In order to investigate the effect of Si/Al ratio of SAPO-34 on the reactivity and coke composition in the methanol to olefins reaction

a series SAPO-34 samples with different Si/Al ratio were prepared with controlling the composition of the synthesis gel. The total acidity

acid strength and the distribution of acid sites of these samples were characterized. The results showed that the amount of close acid sites increased with increasing Si/Al ratio of SAPO-34. The influences of the Si/Al ratio of SAPO-34 on the performances in the reaction of methanol to olefins were investigated. The result showed close acid sites were the main active sites for hydrogen transfer and oligomerizations which increased the selectivity of by-product propane and coke

as a result the life time and the selectivity of olefins decreased. The dissolved coke were analyzed using in-situ thermogravity combined with mass spectrometry and gas chromatography mass spectrometry

the results showed that the close acid sites accelerated the generation of anthracene

phenanthrene

naphthalene

and other polycyclic aromatic products in the cage of SAPO-34

which led the blockage of the product diffusion channel and rapid deactivation of SAPO-34.