tert-BUTYLATION OF TOLUENE CATALYZED
251
In this work, a series of HPW/HBEA catalysts were
IR spectra of the samples after pyridine adsorption
prepared by impregnation method. The catalysts were were recorded on a Bruker Tensor 27 FT-IR spec-
investigated by XRD, TEM, ICP, BET, Py-IR, and trometer equipped with a high temperature vacuum
NH -TPD methods, and their catalytic performance cell. The sample powder was pressed into a self-sup-
3
was evaluated in alkylation of toluene with tert-butanol porting wafer, and the spectra were recorded in a wave-
−1
–1
under liquid reaction conditions.
number range of 4000–400 cm with a 4 cm resolu-
tion. Before each experiment, the samples were
pressed into thin pellets (10–30 mg) with diameter of
2. EXPERIMENTAL
1
6 mm and activated in situ for one night under vac-
−5
uum (10 Pa) at 170°C. Pyridine was introduced in
excess at 150°C after the activation period. The con-
centrations of the Brønsted and Lewis sites were deter-
mined from the integrated area of the bands of
2.1. Preparation of Catalysts
NaBEA zeolite (purchased from Zeolyst Int.) was
used as a starting material. HBEA powder was pre-
pared by ion exchange of NaBEA with NH NO
+
−1
4
3
PyH (around 1540 cm ) and PyL (around
(
Sigma Aldrich, reagent grade) aqueous solution
−1
1
450 cm ) species using the values of the molar
extinction coefficients of both bands.
according to the reported procedure [13]. H PW O ,
3
12 40
xH O (HPW, Sigma-Aldrich, reagent grade) was dried
2
o
at 200 C in a furnace for 24 h to remove a part of water.
2.3. Catalytic Tests
The HPW modified HBEA samples were prepared by
wetness impregnation of the HBEA with solution of
The alkylation of toluene with tert-butanol was car-
HPW in ethylalcohol containing a desired amount of ried out in a 300 mL laboratory autoclave. Catalyst
HPW. The obtained samples were aged at ambient sample (1.0 g) was added into a mixture of toluene
temperature for 8 h and dried at 60°C overnight and (94 mmol) and tert-butanol (283 mmol) using cyclo-
o
then calcined at 450 C for 4 h. The as prepared cata- hexane (60 mL) as the solvent. The reaction system
lysts were referred to as HPW(x)/HBEA(x = 10, 20, was flushed with continuous N purging for 30 min.
2
3
0, 40%), where x corresponds to the HPW weight Then the mixture was heated to a certain temperature.
content in the catalyst.
The stirring speed was 300 rpm. After certain time, the
mixture was cooled down to room temperature, and
the zeolite catalyst was removed by filtration. The liq-
uid phase was analyzed on GC-14C gas chromato-
graph equipped with SE-30 capillary column
2.2. Characterization of Catalyst
X-ray diffraction (XRD) measurements were per-
formed on aD/max-2200PC X-ray diffractometer
(
0.25 mm × 50 m).
using a CuK radiation (40 kV, 30 mA) in 2θ range
α
from 10° to 80° at a scan speed of 4 deg/min.
3
. RESULTS AND DISCUSSION
.1. Characterization of the Catalysts
Figure 1 shows the XRD patterns of parent HBEA
The crystallite sizes of the zeolite catalysts were
evaluated from TEM images obtained on a JEM-1010
instrument. The samples were dispersed in ethanol
and placed on a carbon grid.
3
and HPW(x)/HBEA. The peak positions of HBEA
were not changed even at high HPW content. This fact
proves that the structure of HBEA was retained after
modification with HPW. The peaks of HPW were not
observed at HPW content less than 30%. This indi-
cates that the size of HPW phase crystallites in the cat-
The HPW content in the catalysts was determined
by inductively coupled plasma optical emission spec-
trometry (ICP-OES) using a Perkin Elmer Optima
2
000DV spectrometer.
The porosity of the zeolites was determined by alysts is below the detection limit (<3 nm) [14]. Nev-
nitrogen adsorption at 77 K on an automatic ertheless, the peaks corresponding to HPW appeared
NOVA200e setup (Micromeritics). The total pore vol- when the HPW content was increased to 40%.
ume was then calculated from the adsorbed volume of
The morphologies of HBEA and HPW/HBEA cat-
alysts were consistent with TEM results (Fig. 2). A
nitrogen at p/p = 0.97. The external surface area and
0
micropore volume were determined by the t-plot honeycomb structure of HBEA zeolite (Fig. 2a) was
method using the Harkins–Jura equation
observed. HPW/HBEA catalysts showed the uniform
dispersion of HPW on HBEA, which could be distin-
guished as dark dots in TEM images (Fig. 2b).
The catalyst acidity was measured using NH -TPD
3
(
(
(
Quantachrome Chembet-3000 system). A sample
200 mg) was pretreated at 550°C for 1 h in dry He
Table 1 shows that the actual loading of HPW in
50 mL/min) and cooled to 120°C. It was then the HPW(x)/HBEA catalysts determined via ICP
exposed to 10% NH /90% He mixture for 1 h. After analysis were close to the corresponding theoretical
3
amounts. The parent HBEA exhibited high specific
purging the catalyst with He for 1 h, a TPD plot was
2
obtained at a heating rate of 10°C/min in the tempera- surface area of 492.5 m /g with pore volume of
3
ture from 120 to 600°C.
0.48 cm /g. With increasing the HPW loading from 10
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 93 No. 2 2019
Yuanyuan Wang
