![Definition of Zeolite
• Zeolite（ Zeolite molecular sieve ）
– Am+
y/m[(SiO2)x·(AlO-
2)y]·zH2O
– Zeolites are crystalline aluminosilicates with a framework
forming regular channels with a diameter of up to ca. 1 nm.
These channels contain cations (frequently Na+ ions), which
compensate the negative framework charge and are very
mobile, and water which 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.](https://image.slidesharecdn.com/zeolites1-240428044532-4534a8b0/85/Zeolites1-nanotechnolg-and-ebvironemnt-ppt-5-320.jpg)
Zeolites1. nanotechnolg and ebvironemnt ppt
- 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 solids with small pores (1-20 Å diameter) running throughout the solid They are aluminosilicate framework structures made from corner sharing SiO4 and AlO4 - tetrahedra – related structures can be made from AlPO4, TS and other compositions
- 4. Scopes of Zeolite Landmarks Y for FCC (1960s) ZSM-5 (1970s) AlPO4 & SAPOs (1980s) S.T. Wilson, B.M. Lok, C.A. Messina, T.R. Cannan and E.M. Flanigen J. 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. Vartuli and J.S. Beck. Nature 359 (1992), p. 710
- 5. Definition of Zeolite • Zeolite（ Zeolite molecular sieve ） – Am+ y/m[(SiO2)x·(AlO- 2)y]·zH2O – Zeolites are crystalline aluminosilicates with a framework forming regular channels with a diameter of up to ca. 1 nm. These channels contain cations (frequently Na+ ions), which compensate the negative framework charge and are very mobile, and water which 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/ 1000Å3) • Non-zeolitic framework structures （dense phase): – FD = 20 – 21 • Zeolite with fully cross-linked frameworks: – FD = 12.1 – 20.6
- 7. Types of Zeolite • FD12: – 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: dp 2.0 nm – mesopores: 2.0 nm< dp 50 nm – macropores: dp>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 SiO2 SiO2-Al2O3 M-Si-Al (M=Ti, Fe, Co, Ni, V,…) Phosphates AlPO4 MeAPO SAPO MeAPSO others Others MxSy, SiO2-GeO2 Non-zeolite Carbon molecular sieve Mesoporous Zeolite-like MCM-41, SBA-15, MxOy 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) DeNOx Catalyst 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. dewaxing diesel 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 fuel synthesis. Zeolites can also serve as oxidation or reduction catalysts, often after metals have been introduced into the framework.
- 16. Zeolites and Catalysis It was only with the advent of synthetic zeolites from ca. 1948 to 1955 (thanks, mostly, to the pioneering work of Barrer and Milton) that this class of porous materials began 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.
- 18. The new zeolitic catalysts were not only orders of magnitude more active than 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 in an added value in 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 toluene into benzene and xylenes and the isomerization of xylenes (to produce para-xylene, the precursor chemical for terephthalic acid). Zeolites and Catalysis
- 20. Adsorption and Separation The shape-selective properties of zeolites are also the basis for their use in molecular adsorption. The ability preferentially to adsorb certain molecules, while excluding others, has opened up a wide range of molecular sieving applications. Sometimes it is simply a matter of the size and shape of pores controlling access into the zeolite. In other cases different types of molecule enter the zeolite, but some diffuse through the channels more quickly, leaving others stuck behind, as in the purification of para-xylene by silicalite.
- 22. Cation-containing zeolites are extensively used as desiccants due to their high affinity for water, and also find application in gas separation, where molecules are differentiated on the basis of their electrostatic interactions with the metal ions. Conversely, hydrophobic silica zeolites preferentially absorb organic solvents. Zeolites can thus separate molecules based on differences of size, shape and polarity. Adsorption and Separation
- 24. Zeolite and Environment Zeolites contribute to a cleaner, safer environment in 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 as engine 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 by nuclear fission, from water. Adsorption and Separation