The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Yoshihiro Sugi - One of the best experts on this subject based on the ideXlab platform.
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Shape-Selective Catalysis in the Alkylation of Naphthalene: Steric Interaction with the Nanospace of Zeolites
Journal of nanoscience and nanotechnology, 2015Co-Authors: Yoshihiro Sugi, Ajayan VinuAbstract:Steric interaction of reagents with nanospace of zeolites was studied in alkylation: isopropylation, sec-butylation, and tert-butylation of naphthalene (NP) over several large-pore zeolites to elucidate the mechanism of Shape-Selective Catalysis. Selectivities for β,β- and 2,6-dialkylnaphthalene (DAN) were influenced by the type of zeolite and bulkiness of alkylating agent. Shape-Selective formation of β,β- and 2,6-diisopropylnaphthalene (DIPN) occurred only over H-mordenite (MOR) in the isopropylation of NP. Bulky α,α- and α,β-DIPN are excluded because of steric restriction at their transition states by the MOR channels, resulting in the selective formation of β,β- and 2,6-DIPN. AFI (SSZ-24) gave also high selectivities for 2,6-DIPN, and CFI (CIT-5) and MSE (MCM-68) gave high selectivities for β,β-DIPN. The lower selectivities for 2,6-DIPN were observed over the zeolites, ATS (SSZ-55), LFR (SSZ-42), DON (UTD-1), SFH (SSZ-53), FAU (Y-zeolite), BEA (zeolite β), and CON (CIT-1). Their channels allow the accommodation of bulky isomers, resulting in the Catalysis under kinetic and/or thermodynamic controls. The selectivities for β,β- and 2,6-DAN were enhanced with the increase in bulkiness of alkylating agents: 1-butene for sec-butylation and 2-methylpropene for tert-butylation, even over zeolites with large pores and channels: the transition states of the least bulky isomers only fit the channels, and the other bulky isomers are excluded by steric restriction of the channels. However, tert-butylation over FAU, BEA, and CON had selectivities of around 50-60% for 2,6-DTBN, and almost 100% selectivities for β,β-DTBN. These zeolites cannot recognize the differences between 2,6- and 2,7-DTBN, but they can differentiate β,β-DTBN from the other isomers. The results indicate that the fitting of the least bulky isomers to zeolite channels, resulting in the exclusion of other bulky isomers, is a key for highly Shape-Selective Catalysis.
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Alkylation of Biphenyl over Zeolites: Shape-Selective Catalysis in Zeolite Channels
Catalysis Surveys from Asia, 2015Co-Authors: Yoshihiro Sugi, Ajayan VinuAbstract:Steric interaction of reactants, products, and transition state intermediates with zeolites with 12- and 14-membered ring pore entrances is discussed in the alkylation of biphenyl (BP) by propene, 1-butene, and 2-methylpropene as alkylating agents. The selectivities for the least bulky 4,4′-dialkylbiphenyl (4,4′-DAB) depended on the types of zeolite and alkylating agent. The zeolites are classified as two types: Category I: mordenite (MOR), SSZ-24 (AFI), SSZ-31 (STO), CIT-5 (CFI), MCM-68 (MSE), and ZSM-12 (MTW) with straight (or slightly corrugated) channels with 12-MR or 14-MR pore entrances. Category II: SSZ-42 (IFR), SSZ-55 (ATS), SSZ-60 (SSY), Y (FAU), β (BEA), CIT-1 (CON), UTD-1 (DON), and SSZ-53 (SFH) with large channels. Category I zeolites have Shape-Selective natures in their channels in the isopropylation. Among them, MOR supported the highest selectivities around 85 % for 4,4′-diisopropylbipneyl (4,4′-DIPB) at moderate temperatures as 250 ^oC. The selectivities of 4,4′-DIPB are: MOR > AFI, MSE > MTW, CFI, STO: the differences are due to the recognition of 4,4′- and 3,4′-DIPB by the channels. Category II zeolites allow the accommodation and the formation of bulky DIPB isomers in their channels, resulting in non-shape selective Catalysis under kinetic and/or thermodynamic controls. Bulky alkylating agents, 1-butene and 2-methylpropene, enhance selective formation of the least bulky 4,4′-DAB: 4,4′-di- sec -butylbiphenyl (4,4′-DSSB) and 4,4′-di- tert -butylbiphenyl (4,4′-DTBB), respectively, even over Category II zeolites. The bulky moieties enhance the exclusion of bulky isomers by their interaction with zeolite channels. The selectivities for 4,4′-DSSB were increased remarkably to higher than 80 % for Category I zeolites and to 70 % for ATS in Category II zeolites in the sec -butylation. However, kinetic and thermodynamic controls still worked with the formation of bulky isomers over Category II zeolites: IFR, FAU, BEA, CON, DON, and SFH in the sec -butylation. The high selectivities for 4,4′-DTTB higher than 80 % were observed for the zeolites, except FAU in the tert -butylation. These results indicate that the selectivities for 4,4′-DAB are controlled primarily by space and shape of zeolite channels for active sites, and not always by the size of pore entrances.
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Alkylation of Biphenyl and Naphthalene over Zeolites: Characteristics of Shape-Selective Catalysis in Zeolite Channels
Journal of the Japan Petroleum Institute, 2010Co-Authors: Yoshihiro SugiAbstract:To understand the characteristics of Shape-Selective Catalysis over zeolites, the steric interactions of reactants, products, and transition state intermediates with zeolite channels are discussed in the alkylation of biphenyl (BP) and naphthalene (NP). The selectivities for 4,4'-dialkylbiphenyl (4,4'-DABP) and 2,6-dialkylnaphthalene (2,6-DAN) were varied by using various zeolites and alkylating agents, and determined by the exclusion of bulky isomers by the channels. The results show predominance of the least bulky isomers, 4,4'-DABP and 2,6-DAN, where the structure of zeolite channel and the bulkiness of alkylating agent are the key factors in Shape-Selective Catalysis. Mordenite (MOR) and SSZ-24 (AFI), which have straight channels with 12-membered ring (12-MR) pore entrances, gave high selectivities for 4,4'-diisopropylbiphenyl (4,4'-DIPB) in the isopropylation of BP using propene. However, SSZ-55 (ATS) and SSZ-42 (IFR), which have caged channels with 12-MR pore entrances, gave low the selectivities in the range of 30 to 35%. These results indicate that the channels of MOR and AFI are narrow enough to exclude the transition states of bulky isomers. The isopropylation of BP over ATS and IFR occurs under kinetic and/or thermodynamic controls because their channels are too large for Shape-Selective Catalysis. The bulkiness of the alkylating agent enhanced the selectivities for 4,4'-di-s-butylbiphenyl (4,4'-DSBB) in the s-butylation using 1-butene and 4,4'-di-t-butylbiphenyl (4,4'-DTBB) in the t-butylation using 2-methylpropene. CIT-5 (CFI), UTD-1 (DON), and SSZ-53 (SFH), which have one-dimensional channels with 14-MR pore entrances, and Y (FAU), β (BEA), and CIT-1 (CON), which are three-dimensional channels with 12-MR pore entrances, increased the selectivities for 4,4'-DSBB and 4,4'-DTBB using bulky alkylating agent due to the restrictions on the transition states by their channels.The alkylation of NP was also discussed on the basis of the selectivities for β,β- and 2,6-DAN. Shape-Selective formation of β,β- and 2,6-diisopropylnaphthalene (DIPN) occurred in the isopropylation only over MOR, whereas the other zeolites gave lower selectivities for β,β- and 2,6-DIPN because their channels are too large for the exclusion of the transition states of bulky isomers. The increase in bulkiness of alkylating agent enhanced the formation of β,β-, and 2,6-DAN. However, the selectivities for 2,6-di-t-butylnaphthalene (2,6-DTBN) were around 50 to 60% over FAU, BEA, and CON in the t-butylation, although the selectivities for β,β-DTBN were almost 100%. These results indicate that these zeolites cannot recognize the differences in bulkiness between 2,6- and 2,7-DTBN.These findings in this paper indicate that accommodation of only the least bulky isomers fit with the zeolite channels and resulting exclusion of other bulky isomers, is a key factor for highly Shape-Selective Catalysis, and that steric restriction on the transition states of product isomers by zeolite channels is essential to evaluate for the design of appropriate structures for target reactions.
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The alkylation of naphthalene over three-dimensional large pore zeolites: The influence of zeolite structure and alkylating agent on the selectivity for dialkylnaphthalenes
Catalysis Today, 2008Co-Authors: Yoshihiro Sugi, Kenichi Komura, Hiroyoshi Maekawa, Yukio Hasegawa, Hiroaki Naiki, Yoshihiro KubotaAbstract:Abstract In order to elucidate how zeolite structure and alkylating agent play roles in the Shape-Selective Catalysis, the alkylation, i.e. , isopropylation, sec -butylation, and tert -butylation, of naphthalene (NP) was examined over three-dimensional twelve-membered (12-MR) zeolites, Y (FAU), Beta (BEA), and CIT-1 (CON), and compared to that of H-mordenite (MOR). The β,β-selectivities (for β,β-dialkylnapthalene (β,β-DAN)) and the 2,6-selctivities (for 2,6-dialkylnaphthalene (2,6-DAN)) among DAN isomers varied with the types of zeolites and alkylating agents. FAU, BEA, and CON gave only low selectivities for 2,6-diisopropylnaphthalene (2,6-DIPN) in the isopropylation, and predominant isomers were bulky and thermodynamically unstable α,β-DIPN (1,3-, 1,6-, and 1,7-DIPN) and α,α-DIPN (1,4- and 1,5-DIPN) at lower temperatures, and the formation of the less bulky and thermodynamically stable β,β-DIPN (2,6- and 2,7-DIPN) increased with increasing the temperature: they have quite different features from the Shape-Selective Catalysis over MOR. These results suggest that FAU, BEA, and CON are not Shape-Selective in the isopropylation, and that the isopropylation is principally controlled kinetically at lower temperatures, and thermodynamically at higher temperatures. The β,β-selectivities over FAU, BEA, and CON increased with increasing the bulkiness of alkylating agents, and were almost 100% in the tert -butylation. On the other hand, the 2,6-selectivities over these zeolites were much lower than those over MOR at a typically moderate temperature, 250 °C. These results mean that FAU, BEA, and CON have the Shape-Selective nature to give the less bulky isomers, β,β-DAN, in the sec -butylation and tert -butylation by using bulkier alkylating agents, particularly 2-methyl-2-propene: they can differentiate β,β-DAN from their isomers at the transition states by the steric restriction of zeolite channels. However, the channels of these zeolites are too large for differentiating 2,6- and 2,7-DAN even with 2-methyl-2-propene.
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Pore structure and shape-selectivity in the isopropylation of biphenyl catalyzed by one-dimensional large pore zeolites
Studies in Surface Science and Catalysis, 2004Co-Authors: Yoshihiro Sugi, Hiroyoshi Maekawa, Yoshihiro Kubota, Shogo Tawada, Akira Ito, Ranjeet Kaur Ahedi, Seiji Watanabe, Ikuyo Toyama, C. Asaoka, H.s. LeeAbstract:Abstract Why and where Shape-Selective Catalysis occurs over large pore zeolites are discussed from relationships between pore structure and shape-selectivity in the isopropylation of biphenyl (BP) over zeolites: H-mordenite (HM), ZSM-12, SSZ-31, SSZ-24, and SSZ-42 with one-dimensional twelve membered ring, and UTD-1 and C1T-5 with one-dimensional fourteen membered ring. HM is the best fitted for the Shape-Selective isopropylation of BP to form 4,4'-diisopropylbiphenyl (4,4'-DIPB). However, the selectivity for 4,4'-DIPB was lower for other zeolites. The steric restriction with the pores differentiates the transition states to form DIPB isomers, and the transition state which fits the pore enhances the formation of 4,4'-DIPB.
Jens Weitkamp - One of the best experts on this subject based on the ideXlab platform.
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ruthenium containing small pore zeolites for shape selective Catalysis
Microporous and Mesoporous Materials, 2007Co-Authors: Stefan Altwasser, Roger Glaser, Jens WeitkampAbstract:Abstract Ruthenium-containing small-pore zeolites with the framework types LTA, KFI, MER and RHO were prepared by addition of ruthenium(III) chloride to the gel of the hydrothermal zeolite synthesis in the absence of organic templates. This synthesis strategy was described earlier for the large- and medium-pore zeolites Ru/Na-X (FAU) and Ru/Na-ZSM-5 (MFI), respectively. The majority of the ruthenium species in the modified small-pore zeolites has a diameter in the order of 1 nm or less and is located inside the pores of the frameworks. These species are available for Shape-Selective catalytic conversions as demonstrated by the competitive hydrogenation of 1-hexene and 2,4,4-trimethyl-1-pentene. This test reaction allows to differentiate between ruthenium particles within the zeolite pores and those on the external crystal surface. Consequently, LTA-type zeolites with intrazeolitic ruthenium species could be synthesized with ruthenium loadings of up to 4.0 wt.%. A further increase of the ruthenium content to 8.0 wt.% resulted in a significant fraction of the ruthenium (oxide) clusters on the external crystal surface. Ruthenium species on the outer crystal surface also exist after the hydrothermal zeolite synthesis. These can, however, be removed by ion exchange with an aqueous calcium nitrate solution.
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Zeolites and Catalysis
Solid State Ionics, 2000Co-Authors: Jens WeitkampAbstract:This review covers the fundamentals of zeolite materials science and their application as catalysts. After a brief introduction into their structures, the most important parameters are discussed which allow the preparation of an almost infinite variety of zeolitic materials tailored for a given catalytic application. Zeolites are solid acids, and the chemical nature, the density, strength and location of the acid sites in zeolites are discussed. Shape-Selective Catalysis, which is a unique feature of zeolites, is briefly addressed.
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Shape-Selective Catalysis in Zeolites
Catalysis and Zeolites, 1999Co-Authors: Jens Weitkamp, S. Ernst, H Dauns, Ewald GalleiAbstract:Among the primary tasks of Catalysis is the control of the selectivity in chemical reactions. In heterogeneously catalyzed reactions in zeolites and zeolite-related microporous solids, this can, inter alia, be achieved by exploiting the phenomenon of Shape-Selective Catalysis. In a very simplified manner, Shape-Selective Catalysis can be described as the combination of Catalysis with the molecular sieve effect. Shape selectivity effects can occur, if the sizes and shapes of reactants, of products, of transition states or of reaction intermediates are similar to the dimensions of the pores and cavities of the zeolite.
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Zeolite Zsm-57: Synthesis, Characterization and Shape Selective Properties
Studies in Surface Science and Catalysis, 1991Co-Authors: S. Ernst, Jens WeitkampAbstract:Summary Zeolite ZSM-57 can be synthesized from sodium-containing alumosilicate gels using hexaethyl-C5-diquat as organic template and silica sol as silica source. ZSM-57 can be readily distinguished from the structurally closely related zeolites with the FER framework topology by its X-ray powder pattern and mid-infrared spectrum. From thermogravimetric analysis of as-synthesized ZSM-57 it follows that applying an air calcination at 550°C for several hours is sufficient to remove the organic template from the pores of the zeolite. The results of two selected test reactions for probing the effective pore width of zeolites, viz. ethylbenzene disproportionation and n-decane isomerization suggest that the pore width is larger for ZSM-57 as compared to ZSM-35 (ferrierite) and ZSM-5. This is in agreement with their crystallographic structures and offers new opportunities in shape selective Catalysis and molecular sieve separation.
Yoshihiro Kubota - One of the best experts on this subject based on the ideXlab platform.
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The alkylation of naphthalene over three-dimensional large pore zeolites: The influence of zeolite structure and alkylating agent on the selectivity for dialkylnaphthalenes
Catalysis Today, 2008Co-Authors: Yoshihiro Sugi, Kenichi Komura, Hiroyoshi Maekawa, Yukio Hasegawa, Hiroaki Naiki, Yoshihiro KubotaAbstract:Abstract In order to elucidate how zeolite structure and alkylating agent play roles in the Shape-Selective Catalysis, the alkylation, i.e. , isopropylation, sec -butylation, and tert -butylation, of naphthalene (NP) was examined over three-dimensional twelve-membered (12-MR) zeolites, Y (FAU), Beta (BEA), and CIT-1 (CON), and compared to that of H-mordenite (MOR). The β,β-selectivities (for β,β-dialkylnapthalene (β,β-DAN)) and the 2,6-selctivities (for 2,6-dialkylnaphthalene (2,6-DAN)) among DAN isomers varied with the types of zeolites and alkylating agents. FAU, BEA, and CON gave only low selectivities for 2,6-diisopropylnaphthalene (2,6-DIPN) in the isopropylation, and predominant isomers were bulky and thermodynamically unstable α,β-DIPN (1,3-, 1,6-, and 1,7-DIPN) and α,α-DIPN (1,4- and 1,5-DIPN) at lower temperatures, and the formation of the less bulky and thermodynamically stable β,β-DIPN (2,6- and 2,7-DIPN) increased with increasing the temperature: they have quite different features from the Shape-Selective Catalysis over MOR. These results suggest that FAU, BEA, and CON are not Shape-Selective in the isopropylation, and that the isopropylation is principally controlled kinetically at lower temperatures, and thermodynamically at higher temperatures. The β,β-selectivities over FAU, BEA, and CON increased with increasing the bulkiness of alkylating agents, and were almost 100% in the tert -butylation. On the other hand, the 2,6-selectivities over these zeolites were much lower than those over MOR at a typically moderate temperature, 250 °C. These results mean that FAU, BEA, and CON have the Shape-Selective nature to give the less bulky isomers, β,β-DAN, in the sec -butylation and tert -butylation by using bulkier alkylating agents, particularly 2-methyl-2-propene: they can differentiate β,β-DAN from their isomers at the transition states by the steric restriction of zeolite channels. However, the channels of these zeolites are too large for differentiating 2,6- and 2,7-DAN even with 2-methyl-2-propene.
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Pore structure and shape-selectivity in the isopropylation of biphenyl catalyzed by one-dimensional large pore zeolites
Studies in Surface Science and Catalysis, 2004Co-Authors: Yoshihiro Sugi, Hiroyoshi Maekawa, Yoshihiro Kubota, Shogo Tawada, Akira Ito, Ranjeet Kaur Ahedi, Seiji Watanabe, Ikuyo Toyama, C. Asaoka, H.s. LeeAbstract:Abstract Why and where Shape-Selective Catalysis occurs over large pore zeolites are discussed from relationships between pore structure and shape-selectivity in the isopropylation of biphenyl (BP) over zeolites: H-mordenite (HM), ZSM-12, SSZ-31, SSZ-24, and SSZ-42 with one-dimensional twelve membered ring, and UTD-1 and C1T-5 with one-dimensional fourteen membered ring. HM is the best fitted for the Shape-Selective isopropylation of BP to form 4,4'-diisopropylbiphenyl (4,4'-DIPB). However, the selectivity for 4,4'-DIPB was lower for other zeolites. The steric restriction with the pores differentiates the transition states to form DIPB isomers, and the transition state which fits the pore enhances the formation of 4,4'-DIPB.
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Zeolite Catalyzed Alkylation of Biphenyl. Where Does Shape-Selective Catalysis Occur?
Catalysis Surveys from Japan, 2001Co-Authors: Yoshihiro Sugi, Yoshihiro Kubota, Taka-aki Hanaoka, Takehiko MatsuzakiAbstract:Liquid-phase alkylation of biphenyl (BP) was studied over large-pore zeolites. Selective formation of the least bulky products, 4,4′-diisopropylbiphenyl (4,4′-DIPB) occurred only in the isopropylation of BP over one- or two-dimensional zeolites, H-mordenite (HM), ZSM-12, SSZ-24, SAPO-5, SSZ-31, and CIT-5. These Shape-Selective catalyses are ascribed to steric restriction of transition state and to easiness of the substrates to enter into the pores. HM gave the highest selectivity among them. The dealumination of HM enhanced catalytic activity and the selectivity for 4,4′-DIPB because of the decrease of coke deposition. Non-regioselective Catalysis occurs on external acid sites over HM with the low SiO_2/Al_2O_3 ratio because severe coke deposition deactivates the acid sites inside the pores by blocking pore openings. The selectivity of DIPB isomers was changed with propylene pressure and/or with reaction temperature. Selective formation of 4,4′-DIPB was observed at moderate temperatures such as 250 °C, whereas the decrease of the selectivity of 4,4′-DIPB occurred at higher temperatures as 300 °C. 4,4′-DIPB yielded selectively under high propylene pressure (
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28-P-09-Nature of Shape-Selective Catalysis in the ethylation and the isopropylation of biphenyl over H-mordenites
Studies in Surface Science and Catalysis, 2001Co-Authors: Y. Sugi, Yoshihiro Kubota, Shogo Tawada, T. Sugimura, Y. Imada, Toshiaki Hanaoka, T. MatsuzakiAbstract:Publisher Summary This chapter discusses the nature of Shape-Selective Catalysis in the ethylation and the isopropylation of biphenyl over H-mordenites. 4-isopropylbiphenyl (4-IPBP) is consumed much faster than 3-IPBP in their competitive isopropylation. Selectivity for 4,4′-diisopropylbiphenyl (4,4′-DIPB) in bulk products decreased with the increase of 3-IPBP, however, the selectivity in encapsulated products kept constant. 4-ethylbiphenyl (4-EBP) disappeared much faster than 3-EBP in their competitive ethylation. Selectivity for 4,4′-diethylboiphenyl (4,4'-DEBP) is less than 2%, whereas total selectivity for DEBPs with 4-ethyl group was higher than 65% in both products. DEBPs are predominantly produced from 4-EBP.
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Shape-Selective isopropylation of biphenyl over H-mordenites: Relationships of bulk products and encapsulated products in the pores
Applied Catalysis A: General, 1999Co-Authors: Yoshihiro Sugi, Yoshihiro Kubota, Shogo Tawada, T. Sugimura, Toshiaki Hanaoka, T. Matsuzaki, K. Nakajima, Kimio KunimoriAbstract:Abstract Shape-Selective formation of 4,4′-diisopropylbiphenyl (4,4′-DIPB) was observed in the isopropylation of biphenyl (BP) over H-mordenite (HM). Shape-selectivity was governed by spatial restriction in transition states in the microporous environment of HM. The selectivity for 4,4′-DIPB was influenced by many factors such as the SiO2/Al2O3 ratio, reaction temperature, and propylene pressure. On the other hand, high selectivities for 4,4′-DIPB were observed in encapsulated products under all of our conditions because of Shape-Selective Catalysis in the HM pores. However, the decrease in the selectivity for 4,4′-DIPB occurred with the decrease in the SiO2/Al2O3 ratio and with change in the reaction conditions, such as increase in temperature and decrease in propylene pressure. The discrepancies in bulk products and in encapsulated products in the HM pores are discussed to understand where and why Shape-Selective Catalysis occurs. The decrease in the selectivity for 4,4′-DIPB over HM with a low SiO2/Al2O3 ratio is due to non-regioselective reactions because of choking of the pore entrance by coke-deposition. The decrease in the selectivity for 4,4′-DIPB under high reaction temperatures, or under low propylene pressures was ascribed to the isomerization of 4,4′-DIPB at external acid sites. These conclusions are also supported by discrepancies of bulk and encapsulated products in the isomerization of 4,4′-DIPB under high the corresponding conditions. No significant isopropylation of 4,4′-DIPB to triisopropylbiphenyls (TrIPB) was observed even under high propylene pressure or at high reaction temperatures. This is presumably due to there not being enough space in the pores for the transition state of further isopropylation of 4,4′-DIPB, and it is one of the reasons for the Shape-Selective formation of 4,4′-DIPB.
Mark E. Davis - One of the best experts on this subject based on the ideXlab platform.
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Beyond shape selective Catalysis with zeolites: Hydrophobic void spaces in zeolites enable Catalysis in liquid water
AIChE Journal, 2013Co-Authors: Rajamani Gounder, Mark E. DavisAbstract:Zeolites confine active sites within void spaces of molecular dimension. The size and shape of these voids can be tuned by changing framework topology, which can influence catalytic reactivity and selectivity via coupled reaction-transport phenomena that exploit differences in transport properties among reactants and/or products that differ in size and shape. The polarity and solvating properties of intrazeolite void environments can be tuned by changing chemical composition and structure, ranging from hydrophobic defect-free pure-silica surfaces to silica surfaces containing hydrophilic defect sites and/or heteroatoms. Here, we discuss how the polarity of zeolite voids influences catalytic reactivity and selectivity via the partitioning of reactant, product, and solvent molecules between intrazeolitic locations and external fluid phases. These findings provide a conceptual basis for developing selective catalytic processes in aqueous media using hydrophobic zeolites that are able to adsorb organic reactants while excluding liquid water from internal void spaces.
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Shape-Selective Catalysis with Zeolites and Molecular Sieves
ChemInform, 2010Co-Authors: Charles B. Khouw, Mark E. DavisAbstract:The types of shape selective Catalysis that occur in zeolites and molecular sieves are reviewed. Specifically, primary and secondary acid catalyzed shape selectivity and encapsulated metal ion and zero valent metal particle catalyzed shape selectivity are discussed. Future trends in shape selective Catalysis, such as the use of large pore zeolites and electro- and photo-chemically driven reactions, are outlined. Finally, the possibility of using zeolites as chiral shape selective catalysts is discussed.
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Organic-functionalized molecular sieves. III. Shape selective Catalysis
Microporous and Mesoporous Materials, 2001Co-Authors: Christopher W. Jones, Michael Tsapatsis, Tatsuya Okubo, Mark E. DavisAbstract:Abstract Several organic-functionalized molecular sieves (OFMSs) are investigated for use as Shape-Selective catalysts. OFMSs with the ∗ BEA topology containing ethylcyclohexenyl, phenethyl and mercaptopropyl functional groups are synthesized and characterized by X-ray diffraction, FT-Raman spectroscopy, solid-state 13C NMR spectroscopy, thermogravimetric analysis, nitrogen physisorption, scanning electron microscopy, energy dispersive spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. Acidic OFMSs derived from phenethyl and mercaptopropyl containing OFMSs are used in catalytic tests. Sulfonated phenethyl-containing OFMSs can exhibit poor shape selectivity in discriminating between cyclohexanone and 1-pyrenecarboxaldehyde reactions with ethylene glycol at low temperatures in the liquid phase. This poor selectivity is shown to be due to the introduction of silanol-bound sulfonic acid species on the external surface by sulfonation of extracted phenethyl-functionalized beta samples. Sulfonic acid containing OFMSs derived from the oxidation of mercaptopropyl groups are very selective for the conversion of cyclohexanone relative to 1-pyrenecarboxaldehyde, with an initial rate ratio (RHEX/RPYC) that can exceed 200. The rate of reaction over this Shape-Selective catalyst is significantly slower than over commercial zeolite beta, organic-functionalized mesoporous materials, and homogeneous acids.
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Design for sieving
Nature, 1996Co-Authors: Mark E. DavisAbstract:ZEOLITES and zeolite-like molecular sieves are fascinating materials from both an intellectual and a practical standpoint. Their elegant crystal structures have voids with precise and uniform sizes, in the range of about 0.4-1.5 nn, which can be used for molecular sieving (that is, to discriminate between molecules of similar size). Zeolites are used as Shape-Selective Catalysis they can encourage reactions that favour one particular product over another even when the difference in size between the two species is as little as 0.03 nm, as is the case for p-xylene and o-xylene. Further, zeolites are environmentally benign solids. So their use as catalysts continues to burgeon.
Zhongmin Liu - One of the best experts on this subject based on the ideXlab platform.
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Catalysts and shape selective Catalysis in the methanol-to-olefin (MTO) reaction
Journal of Catalysis, 2021Co-Authors: Jiawei Zhong, Jingfeng Han, Yingxu Wei, Zhongmin LiuAbstract:Abstract Recent advances in the shape selectivity of zeolites and molecular sieve catalysts for the methanol-to-olefins (MTO) reaction are elaborated in this minireview. The concept and classification of shape selectivity are briefly introduced and summarized. The effect of cavity structure of cavity-type zeolites and molecular sieves are comprehensively discussed, with focus on the formation of hydrocarbon pool intermediates, reaction route, diffusion, product selectivity, as well as deactivation in the chemical environment of cavity-type molecular sieves. Furthermore, the impact of topology of zeolites and molecular sieves on reaction route and product selectivity are elucidated, with special attention on the shape selectivity of 1-dimensional 10-membered ring zeolites. The debate regarding the impact of coke formation on product selectivity over SAPO-34 is also discussed in detail. Moreover, the progress of modification strategies including metal cations incorporation and pre-coking process for improving shape selectivity have been summarized. The perspective of shape selective Catalysis in future is outlined and predicted.
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Simultaneous Evaluation of Reaction and Diffusionover Molecular Sieves for Shape-Selective Catalysis
ACS Catalysis, 2020Co-Authors: Jingfeng Han, Zhiqiang Liu, Jiawei Zhong, Wenna Zhang, Jindou Huang, Anmin Zheng, Yingxu Wei, Zhongmin LiuAbstract:Shape selectivity is the critical issue of molecular sieve Catalysis. As an important aspect of Shape-Selective Catalysis, the significance of diffusion in conversion, deactivation, and product selectivity over molecular sieve catalysts has been recognized but still has not been interpreted quantitatively and explicitly. In the present work, direct tracking molecular diffusion in the SAPO-34 catalyst during the methanol-to-olefins (MTO) reaction is successfully realized by combining the MTO reaction with the diffusivity evaluation by a pseudo-gas chromatography method which was operated in one catalyst bed under the real reaction condition. Diffusion behavior over the working catalyst can be measured along with the reaction to reflect the evolution in shape-selectivity Catalysis in real time. For the first time, the accessibility of the catalyst microporous surface for the reactant was quantified during the reaction, which provided a rational understanding of the reaction and deactivation of MTO over the catalyst with continuous coke deposition. The evaluation of configurational diffusion hindrance in SAPO-34, because of the accumulation of organic species retained in the catalyst, corresponds well to the evolution of methanol conversion and product distribution and provides the scientific basis for manipulating the MTO reaction from the point of Shape-Selective Catalysis.
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Cavity-controlled diffusion in 8-membered ring molecular sieve catalysts for shape selective strategy
Journal of Catalysis, 2019Co-Authors: Shushu Gao, Zhiqiang Liu, Anmin Zheng, Yingxu Wei, Xiaoshuai Yuan, Zhongmin LiuAbstract:Abstract Shape selectivity is the most important feature and advantage of molecular sieve Catalysis. Diffusion of reactant and product molecules inside the confined environments with channels and cavities is the essential aspect of shape selective Catalysis of molecular sieve catalysts. Elucidating the diffusion mechanism of molecules in the confined space of catalysts is of great importance for the efficient utilization of the porous materials in the catalytic reaction as well as the strategy proposal of reaction control in Shape-Selective Catalysis. However, it is still a great challenge to understand and quantify the diffusion behavior at the molecular level for the establishment of the diffusion mechanism within the crystal of microporous materials as so far. In this work, with advanced pulsed field gradient (PFG) NMR technique, self-diffusion coefficients of alkanes (methane, ethane and propane) in three cavity-type molecular sieves (LEV, CHA and RHO) with very close eight-membered ring (8-MR) windows were determined. Furthermore, molecular dynamics (MD) simulations predicted the energy barrier for crossing 8-MR to be overcome. Based on MD simulations and a continuous-time random-walk (CTRW) method, not only the diffusion trajectory of the molecule can be visually displayed, but also the diffusion behavior is quantitatively described as the inter-cavity hopping process with the success extraction of the jump frequency (f) and jump length (L). The substantial role played by cavity structure and dimension in diffusion within cavity-type molecular sieves with the close 8-MR windows were revealed in depth, which would help to reveal the mechanism of cavity-controlled diffusion and propose the Shape-Selective strategy in the methanol-to-olefins process.