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.

scholarly journals Zirconia catalysed acetic acid ketonisation for pre-treatment of biomass fast pyrolysis vapours

2018 ◽  
Vol 8 (4) ◽  
pp. 1134-1141 ◽  
Author(s):  
Hessam Jahangiri ◽  
Amin Osatiashtiani ◽  
James A. Bennett ◽  
Mark A. Isaacs ◽  
Sai Gu ◽  
...  
Keyword(s):  
Acetic Acid ◽  
Lewis Acid ◽  
Fast Pyrolysis ◽  
Acid Sites ◽  
Active Species ◽  
Acid Base ◽  
Lewis Acid Sites ◽  
Base Pairs ◽  
Pre Treatment ◽  
Biomass Fast Pyrolysis

Weak Lewis acid sites (and/or resulting acid–base pairs) on monoclinic ZrO2 are identified as the active species responsible for acetic acid ketonisation to acetone.

Brønsted and Lewis Acid Sites in Dealuminated ZSM-12 and β Zeolites Characterized by NH3-STPD, FT-IR, and MAS NMR Spectroscopy

2000 ◽  
Vol 104 (17) ◽  
pp. 4122-4129 ◽  
Author(s):  
Wenmin Zhang ◽  
Panagiotis G. Smirniotis ◽  
M. Gangoda ◽  
Rathindra N. Bose
Keyword(s):  
Nmr Spectroscopy ◽  
Lewis Acid ◽  
Acid Sites ◽  
Mas Nmr ◽  
Lewis Acid Sites ◽  
Ft Ir ◽  
Brønsted And Lewis Acid

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.

scholarly journals Solvent-Free Synthesis of Jasminaldehyde in a Fixed-Bed Flow Reactor over Mg-Al Mixed Oxide

Catalysts ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1033
Author(s):  
Zahra Gholami ◽  
Zdeněk Tišler ◽  
Pavla Vondrová ◽  
Romana Velvarská ◽  
Kamil Štěpánek
Keyword(s):  
Organic Compounds ◽  
Lewis Acid ◽  
Flow Reactor ◽  
Fixed Bed ◽  
Acid Sites ◽  
Economic Benefits ◽  
Solvent Free ◽  
Molar Ratio ◽  
Lewis Acid Sites ◽  
Solvent Free Synthesis

In spite of the rapid developments in synthesis methodologies in different fields, the traditional methods are still used for the synthesis of organic compounds, and regardless of the type of chemistry, these reactions are typically performed in standardized glassware. The high-throughput chemical synthesis of organic compounds such as fragrant molecules, with more economic benefits, is of interest to investigate and develop a process that is more economical and industrially favorable. In this research, the catalytic activity of Mg-Al catalyst derived from hydrotalcite-like precursors with the Mg/Al molar ratio of 3 was investigated for the solvent-free synthesis of jasminaldehyde via aldol condensation of benzaldehyde and heptanal. The reaction was carried out in a fixed-bed flow reactor, at 1 MPa, and at different temperatures. Both Brønsted and Lewis (O2− anions) base sites, and Lewis acid sites exist on the surface of the Mg-Al catalyst, which can improve the catalytic performance. Increasing the reaction temperature from 100 °C to 140 °C enhanced both heptanal conversion and selectivity to jasminaldehyde. After 78 h of reaction at 140 °C, the selectivity to jasminaldehyde reached 41% at the heptanal conversion 36%. Self-condensation of heptanal also resulted in the formation of 2-n-pentyl-2-n-nonenal. The presence of weak Lewis acid sites creates a positive charge on the carbonyl group of benzaldehyde, and makes it more prone to attack by the carbanion of heptanal. Heptanal, is an aliphatic aldehyde, with higher activity than benzaldehyde. Therefore, the possibility of activated heptanal reacting with other heptanal molecules is higher than its reaction with the positively charged benzaldehyde molecule, especially at a low molar ratio of benzaldehyde to heptanal.

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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