Toshiyuki Yokoi

Tokyo Institute of Technology, Edo, Tōkyō, Japan

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Publications (100)448.94 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Locations of Lewis acid sites (LASs) on three MWW-type zeolites, the conventional Al-containing MWW zeolite (Al-MWW), acid-treated Al-containing MWW zeolite (Al-MWW-AT) and interlayer-expanded Al-containing MWW zeolite (Al-IEZ-MWW), were clarified by IR method using hexamethyleneimine (HMI), pivalonitrile (PN) and CO as probe molecules. No significant difference was found for Brønsted acid sites (BASs) in the strength and positions, while the locations of LASs were distinguished. LASs existed only on the external surfaces of Al-MWW, and in the expanded interlayer micropores (12-membered ring, 12-MR) of Al-IEZ-MWW. The simple acid treatment with nitric acid was found to generate LASs in the interlayer 10-MR micropores of Al-MWW-AT. The reactivity of the three zeolites depending on the positions of the active LASs was further confirmed in the Meerwein–Ponndorf–Verley (MPV) reduction of different ketones in size; 4-methylcyclohexanone and 2-butanone. Al-IEZ-MWW was superior for the reduction of 4-methylcyclohexanone over LASs in the interlayer 12-MR micropores, and Al-MWW-AT also showed fair reactivity for the reduction of smaller 2-butanone over LASs in the interlayer 10-MR micropores.
    Microporous and Mesoporous Materials 04/2015; 206. · 3.21 Impact Factor
  • Masato Yoshioka, Toshiyuki Yokoi, Takashi Tatsumi
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    ABSTRACT: Graphical abstract Interlayer-expanded MWW-type titanosilicate has been successfully prepared by utilizing the structural reversibility between the 3D crystalline and the layered structures.
    Microporous and Mesoporous Materials 12/2014; 200:11–18. · 3.21 Impact Factor
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    ABSTRACT: A series of Cu-exchanged Al-rich Beta zeolites from organotemplate-free synthesis was prepared and investigated for selective catalytic reduction (SCR) of NOx with NH3 in exhaust gas streams. In comparison to conventional Cu-Beta zeolite with Si/Al ratio of 19, Cu-Beta zeolite with Si/Al ratio of 4 is a superior low-temperature NH3-SCR catalyst. Very high NO conversion (>95%) can be achieved at temperatures as low as 150 to ∼400 °C. XRD, UV–Vis-NIR and NH3-TPD measurements show that more isolated Cu2+ ions are present at the exchange sites of Al-rich Beta zeolite. The combination of CO-FTIR and H2-TPR analysis demonstrates that Cu2+ ions could be reduced more readily on the Al-rich Beta than on the conventional Beta probably due to the proximity of the isolated Cu2+ ions. These can be correlated to the enhancement of NO conversion at lower temperatures over Cu-exchanged Al-rich Beta zeolite.
    Microporous and Mesoporous Materials 12/2014; 200:304-310. · 3.21 Impact Factor
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    ABSTRACT: One dimensional pore zeolites such as ZSM-22 (TON) are potential catalysts for hydrocarbon conversion reactions, including methanol-to-propylene (MTP) reaction. Different crystal lengths of ZSM-22 zeolite were prepared and examined for the MTP reaction. Nanosized TON zeolites with crystal length of ∼100 nm were synthesized by dynamic hydrothermal synthesis. The zeolite crystal length was tuned by using ethylene glycol as crystal growth modifier. The crystal lengths of ZSM-22 zeolites (approximately 100 and 300 nm) were confirmed from FE-SEM and TEM micrographs. However, the textural properties such as BET surface area and crystallinity of crystals were fairly similar. The effect of ZSM-22 crystal length on catalytic activity and propylene yields in the methanol-to-propylene reaction was investigated. The TON nanocrystals resulted in a higher propylene yield and better catalytic stability compared to the submicrometer zeolite (∼300 nm). Deactivation was observed for all catalysts. However, longer lifetime was observed for the nanosized ZSM-22 with crystal length of ∼100 nm.
    Industrial & Engineering Chemistry Research 11/2014; · 2.24 Impact Factor
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    ABSTRACT: Sn-containing mesoporous silica nanospheres (Sn-MSNSs) with uniform crater-like mesopores were successfully synthesized by a direct synthetic method. The effects of Sn content and calcination temperature on the structural properties of Sn-MSNSs were investigated. Moreover, the catalytic performance of Sn-MSNSs in the Baeyer–Villiger (BV) oxidation of bulky cyclic ketone with hydrogen peroxide (H2O2) was studied. Compared with Sn-MCM-41, which possessed long mesopores, Sn-MSNSs with high hydrophobicity provided by high-temperature calcination exhibited much higher activity in the BV oxidation of bulky cyclic ketone, 2-adamantanone.
    Applied Catalysis A General 11/2014; · 3.67 Impact Factor
  • Tetrahedron 10/2014; 70(41):7584–7592. · 2.82 Impact Factor
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    Materials Chemistry and Physics 10/2014; · 2.13 Impact Factor
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    ABSTRACT: The oligomerization of ethene over H-ZSM-5 was studied by infrared (IR) spectroscopy. The possibility of an ethoxy intermediate for ethene oligomerization was investigated. Ethene oligomerization was found to proceed on the basis of a concerted mechanism with plural ethene molecules and not by a stepwise mechanism with an ethoxy intermediate.
    Catal. Sci. Technol. 09/2014;
  • Microporous and Mesoporous Materials 09/2014; 196:341–348. · 3.21 Impact Factor
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    ABSTRACT: A novel strategy for the synthesis of microporous crystalline titanosilicate catalyst (TS-1) was developed based on the combination of liquid-phase and solid-phase transformation mechanisms. The core concept of this strategy was to crystallize the mixed precursors composed of both liquid-phase and solid-phase precursors. The anionic polyelectrolyte poly(acrylic acid) was used as a unique gelating agent to prepare the solid/liquid mixture, which can partly convert the liquid-phase precursor to the solid-phase precursor. Active framework Ti was formed by in situ conversion of the Ti species from the solid-phase precursor during the crystallization stage, as well as by the transfer of Ti species from the liquid-phase precursor to the solid crystal after the crystallization. In this way, the content of active Ti in TS-1 was significantly increased. The obtained product displayed high activity for the oxidation reaction of n-hexane and 1-hexene.
    ChemCatChem 08/2014; · 5.18 Impact Factor
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    ABSTRACT: Interlayer expanded zeolites are derived from layered zeolite precursors by inserting a tetrahedrally coordinated atom (T-atom) in between the precursor layers. To achieve this expansion, a Si source like dichlorodimethylsilane or diethoxydimethylsilane is typically used. In the interlayer expansion of the layered zeolite precursor RUB-36, an Fe salt instead of a silylating agent was used to fill up the linking sites in between the layers. The obtained material showed a shift of the first XRD reflection similar to that of RUB-36 interlayer expanded with dichlorodimethylsilane, indicating an increase in interlayer distance. Diffuse reflectance UV-vis spectra and EPR characterization proved the incorporation of isolated Fe sites. Using FTIR spectroscopy with pyridine and acetonitrile as probe molecules, it was found that the incorporation of Fe results in an increase in Lewis acidity. The material was successfully used as a catalyst in the acylation of anisole with acetic anhydride and in the alkylation of toluene with benzyl chloride. The Fe incorporation proved to be remarkably stable. In spite of the HCl production during the alkylation reaction, no leaching was observed and the catalyst could be reused after regeneration.
    J. Mater. Chem. A. 06/2014; 2(25).
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    ABSTRACT: Treatment of the zeolitic layered precursor of Al-MWW, so-called Al-MWW(P), with diethoxydimethylsilane (DEDMS) in acidic media leads to the formation of an aluminosilicate-type interlayer-expanded zeolite MWW (Al-IEZ-MWW) with expanded 12-membered ring (12-MR) micropores. However, the silylation process under acidic conditions simultaneously causes dealumination from the MWW framework, resulting in a decrease in the acid amount. We have developed a method for preparing Al-IEZ-MWW without leaching of the Al species. The strategy is to conduct the silylation under weakly acidic conditions; the silylation was conducted in an aqueous solution of an ammonium salt, e.g., NH4Cl, instead of HNO3. Subsequent additional acid treatment led to the formation of Al-IEZ-MWW that shows a high catalytic performance in the acylation of anisole compared to typical Al-MWW as well as Al-IEZ-MWW directly prepared under acidic conditions. The change in the state of Al atoms during the preparation process was investigated by high-resolution solid-state (27)Al MAS NMR and (27)Al MQMAS NMR techniques.
    Dalton Transactions 05/2014; · 4.10 Impact Factor
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    ABSTRACT: COE-4 zeolites possess a unique two-dimensional ten-ring pore structure with the Si(OH)2 hydroxyl groups attached to the linker position between the ferrierite-type layers, which has been demonstrated through the interlayer-expansion approach in our previous work (H. Gies et al. Chem. Mater.­ 2012, 24, 1536). Herein, density functional theory is used to study the framework stability and Brønsted acidity of the zeolite T-COE-4, in which the tetravalent Si is isomorphously substituted by a trivalent Fe, B, Ga, or Al heteroatom at the linker position. The influences of substitution energy and equilibrium geometry parameters on the stability of T-COE-4 are investigated in detail. The relative acid strength of the linker position is revealed by the proton affinity, charge analysis, and NH3 adsorption. It is found that the range of the 〈T-O-Si〉 angles is widened to maintain the stability of isomorphously substituted T-COE-4 zeolites. The smaller the 〈O1-T-O2〉 bond angle is, the more difficult is to form the regular tetrahedral unit. Thus, the substitution energies at the linker positions increase in the following sequence: Al-COE-4 < Ga-COE-4 < Fe-COE-4 < B-COE-4. The adsorption of NH3 as a probe molecule indicates that the acidity can affect the hydrogen-bonding interaction between (NH⋅⋅⋅O2) and (N⋅⋅⋅HO2). The relative Brønsted-acid strength of the interlayer-expanded T-COE-4 zeolite decreases in the order of Al-COE-4 > Ga-COE-4 > Fe-COE-4 > B-COE-4. These findings may be helpful for the structural design and functional modification of interlayer-expanded zeolites.
    ChemPhysChem 03/2014; · 3.36 Impact Factor
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    ABSTRACT: The present study is the first report on the synthesis and characterization of mesoporous composites based on natural rubber (NR) and hexagonal mesoporous silica (HMS). A series of NR/HMS composites were prepared in tetrahydrofuran via an in situ sol–gel process using tetraethylorthosilicate as the silica precursor. The physicochemical properties of the composites were characterized by various techniques. The effects of the gel composition on the structural and textural properties of the NR/HMS composites were investigated. The Fourier-transform infrared spectroscopy (FTIR) and 29Si magic angle spinning nuclear magnetic resonance (29Si MAS NMR) results revealed that the surface silanol groups of NR/HMS composites were covered with NR molecules. The powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) data indicated an expansion of the hexagonal unit cell and channel wall thickness due to the incorporation of NR molecules into the mesoporous structure. NR/HMS composites also possessed nanosized particles (∼79.4 nm) as confirmed by scanning electron microscopy (SEM) and particle size distribution analysis. From N2 adsorption–desorption measurement, the NR/HMS composites possessed a high BET surface area, large pore volume and narrow pore size distribution. Further, they were enhanced hydrophobicity confirmed by H2O adsorption–desorption measurement. In addition, the mechanistic pathway of the NR/HMS composite formation was proposed.
    Materials Chemistry and Physics 02/2014; 143(3):1199–1208. · 2.13 Impact Factor
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    ABSTRACT: In addition to the original preparation route of the RTH-type zeolites using 1,2,2,6,6-pentamethylpiperidine (PMP) as an organic structure directing agent (OSDA), we have found that simpler organic amines such as N-methylpiperidine and pyridine can be used as alternative OSDAs in place of PMP. Furthermore, we have established a synthesis method for preparing the RTH-type zeolites without using any OSDAs. In this study, RTH-type aluminosilicates were synthesized with different types of OSDA or without using any OSDAs. The obtained zeolites synthesized with different preparation methods were characterized by using various techniques, especially high-resolution (27)Al MAS NMR and in situ FT-IR techniques using CO adsorption. The relationship between the preparation method and the catalytic performance in the methanol to olefins (MTO) reaction was discussed. Finally, the distribution of Al species in the RTH-framework was clarified.
    Physical Chemistry Chemical Physics 01/2014; · 4.20 Impact Factor
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    ABSTRACT: To improve the catalytic performance of Beta zeolite in the direct transformation of glucose into 5-hydroxymethylfurfural (HMF), effects of calcination and steam treatment on the structure of Al atoms in the framework and acid properties of Beta zeolite were examined in detail. 27Al MAS NMR measurement and IR observation revealed that a part of Si–O–Al bonds in the framework were cleaved to form Al species out of the *BEA framework during the treatments and these species showed Lewis acidity. Especially, when the ammonium-type Beta was calcined over 700 °C or treated with steam (50 kPa in N2 balance) over 500 °C, the amount of Lewis acid sites was increased at the expense of Brønsted acid sites. Thus prepared Beta zeolite catalysts having a sufficient amount of Lewis acid sites were found to be effective bifunctional catalysts in synthesis of HMF from glucose; for example, Beta zeolite prepared by the calcination at 750 °C showed 55% selectivity to HMF at 78% conversion of glucose. We clarified the roles of Lewis and Brønsted acid sites on the Beta zeolite in the direct transformation of glucose to HMF. Furthermore, the reaction mechanism for the isomerization of glucose was investigated by means of isotope experiment using deuterated glucose. Finally, reusability of the Beta zeolite was also investigated.
    Applied Catalysis A General 01/2014; 470:318–326. · 3.67 Impact Factor
  • ChemInform 12/2013; 44(52).
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    Peng Wu, Yoshihiro Kubota, Toshiyuki Yokoi
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    ABSTRACT: On the occasion of Professor Takashi Tatsumi’s retirement and winning of the Alwin Mittasch Prize, some of his main achievements in zeolite catalysis are summarized, with a focus on the design, synthesis, and catalytic application of new titanosilicate catalysts. He and his co-workers succeeded in the direct synthesis of the MWW-type titanosilicate, Ti-MWW, by employing boric acid in the synthesis and thereafter developed a dry gel conversion method for boron-reduced Ti-MWW as well as a secondary isomorphous substitution route for boron-free Ti-MWW molecular sieves. In particular, the postsynthetic conversion involved a reversible structure interchange between three-dimensional silicalite and a two-dimensional layered precursor. Taking advantage of the structural diversity of the layered MWW zeolite precursor, phase-delaminated Ti-MMW and interlayer expanded Ti-MWW were also prepared. Using hydrogen peroxide as an oxidant, the Ti-MWW/H2O2 system was highly efficient for liquid-phase oxidation of a variety of substrates, particularly the epoxidation of alkenes and ammoximation of ketones. Some of the Ti-MWW-catalyzed reactions have already led to or are becoming practical catalytic technologies in industrial practice. Several other recent achievements in the synthesis and catalytic applications of other titanosilicates, zeolitic hydrid materials, and solid acid zeolite catalysts are also briefly summarized.
    ACS Catalysis 12/2013; 4(1):23–30. · 7.57 Impact Factor
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    ABSTRACT: Eight-membered ring small-pore zeolite of RHO-type topology has been synthesized, characterized and tested for methanol-to-olefin (MTO) reaction. The zeolite was hydrothermally crystallized from the gel with Si/Al ratio of 5.0. It showed a high BET specific surface area (812 m2 g–1), micropore volume (0.429 cm3 g–1), and acid amount (2.53 mmol g–1). Scanning electron microscopy observations showed small crystallites of about 1 μm. The zeolite was active for MTO reaction with 100% methanol conversions at 623–723 K, whereas selectivity to lower olefins changed with time.
    Catalysis Communications 07/2013; 37:1–4. · 3.32 Impact Factor
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    ABSTRACT: Homogeneously mixed silica–alumina samples with various Si/Al ratios (Si/Al = 9/1, 7/3, 5/5, 3/7, and 1/9) were prepared and characterized by infrared spectroscopy. Pyridine, propene, and CO were used as probe molecules to detect Brønsted and Lewis acid sites. The homogeneity of Si and Al in mixed oxides was confirmed by comparison with a physical mixture of pure silica and alumina. The continuous change of spectral appeared by increasing or decreasing the Si/Al ratio in silica–alumina samples. The frequency of the broad band due to surface OH groups hydrogen-bonded to CO was found to be a measure of the Si/Al ratio in silica–alumina samples roughly. This information was used to characterize steam-treated HY and NH4Y zeolites. Dealumination from the framework structure and generation of extra-framework silica–alumina were apparent for both steam-treated zeolites, which were not identified by X-ray diffraction patterns and microscope images. The Si/Al ratios of the formed silica–alumina on steam-treated YH and NH4Y zeolites were roughly estimated to be 5/5 and 7/3, respectively, by the peak position of hydrogen-bonded OH bands when CO was adsorbed. The acid strength of both steam-treated samples was weakened, and it was more apparent for HY than NH4Y zeolite.
    The Journal of Physical Chemistry C 07/2013; 117(27):14043–14050. · 4.84 Impact Factor

Publication Stats

1k Citations
448.94 Total Impact Points

Institutions

  • 2006–2014
    • Tokyo Institute of Technology
      • Chemical Resources Laboratory
      Edo, Tōkyō, Japan
    • Jilin University
      • State Key Laboratory of Inorganic Synthesis and Preparative
      Jilin, Jilin Sheng, China
  • 2013
    • Japan Advanced Institute of Science and Technology
      KMQ, Ishikawa, Japan
  • 2011–2012
    • Saga University
      • Faculty of Sciences & Engineering
      Saga-shi, Saga-ken, Japan
  • 2006–2011
    • The University of Tokyo
      • Department of Chemical System Engineering
      Tokyo, Tokyo-to, Japan
  • 2003–2004
    • Yokohama National University
      • Graduate School of Engineering
      Yokohama-shi, Kanagawa-ken, Japan