Synthesis and Catalytic Behavior of Ferrierite Zeolite Nanoneedles Yoorim Lee, †,§ Min Bum Park, †,§ Pyung Soon Kim, † Aure ́ lie Vicente, ‡ Christian Fernandez, ‡ In-Sik Nam, † and Suk Bong Hong †, * † Department of Chemical Engineering and School of Environmental Science and Engineering, POSTECH, Pohang 790-784, Korea ‡ Laboratoire Catalyse et Spectrochimie, ENSICAEN, Universite ́ de CAEN, CNRS, 6 Boulevard Maré chal Juin, 14050 CAEN, France * S Supporting Information ABSTRACT: The proton form of nanosized, needlelike ferrierite zeolite, which was synthesized using choline and Na + cations as structure-directing agents, was found to be much more efficient for the skeletal isomerization of 1-butene to isobutene than the corresponding cation form of conven- tional, submicrometric ferrierite with a platelike shape, mainly because of the considerably lower density of strong acid sites, but as well as a result of the higher density of 10-ring pore mouths. KEYWORDS: ferrierite zeolite nanoneedles, synthesis, characterization, catalytic properties Z eolites are crystalline, microporous aluminosilicates whose applications as catalysts have led to an innovative shift in the petroleum and petrochemical industries due to the extreme uniformity in size and shape of their channels and cavities that enables shape-selective catalysis. 1,2 However, microporosity often brings about severe intracrystalline diffusion limitations, lowering the accessibility and molecular transport of reactive molecules to/from the active sites confined. 3 One way to solve this problem is to shorten the diffusion path length in zeolite micropores. Over the past decade, in fact, much attention has been devoted to the reduction of zeolite crystal size from the micrometric to the nanometric range. Consequently, more than 10 different structure types of nanocrystalline zeolites and phosphate-based molecular sieves have been successfully synthesized. 4-6 Ferrierite (framework type FER) is a medium-pore, high- silica zeolite that contains a two-dimensional (2D) pore system consisting of 10-ring (4.2 × 5.4 Å) channels intersected by 8- ring (3.5 × 4.8 Å) channels. 7 This zeolite is well-known for the exceptional selectivity in the skeletal isomerization of n-butenes to isobutene. 8-12 Although ferrierite is a rare natural zeolite, it can also be synthesized using a variety of different organic structure-directing agents (SDAs) in the laboratory. 13 However, there is little known on the synthesis of nanosized ferrierite crystals. Here, we describe the synthesis of ferrierite nano- needles with a Si/Al ratio of 9.9 using choline (Ch + , (2- hydroxyethyl)trimethylammonium), one of the cheapest alkylammonium ions, and Na + as SDAs. We also report that the proton form (H-ferrierite) of this nanometric zeolite phase is much more selective and recyclable for the skeletal isomerization of 1-butene to isobutene than that of conven- tional, submicrometric ferrierite with a similar Si/Al ratio (8.9) but a different platelike crystal morphology. Our interest in Ch + as an organic SDA began with the elegant work by Lewis and co-workers on the charge density mismatch synthesis of the large-pore zeolites UZM-4 (BPH) and UZM-22 (MEI) in the presence of this small organic cation together with Li + , Sr 2+ , or both. 14 Tetramethylammonium (TMA + ) and tetraethylammonium (TEA + ) ions, the two most studied organic SDAs in the synthesis of zeolites and molecular sieves, are slightly smaller and larger than Ch + , respectively. Until now, at least 26 zeolitic materials with different framework topologies have been synthesized using one of TMA + and TEA + , with or without inorganic cations present. 13 However, they include neither UZM-4 nor UZM-22, implying that Ch + , although flexible due to its 2-hydroxyethyl chain, could be very selective for a particular zeolite structure once the right synthesis conditions are found. This stimulated us to investigate the influence of inorganic synthesis variables on the phase selectivity of the crystallization under the optimized conditions (ChOH/Si = 0.8 and Si/Al = 5) for UZM-4 formation. 14 As shown in Table 1, we were able to crystallize four different zeolitic phases, depending on the Al content of the synthesis mixtures and the concentration or type (or both) of alkali metal ions employed as a crystallization SDA. When the crystallization was carried out under rotation (60 rpm) at 150 °C for 14 days, for example, ZSM-34, an intergrowth of offretite (OFF) and erionite (ERI), 15 was the product formed from a sodium aluminosilicate solution with Na/Si = 0.2 and Si/Al = 5. In addition, an increase in the Si/Al ratio of this synthesis solution to 20 resulted in the crystallization of ferrierite. When decreasing its Na/Si ratio to Received: January 11, 2013 Revised: February 26, 2013 Published: February 27, 2013 Letter pubs.acs.org/acscatalysis © 2013 American Chemical Society 617 dx.doi.org/10.1021/cs400025s | ACS Catal. 2013, 3, 617-621