Supporting information
Molecular understanding of sorption in mesoscale organized
zeolites with MFI structure
Robin Kolvenbach, Luis Francisco Gonzalez-Peňa, Andreas Jentys, Johannes A.
Lercher
Department Chemie, Catalysis Research Center, Technische Universität München,
Lichtenbergstr. 4, 85748 Garching, Germany
Corresponding Author
*E-mail: Johannes.Lercher@ch.tum.de
Content
(SI1) Materials
(SI2) Methods and Experimental procedures
(SI3) Supplementary figures
(SI4) References of Supplementary information
1
(SI1) Materials
Zeolite HZSM-5 with a Si/Al ratio of 45 (confirmed by AAS) was provided by SüdChemie AG. A concentration of 0.27 mmol g-1 for terminal (SiOH) and of 0.21 mmol/g for
bridging (SiOHAl) hydroxyl-groups was determined using 1H-MAS NMR [1] n-pentane
and n-hexane (Fluka, GC Standard, ≥ 99.8%) were used without further purification. nbutane was obtained from Air Liquide (purity ≥ 99.0%).
The modification of the zeolite surface by chemical liquid deposition (CLD) of tetraethyl
orthosilicate (TEOS) was performed according to Zheng et al. [2, 3]. Following this
procedure, 1.5 mL of TEOS and 10 g of zeolite were dispersed in 164.5 g of hexane and
heated up to 353 K for 1 h under reflux. The hexane was evaporated in a rotary
evaporator. The sample was dried at 343 K for 8 h and calcined at 823 K for 5 h. This
procedure was repeated three times
(SI2) Methods and experimental procedures
In-situ time-resolved infrared spectroscopy
A Bruker IFS 66 v/s Fourier transform IR spectrometer was used to collect IR spectra
during static sorption uptake and periodic pressure modulation experiments. For the
sorption isotherms the spectrometer was run in standard mode, whereas it was operated
in rapid scan mode for the uptake kinetic measurements. The spectrometer was
combined with a high vacuum cell connected to a unit which allows generating a square
wave pressure perturbation over the sample. This unit consists of two magnetically
driven plates sealed with UHV bellows. The volume perturbation was kept as small as
2
possible in order to avoid a temperature gradient over the sample, which would distort
the transport significantly. On the other hand it was sufficiently large to obtain data with
an appropriate signal to noise ratio. In our experiments a perturbation of ΔV=±5% was
used as an optimum compromise between both effects.
The zeolite samples were inserted as self-supporting wafers into the vacuum IR cell
and subsequently activated below 10-7 mbar at 823 K for 1 h (heating rate of 10 K min-1).
Sorbate gas, i.e., n-butane, n-pentane or n-hexane, was added with partial pressure of
0.1 mbar at 343, 373 and 403 K. The sorbate partial pressure changes were followed by
an in-line MKS Baratron (MKS 616A11) pressure transducer. A series of 100 IR spectra
with time resolution of 600 ms was recorded during 400 modulation cycles.
All spectra were normalized to the lattice vibrations between 2105 and 1740 cm -1. The
concentration of the sorbate molecules within the sample was obtained from integration
of their characteristic CH stretching and bending vibrations, respectively, which were
3045-2745 cm-1 and 1406-1506 cm-1 for n-butane, 3020-2745 cm-1 and 1422-1517 cm-1
for n-pentane and 3020-2740 cm-1 and 1406-1506 cm-1 for n-hexane.
Determination of concentration profiles
The concentration on the external surface and inside the pores was calculated from the
overall intensity profiles obtained by fast time resolved IR spectroscopy utilizing the
differences in the molar extinction coefficients of the molecules present inside the zeolite
channel system and at the outer surface of the zeolite particles. The intensity change in
each spectrum collected in the series of time resolved spectra during the pressure
modulation can be described for the CH-stretching or bending vibration by Eqs. (1) and
(2):
3
𝑤
∆𝐼𝐶𝐻−𝑠𝑡𝑟𝑒𝑡𝑐ℎ = (𝜀𝑆𝑖𝑂2, 𝐶𝐻−𝑠𝑡𝑟𝑒𝑡𝑐ℎ ∗ ∆𝑐𝑒𝑥𝑡 + 𝜀𝑍𝑆𝑀−5, 𝐶𝐻−𝑠𝑡𝑟𝑒𝑡𝑐ℎ ∗ ∆𝑐𝑖𝑛𝑡 ) ∗ 𝜋𝑅2
𝑤
∆𝐼𝐶𝐻−𝑏𝑒𝑛𝑑 = (𝜀𝑆𝑖𝑂2 , 𝐶𝐻−𝑏𝑒𝑛𝑑 ∗ ∆𝑐𝑒𝑥𝑡 + 𝜀𝑍𝑆𝑀−5, 𝐶𝐻−𝐵𝑒𝑛𝑑 ∗ ∆𝑐𝑖𝑛𝑡 ) ∗ 𝜋𝑅2
(1)
(2)
With ΔICH-stretch and ΔICH-bend being the change in intensities of the IR-bands obtained
from integration the IR-spectrum at the corresponding wavenumbers, ε is the respective
extinction coefficient, w weight of the IR wafer, R is the radius of the IR wafer, ∆cint is the
concentration change of the sorbate within the zeolite channel system and ∆cext is the
concentration change of the molecules adsorbed at the external surface of the zeolite
particle. The numerical solution of the two equations results ∆cint and ∆cext given by Eqs.
(3) and (4):
𝜀
(∆𝐼𝐶𝐻−𝑏𝑒𝑛𝑑 −∆𝐼𝐶𝐻−𝑠𝑡𝑟𝑒𝑡𝑐ℎ ∗
𝜀
∆𝑐𝑒𝑥𝑡 =
𝜀
𝜀 𝑆𝑖𝑂 ,𝐶𝐻−𝐵𝑒𝑛𝑑 −
2
∆𝑐𝑖𝑛𝑡 =
(∆𝐼𝐶𝐻−𝑏𝑒𝑛𝑑 ∗
𝜋𝑅2
𝑤
𝑍𝑆𝑀−5, 𝐶𝐻−𝐵𝑒𝑛𝑑
𝑍𝑆𝑀−5, 𝐶𝐻−𝑆𝑡𝑟𝑒𝑡𝑐ℎ
𝜋𝑅2
𝜋
)∗
∗𝜀
𝑍𝑆𝑀−5, 𝐶𝐻−𝐵𝑒𝑛𝑑 𝑆𝑖𝑂2 ,𝐶𝐻−𝑆𝑡𝑟𝑒𝑡𝑐ℎ
𝜀
𝑍𝑆𝑀−5, 𝐶𝐻−𝑆𝑡𝑟𝑒𝑡𝑐ℎ
−𝜀 𝑆𝑖𝑂 ,𝐶𝐻−𝐵𝑒𝑛𝑑 ∗∆𝑐𝑒𝑥𝑡 )
2
𝜀 𝑍𝑆𝑀−5, 𝐶𝐻−𝐵𝑒𝑛𝑑
(3)
(4)
The profiles of ∆cint and ∆cext can be obtained applying Eqs. (3) and (4) to each data
point of the series of time resolved IR spectra collected during the periodic pressure
modulations.
Modeling of the transport network
A sketch of the proposed transport network is shown in Figure 1. The concentration
profiles ∆cint and ∆cext are described by a set of equations describing the uptake onto the
external surface (including a pre-adsorbed state), the pore entrance step and the
diffusion inside the micropores. The uptake onto the external surface and the pore
entrance step are described by first order kinetic process as given in Eq. (5) and (6):
4
∆𝑐𝑒𝑥𝑡 (𝑡) = (1 − 𝑒𝑥 𝑝(−𝑘𝑎𝑑𝑠 ∗ 𝑡)) ∗ ∆𝑐𝑒𝑥𝑡,𝑒𝑞
(5)
∆𝑐𝑒𝑥𝑡 (𝑡) = 𝑎 ∗ 𝑒𝑥 𝑝(−𝑘𝑝𝑜𝑟𝑒−𝑒𝑛𝑡𝑟𝑎𝑛𝑐𝑒 ∗ 𝑡)
(6)
Where kads is the rate constant of the adsorption at the external surface, k pore entrance is
the rate constant of transport from the external surface into the micropore and a is an
additional factor describing the amount of molecules being in the pre-adsorbed state. By
merging Eqs. (5) and (6) the concentration change on the external surface can be
obtained (Eq. (7)):
∆𝑐𝑒𝑥𝑡 (𝑡) = [(1 − 𝑒𝑥 𝑝(−𝑘𝐴𝑑𝑠 ∗ 𝑡)) ∗ ∆𝑐𝑒𝑥𝑡,𝑒𝑞 ] + [𝑎 ∗ 𝑒𝑥 𝑝(−𝑘𝑝𝑜𝑟𝑒−𝑒𝑛𝑡𝑟𝑎𝑛𝑐𝑒 ∗ 𝑡) ∗
(1 − 𝑒𝑥 𝑝(−𝑘𝐴𝑑𝑠 ∗ 𝑡))](7)
The concentration change within the zeolitic micropores is described by the uptake
kinetics of a sorbate into a microporous solid at isothermal conditions as described by
Crank [4] for small concentration changes (constant D):
6
∆𝑐𝑖𝑛𝑡 = (1 − ∑𝑛1 𝜋2 𝑛2 ∗ 𝑒𝑥𝑝 (⁡−
𝑛2 𝜋 2 𝐷𝑎𝑝𝑝 𝑡
𝐿2
)) ∗ ⁡∆𝑐𝑒𝑞,𝑖𝑛𝑡
(8)
Both concentration profiles as well as their sums for either the CH-stretching or
bending vibration were fitted using Eqs. (7, 8). The Arrhenius law was used in order to
keep the amount of parameters as low as possible. By this means the activation energy
of diffusion and the corresponding pre-exponential factor according to Eq. (9) were used
as variables:
𝐸𝐴,𝐷,𝑎𝑝𝑝
𝐷𝑎𝑝𝑝 = 𝐷0,𝑎𝑝𝑝 ∗ exp (
𝑅𝑇
)
(9)
The parameters EA,D,app, D0,app, k and a were obtained by nonlinear parameter fitting
using a CMA evolutional strategy implemented in MATLAB [5].
5
Gravimetric sorption experiments
The gravimetric sorption isotherms of n-butane, n-pentane and n-hexane on either
silicon dioxide or ZSM-5 were measured in a Seteram TG-DSC 111 thermoanalyzer
connected to a high vacuum system. About 35 mg of the silicon dioxide or 20 mg of the
ZSM-5 sample was placed in a quartz sample holder and activated at 723 K for 1 h
under vacuum (p<10-4 mbar) with an incremental heating rate of 10 K min-1. The
equilibration with the sorbate was performed in small pressure steps from 3x10 -2 to
13 mbar in case of the zeolite and from 3x10-2 to 150 mbar for the silicon dioxide. In both
cases the mass increase and the thermal flux were measured. The heat of adsorption
was directly obtained by integration of the observed heat flux signal.
The adsorption isotherms were analyzed in terms of a dual site Langmuir model for
the ZSM-5 (Eq. (10)) and a standard Langmuir isotherm (Eq. (11)) for the silicon dioxide.
𝑛(𝑝) =
𝐾1 ∗𝑝∗𝑛𝑚𝑎𝑥,1
1+𝐾1 ∗𝑝
𝑛(𝑝) =
+
𝐾2 ∗𝑝∗𝑛𝑚𝑎𝑥,2
1+𝐾2 ∗𝑝
𝐾∗𝑝∗𝑛𝑚𝑎𝑥
1+𝐾∗𝑝
(10)
(11)
Where K denotes the equilibrium constant of adsorption, n is the amount of sorbate on
the sample, nmax is the maximum surface coverage of the individual adsorption site and
p is the pressure. All three temperatures were analyzed simultaneously using the van’t
Hoff equation in order to reduce the number of parameters.
6
(SI3) Supplementary figures
Figure S1
200
160
3
-1
Amount Adsorbed (cm STP g )
180
140
(a)
120
100
(b)
80
60
40
20
0
1E-5
1E-4
1E-3
0.01
0.1
1
Relative Pressure (-)
Figure S1: Nitrogen physisorption isotherms of the parent (a) and the surface modified
sample (b) adapted from Ref. 1
7
Figure S2
150
Vmi + Vme
125
(b)
3
-1
Amount Adsorbed (cm STP g )
(a)
100
75
Vmi
50
0.0
0.5
1.0
1.5
2.0
s
Figure S2: αs comparitive plot [6] of the parent (a) and the surface modified (b) material
adapted from Ref. 1. Two separated linear regions at αs=0.5, which corresponds to the
micropore volume and at αs=1.2 corresponding to the sum of the micro- and mesopore
volume were identified.
8
Figure S3
343K
373K
403K
c [mmol/gcat]
c [mmol/gcat]
0.9
0.6
0.3
0.0
0.000
1.2
1.2
0.9
0.9
c [mmol/gcat]
1.2
0.6
0.3
0.003
0.006
0.009
0.012
p/p0 [-]
0.0
0.000
343K
373K
403K
0.003
0.006
p/p0 [-]
0.009
0.012
0.6
0.3
0.0
0.000
343K
373K
403K
0.003
0.006
0.009
0.012
p/p0 [-]
Figure S3: Gravimetric adsorption isotherm of n-butane (left), n-pentane (middle) and nhexane (right) on H-ZSM5 at 343, 373 and 403 K. The fitting was performed according
to a dual Langmuir formalism.
9
Figure S4
-1
-2
2.0x10
-2
1.0x10
0.0
0.00
0.05
0.10
0.15
-1
2.0x10
343K
373K
403K
c [mmol/gcat]
c [mmol/gcat]
c [mmol/gcat]
-2
3.0x10
1.0x10
343K
373K
403K
-2
5.0x10
0.0
0.00
p/p0 [-]
0.03
0.06
p/p0 [-]
0.09
0.12
343K
373K
403K
-1
1.0x10
0.0
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14
p/p0 [-]
Figure S4: Gravimetric adsorption isotherm of n-butane (right), n-pentane (middle) and
n-hexane (right) on fumed silica at 343, 373 and 403 K. The fitting was performed
according to the Langmuir formalism.
10
Figure S5
4
0.2
2
4
1
2
0
0
6
2
4
1
2
0
0
0
30
60
c [mol/g]
-1
6
Intensity 1506-1406 cm [a.u.]
0
0
-1
Intensity 3020-2745 cm [a.u.]
2
1
2
343K
373K
403K
0.4
2
1
0.0
0
0.4
2
0.2
1
0.0
0
0.4
c [mol/g]
343K
373K
403K
6
2
0.2
1
0
0.0
0
t [s]
30
60
t [s]
Figure S5: Intensity (left axis) for the CH-stretching (left) and bending (right) vibrations
and the by deconvolution obtained internal (orange) and external (magenta)
concentration profiles (right axis) of n-pentane in parent H-ZSM5 at 343, 373 and 403 K
during a periodic volume perturbation around 0.1 mbar.
11
Figure S6
2
1
0
0
3
4
2
2
1
0
0
8
4
6
3
4
2
2
1
0
0
0
30
60
3
2
0.2
4
6
4
1
0.0
0
4
0.4
3
2
0.2
1
0.0
c [mol/g]
2
-1
4
8
0.4
3
c [mol/g]
-1
Intensity 3020-2745 cm [a.u.]
6
343K
373K
403K
4
Intensity 1506-1406 cm [a.u.]
343K
373K
403K
8
0
4
0.4
3
2
0.2
1
0.0
0
t [s]
30
0
60
t [s]
Figure S6: Intensity (left axis) for the CH-stretching (left) and bending (right) vibrations
and the by deconvolution obtained internal (orange) and external (magenta)
concentration profiles (right axis) of n-hexane in parent H-ZSM5 at 343, 373 and 403 K
during a periodic volume perturbation around 0.1 mbar.
12
Figure S7
1
0.5
0
0.0
0.2
-1
0.5
1
0.0
0
0.4
1.0
0.2
0.5
0.0
0.0
0
30
60
c [mol/g]
2
2
1
0.0
-1
Intensity 3045-2745 cm [a.u.]
2
1.0
0
-1
0.15
0.10
0.5
0.05
0.00
0.0
-0.05
c [mol/g]
3
343K
373K
403K
0.4
1.5
Intensity 1506-1406 cm [a.u.]
343K
373K
403K
4
0.15
0.10
0.5
0.05
0.00
0.0
-0.05
0
t [s]
30
60
t [s]
Figure S7: Intensity (left axis) for the CH-stretching (left) and bending (right) vibrations
and the by deconvolution obtained internal (orange) and external (magenta)
concentration profiles (right axis) of n-butane in surface modified H-ZSM5 at 343, 373
and 403 K during a periodic volume perturbation around 0.1 mbar.
13
Figure S8
6
4
0
0.4
1
0.2
1
0
0.0
0
0.4
2
0.2
1
0.0
0
0.4
2
1
0.2
1
0
0.0
0
-2
2
6
2
4
1
2
0
0
-2
8
6
2
4
2
0
c [mol/g]
-1
8
c [mol/g]
-1
Intensity 3020-2745 cm [a.u.]
2
343K
373K
403K
2
Intensity 1506-1406 cm [a.u.]
343K
373K
403K
8
-2
0
30
60
0
t [s]
30
60
t [s]
Figure S8: Intensity (left axis) for the CH-stretching (left) and bending (right) vibrations
and the by deconvolution obtained internal (orange) and external (magenta)
concentration profiles (right axis) of n-pentane in surface modified H-ZSM5 at 343, 373
and 403 K during a periodic volume perturbation around 0.1 mbar.
14
Figure S9
6
2
0.2
1
0
0
8
2
6
4
1
2
8
4
1
0.0
0
0.4
2
0.2
1
0
0.4
2
1
0.2
1
0
0.0
0
2
6
2
0.0
0
0
c [mol/g]
-1
Intensity 1506-1406 cm [a.u.]
2
-1
Intensity 3020-2745 cm [a.u.]
4
343K
373K
403K
0.4
c [mol/g]
343K
373K
403K
8
2
0
0
30
60
0
t [s]
30
60
t [s]
Figure S9: Intensity (left axis) for the CH-stretching (left) and bending (right) vibrations
and the by deconvolution obtained internal (orange) and external (magenta)
concentration profiles (right axis) of n-hexane in surface modified H-ZSM5 at 343, 373
and 403 K during a periodic volume perturbation around 0.1 mbar.
15
(SI4) References of supplementary information
1.
Reitmeier SJ, Gobin OC, Jentys A, Lercher JA (2009) Angew Chem Int Edit
533:538
2.
Zheng S, Heydenrych HR, Roger HP, Jentys A, Lercher JA (2003) Top Catal
101:106
3.
Zheng SR, Tanaka H, Jentys A, Lercher JA (2004) J Phys Chem B 1337:1343
4.
Crank J (1975) The Mathematics of Diffusion, Oxford University Press, Oxford
5.
Hansen N (2006) Towards a New Evolutionary Computation. Advances on
Estimation of Distribution Algorithms, Springer, New York.
6.
Sing KSW (1970) Surface Area Determination, Butterworths, London
16