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)

ee--mail: rmillini@enitecnologie.eni.itmail: rmillini@enitecnologie.eni.it

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)

Ion-exchange (e.g. water softening)

Catalysis (e.g. isomerization, alkylation, cracking,…)

WHAT IS A ZEOLITE?WHAT IS A ZEOLITE?

ZEOLITE STRUCTURESZEOLITE STRUCTURES

ESV

CHA

SMALL PORE(8 MR)

MFI

FER

MEDIUM PORE(10 MR)

LTL

MOR

LARGE PORE(12 MR)

ZEOLITE SYNTHESISZEOLITE SYNTHESIS

Silica sourceAlumina sourceOrganic additive

Water(alkali metal ions)(sulphuric acid)

….

00:45

1 2 3 4 5

6 7 8 9 0

SeparationDrying

CalcinationCharacterization

….

DESIGN OF SDAMOLECULAR STRUCTURE

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

ZEOLITE STRUCTURE SOLUTION BYZEOLITE STRUCTURE SOLUTION BYSIMULATED ANNEALINGSIMULATED ANNEALING

Simulatedannealing

optimization

- Addition ofO atoms

- Geometry

(DLS-76)

Validation

NO

YES

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

TEMPLATING ABILITY OFTEMPLATING ABILITY OFTETRAALKYLAMMONIUM CATIONSTETRAALKYLAMMONIUM CATIONS

DOCKING ENERGYMFI MEL *BEA

Einter(kJ·mol-1)

Einter(kJ·mol-1)

Einter(kJ·mol-1)

TMA -51.7 TMA -38.7 TMA -43.1TEA -92.1 TEA -73.0 TEA -104.7TPA -133.9 TPA -119.9 TPA -83.4TBA -165.5 TBA -159.5 TBA -56.7

Experimental SDA in blue Predicted SDA in red

PACKING ENERGYSDA/FRAMEWORK ∆Epack (kJ·mol-1)

TPA/MFI -29.7TBA/MFI +14.9TPA/MEL -8.5TBA/MEL -18.3

[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”

D.J. Willock, D.W. Lewis, C.R.A. Catlow, G.J. Hutchings, J.M. Thomas, J. Mol. Catal. A119 (1997) 415

ZEOLITES BY EVOLUTIONARY DE NOVOZEOLITES BY EVOLUTIONARY DE NOVODESIGN (ZEBEDDE)DESIGN (ZEBEDDE)

C

C

C

CCC

CC

CC

C

CC

C

C

C

CC

CC

C

CC

C C

CC

C

C

C

CCC

C

C C

C

C

CCC

C

Actions: Build, Rotate, Shake, Rock, Random Bond Twist, Ring Formation, Energy Minimization (Discover, MOPAC)

SDA VS. POROUS STRUCTURESDA VS. POROUS STRUCTURE

SDA shape Porous structureLinear/cylindrical-shaped Monodimensional channelsBranched Intersecting channelsSpherical-like Cages

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

ASSESSING TEMPLATING PROPERTIESASSESSING TEMPLATING PROPERTIES

SDAMOBILITY

13C MAS NMR

SDALOCATION

MOLECULARDYNAMICS

NEW PROCEDURE

TEMPLATINGPROPERTIES

SDA/UNIT CELL

BINDINGENERGY

DOCKINGMINIMIZATION

TG ANALYSIS

OLD PROCEDURE

XRD

ZEOLITE SYNTHESIS IN THE PRESENCE OFZEOLITE SYNTHESIS IN THE PRESENCE OFAZONIAAZONIA--SPIRO COMPOUNDSSPIRO COMPOUNDS

R. Millini et al., Microporous Mesoporous Mater. 24 (1998) 199

SiO2/Al2O3

5025 ∞

MOR (ERS-10)

MOR

MOR

MTW

ERS-10, MTW

MTW

[5,6]

[5,5]

[4,5]

MTW AND MOR STRUCTURESMTW AND MOR STRUCTURES

MOR[001]

MOR: [001] 12 6.5 x 7.0* ↔ [010] 8 2.6 x 5.7* (17.2 T/1000 Å3)

MTW[010]

MTW: [010] 12 5.5 x 5.9* (19.4 T/1000 Å3)

DOCKING AND PACKING CALCULATIONSDOCKING AND PACKING CALCULATIONSCOMPUTATIONAL DETAILSCOMPUTATIONAL DETAILS

MODELS:MOR: 1·1·3 SUPERCELL WITH 1 AND 5 SDA MOLECULESMTW: 1·4·1 SUPERCELL WITH 1 AND 9 SDA MOLECULES

cff91_czeo FORCEFIELD

PERIODIC BOUNDARY CONDITIONS (PBC) APPLIED

PROGRAMS:CATALYSIS 4.0.0 (MSI, 1996) (Models Building, Docking, Analysis)DISCOVER 2.9.8 (MSI, 1996) (Energy Minimization, Molecular Dynamics)

HARDWARE:Silicon Graphics IndySilicon Graphics Octane

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)

B.E.*ZEOLITE SDA

Docking Packing∆Epack

[4,5] -8.82 -13.91 -50.8[5,5] -7.31 -13.34 -66.4MOR[5,6] -6.40 -12.09 -68.2[4,5] -8.36 -12.36 -39.9[5,5] -7.28 -9.70 -26.7MTW[5,6] -7.01 -7.16 -1.8

∆Epack = E1 - 1/nEnE1 = Binding Energy of 1 SDA MoleculeEn = Binding Energy of n SDA Molecules

DOCKING AND PACKING CALCULATIONSDOCKING AND PACKING CALCULATIONSRESULTSRESULTS

!B.E.* SLIGHTLY INCREASE AS THE DIMENSIONS OF THE SDA INCREASE BOTH IN MOR AND IN MTW

!THE PACKING ENERGY CONTRIBUTES SIGNIFICANTLY TO STABILIZE THE SYSTEM (WITH THE EXCEPTION OF SDA [5,6] IN MTW)

!IN MOR THE PACKING ENERGY (∆Epack) INCREASES IN THE ORDER [4,5] < [5,5] < [5,6], WHILE IN MTW THE OPPOSITE SITUATION IS OBSERVED

!TEMPLATING CHARACTER OF AZONIA-SPIRO COMPOUNDS SEEMS TO BE HIGHER FOR MOR THAN FOR MTW

EVALUATION OF SDA MOBILITYEVALUATION OF SDA MOBILITY1313C MAS NMR SPECTROSCOPYC MAS NMR SPECTROSCOPY

THE HIGHER THE SDA MOBILITY THE SHARPER THE NMR SIGNALS

MOR MTW

[5,6]

[5,5]

[4,5]

CONDITIONS FOR THE MD SIMULATIONSCONDITIONS FOR THE MD SIMULATIONS

!NVT canonical ensemble, T = 300 K, time step = 0.5 fs

!ABM4 velocity integrator, Nosè temperature control method

!Equilibrating step of 1 ps

!1000 ps (2500 ps for single SDA molecule) MD simulation with data collection of coordinates and energy components every 1 ps

!Program used: Discover 2.9.8 (MSI, 1996)

EVALUATION OF SDA MOBILITYEVALUATION OF SDA MOBILITYMD SIMULATIONSMD SIMULATIONS

0 500 1000 1500 2000 2500

time (ps)

0,0

0,2

0,4

0,6

0,8

1,0

MSD

(Å**

2)

N

RING 1

RING 2Molecule

Ring 1N atom

Ring 2

Diffusion tracks

EVALUATION OF SDA MOBILITYEVALUATION OF SDA MOBILITYMD SIMULATIONSMD SIMULATIONS

Molecule

Ring 1N atom

Ring 2

0 500 1000 1500 2000 2500

time (ps)

0

100

200

300

400

500

Dis

tanc

e tr

avel

ed (Å

)

0 500 1000 1500 2000 2500

time (ps)

0,0

0,5

1,0

1,5

2,0

MSD

(Å**

2)

[4,5] IN MTW

0 500 1000 1500 2000 2500

time (ps)

0

5

10

15

20

25

30

MSD

(Å**

2)

0 500 1000 1500 2000 2500

time (ps)

0

100

200

300

400

500

Dis

tanc

e tr

avel

ed (Å

)

[4,5] IN MOR

MD SIMULATIONSMD SIMULATIONSRESULTSRESULTS

!NO TRUE MOLECULAR DIFFUSION PROCESS (D ~1·10-11 m2s-1) SDA MOTION LOCALIZED AROUND PREFERRED SITES

!THE SDA MOBILITY DECREASES IN THE ORDER:[5,5]-MOR ≥ [4,5]-MOR > [5,6]-MOR > [5,5]-MTW ≥ [4,5]-MTW > [5,6]-MTW, IN AGREEMENT WITH THE 13C MAS NMR DATA

!AZONIA-SPIRO COMPOUNDS DISPLAY HIGHER TEMPLATING EFFECT FOR MTW THAN MOR

ARE THESE RESULTS USEFUL FOR DESIGNING NEW SDA’S?

OBSERVATION

SDA [5,5] FITS BETTER MWT THAN MOR

HYPOTHESIS

DIFFERENT ZEOLITE PHASES CAN BE OBTAINED IF WE INCREASE THE STERIC HINDRANCE OF THE SDA AND WE USE THE NEW SDA’S IN THE SAME CONDITIONS WHICH

GIVE MTW (e.g. IN THE PURE SILICA SYSTEM)

MD SIMULATIONSMD SIMULATIONSRESULTSRESULTS

β-Me-[5,5] β,β’-di-Me-[5,5]

α,α’-di-Me-[5,5]α-Me-[5,5]

α-Et-[5,5]

NEW NEW SDA’SSDA’S

ZEOLITE SYNTHESIS WITH THE NEWZEOLITE SYNTHESIS WITH THE NEW SDA’SSDA’S

α,α’-di-Me-[5,5] β-Me-[5,5]α-Me-[5,5]

MTWMOR

β,β’-di-Me-[5,5] α-Et-[5,5]

MELMEL

DOCKING CALCULATIONSDOCKING CALCULATIONSRESULTS RESULTS

ZEOLITE VAN DER WAALS ENERGY (kJ·mol-1)

[5,5] α-Me-[5,5] α,α’-di-Me-[5,5] β-Me-[5,5] β,β’-di-Me-[5,5] α-Et-[5,5]

MEL -109.0 -119.4 -98.8 -121.3 -129.6 -132.2

MFI -87.0 -88.8 -83.6 -71.2 -89.6 -86.2

MOR -100.3 -104.9 -103.2 -103.9 -101.8 -98.3

MTW -103.6 -114.1 -104.4 -111.9 -105.1 -98.1

ZEOLITE RELATIVE VAN DER WAALS ENERGY (kJ·mol-1)

[5,5] α-Me-[5,5] α,α’-di-Me-[5,5] β-Me-[5,5] β,β’-di-Me-[5,5] α-Et-[5,5]

MEL 0 0 +5.6 0 0 0

MFI +22.0 +30.6 +20.8 +50.1 +40.0 +46.0

MOR +8.7 +14.5 +1.2 +17.4 +27.8 +33.9

MTW +5.4 +5.3 0 +9.4 +24.5 +34.1

&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?

MEL/α-Et-[5,5]EvdW = -132.2 kJ·mol-1

MFI/α-Et-[5,5]EvdW = -86.2 kJ·mol-1

MEL/DDPEvdW = -120.5 kJ·mol-1

MFI/DDPEvdW = -111.3 kJ·mol-1

BASE SDASTRUCTURE MODIFICATION Feasibility

CostsStability….

DOCKINGMINIMIZATION Compatibility With

The Porous SystemsObtained With TheParent SDA

SDASYNTHESIS

ZEOLITESYNTHESIS

DESIGN OF NEW DESIGN OF NEW SDA’SSDA’S