Russian Chemical Bulletin, International Edition, Vol. 66, No.11, pp. 2073—2080, November, 2017 2073
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2073—2080, November, 2017.
10665285/17/66112073 © 2017 Springer Science+Business Media, Inc.
Control of the properties of catalysts for methane aromatization
by synthesizing ZSM5 zeolites with different crystallite sizes
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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MFI zeolite materials (ZSM5) with crystal sizes in the range from 0.10 to 1.70
been synthesized. Acidic and surface properties, phase and morphological composition of the
prepared zeolites have been studied by the IR sprectroscopy, nitrogen porosimetry, XRD,
and scanning electron microscopy. Increasing crystal size was shown to decrease the general
acidity of the zeolite. Synthesized zeolites served as supports for molybdencontaining cata
lysts for methane aromatization prepared by using the solid phase synthesis approach. Diffuse
reflectance IR spectroscopy, thermoprogrammed desoption of ammonia and
spectroscopy were used to characterize the physicochemical properties of the catalysts. An
increase in the crystallite size of the zeolite favors a decrease in the acidity of the catalysts and
inhibits the formation of alumina molybdate during the catalyst preparation. As a result,
a tendency to coke formation is suppressed and the performance of the catalysts in methane
aromatization improved: methane conversion and aromatic hydrocarbon yield increase.
Key words: methane, aromatization, molibden, zeolite, IR spectroscopy, thermopro
grammed desorption of ammonia, acidity, Xray diffraction, scanning electron microscopy,
One of the routes for the natural gas processing is
methane aromatization. This method makes it possible to
directly convert methane into aromatic hydrocarbons,
from benzene to naphthalene, with high selectivity and to
synthesize valuable petrochemical products, avoiding the
stage of the synthesis gas production.
on the search for the optimal
composition of the methane aromatization catalyst
showed that Mo/HZSM5 catalytic system exhibits the
highest activity and stability in the methane conversion.
In recent years, a possibility of purposeful changes in the
catalytic properties of zeolitic molybdenumzeolite cata
lysts is attracting the attention of researchers.
of the Si/Al ratio in the zeolite framework and a degree of
crystallinity of the synthesed products on the activity and
selectivity of the catalysts was studied. It was found that
ratios of 30—40 are the most favorable
for the formation of active and stable catalysts. A lower
aluminum content reduces the acidity and deteriorates
the performace of the catalyst significantly.
Another approach to modify the catalytic properties
of zeolite catalysts is to control the size of the crystallites.
By varying the size of the crystals in zeolite material, the
intracrystalline diffusion path of the reactants and reac
tion products can be varied. Synthesis of zeolites with
crystallite sizes below 100 nm is often accompanied by an
incomplete crystallization, which decreases both pore
volume and hydrothermal stability.
Therefore, the con
clusions drawn from the study of the activity of
Mo/HZSM5 zeolite catalysts prepared by mechanical
grinding are contradictory. The crystal size is usually con
trolled by mechanical grinding of the large crystallite
zeolites in ball mills. However, in this case, the bulk crys
tallinity is reduced and surface defects are often formed,
which anyhow affect the acidity of the samples. In partic
ular, Mo/HZSM5 catalysts prepared from mechanically
crushed zeolite crystals are no more active than large
At the same time, Mo/HZSM5 cat
alyst prepared by using a small crystallite zeolite ZSM5
(see Ref. 8)
demonstrated a higher catalytic activity and
stability. Nevertheless, from other studies
clusions can be drawn.
Direct hydrothermal synthesis of zeolites with differ
ent crystal sizes is fraught with numerous difficulties. In
particular, it is necessary to select a suitable structure
directing agent and the optimal composition of the crys