G Model
CATTOD-9631; No. of Pages10
ARTICLE IN PRESS
M. Kub u˚ et al. / Catalysis Today xxx (2015) xxx–xxx
3
2.2.6. MEL
2.4. Adsorption of 2,2-dimethylbutane
As for MEL zeolite, 51 g of TEOS was slowly added dropwise to
the aqueous solution containing 2.6 g of Al(NO ) ·9H O and 26 g
Kinetics of vapor phase adsorption of 2,2-dimethylbutane over
zeolites at room temperature was studied using a Cahn C-2000 bal-
ance coupled with a computer via an ATI-Cahn digital interface (for
details see Ref. [35]). 2,2-Dimethylbutane vapor was delivered from
liquid 2,2-dimethylbutane with a 99.5+% purity (Aldrich). The rel-
ative vapor pressure P/P0 was maintained at ∼0.3 by controlling
the temperature of the liquid adsorbate using a cooling circulator.
Prior to the adsorption experiments, the calcined zeolites (∼20 mg)
3
3
2
of distilled water and the solution was stirred for 90 min. After-
wards, NaOH (0.5 g) dissolved in water (21.4 g) was slowly added
dropwise. Finally, 31.45 g of tetrabutylammonium hydroxide (40%
in H O, Fluka) used as a SDA and 34 g of water were quickly added
2
under vigorous stirring and the reaction mixture was stirred for
1
20 min. The crystallization was carried out under agitation in
◦
Teflon-lined 90 ml autoclaves at 170 C for 6 days.
◦
−3
After synthesis of each zeolite, the autoclaves were immediately
cooled down by stream of water, solids recovered by filtration,
washed repeatedly with copious amount of distilled water and
were degassed at 450 C in a vacuum of 10 Torr for 5 h. The weight
change of the zeolite sample was recorded for the 4 h of adsorp-
tion time. The adsorption capacities are reported in milliliters
of liquid per gram of dry zeolite, assuming that the adsorbed
adsorbate has the same density as the bulk liquid (0.649 g/ml for
2,2-dimethylbutane at room temperature).
◦
dried overnight in the oven at 60 C. The individual zeolites were
◦
calcined under flowing air at 580 C for 12 h with a heating rate of
1
◦
C/min to remove the organic content. To get ammonium form,
calcined samples were four-times treated with 1.0 M NH NO solu-
4
3
tion (99%, Lachner) for 4 h each time at room temperature using
2
.5. Catalytic reactions
1
00 ml of solution per 1 g of sample. In order to obtain its proton
◦
form, calcination at 450 C for 2 h followed.
Structural characteristics of zeolites under study are given in
Table 1.
Toluene disproportionation and alkylation with isopropyl alco-
hol were investigated in the gas phase under atmospheric pressure
using a glass fixed bed microreactor. Each catalyst was pressed into
the pellets, crushed and sieved to obtain particles with a diam-
eter in the range of 0.50–0.71 mm. Prior to the reaction, a given
◦
amount of the catalyst was in situ activated at 500 C for 120 min
2.3. Characterization
−
1
in a stream of nitrogen (40 ml min ), and then the activated cat-
alyst was cooled down to the preset reaction temperature. In the
case of toluene disproportionation, the reaction temperature was
at 450 C, WHSV 20 h , and the concentration of toluene in the
feed stream using N2 as carrier gas was 18.5 mol%. Toluene alkyl-
The structure and crystallinity of as-made and calcined samples
were checked by X-ray powder diffraction. Patterns of prepared
samples were recorded on Bruker AXS D8 Advance equipped
with a graphite monochromator and a position sensitive detector
Våntec-1 using CuK␣ radiation and para focusing in Bragg-Brentano
geometry.
The size and shape of zeolite crystals were examined by
scanning electron microscopy (SEM, JEOL, JSM-5500LV). For mea-
surements crystals were coated with a thin platinum layer by
sputtering in vacuum chamber of a BAL-TEC SCD-050.
For chemical composition of zeolites X-ray fluorescence anal-
ysis (XRF) using a spectrometer Philips PW 1404 provided with
an analytical program UniQuant enabling determination of 74 ele-
ments from fluorine to uranium. For these measurements samples
were mixed with dentacryl as a binder and pressed on the surface
of cellulose pellets.
◦
−1
◦
ation was studied at the reaction temperature of 250 C. The WHSV
−
1
related to toluene was 10 h , the concentration of toluene was
8.5 mol% in the feed stream and toluene to isopropyl alcohol molar
1
ratio was 9.6.
The reaction feeds and products were analyzed using an on-line
gas chromatograph (HP 6890) equipped with an FID detector and
a capillary column (DB-5, 50 m × 320 m × 1 m) in toluene alkyl-
ation, while HP-INNOWax (30 m × 0.32 mm × 0.5 m) was used for
toluene disproportionation studies. The first sample was taken after
1
5 min of time-on-stream (T-O-S) and the other samples were
taken in the interval of 60 min.
Concentration of Lewis and Brønsted acid sites was determined
after adsorption of pyridine by FTIR spectroscopy (Nicolet Pro-
tégé 460 Magna with a transmission DTGS and MTC/A detector).
Samples were pressed into self-supporting wafers with a den-
3. Results and discussion
3.1. Structural and textural characterization of zeolites under
study
2
◦
sity of 8.0–12 mg/cm and activated in situ at 430 C overnight.
◦
Pyridine adsorption took place at 150 C for 20 min at a par-
All zeolites under study were characterized by X-ray powder
diffraction, scanning electron microscopy, adsorption isotherms
and FTIR spectroscopy using pyridine and 2,6-di-tert-butyl pyri-
dine as probe molecules. XRD patterns of zeolites TUN, IMF, –SVR,
and *SFV are provided in Fig. 2, while patterns of MFI and MEL are
not shown here. All patterns exhibit typical features of these zeo-
lites and evidence their phase purity and absence of amorphous
phase.
The size and shape of zeolite crystals under study are given in
Fig. 3. All zeolites, with exception of –SVR, show typical agglom-
erates of small crystals with sizes slightly below 1 m for MFI and
MEL, around 0.4–0.6 m for *SFV, IMF, and TUN. In contrast, zeo-
lite –SVR forms crystals with a higher aspect ratio possessing some
crystals up to 3 m long with smaller size of about 0.8 m.
Nitrogen adsorption isotherms are given in Fig. 4, while the text-
substantial adsorption at low partial pressures followed by long
tial pressure of 800–1000 Pa, followed by desorption at 250 and
◦
−
4
2
50 C for 15 min. All spectra were recorded with a resolution of
1
cm by collecting 128 scans for a single spectrum. The extinc-
tion coefficients for pyridine adsorbed on Brønsted acid sites,
−1
−1
ε(B) = 1.67 cm mol , and Lewis acid sites, ε(L) = 2.22 cm mol ,
were used for the quantitative analysis evaluation [34]. In a sim-
ilar way, 2,6-di-tert-butyl pyridine was used as a probe molecule
to assess the acidity of individual zeolites on their external surface,
the adsorption was carried out at ambient temperature. The same
extinction coefficient for Brønsted acid sites as for pyridine was
used.
Nitrogen sorption isotherms were acquired at liquid nitrogen
◦
temperature (−196 C) on a Micromeritics ASAP 2020 volumet-
ric instrument to determine surface area, pore volume and pore
size distribution of tested catalysts. Prior to the sorption mea-
◦
surements, all samples were degassed at 250 C for at least
1
2 h.
Please cite this article in press as: M. Kub u˚ , et al., Three-dimensional 10-ring zeolites: The activities in toluene alkylation and