Y. Zhou, et al.
AppliedCatalysisA,General577(2019)62–68
alcohol.
2.2. Characterization
The structure and crystallinity of zeolites were determined by
powder X-ray diffraction (XRD) using a Bruker AXS D8 Advance dif-
fractometer with Cu Kα radiation in Bragg-Brentano geometry. The
chemical composition was determined an inductively coupled plasma-
optical emission spectrometry (ICP/OES) (ThermoScientific Icap7000).
Crystal size and shape of all the samples were assessed using a JSM-
5500LV microscope. Nitrogen adsorption measurements were carried
out on a Micromeritics GEMINI II 2370 volumetric Surface Area
Analyzer at −196 °C to determine BET area and pore volume.
2. Experimental
2.1. Materials and synthesis
2.1.1. Materials
1,5-dibromopentane (97%, Sigma Aldrich), cis-2,6-dimethylpiper-
idine(98%, Sigma Aldrich), NaOH (98%, Lanchner), Sodium sulfate
(Sigma Aldrich), Chloroform (Lanchner), Diethyl ether (Lanchner),
Ambersep® 900(OH) (Alfa Aesar), Germanium oxide (99.99%, Sigma
Aldrich), Cab-O-Sil M-5 (Supelco Analytical), Aluminum nitrate non-
ahydrous (99.4%, Lanner), Hydrochloric acid (37 wt. % in H2O,
Lanchner).
Concentration of Lewis (cL) and Brønsted (cB) acid sites was de-
termined after adsorption of pyridine (PyR) by Fourier-transform in-
frared spectroscopy (FTIR) on Nicolet 6700 FTIR with MCT/B detector.
Zeolites were pressed into self-supporting wafers with a density of
8.0–12 mg/cm2 and activated in situ at 450 °C overnight. Pyridine ad-
sorption was carried out at 150 °C for 20 min at partial pressure
600–800 Pa, followed by desorption for 20 min. Before adsorption
pyridine was degassed by freezing and thawing cycles. All spectra were
recorded with a resolution of 4 cm−1 by collecting 128 scans for a
single spectrum at room temperature. Spectra were calculated on wafer
density of 10 mg cm−2. Concentration of cL and cB were evaluated from
the integral intensities of bands at 1454 cm−1 (cL) and at 1545 cm−1
(cB) using molar absorption coefficients, ε(L) = 2.22 cm μmol-1, and
ε(B) = 1.67 cm μmol-1 [27]. For the determination of the strength of
different acid sites, desorption of pyridine was carried out at 150, 250,
350 and 450 °C followed by FTIR measurements. A relatively large
probe molecule 2,6-di-tert-butyl-pyridine (DTBP) was used to de-
termine the accessibility of acid sites within prepared zeolites [28]. The
adsorption of DTBP took place at 150 °C and at equilibrium probe va-
pour pressure with the zeolite wafer for 15 min. Desorption proceeded
at the same temperature for 1 h followed by collection of spectra at
room temperature. Molar absorption coefficient from Ref [27]. was
used for evaluation of cB accessible for DTBPy using integral intensity of
2.1.2. Synthesis
2.1.2.1. Structure directing agent (SDA). The 7, 11-dimethyl-6-
azoniaspiro [5.6] undecane was synthesized with the method similar
to that described in the literature [26]. 140 ml of distilled water, 5.68 g
NaOH, and 32.65 g 1, 5-dibromopentane were mixed in a glass flask.
Then, 16.07 g of (2R, 6S)-2, 6-dimethylpiperidine was added dropwise
under reflux. The mixture was under very intensive stirring to prepare a
milk-like suspension and then cooled in an ice bath. Another small
amount of NaOH was added very slowly under vigorous stirring and
cooling by ice until the appearance of the oil products. Further stirring
for 1 h led to the formation of the crystalline phase, which was
recovered by filtration and extracted with 300 ml chloroform. The
organic fractions were dried using anhydrous sodium sulfate and
partially evaporated. The ammonium salt was precipitated and
washed out with diethyl ether. The salt was converted into hydroxide
form by ion exchange with Ambersep® 900(OH) anion exchange resin.
absorption band ca. 1530 cm−1
.
2.1.2.2. Ge-AFI. The germanosilicate AFI zeolite (referred to as Ge-
AFI) was synthesized from a gel using 7, 11-dimethyl-6-azoniaspiro
[5.6] undecane as SDA with a molar composition: 0.96 SiO2 : 0.24 GeO2
: 0.4 SDA : 30 H2O. The gel was prepared by dissolving germanium
oxide in the solution of SDAOH followed by addition of silica into the
solution and the mixture was stirred at room temperature for 30 min.
Hydrothermal crystallization was conducted at 175 °C for 7 days under
agitation.
The solid state 27Al nuclear magnetic resonance (NMR) spectra were
recorded under magic angle spinning (MAS) with a commercial 3.2 mm
triple resonance MAS probe spinning at 15 kHz on an Agilent DD2
500WB spectrometer operating
130.24 MHz.
a
at resonance frequency of
2.2.1. Catalytic test
The ranges of compositions yielding the germanosilicate AFI can be
varied:
Toluene alkylation with isopropyl alcohol was investigated in a
vapor phase continuous down-flow glass micro-reactor with a fixed bed
of catalyst under atmospheric pressure. Before the catalytic run, all the
zeolite catalysts studied were activated at 500 °C in nitrogen stream for
120 min. The reaction was performed at 250 °C with toluene to iso-
propyl alcohol (Tol/i-PrOH) molar ratio of 9.6 and weight hour space
velocity (WHSV) based on toluene equal to 10 h−1. The reaction pro-
ducts were analyzed using an Agilent 6890 Plus “on-line” gas chro-
matograph with flame ionization detector and a high-resolution capil-
lary DB-5 column (length 50 m, diameter 0.32 mm, and film thickness
1 μm). After 15 min of the time-on-stream (T-O-S), the first analysis was
done, followed by further sampling of the reaction products at approx.
50 min interval.
0.9−0.96 SiO2 : 0.24−0.3 GeO2 : 0.4 SDA : 30 H2O.
The solid products were recovered by filtration with water and then
dry at 65 °C overnight. To remove the SDA from the zeolites, the as-
synthesized samples were calcined in air at 550 °C for 6 h.
2.1.2.3. Al-AFI. Al containing AFI catalyst synthesized though one-step
alumination of calcined Ge-AFI is referred to as Al-AFI. 1 g of calcined
zeolite was treated with 100 ml of 1 M Al(NO3)3 solution at 80 °C for
48 h. The aluminated sample was subsequently centrifuged and washed
with 0.01 M HCl and water and then dried at 65 °C overnight.
2.1.2.4. deGe-Al-AFI. Al containing AFI catalyst synthesized though
two-step alumination of calcined Ge-AFI is referred to as deGe-Al-AFI.
1 g of calcined zeolite was treated with 100 ml of 0.1 M HCl solution at
80 °C for 16 h. After the treatment, the zeolite was centrifuged and
washed with water to PH = 7. The alumination was conducted by
addition of 100 ml of 1 M Al(NO3)3 solution at 80 °C for 48 h. The
aluminated sample were subsequently centrifuged and washed with
0.01 M HCl and water and then dried at 65 °C overnight.
3. Results and discussion
3.1. Synthesis and characterization of aluminated AFI zeolites by using Ge-
AFI as precursors
Germanosilicate Ge-SSZ-24 (Ge-AFI) with Si/Ge of 8.1 in the fra-
mework (Table 1) was prepared under hydrothermal conditions using
7, 11-dimethyl-6-azoniaspiro [5.6] undecane as SDA in this study. The
synthesis of Ge-AFI is sensitive to the Ge content in the gel mixture (Fig.
S1). At Si/Ge ratio ≤ 2, germanosilicate UTL is the main phase, while at
All the aluminated samples were calcined at 450 °C for 4 h prior
further characterization.
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