G Model
CATTOD-9460; No. of Pages6
ARTICLE IN PRESS
C. Chen et al. / Catalysis Today xxx (2015) xxx–xxx
2
2
. Experimental
(TEM) experiments were performed on a 2100F electron micro-
scope (JEOL, Japan) with an acceleration voltage of 200 kV. The
2.1. Materials
platinum dispersion of the samples was assessed by H chemisorp-
tion at 25 C, performed using a Finetec Finesorb-3010 instrument
2
◦
Conventional ZSM-5 zeolite was purchased from the Catalyst
Plant of Nankai University. NaAlO2 (CP), tetraethyl orthosilicate
TEOS, AR), and toluene (AR) were purchased from Sinopharm
equipped with a TCD. Typically, 0.05 g of the sample was pre-
◦
treated in a pure Ar flow (20 mL/min) at 200 C for 0.5 h and then
◦
(
cooled down to 25 C. Pulse chemisorption measurements were
Chemical Reagent Co., Ltd. Tetrapropylammonium hydroxide solu-
performed at this temperature with 10% H /Ar (20 mL/min).
2
tion (TPAOH, 1.0 M in H O), NaCl (AR), KCl (AR), and CsCl (AR)
2
were purchased from Aladdin Co., Ltd. NH NO3 was purchased
4
2
.4. Catalytic evaluation
from Kelong Chemical Reagent Plant. Polydiallyldimethylammo-
5
nium chloride (PDADMAC, 20%, molecular weight of ∼1.5 × 10 )
The catalytic combustion of 1000 ppm toluene experiments
was purchased from Yinhu Chemical Reagent Co., Ltd. Pt(NH ) Cl
2
3
4
were performed in a continuous flow fixed-bed microreactor at the
atmospheric pressure, consisting of a quartz tube (6 mm i.d.) that
was filled with the catalyst. As a typical run, the experiment was
performed using a catalytic bed of 100 mg catalyst (0.45–0.90 mm
was purchased from Zhejiang Metallurgical Research Institute Co.,
Ltd.
2.2. Catalyst preparation
size) and with total flow rate of dry standard air (79% N + 21%
2
O ) at 100 mL/min, giving a space velocity (SV) at 60,000 mL/(g h).
2
Mesoporous ZSM-5 zeolite (Meso-ZSM-5) was synthesized
The 1000 ppm toluene was generated by partial carrier gas bub-
bling toluene in a vessel chilled in an ice-water isothermal bath.
The effect of relative humidity (RH) and CO2 concentration in feed
gas on the catalytic performance were performed by partial car-
rier gas bubbling water in a vessel and mixing CO2 with the dry
standard air, respectively. The RH of the feed gas was determined
by a high accuracy thermo-hygrometer with a probe (WSB-2-H2,
Zhengzhou Boyang Instrument & Meter Co., Ltd.). The concentration
of the toluene and oxidative products in the tail gas was ana-
lyzed by a gas chromatography (Kexiao, GC1690) equipped with
a flame ionization detector (FID) using a 19091N-113 INNOWAX
capillary column (Agilent, 30 m × 0.32 mm × 0.25 m) for toluene,
and a gas chromatography (Kexiao, GC1690) equipped with a ther-
mal conductivity detector (TCD) using a Carboxen packed column
according to the literature [47], followed by ion-exchanges of var-
ious cations (H , Na , K , and Cs ) from using different salts.
+
+
+
+
Typically, NaAlO (0.01 g), TPAOH (2.58 mL), and TEOS (1.75 mL)
2
were mixed with H O (4.45 mL) under stirring, followed by aging
2
◦
at 100 C for 2.5 h. Then, a mixture of PDADMAC (0.5 g), TPAOH
(
1.75 mL), and H O (1.50 mL) was added to the reaction mixture
2
during 1 h. After stirring for 24 h at room temperature, the mixture
◦
was transferred into an autoclave at 180 C for 5.5 days for crys-
tallization. The product was collected by filtration, dried in air, and
◦
calcined at 550 C for 5 h to remove the templates. The product was
designated as Meso-NaZSM-5.
+
The H -form of Meso-ZSM-5 (Meso-HZSM-5) sample was pre-
pared from NH4+-exchange of Meso-NaZSM-5. As a typical run,
Meso-NaZSM-5 zeolite was added into a NH NO solution (1 M)
4
3
(
JieDao, 2 m × 2 mm) for CO and CO . The conversion of toluene was
◦
+
2
at 80 C, stirring for 3 h. To decrease Na concentration in the sam-
ple, the ion-exchange procedures were repeated for one time. After
centrifugating, washing with water, drying in air, and calcinating
obtained based on toluene consumption, calculated by the inlet
and outlet concentration of toluene. The selectivity to CO was cal-
2
culated by toluene consumption and outlet concentration of CO2.
◦
at 500 C for 2 h, the Meso-HZSM-5 was finally obtained. Similarly,
Carbon balance reached 100 ± 5% in this research. The catalytic
Meso-KZSM-5 and Meso-CsZSM-5 samples were also prepared
from ion-exchanges of KCl solution (1 M) and CsCl solution (1 M)
activities were evaluated by the values of T5, T50, and T , which
98
were defined as the temperature at 5%, 50%, and 98% of toluene
conversion, respectively.
◦
at 80 C for 3 h, followed by centrifugation, washing, and drying in
air.
Zeolite-supported Pt (0.5%) catalysts were prepared by incipi-
ent wetness impregnation method using an appropriate amounts
of aqueous solution of Pt(NH ) Cl . The samples were calcined
3. Results and discussion
3
4
2
◦
at 450 C for 4 h under dry air flow, which were denoted as Pt-
3.1. Mesoporosity in Pt loaded NaZSM-5 zeolite catalysts
O/support. After reduction of Pt-O/zeolite under 5% H /Ar flow
2
◦
(
100 mL/min) at 300 C for 2 h, the catalysts were denoted as Pt-
XRD patterns of Meso-NaZSM-5 and NaZSM-5 samples exhibit
well-resolved characteristic peaks associated with MFI zeolite
structure (Fig. S1). Inductively coupled plasma (ICP) analysis shows
that both samples have similar Si/Al ratios (59 and 62).
R/zeolite.
2
.3. Catalyst characterization
Fig. 1 shows TEM image of Meso-NaZSM-5, clearly confirming
the presence of mesoporosity in the sample. Fig. 2 shows nitro-
gen sorption isotherms of Meso-NaZSM-5 and NaZSM-5 samples.
Notably, Meso-NaZSM-5 gives a steep step at a relative pressure
X-ray diffraction (XRD) patterns were obtained with a RIGAKU
Ultimate IV diffractometer using Cu K˛ radiation. Nitrogen sorp-
◦
tion isotherms at −196 C were measured using a Micromeritics
ASAP 2020M system. The surface area was calculated from using
the Brunauer–Emmett–Teller (BET) method. The Si/Al ratios and
(P/P ) of 0.4–0.95, also indicating the presence of mesoporo-
0
sity in the sample. Correspondingly, the BET surface area and
+
+
+
2
3
the Na , K , and Cs content of the samples were determined by
inductively coupled plasma with a Perkin-Elmer plasma 8000 opti-
cal emission spectrometer (ICP-OES). X-ray photoelectron spectra
mesopore volume of Meso-NaZSM-5 are 432 m /g and 0.18 cm /g,
respectively (Table 1). After loading 0.5% Pt in the Meso-NaZSM-5
◦
(Pt-O/Meso-NaZSM-5) and reduction with hydrogen at 300 C (Pt-
(
XPS) of the samples were recorded using a Thermo ESCALAB 250
R/Meso-NaZSM-5), the samples still give the BET surface area at
2
3
with Al K˛ X-ray radiation for the X-ray source. Prior to measure-
ment, the samples were reduced at 300 C for 2 h under 5% H /Ar
flow (100 mL/min). The binding energies (BEs) were calibrated
against C1s (285.0 eV) and Al2p (73.9 eV) peaks. The scanning elec-
tron microscopy (SEM) images of the samples were recorded on
a Hitachi SU 1510 apparatus. Transmission electron microscopy
419–426 m /g and mesopore volume at 0.18 cm /g (Table 1 and Fig.
S2). These results indicate that the Meso-NaZSM-5 still remains its
textural parameters after impregnation, calcination and reduction.
peak strongly overlaps with Pt4f peak in the range of 81–66 eV, it
◦
2
Please cite this article in press as: C. Chen, et al., Superior performance in catalytic combustion of toluene over mesoporous ZSM-5