brønsted and lewis acid
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Synlett ◽  
2021 ◽  
Author(s):  
Benjamin List ◽  
Denis Höfler ◽  
Karl Kaupmees ◽  
Ivo Leito

We report the design and synthesis of a strong, chiral, enantiopure sulfoxide-based C–H acid. Single crystal X-ray analysis confirms the proposed structure and its absolute configuration. The new motif shows a high acidity and activity in Brønsted and Lewis acid catalyzed transformations. So far, only low enantioselectivities were achieved.


2021 ◽  
Vol 2124 (1) ◽  
pp. 012003
Author(s):  
V I Loganina ◽  
N N Laskov ◽  
G G Boldyrev

Abstract Information on the effect of thermal activation of silicate and aluminosilicate rocks used as a filler in dry building mixtures on their reactivity of interaction with lime binder is presented. The change in the distribution of acidic Bronsted and Lewis centers on the filler surface as a result of thermal activation is shown. It was found that the number of Bronsted and Lewis acid centers on the surface of fired clays exceeds the number of the same centers on the surface of unbaked clays. The number of adsorption centers at pKa from 0 to 7 and pKa> 13 on the surface of fired diatomite is 2.435 * 10-5 mol/g, and on the surface of unbaked diatomite -1.678 * 10−5 mol/g. The heat treatment of diatomite at low temperatures (2000C and 3000C) does not significantly affect the values of the compressive strength of the mortar. An increase in the firing temperature to 7000C leads to an increase in strength characteristics up to R = 4.38 MPa. However, the greatest effect is achieved when diatomite is fired at a temperature of t = 9000C. The value of the ultimate strength in compression was R = 5.1 MPa.


Author(s):  
Sorin Avramescu ◽  
Cristian D. Ene ◽  
Madalina Ciobanu ◽  
Josefine Schnee ◽  
François Devred ◽  
...  

Catalytic activity of TiO2, 2%Re-TiO2 and 10%Re-TiO2 in the conversion of carbohydrates into levulinic acid under autoclave conditions was evaluated. These materials were prepared by aerogel method and characterized by...


Author(s):  
Bo Tang ◽  
Shuang Li ◽  
Wei-Chao Song ◽  
Yan Li ◽  
En-Cui Yang

Upgrading of furfural to high value-added chemicals are currently an attractive and challenging route in biorefineries. Herein, hierarchically structured bifunctional Hf-Al-USY zeolite with balanced Brønsted and Lewis acid sites has...


Catalysts ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1331
Author(s):  
Guillaume Fleury ◽  
Maarten B. J. Roeffaers

Zeolites are widely used acid catalysts in research and in industrial processes. The catalytic performance of these materials is affected by the nature and concentration of Brønsted and Lewis acid sites. The balance between these types of active sites—and thus the activity and selectivity of the zeolite—can be altered by the introduction of metal species, e.g., by ion exchange. Although the acidic properties of zeolites are routinely characterized by bulk-scale techniques, this ensemble-averaged approach neglects the local variations in the material. Insights into the distribution of active sites at the single-particle level are thus critical to better understand the impact of post-synthetic modifications on the zeolite acidity. In this contribution, we spatially resolve Brønsted and Lewis acid sites in protonated and Zn-exchanged ZSM-5 crystals. To this end, the vibrational modes of pyridine chemisorbed on active sites are mapped with stimulated Raman scattering (SRS) microscopy. The SRS images reveal sharp inter- and intra-particle heterogeneities in the distribution of Lewis acid sites introduced upon ion exchange, ascribed to local variations in the Al content. Besides assessing the impact of Zn exchange on the active site distribution in ZSM-5 crystals, this approach enables uniquely to map the distribution of Lewis acid sites in catalysts at the single-particle level.


2020 ◽  
Vol 496 ◽  
pp. 111187 ◽  
Author(s):  
Zhenjie Yu ◽  
Hongli Tian ◽  
Kai Sun ◽  
Yuewen Shao ◽  
Lijun Zhang ◽  
...  

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