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

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.

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Synergy between Brønsted acid sites and Lewis acid sites

Chemical Communications ◽

10.1039/b807953f ◽

2008 ◽

pp. 4631 ◽

Cited By ~ 23

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

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

Nature Communications ◽

10.1038/s41467-020-20867-w ◽

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.

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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 ◽

10.1039/c4ra14190c ◽

2015 ◽

Vol 5 (4) ◽

pp. 2531-2535 ◽

Cited By ~ 18

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.

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

Molecules ◽

10.3390/molecules26072015 ◽

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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