ISSN 1070-4272, Russian Journal of Applied Chemistry, 2014, Vol. 87, No. 6, pp. 676−683. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © I.N. Mukhambetov, A.A. Lamberov, 2014, published in Zhurnal Prikladnoi Khimii, 2014, Vol. 87, No. 6, pp. 687−694.
INORGANIC SYNTHESIS AND INDUSTRIAL
Effect of Hydrothermal Treatment on the Structure
and Acid Properties of the Surface of Molded
I. N. Mukhambetov and A. A. Lamberov
Kazan (Volga Region) Federal University, ul. Kremlevskaya 18, Kazan, Tatarstan, 420000 Russia
Received May 13, 2014
Abstract—Mechanism of the hydrothermal modiﬁ cation of gamma–aluminum oxide was studied. A set of
physicochemical methods demonstrated that boehmite crystals are formed in macropores (>500 nm) by the
dissolution/precipitation mechanism, whereas in mesopores (<20 nm), rehydration of primary blocks of aluminum
oxide occurs from the surface into the bulk. As a result of the phase transition, aggregates of primary oxide blocks
are dispersed, which leads, at a certain treatment duration, to an increase in the speciﬁ c surface area. In this case,
the content of acid centers also increases according to the results of a temperature-programmed desorption of
ammonia, as also does the catalytic activity in the reaction of skeletal isomerization of n-butenes.
Gamma–aluminum oxide is widely used as a catalyst
 and support for metallic and metal oxide catalysts in
petrochemical processes [2, 3] owing to the combination
of a developed porous structure and speciﬁ c acid-base
properties of the surface.
One of effective ways to control the phase composition
and porous structure of aluminum oxide is by hydrother-
mal modiﬁ cation of the starting aluminum oxide [1–3]. In
the process, the oxide is hydrated into boehmite, which
is further again converted to the oxide by calcination :
The process of hydrothermal treatment (HTT) changes
the porous structure of the ﬁ nal aluminum oxide. The
speciﬁ c surface area may be either smaller or larger [1, 2]
than that of the base oxide, depending on the treatment
conditions. The same refers to the acid properties of the
surface. The decrease in the acid properties of aluminum
oxide upon a hydrothermal treatment is widely known
[1–4]; the increase in the content of acid centers was
noted by the authors of [3, 4]. However, the mechanism
of the process and reasons for the increase in acidity and
speciﬁ c surface area of γ-Al
have not been determined.
The present study is devoted to an analysis of the ef-
fect of hydrothermal treatment on the structure and acid
properties of the surface of gamma–aluminum oxide and
elucidation of the mechanism of the process.
As objects of study served aluminum oxide samples
obtained in accordance with Scheme 1.
Sample 1 was obtained from high-purity boehmite
manufactured by SASOL company. It contained the fol-
lowing microimpurities (g ton
< 120; Fe
100; CaO < 50; MgO < 50; Na
O < 20; K
O < 20; Ni,
Co, Cr, Pb, Mn, Zn < 100.
The hydrothermal treatment of aluminum oxide was
performed in an autoclave at 150°C and heating/cooling
rate of 7 deg min
. On being kept for a certain time, the
autoclave was cooled to room temperature and the sample
was extracted, dried at 120°C for 2 h, and then calcined
at 550°C for 4 h.