Solvent-free photo-thermocatalytic oxidation of benzyl alcohol on Pd/TiO2 (B) nanowires

Article abstract of DOI:10.1016/j.mcat.2020.110771

TiO₂(B) is typical crystal structure for TiO₂, besides anatase, rutile and brookite. In this work, one-dimensional TiO₂(B) modified by Pd were prepared. The obtained Pd/TiO₂(B) was used for photo-thermocatalytic

Full text of DOI:10.1016/j.mcat.2020.110771

Molecular Catalysis 483 (2020) 110771
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Solvent-free photo-thermocatalytic oxidation of benzyl alcohol on Pd/TiO2
(
B) nanowires
a,
a,
a
a
b
b
Mingming Du *, Ganning Zeng *, Changhui Ye , Hao Jin , Jiale Huang , Daohua Sun ,
b
c
a,
Qingbiao Li , Bing Chen , Xiaonian Li *
College of Chemical Engineering, Zhejiang University of Technology, Hangzhou, 310014, PR China
Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, PR China
Northern Region Persistent Organic Pollution Control (NRPOP) Laboratory, Engineering and Applied Science, Memorial University of Newfoundland, A1B1X5, St. John’s,
a
b
c
NL, Canada
A R T I C L E I N F O
A B S T R A C T
Keywords:
TiO
2 2
(B) is typical crystal structure for TiO , besides anatase, rutile and brookite. In this work, one-dimensional
TiO
Pd
2
(B)
TiO (B) modified by Pd were prepared. The obtained Pd/TiO (B) was used for photo-thermocatalytic benzyl
2
2
alcohol oxidation. Well-matched heterostructure contact boundary between (111) planes of Pd nanoparticles
and (003) planes of TiO (B) was formed, which might facilitate interfacial photo-generated electrons transfer.
The Pd/TiO (B) catalyst exhibited enhanced the photo-thermocatalytic activity, attributed tothe synergistic
effect of Pd, TiO (B) and their well-matched heterojunction, and also the synergism between the thermocatalysis
and photocatalysis.
Photo-thermocatalysis
Benzyl alcohol
Solvent-free
2
2
2
1. Introduction
Only 0.2 % of BzOH conversion was obtained for TiO
solvent-free condition at 60 °C [30]. Although, the TiO
2
(P25) under the
was modified
2
Photocatalytic benzyl alcohol (BzOH) oxidation over semi-
conductors materials [1–4], such as TiO [5–8], CeO [9,10], Bi Br
11], C [12], H Ti [13] and CdS [1] semiconductors, is one of
efficient method to produce benzaldehyde (BzH). Especially, TiO
semiconductor has received a lot of attention among the semi-
conductors materials [14–16], due to its high photocatalytic perfor-
mance and stability [17–21], which is strongly depended on its crystal
structure [5]. Such as, Li, et al. found high BzH selectivity can be ob-
by metal nanoparticles, such as Au, Ag, Pd, Pt, Rh or Ir, the BzOH
conversion still lower than 10 % at 6 h under 250 W Hg lamp [30].
TiO nanowires with special physical and chemical properties have
2
advantages as photocatalysts, which supported on the graphene oxide
exhibited much higher photodegradation activity for methylene blue in
comparison with TiO nanoparticles [31]. In this work, 1D TiO (B)
2 2
nanowires supporting Pd nanoparticles were prepared, and were used
for solvent-free photo-thermocatalytic oxidation of BzOH with atmo-
2
2
4
O
5
2
[
3
N
4
2
3
O
7
2
tained over rutile TiO
TiO gave 56 % selectivity of aldehyde, 3 times higher than that with
anatase/rutile mixed phases [23]. Besides, brookite, anatase and rutile,
TiO (B) is also typical crystallographic forms of TiO , which was dis-
covered by Marchand et al. [24]. TiO (B) as photocatalysts has wide
2
under visible-light irradiation [22]. Brookite
spheric O
2 2
. Pd/TiO (B) nanowire catalyst shows high photo-thermo-
2
catalytic activity and stability in BzOH oxidation to produce BzH, due
to the synergistic effect among Pd, TiO (B) and their well-matched
2
heterojunction.
2
2
2
applications in photodegradation of methyl orange [25], photocatalytic
hydrogen production [26] and so on [27].
2. Experimental section
Usually, high photocatalytic performance of BzOH oxidation over
2.1. Materials
TiO
2
was only obtained under the solvent of acetonitrile [7,28], toluene
O [29] or trifluorotoluene [3]. Actually, it is more en-
[
6], H
2
Chemical reagents (P25, HCl, NaOH) : Sinopharm Chemical
vironmentally friendly for BzOH oxidation under the solvent-free con-
dition, avoiding toxic and harmful solvents. However, there is very poor
Reagent. Palladium Nitrate and C. Platycladi leaves (CP) : Adamas
Reagent Co. Ltd and Xiamen Jiuding Drugstore, respectively.
2
photocatalytic activity over bare TiO under the solvent-free condition.
⁎
Corresponding authors.
E-mail addresses: dumingming2008@126.com (M. Du), gnzeng@zjut.edu.cn (G. Zeng), xnli@zjut.edu.cn (X. Li).
https://doi.org/10.1016/j.mcat.2020.110771
Received 3 November 2019; Received in revised form 6 January 2020; Accepted 8 January 2020
2468-8231/ © 2020 Elsevier B.V. All rights reserved.

M. Du, et al.
Molecular Catalysis 483 (2020) 110771
2 2 2 2
Fig. 1. TEM and corresponding FFT images for TiO (B) and Pd/TiO (B); a-c: TEM and HRTEM images of TiO (B), g: FFT image of TiO (B), d-e: TEM images of Pd/
TiO
2
(B) nanowires, f: HRTEM of Pd/TiO
2
(B) nanowires, h: FFT image of Pd/TiO
2
(B) nanowires.
CP extract was prepared by our previous study [32,33]. Firstly, Pd sol
were prepared by mixing Pd(NO (74 mM) and CP extract at 90 °C.
Then Pd nanoparticles were supported onto TiO (B) nanowires by
(B) nanowires cata-
3 2
)
2
mixing Pd sol and TiO
lysts.
2 2
(B) to obtain the Pd/TiO
2.4. Characterization of the catalysts
The surface area: Tristar 3000; Crystal Structure: XRD, X’Pert Pro X-
ray diffractometer; Light absorption property: DRUV-vis, varian cary-
000 spectrometer; Morphology: TEM, Tecnai F30 microscope; Actual
5
Pd loadings and chemical nature were obtained by AAS and XPS, re-
spectively.
2.5. Catalytic activity measurements
Solvent-free photo-thermocatalytic benzyl alcohol oxidation using
O was carried out in quartz flask at 90 °C. The light source was halogen
2
lamp(150 W). 0.1 g catalyst and 10 mL benzyl alcohol was mixed with
oxygen of 90 mL/min. Gas chromatography was used to analyze the
resulting product.
2 2 2
Fig. 2. XRD (a: TiO (B), b: Pd/TiO (B)) and Visible Raman (c: TiO (B)) spectra
of the samples.
2
2.2. Synthesis of TiO (B)nanowries
3. Results and discussion
TiO
2
(P25) was dispersed in NaOH aqueous solution, then trans-
(B)
3.1. Characterizations of the catalyst
ferred into a teflon-lined autoclave container for 48 hat 200 °C. TiO
2
nanowires were obtained after washed by deionized water and HCl,
dried and calcinated at 300 °C.
TiO
and The Pd/TiO
mobilization method [32,33]. As shown in Fig. 1, the obtained sample
is 1D TiO nanowire in Fig. 1(a and b), and the lattice spacings of the
crystal planes were approximately 0.36 and 0.62 nm, which corre-
sponds to that of the (110) and (001) crystal planes from TiO (B)
2
(B)were prepared by hydrothermal synthesis method [25,37],
2
(B) nanowires catalysts were prepared by sol-im-
2.3. Synthesis of Pd/TiO
2
(B) catalysts
2
The Pd/TiO (B) catalyst was prepared by SI method [32–36]. 10 g/L
2
2
2

M. Du, et al.
Molecular Catalysis 483 (2020) 110771
Table 1
2
Catalytic performance for BzOH oxidation by Pd/TiO (B) catalyst.
o
TOFa (h−1
BzH productivity (mol kgcat.−1 h-1
)
Catalysts
T ( C)
Light
T (h)
Con.(%)
Sel.(%)
BzH
Yield (%)
)
BzA
TOL
BzB
Pd/TiO
2
(B)
90
Light
2
4
2
4
4
4
6
55.6
81.9
39.5
2.7
2.0
1.9
70.3
69.7
72.9
89.7
79.3
92.1
73.8
2.4
17.4
1.9
5.6
8.7
25.4
10.2
24.3
3.7
0.0
0.9
2.1
2.7
0.9
1.0
12.0
3.4
1.8
39.1
57.1
28.8
2.4
1.6
1.7
2735
2016
1944
66
50
47
180
132
133
6
4
4
Pd/TiO
Pd/TiO
2
(B)
(B)
90
30
90
90
90
NO
2
Light
Light
Light
Light
TiO
NO
2
(B)
4.6
22.5
Pd/TiO
2
(P25)
68.8
1.9
50.8
1128
78
BzA: Benzoic acid, BzB: Benzyl benzoate, TOL: Toluene.
a
Moles of converted BzOH per mole of metal per hour.
with TiO
2
(B) after loading Pd NPs in Fig. 2(b). However, no Pd NPs
peak was observed, indicating that Pd NPs might be well dispersed on
TiO
TiO
2
(B) nanowire. Raman spectroscopy excited by 532 nm laser of the
(B) nanowire is displayed in Fig. 2(c), the typical bands of TiO (B)
2
2
−
1
phase appear at 120, 143, 196 cm appear [40], consistent with XRD,
visible Raman spectroscopy and HRTEM results.
2+
ions can ben reduced to Pd0 species for the Pd/TiO
Pd
2
(B) cata-
lyst, which has been demonstrated by the result of the XPS [41], the
detail analysis can be seen in Fig. S2 and Table S1. The detail im-
formation of BET surface area, pore diameter and pore volume can also
be seen in Fig. S1.
3.2. Photocatalytic activity measurements
The photo-thermocatalytic activity of the obtained catalysts was
shown in Table 1. Without light irradiation, Pd/TiO
gave 39.5 % of BzOH conversion at 90 °C after 2 h. Under light irra-
diation, the Pd/TiO (B) nanowire gave higher catalytic activity with
5.6 % of BzOH conversion,70.3 % of BzH selectivity and TOF of 2735
2
(B) nanowires only
Fig. 3. DRUV-Vis spectra and Kubelka–Munk transformed spectra of TiO
and Pd/TiO (B).
2
(B)
2
2
5
h
−1
at 90 °C after 2 h. Only 68.8 % of conversion was obtained for Pd/
(P25) at 6 h, which is much lower than that of Pd/TiO (B) nano-
wire catalyst even at 4 h (81.9 % of BzOH conversion). Almost no
photocatalytic performance for Pd/TiO (B) nanowires at 30 °C, sug-
TiO
2
2
2
gesting that there is a synergism between thermocatalysis and photo-
catalysis [19].
As shown in Fig. 3, Pd/TiO
2
(B) nanowires showed enhanced light
adsorption, compared with bare TiO
2
(B). Therefore, more electrons
e
) and holes (h+) pair can be produced, according to the photo-
−
(
7
,
−
thermocatalytic reaction mechanism The e can been transferred
along the axial direction of TiO
2
(B) nanowire to Pd NPs through the
well-matched heterostructure contact boundary between (111)planes of
−
Pd NPs and (003) planes of TiO
2
(B) nanowires. Therefore, more e and
+
h
were separated efficiently. The holes react with α-C–H of BzOH to
give BzOH radicals . The photo-induced electrons can promote Pd sites
7
Fig. 4. Catalytic performance of the recycled Pd/TiO
2
(B)nanowires catalyst.
−
2
to active oxygen molecules, yielding O
·. It can cleave OHe bond of
benzyl alcohol radical, forming BzH . Without Pd NPs, oxygen mole-
cules activation was decreased [42–44], therefore, bare TiO (B) gave
only 1.9 % of BzOH conversion. Therefore, synergistic effect among Pd,
TiO (B) and their well-matched heterojunction played an important
role photocatalytic synthesis of BzH.
The Pd/TiO (B) nanowires catalyst also present high catalytic sta-
6
nanowire(Fig. 1c). TiO
2
(B) crystal planes were also confirmed by FFT
2
(
Fig. 1g). There are typical (001), (002), (003) and (110) crystal planes
of TiO
2
(B). As shown in Fig. 1(d and e), Pd NPs were highly dispersed
(B) nanowire in Fig. 1(d). We also found that the well-
matched heterostructure contact boundary between (111)planes of Pd
NPs and (003) planes of TiO (B) was obviously seen in the HRTEM
images in Fig. 1(e and f) [37–39]. The Fourier transformation patterns
also display the typical (111) crystal plane of Pd NPs and (003) crystal
2
on the TiO
2
2
bility. There is no obviously decrease for BzOH conversion after six
recycle utilization (Fig. 4). Compared with the catalytic performance
from the previous studies, as shown in Table S2, the obtained Pd/
2
plane of TiO
2
(B) nanowire of Pd/TiO
2
(B) catalyst in Fig. 1(h).
TiO
2
(B) nanowires catalyst present high catalytic activity, especially,
Crystal phase structure of TiO
2
(B) was also characterized using XRD
High BzH yield and TOF are simultaneously achieved.
and visible Raman spectroscopy. As shown in Fig. 2(a), the diffraction
peaksat 2θ = 14.19°, 24.93°, 28.61°, 43.51°and 48.53° are reflections
from the (001), (110) and 002) et al. planes of the TiO (B) (Ref. code:
2
4. Conclusions
46–1237). There is no change for those diffraction peaks associated
2
In summary, Pd/TiO (B) nanowires for photo-thermocatalytic BzOH
3

M. Du, et al.
Molecular Catalysis 483 (2020) 110771
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planes of Pd NPs and (003) planes of TiO
cilitate photo-generated e transfer. Aslo, the Pd/TiO (B) showed en-
hanced light adsorption. Therefore, the catalyst exhibited enhanced
photo-thermocatalytic performance which is mainly due tothe sy-
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