Tuning Brønsted Acid Strength by Altering Site Proximity in CHA Framework Zeolites

ACS Catalysis ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 7842-7860 ◽  
Author(s):  
Steven Nystrom ◽  
Alexander Hoffman ◽  
David Hibbitts
Keyword(s):  
Acid Strength ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Brönsted Acid

Correlation between Brønsted Acid Strength and Local Structure in Zeolites

2009 ◽  
Vol 113 (44) ◽  
pp. 19208-19217 ◽  
Author(s):  
Naonobu Katada ◽  
Katsuki Suzuki ◽  
Takayuki Noda ◽  
German Sastre ◽  
Miki Niwa
Keyword(s):  
Local Structure ◽  
Acid Strength ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Brönsted Acid

An ONIOM study of the distribution of skeletal aluminum and Brønsted acidity in ZSM-48 zeolite

2014 ◽  
Vol 13 (02) ◽  
pp. 1450019 ◽  
Author(s):  
Rui Liu ◽  
Jie Zhang ◽  
Xiuliang Sun ◽  
Chongpin Huang ◽  
Biaohua Chen
Keyword(s):  
Density Functional ◽  
Acid Sites ◽  
Acid Strength ◽  
Molar Ratio ◽  
Am1 Method ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Al Substitution ◽  
Brönsted Acid ◽  
Stretching Vibration

A density functional theory (DFT) study was performed on distribution of skeletal aluminum and Brønsted acid (B-acid) sites as well as the acid strength in ZSM-48 zeolite. The correlation between Si / Al molar ratio and the general acid strength was also investigated. The calculations were performed based on 51T and 90T cluster models by using two-layered ONIOM schemes (B3LYP/6-31G (d,p): AM1) method. The former 51T cluster is used for the calculation of single- Al substitution and the latter is for the multi- Al substitution study. The properties of Si / Al substitution energy, deprotonation energy, bridging hydroxyl stretching vibration frequency and adsorption energy for the probe molecule were calculated and used to measure Brønsted acid location and strength. As the result shows, T2 is the most readily to be replaced by Al and the Brønsted acids prefer to be formed at Al 2– O 7– Si 3 site. Al 2– O 6– Si 2 is the highest in Brønsted acid strength. Besides, the acid strength weakens with the decrease of Si / Al .

Use of pyridine as a probe for the determination, by IR spectroscopy, of the Brønsted acid strength of MIHNaY zeolites

1996 ◽  
Vol 92 (7) ◽  
pp. 1263-1266 ◽  
Author(s):  
Jean-Claude Lavalley ◽  
Rodolphe Anquetil ◽  
Jolanta Czyzniewska ◽  
Maria Ziolek
Keyword(s):  
Ir Spectroscopy ◽  
Acid Strength ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Brönsted Acid

Brønsted acid strength in US-Y: FTIR study of CO adsorption

1994 ◽  
Vol 90 (2) ◽  
pp. 383-386 ◽  
Author(s):  
Marina A. Makarova ◽  
Khalid M. Al-Ghefaili ◽  
John Dwyer
Keyword(s):  
Co Adsorption ◽  
Acid Strength ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Ftir Study ◽  
Brönsted Acid

Acid Strength Measurement of Zeolites by the TPD-IR Technique with Ammonia as Probe Molecule

2013 ◽  
Vol 475-476 ◽  
pp. 1270-1274
Author(s):  
Bin Wang ◽  
Ying Zhang ◽  
Fu Bo Gu ◽  
Min Zuo ◽  
Guang Sheng Guo
Keyword(s):  
Acid Sites ◽  
Acid Strength ◽  
Probe Molecule ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Brønsted Acid Sites ◽  
Hy Zeolite ◽  
Brönsted Acid ◽  
Brönsted Acid Sites ◽  
Bronsted Acid Sites

An improved TPD-IR technique was developed recently. By which means, acid properties of Brønsted acid sites on HY zeolite and SAPO-34 zeolite were studied by an advanced TPD-IR technique with ammonia as probe molecule. Desorption activation energy (DAE) of the probe molecule adsorbed on zeolite was used as a measure of the acid strength. The result indicates the Brønsted acid sites of HY Zeolite or SAPO-34 zeolite were divided into two types with the strength of DAE of ammonia 43.4KJ/mol, 24.4KJ/mol and 33.2KJ/mol, 20.5KJ/mol. It is concluded that HY zeolite has the stronger Brønsted acid sites than that of SAPO-34 zeolite.

scholarly journals Confinement effects and acid strength in zeolites

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Emanuele Grifoni ◽  
GiovanniMaria Piccini ◽  
Johannes A. Lercher ◽  
Vassiliki-Alexandra Glezakou ◽  
Roger Rousseau ◽  
...  
Keyword(s):  
Pore Size ◽  
Acid Sites ◽  
Acid Strength ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Brønsted Acid Sites ◽  
Hydronium Ions ◽  
Brönsted Acid ◽  
Brönsted Acid Sites ◽  
Bronsted Acid Sites

AbstractChemical reactivity and sorption in zeolites are coupled to confinement and—to a lesser extent—to the acid strength of Brønsted acid sites (BAS). In presence of water the zeolite Brønsted acid sites eventually convert into hydronium ions. The gradual transition from zeolite Brønsted acid sites to hydronium ions in zeolites of varying pore size is examined by ab initio molecular dynamics combined with enhanced sampling based on Well-Tempered Metadynamics and a recently developed set of collective variables. While at low water content (1–2 water/BAS) the acidic protons prefer to be shared between zeolites and water, higher water contents (n > 2) invariably lead to solvation of the protons within a localized water cluster adjacent to the BAS. At low water loadings the standard free energy of the formed complexes is dominated by enthalpy and is associated with the acid strength of the BAS and the space around the site. Conversely, the entropy increases linearly with the concentration of waters in the pores, favors proton solvation and is independent of the pore size/shape.

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