scholarly journals Effects of Framework Disruption of Ga and Ba Containing Zeolitic Materials by Thermal Treatment

Catalysts ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 975
Author(s):  
Siyabonga S. Ndlela ◽  
Holger B. Friedrich ◽  
Mduduzi N. Cele
Keyword(s):  
Thermal Treatment ◽  
Calcination Temperature ◽  
Lewis Acid ◽  
Acid Sites ◽  
Deep Oxidation ◽  
Isomorphic Substitution ◽  
Lewis Acid Sites ◽  
Different Temperatures ◽  
Strong Lewis Acid ◽  
Zeolitic Materials

The effect of the thermal treatment of some zeolitic materials was studied on oxidative dehydrogenation (ODH) of n-octane. Gallium containing faujasite catalysts were synthesized using isomorphic substitution, specifically, a galosilicalite (Ga-BaY(Sil)) and an aluminosilicalite substituted with gallium (Ga-BaY(IS)), with constant Si/M ratio. The catalysts were thermally treated at different temperatures (250, 550, and 750 °C) before catalytic testing. The quantification of total and strength of acid sites by FT-IR (O-H region), pyridine-IR, and NH3-temperature-programmed desorption (TPD) confirmed a decrease in the number of Brønsted acid sites and an increase in the number of Lewis acid sites upon increasing the calcination temperature. Isothermal n-octane conversion also decreased with the catalysts’ calcination temperature, whereas octene selectivity showed the opposite trend (also at iso-conversion). The COx selectivity showed a decrease over the catalysts calcined from 250 to 550 °C and then an increase over the 750 °C calcined catalysts, which was due to the strong adsorption of products to strong Lewis acid sites on the catalysts leading to the deep oxidation of the products. Only olefinic-cracked products were observed over the 750 °C calcined catalysts. This suggested that the thermal treatment increases Lewis acid sites, which activate n-octane using a bimolecular mechanism, instead of a monomolecular mechanism.

Highly-efficient Ru/Al–SBA-15 catalysts with strong Lewis acid sites for the water-assisted hydrogenation of p-phthalic acid

2020 ◽  
Vol 10 (8) ◽  
pp. 2443-2451
Author(s):  
Cong Mao ◽  
Jingwei Zheng ◽  
Babasaheb M. Matsagar ◽  
Ranjith Kumar Kankala ◽  
Tansir Ahamad ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Phthalic Acid ◽  
Acid Sites ◽  
Lewis Acid Sites ◽  
Highly Efficient ◽  
Strong Lewis Acid ◽  
Exceptional Stability ◽  
Isomer Selectivity

A Ru/Al–SBA-15 catalyst with excess Lewis acid sites displayed excellent efficiency (100%), high cis-isomer selectivity (84%), and exceptional stability towards hydrogenation of p-phthalic acid in water.

Role of Zinc in Zn-Loaded ZSM-5 Zeolites in the Aromatization of n-Hexane

1999 ◽  
Vol 64 (1) ◽  
pp. 168-176 ◽  
Author(s):  
Edita Rojasová ◽  
Agáta Smiešková ◽  
Pavol Hudec ◽  
Zdenek Židek
Keyword(s):  
Solid State ◽  
Ion Exchange ◽  
Lewis Acid ◽  
Acid Site ◽  
Acid Sites ◽  
Partial Migration ◽  
Simultaneous Presence ◽  
Lewis Acid Sites ◽  
Strong Lewis Acid

Aromatization of n-hexane over zinc-modified ZSM-5 zeolites was investigated. It was shown that incorporation of zinc by ion exchange into cationic positions of NH4-ZSM-5 zeolite causes acid-site strength redistribution and generation of new relatively strong Lewis acid sites in zeolite increasing the selectivity of n-hexane aromatization in comparison with the parent NH4-ZSM-5 zeolite. Simultaneous presence of Lewis and Broensted acid sites in ZSM-5 zeolite does not affect the strength of Broensted acid sites in zeolite. For the activity/selectivity of aromatization of n-hexane on Zn-modified ZSM-5 zeolites, the amount of Zn and its localization in the cationic positions are decisive. The reaction of n-hexane can be also initiated by the Zn species alone in the cationic positions. ZnO species alone as an extraframework phase was found inactive in the catalyst for aromatization of n-hexane. The influence of ZnO addition on the performance of pure ammonium forms of ZSM-5 zeolites in n-hexane conversion is a result of partial migration of zinc into cationic positions of zeolite by solid-state ion exchange.

Direct synthesis of alkynylphosphonates from alkynes and phosphite esters catalyzed by Cu/Cu2O nanoparticles supported on Nb2O5

2018 ◽  
Vol 42 (16) ◽  
pp. 13957-13962 ◽  
Author(s):  
Tao Yuan ◽  
Fei Chen ◽  
Guo-ping Lu
Keyword(s):  
Lewis Acid ◽  
Synergistic Effects ◽  
Copper Catalyst ◽  
Direct Synthesis ◽  
Acid Sites ◽  
Lewis Acid Sites ◽  
Strong Lewis Acid ◽  
Cu2o Nanoparticles

A new, recyclable and efficient copper catalyst for cross-couplings of alkynes and phosphite esters has been disclosed, in which the synergistic effects of Nb2O5 on the catalyst are found owing to its strong Lewis acid sites.

One-dimensional alignment of strong Lewis acid sites in a porous coordination polymer

2013 ◽  
Vol 49 (89) ◽  
pp. 10459 ◽  
Author(s):  
Takashi Kajiwara ◽  
Masakazu Higuchi ◽  
Akihiro Yuasa ◽  
Hideyuki Higashimura ◽  
Susumu Kitagawa
Keyword(s):  
Coordination Polymer ◽  
Lewis Acid ◽  
Acid Sites ◽  
Lewis Acid Sites ◽  
One Dimensional ◽  
Strong Lewis Acid ◽  
Porous Coordination Polymer

Synthesis of microscale and nanoscale ZSM-5 zeolites: effect of particle size and acidity of Zn modified ZSM-5 zeolites on aromatization performance

2017 ◽  
Vol 7 (9) ◽  
pp. 1943-1952 ◽  
Author(s):  
Xiaofang Su ◽  
Wang Zan ◽  
Xuefeng Bai ◽  
Gaoliang Wang ◽  
Wei Wu
Keyword(s):  
Particle Size ◽  
Lewis Acid ◽  
Acid Sites ◽  
Lewis Acid Sites ◽  
Strong Lewis Acid ◽  
Effect Of Particle Size

Zn/NZ5 zeolite exhibits a higher BTX yield because of the higher mesoporosity and strong Lewis acid sites formed by [ZnOZn]2+ species.

scholarly journals Photoisomerization of n-pentane over nano ZnO/MoO3-ZrO2

2014 ◽  
Vol 10 (4) ◽  
Author(s):  
Sugeng Triwahyono ◽  
Aishah Abdul Jalil ◽  
Che Rozid Mamat
Keyword(s):  
Lewis Acid ◽  
Acid Sites ◽  
Nitrogen Atmosphere ◽  
Hydrogen Gas ◽  
Bet Surface Area ◽  
Impregnation Method ◽  
High Concentration ◽  
Lewis Acid Sites ◽  
Nano Zno ◽  
Strong Lewis Acid

A series of nano ZnO/MoO3-ZrO2 catalysts with different ZnO loading (1.0, 2.5, 5.0 wt%) were prepared by impregnation method for n-pentane photoisomerization under hydrogen or nitrogen atmosphere. The properties of the catalysts were characterized with X-ray Diffraction (XRD), Brunauer Emmett Teller (BET), Transmission Electron microscope (TEM) and FTIR. The XRD result showed that the fraction of tetragonal phase of ZnO/MoO3-ZrO2 was about 0.67 for all samples. While, the specific BET surface area was about 24 m2/g. Pyridine adsorbed FTIR results showed that all samples possessed high concentration of strong Lewis acid sites and small concentration of weak Bronsted acid sites. The interaction of hydrogen and surface samples at 298-523 K formed protonic acid sites with the concomitant of the partial elimination of Lewis acid sites. Whereas no changes of the concentration of acid sites were observed in the presence of nitrogen atmosphere. The activity of all samples in the n-pentane photoisomerization was strongly determined by the presence of hydrogen gas. In fact no activity was observed in the absence of hydrogen________________________________________GRAPHICAL ABSTRACT

Nb-doped variants of high surface aluminium fluoride: a very strong bi-acidic solid catalyst

2019 ◽  
Vol 48 (20) ◽  
pp. 6834-6845 ◽  
Author(s):  
Clara Patricia Marshall ◽  
Gudrun Scholz ◽  
Thomas Braun ◽  
Erhard Kemnitz
Keyword(s):  
Lewis Acid ◽  
Aluminium Hydroxide ◽  
High Surface ◽  
Acid Sites ◽  
Solid Catalyst ◽  
Lewis Acid Sites ◽  
Brønsted Acid Sites ◽  
Brönsted Acid ◽  
Aluminium Fluoride ◽  
Strong Lewis Acid

Novel aluminium Nb-doped fluoride catalysts were synthesized using an aluminium hydroxide precursor to afford solids where very strong Lewis acid sites coexist with Brønsted acid sites.

scholarly journals How TiO2 facets determine arsenic adsorption and photooxidation: spectroscopic and DFT studies

2016 ◽  
Vol 6 (7) ◽  
pp. 2419-2426 ◽  
Author(s):  
Li Yan ◽  
Jingjing Du ◽  
Chuanyong Jing
Keyword(s):  
Lewis Acid ◽  
Acid Sites ◽  
Dft Studies ◽  
High Adsorption ◽  
Lewis Acid Sites ◽  
Arsenic Adsorption ◽  
Adsorption Affinity ◽  
Strong Lewis Acid

TiO2 {001} facets with strong Lewis acid sites exhibit high adsorption affinity to O2 to generate O2˙− and then oxidize adsorbed As(iii).

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