Direct Dual‐Template Synthesis of MWW Zeolite Monolayers

Abstract

A two dimensional zeolite with the topology of MWW sheets has been obtained by direct synthesis with a combination of two organic structure directing agents. The resultant material is formed in about 70% by single and double layers with a well structured external surface area of about 300 m2·g-1. The delaminated zeolite prepared by means of this single step synthesis route presents not only a high delamination degree, but a well preserved structural integrity of the MWW layers. It presents an excellent activity, selectivity and catalyst life for alkylation of benzene with propylene, being better than catalysts used today for producing cumene.The importance of zeolites as adsorbents and heterogeneous catalysts is well recognized [1]. When used as catalysts, the microporous structure of these crystalline solids confers the reactants a confined environment that, besides pre-activating the molecules, may direct the reaction towards the formation of the desired products by stabilizing the reaction transition states. However, the narrow pore dimensions of most of the zeolites, in the range of 4 to 7 Å, limit their use to processes involving relatively small molecules. Many efforts have been directed to increase the accessibility to the active sites, and to reduce the diffusional problems of bulkier reactants while preserving a degree of confinement. Traditionally, the accessibility to the active sites has been increased by means of post-synthesis methods that combine acid and hydrothermal treatments, such as in ultra-stabilized Y based catalysts for FCC [2] or mordenite based catalysts for hydroisomerization [1,3], or by combining acid and basic treatments [4]. These top-down procedures are effective but enclose several steps and, depending on the conditions employed, may result in crystallinity and micropore volume loss. Addition of soft or hard templates to the synthesis gel has also been described as a possible route to obtain hierarchical zeolites presenting micro and mesoporosity [4b, 5]. Direct synthesis of single layers of ZSM-5 was achieved by using diquaternary ammonium surfactants and tetraalkylphosphonium as directing agents (OSDA) [6]. The use of these type of OSDAs has also allowed the synthesis of other micro-mesoporous zeolites, with structural mesoporosity [7] or intercrystalline mesoporosity due to small crystallite size [8].A different approach for increasing zeolite's accessibility was described in the middle 1990's, and consisted in the delamination of layered zeolite precursors. The concept was proved to be applicable to different structures, and new delaminated zeolites ITQ-2 [9], [10], were prepared starting from MCM-22(P), PRE-FER, NU-6(1), and ITQ-19, respectively [13]. The resultant zeolitic materials showed very high accessible surface areas and interesting catalytic properties for a large number of reactions [14]. The first of those delaminated zeolites described, ITQ-2, is formed by disordered MWW layers in a "house of

High Ethylene Selectivity in Methanol‐to‐Olefin (MTO) Reaction over MOR‐Zeolite Nanosheets

“…The MFI nanosheets exposed large amount of acid sites on the external surface, improving the catalytic conversion of large organic molecules. Using the similar strategy, the Beta, MRE, MTW, MOR, FAU, CHA and MWW zeolites with nanosheet, nanosponge, nanoparticle, or nanorod morphologies were synthesized with two or more quaternary ammonium head group‐containing amphiphilic surfactants.…”

Recent Advances in the Synthesis and Application of Two‐Dimensional Zeolites

“…[ 36 ] Copyright 2012, American Association for the Advancement of Science; e) Reproduced with permission. [ 52 ] Copyright 2015, Wiley-VCH. [ 51 ] Copyright 2015, Royal Society of Chemistry; g) Reproduced with permission.…”

“…[ 50 ] Moreover, MFI nanosheets joining with a 90 o rotational boundary (SCZN-2) was obtained by adopting bolaform-form amphiphilic molecules with diaquaternary ammonium head groups and [ 50 ] These special bifunctional surfactants have strong self-assembly function through the π-π stacking between aromatic group in the hydrophobic tail, which stabilized the mesostructured MFI nanosheets. [ 52 ] The hydrophilic part of the surfactant was assumed to be involved in the cavities of the mww layers, while the hydrophobic chain prevented the H-bond interaction between layers, resulting in layer separation. [ 99 ] Recently, the methodology has been proved to be effective to prepare zeolite nanosheets with other topologies by adopting carefully-designed bifunctional surfactants as OSDA.…”

Single‐Layered Hybrid Materials Based on 1D Associated Metalorganic Nanoribbons for Controlled Release of Pheromones

“…[1][2][3] These layered materials can be modified by the spatial alteration of the individual layers through swelling,intercalation, or exfoliation processes to obtain more accessible solids, [4][5][6] and it is possible to incorporate additional functions during post-synthesis treat-ments. They are based on an ordered nickel cluster-type nanoribbons separated from each other by specific alkyl (heptyl-or dodecyl-)a rylic mono-carboxylate moieties acting as molecular spacers,p erpendicular to the 1D inorganic chains.T hese organic spacers contain hydrocarbon tails with different length which control the separation level between inorganic 1D subunits,i nhibiting the 3D growth of conventional DUT-8-type metal-organic frameworks (MOFs).…”

“…[1][2][3] These layered materials can be modified by the spatial alteration of the individual layers through swelling,intercalation, or exfoliation processes to obtain more accessible solids, [4][5][6] and it is possible to incorporate additional functions during post-synthesis treat-ments. [1][2][3] These layered materials can be modified by the spatial alteration of the individual layers through swelling,intercalation, or exfoliation processes to obtain more accessible solids, [4][5][6] and it is possible to incorporate additional functions during post-synthesis treat-ments.…”