1070-4272/02/7503-0396$27.00C2002 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 75, No. 3, 2002, pp. 396!401. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 3,
2002, pp. 407!412.
Original Russian Text Copyright + 2002 by Lamberov, Romanova, Shmelev, Sopin.
AND ION-EXCHANGE PROCESSES
Effect of Acid Modification on the Structure
and Catalytic Activity of Aluminum Oxide
A. A. Lamberov, R. G. Romanova, I. G. Shmelev, and V. F. Sopin
Kazan State Technological University, Kazan, Tatarstan, Russia
Received July 6, 2001
Abstract-The effect of acetic acid introduced as modifying additive into active aluminum oxide on its
structural characteristics is considered. A relationship is established between the structural characteristics,
content and features of aprotic acid centers, and catalytic activity of the obtained catalysts in dehydration
One of industrial methods for styrene production is
based on dehydration of methylphenylcarbinol (MPC).
The main disadvantage of the process is its high
energy consumption, resulting from the fact that the
reaction is endothermic and proceeds in the gas phase.
In this connection, development of effective catalysts
making it possible to reduce the energy consumption
by lowering the process temperature is a topical prob-
lem. It is known that active aluminum oxide (g-Al
AAO) is used as catalyst for dehydration of aromatic
alcohols, and the process occurs by the acid3base
mechanism . Consequently, the catalyst activity
will depend on structural characteristics and distribu-
tion of acid3base centers over the surface. It has been
shown previously that dehydration proceeds the most
efficiently on an AAO surface with the pore diameter
distribution peaked at about 150 A . One of prom-
ising ways to change the structure and surface distri-
bution of active centers is to introduce modifying
agents into the catalyst composition.
In this paper we analyze the effect of modification
with acetic acid on the structure and activity of the
catalyst in MPC dehydration to give styrene.
Commercial AAO manufactured by the aluminate3
nitrate method was modified by impregnation .
The thus treated aluminum oxide was dried to con-
stant weight at 110oC and then calcined at 550oC
for 2 h.
MPC dehydration was performed in an isothermal
reactor at 220oC in the presence of water vapor
(MPC : H
O = 1 : 1) under conditions of incomplete
conversion, since only in this case the catalyst activi-
ties can be compared. The temperature was main-
tained constant to within +5oC, the space velocity of
the raw material and water was 5.4 h
, and the cata-
lyst volume, 50 cm
Liquid catalyzate was analyzed on a Tsvet chroma-
tograph with a thermal conductivity detector and a
steel column 2 m long and 3 mm in diameter, sta-
tionary phase 12% PEG-20000 on Porokhrom support
(0.2530.315 fraction), carrier gas helium. The col-
umns and the detector were thermostated at, respec-
tively, 150 and 180oC; the vaporizer was heated to
Adsorption measurements aimed at determining the
specific surface area, pore volume, and pore diameter
distribution were performed by the method of nitrogen
desorption on a Micromeritics ASAP-2400 installa-
tion. Adsorption isotherms were measured at 200oC,
and degassing was done at 500oC to a residual pres-
sure of 10
mm Hg. The model of slit-like pores
open on all sides was used in calculations.
The crystal structure was studied on a DRON-3M
diffractometer with FeK
radiation and secondary
beam passed through a graphite monochromator. Dif-
fraction patterns were processed using RIETQUAN
2.3 software [4, 5] applicable to both crystalline and
amorphous structures. As reference were used struc-
tures represented in the Inorganic Crystal Structure
Database (ICSD for WWW).
The acid-base properties of the aluminum oxide
surface were studied by IR spectroscopy.
Investigations were carried out under supervision of E.A. Pauk-
shtis (Boreskov Institute of Catalysis, Siberian Division,
Russian Academy of Sciences, Novosibirsk).