G Model
CATTOD-9754; No. of Pages8
ARTICLE IN PRESS
H. Chen et al. / Catalysis Today xxx (2015) xxx–xxx
2
monolith-like structure and confinement effect in Pt/TiNT. A HCHO
conversion of 95% with a more than 100 h stable performance was
achieved over Pt/TiNT at 30 C with a 0.4 wt.% Pt loading. In addi-
photoelectron spectra (XPS) were recorded on a ESCALAB 250 spec-
trometer (Thermo Fisher Scientific, Al K␣, hꢀ = 1486.6 eV) under
◦
−7
a vacuum of ∼2 × 10 Pa. Charging effects were corrected by
tion, the negative effect of diffusion on the performance can also
be alleviated by a concept of “storage-oxidation” process [9,14]. In
adjusting the main C 1s peak to a position of 284.8 eV. Metal
nanoparticle size distribution was observed by a JEOL 2100F trans-
mission electron microscopy (TEM). BET surface area of the catalyst
was determined by N2 adsorption isotherms at 77 K, operated on
ASAP 2020 adsorption equipment. The samples were degassed
−
this process, HCHO was first partially oxidized and stored as HCOO
−
species. When the catalyst reached saturation, the stored HCOO
species were completely oxidized into CO2 and H O by heating
2
◦
[
9]. The effect of HCHO adsorption and storage on the catalyst
at 300 C for 2 h in vacuum before N2 adsorption experiment. In
performance was further addressed by Chen et al. [14]. A multi-
functional Pt/ZSM-5 catalyst for the treatment of trace HCHO in air
was developed, which could selectively trap HCHO molecules from
situ Diffuse Reflectance Infrared Fourier Transformed Spectroscopy
(DRIFTS) was carried out on EQVINOX-55 FFT spectroscope appa-
ratus (Bruker), equipped with a diffuse reflectance accessory and
a MCT detector. Finely ground sample (ca. 10 mg) was placed in
a ceramic crucible in the in situ chamber. The total gas flow rate
−
the environment, efficiently store the adsorbed HCHO as HCOO ,
and rapidly oxidize the intermediates to CO2 and H O [14].
2
−
1
Against the background aforementioned, the aim of the present
work is to improve the performance of monolith-like Pt/TiNT for
the efficient treatment of trace HCHO by enhancing its HCHO
adsorption/storage ability through the surface modification with
zinc oxide. Zinc oxide (ZnO) has unique and fascinating properties
that trigger tremendous motivation to design and fabricate novel
structures of functional materials for various applications [27–29].
Jeroro et al. [27] incorporated Zn into the Pd (1 1 1) surface and
was 100 mL min . HCHO was bubbled into the chamber with He
and O2 acted as another flow gas to react with HCHO (He/O = 4,
2
−
1
100 mL min ). The gas flow of each stream was controlled by the
mass flow controller. The spectra under reaction conditions were
−
1
recorded after 64 scans with a resolution of 4 cm
.
2.3. HCHO catalytic oxidation and adsorption test
altered the adsorption and reaction of HCHO and CH OH over Pd
The catalytic oxidation of HCHO was performed in a quartz
tubular (i.d. = 7 mm) fixed-bed reactor under atmospheric pres-
sure with a home-made setup. Approximately 0.2 g of the catalyst
was packed in the reactor [12]. A simulated air stream (N /O = 4,
3
significantly. Hussain et al. [28] reported the preparation of ZnO
hexagonal nanocones for the sensing of HCHO. These previous find-
ings in the literature indicate the special interaction between the
ZnO and HCHO. Herein, the TiNT modified with 0.5 wt.% ZnO is
used as a support for the monolith-like Pt/ZnO/TiNT catalyst for
HCHO removal. A HCHO conversion of (>) 95% is achieved over
2
2
−
1
100 mL min ) containing ∼50 ppm HCHO and water vapor (∼35%
relative humidity) was introduced as the reactants. Gaseous HCHO
was generated by passing a stream of simulated air through a bub-
bler containing an HCHO solution (35 wt.% HCHO). The gas hourly
◦
Pt/ZnO/TiNT at 30 C with an extreme low Pt loading amount of
−
1
−1
0.2 wt.%. The mechanism leading to its high catalytic activity and
space velocity is 30,000 mL h
g . The gas flow of each stream was
stability is studied by various characterizations, especially with
in situ DRIFTS study.
controlled by the mass flow controller. HCHO concentration in the
reactant or product gas stream was analyzed by phenol spectro-
photometric method [12]. The conversion of HCHO was calculated
based on its concentration change. Each datum was measured in
2
. Experimental procedure
−
1
triplicates. HCHO equilibrium adsorption amount (Qe, mg g ) over
◦
the TiNT or ZnO/TiNT at 30 C was calculated by measuring the
2.1. Catalysts preparation
−
3
HCHO concentrations (mg m ) of inlet gas (Cin) and outlet gas
Cout) with the same setup for the activity evaluation, as listed
below [14].
(
The procedure for the TiNT preparation by an electrochemi-
cal anodization method follows the well-established procedures
in our previous paper [11]. The as-synthesized TiNT was dried at
t
ꢀ
◦
◦
Q (C − Cout
)
in
1
20 C, and subsequently calcined at 500 C for 5 h with a heating
v
Qe =
dt.
(1)
◦
−1
rate of 10 C min in air. ZnO modified TiNT (or ZnO/TiNT) was
W
0
prepared by immersing TiNT with Zn(NO ) ·6H O (A.R.) solution
3
2
2
containing an appropriate amount of Zn(NO ) to obtain a ZnO
3
−1
3
2
Here, t (min) stands for the adsorption time, Qv (m min ) and
W (g) represent the total gas flow rate and the weight of the loaded
sample, respectively.
◦
loading amount of 0.5 wt.%, and then, calcined at 500 C for 5 h.
The supported Pt catalysts were prepared via impregnation using
the incipient wetness technique. The support TiNT and ZnO/TiNT
were, respectively, dispersed into the H PtCl solution (Alfa Aesar)
with an appropriate volume to obtain a Pt loading amount of 0.08,
2
6
3. Results and discussion
0
.16, 0.2 or 0.4 wt.%, which were confirmed by ICP. The samples
3
.1. Structural properties
◦
were then dried at 120 C overnight to evaporate the solvent and
finally calcined at 400 C for 4 h with a heating rate of 10 C min
in air. The samples were then reduced in the H stream at 300 C for
3
were, respectively, denoted as Pt/TiNT and Pt/ZnO/TiNT with a Pt
loading amount number in front for simplicity.
◦
◦
−1
The top, bottom and cross-section morphologies of the annealed
◦
2
ZnO/TiNT are presented in Fig. 1. As shown, the nanotube array
structure of TiNT keeps well after ZnO modification, although the
pore wall becomes thick after modification in comparison with the
TiNT morphology presented in the former study [11]. The BET-area,
h before reaction and characterization. The as-prepared catalysts
2
−1
3
−1
pore volume and average pore size are 39.3 m g , 0.2670 cm g
2
−1
3
2.2. Characterization
and 23.2 nm for 0.2 wt.% Pt/TiNT, and 33.7 m g , 0.2103 cm /g and
3.5 nm for 0.2 wt.% Pt/ZnO/TiNT. The results indicate that the mod-
2
The phase purity and crystal structure of the samples were
ification process has slight effect on the pore size of the samples.
Fig. 2 presents the XRD patterns of TiNT, ZnO/TiNT, 0.4 wt.% Pt/TiNT
subsequent Pt loading process have no effect on the phase structure
examined by XRD using a D-MAX diffractometer with Cu K␣ radi-
◦
−1
◦
ation at a scanning rate of 10 min
pled Plasma-atomic Emission Spectrometry (ICP, TJ IRIS). X-ray
Please cite this article in press as: H. Chen, et al., ZnO modified TiO nanotube array supported Pt catalyst for HCHO removal under mild
2
Chen, Huayao
