Molecular Sieves - Science and Technology - Vol. 6 - Characterization II / 06-Isomorphous Substitution in Zeolites
.pdfMol Sieves (2007) 5: 365–478 DOI 10.1007/3829_006
♥ Springer-Verlag Berlin Heidelberg 2006 Published online: 17 February 2006
Isomorphous Substitution in Zeolites
J. B.Nagy1 ( ) · R. Aiello2 · G. Giordano2 · A. Katovic2 · F. Testa2 · Z. Kónya3 · I. Kiricsi3
1Laboratoire de RMN, Facultes Universitaires Notre-Dame de la Paix, 61 rue de Bruxelles, 5000 Namur, Belgium
janos.bnagy@fundp.ac.be
2Department of Applied Chemistry, University of Calabria, Via Pietro Bucci, 87030 (CS) Arcavacata di Rende, Italy
3Department of Applied and Environmental Chemistry, University of Szeged, Rerrich Bela ter 1., 6720 Szeged, Hungary
1 |
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
371 |
2 |
Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
373 |
2.1 |
Synthesis Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
373 |
2.1.1 |
[B]-MFI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
373 |
2.1.2 |
[Ga]-MFI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
381 |
2.1.3 |
[Fe]-MFI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
381 |
2.1.4 |
[Fe]-BEA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
383 |
2.1.5 |
[Fe]-MOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
384 |
2.1.6 |
[Co]-MFI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
384 |
2.1.7 |
[Zn]-MFI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
385 |
2.1.8 |
Cu-TON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
385 |
2.2 |
Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
386 |
2.2.1 |
General Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . |
386 |
2.2.2 |
The Cu-TON Obtained by Ion Exchange . . . . . . . . . . . . . . . . . . . |
387 |
3 |
Results and General Discussion . . . . . . . . . . . . . . . . . . . . . . . . |
388 |
3.1 |
[B]-MFI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
388 |
3.2 |
[Ga]-MFI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
392 |
3.3Influence of Alkali Cations on the Incorporation of Al, B and Ga
|
Into the MFI Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
398 |
3.4 |
[Fe]-MFI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
402 |
3.4.1 |
Fluoride Route . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
402 |
3.4.2 |
Alkaline Route . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
413 |
3.4.3 |
Catalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
424 |
3.4.4 |
Role of the Catalyst Composition . . . . . . . . . . . . . . . . . . . . . . . |
425 |
3.4.5 |
Role of Methodology in Iron Introduction in [Fe]-MFI Catalysts . . . . . . |
428 |
3.5 |
[Fe]-BEA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
429 |
3.6 |
[Fe]-MOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
432 |
3.7 |
[Fe]-TON, [Fe]-MTW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
433 |
3.8 |
[Fe,Al]-MCM-22 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
435 |
3.9 |
[Co]-MFI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
441 |
3.10 |
Calcination Using Ozone: Preservation of Framework Elements . . . . . . |
446 |
3.11 |
Cu-TON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
453 |
3.12 |
[Zn]-MFI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
455 |
366 |
J. B.Nagy et al. |
3.13Dealumination of Levyne –
|
Characterization of Framework and Extra-Framework Species . . . . . . . |
460 |
|
4 |
Conclusions . |
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
466 |
References . . . . . |
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
467 |
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Abbreviations1 |
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|
|
1D NMR |
One-dimensional nuclear magnetic resonance (spectroscopy) |
|
|
2D 3QMAS NMR |
Two-dimensional three quantum magic angle spinning nuclear |
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|
|
magnetic resonance (spectroscopy) |
|
3QMAS NMR |
Three quantum magic angle spinning nuclear magnetic resonance |
||
A|| |
|
(spectroscopy) |
|
|
Electron-nucleus coupling constant for the component parallel to |
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|
|
the symmetry axis |
|
AAS |
|
Atomic absorption spectroscopy |
|
27Al MAS NMR |
Aluminum magic angle spinning nuclear magnetic resonance |
||
|
|
(spectroscopy) |
|
AlO |
|
Octahedrally coordinated framework aluminum atom |
|
AlT |
|
Tetrahedrally coordinated framework aluminum atom |
|
AlPO4-11 |
Microporous aluminophosphate zeolite-like structure (cf. [70]) |
|
|
[Al]-ZSM-5 |
Zeolite structure (MFI, cf. [70]) containing aluminum in the |
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|
|
framework2 |
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Amp |
|
Peak-to-peak amplitude |
|
AS |
|
As synthesized |
|
AST |
|
Page 86 zeolite structure (cf. [70]) |
|
AV-1 |
|
Sodium yttrium silicate structure (cf. [156]) |
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9Be NMR |
Beryllium nuclear magnetic resonance (spectroscopy) |
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|
BET |
|
Brunauer-Emmett-Teller specific surface measurement |
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BEA |
|
Zeolite structure, acronym for zeolite Beta (cf. [70]) |
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[B]-BEA |
Zeolite structure (BEA, cf. [70]) containing boron in the framework |
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[B]-EUO |
Zeolite structure (EUO, cf. [70]) containing boron in the framework |
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[B]-FER |
Zeolite structure (FER, cf. [70]) containing boron in the framework |
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[B]-LEV |
Zeolite structure (LEV, cf. [70]) containing boron in the framework |
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[B]-MEL |
Zeolite structure (MEL, cf. [70]) containing boron in the framework |
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[B]-MFI |
Zeolite structure (MFI, cf. [70]) containing boron in the framework |
||
|
|
(cf. [181–183]; Testa F, Chiappetta R, Crea F, Aiello R, Fonseca A, |
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|
|
Bertrand JC, Demortier G, Guth JL, Delmotte L, B.Nagy J, submitted |
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|
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for publication) |
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[B]-SSZ24 |
Zeolite structure (SSZ24, cf. [70]) containing boron in the frame- |
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|
|
work |
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1 Unfortunately, many of the above-indicated abbreviations have various meanings (vide supra); in view of the current conventions in the literature, this is hardly avoidable. However, the correct meaning of the abbreviations should follow from the respective context.
2 Presenting an element symbol in square brackets should indicate that the respective element is supposed to be incorporated into the framework of the material designated by the subsequent acronym or abbreviation. For instance, “[B]-ZSM-5” is indicating that boron is incorporated into the framework of ZSM-5.
Isomorphous Substitution in Zeolites |
367 |
|
[B]-ZSM-5 |
Zeolite structure (MFI, cf. [70]) containing boron in the framework |
|
BU |
Chemical identity of the Fe(III) species |
|
13C MAS NMR |
Carbon magic angle spinning nuclear magnetic resonance (spec- |
|
|
troscopy) |
|
Cs-[Fe]-silicalite-1 Zeolite structure (cf. [70]) containing iron in the framework and
|
charge-compensating cesium ion in extra-framework position |
Cs-[Fe]-ZSM-5 |
Zeolite structure (cf. [70]) containing iron in the framework and |
|
charge-compensating cesium ion in extra-framework position |
CIT-6 |
Zeolite structure (BEA structure, cf. [70]) |
[Co]-MFI |
Zeolite structure (MFI, cf. [70]) containing Co in the framework |
|
(cf. [196, 197]) |
Cu-TON |
Zeolite structure (TON, cf. [70]) containing Cu in charge-compen- |
|
sating extra-framework position (cf. [203]) |
CVD |
Chemical vapor deposition |
CCVD |
Catalytic chemical vapor deposition |
CQ |
Quadrupole coupling constant |
DAS |
Dynamic angle spinning (spectroscopy) |
deferrization |
Removal of iron |
DR |
Diffuse reflectance (spectroscopy) |
DSC |
Differential scanning calorimetry |
DTA |
Differential thermal analysis |
DTG |
Differential thermogravimetry |
EFW |
Extra framework |
EG |
Ethylene glycol |
EMT |
Zeolite structure; hexagonal faujasite (cf. [70]) |
EPR |
Electron paramagnetic resonance (spectroscopy) (acronym for |
|
ESR) |
EPMA |
Electron probe micro-analysis |
ESEM |
Environmental scanning electron microscopy |
ESCA |
Electron spectroscopy for chemical analysis (acronym for XPS) |
ESR |
Electron spin resonance (spectroscopy) (acronym for EPR) |
ETS-10 |
Zeolite structure (cf. [70]) |
EUO |
Zeolite structure (cf. [70]) |
EXAFS |
Extended X-ray absorption fine structure |
FAAS |
Flame atomic absorption spectroscopy |
FAU |
Zeolite structure; acronym for faujasite (cf. [70]) |
[Fe]-BEA |
Zeolite structure (BEA, cf. [70]) containing iron in the framework |
|
(cf. [194]) |
[Fe,Al]-BEA |
Zeolite structure (BEA, cf. [70]) containing iron and aluminum in |
|
the framework |
[Fe,Al]-MOR |
Zeolite structure (MOR, cf. [70]) containing iron and aluminum in |
|
the framework |
[Fe]-MCM-22 |
Zeolite structure (acronym or IZA structure code is MWW; cf. [70]) |
|
containing iron in the pore walls |
[Fe,Al]-MCM-22 |
Zeolite structure (acronym or IZA structure code is MWW; cf. [70]) |
|
containing iron and aluminum in the pore walls |
[Fe]-MCM-41 |
Mesoporous MCM-41 material containing iron in the pore walls |
[Fe]-MFI |
Zeolite structure (MFI, cf. [70]) containing iron in the framework |
|
(cf. [185, 186]) |
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[Fe]-MTW |
Zeolite structure (MTW, cf. [70]) containing iron in the framework |
|
(cf. [189]) |
[Fe]-TON |
Zeolite structure (TON, cf. [70]) containing iron in the framework |
|
(cf. [189]) |
FER |
Zeolite structure; acronym for ferrierite (cf. [70]) |
FID |
Flame ionization detector (GC) |
FTIR |
Fourier transform infrared (spectroscopy) |
FW |
Framework |
FWHM |
Full line width at half-maximum (of a band) |
g |
g factor |
g|| |
g factor for the component parallel to the symmetry axis |
g |
g factor for the component perpendicular to the symmetry axis |
71Ga NMR |
Ga nuclear magnetic resonance (spectroscopy) |
[Ga]-BEA |
Zeolite with Beta (BEA) structure containing gallium in the frame- |
|
work, (cf. [146]) |
[Ga]-MCM-22 |
Zeolite structure (acronym or IZA structure code is MWW; cf. [70]) |
|
containing boron in the pore walls |
[Ga]-MFI |
Zeolite with MFI structure containing gallium in the framework, |
|
(cf. [183, 184]) |
[Ga]-ZSM-5 |
Zeolite with MFI structure containing gallium in the framework, |
|
(cf. [183, 184]) |
GC |
Gas chromatography |
H |
Magnetic field (in Tesla) |
1H MAS NMR |
Proton magic angle spinning nuclear magnetic resonance (spec- |
|
troscopy) |
HMI |
Hexamethylene imine |
HT |
High temperature |
I |
Intensity |
Irel |
Relative intensity |
ICP-AES |
Inductively coupled plasma atomic emission spectroscopy |
IR |
Infrared (spectroscopy) |
IS |
Isomer shift (Mössbauer spectroscopy) |
K-[Fe]-silicalite-1 |
Zeolite structure (cf. [70]) containing iron in the framework and |
|
charge-compensating potassium ion in extra-framework position |
L |
Length |
L |
Liter |
L/W |
Aspect ratio |
LEV |
Zeolite structure (acronym of levyne; cf. [70]) |
LT |
Low temperature |
LTL |
Linde-type L zeolite (cf. [70]) |
M |
Metal or metal cation |
MAS NMR |
Magic angle spinning nuclear magnetic resonance (spectroscopy) |
MFI |
Zeolite structure (of, e.g., ZSM-5 or silicalite, cf. [70]) |
MCM-22 |
Zeolite structure (acronym or IZA structure code is MWW; cf. [70]) |
MCM-41 |
Mesoporous material with hexagonal arrangement of the uniform |
|
mesopores (cf. Volume 1, Chapter 4 of this series) |
MCM-48 |
Mesoporous material with cubic arrangement of the uniform meso- |
|
pores (cf. Volume 1, Chapter 4 of this series) |
MCM-58 |
Zeolite structure (acronym or IZA structure code is IFR, cf. [70]) |
MEL |
Zeolite structure (cf. [70]) |
Isomorphous Substitution in Zeolites |
369 |
|
MeQ+ |
Methyl quinuclidinium cation |
|
MOR |
Zeolite structure; acronym for mordenite (cf. [70]) |
|
MQMAS |
Multiquantum magic angle spinning (NMR) |
|
MTT |
Zeolite structure (cf. [70]) |
|
MTW |
Zeolite structure (cf. [70]) |
|
Na-[Fe]-silicalite-1 Zeolite structure (cf. [70]) containing iron in the framework and
|
charge-compensating sodium ion in extra-framework position |
NCL-1 |
High-silica (nSi/nAl = 20 to infinity) zeolite (cf. [70]) |
NH4 -[Fe]-silicalite-1 |
Zeolite structure (cf. [70]) containing iron in the framework and |
|
charge-compensating ammonium ion in extra-framework position |
NMR |
Nuclear magnetic resonance |
Oh |
Octahedrally coordinated species |
OFF |
Zeolite structure, acronym for offretite (cf. [70]) |
PIGE |
Proton induced γ -ray emission |
PIXE |
Proton induced X-ray emission |
PQ |
Quadrupole-quadrupole interaction |
PTFE |
Polytetrafluorethylene |
PULSAR |
NMR simulation program (cf. [284]) |
Qcc |
Quadrupole coupling constant |
QS |
Quadrupole shift (Mössbauer spectroscopy) |
R |
Crystallization rate |
REDOR |
Rotational-echo double-resonance NMR experiments (cf. [87]) |
RI |
Spectral contribution (Mössbauer spectroscopy) |
SAM |
Scanning Auger microscopy |
SEM |
Scanning electron microscopy |
29Si MAS NMR |
Silicon magic angle spinning nuclear magnetic resonance (spec- |
|
troscopy) |
Si(1Ga) |
Si with 1 Ga in the neighborhood |
Sil-1 |
Zeolite structure (acronym of SIL-1, cf. [70]) |
Silicalite-1 |
Zeolite structure (cf. [70]) |
119Sn NMR |
Tin nuclear magnetic resonance (spectroscopy) |
SiOM |
Defect group (M = NH4, Na, K, Cs) |
SiOTPA |
Defect group |
SiOX |
Defect group (X =NH4, Na, K, Cs, H, TPA, . . .) |
SOD |
Zeolite structure, acronym for sodalite (cf. [70]) |
SSIMS |
Static secondary ion mass spectroscopy |
SSR |
Solid-state reaction |
SSZ-n |
Series of zeolite structures; aluminosilicates, e.g., SSZ-24 and SSZ- |
|
13, isostructural with corresponding aluminophosphates, AlPO4 |
|
(AFI) and AlPO4-34 (CHA structure) (cf. [70]) |
T |
Tetrahedrally coordinated framework atom (cation) such as Si, Al, |
|
Ti, Fe, V, B |
T |
Absolute temperature, in Kelvin (K) |
TIII |
Tetrahedrally coordinated trivalent framework atom (cation) such |
|
as Al, B, Ga |
Th |
Tetrahedrally coordinated species |
t1 |
Longitudinal relaxation time |
tind |
Reaction induction time |
tpulse |
Pulse length |
TA |
Thermal analysis |
370 |
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J. B.Nagy et al. |
TCD |
Thermal conductivity detector (GC) |
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TEAOH |
Tetraethylammonium hydroxide |
|
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TEOS |
Tetraethyl orthosilicate |
|
|
TEM |
Transmission electron microscopy |
|
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TG |
Thermogravimetry |
|
|
TMA |
Tetramethyl ammonium |
|
|
TON |
Zeolite structure; acronym for theta-1 (cf. [70]) |
|
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TPA |
Tetrapropyl ammonium |
|
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TPABr |
Tetrapropyl ammonium bromide |
|
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TPD |
Temperature-programmed desorption |
|
|
TPR |
Temperature-programmed reduction |
|
|
TS-1 |
ZSM-5 (MFI) structure containing small amounts of titanium be- |
||
|
sides silicon in the framework |
|
|
TsG-1 |
Zeolite structure (BEA, cf. [70]) |
|
|
VS-1 |
Zeolite structure (MFI, cf. [70]) containing vanadium besides sili- |
||
|
con in the framework |
|
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W |
Width |
|
|
UV |
Ultraviolet (spectroscopy) |
|
|
UV Res Raman |
Ultraviolet resonance Raman (spectroscopy) |
|
|
UV-Vis |
Ultraviolet-visible (spectroscopy) |
|
nSi/nAl ≤ 2.5, |
X |
Zeolite structure (faujasite type structure |
with |
|
|
cf. [70]) |
|
|
XANES |
X-ray absorption near edge spectroscopy |
|
|
XRD |
X-ray diffraction |
|
|
XRF |
X-ray fluorescence spectroscopy |
|
|
XPS |
X-ray photoelectron spectroscopy |
|
nSi/nAl ≥ 2.5, |
Y |
Zeolite structure (faujasite-type structure |
with |
|
|
cf. [70]) |
|
|
YAG |
Yttrium aluminum garnet (laser) |
|
|
[Zn]-MFI |
Zeolite structure (MFI, cf. [70]) containing Zn in the framework |
||
|
(cf. [198–200]) |
|
|
ZSM-5 |
Zeolite structure (MFI, cf. [70]) |
|
|
ZSM-12 |
Zeolite structure (cf. [70]) |
|
|
α |
Indicates the large cage in the structure of zeolite A (cf. [70]) |
||
α |
The main channel of ZSM-5 zeolite |
|
|
β |
Indicates the sodalite cage in, e.g., A-type or faujasite-type struc- |
||
|
ture (cf. [70]) |
|
|
β |
Mid positions in the six-membered rings of ZSM-5 zeolite |
||
γ |
Mid positions in the five-membered rings of ZSM-5 zeolite |
||
δ |
Chemical shift (NMR) |
|
|
δCS |
Chemical shift (NMR) |
|
|
2Θ |
Degree |
|
|
Θ |
Pulse angle |
|
|
λ |
Wavelength (in µm) |
|
|
ν |
Resonance frequency |
|
|
∆H |
Full line width at half-maximum (of a band) |
|
|
νL |
Larmor frequency |
|
|
νQ |
Quadrupole frequency |
|
|
νrot |
Rotation frequency |
|
|
νRF |
Radio frequency |
|
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Isomorphous Substitution in Zeolites |
371 |
1 Introduction
The isomorphous substitution of Si by other tetrahedrally coordinated heteroatoms such as BIII [1, 2], AlIII (ZSM-5) [3], TiIV(TS-1) [4–9], GaIII [10–14] and FeIII [15–18] in small amounts (up to 2–3 wt %) provides with new ma-
terials showing specific catalytic properties in oxidation and hydroxylation reactions related to the coordination state of the heteroatom [19]. Moreover, MFI-type materials with trivalent metal present in tetrahedral (T) sites have had tremendous impact as new shape-selective industrial catalysts hav-
ing tunable acidic strength. In fact, the acidic strength of the protons in the bridged Si(OH)TIII (T = B, Al, Fe, Ga) groups depends on the nature of the
trivalent heteroatom. Indeed, the choice of TIII critically affects this property according to the sequence of Al > Fe = Ga B [20–23]. The recent discovery of an Al-containing natural zeolite (mutinaite) with the MFI topology [24] also makes this structure relevant to the mineralogy.
[Ga]-ZSM-5 zeolites are interesting materials as selective catalysts in the transformation of low molecular weight alkanes to aromatics [25–27]. These catalysts were mostly synthesized in alkaline media, however, several fluorine-containing media (adding either HF or NH4F to the initial gel) have already been used [28, 29]. Note that the incorporation of gallium into the ZSM-5 structure is less effective than the incorporation of aluminum in the same reaction media [30]. The fluorine-containing reaction medium is generally made using either HF or NH4F as a source of F– ions [28, 29, 31]. Guth et al. have published a series of very interesting papers in which TIII elements (T = B, Al, Fe, Ga) were partially substituted for silicon in the MFI framework [32]. We have previously initiated a series of studies where the role of alkali cations was systematically explored. These studies include the synthesis of silicalite-1 [33–35], silicalite-2 [36], borosilicalite-1 [37, 38], ferrisilicalite-1 [39], ZSM-5 [40] and zeolite Beta [40, 41]. The differences in the catalytic activity of iron-containing and iron-supported zeolites are also very interesting, and several methods of preparation have been developed [42–44]. [Fe]-silicates with MFI [45, 46], MOR [47], BEA [48], MTT [49], TON [50] and MWW [51] structures have been synthesized in alkaline media. However, despite the fact that isomorphous substitution seems to be easier in fluoride-containing media [52], only [Fe]-ZSM-5 has been synthesized so far in the presence of NH4F as a mineralizing agent [53]. Although the introduction of boron, gallium, or iron is relatively easy and well documented [19], few studies are devoted to the introduction of Co(II) into the framework of zeolites [54]. As both the framework and the extra-framework Co-species seem to be active in catalysis [55], it is of paramount importance to synthesize and thoroughly characterize Co-containing zeolites [56]. Zinc has been reported as a component of various molecular sieves such as zincophosphates, zincoarsenates [57–60], zincoalumino-silicates [61–63],
372 |
J. B.Nagy et al. |
zincosilicates [64–68], and zincoaluminonophosphates [19]. In some cases crystalline analogs of zeolite structures have been obtained under unusually mild conditions and crystallization occurred almost spontaneously on mixing the substrate solutions [57] or even on grinding the substrates [69]. The resulting zincophosphates and zincoarsenates, however, were unstable and usually decomposed above 200 ◦C. The reported zincosilicates were more stable, although most novel structures showed a narrow pore system [54, 64– 68], not suitable for catalysis and adsorption. The MFI structure (zeolites ZSM-5) [70] has been very often used as a catalyst. Besides the efficiency of active sites (mainly strong acid sites), the medium-sized channels provide shape selective effects for the reactions of commercial importance. Therefore, the preparation of the zincosilicalite structure is also of interest. Due to the double negative charge of the tetrahedral lattice zinc, it could be modified with various cations including protons and might be considered as catalysts for various reactions. Moreover, some redox activity could result from the presence of zinc in the lattice. The zinc-modified MFI zeolites have been applied as active catalysts in the Cyclar process [62, 63, 71], which consists in the formation of aromatics from light paraffins. The catalysts used in methanol synthesis contain mostly zinc and copper oxides [72]; it is conceivable that MFI zincosilicate modified with copper cations could be efficient for this reaction. The well-ordered crystalline structure as well as the uniform pore system could be advantageous for the catalyst performance. Attempts to synthesize MFI aluminosilicate with some admixture of zinc [62, 73–75] as well as zincosilicate [68, 76] have been reported.
Due to environmental problems in the last years great attention has been devoted to air pollution. The automotive air pollutants (NOX , CO and hydrocarbons) give large contribution to the total air pollutants. In order to reduce emission of pollutants, the trend in the automotive industry is to substitute traditional engines with engines operating under lean burn conditions. However, under these conditions the traditional three-way catalysts are not effective. With this new kind of engines, interesting results were obtained by using Cuor Co-zeolite catalysts at the engine exhaust [77–79]. Unfortunately, one of the most active and selective catalysts (i.e., [Cu]-MFI-type), exhibits very rapid deactivation in the presence of water that is, of course, present in the automotive exhaust [80]. In a large number of papers on Cu zeolites, the introduction of Cu is carried out by ionic exchange from the Na form to obtain the Cu form. On the other hand, literature indicates that the solid-state reaction is a very good method for metal incorporation into the zeolites [81–83]. It is also indicated that during the zeolite synthesis with alcohols, the presence of sodium can occlude the zeolitic channels [84] and that the ionic exchange to the ammonium form followed by calcination opens the zeolitic channels. As an example the Na+-TON presents a micropore vol-
ume equal to 0.05 ml g–1, on the contrary the H+-TON shows a value equal to
0.91 ml g–1.
Isomorphous Substitution in Zeolites |
373 |
Isomorphous substitution was essentially performed with the MFI structure. Table 1 gives an overview of additional references to be used for entering into the subject. It can be seen that boron, gallium, vanadium and iron are the most commonly used elements. It is worthwhile to mention that the introduction of other elements such as Ti, In, Be, Mn, Sn, Cr, Mo, Ge and Zn, was also successful.
The second most studied zeolite for isomorphous substitution is the zeolite BEA [70] (Table 2). However, the number of publications remains far smaller than that dealing with ZSM-5. The most studied elements are still B, Ga, and Fe, but some reports also concern Zn, Sn, Ge and Ti.
Finally, Table 3 illustrates the isomorphous substitution of various elements into the remaining zeolitic structures.
In this review we shall focus on our works published on [B]-MFI, [Ga]- MFI, [Fe]-MFI, [Fe]-BEA, [Fe]-MCM-22, Zn-zeolite, and Cu-containing zeolites. Essentially, the various synthesis methods together with characterization techniques will be reviewed. The catalytic part will only be included, where it is considered essential.
2 Experimental
2.1
Synthesis Procedures
2.1.1 [B]-MFI
The gels were prepared by dissolving H3BO3 (Carlo Erba) in distilled water, adding the fluoride source (NH4F, NaF, KF Carlo Erba; CsF, Aldrich) and tetrapropylammonium bromide, Fluka (TPABr) to the H3BO3 aqueous solution and then adding this solution to fumed silica (Serva) [181–183] (Testa F, Chiappetta R, Crea F, Aiello R, Fonseca A, Bertrand JC, Demortier G, Guth JL, Delmotte L, B.Nagy J, submitted for publication). The composition of the as-prepared gels was 9MF – xH3BO3 – 10SiO2 – 1.25TPABr – 330H2O with M = NH4, Na, K and Cs and x = 0.1 and 10. Syntheses were carried out in Morey-type PTFE-lined 20 cm3 autoclaves at 170 ± 2 ◦C, without stirring, under autogenous pressure. After being heated for various times required by the crystallization kinetics, the autoclaves were quenched in tap water, and the products were filtered, washed with distilled water until pH = 7 and dried overnight at 105 ◦C.
Table 1 Isomorphous substitution of MFI zeolites
Zeolite |
Substituting |
Synthesis |
Si/T or |
Techniques of |
Precursors |
|
|
|
Refs. |
||
|
element |
|
T content |
characterization |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
MFI |
B |
Theoretical Study |
— |
— |
— |
|
|
|
|
|
[85] |
MFI |
B |
Hydrothermal |
|
Gas diffusion and permeance |
|
|
|
|
|
|
[86] |
membrane |
|
|
|
11B NMR, REDOR |
|
|
|
|
|
|
|
MFI |
B |
Hydrothermal |
|
B(OH) |
, Na |
B |
O |
7 |
[87] |
||
MFI |
B |
Hydrothermal |
30–80 |
FTIR, TPD, C2H4 reaction |
|
3 |
2 |
4 |
|
|
|
H3BO3 |
|
|
|
|
[88] |
||||||
MFI |
B |
Hydrothermal |
24 |
Catalysis |
|
|
|
|
|
|
[89] |
MFI |
B |
Hydrothermal |
95 |
IR of OH groups, acidity IR |
H3BO3 |
|
|
|
|
[90–92] |
|
MFI |
B |
Hydrothermal |
|
Catalysis |
|
|
|
|
|
|
[93] |
MFI |
B |
Theoretical study |
|
B-siting |
|
|
|
|
|
|
[94] |
MFI |
B |
Hydrothermal |
1–2 B/u.c. |
XRD, 11B NMR, SEM, Sorption |
H BO |
3 |
|
|
|
|
[95] |
|
|
|
|
|
3 |
|
|
|
|
|
|
MFI |
B |
Hydrothermal |
25 |
TA, XPS, Catalysis |
H3BO3 |
|
|
|
|
[96] |
|
MFI |
B |
Hydrothermal |
0.6, 1.3, 2.1/u.c. |
11B NMR, IR |
H BO |
3 |
|
|
|
|
[97] |
|
|
|
|
11B NMR, XRD, SEM, FTIR, |
3 |
|
|
|
|
|
|
MFI |
B |
Hydrothermal |
0.1–0.5 wt % B |
H BO |
3 |
|
|
|
|
[98] |
|
|
|
|
|
XPS, TPD, SAM |
3 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
MFI |
B |
Hydrothermal |
2.5/u.c. |
FTIR, XRD, 1H-, 11B-, 29Si NMR |
H BO |
3 |
|
|
|
|
[99] |
|
|
|
|
|
3 |
|
|
|
|
|
|
MFI |
B |
Hydrothermal |
6 |
XRD, MAS NMR, TA |
H3BO3 |
|
|
|
|
[100] |
|
MFI |
B |
Hydrothermal |
|
XRD |
|
|
|
|
|
|
[101] |
MFI |
B |
Hydrothermal |
0.40 wt % |
Acidity, n-butene, isomerization |
H3BO3 |
|
|
|
|
[102] |
|
MFI |
B |
Hydrothermal |
37 |
TPD, C3H8 oxidation |
H3BO3 |
|
|
|
|
[103] |
|
MFI |
Fe-Mo-B |
Hydrothermal |
4.6 wt % Mo 1.41 |
C6H6 + N2O = C6H5 OH |
BET, TPD |
|
|
|
[104] |
||
|
|
CVD |
wt% Fe 0.15 wt % B |
|
|
|
|
|
|
|
|
MFI |
B,Al |
Hydrothermal |
0.40 wt % |
Acidity, n-butene, isomerization |
H3BO3 |
|
|
|
|
[102] |
|
MFI |
Al |
Hydrothermal |
14–42 14–23; 45 9.25 |
27Al NMR, FTIR |
|
|
|
|
|
|
[105] |
MFI |
Ga |
Theoretical Study |
|
|
|
|
|
|
|
|
[85] |
MFI |
Ga |
Hydrothermal |
|
Gas diffusion and permeance |
|
|
|
|
|
|
[86] |
membrane |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
374
.al et Nagy.B .J