The side-chain hydrocarbon pool mechanism for the methanol-to-olefins (MTO) conversion catalyzed by methylnaphthalene in SAPO-34 zeolite was investigated by means of periodic density functional theory calculations. The alkyl side-chain was propagated by the methylation step and was eliminated into ethene and propene by the indirect proton shift steps in the mechanism. As shown, dimethylnaphthalene is more active than methylbenzenes for the MTO reaction when the organic intermediates are not rotationally limited inside the pore of catalyst. Propene is intrinsically more favorable than ethene as the product. The rate-determining step to produce ethene is the elimination of side ethyl chain, while that to produce propene is the methylation of exocyclic double bond in the reaction intermediates. However, the MTO activity of methylnaphthalene may be decreased by the limitation of SAPO-34 zeolite for the rotation of organic intermediates.

Key words: methanol-to-olefins reaction, SAPO-34 zeolite, methylnaphthalene, hydrocarbon pool mechanism, density functional theory