In-situ construction and catalytic property of highly exposed Lewis acidity on hierarchical Zr-zeolite assisted by K+ cation

2021 ◽  
pp. 110898
Author(s):  
Yun Yang ◽  
Dan Zhou ◽  
Huaxin Zhang ◽  
Binyi Yin ◽  
Qingrui Liu ◽  
...  
Keyword(s):  
Catalytic Property ◽  
Lewis Acidity

scholarly journals Determination of the Lewis acidity of amide–AlCl3 based ionic liquid analogues by combined in situ IR titration and NMR methods

RSC Advances ◽  
2018 ◽  
Vol 8 (24) ◽  
pp. 13248-13252 ◽  
Author(s):  
Pengcheng Hu ◽  
Wei Jiang ◽  
Lijuan Zhong ◽  
Shu-Feng Zhou
Keyword(s):  
Ionic Liquid ◽  
Lewis Acidity ◽  
Nmr Analysis ◽  
In Situ Ir ◽  
Nmr Methods

The Lewis acidic strength and amount of amide–AlCl3 IL analogues are determined by the combination of in situ IR titration and NMR analysis.

Synergetic effects of Cu-Zn bimetallic ions exchanged in NaX on acid sites of M(x)X zeolites (M = Cu2+ and/or Zn2+, x = level of exchange). An in situ FTIR study using pyridine adsorption/desorption

2019 ◽  
Vol 107 (3) ◽  
pp. 304
Author(s):  
Habib Hammoudi ◽  
Souhila Bendenia ◽  
Isabelle Batonneau-Gener ◽  
Jean-dominique Comparot ◽  
Kheira Marouf-Khelifa ◽  
...  
Keyword(s):  
Synergetic Effect ◽  
Nitrogen Adsorption ◽  
Acid Sites ◽  
Lewis Acidity ◽  
Pyridine Adsorption ◽  
In Situ Ftir ◽  
Desorption Temperature ◽  
X Zeolites ◽  
Adsorption Desorption

X zeolites were prepared by ion-exchange with Cu2+ and/or Zn2+ cations, at different concentrations of the exchange solution, and characterized by thermal analysis and nitrogen adsorption. The acidity of the samples was investigated by pyridine adsorption–desorption followed by in situ Fourier transform infrared (FTIR) spectroscopy. Desorption was carried out at 150, 250 and 350 °C. The objective is to estimate the nature and concentration of acid sites. A comparison between the binary (Cu(x)X, Zn(x)X) and ternary (CuZn(x)X) exchanges was also established (x = level of exchange) through the Cu(43)X, Zn(48)X and CuZn(50)X samples. Lewis acidity decreases overall with desorption temperature and the level of exchange. As the latter increases, there is a conversion of some Lewis sites into those of Brønsted during thermal treatment. In return, the concentration of Brønsted sites increases with the degree of exchange. The Brønsted acidity of CuZn(50)X at 350 °C is more important than the sum of those of Cu(43)X and Zn(48)X with respectively values of 73, 32 and 15 μmol g−1. Besides, the concentration of Brønsted sites for CuZn(50)X increases with desorption temperature. These features indicate the presence of a synergetic effect amplifying the strength of these sites when Cu2+ and Zn2+ cations compete for the occupancy of sites distributed in zeolite cavities.

In situ determination of Brønsted/Lewis acidity on cation-exchanged clay mineral surfaces by ATR-IR

Clay Minerals ◽  
1996 ◽  
Vol 31 (4) ◽  
pp. 513-522 ◽  
Author(s):  
J. Billingham ◽  
C. Breen ◽  
J. Yarwood
Keyword(s):  
Acid Sites ◽  
Lewis Acidity ◽  
Attenuated Total Reflectance ◽  
Mineral Surfaces ◽  
Lewis Acid Sites ◽  
Absorption Bands ◽  
Total Reflectance ◽  
Liquid Benzene

AbstractAttenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy has been used to determine the nature of acid sites present in Na+-, Ni2+- and Al3+-exchanged montmorillonite using the diagnostic base, pyridine. The pyridine additions were performed in situ at 25°C in the presence of liquid benzene or deuterated 1,4-dioxan to ascertain whether the acidity profile was influenced by the presence of either the non-polar or oxygenated solvent. Pyridine treated Ni2+-montmorillonite exhibited absorption bands characteristic of Lewis bound base in both benzene and deuterated 1,4-dioxan indicating that the Lewis acid sites were present at low temperature and were accessible in both solvents. The presence of a strong 1537 cm−1 band in pyridine-saturated Al3+-montmorillonite confirmed that this clay acted as a Brønsted acid in benzene. However, this diagnostic band was significantly reduced in the presence of deuterated 1,4-dioxan.

Sulphur reduction in fluid catalytic cracking using a kaolin in situ crystallization catalyst modified with vanadium

Clay Minerals ◽  
2009 ◽  
Vol 44 (3) ◽  
pp. 281-288 ◽  
Author(s):  
Ya-Li Dai ◽  
Shu-Qin Zheng ◽  
Dong Qian
Keyword(s):  
Catalytic Cracking ◽  
Comprehensive Evaluation ◽  
Catalyst Activity ◽  
Reduction Rate ◽  
Liquid Product ◽  
Fluid Catalytic Cracking ◽  
Lewis Acidity ◽  
Sulphur Reduction ◽  
In Situ Crystallization

AbstractSulphur reduction catalysts represent a viable option for S reduction in the fluid catalytic cracking (FCC) process. In this paper, a kaolin in situ crystallization catalyst was modified with vanadium and evaluated in a fixed fluid bed (FFB) reactor. The relation between the acidity of the catalyst, the S reduction rate and the catalyst activity is discussed. The results show that increasing weak Lewis acid acidity favours S reduction in the FCC process. Increasing the V content enhances the weak Lewis acidity, so causing the S reduction rate to increase. The kaolin in situ crystallization catalyst modified with 0.6 wt.% of V leads to a 34.5% reduction in the S content of the liquid product. Comprehensive evaluation of the FFB results and the S reduction ability indicates that the catalyst modified with 0.45 wt.% V provided the best performance.

scholarly journals Stable Performance of Supported PdOx Catalyst on Mesoporous Silica-Alumina of Water Tolerance for Methane Combustion under Wet Conditions

Catalysts ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 670
Author(s):  
Minseok Kim ◽  
Suhyun Lim ◽  
Chansong Kim ◽  
Chae-Ho Shin ◽  
Joon Hyun Baik ◽  
...  
Keyword(s):  
Mesoporous Silica ◽  
Particle Surface ◽  
Textural Properties ◽  
Methane Combustion ◽  
Lewis Acidity ◽  
Water Tolerance ◽  
Silica Alumina ◽  
Stable Performance ◽  
Temperature Programmed

In methane combustion, water tolerance of Pd-based catalysts is quite critical for stable performance, because water is produced in situ and a water-containing feed is used under real conditions. Herein, water-tolerant mesoporous silica-alumina (H-MSA) was prepared by solvent deficient precipitation (SDP) using triethoxy(octyl)silane (TEOOS) and aluminum isopropoxide (AIP). The H-MSA was more tolerant to water than γ-alumina, mesoporous alumina (MA), and mesoporous silica-alumina (MSA) synthesized by using tetraethyl orthosilicate (TEOS), because of the silica present on the external particle surface. Moreover, it exhibited better textural properties, leading to higher dispersion of PdOx. The PdOx catalyst supported on H-MSA was quite durable in repeated temperature-programmed cycles and isothermal tests in the presence of water vapor, compared to the reference PdOx catalysts. The measured stability was attributed to the water tolerance, weak Lewis acidity, and penta-coordinated Al species of the H-MSA support, which was preferentially imparted when TEOOS was added for substitution of 5 mol% AIP for the synthesis of H-MSA. Therefore, the SDP method employed herein is useful in endowing supported PdOx catalysts with the water tolerance necessary for stable methane combustion performance under wet conditions.

scholarly journals A General Approach to Deboronative Radical Chain Reaction with Pinacol Alkylboronic Esters

2020 ◽  
Author(s):  
Emy André-Joyaux ◽  
Andrey Kuzovlev ◽  
Nicholas D. C. Tappin ◽  
Philippe Renaud
Keyword(s):  
Coupling Reaction ◽  
Lewis Acidity ◽  
One Pot ◽  
Radical Chain ◽  
Boronic Esters ◽  
Boron Chemistry ◽  
Substoichiometric Amount ◽  
Radical Traps ◽  
Radical Chain Reaction

The generation of carbon-centered radicals from air-sensitive organoboron compounds via nucleohomolytic substitution at boron is one of the most general methods to generate non-functionalized and functionalized radicals. Due to their reduced Lewis acidity, the very popular, air-stable, and readily available alkylboronic pinacol esters are not suitable substrates for this process. Herein, is reported their <i>in situ</i> conversion to alkylboronic catechol esters by boron-transesterification with a substoichiometric amount of catechol methyl borate (MeO–Bcat) telescoped onto a wide array of radical chain processes. This simple one-pot, radical-chain, deboronative protocol allows for the conversion of pinacol boronic esters into iodides, bromides, chlorides, and thioethers. The process is also suitable the formation of nitriles and allylated compounds via C–C bond formation using sulfonyl radical traps. Finally, a particularly mild protocol for the protodeboronation of pinacol boronic esters is given. The power of combining radical and classical boron chemistry, is illustrated with a highly modular 5-membered ring formation using a combination of a three-component coupling reaction and a protodeboronative cyclization.

Template-induced in situ dispersion of enhanced basic-sites on sponge-like mesoporous silica and its improved catalytic property

RSC Advances ◽  
2016 ◽  
Vol 6 (94) ◽  
pp. 91968-91980 ◽  
Author(s):  
Fu Yang ◽  
Bangbang Wang ◽  
Shijian Zhou ◽  
Xiaoning Yang ◽  
Yan Kong
Keyword(s):  
Mesoporous Silica ◽  
Catalytic Property ◽  
Reaction Temperature ◽  
Solid Base ◽  
Basic Sites

Well-dispersed and enhanced CaO solid base were directly formed on sponge-like mesoporous silica, improved activity occurred at a lower reaction temperature.

scholarly journals Low-Temperature IR Spectroscopy of CO Adsorption on Calcined Supported CeO2: Probing Adsorbed Species and Adsorbing Sites

1997 ◽  
Vol 15 (5) ◽  
pp. 377-389 ◽  
Author(s):  
Gamal A.H. Mekhemer ◽  
Mohamed I. Zaki
Keyword(s):  
Ir Spectroscopy ◽  
Co Adsorption ◽  
Acid Sites ◽  
Ex Situ ◽  
Lewis Acidity ◽  
Adsorbed Species ◽  
Support Materials ◽  
Defect Sites ◽  
The Individual

Carbon monoxide adsorption on ceria dispersed on silica (CeSi) and alumina (CeAl) at 300–80 K was observed by in-situ IR spectroscopy. For control purposes, CO adsorption was also observed on unsupported CeO2 and the individual support materials (SiO2 and Al2O3). The adsorbents were prepared ex situ by heating at 770 K (3 h) in air, and pretreated in situ by heating at 720 K (1 h) in oxygen and then in vacuum. The results, as disclosed by v(OH) (3900–3300 cm−1) and v(CO) (2250–2050 cm−1) spectra taken before and after CO adsorption, reveal that CO adsorbs on all of the test adsorbents at temperatures < 300 K only. The resulting adsorbed species include CO coordinated to Lewis acid sites (on all of the adsorbents, but not SiO2), hydrogen-bonded CO (on all of the adsorbents, but not CeO2) and CO bound to electron-rich defect sites (only on unsupported CeO2). It is concluded that the dispersion of ceria, particularly on alumina, is associated with a considerable development of the Lewis acidity of Ce4+ sites.

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