Non-hydrolytic sol–gel as a versatile route for the preparation of hybrid heterogeneous catalysts

Smeets, Valentin; Stýskalík, Aleš; Debecker, Damien P.

doi:10.1007/s10971-021-05486-1

Cited by 17 publications

(11 citation statements)

References 127 publications

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“…In such non‐hydrolytic sol‐gel (NHSG) route, water is replaced by organic molecules (alkoxide, alcohol, ether, etc.) as oxygen‐donors [229–233] . These conditions offer a better control over the condensation kinetics of the precursors (halide, alkoxide, acetylacetonate, etc.)…”

Section: Strategies To Improve Ti‐based Heterogeneous Epoxidation Catalystsmentioning

confidence: 99%

“…In NHSG methods (see also Section 3.3.1), water is absent from the synthesis medium, and the synthesis is carried out in organic conditions, with organic oxygen‐donors [213] . Due to the low tensile strength of the organic solvent, the liquid phase can be easily removed upon drying without impacting the pore network of the gel [232,233] . In these conditions, mesoporous xerogels are formed and the materials usually feature large pore volumes, even in the absence of sacrificial pore‐generating agents, simply owing to the liquid phase trapped in the gel [260] .…”

Section: Strategies To Improve Ti‐based Heterogeneous Epoxidation Catalystsmentioning

confidence: 99%

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Titanosilicate Epoxidation Catalysts: A Review of Challenges and Opportunities

2021

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Epoxidation reactions are tremendously important for modern chemistry, as they lead to series of highly useful bulk and fine chemicals, monomers, and intermediates for organic synthesis. Progress in epoxidation processes goes hand in hand with the advancement made in catalysis science. In this context, heterogeneous catalysts, and particularly Ti‐based formulations, are playing a central role and have seen tremendous developments over the past two decades, leveraging on advanced materials science. The aim of this review is to illustrate the various strategies of titanosilicate catalysts preparation that can lead to more versatile, more performant, and greener epoxidation processes. We successively cover (i) supported catalysts, obtained by the grafting of Ti species onto preformed silica supports, (ii) microporous crystalline titanosilicates (zeolites), and (iii) amorphous titanosilicates obtained by sol‐gel chemistry. For each category, with an emphasis on catalyst preparation, the challenges that have to be tackled to boost catalyst performance are highlighted. From that point, we present a critical review of the different approaches that have been proposed in the primary literature to tailor the properties that govern catalysts performance (activity, selectivity, stability, ease of handling). This is done by better controlling the nature of the active surface species, adapting particles size and shape, optimizing texture, modifying surface chemistry, etc. These lines of attack encompass molecular approaches for the grafting of well‐defined species, top‐down and bottom‐up synthesis of hierarchically porous zeolites, advanced sol‐gel routes potentially performed in non‐conventional media or coupled with original processing, preparation of self‐standing monoliths, etc. Future research directions are discussed with emphasis on the application scope of new catalytic materials and possible approaches to increase catalyst performance.

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Section: Strategies To Improve Ti‐based Heterogeneous Epoxidation Catalystsmentioning

confidence: 99%

Section: Strategies To Improve Ti‐based Heterogeneous Epoxidation Catalystsmentioning

confidence: 99%

Titanosilicate Epoxidation Catalysts: A Review of Challenges and Opportunities

2021

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“…Research aimed at identifying the active sites of molybdenum-based silica catalysts and understanding their mode of activation has intensified in recent years. ,,– What unambiguously emerges from the scientific literature is that the catalyst preparation methods leading to molybdenum-silicate metathesis catalysts have a tremendous impact on the level of performance that can be attained. Classical preparation methods mostly revolve around the impregnation of a Mo precursor onto a preformed support, followed by thermal treatments. ,– Several studies, however, have shown that alternative preparation methods (e.g., thermal spreading and flame spray pyrolysis) can lead to significantly more active catalysts. ,, Of particular interest are nonhydrolytic sol–gel (NHSG) approaches, which are known to give access to well-defined, porous, heterogeneous catalysts with homogeneously dispersed active sites for various catalytic reactions. , …”

Section: Introductionmentioning

confidence: 99%

Propylene Metathesis over Molybdenum Silicate Microspheres with Dispersed Active Sites

Skoda,

Zhu,

Hanulikova

et al. 2023

ACS Catal.

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In this work, we demonstrate that amorphous and porous molybdenum silicate microspheres are highly active catalysts for heterogeneous propylene metathesis. Homogeneous molybdenum silicate microspheres and aluminum-doped molybdenum silicate microspheres were synthesized via a nonaqueous condensation of a hybrid molybdenum biphenyldicarboxylatebased precursor solution with (3-aminopropyl)triethoxysilane. The as-prepared hybrid metallosilicate products were calcined at 500 °C to obtain amorphous and porous molybdenum silicate and aluminum-doped molybdenum silicate microspheres with highly dispersed molybdate species inserted into the silicate matrix. These catalysts contain mainly highly dispersed MoO x species, which possess high catalytic activity in heterogeneous propylene metathesis to ethylene and butene. Compared to conventional silica-supported MoO x catalysts prepared via incipient wetness impregnation (MoIWI), the microspheres with low Mo content (1.5−3.6 wt %) exhibited nearly 2 orders of magnitude higher steady-state propylene metathesis rates at 200 °C, approaching site time yields of 0.11 s −1 .

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“…However, most researchers have reported that the use of acidic catalysts is more effective than base catalysts. [9] Acids such as sulfuric acid, hydrochloric acid, and nitric acid are the most commonly used catalysts and hydrolysis is done in a very short time (in a few minutes). [10] However, using these acids is associated with problems such as the production of the by-products in the final product.…”

Section: Introductionmentioning

confidence: 99%

Preparation of Self‐Catalyzing Sols in the 40SiO₂ – 30FeO – 20FeO – 20CaO – 10Na₂O Glass System by Sol‐Gel Method

2023

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In this research, the self‐catalyzing sol method was used to prepare amorphous glass. In this method, as a result of the reaction between iron nitrate and ethanol, nitrous acid was synthesized. Nitrous acid reduced pH and acted as a catalyst ethanol oxidation to ethanoic acid. Different factors affect the preparation of self‐catalyzing sol and the amount of synthesized acid (aging time, temperature of sol preparation, and ratio of precursor to solvent). It was seen that the aging time had the greatest effect in reducing the pH of the sol. Ethanol oxidation was measured by gas chromatography (GC), and it was observed that approximately 95 % of ethanol was converted to ethanoic acid. The optimum glass was heat treated at different temperatures. Maghemite, hematite, and sodium calcium silicate phases were crystallized. The maximum saturation magnetization of the sample treated at 680 °C was 0.27 emu/g.

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Non-hydrolytic sol–gel as a versatile route for the preparation of hybrid heterogeneous catalysts

Cited by 17 publications

References 127 publications

Titanosilicate Epoxidation Catalysts: A Review of Challenges and Opportunities

Titanosilicate Epoxidation Catalysts: A Review of Challenges and Opportunities

Propylene Metathesis over Molybdenum Silicate Microspheres with Dispersed Active Sites

Preparation of Self‐Catalyzing Sols in the 40SiO₂ – 30FeO – 20FeO – 20CaO – 10Na₂O Glass System by Sol‐Gel Method

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Non-hydrolytic sol–gel as a versatile route for the preparation of hybrid heterogeneous catalysts

Cited by 17 publications

References 127 publications

Titanosilicate Epoxidation Catalysts: A Review of Challenges and Opportunities

Titanosilicate Epoxidation Catalysts: A Review of Challenges and Opportunities

Propylene Metathesis over Molybdenum Silicate Microspheres with Dispersed Active Sites

Preparation of Self‐Catalyzing Sols in the 40SiO2 – 30FeO – 20FeO – 20CaO – 10Na2O Glass System by Sol‐Gel Method

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Preparation of Self‐Catalyzing Sols in the 40SiO₂ – 30FeO – 20FeO – 20CaO – 10Na₂O Glass System by Sol‐Gel Method