Kinetics and mechanisms of alcohol dehydration pathways on alumina materials

2016 ◽  
Vol 6 (17) ◽  
pp. 6667-6678 ◽  
Author(s):  
Minje Kang ◽  
Aditya Bhan
Keyword(s):  
Active Sites ◽  
Ethanol Dehydration ◽  
Alcohol Dehydration ◽  
Rate Expression

Ethanol dehydration on α,γ,η-alumina mechanistically and kinetically described by the same rate expression implicating similar active sites on all alumina materials.

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

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

<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>

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

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

<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>

scholarly journals High field 27Al MAS NMR and TPD studies of active sites in ethanol dehydration using thermally treated transitional aluminas as catalysts

2016 ◽  
Vol 336 ◽  
pp. 85-93 ◽  
Author(s):  
Jian Zhi Hu ◽  
Suochang Xu ◽  
Ja Hun Kwak ◽  
Mary Y. Hu ◽  
Chuan Wan ◽  
...  
Keyword(s):  
High Field ◽  
Active Sites ◽  
Mas Nmr ◽  
Ethanol Dehydration ◽  
27Al Mas Nmr ◽  
Thermally Treated

Characterization of the active sites on the surface of Al2O3 ethanol dehydration catalysts by EPR using spin probes

2011 ◽  
Vol 278 (1) ◽  
pp. 71-77 ◽  
Author(s):  
Ruslan A. Zotov ◽  
Viktor V. Molchanov ◽  
Alexander M. Volodin ◽  
Alexander F. Bedilo
Keyword(s):  
Active Sites ◽  
Spin Probes ◽  
Ethanol Dehydration

scholarly journals Role of Lewis Acids of MIL-101(Cr) in the Upgrading of Ethanol to n-Butanol

2020 ◽  
Vol 2 ◽  
Author(s):  
Jian Zhou ◽  
Yuqin Tong ◽  
Yaohui He ◽  
Pengxiang Tu ◽  
Bing Xue ◽  
...  
Keyword(s):  
Particle Size ◽  
Linear Relationship ◽  
Diethyl Ether ◽  
Lewis Acids ◽  
Active Sites ◽  
Lewis Acidity ◽  
Ethanol Dehydration ◽  
Basic Sites

The upgrading of bioethanol to n-butanol has recently been a focus of considerable attention due to the advantages of n-butanol over bioethanol as a sustainable fuel. The efficiency of this reaction is highly dependent on the development of catalysts, where understanding how catalysts perform is essential. However, traditional catalysts are normally composed of several kinds of active sites that work together synergistically in reactions, making it challenging to identify the role that individual active sites play. Herein, we synthesized three chromium-based MOFs ((MIL-101(Cr), where MIL stands for Matériaux Institut Lavoisier) with different Lewis acidities but without any basic sites. The linear relationship between Lewis acidities and their dehydration and condensation abilities suggests that there is a competition between the ethanol dehydration to diethyl ether and acetaldehyde condensation on Lewis acids. Upon the introduction of Pd, the Lewis acidity also dominates the particle size of Pd and then the dehydrogenation and hydrogenating abilities of catalysts.

Ultrastructure of Some Planktonic Formainifera

1974 ◽  
Vol 32 ◽  
pp. 190-191
Author(s):  
William H. Zucker
Keyword(s):  
Cell Biology ◽  
Water Mass ◽  
Planktonic Foraminifera ◽  
Uranyl Acetate ◽  
Ethanol Dehydration ◽  
Globigerinoides Ruber ◽  
Light Microscope Level ◽  
Globigerina Bulloides ◽  
Glutaraldehyde Solution ◽  
Diamond Knife

Planktonic foraminifera are widely-distributed and abundant zooplankters. They are significant as water mass indicators and provide evidence of paleotemperatures and events which occurred during Pleistocene glaciation. In spite of their ecological and paleological significance, little is known of their cell biology. There are few cytological studies of these organisms at the light microscope level and some recent reports of their ultrastructure.Specimens of Globigerinoides ruber, Globigerina bulloides, Globigerinoides conglobatus and Globigerinita glutinata were collected in Bermuda waters and fixed in a cold cacodylate-buffered 6% glutaraldehyde solution for two hours. They were then rinsed, post-fixed in Palade's fluid, rinsed again and stained with uranyl acetate. This was followed by graded ethanol dehydration, during which they were identified and picked clean of debris. The specimens were finally embedded in Epon 812 by placing each organism in a separate BEEM capsule. After sectioning with a diamond knife, stained sections were viewed in a Philips 200 electron microscope.

The significance of SEM in the diagnosis of haematopoietic malignancies

1978 ◽  
Vol 36 (2) ◽  
pp. 314-315
Author(s):  
Etienne de Harven ◽  
Nina Lampen
Keyword(s):  
Room Temperature ◽  
Culture Medium ◽  
Cell Attachment ◽  
Ethanol Dehydration ◽  
Moist Chamber ◽  
Efficient Alternative ◽  
Mononuclear Leucocytes ◽  
Fast Quenching ◽  
Freeze Dryer ◽  
Scanning Electron

Samples of heparinized blood, or bone marrow aspirates, or cell suspensions prepared from biopsied tissues (nodes, spleen, etc. ) are routinely prepared, after Ficoll-Hypaque concentration of the mononuclear leucocytes, for scanning electron microscopy. One drop of the cell suspension is placed in a moist chamber on a poly-l-lysine pretreated plastic coverslip (Mazia et al., J. Cell Biol. 66:198-199, 1975) and fifteen minutes allowed for cell attachment. Fixation, started in 2. 5% glutaraldehyde in culture medium at room temperature for 30 minutes, is continued in the same fixative at 4°C overnight or longer. Ethanol dehydration is immediately followed by drying at the critical point of CO2 or of Freon 13. An efficient alternative method for ethanol dehydrated cells is to dry the cells at low temperature (-75°C) under vacuum (10-2 Torr) for 30 minutes in an Edwards-Pearse freeze-dryer (de Harven et al., SEM/IITRI/1977, 519-524). This is preceded by fast quenching in supercooled ethanol (between -90 and -100°C).

What catalysis needs from the electron microscopist

1988 ◽  
Vol 46 ◽  
pp. 694-695
Author(s):  
Alexis T. Bell
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Catalyst Deactivation ◽  
Surface Composition ◽  
Internal Surface ◽  
Active Phase ◽  
Atomic Scale ◽  
Metal Catalyst ◽  
Internal Surface Area ◽  
Porous Support

Heterogeneous catalysts, used in industry for the production of fuels and chemicals, are microporous solids characterized by a high internal surface area. The catalyticly active sites may occur at the surface of the bulk solid or of small crystallites deposited on a porous support. An example of the former case would be a zeolite, and of the latter, a supported metal catalyst. Since the activity and selectivity of a catalyst are known to be a function of surface composition and structure, it is highly desirable to characterize catalyst surfaces with atomic scale resolution. Where the active phase is dispersed on a support, it is also important to know the dispersion of the deposited phase, as well as its structural and compositional uniformity, the latter characteristics being particularly important in the case of multicomponent catalysts. Knowledge of the pore size and shape is also important, since these can influence the transport of reactants and products through a catalyst and the dynamics of catalyst deactivation.

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