254
PONOMAREVA et al.
type [17]. The recrystallization procedure includes angular range of 5° < 2
partial dissolution of zeolite in an alkaline solution scattering (SAXS) patterns were recorded in the anguꢀ
containing a structureꢀdirecting agent, which can be lar range of 1.5° < 2 < 5°. The diffractograms were
θ
< 50°. Smallꢀangle Xꢀray
θ
selected from a number of different surfactants.
It is assumed that partial degradation of the zeolite
structure and removal of zeolitic fragments, in the
place of which mesopores are formed, occurs at the
dissolution stage. The next stage involves the reassemꢀ
bly of the dispersed particles into a mesoporous phase
that, depending on the degree of dissolution of initial
zeolite, can simply cover its surface (RZEOꢀ1), form
micro–mesoporous composites (RZEOꢀ2), or create
a mesoporous material with small fragments of zeolitic
particles into embedded its walls (RZEOꢀ3) [17].
In this work, we first studied the conversion of aceꢀ
tone into isobutylene over micro–mesoporous cataꢀ
lysts with different mesopore contents that had been
prepared via the recrystallization of mordenite (MOR)
and examined the effects of porosity characteristics
and cesium modification of the catalyst on its physicꢀ
ochemical and catalytic properties.
processed using the Bruker software package difꢀ
frac.EVA. Phases were identified according to the
ICDD PDF2 database.
Electron microscope (TEM) images of the samples
were obtained on a Jeol JEM 2010 transmission elecꢀ
tron microscope with a 200ꢀkeV electron beam.
Lowꢀtemperature nitrogen adsorptionꢀdesorbtion
isotherms were obtained on a Micromeritics
ASAP2000 automatic porosimeter. The micropore
volume was determined using the tꢀplot method. The
pore volume, which takes into account adsorption in
micropores and mesopores and on the external surꢀ
face, was calculated from the amount of nitrogen
sorbed at a relative pressure of p/p0 = 0.95.
The acid properties of the samples were studied
using the technique of temperatureꢀprogrammed desꢀ
orption of ammonia (NН3 TPD) on a USGAꢀ101
multipurpose sorption gas analyzer. A weighed portion
of the sample was placed in a quartz reactor, heated in
a helium flow to 550
calcined at this temperature for 1 h in a helium flow,
and then cooled to 60 . Saturation with ammonia
was conducted for 15 min in a flow of dry NH3/N2
(1 : 1) mixture. Physisorbed ammonia was removed at
°С at a heating rate of 10°C/min,
EXPERIMENTAL
Mordenite (MOR) with a silica ratio of
SiO2/Al2O3 = 97 (Zeolyst, trade name CBV 90A) was
used as initial zeolite. Mesoporous aluminosilicate
MCMꢀ41 with SiO2/Al2O3 = 100 was prepared from
an aluminosilicate gel via hydrothermal synthesis at
140°С for 24 h using cetyltrimethylammonium broꢀ
mide as the template. After crystallization, the
obtained mesoporous material was washed with water,
°С
100
sample was cooled to 60
(flow rate of 30 mL/min), and the reactor temperature
was linearly raised to 800 at a rate of 8°C/min. The
°С
in a flow of dry helium for 1 h. After that the
°
С
in a flow of dry helium
°С
change in the thermal conductivity of the flow was
recorded using a katharometer.
dried at 100°С, and calcined at 550°С in a flow of air
for 24 h in order to remove the organic template.
The recrystallization of MOR was conducted by
the partial dissolution of zeolite in an alkali solution
with the subsequent hydrothermal treatment in the
presence of cetyltrimethylammonium bromide
according to the procedure described in [18]. The
degree of recrystallization was varied by changing
the alkali concentration. In order to obtain materials
RMꢀ1, RMꢀ2, and RMꢀ3 with different micropore
and mesopore contents, alkali to zeolite ratios of 3, 5,
and 10 mmol(NaOH)/g(MOR) were used, respecꢀ
tively. The prepared samples were washed to free of the
IR spectra were recorded on a Bruker Vector 22
instrument equipped with a deuterated triglycidyl sulꢀ
fate (DTGS) detector with the optical resolution of
1
4 cm⎯ in the range of 4000–400 cm–1. The catalysts
were activated in the IR cell at 400
2 h. The adsorption of pyridine (Py) was conducted at
°С
and 10–5 torr for
200
200
°
C
for 30 min with the subsequent evacuation at
for 15 min. The obtained IR spectra were proꢀ
°C
cessed using the software package OMNIC ESP Verꢀ
sion 6.0.
The conversion of acetone into isobutylene was
studied in a flow reactor at atmospheric pressure using
dilution of the reaction mixture with nitrogen
template and calcined in air at 550°С for 24 h. The
synthesized MCMꢀ41 and micro–mesoporous alumiꢀ
nosilicates were subjected to triple ion exchange with
ammonium nitrate and subsequent calcining in a flow
(20 mL/min), a temperature 500°С, and a feedstock
weight hourly space velocity (WHSV) of 2 to 72 h–1.
Liquid and gaseous reaction products were deterꢀ
mined by chromatographic analysis on a Chromatec
Analytic Kristall 2000M gas chromatograph with a
flame ionization detector (FID) and an SEꢀ30ꢀcoated
capillary column using nitrogen as a carrier gas. To
of air at 550°С for 6 h to prepare the Hꢀforms. The
catalysts were modified with cesium by incipient wetꢀ
ness impregnation with a cesium acetate solution to
have a metal loading of 3 wt %.
The chemical composition of the obtained materiꢀ determine CO2 and light С1 and С2 hydrocarbons, gasꢀ
als was determined using Xꢀray fluorescence analysis eous samples were also analyzed on the Kristall 2000M
on a Thermo Scientific ARL Perform’X instrument chromatograph using a thermal conductivity detector,
equipped with a 3.5ꢀkW rhodium tube. Xꢀray diffracꢀ and a packed PorapakꢀQ column, hydrogen as a carꢀ
tion (XRD) patterns were recorded on a Bruker D2 rier gas. The products were identified using authentic
PHASER diffractometer (Cu
K
α
radiation) in the organic substances and the coupled gas chromatograꢀ
PETROLEUM CHEMISTRY Vol. 56
No. 3
2016