Synergy between Brønsted acid sites and Lewis acid sites

2008 ◽  
pp. 4631 ◽  
Author(s):  
Selvedin Telalović ◽  
Jeck Fei Ng ◽  
Rajamanickam Maheswari ◽  
Anand Ramanathan ◽  
Gaik Khuan Chuah ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Acid Sites ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Lewis Acid Sites ◽  
Brønsted Acid Sites ◽  
Brönsted Acid ◽  
Brönsted Acid Sites ◽  
Bronsted Acid Sites

Effective co-sensitization using D–π–A dyes with a pyridyl group adsorbing at Brønsted acid sites and Lewis acid sites on a TiO2 surface for dye-sensitized solar cells

RSC Advances ◽  
2015 ◽  
Vol 5 (4) ◽  
pp. 2531-2535 ◽  
Author(s):  
Yousuke Ooyama ◽  
Koji Uenaka ◽  
Takafumi Sato ◽  
Naoyuki Shibayama ◽  
Joji Ohshita
Keyword(s):  
Lewis Acid ◽  
Acid Sites ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Lewis Acid Sites ◽  
Brønsted Acid Sites ◽  
Pyridyl Group ◽  
Brönsted Acid ◽  
Brönsted Acid Sites ◽  
Bronsted Acid Sites

Effective and convenient co-sensitization method for DSSC have been newly developed by employing two kinds of D–π–A dyes with pyridyl group capable of adsorbing at the Brønsted acid sites and the Lewis acid sites on TiO2 surface.

PHOSPHOTUNGSTIC ACID SUPPORTED ON ACID-LEACHED POROUS KAOLIN FOR FRIEDEL-CRAFTS ACYLATION OF ANISOLE

2015 ◽  
Vol 76 (13) ◽  
Author(s):  
Norsahika Mohd Basir ◽  
Hendrik Oktendy Lintang ◽  
Salasiah Endud
Keyword(s):  
Lewis Acid ◽  
Phosphotungstic Acid ◽  
Acid Sites ◽  
Impregnation Method ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Brønsted Acid Sites ◽  
Brönsted Acid ◽  
Brönsted Acid Sites ◽  
Bronsted Acid Sites

Porous clay heterostructures (PCH) was derived from natural kaolin through intercalation with cationic potato starch as the template. Leaching of PCH was performed in concentrated acid solutions consisting of HCl and H2SO4. Phosphotungstic acid (HPW) supported on PCH and modified PCH were synthesized by wet impregnation method. The resulting PCH showed remarkable increase in surface area starting from 15 m2g–1 for the parent kaolin to maximium value of 725 m2g–1 for PCH. Acidity studies by pyridine adsorption and FTIR spectra showed that both natural kaolin and PCH possessed strong Lewis acid sites. In contrast, the surface acidity of HPW supported on PCH was significantly enhanced and comprising mainly Brönsted acid sites. The correlation between the Brönsted to Lewis acid ratios (B/L) and either conversion or selectivity of the catalysts has been studied in Friedel-Crafts acylation of anisole. The PCH/30HPW catalyst with the highest number of Brönsted acid sites showed excellent catalytic activity giving 86% conversion of anisole and high selectivity of 95% toward p-methoxypropiophenone.

scholarly journals Bulk tungsten-substituted vanadium oxide for low-temperature NOx removal in the presence of water

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yusuke Inomata ◽  
Hiroe Kubota ◽  
Shinichi Hata ◽  
Eiji Kiyonaga ◽  
Keiichiro Morita ◽  
...  
Keyword(s):  
Low Temperature ◽  
Vanadium Oxide ◽  
Acid Sites ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Lewis Acid Sites ◽  
Brønsted Acid Sites ◽  
Brönsted Acid ◽  
Brönsted Acid Sites ◽  
Bronsted Acid Sites

AbstractNH3-SCR (selective catalytic reduction) is important process for removal of NOx. However, water vapor included in exhaust gases critically inhibits the reaction in a low temperature range. Here, we report bulk W-substituted vanadium oxide catalysts for NH3-SCR at a low temperature (100–150 °C) and in the presence of water (~20 vol%). The 3.5 mol% W-substituted vanadium oxide shows >99% (dry) and ~93% (wet, 5–20 vol% water) NO conversion at 150 °C (250 ppm NO, 250 ppm NH3, 4% O2, SV = 40000 mL h−1 gcat−1). Lewis acid sites of W-substituted vanadium oxide are converted to Brønsted acid sites under a wet condition while the distribution of Brønsted and Lewis acid sites does not change without tungsten. NH4+ species adsorbed on Brønsted acid sites react with NO accompanied by the reduction of V5+ sites at 150 °C. The high redox ability and reactivity of Brønsted acid sites are observed for bulk W-substituted vanadium oxide at a low temperature in the presence of water, and thus the catalytic cycle is less affected by water vapor.

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.

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.

scholarly journals Adsorption Thermodynamics and Intrinsic Activation Parameters for Monomolecular Cracking of n-Alkanes on Brønsted Acid Sites in Zeolites

2015 ◽  
Vol 119 (19) ◽  
pp. 10427-10438 ◽  
Author(s):  
Amber Janda ◽  
Bess Vlaisavljevich ◽  
Li-Chiang Lin ◽  
Shaama Mallikarjun Sharada ◽  
Berend Smit ◽  
...  
Keyword(s):  
Activation Parameters ◽  
Acid Sites ◽  
Adsorption Thermodynamics ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Brønsted Acid Sites ◽  
Brönsted Acid ◽  
Brönsted Acid Sites ◽  
Bronsted Acid Sites
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