XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
58
T1: O–16
2D COS analysis as the efficient tool for analyzing of molecule
transformation on heterogeneous catalysts: the case of xylenes
transformations over ZSM-5
Kinga Gołąbek
1
, Karolina A. Tarach
1
, and Kinga Góra-Marek
1
1
Faculty of Chemistry, Jagiellonian University in Krakow, 3 Ingardena St., Krakow, Poland,
e-mail: kmgolabek@gmail.com
The ZSM-5 zeolite is widely applied in several industrial process requiring the shape-
selectivity property, including the alkylation, isomerization and disproportionation. Among
considered processes, one of the most shape-selectivity dependent is isomerization of meta- and
ortho-xylenes to para-isomer. During xylene transformation process two main reactions take
place: (i) isomerization, which is aimed to increase the relative content of p-xylene and (ii)
disproportionation leading to trimethylbenzene and toluene in equal amounts. It is well know
that the isomerization reaction occurs through the monomolecular mechanism while the
disproportionation involves the bimolecular mechanism with bulky intermediates.
The 2D COS analysis is based on Fourier transform, which is used to extract spectral
correlations occurring upon external modulation of system. As a result two types of maps are
obtained with two axes for wavenumbers and one for correlation level, expressed as intensity.
Synchronous correlation map represents the simultaneous or coincident changes of two separate
spectral intensity variations measured at ν
1
and ν
2
during the specific time of the externally
defined perturbation. Asynchronous correlation map represents sequential or successive changes
of spectral intensities measured separately at ν
1
, and ν
2
. An asynchronous spectrum is
antisymmetric with respect to the diagonal line. The use of 2D COS analysis significantly
enhanced the use of IR spectroscopy to follow even the slightest changes in IR spectrum during
heterogeneous reactions at high temperatures.
The studies presented in this work offer an insight into xylene isomerization process,
followed by 2D COS analysis, in the terms of different acidity of microporous zeolites ZSM-5.
From the maps presented in Fig. 1 it can be concluded that decreasing number of framework
aluminium atoms (reduced Brønsted acidity) facilitated the disproportionation path (zeolites of
Si/Al=25 and 40) while the isomerisation reaction proceeded effectively only over on ZSM-5 of
the highest Al content. The analysis of asynchronous maps allowed for concluding on the order
of the appearance of the respective products on the zeolite surface. Finally, both microporous
character of zeolite and the optimised acidity are crucial for high selectivity to the most desired
product i.e. p-xylene.
ZSM-5 Si/Al =11.5 ZSM-5 Si/Al =25 ZSM-5 Si/Al =40
1650
1600
1550
1500
1450
1400
1350
1650
1600
1550
1500
1450
1400
1350
ν
1
/
cm
-1
ν
2
/c
m
-1
-3x10
-5
-2x10
-5
-1x10
-5
3x10
-7
1x10
-5
2x10
-5
3x10
-5
4x10
-5
6x10
-5
1650
1600
1550
1500
1450
1400
1350
1650
1600
1550
1500
1450
1400
1350
ν
/cm
-1
ν/
cm
-1
-3,9x10
-5
-2,7x10
-5
-1,5x10
-5
-3,6x10
-6
8,2x10
-6
2,0x10
-5
3,2x10
-5
4,4x10
-5
5,5x10
-5
1650
1600
1550
1500
1450
1400
1350
1650
1600
1550
1500
1450
1400
1350
ν
/cm-1
ν/
c
m
-1
-8,5x10
-6
-5,6x10
-6
-2,8x10
-6
8,8x10
-8
3,0x10
-6
5,8x10
-6
8,7x10
-6
1,2x10
-5
1,4x10
-5
Fig. 1. 2D COSY of IR spectra of o-xylene isomerization over ZSM-5 with various acidic properties.
Keywords: zeolite; ZSM-5, IR spectroscopy, 2D COS, xylene isomerization
Acknowledgment
This work was financed by Grant No. 2015/18/E/ST4/00191 from the National Science Centre, Poland.
XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
59
T1: O–17
IR studies of the interaction of organic molecules with acidic active sites
in erionite
Justyna Tekla
1
, Karolina. A. Tarach
1
, Katarzyna Kwaśnik
1
, and Kinga Góra-Marek
1
1
Faculty of Chemistry, Jagiellonian University in Krakow, 3 Ingarden St., Krakow, Poland,
e-mail: justyna.tekla@doctoral.uj.edu.pl
The unique properties of zeolites, such as considerably developed specific surface area as well as
high acidity and shape-selectivity give a significant input to the performance in numerous catalytic
and industrial applications; the zeolites are catalysts in transformations of hydrocarbons and their
derivatives where the confinement effect rules the stability of carbocation in zeolitic matrix. The
investigation of the interaction between the active centers and organic reagents is therefore a crucial
issue for description of catalytic potential of zeolite.
Among the techniques used in the studies of acidic properties of zeolites, the IR spectroscopy is
unique method. It allows for obtaining information on the nature of active centers their selves by the
modification of the properties of the probe molecules interacting with respective center, in this respect
IR spectroscopy is the only method that offers discrimination between Brønsted and Lewis acid sites.
Pyridine, ammonia and carbon monoxide as the probes are particularly devoted to the acidity
measurement, since the proper assignment of diagnostic bands of chemisorbed individuals has been
well recognized. The IR spectra of sorbed probes, which are chemically similar to the reactants or
being the reactant themselves, can be straightforwardly used to predict the catalytic behavior of
zeolite.
The main goal of this work was focused on examination of interaction of acidic active sites in
erionite with adsorbed organic probe molecules (such as CH
3
OH, CH
3
CH
2
OH, (CH
3
CH
2
)
2
O, C
2
H
4
,
C
2
H
2
…) followed by IR spectroscopy. The probe was chosen as representative for the molecules
participating as reagents in the ethanol-to-hydrocarbons process (ETH). Erionite (ERI, Clariant
International
Ltd., Si/Al~3.5, SBET=621 m
2
g
–1
, Vmicro=0.24 cm
3
g
–1
) possessing a three dimensional
network of channels where the access to its porosity is controlled by 8-MR elliptical apertures
(0.36×0.51 nm) was successfully used in the Selectoforming® process (selective cracking of the
lowest octane, linear paraffins present in a reformate stream). The unique microporous pore system is
believed to be responsible for the confinement effect ruling high selectivity in ETH [1]. The
interaction of probes with acidic Si(OH)Al groups in ERI was studied with the use of 2D COSy
analysis which allows for following even the slightest changes in IR spectrum during heterogeneous
reactions.
1400
1600
1800
2500
3000
3500
Si(OH)Al
3560
3616
RT
1450
1390
2935-2877
Et-OH
A=0.1
ν
ν
ν
ν
[cm
-1
]
c = b -a
b
a
Si-OH
3745
1400
1600
1800
2500
3000
3500
Si(OH)Al
3560
3616
RT
3007-2850
Met-OH
A=0.1
ν
ν
ν
ν
[cm
-1
]
c = b -a
b
a
Si-OH
3745
Fig. 1. The IR spectra of the hydroxyl groups in zeolite ERI perturbed by the interaction with ethanol and
methanol: a – activated zeolite, b – after saturation of all accessible hydroxyls at room temperature,
c – the difference spectrum (b-a),
Keywords: zeolite; erionite; IR spectroscopy; organic molecules
Acknowledgment
This work was financed by Grant No. 2015/18/E/ST4/00191 and Grant No. 2014/13/D/ST5/02761 from the
National Science Centre, Poland.
References
[1] K.A. Tarach, J. Tekla, U. Filek, A. Szymocha, I. Tarach, K. Góra-Marek, Micro. Meso. Mat., 241 (2017)
132.
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