Zeolites1. nanotechnolg and ebvironemnt ppt

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1. Introduction to Zeolites Reactions
DR. ROOH ULLAH

2. Outlines
What is the zeolites
Structures and definitions
Broad features of zeolitic materials available
Acidity of zeolites
Shape-selective catalysis in zeolites
Modification of zeolites
The use of zeolites in catalysis today

3. Scope of Zeolite
Zeolites are inorganic crystalline solidswithsmall pores
(1-20 Å diameter) running throughout the solid
They are aluminosilicate framework structuresmade from
corner sharing SiO
4 and AlO
4
-
tetrahedra
–related structures can be made from AlPO
4,
TSand other compositions

4. Scopes of Zeolite
Landmarks
Y for FCC (1960s)
ZSM-5 (1970s)
AlPO
4& SAPOs(1980s)
S.T. Wilson, B.M. Lok, C.A. Messina, T.R. Cannanand E.M. FlanigenJ. Am.
Chem. Soc.104 (1982), p. 1146.
TS-1 (1980s)
M. Taramasso, G. Perego, B. Notari, US Patent No. 4410501 (1983).
MCM-41 (1990s)
C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuliand J.S. Beck. Nature359
(1992), p. 710

5. Definition of Zeolite
•Zeolite（Zeolite molecular sieve ）
–A
m+
y/m[(SiO
2)
x·(AlO
-
2)
y]·zH
2O
–Zeolites are crystalline aluminosilicateswith aframework
forming regular channelswith a diameter of up to ca. 1 nm.
These channels contain cations (frequently Na
+
ions), which
compensate the negative framework chargeand are very
mobile, and waterwhich desorbs upon heating without
destruction of the crystalline structure.
•With the discovery of a large number of molecular sieve materials,
the definition of Zeolite is also changing.

6. Types of Zeolite
•Framework Density (FD)
•Definition: (Number of T-Atoms/ 1000Å
3
)
•Non-zeolitic framework structures （dense phase):
–FD = 20 –21
•Zeolite with fully cross-linked frameworks:
–FD = 12.1 –20.6

7. Types of Zeolite
•FD12:
–FD’s less than 12 have only been encountered for the
interrupted framework
–The FD is obviously related to the pore volume but does
not reflect the size of the pore openings

8. Types of Zeolite
•IUPAC
•micropores: d
p 2.0 nm
–mesopores:2.0 nm< d
p50 nm
–macropores: d
p>50 nm
•ZeoliteUsually referred to as Si-Al molecular sieve

9. Types of Zeolite Catalysts
•There are many suggestions
•zeolite-like microporous materials
–zeotypes
–The most exact definition has not been given
–The famous Zeolite journal are "Microporous and
Mesoporous Materials".
–The corresponding classification is not uniform

10. Types of Zeolite Catalysts
Regular channel structure
The diameter of the channel is equivalent to the usual
molecular size
Zeolike material or zeotype can be used to represent materials
with a crystal structure similar to traditional zeolite
Micorporous, mesoporous
Microporous molecular sieve
Mesoporous material with uniform channels

11. Porous
Materials
Ordered
Porous
Materials
Zeolite-
like
Porous
Materials
Microporous
(Molecular
sieve)
Zeolite
Silicates
SiO
2
SiO
2
-Al
2
O
3
M-Si-Al
(M=Ti, Fe, Co, Ni,
V,…)
Phosphates
AlPO
4
MeAPO
SAPO
MeAPSO
others
Others M
xS
y, SiO
2
-GeO
2
Non-zeoliteCarbon molecular sieve
Mesoporous
Zeolite-likeMCM-41, SBA-15, M
x
O
y
Non-zeolite
Organic-ingornac
framework
Macroporous Materials
Non-Ordered Porous Materials (Amorphous)
Types of Zeolite

12. Why so much interest in Zeolites?
Well-defined molecular structure
Establish structure-property relationships
Prediction of properties from structure
BUT…
Disorder is an inescapable fact on zeolitic materials
Structure-Property relations are not always simple

13. Types of Zeolite Catalysts
Crystalline aluminosilicates
Most important class of solid acids
Important Environmental Applications
Catalytic Converters (Diesel and Gasoline)
DeNOxCatalyst in Power Plants
VOC Removal
Structure-property relation require detailed atomic
information

14. What types of applications are
zeolites used for?
Drying agents
–used for drying solvents
Shape selective separations
–e.g. dewaxingdiesel fuel
Shape selective catalysis
–predominantly acid catalysis, but also redox
Selective ion exchangers
–water softeners, radioactive waste treatment

15. Zeolites and Catalysis
Zeolites have the ability to act as catalysts for chemical
reactions which take place within the internal cavities.
An important class of reactions is that catalyzed by
hydrogen-exchanged zeolites, whose framework-bound
protons give rise to very high acidity.
This is exploited in many organic reactions, including crude
oil cracking, isomerization and fuelsynthesis.
Zeolites can also serve as oxidation or reductioncatalysts,
often after metals have been introduced into the framework.

16. Zeolites and Catalysis
It was only with the advent of synthetic zeolitesfrom ca.
1948 to 1955 (thanks, mostly, to the pioneering work of
Barrerand Milton) that thisclass of porous materialsbegan
to play a role in catalysis.
A landmark event was the introduction of synthetic (zeolites
X and Y) on an industrial scale in fluid catalytic cracking
(FCC)of heavy petroleum distillates in 1962, one of the
most important chemical processes worldwide.

17. Zeolites and Catalysis

18. The new zeolitic catalysts were not only orders of magnitude
more activethan the previously used amorphous silica–
alumina catalysts, but they also brought about a significant
increase in the yield of gasoline.
It can be estimated that this yield enhancement alone resulted
inan added valuein the order of at least several billion US
dollars per year.
It has further been estimated that, as a whole, the cost of
petroleum refining worldwide would be higher by at least 10
billion US dollars per year, if zeolites were not available today.
Zeolites and Catalysis

19. In the period after 1962, zeolite catalysts rapidly conquered
additional processes in the fields of petroleum refining and
basic petrochemistry.
The most important of these processes are hydrocracking of
heavy petroleum distillates, octane number enhancement of
light gasoline by isomerization, the synthesis of ethylbenzene
from benzene and ethene after the Mobil–Badger process, the
disproportionation of tolueneinto benzene and xylenes and
theisomerization of xylenes(to produce para-xylene, the
precursor chemical for terephthalic acid).
Zeolites and Catalysis

20. Adsorption and Separation
Theshape-selective propertiesof zeolites are also the basis
for their use inmolecular adsorption.
The ability preferentially to adsorb certain molecules, while
excluding others, has opened up a wide range ofmolecular
sieving applications.
Sometimes it is simply a matter of the size and shape of pores
controllingaccess into the zeolite. In other cases different
types of molecule enter the zeolite, but some diffusethrough
the channels more quickly, leaving others stuck behind, as in
the purification of para-xylene by silicalite.

21. Adsorption and Separation

22. Cation-containing zeolites are extensively used as
desiccantsdue to their high affinity for water, and also find
application in gas separation, where molecules are
differentiated on the basis of theirelectrostatic interactions
with the metal ions.
Conversely,hydrophobicsilica zeolites preferentially absorb
organic solvents.
Zeolites can thus separate molecules based on differences
of size, shape and polarity.
Adsorption and Separation

23. Adsorption and Separation

24. Zeolite and Environment
Zeolites contribute to a cleaner, safer environmentin a great
number of ways.
In fact nearly every application of zeolites has been driven by
environmental concerns, or plays a significant role in
reducing toxic waste and energy consumption.
In powder detergents, zeolites replaced harmful phosphate
builders, now banned in many parts of the world because of
water pollution risks.
Catalysts make a chemical process more efficient, thus saving
energy and indirectly reducing pollution.

25. As solid acids, zeolites reduce the need for corrosive
liquid acids, and as redox catalysts and sorbents, they
can remove atmospheric pollutants, such asengine
exhaust gases and ozone-depleting CFCs.
Zeolites can also be used to separate harmful organics
from water, and in removing heavy metal ions, including
those produced bynuclear fission, from water.
Adsorption and Separation

26. Applications of Zeolites