Energetics of the Local Environment of Structure-Directing Agents Influence Zeolite Synthesis
TL;DR: In the synthesis of zeolites like SSZ-13 (CHA structure), organic structure-directing agents (SDAs) play a crucial role in the synthesis as discussed by the authors.
Abstract: Organic structure-directing agents (SDAs) play a crucial role in the synthesis of zeolites like SSZ-13 (CHA structure), with novel frameworks and compositions. Zeolite crystallization is aided by t...
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TL;DR: In this paper, the role of Al during parent dissolution, and all consecutive stages of crystallization, are discussed by revising a vast body of literature, which is possible to elucidate some generic features and to propose some synthetic guidelines for making advantageous catalytic zeolites.
Abstract: Interzeolite conversion, a synthesis technique for several zeolite frameworks, has recently yielded a large amount of high-performing catalytic zeolites. Yet, the mechanisms behind the success of interzeolite conversion remain unknown. Conventionally, small oligomers with structural similarity between the parent and daughter zeolites have been proposed, despite the fact these have never been observed experimentally. Moreover, recent synthesis examples contradict the theory that structural similarity between the parent and daughter zeolites enhances interzeolite conversion. In this perspective it is proposed that heteroatoms, such as aluminium, are key players in the processes that determine the successful conversion of the parent zeolite. The role of Al during parent dissolution, and all consecutive stages of crystallization, are discussed by revising a vast body of literature. By better understanding the role of Al during interzeolite conversions, it is possible to elucidate some generic features and to propose some synthetic guidelines for making advantageous catalytic zeolites. The latter analysis was also expanded to the interconversion of zeotype materials where heteroatoms such as tin are present.
14 citations
TL;DR: A generalized mathematical structure for GEP centred on techno-economic criteria is put forth which duly addresses uncertainties associated with RES and correspondingly proposes a plan for addition of RES and storage units.
9 citations
TL;DR: In this paper, the roles of different structure-directing agents (SDAs) in selective substitution of MCM-49 zeolite are investigated comprehensively by multinuclear solid-state NMR.
Abstract: Organic and inorganic structure-directing agents (SDAs) impact Al distributions in zeolite, but the insights into how SDAs manipulate Al distribution have not been elucidated yet. Herein, the roles of different SDAs such as cyclohexylamine (CHA), hexamethylenimine (HMI), and Na+ in selective Al substitution of MCM-49 zeolite are investigated comprehensively by multinuclear solid-state NMR. The results demonstrate that MCM-49 synthesized with HMI shows relatively more T6 and T7 Al, while more T2 Al is observed using CHA. The formation of T2 Al in both MCM-49(HMI) and MCM-49(CHA) is derived from Na+, while protonated HMIs show bias in incorporation of T6 and T7 Al. Most HMIs are occluded in protonated status, and about half of CHAs are occluded in nonprotonated status. The close spatial proximity between nonprotonated CHAs and Na+ synergistically promotes the formation of zeolite structure, leading to more Na+ ions occluded in the zeolite channel with preferential T2 Al substitution.
9 citations
TL;DR: In this paper, the authors acknowledge the financial support from the Technology Mission Division (Department of Science and Technology, Government of India) under the Materials for Energy Storage (MES-2018) program (DST/TMD/MES/2K18/207).
Abstract: The authors acknowledge the financial support from the Technology Mission Division (Department of Science and Technology, Government of India) under the Materials for Energy Storage (MES-2018) program (DST/TMD/MES/2K18/207). S.S. and P.K.J. thank the Ministry of Human Resource Development (MHRD) for financial support. P.K.J. thanks Prof. M. Shrivastava and Prof. S. G. Gopalakrishnan for computational resources and scientific discussions, respectively. H.N.A. is grateful to the King Abdullah University of Science and Technology (KAUST) for partial financial support. A.N. and K.J. sincerely acknowledge financial support from the U.S. Department of Energy, Office of Basic Energy Sciences, Grant DE-FG02-03ER46053.
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TL;DR: In this paper, a new picture of water as consisting of flickering clusters of hydrogen-bonded molecules is presented, in which the cooperative nature of cluster formation and relaxation is related to the partially covalent character which is postulated for the hydrogen bond.
Abstract: : In addition to the direct action of the ionic charge on water as a dielectric medium, ions may exert an influence on the equilibrium between the ice-like and non-ice-like forms which are present in room-temperature water. This provides a way of accounting for experimental results in a variety of areas, including entropy, heat capacity, temperature of maximum density, tracer selfdiffusion, thermal conductivity, and dielectric relaxation, as well as viscosity and ionic mobility and their temperature coefficients. The tetrabutyl ammonium cation acts as a structure-promoter in the same way as do non-polar solutes, amino acids and fatty acid anions. These various effects seem explicable in a straightforward manner in terms of a new picture of water as consisting of flickering clusters of hydrogen-bonded molecules, in which the cooperative nature of cluster formation and relaxation is related to the partially covalent character which is postulated for the hydrogen bond. (Author)
1,577 citations
TL;DR: In this paper, a generalized process of solvation is defined, and it is argued that the thermodynamics of this solvation process is more informative as compared with other processes suggested before, and numerical examples are presented and compared with some recently published related data.
Abstract: A generalized process of solvation is defined. It is argued that the thermodynamics of this solvation process is more informative as compared with other processes suggested before. Numerical examples are presented and compared with some recently published related data.
915 citations
TL;DR: This review first focuses on the relevant synthesis details of all 8MR zeolites and provides some generalized findings and related insights, and catalytic applications where 8MRZeolites either have been commercialized or have dominated investigations are presented, with the aim of providing structure-activity relationships.
Abstract: In the past decade or so, small-pore zeolites have received greater attention than large- and medium-pore molecular sieves that have historically dominated the literature. This is primarily due to the commercialization of two major catalytic processes, NOx exhaust removal and methanol conversion to light olefins, that take advantage of the properties of these materials with smaller apertures. Small-pore zeolites possess pores that are constructed of eight tetrahedral atoms (Si4+ and Al3+), each time linked by a shared oxygen These eight-member ring pores (8MR) provide small molecules access to the intracrystalline void space, e.g., to NOx during car exhaust cleaning (NOx removal) or to methanol en route to its conversion into light olefins, while restricting larger molecule entrance and departure that is critical to overall catalyst performance. In total, there are forty-four structurally different small-pore zeolites. Forty-one of these zeolites can be synthesized, and the first synthetic zeolite (KFI, 1...
452 citations
TL;DR: The role of tetrapropylammonium (TPA) as a structure-directing agent in the sodium-free synthesis of pure-silica ZSM-5 was investigated by solid-state Si CP MAS NMR as discussed by the authors.
Abstract: The role of tetrapropylammonium (TPA) as a structure-directing agent in the sodium-free synthesis of pure-silica ZSM-5 (Si-ZSM-5) is investigated by solid-state ^1H-^(29)Si CP MAS NMR. It has previously been proposed that the mechanism of structure direction in a sodium-containing system involves preorganization of silicate species around the TPA ions with subsequent assembly of these inorganic-organic composite structures to yield crystalline Si-ZSM-5 with occluded TPA molecules.l ^1H-^(29)Si CP MAS NMR results indicate that short-range intermolecular interactions, i.e., on the order of van der Waals contact distances, are established during heating of the zeolite synthesis gel prior to the development of long-range order indicative of the ZSM-5 structure. These interactions are independent of the presence of sodium in the gel or the silica source used. An attempt to isolate the composite species by trimethylsilylation of the synthesis mixture was partially successful. These results provide additional evidence for the existence of preorganized, inorganic-organic composite structures during the synthesis of Si-ZSM-5. A modified mechanism of structure direction and crystal growth of Si-ZSM-5 is proposed.
277 citations