Mechanistic insight to acidity effects of Ga/HZSM-5 on its activity for propane aromatization

RSC Advances ◽  
2015 ◽  
Vol 5 (112) ◽  
pp. 92222-92233 ◽  
Author(s):  
He Xiao ◽  
Junfeng Zhang ◽  
Peng Wang ◽  
Zhenzhou Zhang ◽  
Qingde Zhang ◽  
...  
Keyword(s):  
Synergistic Effect ◽  
Lewis Acidity ◽  
Brønsted Acidity ◽  
Brönsted Acidity ◽  
Mechanistic Insight ◽  
Propane Aromatization ◽  
Strong Lewis Acidity

Mechanistic insight to the synergistic effect between Brønsted acidity and strong Lewis acidity of Ga/HZSM-5 on propane aromatization activity.

scholarly journals Reactivity and Reusability of Mesoporous Alumina Nanoparticles Modified with Sulfuric Acid and Niobic Acid in the Alkylation of Resorcinol

2014 ◽  
Vol 4 (1) ◽  
Author(s):  
Zainab Ramli ◽  
Hadi Nur ◽  
Sheela Chandren
Keyword(s):  
Sulfuric Acid ◽  
High Surface ◽  
Mesoporous Alumina ◽  
Alumina Nanoparticles ◽  
Lewis Acidity ◽  
Methyl Tert Butyl Ether ◽  
Solid Catalyst ◽  
Brønsted Acidity ◽  
Brönsted Acidity ◽  
Niobic Acid

With the development of large molecule hydrocarbon processes, mesoporous alumina which possesses high surface area with narrow pore size distribution has received a great deal of attention. However, its acid properties lack Bronsted acidity and showed only Lewis acid sites, making it an inactive solid catalyst in the alkylation of resorcinol, a reaction which requires the usage of solid acid catalysts with both Bronsted and Lewis acidity. In this study, in order to introduce Bronsted acidity to mesoporous alumina, sulfuric acid (H2SO4) and niobic acid (Nb2O5.nH2O) are introduced to the alumina. The reactivity of mesoporous alumina nanoparticles (MAN), Nb2O5.nH2O/MAN and H2SO4/MAN were tested out on the alkylation of resorcinol with methyl tert-butyl ether. No product was obtained using pure MAN, while both H2SO4/MAN and Nb2O5.nH2O/MAN managed to produce butylated resorcinol. Mesoporous alumina nanoparticles incorporated with sulfuric acid produced a greater amount of dibutylated resorcinol, which theoretically is a better antioxidant compared to monobutylated resorcinol. The reusability of the H2SO4/MAN catalyst was also better as dibutylated product was still obtained even in the second use. This indicates that sulfuric acid has created a more stable and also higher strength of Bronsted acidity in alumina as compared to niobic acid.

Metal-free hydroxyl functionalized quaternary phosphine type ionic liquids polymer for cycloaddition of CO2 and epoxide

2021 ◽  
Author(s):  
Wuying Zhang ◽  
Qian He ◽  
Yaju Chen ◽  
Rongchang Luo ◽  
Xiantai Zhou ◽  
...  
Keyword(s):  
Ionic Liquids ◽  
Synergistic Effect ◽  
Hydroxyl Group ◽  
Brønsted Acidity ◽  
Metal Free ◽  
Brönsted Acidity ◽  
Free Hydroxyl ◽  
Alkylation Reactions

Quaternary phosphine type hypercrosslinked polymer catalysts were successfully fabricated with the Friedel-Crafts alkylation reactions, benefit from synergistic effect between the Brönsted acidity of the hydroxyl group and nucleophilic of the...

DFT Studies Provide Mechanistic Insight into Nickel-Catalyzed Cross-Coupling Involving Organoaluminum-Mediated C–O Bond Cleavage

Synlett ◽  
2017 ◽  
Vol 28 (19) ◽  
pp. 2565-2568 ◽  
Author(s):  
Chao Wang ◽  
Masanobu Uchiyama ◽  
Ze-Kun Yang
Keyword(s):  
Density Functional ◽  
Reaction Pathway ◽  
Bond Cleavage ◽  
Cross Coupling ◽  
Reductive Elimination ◽  
Lewis Acidity ◽  
Functional Theory ◽  
Mechanistic Insight ◽  
Insight Into ◽  
Strong Lewis Acidity

Density functional theory (DFT) calculations were performed to examine the reaction pathway of Ni-catalyzed cross-coupling with organoaluminum through C–O bond cleavage. The results indicate that the strong Lewis acidity of organoaluminums significantly facilitates the transmetalation step, but not the oxidative addition or reductive elimination step.

scholarly journals Synthesis and Properties of Magnetic Aryl-Imidazolium Ionic Liquids with Dual Brønsted/Lewis Acidity

Materials ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 2539 ◽  
Author(s):  
Jui-Cheng Chang ◽  
Che-Hsuan Yang ◽  
I-Wen Sun ◽  
Wen-Yueh Ho ◽  
Tzi-Yi Wu
Keyword(s):  
Ionic Liquids ◽  
Lewis Acidity ◽  
Brønsted Acidity ◽  
Good Thermal Stability ◽  
Magnetic Ionic Liquids ◽  
Good Solubility ◽  
Brönsted Acidity ◽  
Lewis Acidic Sites ◽  
Acidic Sites ◽  
Electron Withdrawing Group

A series of unique tunable aryl-imidazolium magnetic ionic liquids (MILs) with dual acidity that contain both Brønsted and Lewis acidic sites (abbreviated as B-L MILs) were synthesized and characterized using nuclear magnetic resonance and mass spectrometry. Physical properties, such as thermal properties, magnetic susceptibility, and Brønsted and Lewis acidity, were measured. These properties were found to depend on the cation structure. These B-L MILs had good solubility in many organic solvents, good thermal stability, and low melting points, and exhibited magnet-like behavior. For these B-L MILs, the Brønsted acidity was measured using ultraviolet-visible (UV-Vis), and the Lewis acidity was measured using Fourier transform infrared spectroscopy (FTIR). The results showed that B-L MILs with an electron-withdrawing group in the aryl-imidazolium moiety had higher Brønsted acidity, whereas those with an electron-donating group had higher Lewis acidity. This type of ionic liquid, with both Brønsted and Lewis acidic sites, is expected to be a useful solvent and catalyst for organic reactions.

scholarly journals Dehydration of ethanol over zeolites, silica alumina and alumina: Lewis acidity, Brønsted acidity and confinement effects

2015 ◽  
Vol 493 ◽  
pp. 77-89 ◽  
Author(s):  
Thanh Khoa Phung ◽  
Loriana Proietti Hernández ◽  
Alberto Lagazzo ◽  
Guido Busca
Keyword(s):  
Lewis Acidity ◽  
Confinement Effects ◽  
Brønsted Acidity ◽  
Brönsted Acidity ◽  
Silica Alumina

scholarly journals On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity

2021 ◽  
Author(s):  
Manoj Ravi ◽  
Vitaly L. Sushkevich ◽  
Jeroen A. van Bokhoven
Keyword(s):  
Lewis Acid ◽  
Acid Sites ◽  
Lewis Acidity ◽  
Brønsted Acidity ◽  
Lewis Acid Sites ◽  
Brönsted Acidity ◽  
Brønsted And Lewis Acidity

Framework-associated aluminum is demonstrated to facilitate a reversible switch between Lewis and Brønsted acidity in zeolites with the Lewis acid sites preferentially populating the side-pockets in the case of mordenite.

Proton Acidity and Proton Mobility in ECR-40, a Silicoaluminophosphate That Violates Löwenstein’s Rule

2019 ◽  
Author(s):  
Michael Fischer
Keyword(s):  
Density Functional ◽  
Water Clusters ◽  
Computational Study ◽  
Acid Catalyst ◽  
Ab Initio Molecular Dynamics ◽  
Brønsted Acidity ◽  
Hydrothermal Route ◽  
Proton Mobility ◽  
Brönsted Acidity ◽  
A Minor

<p>The silicoaluminophosphate zeotype ECR-40, which has the MEI topology, contains linkages of AlO<sub>4</sub> tetrahedra via a common oxygen atom, thereby violating the famous “Löwenstein’s rule”. Due to the proven existence of Al-O-Al linkages in this material, it constitutes an ideal model system to study the acidity and mobility of protons associated with such unusual linkages. In addition, their properties can be directly compared to those of protons associated with more common Si-O-Al linkages, which are also present in ECR-40. In this work, static density functional theory (DFT) calculations including a dispersion correction were employed to study the preferred proton sites as well as the Brønsted acidity of the framework protons, followed by DFT-based ab-initio molecular dynamics (AIMD) to investigate the proton mobility in guest-free and hydrated ECR-40. Initially, two different proton arrangements were compared, one containing both H[O6] protons associated with Al-O-Al linkages and H[O10] protons at Si-O-Al linkages, the other one containing only H[O10] protons. The former model was found to be thermodynamically favoured, as a removal of protons from the Al-O-Al linkages causes a local accumulation of negative charge. Calculations of the deprotonation energy showed a moderately higher Brønsted acidity of the H[O10] protons, at variance with previous empirical explanations, which attributed the exceptional performance of ECR-40 as acid catalyst to the presence of Al‑O‑Al linkages. The AIMD simulations (<i>T</i> = 298 K) delivered no appreciable proton mobility for guest-free ECR-40 and for low levels of hydration (one H<sub>2</sub>O per framework proton). Under saturation conditions, framework deprotonation occurred, leading to the formation of protonated water clusters in the pores. Pronounced differences between the two types of framework protons were observed: While the H[O10] protons were always removed from the Si-O-Al linkages, the Al-O-Al linkages remained mostly protonated, but deprotonation did occur to a minor extent. The observation of a degree of framework deprotonation of Al-O-Al linkages differs from the findings reported in a recent computational study of hydrated aluminosilicate zeolites with such linkages (Heard et al., <i>Chem. Sci.</i> <b>2019</b>, <i>10</i>, 5705), pointing to an influence of the overall framework composition. Further inspection of the AIMD results showed that a coordination of water molecules to framework Al atoms occurred in many cases, especially in the vicinity of the Al-O-Al linkages, sometimes resulting in a pronounced modification of the linkages through additional bridging oxygen atoms. Given the changes in the local structure, it can be expected that such modified linkages are especially prone to break upon dehydration. Thus, in addition to elucidating the deprotonation behaviour of protons associated with different types of linkages, the calculations also provide insights into possible reasons for the instability of Al-O-Al linkages, clarifying why Löwenstein’s rule is mostly obeyed in materials that are formed via a hydrothermal route.</p>

scholarly journals Theoretical Study of Zirconium Isomorphous Substitution into Zeolite Frameworks

Molecules ◽  
2019 ◽  
Vol 24 (24) ◽  
pp. 4466
Author(s):  
Duichun Li ◽  
Bin Xing ◽  
Baojun Wang ◽  
Ruifeng Li
Keyword(s):  
Acid Site ◽  
Density Functional ◽  
Theoretical Study ◽  
Atomic Radius ◽  
Acid Sites ◽  
Isomorphous Substitution ◽  
Dispersion Correction ◽  
Brønsted Acidity ◽  
Functional Theory ◽  
Brönsted Acidity

Systematic periodic density functional theory computations including dispersion correction (DFT-D) were carried out to determine the preferred location site of Zr atoms in sodalite (SOD) and CHA-type topology frameworks, including alumino-phosphate-34 (AlPO-34) and silico-alumino-phosphate-34 (SAPO-34), and to determine the relative stability and Brönsted acidity of Zr-substituted forms of SOD, AlPO-34, and SAPO-34. Mono and multiple Zr atom substitutions were considered. The Zr substitution causes obvious structural distortion because of the larger atomic radius of Zr than that of Si, however, Zr-substituted forms of zeolites are found to be more stable than pristine zeolites. Our results demonstrate that in the most stable configurations, the preferred favorable substitutions of Zr in substituted SOD have Zr located at the neighboring sites of the Al-substituted site. However, in the AlPO-34 and SAPO-34 frameworks, the Zr atoms are more easily distributed in a dispersed form, rather than being centralized. Brönsted acidity of substituted zeolites strongly depends on Zr content. For SOD, substitution of Zr atoms reduces Brönsted acidity. However, for Zr-substituted forms of AlPO-34 and SAPO-34, Brönsted acidity of the Zr-O(H)-Al acid sites are, at first, reduced and, then, the presence of Zr atoms substantially increased Brönsted acidity of the Zr-O(H)-Al acid site. The results in the SAPO-34-Zr indicate that more Zr atoms substantially increase Brönsted acidity of the Si-O(H)-Al acid site. It is suggested that substituted heteroatoms play an important role in regulating and controlling structural stability and Brönsted acidity of zeolites.

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