A synthetic, fault-free gmelinite (GME) zeolite is prepared using a specific organic structure-directing agent (OSDA); cis-3,5-dimethylpiperidinium. The cis-isomers align in the main 12-membered ring (MR) channel of GME. Trans-isomer OSDA leads to the smallpore zeolite SSZ-39 with the OSDA in its cages. Data from N2-physisorption and rotation electron diffraction provide evidence for the openness of the 12 MR channel in the GME 12x8x8 pore architecture and the absence of stacking faults, respectively. CIT-9 is hydrothermally stable when K + -exchanged, while in the absence of exchange, the material transforms into an aluminous AFI-zeolite. The process of this phase-change was followed by in-situ variable temperature powder X-ray diffraction. CIT-9 has the highest Si/Al ratio reported for GME, and along with its good porosity, opens the possibility of using GME in a variety of applications including catalysis.Zeolites and other microporous molecular sieves continue to find new uses in catalysis, sorption and specialty applications. [1] Besides their dominant presence in petrochemistry, [2] their potential in the conversion of renewables [3] or gas is huge, [4] and often a single framework excels at a specific task. Although new structures are being reported frequently, for some long-known topologies, no effective synthesis recipe has been reported yet. Natural occurring gmelinite, as well synthetic aluminosilicates with the GME topology, nearly always display stacking faults (CHA intergrowths) blocking the main channel and thus limiting porosity. The search for fault-free, synthetic GME has been going on for 40 years because the framework is a 3-dimensional 12x8x8 channel system with promise for relevant hydrocarbon chemistries, e.g. hexane isomerization and molecular traffic control (compare to LTL). [1b] Using a cationic dabco-polymer as OSDA, Mobil presented a new route to synthetic GME in 1978. [5] Later, Chiyoda and Davis reported a hydrothermal interzeolite conversion route from zeolite Y (induced by Sr 2+ ), and benchmarked faulting via electron diffraction and sorption, against both dabco-GME and gmelinite. [6] All materials showed faulting to some extent, even dabco-GME, that showed a micropore volume (N2-adsorption) there of only 0.055 cm 3 .g -1 . [6] We here present a convenient new method, based on a straightforward OSDA, i.e., cis-3,5-dimethylpiperidinium hydroxide, that produces fault-free GME zeolites, denoted CIT-9, with high porosity of over 0.17 cm 3 .g -1 .Moreover, a fair comparison with dabco-GME (0.12 cm 3 .g -1 ) made in our hands, and Sr-GME confirms the absence of faulting in CIT-9 while some disorder is present in all other known GME zeolites. Earlier, we reported the role of geometric cis/trans-isomerism of dimethylpiperidinium-derived OSDAs in the synthesis of zeolite SSZ-39, a useful small-pore zeolite (AEI) with large cages. [7] It was shown that cis-and different mixtures of cis/trans-3,5-dimethylpiperidinium and even cis-2,6 could direct toward SSZ-39. [7][8] In th...
