日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

The MFI-type zeolite has two kinds of orthogonal channels: sinusoidal channel and straight channel. The mouths of the sinusoidal channels are on (100) crystal faces, while those of the straight channels are on (010) faces. The entrance and diffusion pathway of CO₂ and dimethyl ether (DME) in MFI-type zeolite channels are investigated by a selective sealing method. The channel mouths are directly sealed by silicone resin so as to restrict the entrance and diffusion pathways to the sinusoidal channel pathway or the straight channel pathway. The locations and loadings of the guest CO₂ and DME molecules are determined by single-crystal X-ray diffraction structural analysis. The structures show the difference of the adsorption rates between the pathways. CO₂, favoring the straight channel as its stable adsorption site, selects the straight channel pathway as the dominant pathway. DME, favoring the sinusoidal channel as its stable adsorption site, selects the sinusoidal channel pathway as the dominant pathway. The dominant pathway correlates with the stability of the channel as adsorption sites. The straight channel pathway is 4.2 times faster than the sinusoidal channel pathway for the CO₂, and the sinusoidal channel pathway is 5.1 times faster than the straight channel pathway for the DME. This is the first report to describe the quantitatively-measured adsorption anisotropy of the MFI-type zeolites.