IR study on methanol-to-olefin reaction over zeolites with different pore structures and acidities

The effects of the pore structure and acidity of zeolites on their product distribution and deactivation rates in the methanol-to-olefin(MTO) reaction were studied according to the different topologies of CHA, LTA, MFI, BEA, MOR and FAU zeolites. The in situ IR study of the MTO reaction over various zeolites with different pore structures and acidities confirmed the considerable effect exerted by these factors on the species of alkylaromatics formed and on the rates of further condensation of alkylaromatics to polycyclic aromatic hydrocarbons (PAHs). The nature and continuing concentration of alkylaromatics formed in the zeolite pores determined their product composition and deactivation rate in the MTO reaction. LTA and FAU zeolites with large cages and high acid site density were deactivated rapidly due to the high concentration of alkylaromatics with large substituents and their rapid condensation to PAHs. However, the small cages of CHA zeolite and the sinusoidal pores of MFI zeolite suppressed the accumulation of large hydrocarbon molecules in their pores and lengthened their catalyst lives, although the composition of the products formed over them clearly differed because of their different pore structures. (C) 2009 Elsevier B.V. All rights reserved.