Methanol-to-olefin over gallosilicate analogues of chabazite zeolite

Gallosilicate analogues of chabazite zeolite with CHA topology have been synthesized, characterized and employed as catalysts for the methanol-to-olefin (MTO) process. Ga-71 NMR spectra indicate that Ga is incorporated into the framework of these zeolitic materials during the hydrothermal synthesis. IR measurements show that stretching vibration of the hydroxyl groups associated with the framework Ca appears at 3600 cm(-1). The gallosilicates with high Ga contents show Lewis acidity, which is possibly caused by degalliation during calcination, whereas only Bronsted acid sites are observed on the sample with relatively low Ga content. The catalysts show promising catalytic performance in the MTO reaction, particularly from the stability point of view, compared with H[Al]CHA zeolites. This is attributed to the weak Bronsted acidity associated with the framework Ga in the gallosilicates. (C) 2008 Elsevier Inc. All rights reserved.