Highly Porous Hybrid Metallosilicate Materials Prepared by Non-Hydrolytic Sol-Gel: Hydrothermal Stability and Catalytic Properties in Ethanol Dehydration

<div> Herein, we present novel phenylene- and xylylene-bridged silica and metallosilicate materials prepared by non-hydrolytic sol-gel. The hybrid silica are highly porous, chemically similar to periodic mesoporous organosilica (PMO), but amorphous. Analogous hybrid metallosilicates are obtained by directly incorporating Al, Nb, or Sn in the hybrid silica framework. Exhibiting open texture, surface acidity and tunable hydrophobicity, these materials are excellent candidates for catalytic alcohol dehydration reactions. The gas-phase hydrothermal and thermal stability of these materials is examined. While the hybrid silica is expectedly stable, a stark decrease in stability is observed for phenylene bridged silsesquioxanes upon metal introduction. The extent of the hydrolytic Si−C(sp2) bond cleavage is quantitatively followed by 29Si MAS NMR, TG analysis, and GC-FID analysis of effluent coming from samples exposed to water vapor. Two important features affecting the hydrothermal and thermal stability are identified: (i) the homogeneity of metal dispersion within the silica matrix, and (ii) the electronegativity of the incorporated metal. The stability of hybrid metallosilicates is significantly improved by replacing the phenylene bridges with xylylene bridges, due to the presence of more stable Si−C(sp3) bonds. Interestingly, the latter hybrid metallosilicate proves to be an active catalyst for the dehydration of ethanol to ethylene. Unlike the other hybrid materials presented here, it reaches high ethylene yields without undergoing degradation and deactivation. </div>

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Development of Novel Silica-Based Formulation of α-Lipoic Acid: Evaluation of Photo and Thermal Stability of the Encapsulated Drug

Pharmaceutics ◽

10.3390/pharmaceutics12030228 ◽

2020 ◽

Vol 12 (3) ◽

pp. 228 ◽

Cited By ~ 1

Author(s):

Ekaterina S. Dolinina ◽

Elizaveta Yu. Akimsheva ◽

Elena V. Parfenyuk

Keyword(s):

Thermal Stability ◽

Thermal Degradation ◽

Lipoic Acid ◽

Sol Gel ◽

Silica Matrix ◽

Matrix Modification ◽

Drug Stabilization ◽

Further Development ◽

Kinetics Of ◽

Thermal Stability Of

Powerful antioxidant α-lipoic acid (LA) is easily degraded under light and heating. This creates difficulties in its manufacture, storage and reduces efficiency and safety of the drug. The purpose of this work was to synthesize novel silica-based composites of LA and evaluate their ability to increase photo and thermal stability of the drug. It was assumed that the drug stabilization can be achieved due to LA-silica interactions. Therefore, the composites of LA with unmodified and organomodified silica matrixes were synthesized by sol-gel method at the synthesis pH below or above the pKa of the drug. The effects of silica matrix modification and the synthesis pH on the LA-silica interactions and kinetics of photo and thermal degradation of LA in the composites were studied. The nature of the interactions was revealed by FTIR spectroscopy. It was found that the rate of thermal degradation of the drug in the composites was significantly lower compared to free LA and mainly determined by the LA-silica interactions. However, photodegradation of LA in the composites under UV irradiation was either close to that for free drug or significantly more rapid. It was shown that kinetics of photodegradation was independent of the interactions and likely determined by physical properties of surface of the composite particles (porosity and reflectivity). The most promising composites for further development of novel silica-based formulations were identified.

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Luminescent and Thermal Properties of Eu3+ Complex with Salicylic Acid and o-Phenanthroline Trapped in Sol–Gel Glass

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.239-242.294 ◽

2011 ◽

Vol 239-242 ◽

pp. 294-297

Author(s):

Cun Jin Xu ◽

Qun Lü ◽

Hai Ke Feng

Keyword(s):

Thermal Stability ◽

Salicylic Acid ◽

Thermal Properties ◽

Silica Gel ◽

Sol Gel ◽

Silica Matrix ◽

Emission Lines ◽

Excitation Spectra ◽

Thermal Stability Of ◽

Luminescence Behavior

A ternary Eu(III) complex with salicylic acid (Hsal) ando-phenanthroline (phen) was synthesized and then incorporated into silica matrix by sol-gel method. The luminescence behavior of the complex in silica gel was studied compared with that of the pure complex by means of emission, excitation spectra and thermogravimetic analysis. The results indicate that the complex Eu(sal)3(phen) in silica gel shows fewer emission lines than pure Eu(sal)3(phen) and the luminescence intensity ratio of the5D0→7F2transition to the5D0→7F1transition is lower than that of the latter. The thermal stability of Eu(sal)3(phen) is enhanced greatly through the introduction of the complex into silica matrix.

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Luminescence and thermal stability of sodium tris(pyridine dicarboxylate) terbate(III) complex incorporated in silica matrix by sol-gel method

Materials Research Bulletin ◽

10.1016/s0025-5408(01)00618-3 ◽

2001 ◽

Vol 36 (7-8) ◽

pp. 1335-1346 ◽

Cited By ~ 10

Author(s):

Bao-li An ◽

Jian-qing Ye ◽

Meng-lian Gong ◽

Xian-hong Yin ◽

Yan-sheng Yang ◽

...

Keyword(s):

Thermal Stability ◽

Sol Gel ◽

Silica Matrix ◽

Gel Method ◽

Sol Gel Method ◽

Thermal Stability Of

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Structure, Texture, Surface Acidity, and Catalytic Activity of AlPO4–ZrO2(5–50 wt% ZrO2) Catalysts Prepared by a Sol–Gel Procedure

Journal of Catalysis ◽

10.1006/jcat.1998.2202 ◽

1998 ◽

Vol 179 (2) ◽

pp. 483-494 ◽

Cited By ~ 29

Author(s):

Felipa M. Bautista ◽

Juan M. Campelo ◽

Angel Garcia ◽

Diego Luna ◽

Jose M. Marinas ◽

...

Keyword(s):

Catalytic Activity ◽

Surface Acidity ◽

Sol Gel ◽

Texture Surface

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Non-Hydrolytic Sol-Gel Route to a Family of Hybrid Mesoporous Aluminosilicate Ethanol Dehydration Catalysts

10.26434/chemrxiv.13377212 ◽

2020 ◽

Author(s):

Ales Styskalik ◽

Imène Kordoghli ◽

Claude Poleunis ◽

Arnaud Delcorte ◽

Denis Dochain ◽

...

Keyword(s):

Gas Phase ◽

Sol Gel ◽

Catalytic Performance ◽

Silica Matrix ◽

Ethanol Dehydration ◽

One Pot ◽

Water Contact ◽

Hybrid Silica ◽

Mesoporous Aluminosilicate ◽

Improved Performance

Organic-inorganic hybrid materials are nowadays intensely studied for potential applications in heterogeneous catalysis because their properties and catalytic behavior differ from pristine inorganic counterparts. The organic groups at the catalyst surface can modify not only its hydrophilicity, but also acidity, hydrothermal stability, porosity, etc. In some cases, such properties alteration leads to improved catalytic performance in terms of activity, selectivity, or stability. However, the choice of organic groups stays relatively narrow, as most reports focus on pendant methyl groups. Here, a series of mesoporous hybrid aluminosilicate materials containing various organic groups was prepared in one pot by non-hydrolytic sol-gel (NHSG). Both aromatic and aliphatic, pendant and bridging organic groups were incorporated. The presence of the organic groups in the bulk and at the outermost surface of the materials was verified by solid-state NMR and ToF-SIMS, respectively. Aluminum is mostly incorporated in tetrahedral coordination in the hybrid silica matrix. The organically modified mesoporous aluminosilicate samples were tested as catalysts in the gas phase ethanol dehydration (which relies on solid acids) and most of them outperformed the purely inorganic catalyst benchmark. While a direct influence of surface hydrophilicity or hydrophobicity (as probed by water sorption and water contact angle measurements) appeared unlikely, characterization of acidity (IR-pyridine) revealed that the improved performance for hybrid catalysts can be correlated with a modification of the acidic properties. In turn, acidity is determined by the quality of the dispersion of Al centers in the form of isolated sites in the hybrid silica matrix. All in all, this study establishes a "ranking" for a variety of organic groups in terms of their effect on gas-phase ethanol dehydration to ethylene; ethylene yield decreases in this order: bridging xylylene ≈ pendant methyl > pendant benzyl > bridging methylene ≈ inorganic benchmark (no organic groups) > bridging ethylene.

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Ethanol Dehydration over Hybrid Mesoporous Aluminosilicate Catalysts Obtained in One Pot by Non-Hydrolytic Sol-Gel

10.26434/chemrxiv.12354770 ◽

2020 ◽

Author(s):

Ales Styskalik ◽

Imène Kordoghli ◽

Claude Poleunis ◽

Arnaud Delcorte ◽

Zdenek Moravec ◽

...

Keyword(s):

Catalyst Activity ◽

Sol Gel ◽

Acid Sites ◽

Silica Matrix ◽

Methyl Groups ◽

Ethanol Dehydration ◽

Alcohol Dehydration ◽

One Pot ◽

Surface Hydrophilicity ◽

Silica Alumina

Ethanol dehydration is effectively catalyzed by solid acids, such as HZSM-5, alumina, or silica-alumina. In these catalysts, the amount, nature, and strength of acid sites is believed to determine catalyst activity and stability. However, surface hydrophilicity or hydrophobicity can be suggested as another decisive catalyst property that can directly influence performance. For example, a more hydrophobic surface might be beneficial in repelling the co-product of the reaction, water. However, these aspects have been studied only scarcely in the context of alcohol dehydration. Here, a series of mesoporous hybrid aluminosilicate catalysts containing CH3Si groups was prepared in one pot by non-hydrolytic sol-gel (NHSG). The presence of the methyl groups was verified by IR, solid-state NMR, and ToF-SIMS. Aluminum is mostly incorporated in tetrahedral coordination in the hybrid silica matrix. Two parameters were varied: (i) the Si:Al ratio and (ii) the Si:MeSi ratio. On the one hand, changing the Si:Al ratio had a marked impact on hydrophilicity, as attested by water sorption measurements. On the other hand, unexpectedly, the introduction of methyl groups had no clear influence on sample hydrophilicity. Nevertheless, some of the methylated aluminosilicate catalysts markedly outperformed the purely inorganic catalysts and a commercial silica-alumina benchmark. While a direct influence of surface hydrophilicity or hydrophobicity could be excluded, characterization of acidity (IR-pyridine) revealed that these improved performances are correlated with a modification of the acidic properties in the hybrid catalysts caused by the presence of methyl groups. A decisive role of acidity in ethanol dehydration was confirmed by an experiment with delayed addition of the Al precursor in the NHSG synthesis. This led to a higher Al surface concentration, marked acid sites number increase, and better catalytic performance, even competing with HZSM-5 in terms of activity.

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Ethanol Dehydration over Hybrid Mesoporous Aluminosilicate Catalysts Obtained in One Pot by Non-Hydrolytic Sol-Gel

10.26434/chemrxiv.12354770.v1 ◽

2020 ◽

Author(s):

Ales Styskalik ◽

Imène Kordoghli ◽

Claude Poleunis ◽

Arnaud Delcorte ◽

Zdenek Moravec ◽

...

Keyword(s):

Catalyst Activity ◽

Sol Gel ◽

Acid Sites ◽

Silica Matrix ◽

Methyl Groups ◽

Ethanol Dehydration ◽

Alcohol Dehydration ◽

One Pot ◽

Surface Hydrophilicity ◽

Silica Alumina

Ethanol dehydration is effectively catalyzed by solid acids, such as HZSM-5, alumina, or silica-alumina. In these catalysts, the amount, nature, and strength of acid sites is believed to determine catalyst activity and stability. However, surface hydrophilicity or hydrophobicity can be suggested as another decisive catalyst property that can directly influence performance. For example, a more hydrophobic surface might be beneficial in repelling the co-product of the reaction, water. However, these aspects have been studied only scarcely in the context of alcohol dehydration. Here, a series of mesoporous hybrid aluminosilicate catalysts containing CH3Si groups was prepared in one pot by non-hydrolytic sol-gel (NHSG). The presence of the methyl groups was verified by IR, solid-state NMR, and ToF-SIMS. Aluminum is mostly incorporated in tetrahedral coordination in the hybrid silica matrix. Two parameters were varied: (i) the Si:Al ratio and (ii) the Si:MeSi ratio. On the one hand, changing the Si:Al ratio had a marked impact on hydrophilicity, as attested by water sorption measurements. On the other hand, unexpectedly, the introduction of methyl groups had no clear influence on sample hydrophilicity. Nevertheless, some of the methylated aluminosilicate catalysts markedly outperformed the purely inorganic catalysts and a commercial silica-alumina benchmark. While a direct influence of surface hydrophilicity or hydrophobicity could be excluded, characterization of acidity (IR-pyridine) revealed that these improved performances are correlated with a modification of the acidic properties in the hybrid catalysts caused by the presence of methyl groups. A decisive role of acidity in ethanol dehydration was confirmed by an experiment with delayed addition of the Al precursor in the NHSG synthesis. This led to a higher Al surface concentration, marked acid sites number increase, and better catalytic performance, even competing with HZSM-5 in terms of activity.

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Ag- and Cu-Promoted Mesoporous Ta-SiO2 Catalysts Prepared by Non-Hydrolytic Sol-Gel for the Conversion of Ethanol to Butadiene

10.26434/chemrxiv.9917000 ◽

2019 ◽

Author(s):

Denis Dochain ◽

Ales Styskalik ◽

Damien Debecker

Keyword(s):

Active Sites ◽

Sol Gel ◽

Relative Proportion ◽

Space Velocity ◽

Silica Matrix ◽

Small Contribution ◽

Average Pore ◽

Dehydration Reactions ◽

Bulk Chemical ◽

Metal Catalyzed

The direct catalytic conversion of bioethanol to butadiene, also known as the Lebedev process, is one of the most promising solution to replace the petro-based production of this important bulk chemical. Considering the intricate reaction mechanism – where a combination of acid-catalyzed dehydration reactions and metal-catalyzed dehydrogenation have to take place simultaneously – tailor-made bifunctional catalysts are required. We propose to use non-hydrolytic sol-gel (NHSG) chemistry to prepare mesoporous Ta-SiO2 materials which are further promoted by Ag via impregnation. An acetamide elimination route is presented, starting from silicon teraacetate and pentakis(dimethylamido)tantalum(V), in the presence of a pluronic surfactant. The catalysts display advantageous texture, with specific surface area in the 600-1000 m².g-1 range, large pore volume (0.6-.1.0 cm³.g-1), an average pore diameter of 4 nm and only a small contribution from micropores. Using an array of characterization techniques, we show that NHSG allows achieved a high degree of dispersion of tantalum, mainly incorporation as single sites in the silica matrix. The presence of these monomeric TaOx active sites is responsible for the much higher dehydration ability, as compared to the corresponding catalyst prepared by impregnation of Ta onto a pristine silica support. We attempt to optimize the butadiene yield by changing the relative proportion of Ta and Ag and by tuning the space velocity. We also demonstrate that Ag or Cu can be introduced directly in one step, during the NHSG process. Copper doping is shown to be much more efficient than silver to guide the reaction towards the production of butadiene.

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Non-Hydrolytic Sol-Gel Route to a Family of Hybrid Mesoporous Aluminosilicate Ethanol Dehydration Catalysts

10.26434/chemrxiv.13377212.v1 ◽

2020 ◽

Author(s):

Ales Styskalik ◽

Imène Kordoghli ◽

Claude Poleunis ◽

Arnaud Delcorte ◽

Denis Dochain ◽

...

Keyword(s):

Gas Phase ◽

Sol Gel ◽

Catalytic Performance ◽

Silica Matrix ◽

Ethanol Dehydration ◽

One Pot ◽

Water Contact ◽

Hybrid Silica ◽

Mesoporous Aluminosilicate ◽

Improved Performance

Organic-inorganic hybrid materials are nowadays intensely studied for potential applications in heterogeneous catalysis because their properties and catalytic behavior differ from pristine inorganic counterparts. The organic groups at the catalyst surface can modify not only its hydrophilicity, but also acidity, hydrothermal stability, porosity, etc. In some cases, such properties alteration leads to improved catalytic performance in terms of activity, selectivity, or stability. However, the choice of organic groups stays relatively narrow, as most reports focus on pendant methyl groups. Here, a series of mesoporous hybrid aluminosilicate materials containing various organic groups was prepared in one pot by non-hydrolytic sol-gel (NHSG). Both aromatic and aliphatic, pendant and bridging organic groups were incorporated. The presence of the organic groups in the bulk and at the outermost surface of the materials was verified by solid-state NMR and ToF-SIMS, respectively. Aluminum is mostly incorporated in tetrahedral coordination in the hybrid silica matrix. The organically modified mesoporous aluminosilicate samples were tested as catalysts in the gas phase ethanol dehydration (which relies on solid acids) and most of them outperformed the purely inorganic catalyst benchmark. While a direct influence of surface hydrophilicity or hydrophobicity (as probed by water sorption and water contact angle measurements) appeared unlikely, characterization of acidity (IR-pyridine) revealed that the improved performance for hybrid catalysts can be correlated with a modification of the acidic properties. In turn, acidity is determined by the quality of the dispersion of Al centers in the form of isolated sites in the hybrid silica matrix. All in all, this study establishes a "ranking" for a variety of organic groups in terms of their effect on gas-phase ethanol dehydration to ethylene; ethylene yield decreases in this order: bridging xylylene ≈ pendant methyl > pendant benzyl > bridging methylene ≈ inorganic benchmark (no organic groups) > bridging ethylene.

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