1
Zeolites and Zeolitic Materials
Molecular sieves = highly organized matrices of tunable pore shape,
size, and polarity for separation, recognition, and organization of
molecules with precision of about 1 Å
IUPAC classification of porous materials
Macroporous > 50 nm
Mesoporous 250 nm
Microporous  2 nm
Ultramicroporous  0.7 nm
Applications: detergent builders, adsorbents,
size-shape selective catalysts, supramolecular
chemistry, nanotechnology
Chemical composition
Silica SiO2
Aluminosilicates Mx
IAlxSi2-xO4 . nH2O
Aluminophosphates AlPO4 (isoelectronic with Si2O4)
Metallophosphates MPO4
Silicoaluminophosphates Mx
ISixAlP1-x O4
STEM ADF
Pores and Channels
2
ACO
AFI
SSY
UFI
STI
-CLO
3
Zeolite Types
>60 naturally occurring zeolites - large deposits of analcime, chabazite,
clinoptilolite, erionite, mordenite and phillipsite
>253 zeolite framework types (IZA - 2020)
many hundreds of synthetic zeolite compounds
Nomenclature http://www.iza-structure.org/
Structure types - three capital letter codes
Most well known zeolite archetypes: SOD, LTA, FAU, MOR, MFI
Aluminium Cobalt Phosphate - 1 (One) = ACO
• Four-connected (4c) frameworks
(over 1 000 000 possible 4c frameworks)
• Interrupted frameworks (denoted by a hyphen: –CLO, cloverite)
Structure types do not depend on: chemical composition, element
distribution, cell dimensions, symmetry
Several zeolite compounds can belong to the same structure type:
FAU – faujasite, Linde X, Y, Beryllophosphate-X, SAPO-37,
Zincophosphate-X
4
Zeolite Names
Names of zeolite materials:
• Trivial names – Alpha, Beta, Rho
• Chemical names – Gallogermanate-A
• Mineral names – Chabazite, Mordenite, Stilbite,
Sodalite
• Codes – AlPO4-5, 8, 11, ..., 54, ZSM-4, 18, 57, ...
• Brand names – Linde A, D, F, L, N, Q , R, T, W, X, Y
• University names
VPI-5 (Virginia Polytechnical Institute)
ULM-x (University Le Mans)
MU-n (Mulhouse, Université de Haute Alsace)
5
T
O
O
O
O
Zeolites Building Units
Isoelectronic relationship
(SiO2)2 [AlSiO4 ]- AlPO4
Primary building units = tetrahedra
Al(III)O4, P(V)O4, Si(IV)O4 and MO4
6
3R 4R
6R
8R
D4R
D6R
D8R
spiro-5
5-1 5-2 5-3
2-6-2 6 1 (C6R)6-2
4-1
4=1 4-2
5R
4-4=1
Secondary (Structural) Building Units (SBU)
P
O
Al
O
Al
O
PO
O
Al
O P
O
O
Al
O
O
P
O
O
R1
R2
R2
R1
R2
R1
R2
R1
Framework Type ACO
D4R = double four-ring
(= 8 T-atoms, Al, Si, P,…)
The whole network is constructed
by connection a single type of
SBU by oxygen bridges
7
Polyhedral
Composite
Building Units
Truncated octahedra
[4668] sodalite- or -cages)
Truncated cubeoctahedra
[4126886] (-cavities)
8
Chain Composite Building Units
(a) zig-zag unbranched single chain, periodicity of two
(b) sawtooth unbranched single chain, periodicity of three
(c) crankshaft unbranched single chain, periodicity of four
(d) natrolite branched single chain
(e) double crankshaft chain, an unbranched double chain
(f) narsarsukite chain, a branched double chain
(g) a pentasil chain
9
Sodalite Unit
Sodalite cage = Truncated octahedron
Truncated octahedra
[4668] sodalite- or -cages)
Truncated cubeoctahedra
[4126886] (-cavities)
10
Sodalite Unit
Packing of the sodalite (-cage) units:
SOD – bcc, sharing of 4-rings
LTA – sc, 4-rings connected through O bridges
FAU (faujasite) – cubic diamond, 6-rings connected through O bridges
EMT – hexagonal diamond, 6-rings connected through O bridges
Building Units in Zeolite A (LTA)
11
(a) [TO4] tetrahedra as primary BU
(b) Four-rings 4R SBU
(c) lB fuenfer chains
(d) Cubes D4R [46] SBU
(e) Truncated octahedra [4668] (sodalite- or -cages)
(f) Truncated cubeoctahedra [4126886] (-cavities)
12
Pores and Channels in Zeolite A (LTA)
(a) the sodalite -cage [4668]
(b) the -cavity [4126886]
(c) the 3-dimensional channel
system
(d) the 8-ring defining the 0.41
nm effective channel width
13
AFM growth studies of LTA
S. Sugiyama et. al. Microporous and Mesoporous Materials 28 (1999) 1–7
Zeolite A (LTA)
D4R
AFM growth studies of LTA
S. Sugiyama et. al. Microporous and Mesoporous Materials 28 (1999) 1–7
14
Zeolite A (LTA)
D4R
HRTEM of a Zeolite A (LTA) Crystal
15
Zeolite A crystal in an amorphous gel particle after
a synthesis time of 3 days at room temperature
16
Zeolite FAU (X and Y) and EMT
17
Zeolite FAU (X and Y) and EMT
Cubic diamond (sfalerite) Hexagonal diamond (wurzite)
Sodalite -cage = carbon atom
18
Molecular Sieves
Zeolite Cation Code Pore diameter
A Na 4A 0.42 nm
Ca 5A 0.48 nm
Na, K 3A 0.38 nm
X Na 13X 0.8-1.0 nm
Ca 10X 0.7 nm
Y as X, contains more Si
Zeolite A = LTA
Zeolite X and Y = FAU
19
Framework Density
Framework density (FD)
FD = the number of tetrahedral
atoms (T-atoms = Si, Al, P,…) per
cubic nanometer (1000 Å3)
FD is related to the void volume
of the crystal: as the FD value
decreases, the void volume and
capacity for adsorption increases
FD < 20 are characteristic of
microporous structures
the minimum known FD is 12.5
with the void occupying just over
half of the crystal volume
Quartz
Crist/Tridym
LTA/FAU/EMT
-CLO
Dense
structures
Zeolite
frameworks
Pores
20
Various sizes (4 - 13 Å), shapes (circular, elliptical, cloverleaf-like),
and connectivity (1-3D)
The size of the rings formed by the TO4 tetrahedra ranges from 4 to
18 of the T-atoms and determines the pore aperture
Extraframework charge-balancing cations
Ion-exchangeable, size, charge, positions, distribution, ordering,
coordination number
Si-to-Al ratio
Influences cation content, hydro-phobicity/-philicity, acidity
Löwenstein rule:
absence of the Al-O-Al moieties, in aluminosilicates Si/Al > 1
Linde A (LTA) Si/Al = 1
ZK-4 (LTA) Si/Al = 2.5
ZSM-5 Si/Al = 20 - 
Pure SiO2 Si/Al = 
Pores Sizes
21
2 nm 50 nm
-CLO: GaPO4, 20-membered clover
ring, the lowest FD = 11.1
-CLO
22
Zeolite Synthesis
Synthesis - an empirical and heuristic process, new phases
are often discovered by serendipity
Aluminosilicates – at high pH
 Mixing of precursors
NaAl(OH)4(aq) + Na2SiO3 (aq) + NaOH (aq), 25 C
Condensation-polymerization, gel formation
 Ageing of gel
Na(H2O)n
+ template effect  Naa(AlO2)b(SiO2)c.NaOH.H2O (gel) at 25-175 C
 Hydrothermal crystallization of amorphous gel, 60-200 C
Nax(AlO2)x(SiO2)y.zH2O (microcrystals)
 Separation of the solid product by filtration
 Calcination
- occluded water, removed by 25-500 C vacuum thermal dehydration
- template removal – calcination in O2 at 400-900 C removes the guest
molecules from the framework without altering it
 Extraction (neutral templates)
23
Zeolite Synthesis
Structure of the zeolite product depends on many
reaction parameters:
- Composition, precursors
- Concentrations and reactant ratios
- Order of mixing
- Temperature
- Ageing time (hours to weeks)
- Crystallization time (days to weeks, kinetics of the
structure-directing process is slow)
- pH
- Stirring/no stirring
- Pressure
- Seeding
- Reactor material (PTFE, glass, steel)
- Templates
Templates: Inorganic cations (Na+), organic cationic
quaternary alkylammonium salts, alkylamines,
aminoalcohols, crownethers, structure-directing, spacefilling,
charge-balancing
24
Templates
Space-filling - the least specific, observed, e.g., in the synthesis
of AlPO4-5: 23 different, structurally unrelated compounds, could be
employed, packing in the channels thereby increasing its stability
Structure-directing - a higher degree of specificity, only
tetramethylammonium hydroxide is effective in the synthesis of
AlPO4-20
- elongated molecules, such as linear diamines, initiate the
formation of channels
- nondirectional-shaped guests leads to the formation of cage-like
cavities, the size of these cavities correlates with the size of freely
rotating guests
True templating - very rare, it requires even more precise hostguest
fit which results in the cessation of the free guest-molecule
rotation
A curiosity: aluminophosphate VPI-5 does not require any guest for
its formation!
Templates or guest compounds – Structure directing agents (SDA)
Three levels of the guest action with increasing structure-directing specificity:
25
Templates
The ratio TO2/(C + N + O) is a measure of space-filling of the framework
by the guest molecules, characteristic for a specific guest and structure
Existence of primary and secondary units in a synthesis mixture
4R, 6R, 8R, D4R, D6R, 5-1, cubooctahedron
26
Zeolite Synthesis Mechanisms
Structure directing agents (SDA)
(1) Formation of hydrogen
bonds / charge attraction
between the structure directing
agent (SDA) and the silicates
present in the synthesis
solution
(2) Oligomerisation of silicates
to primary units (2-3 nm)
(3) Condensation of the silicateSDA
species to give the first
stable crystalline nuclei (10 nm)
(4) Crystal growth (10-100 m)
27
Zeolite Synthesis Mechanisms
Gel dissolution and solution
mediated crystallization
(SBU in solution)
“In situ” rearrangement of
the gel
28
Crystallization Mechanism
Crystallization kinetics of zeolite formation
29
Zeolites
Wide range of solid state characterization methods for zeolites:
diffraction, microscopy, spectroscopy, thermal, gas adsorption
Zeolite post modification for controlling properties of zeolites
Tailoring channel, cage, window dimensions:
Cation choice (Ca2+ exchanged for Na+)
Larger Si/Al
decreases unit cell parameters, window size
decreases number of cations, free space
increases hydrophobicity
Reaction temperature, higher T, larger pores
 Stability Rules
- Lőwenstein rule - the principle of aluminium avoidance: never Al-O-Al
- Dempsey rule: Al-O-Si-O-Si-O-Al is more stable than Al-O-Si-O-Al,
negative charges at Al as far as possible
- NNN-principle: minimalization of Al-Al-next-nearest neighbor interactions
30
Cation Positions
FAU
Several extra framework sites are occupied
by cations in faujasites (FAU)
A standard nomenclature:
I at the center of the double 6-rings
I' in the sodalite cage, adjacent to a
hexagonal ring shared by the sodalite cage
and a double 6-ring
II in the supercage, adjacent to an
unshared hexagonal face of a sodalite cage
II' in the sodalite cage, adjacent to an
unshared hexagonal face
III is located on the walls of the supercage
Applications of Natural Mineral Zeolites
31
Aquaculture - Ammonia filtration in fish hatcheries - Biofilter media
Agriculture - Odor control - Confined animal environmental control
Livestock feed additives
Horticulture - Nurseries, Greenhouses
Floriculture - Vegetables/herbs - Foliage
Tree and shrub transplanting
Turf grass soil amendment
Reclamation, revegetation, landscaping
Silviculture (forestry, tree plantations)
Medium for hydroponic growing
Household Products - Household odor control - Pet odor control
Industrial Products - Absorbents for oil and spills - Gas separations
Radioactive Waste - Site remediation/decontamination
Water Treatment - Water filtration - Heavy metal removal - Swimming
pools - Wastewater Treatment - Ammonia removal in municipal
sludge/wastewater
Heavy metal removal - Septic leach fields
32
Applications of Synthetic Zeolite
Production 1.6 million tons p.a. (about half that of natural
zeolites)
Detergents - water softening by ion exchange (82 %) zeolites
A and X
Desiccants/absorption (5 %) - zeolites A, X, Y and
mordenite
Host-guest inclusion, atoms, ions, molecules, radicals,
organometallics, coordination compounds, clusters,
polymers (conducting, insulating)
Nanoreaction chambers (ship-in-a-bottle)
Advanced zeolite devices, electronic, optical, magnetic
applications, nanoscale materials, size tunable
properties, QSEs
Heterogeneous catalysts (8 %) - zeolite Y (faujasite, 96
wt.%), mordenite, ZSM-5, zeolite Beta
33
Solid acid catalysts for the hydrocarbon cracking
Introducing Bronsted acidity into zeolites:
(1) direct H+-exchange of the charge-compensating metal
cations
(2) NH4
+ -exchange of the compensating metal cations
followed by calcination to decompose the ammonium
cation leaving a proton on the surface
(3) exchange with polyvalent cations that can generate H+
via partial hydrolysis of H2O molecules
(4) exchange by metal cations that can be reduced by H2 to
a lower valence state, generating protons on the surface
Brønsted Acidity
34
Tuning Brønsted acidity:
• Ion exchange for NH4
+
• Pyrolysis to expel NH3
• Calcination to expel H2O
Solid acid for the hydrocarbon
cracking
The larger the Si/Al ratio of a
zeolite, the more Brønsted
acidic is the OH, but the
number of these sites
decreases
Brønsted Acidity
Na Na
O
Si
O
Al
O
Si
O
Al
O
Si
O
O O O O O O O O O O
O
Si
O
Al
O
Si
O
Al
O
Si
O
O O O O O O O O O O
-Na+NH4
NH4 NH4
Ion Exchange
O
Si
O
Al
O
Si
O
Al
O
Si
O
O O O O O O O O O O
H H
O
Si
O
Al
O O O O
Si
O
Al
O
Si
O
O O O O O O
Heating -NH3
-H2OCalcination 600 oC
Bronsted acid
Lewis acid
450 °C
35
Strong Brønsted Acidity
Protonation of benzene
-complex Transition state for
H/D exchange
Low T High T
Not present in zeolites
Brønsted Acidity
36
37
Brønsted Acidity
FAU
3648 cm−1 site 1 (pointing to the supercage)
3625 cm−1 site 1‘ or 4 (pointing to the supercage)
3571 cm−1 site 2 (pointing to the sodalite cage)
3526 cm−1 site 3 (pointing to the hexagonal prism)
3744 cm−1 free terminal OH at the external surface
IR vibrations for OH groups
located at different sites in FAU
( = lattice oxygens)
38
Size-shape selective
catalysis, separations,
sensing
Selectivity at:
• Reactants
• Products
• Transition state
Size-Shape Selectivity
39
Size-shape selective catalysis of hexane cracking
MSE zeolite - framework with 3-dimensional 10-MR or 12-MR micropores
Si/Al = 51
High selectivity to propylene, low coking
Fluid Catalytic Cracking (FCC)
40
Gas Separation by Zeolites
Separation of xylene isomers by pervaporation through a
MFI membrane
41
Isoelectronic relationship of AlPO4 to (SiO2)2
Ionic radius of Si4+ (0.26 Å) is very close to the average of the
ionic radii of Al3+ (0.39 Å) and P5+ (0.17 Å)
Many similarities between aluminosilicate and AlPO4 molecular
sieves
Dense AlPO4 phases are isomorphic with the structural forms
of SiO2: quartz, tridymite, and cristobalite
Aluminosilicate framework charge balanced by extraframework
cations
Aluminophosphate frameworks neutral (AlO2
-)(PO2
+) = AlPO4
Aluminophosphates
42
Aluminophosphates
Some AlPO4 structures are analogous to zeolites while other are
novel and unique to this class of molecular sieves
Only even-number rings = the strict alternation of Al and P atoms
Incorporation of elements such as Si, Mg, Fe, Ti, Co, Zn, Mn, Ga,
Ge, Be, Li, As, and B into the tetrahedral sites of AlPO4 gives a
vast number of element-substituted molecular sieves (MeAPO,
MeAPSO, SAPO) important heterogeneous catalysts
M1+, M2+, and M3+ incorporate into the Al sites
M5+ elements incorporate into the P sites
This substitution introduces a negative charge on these
frameworks
Si4+, Ti4+, and Ge4+ can either replace P and introduce a negative
charge or a pair of these atoms can replace an Al/P pair and
retain the charge neutrality
43
Aluminophosphates
AFI(ve)
AEL(even)
ATO(three-one)
AFO(four-one)
44
Aluminophosphate Synthesis
Aluminophosphates prepared by the hydrothermal synthesis
Source of Al: pseudoboehmite, Al(O)(OH), Al(Oi-Pr)3
Mixing with aqueous H3PO4 in the equimolar ratio – low pH !
Forms an AlPO4 gel, left to age
One equivalent of a guest compound = template
Crystallization in a reactor
Separated by filtration, washed with water
Calcination
Other zeolite materials
Oxide and non-oxide frameworks, sulfides, selenides
Coordination frameworks, supramolecular zeolites
The quest for larger and larger pore sizes
45
Cobalto-Aluminophosphate
ACP-1 (Co/Al 8.0)
bcc arrangement of the double 4-ring units (D4R)
Ethylenediamine molecules are located inside 8-ring channels
At the centre of each D4R, there is a water molecule, 2.31 Å away from
four metal sites
Al(O-iPr)3, CoCO3.H2O, 85% H3PO4, ethylene glycol, ethylenediamine, pH 8.4
Heated in a Teflon-coated steel autoclave at 180 °C for 4 d
ACO
46
Synthesis of Double 4-ring Units (D4R)
P
O
Al
O
Al
O
PO
O
Al
O P
O
O
Al
O
O
P
O
O
R1
R2
R2
R1
R2
R1
R2
R1
ACO
Connect the double 4-ring units (D4R)
47
Metallo-Organic Framework (MOF)
Structures
20 000 structures known (2019), 1000 new per year
Porous coordination polymers (PCP)
Metal centers
• Coordinative bonds
• Coordination numbers 3-6
• Bond angles
Polytopic Ligands
• Organic spacers
• Flexible – rigid
• Variable length
• Directionality
Reticular Chemistry
48
A building-block approach to the synthesis of nanostructured
materials
Materials formed by a bottom-up self-assembly of building blocks
(reticuli) with predetermined symmetry
Targeted, predictable, and straightforward design and synthesis
Chemistry of the self-assembly and the design should not interact
Building blocks:
• Discrete symmetry: C∞, C2, C3, C4, Td
• Rigid, inert
• Functional groups for linking
• Suitable linking reaction
• Discrete bonding direction
Reticular Chemistry
49
50
Basic Nets
51
Polytopic Organic Linkers
• N-based polydentate donors
• Carboxylates
52
Polytopic N-bound Organic Linkers
Cationic framework structures
Evacuation of guests within the pores usually results in
collapse of the host framework
53
Metallo-Organic Framework Structures
54
Polytopic Carboxylate Linkers
55
Polytopic Carboxylate Linkers
Aggregation of metal ions into M-O-C clusters
• form more rigid frameworks
• frameworks are neutral
• no need for counterions
56
Inorganic Secondary Building Units (SBUs)
(a) the square ‘‘paddlewheel’’, with two terminal ligand sites
(b) the octahedral ‘‘basic zinc acetate’’ cluster
(c) the trigonal prismatic oxo-centered trimer, with three terminal
ligand sites
The SBUs are reticulated into MOF by linking the carboxylate
carbons with organic units or by replacement of the terminal
ligands
57
Inorganic Secondary Building Units (SBUs)
58
Organic Secondary Building Units (SBUs)
(d) square tetrakis(4-carboxyphenyl)porphyrin
(e) tetrahedral adamantane-1,3,5,7-tetracarboxylic
acid
(f) trigonal 1,3,5-tris(4-carboxyphenyl)benzene
MOF Crystallization
59
Entropy-driven errors in self-assembly
Mechanism for error correction required
The reaction should be reversible to allow for thermodynamic
control
No side-reactions should exist (loss of reagents, contamination)
The building block rigidity, symmetry and discrete bonding
direction decrease the incidence of errors
Solvothermal methods – control over p, T, μ – to establish
equilibrium
Low energy difference
(ΔH < –TΔS)
Isoreticular Metal-Organic Frameworks
(IRMOFs)
60
The same cubic topology, the links differ both in functionality (IRMOF-1 to -7)
and in length (IRMOF-8 to -16), expansion of the links increases the internal
voidspace (yellow spheres), it also allows the formation of catenated phases
(IRMOF-9, -11, -13, and -15)
Isoreticular Metal-Organic Frameworks
(IRMOFs)
61
IRMOF-1 IRMOF-14
Organic linkers
for IRMOFs-X
BDC
62
Zn4O(BDC)3.(DMF)8(C6H5Cl)
MOF-5
a primitive cubic lattice
Cavity diam. 18.5 Å
Nature, 1999, 402, 276
Synthesis
• Zn(NO3)2 + H2BDC in DMF/PhCl
• Addition of TEA: deprotonation of
H2BDC
• Addition of Zn2+
• Addition of H2O2: formation of O2- in
the cluster center = Zn4O
63
Metal-Organic Framework MOF-5
cluster Zn4O(O2CR)6
a primitive cubic lattice
64
MOF-5
Stable even after desolvation
at 300 °C in air
Gas sorption isotherms
Metal-Organic Framework MOF-5
65
Interpenetration
MOF-9
66
MIL-100 and MIL-101
MIL-101 Record surface area 5 900 m2/g
67
Inorganic and Metallo-Organic Quartz
68
COF - Covalent Organic Frameworks
Linking reactions
produce covalent bonds
Covalent Organic Frameworks
69
Linking reactions
70
Covalent Organic Frameworks
COF-1
Solvents - reactants are poorly soluble
(to slow down the reversible condensation)
mesitylene-dioxane (1:1)
Sealed pyrex tubes, 110 °C, 72 h, minimize defects
by self-healing
COF-1 = microcrystalline, high yield, high structural
order by XRD
Solvent molecules are enclosed inside the pores,
can be removed at 200 ºC without collapse of the
crystalline structure
Surface area of 711 m2 g-1, pore size 0.7 nm
Interlayer spacing: 0.333 nm
Covalent Organic Frameworks
71
+ 23
COF-5
Surface area 1590
m2/g
Pore size: 2.7 nm
Interlayer spacing:
0.346 nm
Covalent Organic Frameworks
72
Covalent Organic Frameworks
73
Layer stackings: AA, AB, serrated and inclined
74
Covalent Organic Frameworks
3D frameworks
COF-102, COF-103, COF-105,
and COF-108
COF-108 - bor structure
two different types of pores
diameters of 15.2 and 29.6 Å
density 0.17 g cm-3
Surface area, m2 g-1
COF 102 3472
COF 103 4210
Covalent Organic Frameworks
75
Borazine COFs
76
BET: 1178 m2/g
Pore size: 0.64 nm
Jackson K., Reich T., Chem. Commun., 2012, 48,
8823–8825