The Experts below are selected from a list of 13038 Experts worldwide ranked by ideXlab platform
Rafal Baran - One of the best experts on this subject based on the ideXlab platform.
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incorporation of mn into the vacant t atom sites of a bea zeolite as isolated mononuclear mn ftir xps epr and dr uv vis studies
Physical Chemistry Chemical Physics, 2016Co-Authors: Rafal Baran, L Valentin, Stanislaw DzwigajAbstract:A MnSiBEA zeolite has been prepared via a two-step postsynthesis procedure which consisted, in the first step, of the treatment of a tetraethylammonium BEA zeolite with nitric acid for the formation of vacant T-atom sites and then, in the second step, of the incorporation of Mn ions into the framework, resulting in a SiBEA zeolite, through their reaction with the Silanol Group of the vacant T-atom sites. The incorporation of Mn ions into the framework of the SiBEA zeolite has been evidenced using XRD. The formation of isolated mononuclear Mn(ii) and Mn(iii) in a MnSiBEA zeolite has been shown using FTIR, diffuse reflectance UV-Vis, EPR and XPS. The acidic properties of the mononuclear manganese species have been investigated via FTIR spectroscopy using pyridine as the probe molecule. The changes in the oxidation state of the Mn species under various treatments have been proven using EPR.
Stanislaw Dzwigaj - One of the best experts on this subject based on the ideXlab platform.
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incorporation of mn into the vacant t atom sites of a bea zeolite as isolated mononuclear mn ftir xps epr and dr uv vis studies
Physical Chemistry Chemical Physics, 2016Co-Authors: Rafal Baran, L Valentin, Stanislaw DzwigajAbstract:A MnSiBEA zeolite has been prepared via a two-step postsynthesis procedure which consisted, in the first step, of the treatment of a tetraethylammonium BEA zeolite with nitric acid for the formation of vacant T-atom sites and then, in the second step, of the incorporation of Mn ions into the framework, resulting in a SiBEA zeolite, through their reaction with the Silanol Group of the vacant T-atom sites. The incorporation of Mn ions into the framework of the SiBEA zeolite has been evidenced using XRD. The formation of isolated mononuclear Mn(ii) and Mn(iii) in a MnSiBEA zeolite has been shown using FTIR, diffuse reflectance UV-Vis, EPR and XPS. The acidic properties of the mononuclear manganese species have been investigated via FTIR spectroscopy using pyridine as the probe molecule. The changes in the oxidation state of the Mn species under various treatments have been proven using EPR.
Dionisios G. Vlachos - One of the best experts on this subject based on the ideXlab platform.
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Role of Silanol Group in Sn-Beta Zeolite for Glucose Isomerization and Epimerization Reactions
ACS Catalysis, 2013Co-Authors: Neeraj Rai, Stavros Caratzoulas, Dionisios G. VlachosAbstract:Density functional calculations are used to elucidate the role of the Silanol Group adjacent to the active site Sn metal center of the Sn-BEA zeolite in the isomerization and epimerization of glucose. We find that the Silanol Group plays an important role in the isomerization reaction, wherein hydride transfer and subsequent proton transfer occur in a single step with a lower energy of activation. Epimerization, on the other hand, proceeds via a mechanism similar to the Bilik mechanism and has lower activation barrier when the Silanol Group does not participate directly in the transition state. Our calculations indicate that cooperative effects, often encountered in enzymatic catalysis, promote hydride transfer in the isomerization reaction but not for the Bilik mechanism for epimerization.
Samir H. Mushrif - One of the best experts on this subject based on the ideXlab platform.
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Brønsted and Lewis acid sites of Sn-beta zeolite, in combination with the borate salt, catalyze the epimerization of glucose: A density functional theory study
Journal of Catalysis, 2015Co-Authors: B.k. Chethana, Samir H. MushrifAbstract:Abstract Sn-beta zeolite, in combination with borate salts, is a potential inorganic catalyst for sugars epimerization. We investigate, at molecular level, the catalytic mechanism of glucose epimerization to mannose, using density functional theory. Our calculations suggest that the tetrahedral borate ion forms a complex with glucose and inhibits the competitive isomerization reaction. The Lewis-acidic stannanol Group of Sn-beta catalyzes glucose ring opening, which is followed by the Silanol Group (Bronsted acid site) catalyzed enolization. The epimerization then proceeds via an intramolecular 1,2 carbon shift and is found to be the rate-limiting step with an activation enthalpy of 26.3 kcal/mol. Catalytic activities of different tetravalent metal centers are compared, and Sn is found to be the most active metal. Additionally, it was found that the proximity of Silanol Group to the stannanol Group, within the zeolitic framework, plays a key role in enhancing the catalytic activity of the Silanol Group. Hence, it is crucial to perform calculations with the entire ring structure of Sn-beta that opens up due to the hydrolysis of Sn–O–Si bridge.
Michio Komatsu - One of the best experts on this subject based on the ideXlab platform.
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a convenient determination of surface hydroxyl Group on silica gel by conversion of Silanol hydrogen to dimethylsilyl Group with diffuse reflectance ftir spectroscopy
Journal of Colloid and Interface Science, 1992Co-Authors: Kohji Yoshinaga, Yukiko Yamamoto, Hiroshi Yoshida, Kazuaki Takakura, Michio KomatsuAbstract:Abstract A new and convenient determination method of Silanol Groups on silica gels is proposed. The dimethylsilyl(Si(CH 3 ) 2 H) substitution of hydroxyl hydrogen on surfaces successfully led to Silanol quantitation by diffuse reflectance FTIR spectroscopy. This procedure was compared with a typical accepted method utilizing the reaction of Silanol Group with LiAlH 4 , and found to be available as one of the simple Silanol analytical methods. The method is also shown to be applicable for residual Silanol Group determination of organic compound-modified silica gels.
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A Convenient Determination of Surface Hydroxyl Group on Silica Gel by FT-IR Spectroscopy.
Chemistry Letters, 1991Co-Authors: Kohji Yoshinaga, Masaru Rikitake, Taketoshi Kito, Yukiko Yamamoto, Hiroshi Eguchi, Michio KomatsuAbstract:The dimethylsilyl(–Si(CH3)2H) substitution of hydroxyl hydrogen led to a convenient determination of surface Silanol Group on silica gels by Si-H bond stretching vibrational absorption analysis. The proposed procedure can be freed from influences of adsorbed water and moisture through the measurement process.