scholarly journals Operando Dual Beam FTIR Study of Hydroxyl Groups and Zn Species over Defective HZSM-5 Zeolite Supported Zinc Catalysts

Catalysts ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 100 ◽  
Author(s):  
Long Lin ◽  
Xiaotong Zhang ◽  
Ning He ◽  
Jiaxu Liu ◽  
Qin Xin ◽  
...  
Keyword(s):  
Strong Acid ◽  
Acid Sites ◽  
Weak Acid ◽  
Acid Strength ◽  
Bronsted Acid ◽  
Brønsted Acid Sites ◽  
Dual Beam ◽  
Brönsted Acid ◽  
Ft Ir ◽  
Brönsted Acid Sites

A series of defective ZSM-5 zeolites (~300 nm, SiO2/Al2O3 ratio of 55, 100, 480 and 950) were systematically studied by XRD, SEM, 29Si MAS NMR, argon physisorption, NH3-TPD and FT-IR technologies. The nature, the amount and the accessibility of the acid sites of defective ZSM-5 zeolites are greatly different from reported ZSM-5 zeolites with a perfect crystal structure. The Brønsted acid sites (Si(OH)Al) with strong acid strength and the Brønsted acid sites (hydroxyl nests) with weak acid strength co-existed over defective ZSM-5 zeolites, which leads to a unique catalytic function. Zn(C2H5)2 was grafted onto defective ZSM-5 zeolites through the chemical liquid deposition (CLD) method. Interestingly, FT-IR spectroscopic studies found that Zn(C2H5)2 was preferentially grafted on the hydroxyl nests with weak acid strength rather than the Si(OH)Al groups with strong acid strength over different defective ZSM-5 zeolites. In particular, home-built operando dual beam FTIR-MS was applied to study the catalytic performance of Zn species located in different sites of defective ZSM-5 zeolites under real n-hexane transformation conditions. Results show that Zn species grafted over hydroxyl nests obtain better dehydrogenative aromatization performance than Zn species over Si(OH)Al groups. This study provides guidance for the rational design of highly efficient alkane dehydrogenative aromatization catalysts.

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.

scholarly journals Confinement Effects and Acid Strength in Zeolites

2020 ◽  
Author(s):  
Emanuele Grifoni ◽  
GiovanniMaria Piccini ◽  
Johannes 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

Abstract Chemical reactivity and sorption in zeolites is 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 conversion 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.

Perturbation of Surface Species on Zeolite HY by Xe Observed by FT-IR Spectroscopy

1989 ◽  
Vol 43 (8) ◽  
pp. 1370-1374
Author(s):  
H. Paul Wang ◽  
Ben A. Garland ◽  
Achim Gerhard ◽  
Jim Liang ◽  
Edward M. Eyring
Keyword(s):  
Acid Sites ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Surface Species ◽  
Brønsted Acid Sites ◽  
Brönsted Acid ◽  
Ft Ir ◽  
Brönsted Acid Sites ◽  
Bronsted Acid Sites ◽  
Ft Ir Spectroscopy

The perturbation of surface species of zeolite HY by Xe has been studied with the use of in situ FT-IR spectroscopy. The Brönsted acid sites, characterized by a band at 3638 cm−1, are located in the zeolite supercages, as suggested previously, while Brönsted acid sites attributed to a 3545-cm−1 band are located in the small zeolite cages and are inaccessible to the Xe molecules. The Brönsted acid sites in the supercages are found to have a weaker acidity than those in the small cages. The data also indicate that pyridine molecules are more strongly bonded to the super-cage Brönsted acid sites than are the NH3 molecules. This work is an example of the usefulness of liquid-nitrogen-temperature FT-IR techniques, coupled with multiple-scan data acquisition methods, for studying weak interactions between Xe and zeolite surface species in detail. This work also shows how FT-IR spectroscopy can complement Xe-129 NMR spectroscopy in studies of the nature of zeolite surface species using Xe as a probe molecule.

Development of AEI type germanoaluminophosphate (GeAPO-18) with ultra-weak acid sites and its catalytic properties for the methanol to olefin (MTO) reaction

2017 ◽  
Vol 7 (20) ◽  
pp. 4622-4628 ◽  
Author(s):  
Kaito Ono ◽  
Koji Miyake ◽  
Masahiro Nakai ◽  
Hasna Al Jabri ◽  
Yuichiro Hirota ◽  
...  
Keyword(s):  
Catalytic Properties ◽  
Acid Sites ◽  
Weak Acid ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Brønsted Acid Sites ◽  
Mto Reaction ◽  
Brönsted Acid ◽  
Methanol To Olefin ◽  
Brönsted Acid Sites

Incorporating Ge into the aluminophosphate framework generated weakened Brønsted acid sites, leading to prolonged catalyst lifetimes in the MTO reaction.

Transient Brønsted Acid Sites in Propene Aromatization over Zn-Modified HZSM-5 Detected by Operando Dual-Beam FTIR

2019 ◽  
Vol 123 (12) ◽  
pp. 7283-7289 ◽  
Author(s):  
Jiaxu Liu ◽  
Long Lin ◽  
Jilei Wang ◽  
Wei Zhou ◽  
Cuilan Miao ◽  
...  
Keyword(s):  
Acid Sites ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Brønsted Acid Sites ◽  
Dual Beam ◽  
Brönsted Acid ◽  
Brönsted Acid Sites ◽  
Bronsted Acid Sites

scholarly journals On the Role of Protonic Acid Sites in Cu Loaded FAU31 Zeolite as a Catalyst for the Catalytic Transformation of Furfural to Furan

Molecules ◽  
2021 ◽  
Vol 26 (7) ◽  
pp. 2015
Author(s):  
Łukasz Kuterasiński ◽  
Małgorzata Smoliło-Utrata ◽  
Joanna Kaim ◽  
Wojciech Rojek ◽  
Jerzy Podobiński ◽  
...  
Keyword(s):  
Active Sites ◽  
Acid Sites ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Brønsted Acid Sites ◽  
Protonic Acid ◽  
Brönsted Acid ◽  
Brönsted Acid Sites ◽  
Bronsted Acid Sites

The aim of the present paper is to study the speciation and the role of different active site types (copper species and Brønsted acid sites) in the direct synthesis of furan from furfural catalyzed by copper-exchanged FAU31 zeolite. Four series of samples were prepared by using different conditions of post-synthesis treatment, which exhibit none, one or two types of active sites. The catalysts were characterized by XRD, low-temperature sorption of nitrogen, SEM, H2-TPR, NMR and by means of IR spectroscopy with ammonia and CO sorption as probe molecules to assess the types of active sites. All catalyst underwent catalytic tests. The performed experiments allowed to propose the relation between the kind of active centers (Cu or Brønsted acid sites) and the type of detected products (2-metylfuran and furan) obtained in the studied reaction. It was found that the production of 2-methylfuran (in trace amounts) is determined by the presence of the redox-type centers, while the protonic acid sites are mainly responsible for the furan production and catalytic activity in the whole temperature range. All studied catalysts revealed very high susceptibility to coking due to polymerization of furfural.

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