Microstructure of Cesium Hydrogen Salts of 12-Tungstophosphoric Acid Relevant to Novel Acid Catalysis

Okuhara, Toshio; Watanabe, Hiromu; Nishimura, Tōru; Inumaru, Kei; Misono, Makoto

doi:10.1021/cm9907561

Cited by 268 publications

(159 citation statements)

References 47 publications

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“…3c) is similar to that of Cs 3 -PW12, clearly indicating that the heteropoly anion in Cs 4 -PW11(Sn-n-Bu) (Fig. 5a) was assigned to a body-centered cubic (bcc) structure [26]. The XRD pattern for Cs 4 -SiW12, which has a bcc structure [31] (Fig.…”

Section: Structures Of Keggin-poms In Solution and Of Their Cs Saltsmentioning

confidence: 62%

Microporous cesium salts of tetravalent Keggin-type polyoxotungstates Cs4[SiW12O40], Cs4[PW11O39(Sn-n-C4H9)], and Cs4[PW11O39(Sn-OH)] and their adsorption properties

Miura

Imai

Yokoi

et al. 2013

Microporous and Mesoporous Materials

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ABSTRACTwere synthesized. The crystalline structures, which had body-centered cubic (bcc) arrangements, the lattice constants, and the pore-size distributions of the three Cs salts were similar, regardless of the presence or absence and types of functional groups introduced. The Cs salts had only micropores and no mesopores. The micropore size distributions were determined from adsorption isotherms of Ar, which showed a sharp peak at 0.59 nm and a shoulder at 0.62 nm. The fractions of the external surface areas to the total surface areas of the Cs salts were less than 6%. It is plausible that the micropores originate from the heteropoly anion defects in the crystallite, which form to avoid mismatches in the Cs + /(heteropoly anion) ratio required for charge balance (= 4) and for a bcc structure (= 3). The surface of the Cs salt introduced with n-butyl groups was hydrophobic, although the surface density of the n-butyl groups was low. On the other hand, the hydroxyl groups present on the surface of Cs 4 [PW 11 O 39 (Sn-OH)] had little effect on the adsorption of water, methanol, ethanol, and hexane but a great impact on that for benzene due to the interactions between the -OH groups and the aromatic rings (-OH···π).3

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Section: Structures Of Keggin-poms In Solution and Of Their Cs Saltsmentioning

confidence: 62%

Microporous cesium salts of tetravalent Keggin-type polyoxotungstates Cs4[SiW12O40], Cs4[PW11O39(Sn-n-C4H9)], and Cs4[PW11O39(Sn-OH)] and their adsorption properties

Miura

Imai

Yokoi

et al. 2013

Microporous and Mesoporous Materials

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“…However, successful stereoselective catalyses by the POM-based compounds have scarcely been reported [156,[174][175][176][177][178]. Various kinds of POMs have controlled the pores between particles (crystallites) [179][180][181][182][183][184][185][186][187], in their crystal lattices [188][189][190][191][192][193][194][195][196], or in the molecules [197][198][199][200][201][202][203][204][205], and show unique sorption and catalytic properties. Shape-and stereoselective oxidations using porous POMs are interesting future research areas.…”

Section: Resultsmentioning

confidence: 99%

Liquid-Phase Selective Oxidation by Multimetallic Active Sites of Polyoxometalate-Based Molecular Catalysts

Mizuno

Kamata

Yamaguchi

2011

Bifunctional Molecular Catalysis

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The catalytic oxidation is an area of the key technologies for converting petroleum-based feedstocks to useful chemicals such as diols, epoxides, alcohols, and carbonyl compounds. Many efficient homogeneous and heterogeneous oxidation systems based on polyoxometalates (POMs) with green oxidants such as H 2 O 2 and O 2 have been developed. This chapter summarizes the remarkable oxidation catalyses by POMs with multimetallic active sites. The multifunctionality of multimetallic active sites in POMs such as cooperative activation of oxidants, simultaneous activation of oxidants and substrates, stabilization of reaction intermediates, and multielectron transfer leads to their remarkable activities and selectivities in comparison with the conventional monometallic complexes. Finally, the future opportunities for the development of shape-and stereoselective oxidation by POM-based catalysts are described.

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“…Cs2 salt is composed of aggregates of 50-100 nm in size, whereas the aggregates in the case of Cs2.5 and Cs3 salts [15,[18][19][20]. The Cs2 salt obtained according to the standard procedure was the base to prepare the Cs2.5 and Cs3 salts by two-stage procedures.…”

Section: Resultsmentioning

confidence: 99%

A Comparison of Catalytic Properties of Cs x H3−x PW12O40 Salts of Various Cesium Contents in Gas Phase and Liquid Phase Reactions

et al. 2009

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The cesium salts Cs x H 3-x PW 12 O 40 of Cs content x = 2 up to x = 3 were tested as the catalysts in the gas and liquid phase reactions. Dehydration of ethanol and transesterification of triglycerides with methanol were selected as the catalytic reactions. Apart from the standard preparation, the catalysts were prepared by two-stage procedure with methanol or water as a solvent. The Cs-salts were characterized by FT-IR, XRD, scanning electron microscopy and energy dispersive X-ray techniques. In turn, the influence of Cs-salts composition on the pH and conductivity of their aqueous colloidal solutions was investigated. The results obtained by the latter techniques were also characteristic for acidity of surface layer of colloidal particles because of surface layer-solution equilibrium. It has been shown that the secondary structure of acidic cesium salts existing in crystalline samples (solid solution of H 3 PW 12 O 40 in Cs 3 PW 12 O 40 ) changes after contacting with polar medium to the system consisting most probably of Cs 3 PW 12 O 40 core with epitaxial layer of heteropolyacid. This is result of the protons migration from bulk to surface layer of primary particles enhanced by polar medium. It strongly influences the surface acidity of primary particles as well as the activity of Cs-salts in transesterification of triglycerides with methanol. In such polar medium, Cs 2 HPW 12 O 40 salt becomes the most active catalyst, more active than Cs 2.5 H 0.5 PW 12 O 40 . An accumulation of partial glycerides and in particular glycerol on the surface of primary particles of Cs-salts resulted in relatively low maximum conversion of triglycerides, most probably due to partial blockage of the catalytic centers. This effect and the almost constant activity of Cs-salts under recycling use in the transesterification experiments are considered to be experimental evidences that methanolysis over Cs-salts was accomplished with the participation of surface protons.

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Microstructure of Cesium Hydrogen Salts of 12-Tungstophosphoric Acid Relevant to Novel Acid Catalysis

Cited by 268 publications

References 47 publications

Microporous cesium salts of tetravalent Keggin-type polyoxotungstates Cs4[SiW12O40], Cs4[PW11O39(Sn-n-C4H9)], and Cs4[PW11O39(Sn-OH)] and their adsorption properties

Microporous cesium salts of tetravalent Keggin-type polyoxotungstates Cs4[SiW12O40], Cs4[PW11O39(Sn-n-C4H9)], and Cs4[PW11O39(Sn-OH)] and their adsorption properties

Liquid-Phase Selective Oxidation by Multimetallic Active Sites of Polyoxometalate-Based Molecular Catalysts

A Comparison of Catalytic Properties of Cs x H3−x PW12O40 Salts of Various Cesium Contents in Gas Phase and Liquid Phase Reactions

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