EU‐12: A Small‐Pore, High‐Silica Zeolite Containing Sinusoidal Eight‐Ring Channels

Abstract

Zeolite EU-12, the framework structure of which has remained unsolved during the past 30 years, is synthesized at a specific SiO2 /Al2 O3 ratio using choline as an organic structure-directing agent, with both Na(+) and Rb(+) ions present. Synchrotron powder X-ray diffraction and Rietveld analyses reveal that the EU-12 structure has a two-dimensional 8-ring channel system. Among the two distinct 8-ring (4.6×2.8 and 5.0×2.7 Å) channels along c axis, the smaller one interconnects with the sinusoidal 8-ring (4.8×3.3 Å) channel along a axis. The other large one is simply linked up with the sinusoidal channel by sharing 8-rings (4.8×2.6 Å) in the ac plane. The proton form of EU-12 was found to show a considerably higher ethene selectivity in the low-temperature dehydration of ethanol than H-mordenite, the best catalyst for this reaction.

Phase Transformation Behavior of a Two‐Dimensional Zeolite

“…The geometric refinement in space group Pmma gave the most suitable structure model with ag eometrical residual (R dls )o f 0.0032. Among the 13 topologically distinct T-atoms,o nly two (i.e., sites T3 and T7) of them terminate the external surface of the layers.W e note here that not only the two unit cell dimensions of PST-9 and EU-12 are quite similar to each other, [1,6] but also both structures contain the saw-tooth chains that are combined to form 5-ring layers,which are ultimately connected to form 8ring channels.The saw-tooth chains are only part of the 5-ring layers in the EU-12 structure.H owever, they are located between the two neighboring layers in the PST-9 structure,as well as within its 5-ring layers ( Figure S6). Thef inal atomic positions and selected bond lengths and angles of this 2D zeolite are given in Tables S2 and S3, Thef ramework structure of PST-9 contains an intralayer 2D pore system consisting of straight 8-ring (3.5 4.7 ) channels along the b-axis intersected by sinusoidal 8-ring (3.7 4.8 )c hannels along the a-axis (Figure 1g,h).…”

“…No openings larger than 6-rings exist along the c-axis (perpendicular to the PST-9 sheet), partly explaining the low external surface area (143 m 2 g À1 )o ft he proton form (H-PST-9) of ChRbLi-PST-9 determined by N 2 adsorption. Among the 13 topologically distinct T-atoms,o nly two (i.e., sites T3 and T7) of them terminate the external surface of the layers.W e note here that not only the two unit cell dimensions of PST-9 and EU-12 are quite similar to each other, [1,6] but also both structures contain the saw-tooth chains that are combined to form 5-ring layers,which are ultimately connected to form 8ring channels.The saw-tooth chains are only part of the 5-ring layers in the EU-12 structure.H owever, they are located between the two neighboring layers in the PST-9 structure,as well as within its 5-ring layers ( Figure S6). Thus,P ST-9 is structurally rather different from EU-12.…”

“…[6] We were able to obtain this material as its pure form after 2days of heating, although its crystallization prefers the use of two different types of alkali metal cations in the presence of choline used as an organic SDA, that is,the socalled multiple inorganic cation approach. [6] We were able to obtain this material as its pure form after 2days of heating, although its crystallization prefers the use of two different types of alkali metal cations in the presence of choline used as an organic SDA, that is,the socalled multiple inorganic cation approach.…”

“…We first noticed PST-9 as an intermediate phase during EU-12 synthesis under rotation (60 rpm) at 150 8 8Cu sing an aluminosilicate gel with the oxide composition 2.0 ChCl·0.7 Rb 2 O·0.3 Na 2 O·0.25 Al 2 O 3 ·5.0 SiO 2 ·100 H 2 O, where ChCl is choline ((2-hydroxyethyl)trimethylammonium) chloride. [6] We were able to obtain this material as its pure form after 2days of heating, although its crystallization prefers the use of two different types of alkali metal cations in the presence of choline used as an organic SDA, that is,the socalled multiple inorganic cation approach. [6,7] Interestingly, the stability of PST-9 in the crystallization medium was found to differ notably according to the type of secondary alkali metal cations (Table S1 in the Supporting Information).…”

“…[6] We were able to obtain this material as its pure form after 2days of heating, although its crystallization prefers the use of two different types of alkali metal cations in the presence of choline used as an organic SDA, that is,the socalled multiple inorganic cation approach. [6,7] Interestingly, the stability of PST-9 in the crystallization medium was found to differ notably according to the type of secondary alkali metal cations (Table S1 in the Supporting Information). Thus, to minimize impurity effects,t he sample (ChRbLi-PST-9) obtained after 28 days of heating at 150 8 8Cw as used in the structural characterization of PST-9.…”