Entrance and diffusion pathway of CO₂and dimethyl ether in silicalite-1 zeolite channels as determined by single-crystal XRD structural analysis

Abstract

The entrance and diffusion pathway of CO2 and dimethyl ether (DME) in MFI-type zeolite channels were investigated by a selective sealing method using large silicalite-1 crystals. The MFI-type zeolite has two kinds of orthogonal channels: straight channels and sinusoidal channels. The mouths of the straight channels are on (010) crystal faces, while those of the sinusoidal channels are on (100) faces. The channel mouths are directly sealed by silicone resin on the (100) and (010) faces so as to restrict the entrance and diffusion pathways to straight and sinusoidal channel pathways, respectively. The locations and loadings of the guest CO2 and DME molecules are determined by single-crystal X-ray diffraction structural analysis. The loadings show the difference of the adsorption rates between the pathways. 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. It reveals their dominant pathways and the anisotropy of adsorption. The dominant pathway correlates to the stability of the channel as adsorption sites.

Adsorption of CO2 Molecules in Silicalite: Structural Investigation and Isotherm Modeling Using In Situ High-Resolution Powder X-ray Diffraction

“…Because of its hydrophobic nature, silicalite can be used to adsorb nonpolar hydrocarbons selectively, with applications in separation processes and environmental science. 31,32 Carbon dioxide (CO 2 ) belongs to the family of nonpolar small linear chain molecules, and its sorption in MFI zeolites has been studied intensively over the last 40 years. In particular, silicalite can be used for the selective removal of CO 2 from gas mixtures such as CO 2 /N 2 33 found in the atmosphere or in postcombustion flue gas, CO 2 /CH 4 34,35 present in natural gas and biogas, or CO 2 /H 2 36,37 in synthesis gas.…”

“…This unique channel system allows different kinds of molecules to diffuse and be trapped at specific positions in the zeolite, from large aromatic molecules − to smaller chain compounds, for applications in catalysis, pollutant removal, or to design new nanoelectronic devices with nonlinear optical effects. Because of its hydrophobic nature, silicalite can be used to adsorb nonpolar hydrocarbons selectively, with applications in separation processes and environmental science. , …”

Event driven 4D STEM acquisition with a Timepix3 detector: microsecond dwell time and faster scans for high precision and low dose applications

“…The same type of data acquisition at 60 kV can be per-formed at 200 kV where the main difference is the larger cluster size at 200 kV. However in terms of lost electrons, the 200 kV is better since only a small fraction (3%) seems to be lost by increasing the energy threshold to the 31 keV used for the 200 kV data presented here taken of a silicalite-1 zeolite [41]. A 10 × 1024 × 1024 probe position scan is performed at a dwell time of 1 µs where the dose per frame was 300 e − Å −2 and the total dose over the ten scans was 3000 e − Å −2 .…”