Russian Chemical Bulletin, International Edition, Vol. 66, No. 11, pp. 2066—2072, November, 2017
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2066—2072, November, 2017.
10665285/17/66112066 © 2017 Springer Science+Business Media, Inc.
Selective conversion of methane to aromatic hydrocarbons
on large crystallite zeolite catalysts with mesoporous structure
S. A. Mikhaylov,
N. A. Mamonov,
L. M. Kustov,
and M. N. Mikhaylov
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. Email: email@example.com
Build. 2, 55/1 Leninsky prosp., 119333 Moscow, Russian Federation.
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Large crystallite mesoporous MFI (ZSM5) zeolite was synthesized by using carbon nano
powder as a secondary template. The surface properties, morphological and phase composi
tion of the synthesized material and of the commercial ZSM5 (Zeolyst) zeolite were studied
by nitrogen porosimetry, XRD and scanning electron microscopy. The results showed that
the volume of mesopores volume increases with development of a secondary mesoporosity in
the structure of zeolite. The obtained zeolite supports were used to prepare molybdenum
containing catalysts for the methane aromatization by solid phase preparation technique.
Based on the XPS data, molybdenum particles in these catalysts are characterized by more
uniform size distribution. The formation of a secondary pore structure restrains the carbon
deposit formation as well as increases the methane conversion and the yield of the aromatic
Key words: methane, aromatization, molybdenum, zeolite, thermoprogrammed oxida
tion, acidity, Xray diffraction, scanning electron microscopy, mesoporosity, template.
Recently, the methane aromatization has been con
sidered as an alternative approach for the natural and
casinghead gas processing. Metal zeolite catalysts are
highly active in the methane aromatization. However,
narrow channels formed by micropores of zeolites com
plicate the mass transfer and promote the coke formation;
hence, a rapid decrease in activity with the time occurs.
One of the methods for improving the stability of zeolite
catalysts is associated with the development of a secondary
mesoporous structure. The presence of mesopores with a
diameter of 2—50 nm facilitates the diffusion processes in
catalysts and contributes to an increase in their activity.
Therefore, numerical studies have been conducted to pro
duce zeolite supports a secondary mesoporosity and in
this way to enhance the availability to the active sites.
One of the known technique producing mesoporous
solids is a postsynthetic hydrothermal treatment, such
However, such treatments change
not only the poresize distribution, but the total acidity,
since the strong Brönsted acid sites (BAS) are removed.
However, acidic properties can be preserved if a second
ary mesoporous structure in zeolite is developed in the
presence of solid templates at the step of the reactive gel
preparation. Following this procedure, the Si/Al ratio in
a zeolite lattice remains unchanged, as well as the ratio
between the BAS and Lewis acid sites (LAS).
At crystallization of zeolite material in the medium of
a structuredirecting agent, the solid template is com
pletely incorporated into the crystals of zeolite, and then it is
removed upon calcination. Zeolites, which have both micro
pores and mesopores or intracrystal mesopores in their
structure, are referred to as hierarchical zeolite systems.
The formation of the secondary mesoporous structure
in the zeolite crystal lattice can improve the distribution
of molybdenum in the pores of zeolite material.
The purpose of this work is to synthesize MFI (ZSM5)
zeolites with a secondary mesoporous structure formed
by introducing carbon nanopowder as a secondary tem
plate at the step of the gel formation, and to compare
physical and chemical properties of the synthesized large
crystallite zeolites to those of the commercial ZSM5
zeolite. In addition, it was of interest to prepare molybde
numzeolite catalysts based on the synthesized supports
and to study their physicochemical properties and cata
lytic activity in the methane aromatization.
Synthesis of ZSM5 zeolite. A weighted amount of sodium
hydroxide (Labtech) was dissolved in distilled water and sodi
um aluminate (Sigma—Aldrich, 53.6 wt.% of Al
) was added
at regular stirring. After the complete dissolution of the re