Characterization of Lewis-acid sites in zeolites by EPR using the NO molecule as a probe

1996 ◽  
Vol 92 (13) ◽  
pp. 2495 ◽  
Author(s):  
Aleksander Gutsze ◽  
Martin Plato ◽  
Hellmut G. Karge ◽  
Frank Witzel
Keyword(s):  
Lewis Acid ◽  
Acid Sites ◽  
Lewis Acid Sites

Unraveling the ultrafast behavior of nile red interacting with aluminum and titanium co-doped MCM41 materials

2016 ◽  
Vol 18 (3) ◽  
pp. 2152-2163 ◽  
Author(s):  
Cristina Martin ◽  
Boiko Cohen ◽  
María Teresa Navarro ◽  
Avelino Corma ◽  
Abderrazzak Douhal
Keyword(s):  
Lewis Acid ◽  
Nile Red ◽  
Acid Sites ◽  
Lewis Acid Sites ◽  
Brønsted And Lewis Acid ◽  
Co Doped

Spectroscopic and photodynamic characterization of Nile Red during interaction with Brønsted and Lewis acid sites within single- and multi-metal(X)-doped MCM41 materials (X = Ti and/or Al).

scholarly journals Characterization of Lewis acid sites on the (100) surface of β-AlF3: Ab initio calculations of NH3 adsorption

2008 ◽  
Vol 128 (22) ◽  
pp. 224703 ◽  
Author(s):  
C. L. Bailey ◽  
A. Wander ◽  
S. Mukhopadhyay ◽  
B. G. Searle ◽  
N. M. Harrison
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Lewis Acid ◽  
Acid Sites ◽  
Lewis Acid Sites ◽  
Nh3 Adsorption

Incorporation of Aluminum and Iron Into the ZSM-12 Zeolite: Synthesis and Characterization of Acid Sites

2002 ◽  
Vol 67 (12) ◽  
pp. 1760-1778 ◽  
Author(s):  
Gabriela Košová ◽  
Jiří Čejka
Keyword(s):  
Lewis Acid ◽  
Crystallization Rate ◽  
Acid Sites ◽  
Sodium Ion ◽  
Synthesis And Characterization ◽  
Lewis Acid Sites ◽  
Structure Directing Agent ◽  
Trivalent Cations ◽  
Brønsted And Lewis Acid

Zeolite ZSM-12 with aluminum and iron in the framework was synthesized in a broad range of Si/Al (Si/Fe) ratios using triethylmethylammonium bromide as structure-directing agent with the aim to characterize the type and concentration of acid sites in dependence on the Si/Al (Si/Fe) ratio and calcination procedure. It was shown that the minimum Si/Al ratio achieved for (Al)ZSM-12 is around 35, which is very close to the minimum Si/Fe ratio ca 37 for (Fe)ZSM-12. The rate of crystallization of (Al)ZSM-12 and (Fe)ZSM-12 depends on the concentration of Al and Fe in the reaction mixture. The higher was the concentration of these trivalent cations, the slower was the apparent crystallization rate. It is suggested that the crystallization rate is controlled by the number of nucleation centers, which depends on the amount of trivalent cations (Al, Fe) in the reaction mixture. Zeolites (Al)ZSM-12 and (Fe)ZSM-12 were calcined under a variety of carefully controlled conditions to investigate the resulting concentration of Brønsted and Lewis acid sites. FTIR spectroscopy used to study the adsorption of acetonitrile-d3 and pyridine on Brønsted and Lewis acid sites revealed that both sites are present in significant concentrations in all calcined (Al)ZSM-12 and (Fe)ZSM-12 zeolites. The highest concentrations of Brønsted sites especially at low Si/Al or Si/Fe ratios were achieved via calcination of the zeolites in a stream of ammonia followed by a repeated sodium ion exchange and further calcination in a stream of air.

Generation and Characterization of Well-Defined Zn2+Lewis Acid Sites in Ion Exchanged Zeolite BEA

2004 ◽  
Vol 108 (13) ◽  
pp. 4116-4126 ◽  
Author(s):  
Jochen Penzien ◽  
Anuji Abraham ◽  
Jeroen A. van Bokhoven ◽  
Andreas Jentys ◽  
Thomas E. Müller ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Acid Sites ◽  
Lewis Acid Sites

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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