scholarly journals IR and NMR Studies of the Status of Al and Acid Sites in Desilicated Zeolite Y

Molecules ◽  
2019 ◽  
Vol 25 (1) ◽  
pp. 31 ◽  
Author(s):  
Mariusz Gackowski ◽  
Jerzy Podobiński ◽  
Ewa Broclawik ◽  
Jerzy Datka
Keyword(s):  
Zeolite Y ◽  
Acid Sites ◽  
Tetrahedral Coordination ◽  
Lewis Acid Sites ◽  
Nmr Studies ◽  
Ir Studies ◽  
Lewis Site ◽  
Alkali Solutions ◽  
27Al Mas Nmr ◽  
The Status

The desilication of zeolite Y (of Si/Al = 31) that was previously dealuminated by steaming and acid treatment was studied. Desilication of zeolites of high Si/Al module in alkali solutions extracts both Si and Al from zeolite crystals, but while Si remains in solution, Al is reinserted into the zeolite grain. The main goal of our study was to follow the status of Al reinserted into zeolite during the desilication procedure, and its role in the formation of acid sites of the Brønsted and Lewis types. The properties of Al were followed by 27Al MAS NMR spectroscopy (for parent samples and zeolites treated either with NaOH or NaOH/tetrabutylammonium hydroxide), whereas the acid sites generated in the final stages were studied by IR spectroscopy with NH3 and CO as probe molecules. In non-desilicated zeolite, most of the Al was in a typically zeolitic tetrahedral coordination, while both NMR and quantitative IR studies of NH3 sorption evidenced that Al that was extracted by desilication and was subsequently reinserted had a tetrahedral coordination similar to amorphous aluminosilicates and showed an ion exchange ability. After the exchange of Na+ to NH4+ and decomposition of NH4+ ions, reinserted Al forms generated protonic sites from which some condensed at higher temperatures producing Lewis acid sites (with stoichiometry typical for zeolites i.e., the condensation of two protonic sites produces one Lewis site) but some other kept their character.

THE USE OF THE COMBINATION OF FTIR, PYRIDINE ADSORPTION, 27Al AND 29Si MAS NMR TO DETERMINE THE BRÖNSTED AND LEWIS ACIDIC SITES

2016 ◽  
Vol 78 (6) ◽  
Author(s):  
Djoko Hartanto ◽  
Lai Sin Yuan ◽  
Sestriana Mutia Sari ◽  
Djarot Sugiarso ◽  
Irmina Kris Murwarni ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Aluminum Atom ◽  
Xrd Analysis ◽  
Acid Sites ◽  
Mas Nmr ◽  
Molar Ratio ◽  
Pyridine Adsorption ◽  
Lewis Acid Sites ◽  
27Al Mas Nmr ◽  
Pre Treatment

Lewis and Brönsted acidity were studied on ZSM-5 with combination of pyridine adsorption and FTIR vibration, ZSM-5 synthesized using kaolin Bangka Indonesia with an increase in the molar ratio of Si/Al 30-60 without pre-treatment and without organic templates and with seeds silicalite. Interestingly, the intensity of the infrared showed an increase of band vibration pyridine as absorbed Brönsted and Lewis acid sites in a molar ratio increase of Si/Al in ZSM-5, indicating an increase in the number of silanol (Brönsted acid) and deformed silica (Lewis acid) because the amount of Aluminum in ZSM-5 decrease with increase Si/Al but amount acidity increase. 29Si and 27Al MAS NMR analysis was supported by the results of infrared to indicate that all of the aluminum atom is coordinated with their neighbors are the same in ordering the ZSM-5 framework and 27Al MAS NMR showed a sharp peak of all the variations of Si/Al except the Si/Al 30 shows a low peak area. XRD analysis supported that the ZSM-5 structure formed is pure and crystal and a decrease in crystallinity proven for more than Si/Al 50, that defects silica occurs in ZSM-5, this corresponds to the growing number of Lewis acid sites caused by defects silica described the infrared results.

The acidity of trivalent cation-exchanged montmorillonite. Temperature-Programmed desorption and infrared studies of pyridine and n-butylamine

Clay Minerals ◽  
1987 ◽  
Vol 22 (2) ◽  
pp. 169-178 ◽  
Author(s):  
C. Breen ◽  
A. T. Deane ◽  
J. J. Flynn
Keyword(s):  
Variable Temperature ◽  
Temperature Programmed Desorption ◽  
Acid Sites ◽  
Trivalent Cation ◽  
Desorption Peak ◽  
Lewis Acid Sites ◽  
Ir Studies ◽  
Infrared Studies ◽  
Interlamellar Space ◽  
Temperature Programmed

AbstractTemperature-programmed desorption (TPD) and IR spectroscopy were used to characterize the number and strength of acid sites in Al3+-, Cr3+- and Fe3+-exchanged montmorillonite. The bases pyridine and n-butylamine occupied three different sites in the interlamellar space: (i) physisorbed base, (ii) base bound to Lewis acid sites, and (iii) protonated base. TPD profiles for pyridine were characterized by maxima at 40°, 150° and 340°C, whilst those for n-butylamine occurred at 30°, 200° and 410°C. The Al3+- and Cr3+-exchanged forms were stable up to pretreatment temperatures of 300°C, but the Fe3+-form required > 3 day exposure to base vapour to re-establish the high-temperature desorption peak. Variable-temperature IR studies showed that the number of Brönsted-bound pyridine molecules increased with increased outgassing temperature.

scholarly journals Relationship between Acidity and Activity on Propane Conversion over Metal-Modified HZSM-5 Catalysts

Catalysts ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1138
Author(s):  
Hao Zhou ◽  
Fucan Zhang ◽  
Keming Ji ◽  
Junhua Gao ◽  
Ping Liu ◽  
...  
Keyword(s):  
Physicochemical Properties ◽  
Lewis Acid ◽  
Systematic Study ◽  
Acid Sites ◽  
Propane Conversion ◽  
Lewis Acid Sites ◽  
High Olefin ◽  
27Al Mas Nmr ◽  
Strong Acidity ◽  
Olefin Selectivity

A systematic study of the comparative performances of different metal-impregnated HZSM-5 catalysts (Zn, Ga, Mo, Co, and Zr) for propane conversion is presented. The physicochemical properties of catalysts were characterized by means of XRD, BET, SEM, TEM, FTIR, XPS, 27Al MAS NMR, NH3-TPD and Py-FTIR. It was found that the acidities of the catalysts were significantly influenced by loading metal. More specifically, Mo-, Co- or Zr-modified catalysts showed a large metal size and low acidic density, resulting high olefin selectivity, while Zn- or Ga-modified catalysts maintained their small metal size and acidic density, and mainly reduced B/L due to the Lewis acid sites created by Zn or Ga species, resulting in high aromatics selectivity. Experimental results also showed that there is a balance between metals size and medium and strong acidity on propane conversion. Moreover, based on the different acidity of metal-modified HZSM-5 catalysts, the mechanism of propane conversion was also discussed.

IR Studies of Acid Properties of H-Boralites Activated at Various Temperatures

1992 ◽  
Vol 57 (4) ◽  
pp. 745-749 ◽  
Author(s):  
Jerzy Datka ◽  
Marek Kawałek
Keyword(s):  
Acid Sites ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Lewis Acid Sites ◽  
Brønsted Acid Sites ◽  
Activation Temperature ◽  
Ir Studies ◽  
Brönsted Acid ◽  
Brönsted Acid Sites ◽  
Bronsted Acid Sites

Four kinds of hydroxyls are present in H-boralite: 3450 cm-1 (Si-OH...O), 3670 cm-1 (B-OH), 3700-3720 cm-1 (Si-OH...B) and 3740 cm-1 (Si-OH). Only 3700-3720 cm-1 (Si-OH...B) hydroxyls are Bronsted acid sites. Their concentration, as well as the concentration of Lewis acid sites, was found to be independent of the activation temperature (in the range 473-873 K). On the other hand, both 3450 and 3670 cm-1 hydroxyls are very prone to dehydroxylation which starts at as low temperature as 473 K. This is due to a reaction: Si-OH + O(H)-B → SiOB + H2O. It has been found that the stretching frequency of Si-OH···B groups (Bronsted acid sites) depends on the activation temperature (3700 cm-1 at 573 K and 3720 cm-1 at 773 K) suggesting a variation of the properties of Bronsted sites with temperature. We explain it by the loss of Si-OHO and B-OH hydroxyls situated in close vicinity of Si-OH...B ones.

Platinum and cobalt intermetallic nanoparticles confined within MIL-101(Cr) for enhanced selective hydrogenation of the carbonyl bond in α,β-unsaturated aldehydes: synergistic effects of electronically modified Pt sites and Lewis acid sites

2021 ◽  
Author(s):  
Muhammad Zahid ◽  
Jiang Li ◽  
Ahmed Ismail ◽  
Francisco Zaera ◽  
Yujun Zhu
Keyword(s):  
Synergistic Effect ◽  
Reduction Method ◽  
Synergistic Effects ◽  
Acid Sites ◽  
Lewis Acid Sites ◽  
Unsaturated Aldehydes ◽  
Uniform Dispersion ◽  
Carbonyl Bond ◽  
Method Show ◽  
Intermetallic Nanoparticles

PtCo/MIL-101(Cr) with high uniform dispersion Pt–Co IMNs synthesized by a polyol reduction method show higher activity for selective catalytic hydrogenation of α,β-unsaturated aldehydes due to the synergistic effect of PtCo and MIL-101(Cr) support.

scholarly journals Glucose Conversion into 5-Hydroxymethylfurfural over Niobium Oxides Supported on Natural Rubber-Derived Carbon/Silica Nanocomposite

Catalysts ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 887
Author(s):  
Rujeeluk Khumho ◽  
Satit Yousatit ◽  
Chawalit Ngamcharussrivichai
Keyword(s):  
Natural Rubber ◽  
Lewis Acid ◽  
Value Added ◽  
Acid Sites ◽  
Superior Performance ◽  
Lewis Acidity ◽  
Lewis Acid Sites ◽  
Niobium Oxides ◽  
Silica Nanocomposite ◽  
Loading Amount

5-Hydroxymethylfurfural (HMF) is one of the most important lignocellulosic biomass-derived platform molecules for production of renewable fuel additives, liquid hydrocarbon fuels, and value-added chemicals. The present work developed niobium oxides (Nb2O5) supported on mesoporous carbon/silica nanocomposite (MCS), as novel solid base catalyst for synthesis of HMF via one-pot glucose conversion in a biphasic solvent. The MCS material was prepared via carbonization using natural rubber dispersed in hexagonal mesoporous silica (HMS) as a precursor. The Nb2O5 supported on MCS (Nb/MCS) catalyst with an niobium (Nb) loading amount of 10 wt.% (10-Nb/MCS) was characterized by high dispersion, and so tiny crystallites of Nb2O5, on the MCS surface, good textural properties, and the presence of Bronsted and Lewis acid sites with weak-to-medium strength. By varying the Nb loading amount, the crystallite size of Nb2O5 and molar ratio of Bronsted/Lewis acidity could be tuned. When compared to the pure silica HMS-supported Nb catalyst, the Nb/MCS material showed a superior glucose conversion and HMF yield. The highest HMF yield of 57.5% was achieved at 93.2% glucose conversion when using 10-Nb/MCS as catalyst (5 wt.% loading with respect to the mass of glucose) at 190 °C for 1 h. Furthermore, 10-Nb/MCS had excellent catalytic stability, being reused in the reaction for five consecutive cycles during which both the glucose conversion and HMF yield were insignificantly changed. Its superior performance was ascribed to the suitable ratio of Brønsted/Lewis acid sites, and the hydrophobic properties generated from the carbon moieties dispersed in the MCS nanocomposite.

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