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International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
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T1: O–14
IR and NMR studies of hierarchical zeolites Y
Mariusz Gackowski
1
, Karolina Tarach
2
, Łukasz Kuterasiński
1
,
Jerzy Podobiński
1
, Bogdan Sulikowski
1
, and Jerzy Datka
1,2
1
J. Haber Institute of Catalysis and Surface Chemistry PAN 30-239 Cracow, Poland
2
Faculty of Chemistry, Jagiellonian University 30-060 Cracow, Poland
Active sites in zeolites are localized inside micropores, resulting in some advantages. The
disadvantage of zeolitic catalysts is slow diffusion of reactants inside micropores. The remedy is
the preparation of hierarchical zeolites containing an additional system of mesopores.
Desilication in alkaline solutions was found to be an effective and non-expensive way of
producing of hierarchical zeolites. Most of the previous desilication studies were performed for
ZSM-5.
In this work we describe desilication of dealuminated zeolite Y (Si/Al = 31). Desilication
was realized with NaOH, tetrabutylammonium hydroxide (TBAOH), NaOH/TBAOH mixtures
and ammonia solutions. The properties of desilicated zeolites were followed by NMR and IR
spectroscopies. NMR informed on the status of framework Si and Al atoms, whereas IR
informed on the properties of active sites (Si–OH–Al groups and Lewis acid sites).
Concentration of acid sites was determined in quantitative IR studies of pyridine sorption, the
acid strength of Si–OH–Al as well as their heterogeneity were followed by low temperature CO
sorption. Besides of spectroscopic characterization BET studies of pore system were done, and
catalytic properties of hierarchical zeolites in α-pinene isomerization were studied.
Parent dealuminated zeolite Y (Si/Al = 31) was found to be the only zeolite containing very
strongly acidic and homogeneous Si–OH–Al groups. The desilication with NaOH caused
amorphization, loss of microporosity, acidity and loss of catalytic activity. On the other hand,
TBAOH alone caused only very small desilication, all the properties of zeolite changed only a
little. The best results were obtained with NaOH/TBAOH mixture. Crystallinity, micropore
structure, and very high acid strength of Si–OH–Al were preserved. The mesopores of big
volume and surface were formed. As the consequence catalytic activity increased significantly.
27
Al MAS NMR evidenced the change of Al status during formation of hierarchical zeolite Y.
Parent dealuminated zeolite contained both tetrahedral zeolitic Al and extraframework
octahedral Al. Desilication caused transformation of octahedral Al into tetrahedral non zeolitic
Al (similar as in amorphous aluminosilicates). A reverse transformation of non zeolitic
tetrahedral Al into octahedral one was observed upon calcination which was indispensable to
remove TBA
+
ions remaining in zeolite treated with TBAOH.
As TBAOH is an expensive chemical we investigated a possibility of preparation of
hierarchical zeolites Y in a more economical way. We found, that ammonia solution produces
hierarchical zeolite Y of good catalytic properties in α-pinene isomerization. XRD showed a
partial loss of crystallinity and loss of long distance of typical zeolitic ordering, but according to
29
Si NMR short distance ordering i.e. typically zeolitic environment of Si was preserved.
Similarly,
27
Al MAS NMR evidenced, that most of Al was in typically zeolitic tetrahedral
positions. IR studies showed the presence of strongly acidic and heterogeneous Si–OH–Al. Such
heterogeneity is due to less ordered structure of zeolites treated with ammonia solution. Zeolites
desilicated with ammonia may be a non-expensive promising hierarchical zeolitic catalyst.
Acknowledgment
This study was sponsored by the grant of NSC 2015/17/B/ST5/00023
XIV
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International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
57
T1: O–15
Cobalt-exchanged-MCM-56 zeolites treated by fluoride
and nitric acid media
Justyna Grzybek
1
, Klaudia Wrzesińska
1
, Aleksandra Korzeniowska
1
,
Andrzej Kowalczyk
1
, Lucjan Chmielarz
1
, and Barbara Gil
1
1
Faculty of Chemistry, Jagiellonian University Kraków, Ingardena 3, 30-060 Krakow, Poland,
e-mail: grzybek@chemia.uj.edu.pl
Zeolites, a group of microporous, crystalline aluminosilicates, are one of the main pillars of
industry and heterogeneous catalysis [1]. Their strong acidic sites are located inside the channels
available through windows with diameters not exceeding 1 nm. This constrain appears to limit
accessibility of catalytic sites and does not allow complete utilization of the potential of these
materials, both in acid and redox catalysis. This leads to an increased interest in the synthesis of
new and modifications of already known zeolites with more open structures. Zeolites containing
transition-metal ions often show promising activity as heterogeneous catalysts in pollution
abatement and selective redox reactions. One of the most important greenhouse pollutant,
characterized as a strong and long-lived absorber of infrared radiation is nitrous oxide. The first
choices for decomposition of N
2
O from a cost-effective point of view are cobalt oxide-
containing catalysts which show excellent catalytic activities due to its relatively high redox
properties [2].
On this field very promising seem to be relatively new class of zeolites named lamellar or
two-dimensional zeolites, characterized by the enhanced accessibility of active centers [3]. One
of the most interesting lamellar zeolite is MCM-56, belonging to the MWW family. MCM-56
consists of 2.5 nm thick monolayers and is an intermediate product transforming to the classical
three-dimensional MCM-49. To improve its textural and ion-exchange properties, the parent
MCM-56 was treated with nitric acid and a novel method, with the use of HF solution in NH4F,
recently published by Valtchev et al. [4]. After acid treatment the classical ion-exchange for
cobalt cations was carried out. Such treatment led to the formation of zeolite having relatively
high loading of cobalt (0.4–0.7 wt%, depending on the pretreatment procedure). Co was present
mainly in the form of the small clusters of cobalt oxides, with nominal oxidation state of cobalt
equal 3+ and well-dispersed Co
2+
cations. FTIR spectroscopy confirmed that cobalt speciation
and properties strongly depend on the calcination temperature. At standard activation
temperature (450°C), cobalt-containing MCM-56 strongly adsorbed N
2
O, with minimum
interaction with the NO. When the sample was activated above 500°C, NO was adsorbed mainly
as the –ONO moieties and transformed into more stable nitrates. For that reason, cobalt-
containing MCM-56 was tested as a potential catalyst for deNO
x
process.
Keywords: MWW; cobalt; NO
x
decomposition
Acknowledgment
Financial support from National Science Centre in Poland, grant no 2016/21/B/ST5/00858 is gratefully
acknowledged.
References
[1] C.P Nicholas in Zeolites in Industrial Separation and Catalysis, S. Kulprathipanja Ed., Wiley,
Weinheim, Germany (2010) 355.
[2] Q. Shen, L.D. Li, J.J. Li, H. Tian, Z.P. Hao. J. Hazard. Mater. 163(2009) 432.
[3] W.J. Roth, J. Čejka, Catal. Sci. Technol. 1 (2011) 43.
[4] Z. Qin, L. Lakiss, J.P. Gilson, K. Thomas, J.M. Goupil, C. Fernandez, V. Valtchev, Chem. Mater. 25
(2013) 2759.
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