TOWARDS THE RATIONAL TOWARDS THE RATIONAL SYNTHESIS OF ZEOLITES SYNTHESIS OF ZEOLITES Roberto MILLINI Roberto MILLINI Physical Physical - - Chemistry Dept., EniTecnologie S.p.A. Chemistry Dept., EniTecnologie S.p.A. Via F. Maritano 26, I Via F. Maritano 26, I - - 20097 San Donato Milanese (MI 20097 San Donato Milanese (MI - - ITALY) ITALY) e e - - mail: [email protected]mail: [email protected]
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TOWARDS THE RATIONALTOWARDS THE RATIONALSYNTHESIS OF ZEOLITESSYNTHESIS OF ZEOLITES
Roberto MILLINIRoberto MILLINI
PhysicalPhysical--Chemistry Dept., EniTecnologie S.p.A.Chemistry Dept., EniTecnologie S.p.A.Via F. Maritano 26, IVia F. Maritano 26, I--20097 San Donato Milanese (MI 20097 San Donato Milanese (MI -- ITALY)ITALY)
ZEOLITE: Microporous crystalline aluminosilicate with a framework based on a 3D network of corner-sharing [TO4] (T = Si, Al) tetrahedra. Depending on the structure, it contains channels and/or cages with dimensions in the range 3 - 12 Å. The negative framework charge is compensated by cations localized within the pores (extraframework cations).
USES:
Molecular Sieve (e.g. separation of linear alkanes from branched ones)
COMPUTERCOMPUTER--ASSISTED SYNTHESISASSISTED SYNTHESISOF NEW ZEOLITESOF NEW ZEOLITES
IDENTIFICATIONOF NEW (HYPOTHETICAL)
MICROPOROUSFRAMEWORKS
SDA AND ZEOLITE SYNTHESIS
No Well EstablishedProcedures Available
Computer Codes Available
(e.g. ZEBEDDE;D.W. Lewis et al., Nature
382 (1996) 604)
METHODS FOR GENERATING NEW METHODS FOR GENERATING NEW HYPOTHETICAL ZEOLITE FRAMEWORKSHYPOTHETICAL ZEOLITE FRAMEWORKS
!Subdivide a known framework into layers that are then reconnected after a crystallographic transformation (e.g. FAU/EMT, MFI/MEL,…)
!Build new zeolite structures from molecular building units (“Lego chemistry”; M.E. Davis CHEMTECH 24(9) (1994) 22)
!Simulated annealing (M.W. Deem and J.M. Newsam J. Am. Chem. Soc. 114 (1992) 7189; M.B. Boisen Jr. et al., Microporous Mesoporous Mat. 29 (1999) 219)
!Systematic enumeration of periodic 4-connected frameworks; considering 1 unique T-atom, more than 6400 4-connected periodic solutions were found and ~3% of these were refined to regular tetrahedral topologies; when 2 unique T-atoms are considered, the number of solutions is too high for being analyzed in reasonable time (M.M.J. Treacy, K.H. Randall and S. Rao, Proc. 12th Intern. Zeolite Conf., Baltimore (MD), 1998, p. 517)
THE ROLE OF THE ORGANIC ADDITIVESTHE ROLE OF THE ORGANIC ADDITIVESIN ZEOLITE SYNTHESISIN ZEOLITE SYNTHESIS
" VOID FILLERS
# GEL MODIFIERS
$ TEMPLATES
% STRUCTURE DIRECTING AGENTS (SDA’S)
New crystalline microporous compounds can be synthesized either by using new SDA’s with increasing complexity or by systematically varying the synthesis parameters
TOWARDS NEW ZEOLITE STRUCTURESTOWARDS NEW ZEOLITE STRUCTURES
NEWNEWZEOLITESZEOLITES
“NEW” SDA’S
SCREENING OFSYNTHESIS PARAMETERS
“OLD” SDA’S
N,NN,N--DIMETHYLPIPERIDINIUMDIMETHYLPIPERIDINIUM
ZSM-51 (NON)US 4,568,654 ERSERS--77
LEV MOR MTW
(ANA)
?
THE SYNTHESIS OF ERS-7 (ESV) ZEOLITE
130°C 155°C 170°C3 days Amorphous ANA MOR5 days Amorphous ANA ERS-77 days Amorphous ANA + ERS-7 ERS-7
14 days Amor. + ANA ERS-7
Temperature and crystallization time (SiO2/Al2O3 = 25)
SiO2/Al2O3 molar ratio (temp. 170°C, cryst. time > 5 days)
15 20 25 30 80 > 214LEV ERS-7 + U ERS-7 ERS-7 + U MTW NON
R. Millini, G. Perego, L. Carluccio, G. Bellussi, D.E. Cox, B.J. Campbell, A. K. Cheetham, Proc. 12th Int. Zeolite Conf. (Baltimore, MD, 1998) 541
Refinement- Unit cell size- Space group- Total T atoms- Indep. T atoms- (PXD, PND) Deem & Newsam, JACS 114, 7189 (1992)
ERSERS--7 STRUCTURE SOLUTION7 STRUCTURE SOLUTION
Primitive orthorhombic cella = 9.81, b = 12.50, c = 23.01 ÅSpace group: Pna21 or Pnma
No significant SHG signal suggests Pnma
INDEXATION (TREOR90)
5 10 15 20 25 30 35 40
λ = 1.1528 Å
Chemical composition:Na0.04R0.08(Si0.89Al0.11)O2Total density: 2.04 g·cm-3
R + H2O = 15.5 wt% (TGA)Na = 1.2 wt% (AA)
Density: 1.70 g·cm-3
Unit cell volume: 2821 Å3
48.1 T-sites/unit cell6 to 12 independent T-sites
ERSERS--7 STRUCTURE SOLUTION7 STRUCTURE SOLUTION
1000 simulated annealing cycles were run, with different random seeds, assuming 6 independent T-sites373 unique framework topologies were generatedThe topology with the best zeolite figure-of-merit was found to be correct upon comparing experimental and simulated XRD patterns
DLS-76
R = 0.000062σ = 0.000324
c
a
c
a
THE ERSTHE ERS--7 STRUCTURE7 STRUCTURE
THE [46546582] CAGE
THE [445463] CAGE
THE ROLE OF SDA MOLECULESTHE ROLE OF SDA MOLECULESIN ZEOLITE SYNTHESISIN ZEOLITE SYNTHESIS
The zeolite which fits most closely around the SDA molecule will be stabilized best by the SDA itself and, consequently, its formation will be favoredStabilizing effects of SDA are mainly due to the van der Waals interactions while the chemical character of the organic molecule is not very important [1,2]An effective packing of SDA molecules is also fundamental for stabilizing the overall system [2]however:depending on the synthesis conditions, a given SDA favors the formation of different microporous frameworks, therefore, the relation SDA/zeolite structure must be better understood
[1] H. Gies and B. Marler, Zeolites 12 (1992) 42[2] R. G. Bell et al., Stud. Surf. Sci. Catal. 84 (1994) 2075
THE DOCKING (PACKING) SCHEMETHE DOCKING (PACKING) SCHEME
ORGANIC MOLECULE(SDA)
HIGH-TEMP. (e.g. 1500 K)MOLECULAR DYNAMICS
ENERGY MINIMIZATION/SIMULATED ANNEALING
MONTE CARLO DOCKING(PACKING) ZEOLITE FRAMEWORK
DOCKED (PACKED)STRUCTURE
PACKING OF TPA IONS IN MFIPACKING OF TPA IONS IN MFI
[1] R. G. Bell et al., Stud. Surf. Sci. Catal. 84 (1994) 2075
TEMPLATE SELECTION USING DE NOVOTEMPLATE SELECTION USING DE NOVOMOLECULAR DESIGN METHODSMOLECULAR DESIGN METHODS
To be effective as a templating agent, a molecule must effectively fill the void cavity of the host frameworkA cost function, fc, based on the overlap of van der Waals spheres provides a suitable measure of the efficacy of a particular molecule for the synthesis of a target framework
fc = Σt C(tz)/nC(tz) is the closest contact between a template atom t and any host atom z; n is the number of atoms in the template
fc MUST BE THE MAXIMUM AT ANY TIME AND PROVIDES A MEASURE OF “TIGHTNESS OF FIT”
IN GENERAL, THE SDA DIMENSION AND SHAPE DETERMINE THE SIZE AND THE SHAPE OF THE PORES
The presence of high concentration of trivalent metal ions (e.g. Al, B, Ga, Fe, …) may influence the nature of the products
SYNTHESIS OF NEW ZEOLITESSYNTHESIS OF NEW ZEOLITES
- COMPUTATIONAL-AIDED ROUTE
• Design of SDA’s through information coming from:– Evaluation of “templating” character of a given SDA in given framework (modeling tools)– Investigation of SDA/framework interactions (experimental and modeling tools)
- EXPERIMENTAL ROUTE
• Trying new SDA’s with more and more complex molecular structure (limits: costs, availability,…)• Exploring deeply the parameters involved in the zeolite synthesis
DOCKING AND PACKING CALCULATIONSDOCKING AND PACKING CALCULATIONSRESULTSRESULTS
Binding energy, normalized to the number of non-H atoms (B.E.*) and packing energy (∆Εpack) for the various zeolite/SDA combinations (data in kJ·mol-1)
&TBA favors the crystallization of MFI/MEL intergrowth with 75% probability of i-type of stacking (MFI) and 25% probability of σ-type of stacking (MEL) [1]
&The first synthesis of defect-free MEL was reported in 1995, using N,N-diethyl-3,5-dimethylpiperidinium (DDP) [2]
[1] G. Perego et al., J. Appl. Cryst. 17 (1984) 403[2] Y. Nakagawa, WO Patent 95/09812
α-Et-[5,5]β,β’-di-Me-[5,5]
SIMILAR
DDP
SYNTHESIS OF DEFECTSYNTHESIS OF DEFECT--FREE MEL FREE MEL
i a
c
b
c
m a
c
b
c
a
c
MFI
MEL
MFI/MEL
SBU5-1
PerBU
THE PENTASIL FAMILYTHE PENTASIL FAMILY
Standard laboratory XRD
Sharp 110 reflection indicates the lack of intergrowth
SXPD (GILDA -BM08, ESRF)
I4m2 space group
a = 20.0777(3), c = 13.4154(2) Å
Rwp = 0.0276, R(F2) = 0.0703, Red. χ2 = 1.213
R. Millini et al., 2nd FEZA Conf. (2002)
IS IT REALLY DEFECTIS IT REALLY DEFECT--FREE MEL?FREE MEL?
IS IT REALLY DEFECTIS IT REALLY DEFECT--FREE MEL?FREE MEL?