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

Abstract

Zeolite EU-12, the framework structure of whichhas remained unsolved during the past 30 years,i ss ynthesized at as pecific SiO 2 /Al 2 O 3 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 at wo-dimensional 8-ring channel system. Among the two distinct 8-ring (4.6 2.8 and 5.0 2.7 ) channels along caxis,the smaller one interconnects with the sinusoidal 8-ring (4.8 3.3 ) channel along aaxis. The other large one is simply linked up with the sinusoidal channel by sharing 8-rings (4.8 2.6 ) in the ac plane.T he proton form of EU-12 was found to show ac onsiderably higher ethene selectivity in the low-temperature dehydration of ethanol than H-mordenite,t he best catalyst for this reaction.While zeolites and related crystalline materials have awide variety of commercial applications in catalysis,ion exchange, and gas adsorption and separation, their performance is inherently associated with the shape,size,accessibility and/or dimensionality of the crystallographically well-defined cavities and channels.O ver the past several decades,t herefore, extensive efforts have been devoted to the synthesis of zeolites with novel framework topologies using numerous different organic amines and alkylammonium ions as organic structure-directing agents (SDAs). [1] Among the organic SDAs studied thus far,t he choline (Ch + ,(2-hydroxyethyl)trimethylammonium) ion is interesting because it crystallizes ferrierite (framework type FER) nanoneedles and SSZ-13 (CHA), [2] with Na + present, mainly depending on the Na 2 O/SiO 2 ratio in the synthesis mixture. Also,zeolite UZM-22 (MEI) containing 3-rings as part of the structure is the phase formed from the strontium aluminosilicate synthesis mixture containing Ch + . [3] In particular,C h + can direct the synthesis of anew crystalline inorganic-organic material, that is,the framework-bound organic SDA-containing molecular sieve denoted ECR-40C. [4] These results have prompted us to systematically investigate the effects of inorganic gel chemistry on the phase selectivity in this cheap organic SDA-mediated synthesis of zeolites.H ere we report the synthesis of zeolite EU-12 in the mixed Ch + -Na + -Rb + SDAsystem and its structure determined by synchrotron powder X-ray diffraction (XRD) and Rietveld analyses.EU-12 was first reported by Araya and Lowe in 1986, [5] but its structure has remained unknown until now.Wealso show that the proton form of this zeolite is quite selective to ethene formation in the low-temperature dehydration of ethanol. Table 1l ists the representative products obtained using Ch + as an organic SDAf rom aluminosilicate gels with different oxide compositions,w hich were heated under rotation (60 rpm) at 150 8 8Cf or 7days.T hese data reveal that the crystallization of EU-12 is very sensitive to both Al and Rb contents in the synthesis mixture.W hent he Rb 2 O/ (Rb 2 O + Na 2 O) ratio in the synthesis mixture was fixed to 0.7, ...

Small-Pore Zeolites: Synthesis and Catalysis

“…Ethylene can be formed via simple dehydration, e.g. shown with 8MRzeolite ETL at 200°C, 77 but the mechanisms of olefin generation in ETO are more complex as higher olefins are also formed and multiple routes can be at work, e.g., identified in ZSM-5 by Galvita and co-workers. 436 Also, the often considered crucial first C−C bond's formation present in MTO is absent with ETO.…”

“…The most recent example of Method C (OSDA/hydroxide media) is the synthesis of EU-12 by using choline (N,N,N-trimethylethanolammonium), Rb + , and Na + (8MR-zeolite ETL, 2016). 77 Barrer also introduced the use of a zeolite as sole source for making another zeolite, by studying the hydrothermal transformations of analcime in the presence of metal salts (yielding KFI with barium halides for instance). 139 Dwyer and Chu presented the transformation of FAU, still in its growth medium and considered metastable, into a MAZ-zeolite (ZSM-4, or Omega) in the presence of TMA at 100°C.…”