ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 10, pp. 1723!1725. + Pleiades Publishing, Inc., 2006.
Original Russian Text + S.E. Mamedov, E.I. Akhmedov, F.Sh. Kerimli, M.I. Makhmudova, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79,
No. 10, pp. 1741!1743.
Influence of Phosphorus Content on Physicochemical
and Catalytic Properties of H-Pentasil in m-Xylene
Isomerization and Toluene Methylation
S. E. Mamedov, E. I. Akhmedov, F. Sh. Kerimli, and M. I. Makhmudova
Baku State University, Baku, Azerbaijan
Received February 21, 2006
Abstract-Physicochemical and catalytic properties of H-pentasils in m-xylene isomerization and toluene
methylation were studied.
Control of the zeolite pore size and acid properties
by elimination of the strongest acidic centers and
by variation of their nature is one of probable
ways to modify the catalytic and molecular-sieve
properties of zeolites. Chemical modification of
the zeolite surface with compounds of B, Mg, P,
Si, etc. , which have a para-orienting effect
upon the activity of zeolite catalysts in transforma-
tions of aromatic hydrocarbons, is promising in this
Since pentasil-type high-silica zeolites offer wide
opportunities in oil refining, it is interesting to study
how modification of such zeolites with a phosphorus
compound will affect their catalytic and physico-
chemical characteristics in m-xylene isomerization
and toluene methylation.
Pentasil-type zeolite with a SiO
of 58 was used. It was converted into the NH
by ion exchange as in  and then into the H form
by thermal decomposition of the NH
form for 4 h
at 500oC. Catalysts modified with 0.53 4 wt % phos-
phorus were prepared by impregnation of the zeo-
lite H form with ammonium hydrophosphate for 6 h
at 80oC. The samples were dried in air for 16 h, then
for 4 h in a desiccator at 110oC, and finally calcined
in a muffle for 4 h at 550oC.
The catalysts obtained were subjected to chemical
analysis, X-ray phase analysis, and adsorption anal-
ysis and studied by IR spectroscopy.
The IR spectra were recorded on a Specord spec-
trophotometer. Zeolites were compacted into thin pel-
lets containing 638 mg of the substance per square
centimeter. Before adsorption, they were heated in
a vacuum for 2 h at 500oC. Adsorption of pyridine
was performed at room temperature and saturated
vapor pressure. The IR spectra in the region of alu-
minosilicate framework vibrations were recorded with
samples pelletized with KBr. Adsorption measure-
ments were performed by the method described in .
The experiments were performed on a flow-type
device with a fixed catalyst bed (4 cm
), in a plug-
flow reactor, at atmospheric pressure within the 2503
450oC range, volumetric flow rate of the raw material
of supply 1 h
, and m-C
OH : H
molar ratios of 3 : 1 and 2 : 1 : 2, re-
spectively. The reaction products were analyzed chro-
The X-ray phase analysis showed that the crystal-
line structure of the zeolite is preserved during mod-
ification with ammonium hydrophosphate. The IR
study confirmed this conclusion. In the region of alu-
minosilicate framework vibrations (40031300 cm
which are the most sensitive to the degree of crystal-
linity of the zeolite, the bands of the external Si3O
bonds at 5503560 and 7903 800 cm
ly unchanged upon modification with phosphorus.
An increase in the intensity of the high-frequency
branch of the asymmetrical stretching band (10003
) may be due to interaction of phosphorus
atoms with structural aluminum atoms .