Determination of hydrogen-bonding acid sites on silica using the Cal-Ad method

Chronister, Chris W.; Drago, Russell S.

doi:10.1021/ja00064a045

Cited by 85 publications

(110 citation statements)

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“…We have taken the approach that this is a reasonable assumption only when comparing closely related solid acids, and we believe that the series of supported sulfonic acids used in this study are suitably similar to justify the use of this technique to compare their acid strengths. This approach to using titration calorimetry to study the strength of solid acids in the presence of solvents is in line with the work of others in the field [17][18][19][20].…”

Section: Introductionsupporting

confidence: 78%

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The Influence of Solvent on the Acidity and Activity of Supported Sulfonic Acid Catalysts

Koujout

Brown

2004

Catalysis Letters

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The acid strengths and catalytic activities of sulfonic acids supported on polystyrene resins and ordered mesoporous HMS and SBA-15 silicas are compared. Acid strengths are measured by acid-base titration calorimetry in terms of the molar enthalpies of neutralisation with either NaOH or n-butylamine in water, acetonitrile and cyclohexane. Catalytic activities (turnover numbers) are reported in model reactions in water, 1,2-dichlorobenzene and anisole, and compared with acid strengths. In water, sulfonated resins are both stronger acids and more active catalysts than sulfonated silicas. Catalytic activities in water correlate well with these measured acid strengths. In acetonitrile the order of acid strengths is reversed and the sulfonated silicas are the stronger acids. Catalytic measurements in 1,2-dichlorobenzene, a similar dipolar aprotic solvent, show the same reversed order of activities. In the non-polar solvent cyclohexane (where only macroporous sulfonated resins show measurable acidity) the sulfonated silicas are again the stronger acids but by a larger margin. Catalytic activities in anisole, which is also only very weakly solvating towards sulfonic acid groups, show a similar trend. The results illustrate the role of the solvent in controlling the acid strength of solid acid catalysts, and the importance of taking this into account when designing acid catalysts for liquid phase processes.

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Section: Introductionsupporting

confidence: 78%

“…Pluronic 123 (EO 20 The solid product was recovered by filtration and airdried. The template was extracted with excess ethanol under reflux for 24 h (1.5 g of as-synthesised material per 400 ml of ethanol) [6].…”

Section: Sulfonated Mesoporous Silicasmentioning

confidence: 99%

The Influence of Solvent on the Acidity and Activity of Supported Sulfonic Acid Catalysts

Koujout

Brown

2004

Catalysis Letters

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“…This must be tested for each dye, polymer sample, and liquid in order to decide the best conditions for the measurement. However, this method is especially useful for fairly large polar macromolecules and inorganic oxidic materials which are absolutely insoluble in the solvent employed 56, 59,60) .…”

Section: Synthetic Polymersmentioning

confidence: 99%

Empirical polarity parameters for various macromolecular and related materials

Spange¹,

Vilsmeier

Fischer

et al. 2000

Macromol. Rapid Commun.

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Empirical polarity parameters are recommended as useful characteristics for describing the internal and external surface properties of various solid materials, e. g. synthetic polymers, native polymers, inorganic oxides, sol‐gel hybrids, and composites. The polarity properties of a macromolecule have been expressed by three independent terms: the α value (the hydrogen bond donating, HBD, capacity or acidity), the β value (the hydrogen bond accepting, HBA, capacity or basicity), and the π* value (the dipolarity/polarizability). These terms can be defined using the Kamlet‐Taft solvents parameter set as the reference system. A complex property, XYZ, of a macromolecular material under study, with reference to a standard system (XYZ)0 (i. e. gas phase or a nonpolar polymer), can then be described by a simplified Kamlet‐Taft LSE (linear solvation energy) equation: XYZ = (XYZ)0 + sπ* + aα + bβ. a, b, and s are coefficients reflecting the susceptibility of the polarity terms upon XYZ. Empirical solvatochromic polarity parameters [α, β, π*, ET (30)] for synthetic polymers, copolymers, native polymers, inorganic oxidic materials, functionalized silica particles, hybrids, and composite materials have been determined by means of the following solvatochromic probe dyes: 2,6‐diphenyl‐(2,4,6‐triphenyl‐1‐pyridinio)‐4‐phenolate (1 a), Michler's ketone (2), dicyano‐bis(1,10‐phenanthrolin)iron II (3), and a novel aminobenzodifuranone dye (7). The solvatochromic band shifts of these indicators correlate precisely with the Kamlet‐Taft solvent parameters α, β, and π*. The results are compared with each other, with related solvent model compounds, and literature values. The relation of the well established ET (30) solvent polarity scale to the Kamlet‐Taft parameters α and π* of solid materials is demonstrated. Hence, a general polarity scale for solid materials is suggested.

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“…Pyridine was used to probe the acidity of Ce-USY samples by FTIR (Figure 8), which identified Brønsted and Lewis sites. 44,45 The spectra showed three bands at 1545, 1490 and 1445 cm -1 , which are associated to Brønsted sites, a combination of Brønsted/ Lewis sites and Lewis sites respectively. [46][47][48] The acidity of cerium materials has been widely discussed, but there is no consensus about the types of acid sites present on their surfaces.…”

Section: Ce-usy Aciditymentioning

confidence: 99%

“…There was also a convoluted signal between −0.4 and 59.1 ppm, which might be related to the presence of aluminum in distorted octahedral and/or tetrahedral sites. 43,44 The distribution of tetrahedral, octahedral and convoluted signals (intermediate aluminum sites) allowed a better comprehension of the dealumination process that the USY zeolite underwent upon calcination ( Figure 6). The dealumination process involves the transformation of Al atoms from the structure to extra-framework atoms.…”

Section: Solid-state Nuclear Magnetic Resonance Spectroscopymentioning

confidence: 99%

Effect of cerium loading on structure and morphology of modified Ce-USY zeolites

Garcia¹,

Araújo²,

Silva³

et al. 2011

J. Braz. Chem. Soc.

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Este trabalho descreve detalhadamente o efeito da quantidade de cério na estrutura e morfologia da zeólita NH 4 USY. Ce-USY (2-25% m/m de CeO 2 ) foi obtido por impregnação úmida de CeCl 3 seguida de calcinação a 550 ºC por 8 h. Em quantidades baixas (2-10%), foi observado que as espécies de cério encontram-se nas posições de troca iônica na rede, enquanto em maiores teores (15-25%) pequenos agregados formaram-se na superfície da HUSY. Difratometria de raios X (XRD) mostrou apenas reflexões relacionadas à HUSY, confirmando a alta dispersão das espécies de cério, porém as análises por espectroscopia Raman com transformada de Fourier (FT-Raman) detectaram CeO x para os materiais acima de 10%. A reação do CeCl 3 com NH 4 USY produziu NH 4 Cl, o qual se decompõe em HCl, ocasionando a desaluminização da rede. Os materiais apresentaram um aumento da razão Lewis/Brønsted com o aumento da quantidade de cério, devido a interação do excesso de cério com os grupos OH da USY e consequente formação de espécies CeO x . This work describes comprehensibly the effect of cerium loading on the structure and morphology of NH 4 USY zeolite. The Ce-USY (2-25 wt.% of CeO 2 ) was obtained by wet impregnation of CeCl 3 followed by calcination at 550 ºC for 8 h. At low loadings (2-10%), cerium species are mainly located at ion exchange positions in the framework, whereas at higher loadings (15-25%), small aggregates were formed on the HUSY surface. X-ray diffractograms (XRD) exhibited only the reflections related to HUSY, demonstrating the high dispersion of cerium species, but Fourier transform Raman spectroscopy (FT-Raman) detected CeO x for the materials above 10%. Reaction of CeCl 3 with NH 4 USY produced NH 4 Cl, which decomposed to form HCl, leading to framework dealumination. The materials showed an increased Lewis/Brønsted ratio with increasing cerium loadings due to the interaction between the excess cerium and the OH groups of USY, and the consequent formation of CeO x species.Keywords: cerium USY zeolite, cerium oxide, ultra stable Y zeolite, solid-state ion exchange, 27 Al and 29 Si MAS NMR spectroscopy IntroductionFaujasite-type zeolites (X and Y) are largely applied in fluid catalytic cracking (FCC) of crude oil distillates and in hydrodesulfurization of fossil diesel oil and gasoline. 1 Y zeolites, either in their sodium or ammonium form, can be exchanged for rare earth ions to achieve the following main goals: (i) to prevent aluminum loss from the zeolite structure, which results in enhanced structural resistance to the severe hydrothermal conditions of the regeneration step of FCC, 2 and (ii) to increase the activity, because the introduction of rare earth species modifies the number of acidic protons through either hydrolysis or enhancement of ionic fields inside the zeolite structure. 3 Because rare earth cations modify the acidic properties of zeolites, their insertion has an effect on both thermal and mechanical stability, which are important for zeolite application to industrial processes such as pyrolysis, 4 oxidat...

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Determination of hydrogen-bonding acid sites on silica using the Cal-Ad method

Cited by 85 publications

References 0 publications

The Influence of Solvent on the Acidity and Activity of Supported Sulfonic Acid Catalysts

The Influence of Solvent on the Acidity and Activity of Supported Sulfonic Acid Catalysts

Empirical polarity parameters for various macromolecular and related materials

Effect of cerium loading on structure and morphology of modified Ce-USY zeolites

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