Mildly acidic aluminosilicate catalysts for stable performance in ethanol dehydration

Stýskalík, Aleš; Vykoukal, Vít; Fusaro, Luca; Aprile, Carmela; Debecker, Damien P.

doi:10.1016/j.apcatb.2020.118926

Cited by 33 publications

(26 citation statements)

References 77 publications

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“…However, the B/L ratio drops in all cases upon evacuation, showing that Brønsted acid sites display lower strength in comparison to Lewis acid sites. Similar characteristicswere observed for purely inorganic aluminosilicates prepared by NHSG and calcined at 500 °C [37]. Comparison with commercial silica-alumina (amorphous) and zeolite HZSM-5 enabled to describe the acidity of the samples as being intermediate between commercial silica-alumina (mostly weak Lewis acid sites) and HZSM-5 (mostly strong Brønsted acid sites) thanks to a good homogeneity…”

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confidence: 63%

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

Stýskalík¹,

Kordoghli²,

Poleunis³

et al. 2020

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<p>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 CH<sub>3</sub>Si 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.</p>

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confidence: 63%

“…Interestingly, the aluminosilicates with low Al loading (15Si-1MeSi-0.25Al and 15Si-1MeSi-0.5Al) displayed very sharp signal around 0 ppm indicating presence of some mobile octahedrally coordinated Al species. These were tentatively attributed to loosely bound surfaceAl moieties with their coordination sphere filled with water molecules [37].…”

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confidence: 99%

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

Stýskalík¹,

Kordoghli²,

Poleunis³

et al. 2020

Preprint

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“…NHSG is known to produce mixed metal oxides with good textural properties (even without requiring the use of a sacrificial templating agent). [24][25][26] Here, the synthetic procedure is similar to the protocol typically proposed for purely inorganic metallosilicates [33][34][35][36][37], but including a methylated silicon precursor (methyltrichlorosilane). [7,38] Also, the calcination temperature was decreased from 500 °C to 300 °C in order to prevent organic groups oxidation in hybrid materials.…”

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confidence: 99%

Hybrid mesoporous aluminosilicate catalysts obtained by non-hydrolytic sol–gel for ethanol dehydration

et al. 2020

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“…Finally, the selectivity improvement for p_Me, p_PhCH2 and b_Xy might be explained by the marked lowering the B/L ratio in the case of the hybrid samples: catalysts with more abundant strong Lewis acid sites have been shown to produce ethylene with higher selectivity. 12,38,54,58 200 To confirm that the organic groups presence (hydrophilicity/hydrophobicity) had only negligible direct effect on catalytic performance, p_PhCH2 was calcined at 500 °C in order to completely remove organic groups and the resulting catalyst (p_PhCH2-500) was tested again in ethanol dehydration. As a reference, 16Si-1Al was also re-calcined and re-tested (compare samples p_PhCH2-500 and 16Si-1Al-500).…”

Section: Resultsmentioning

confidence: 99%

“…8,[34][35][36][37] In the specific case of gas-phase ethanol dehydration to ethylene, we have shown two important factors influencing strongly the behavior of methylated metallosilicates: (i) the hydrothermal stability of Si-C bonds (which is unsatisfactory if aromatic organic groups are directly bound to Si atoms) 27 and (ii) the number, nature, and strength of acid sites. 12,38 On the other hand, studying a series of methylated aluminosilicate materials, a direct influence of hydrophobicity on the catalytic performance was not demonstrated. 12 Herein we report on a series of hybrid aluminosilicates prepared by NHSG, in which the organic groups attached to the inorganic matrices were varied: bridging and terminal, aliphatic and aromatic groups were incorporated.…”

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confidence: 99%

Non-hydrolytic sol–gel route to a family of hybrid mesoporous aluminosilicate ethanol dehydration catalysts

et al. 2021

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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 nonhydrolytic 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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Mildly acidic aluminosilicate catalysts for stable performance in ethanol dehydration

Cited by 33 publications

References 77 publications

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

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

Hybrid mesoporous aluminosilicate catalysts obtained by non-hydrolytic sol–gel for ethanol dehydration

Non-hydrolytic sol–gel route to a family of hybrid mesoporous aluminosilicate ethanol dehydration catalysts

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