Eliezer Ladeia Gomes
* 6.53
* Universidade Federal de S?o Paulo
I've prepared some zeolites and I would like to dessilicate them. What are the
best reagents, concentrations and times to do that?
I've prepared well cristallized ZSM-5,Beta and modernite zeolites. I want to
create mesopority in them. I've used HF and NH4F solutions of low concentration.
Sometimes the zeolite simply is digested. Other times the effect is minimal. I'm
looking for the best or optimal conditions to do the dessilication. Someone
could help me?
* Digestion
* Reagents
* Zeolites
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All Answers (3)
5 days
Chada Raji Reddy
Sodium hydroxide reacts with silica to form sodium silicate, which is water
soluble. So, you can try with 1M concentration of sodium hydroxide with diffrent
time. Then filter the solution with water and wash with water to remove the
formed sodium silicate. finally you will get desilicated material.
How to synthesize pure Bronsted acid sites
zeolite?
Does anybody have experience with the synthesis of purely or mostly Bronsted acid site zeolite? I would like to prepare a zeolite containing mainly Bronsted acid sites
and then the same one with mixed Bronsted and Lewis acidity. If possible with the same Si/Al molar ratio. The topology is not so important if it has at least 10membered ring channels. Please, share your experience.
13 days ago
Trino Romero
Added an answer
Hi Pavla
in zeolites the number of bronsted sites depende on the ratio of Si/Al and is constant for a specific structure. If the ratio Si/Al increases the number of bronsted sites
decreases and de lewis sites increases, leading to distribution of acidic sites on surface of different acidic forces that leads to interesting chemical transformations. If
you want to maintain the same ratio of Si/Al, you will have to promote acid bronsted sites with zirconia, for example.
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7 days ago
Carlos Otero Areán
Added an answer
Dear Pavla,
We are currently doing some experimental work on that subject, but didn't advance much yet. Meanwhile, I wonder whether you have seen the enclosed paper.
All the best.
Sincerely,
Carlos
co.arean@uib.es
Modification of acid sites in ZSM5.pdf
7 days ago
Bruno Azambre
Added an answer
Hello,
You can possibly start from a zeolite in ammonium form and simply do repeated exchanges with a diluted acid (by taking care about the dealumination at low pH).
Then avoid calcination ? In this paper, you can find the populations of acid B and L sites in function of the temperature and Si/Al ratio for Y zeolites.
Adsorption and Desorption of a Model Hydrocarbon Mixture Over HY Zeolite Under Dry and Wet Conditions J. Phys. Chem. C 119 (2014) p. 315-331.
Bruno
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6 days ago
Pavla Eliášová
Added an answer
Dear Carlos,
thanks for the paper, it is very nice work but unfortunatelly this procedure is not suitable for our purposes. We would like to study experimentally and theorethically the
role of Lewis and Bronsted sites in one particular reaction. Therefore ion-exchange which maby cause channel constriction or generation of extra-framework alumina
Lewis sites is not the best way for us.
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6 days ago
Pavla Eliášová
Added an answer
Dear Bruno,
I am afarid that by this ion-exchange we will increase the total acid sites amounts and also the ratio of Lewis and Bronsted sites (similarly as reported in the paper,
which Carlos posted here). Then it will be hard to judge which factor has influenced the catalytic results.. Anyway thanks for answer and the paper.
Pavla

10.11113/jt.v78.8821
The use of the combination of ftir, Pyridine adsorption, 27Al and 29Si MAS NMR to
determine the Brönsted and lewis acidic sites
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
June 2016
Jurnal Teknologi 78(6):223-228
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
DOI
10.11113/jt.v78.8821

Djoko Hartanto

Lai Sin Yuan


Sestriana Mutia Sari
Show all 8 authors

Hadi Nur
ArticleThe use of the combination of ftir, Pyridine adsorption, 27Al and 29Si MAS NMR to
determine the Brönsted and lewis acidic sites
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Comments (4)
Citations (11)
References (11)
Related research (10+)
Abstract
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.
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