids microporous nature and volume (0.36 and 0.43 cm3 g−1). The number of acidic sites was determined by NH3-TPD (976 and 848 µmol g−1), which also revealed sites with weak and moderate to strong acidity. Finally, the samples’ catalytic activity was evaluated by the ethanol dehydration reaction performed at low temperature (150 °C). The synthesized materials were compared to a commercial sample and all the catalysts showed ethanol conversion around 70%, producing ethene and diethyl ether; the latter being the major product at the employed temperature. Unlike the commercial sample, the synthesized ones did not present any deactivation during the time on stream. This feature was attributed to their low-defect structure and subtle mesoporosity.