The presentation is prepared to give a general idea to the reader about zeolite, and its application. Various zeolites and their molecular structure is also discussed. Further, Si/Al, pore geometry, and their effect on the zeolite application are also discussed.

1. Z E O L I T E : A C ATA LY T I C
I N S I G H T
D R . D E B A S H I S P A N D A
1

2. • Zeolite consists of tectosilicate framework (TO4) formed by oxygen-sharing T (Si or Al)
atoms, each T atom linked to four oxygen making tetrahedra.
• These tetrahedra are linked to form rings containing equal number of oxygen and
silicon atoms. The rings share common oxygen (or silicon) forming different
polyhedra.
• The polyhedra then forming the three -dimensional network structure giving rise to
pores. Counter ions (cations) are present in order to compensate negative for
negative framework charge created by Al substitution.
Common formula: Mn
x/nSi1-x AlxO2.yH2O (M= Na+, Ca2+)
• Various type zeolite structure: Natural, and synthetic (LTA, FAU, ZSM, Erionite)
A B O U T S T R U C T U R E
Zeolite Pore type Ring
4A Small, 0.4 nm 8
ZSM-5 Medium, (0.54 X0.56) nm 10
X,Y, beta Large, (0.74 nm) 12
SAPO-8 Extra-large (0.87 nm) 14
2

3. • A major application of the zeolites in catalysis is in acid catalyzed reactions such as
alkylation, acylation, electrophilic aromatic substitution, cyclization, isomerization and
condensation the framework.
• Zeolite A commonly used for Laundry detergent (water softening), X,Y are used for
catalytic cracking, and ZXM-5 for petroleum cracking.
• Zeolite can hold water up to 60% of its weight due to high porosity of the crystalline
structure. Water can be desorb and readsorb easily without affecting crystal structure.
• Zeolite is often called molecular sieve due to ability to selectively short molecules, so
mostly used for separation application. Zeolite also used cation exchange application
to adsorb heavy metals from wastewater.
• The adsorption on zeolites dependent on the following physical molecular properties:
• Size and Shape: molecules or ions larger than the pore opening of the zeolite can not
be adsorbed, smaller molecules or ions can.
• Molecular Polarity: due the charge on outer and inner zeolitic surface particle,
molecules with large polarity or polarisability can be adsorbed preferentially under
identical conditions (e,g, removal of CO2, H2S from natural gas)
A P P L I C A T I O N S
3

4. • Beta structured zeolites are widely used for automotive emission control, industrial
off-gas purification, and reduction of VOC, NOx and N2O.
• As process catalysts, they are ideal for fuel upgrading, production of petrochemical
intermediates, and processing chemicals.
• Examples: Beta structure type are CZB 25 (BEA 25), CZB 30 (BEA 30), and CZB 150
(BEA 150).
• Structurally zeolite Beta has 3-dimensional pore structure, 12 rings and an opening of
0.7 nm.
• Application: Dealuminated beta zeolites were found to be effective bifunctional
catalysts for the conversion of glucose into HMF; Lewis acid sites in the beta zeolites
promoted the isomerization of glucose, which is the rate-determining step, through a
hydride transfer mechanism and Brønsted acid sites promptly promoted the
dehydration of fructose to HMF.
Z E O L I T E B E T A
Catalysis today, 2018, 304, 97-102
Zeolite Beta
4

5. • Zeolite Y is a faujasite molecular sieve with 0.74 nm diameter pores and a three-
dimensional pore structure.
• The primary application for Y zeolites has been in catalytic cracking of petroleum into
gasoline range hydrocarbons. Among the zeolites used in industrial scale, zeolite Y or
faujasite including ultra-stable Y zeolite (USY) is the most widely employed materials.
It is the main component of fluid catalytic cracking (FCC) catalyst at a volume above
100,000 tons/yr like refining processing in petrochemical industries.
• Zeolite Y can be directly synthesized with Si/Al ratios above 3, catalytically relevant
materials with high Si/Al ratios must be prepared by post-synthetic removal of the
framework aluminum. Furthermore, heating NH4Y in dry vs. wet air brings about
different dealumination effects and structural characteristics.
• Ultrastable Y (USY) zeolite is an effective catalyst used for catalytic cracking in
petroleum refining. This catalyst is prepared from ammonium Y zeolite by steaming at
high temperatures above 773 K. From this process, aluminum cations are dislodged
from the framework of the Y zeolite. Through this process, as the actual catalytic
cracking occurs, the structure of the Y zeolite is simultaneously stabilized
Z E O L I T E Y
Catal. Sci. Technol., 2015, 5, 4001-4007
Zeolite Y
5

6. • NH4
+-exchanged zeolites are typically prepared in the synthesis of zeolites as
intermediate step to transform the Na+-form obtained during hydrothermal synthesis
in basic conditions to the final H+-form obtained by calcination of the NH4
+-exchanged
zeolite.
• The NH4+ form was obtained after treatment with an NH4NO3/NH4OH aqueous solution
(pH = 10.5) to ion exchange Na+ with NH4
+. The H+-zeolites were obtained by
calcination in air (ramp 2 °C/min to 500 °C, hold the isotherm for 5 h and then cooled
down to room temperature)
• Ammonium form are very usual because, to transform a Na-zeolite in a H-zeolite, one
usually proceeds by ion exchange of Na+ by NH4+ (and not by directly H+, which
would imply exposing the zeolite to too acidic solution) followed by calcination
(formation of the H form and release of NH3).
H + A N D N H 4
+ Z E O L I T E S
Catalysis today, 2018, 304, 97-102
Zeolite NH4
+Zeolite H+ Zeolite
heat
H+ Zeolite
6

7. • Zeolite dealumination and desilication are common postsynthesis methods, which
improve accessibility of the active sites located inside the zeolite crystallites and tune
the zeolite acidity.
• Dealumination is a well-known post-synthesis method of removing aluminum from
zeolite structure with the use of chemical agents or by hydrothermal treatment. The
goal of dealumination is to modify the Si/Al ratio in the zeolite framework and zeolite
acidity.
• The “desilication” method, which preferentially extracts silicon atoms from the zeolite
framework, has been efficient for introducing additional mesopores, in particular, into
high silica zeolites such as ZSM-5, Beta and mordenite. Post-synthesis chemical
modification of zeolite crystals carried out by steam treatment or treatment with acid
or basic agents.
• Dealumination and desilication could be used as complementary methods to control
zeolite acidity, to create porosity and to improve the transport properties.
• Desilication leads to more mesopore formation, voids between and in the irregular
zeolite crystallites, whereas dealumination leads to pore blockage.
D E - A L U M I N A T I O N A N D D E - S I L I C A T I O N O F Z E O L I T E
J. CO2. Util. 2020, 40, 101223, Micropor. Mesopor. Mat. 2019, 286, 57-64
Pristine
7
Desilicated