N-vinyl pyrrolidone promoted aqueous-phase dehydrogenation of formic acid over PVP-stabilized Ru nanoclusters

Article abstract of DOI:10.1007/s11426-016-0223-0

In this work, we fabricated the poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized ruthenium(0) nanoclusters by reduction of RuCl₃ using different reducing agents, and studied their catalytic activity in hydrogen generation from the decomposition of

Full text of DOI:10.1007/s11426-016-0223-0

SCIENCE CHINA
Chemistry
October 2016 Vol.59 No.10:1342–1347
doi: 10.1007/s11426-016-0223-0
• ARTICLES •
· SPECIAL ISSUE · Dedicated to the 60th Anniversary of Institute of Chemistry, CAS
N-vinyl pyrrolidone promoted aqueous-phase dehydrogenation
of formic acid over PVP-stabilized Ru nanoclusters
Hangyu Liu1,2, Qingqing Mei1,2, Yanyan Wang1,2, Huizhen Liu1,2* & Buxing Han1,2*
1Beijing National Laboratory for Molecular Sciences, Key Laboratory of Colloid and Interface and Thermodynamics, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100190, China
2School of Chemistry and Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
Received May 13, 2016; accepted July 3, 2016; published online August 30, 2016
In this work, we fabricated the poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized ruthenium(0) nanoclusters by reduction of RuCl3
using different reducing agents, and studied their catalytic activity in hydrogen generation from the decomposition of formic acid.
It was demonstrated that N-vinyl-2-pyrrolidone (NVP), which is a monomer of PVP, could promote the reaction by coordination
with Ru nanoparticles. The Ru nanoparticles catalyst reduced by sodium borohydride (NaBH4) exhibited highest catalytic activity
for the decomposition of formic acid into H2 and CO2. The turnover of numenber (TOF) value could reach 26113 h–1 at 80 °C. We
believe that the effective catalysts have potential of application in hydrogen storage by formic acid.
carbon dioxide, NVP, ruthenium, dehydrogenation of formic acid
Citation:
Liu H, Mei Q, Wang Y, Liu H, Han B. N-vinyl pyrrolidone promoted aqueous-phase dehydrogenation of formic acid over PVP-stabilized Ru nanoclusters.
Sci China Chem, 2016, 59: 1342–1347, doi: 10.1007/s11426-016-0223-0
1 Introduction
Hydrogen, producing only water as a byproduct, has been
considered as a promising candidate for the sustainable and
clean energy [1]. However, many difficulties still need to be
overcome for the practical production, storage, and handling
of hydrogen [2]. Various hydrogen storage approaches
including metal hydrides [3], sorbent materials [4], and
chemical hydride systems [5] are currently being investi-
gated. Among them, formic acid is a renewable bioresource
and possible source and reservoir of hydrogen that is safe
to use, not flammable, nontoxic, and has a relatively high
energy density [6]. Hydrogen can be released via a complete
decomposition method, making CO2 as the only by-product
[6–8] (Scheme 1). Furthermore, formic acid can be produced
Scheme 1 Two paths of dehydrogenation of formic acid.
from biomass, so the production of hydrogen from formic
acid can be considered as a promising alternative route from
the renewable biomass, which has been extensively investi-
gated [9]. However, the undesired reaction pathway (Eq. (2))
should be avoided (Scheme 1) from the perspective of hy-
drogen storage application [10]. Recently, selective and ef-
ficient decomposition of formic acid was achieved with ho-
mogeneous organometallic catalysts [11] and heterogeneous
noble metals deposited on different supports such as metal
oxides and activated carbons [12].
Semi-heterogeneous or Quasi-homogeneous catalysis
based on metal nanoparticles (NPs) catalysts combines the
virtues of both homogeneous and heterogeneous cataly-
*Corresponding authors (email: liuhz@iccas.ac.cn; hanbx@iccas.ac.cn)
© Science China Press and Springer-Verlag Berlin Heidelberg 2016
chem.scichina.com link.springer.com

Liu et al. Sci China Chem October (2016) Vol.59 No.10
1343
sis. The catalyst can efficiently and selectively catalyze
reactions and is easy to be recovered. It exhibits superior
catalytic properties in hydrogenation and hydrogenolysis
reactions [13–16], such as low-temperature aqueous-phase
Fisher-Tropsch synthesis [13], selective hydrogenation of
chloronitrobenzene [14], selective hydrogenation of phenol
[15] and biphasic aerobic oxidation of alcohols [16]. The su-
perior performances of nanoparticles most likely arise from
their controllable sizes and morphologies as well as their
unique accessibility to reactants [17,18]. However, the report
about the decomposition of formic acid using quasi-homoge-
neous or semi-heterogeneous catalysis is limited. Tsang and
his co-workers [6] reported the decomposition of formic acid
over Ag-Pd core-shell nanocatalyst at room temperature;
however, the turnover of numenber (TOF) of the catalyst is
only 626 h–1.
In this work, we found that N-vinyl pyrrolidone (NVP),
which is the monomer of poly(N-vinyl-2-pyrrolidone) (PVP),
could promote the dehydrogenation of formic acid using
PVP-stabilized Ru nanocluster as the catalyst. The TOF
value was only 1751 h–1 in the absence of NVP and could
reach 8434 h–1 in the presence of NVP. The PVP as the
protecting agent and NVP as the ligand synergistically pro-
moted the decomposition of formic acid. The reducing agent
NaBH4 could introduce B into the catalyst, and the existence
of B also boosted the decomposition of formic acid. After
the catalyst was recycled 6 times, the TOF value could reach
26113 h–1.
The NPs reduced by formic acid were synthesized as fol-
lows: RuCl3 (21 mg, 0.1 mmol) and PVP (111 mg, 1 mmol)
were dissolved into 2 mL deionized water and 2 mL formic
acid in a round bottle under vigorous stirring for 2 h at 353
K. A homogeneous black solution of colloidal dispersion of
Ru was obtained. The as-prepared catalyst was labelled as
Ru-F-PVP.
2.2 Dehydrogenation of formic acid
In general, a mixture of the as-synthesized catalyst and water
(2 mL) was placed in a two-necked round-bottom flask (30
mL), which was placed in an oil bath at 80 °C. A gas burette
filled with water was connected to the reaction flask to mea-
sure the volume of released gas (temperature kept constant
at 298 K during measurements). The reaction started when
formic acid (6.5 mmol) and sodium formate (2 mmol) were
introduced into the mixture. The molar ratios of Ru/formic
acid were theoretically fixed at 0.015 for all the catalytic re-
actions. The volume of the evolved gas was monitored by
recording the displacement of water in the gas burette.
2.3 Durability testing of the catalysts
For testing the durability of catalysts, 6.5 mmol of pure formic
acid was subsequently added into the reaction flask after the
completion of the first-run decomposition of formic acid and
vacuum-rotary evaporation procedure. Such test cycles of the
catalyst for the decomposition of formic acid were carried out
for 6 runs at 80 °C by adding aliquots of pure formic acid.
2 Experimental
2.4 Characterization of metal NPs
X-ray photoelectron spectroscopy (XPS) was performed on
the Thermo Scientific ESCALab 250Xi (USA) using 200 W
monochromated Al Kα radiation. The 500 μm X-ray spot
was used for XPS analysis. The base pressure in the analy-
sis chamber was about 3×10–10 mbar. Typically the hydrocar-
bon C1s line at 284.8 eV from adventitious carbon is used for
energy referencing. The transmission electron microscopy
(TEM) images of the catalysts were obtained using a TEM
JEOL-2011 (JEOL, Japan) with an accelerating voltage of
120 kV. The sample was dispersed in ethanol with the aid
of sonication and dropped on an amorphous carbon film sup-
ported on a copper grid for the TEM analysis. UV-Vis absorp-
tion spectra were recorded with a Persee TU-1901 UV-Vis
spectrophotometer (China). The adsorption isotherms of Ru
NPs were determined at 298 K in the pressure range of 0–1
atm on a TriStar II 3020 device (Micromeritics Instrument
Corporation, USA).
2.1 Synthesis of metal NPs
The detailed procedure for synthesizing Ru nanoparticles is
similar to that described in the literature [19]. RuCl3 (21
mg, 0.1 mmol) and PVP (111 mg, 1 mmol) were dissolved
in 20 mL deionized water in a 100 mL round-bottom flask
and stirred for 30 min at 0 °C. A fresh aqueous NaBH4 solu-
tion was dropped into the above solution to reduce the Ru3+
ions under vigorous stirring. A homogeneous black solution
of colloidal dispersion of Ru was obtained after 2 h. The ratio
of Ru and NaBH4 was changed from 1:8 to 1:1. The as-pre-
pared catalyst was labelled as Ru-B-PVP-8 and Ru-B-PVP-1.
The Ru NPs solution was concentrated to 2 mL and directly
used for the dehydrogenation of formic acid. In a similar way,
Pt and Pd NPs were synthesized with a molar ratio of metal to
PVP 1:10. The as-prepared catalyst was labelled as Pt-B-PVP
and Pd-B-PVP.
The Ru nanoparticles using PVA (polyvinyl alcohol) or
PEG (polyethylene glycol) as the protecting agent were syn-
thesized using the similar method. The as-prepared catalysts
were labelled as Ru-B-PVA and Ru-B-PEG.
3 Results and discussion
Figure 1 shows the volume of the generated gas (H2+CO2)

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Liu et al. Sci China Chem October (2016) Vol.59 No.10
F-PVP) yielded much lower reaction rate compared with
NaBH4 (Figure 3). The final amount of gas produced was
also lower than that of Ru NPs reduced by NaBH4. The
reason will be discussed below.
Detailed studies showed that different amount of PVP
and NaBH4 also had a significant effect on the reaction rate
(Figure 4). By decreasing the ratio of PVP:Ru from 10:1
to 2:1, the reaction rate was decreased. The decrease of the
reaction rate might be due to the instability of the catalyst
in the presence of less amount of PVP. On the other hand,
the conversion of formic acid decreased with decreasing the
amount of NaBH4 which might be attributed to that the metal
could not be completely reduced.
The reason for the better activity of Ru-B-PVP-8 than that
of Ru-B-PVA and Ru-B-PEG may result mainly from the
existence of nitrogen atom in PVP. The addition of NVP,
which is monomer of PVP, could increase the concentration
of nitrogen atom and the reaction rate was greatly improved
(Figure 5). Finally, Ru-B-PVP-8 catalyst could release 58%
Figure 1 Hydrogen generation from formic acid (6.5 mmol) and sodium
formate (2 mmol) over Pt-B-PVP (a), Pd-B-PVP (b) and Ru-B-PVP-8 (c)
catalysts. nmetal/nformic acid=0.015, T=80 °C.
versus time for the dehydrogenation of formic acid over
Ru-B-PVP-8, Pt-B-PVP and Pd-B-PVP. It shows that Ru-B
catalyst exhibited the highest activity for the dehydrogena-
tion of formic acid at 80 °C. The reaction can produce 64
mL gas in 30 min and finally 78 mL (H2+CO2) gas could
be generated from formic acid at 80 °C over Ru-B-PVP-8
catalyst. The activity of the Pt-B-PVP or Pd-B-PVP was
much lower for the reaction and only 12.5 and 22 mL gas
could be produced.
The protective agent also has an effect on the activity of the
catalyst. The activity of Ru-B-PVP-8, Ru-B-PVA and Ru-B-
PEG was compared and the results are shown in Figure 2.
The reaction rate of hydrogen gas production at 80 °C in 30
min was determined. The reaction rate of Ru-B-PVA and
Ru-B-PEG was much lower than that of Ru-B-PVP-8. The
activity of Ru-B-PVA and Ru-B-PEG was similar. The better
performance of PVP stabilized Ru nanocluster might be at-
tributed to the existence of nitrogen atom. In the light of the
better performance of Ru-B-PVP-8 catalyst, the effect of the
other parameters such as reducing agent, the ratio of PVP and
Ru was checked. The Ru NPs reduced by formic acid (Ru-
Figure 3 Hydrogen generation from formic acid (6.5 mmol) and sodium
formate (2 mmol) over Ru-F-PVP (a) and Ru-B-PVP-8 (b) catalysts.
nRu/nformic acid=0.015, T=80 °C.
Figure 4 Hydrogen generation from formic acid (6.5 mmol) and sodium
Figure 2 Hydrogen generation from formic acid (6.5 mmol) and sodium
formate (2 mmol) over Ru-B-PEG (a), Ru-B-PVA (b) and Ru-B-PVP-8 (c)
catalyst. nRu/nprotectant=0.1, nRu/nformic acid=0.015, T=80 °C.
formate (2 mmol) over Ru-B-PVP-8 catalysts. (a) PVP/NaBH4/Ru=2:8:1;
(b) PVP/NaBH4/Ru=10:1:1; (c) PVP/NaBH4/Ru=10:8:1, nRu/nformic
0.015, T=80 °C.
=
acid

Liu et al. Sci China Chem October (2016) Vol.59 No.10
1345
Table 1 The TOF value of the fresh catalyst and catalyst recycled 6 times a)
b)
Catalyst
Metal dispersion (%)
0.1305
TOF (h–1)
1751
Fresh catalyst
Recycled catalyst
0.0398
26113
a) Reaction conditions: hydrogen generation from formic acid
(6.5 mmol) and sodium formate (2 mmol) over Ru-B-PVP-8 catalyst,
nRu/nformic acid= 0.015, NVP: 2 mL, T: 80 °C; b) TOF was calculated based
on the surface active metal atoms.
To study the reason for the good performance of Ru-B-
PVP-8, the catalyst was characterized by UV-Vis method.
There was two ultraviolet absorption peaks at 310 and 496 nm
for the RuCl3 with PVP. The ultraviolet absorption peaks dis-
appeared for Ru-B-PVP-8 and still existed for Ru-B-PVP-1.
It means that 1 equivalent NaBH4 could not completely re-
duce the Ru(III) and the activity of Ru-B-PVP-1 was lower
than that of Ru-B-PVP-8 (Figure 7). The peak at 310 nm
moved to 294 nm and the peak at 496 nm disappeared when
formic acid was used as reducing agent. Ru(III) could be
completely reduced to Ru(0) by NaBH4 for Ru-B-PVP-8, but
formic acid could not reduce Ru(III) to Ru(0) at 80 °C for
Ru-F-PVP and thus the activity was lower than that of Ru-B-
PVP-8. After 6 cycles, there was also no ultraviolet absorp-
tion peak. These results indicated that the active component
for the decomposition of formic acid was Ru(0).
The morphology and particle size distribution of fresh Ru
NPs and that after recycled 6 times was characterized by
TEM. Ru nanoparticles with the size around 2.7 nm and nar-
row size distribution were observed (Figure 8(a)). The mor-
phology and particle size distribution were not changed obvi-
ously after reuse (Figure 8(b)). The Ru NPs were character-
ized by XPS and the results are shown in Figure 9. Ru, B and
Cl were detected on the surface of the catalyst for the fresh
catalyst, while Cl was not detected for the catalyst after recy-
cled 6 times. It means the Cl was moved from the surface of
the catalyst to the bulk phase. This may be one of the reasons
Figure 5 Hydrogen generation from formic acid (6.5 mmol) and sodium
formate (2 mmol) over Ru-B-PVP-8 catalysts without (a) and with (b) 2 mL
NVP was added. nRu/nformic acid=0.015, T=80 °C.
of hydrogen (H2+CO2, 185 mL) from formic acid in the pres-
ence of NVP, while only 24% of hydrogen (H2+CO2, 78 mL)
was released in the absence of NVP. The better performance
of the catalyst in the presence of NVP may originate from the
coordination effect of Ru NPs and nitrogen atom.
Stability and reusability are crucial properties of catalysts.
The catalyst Ru-B-PVP-8 in the presence of NVP was reused.
It was proved that the catalyst still had excellent catalytic per-
formance after reused 6 times (Figure 6). Interestingly, the
activity of the catalyst recycled 6 times was much higher than
that of the fresh catalyst, and 330 mL gas (H2+CO2) was gen-
erated from formic acid at 80 °C, and 99% of formic acid
could be decomposed. The surface active metal atoms of the
fresh catalyst and the catalyst recycled 6 times were deter-
mined by chemisorption method as previously reported [20],
and the results are shown in Table 1. The TOF value was cal-
culated based on the surface active metal atoms. The num-
ber of surface active metal atoms decreased after recycled 6
times; however, the reaction rate increased. The TOF value
could reach 26113 h–1 for the catalyst that was recycled 6
times.
Figure 6 Hydrogen generation from formic acid (6.5 mmol) and sodium
formate (2 mmol) recycle 6 times over Ru-B-PVP-8 catalyst. nRu/nformic acid
0.015, NVP 2 mL, T=80 °C.
=
Figure 7 UV-Vis spectra of different catalysts.

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Liu et al. Sci China Chem October (2016) Vol.59 No.10
Figure 8 TEM images and particle size distributions of different catalysts. (a) Fresh Ru-B-PVP-8 NPs; (b) Ru-B-PVP-8 NPs after recycled 6 times (color
online).
Figure 9 XPS spectra of different catalysts (color online).
for the higher activity of the used catalyst because Cl can
poison the catalyst.
and the peaks at 192.3 and 191.8 eV vested in B2O3. We can
see that the binding energy of Ru, B and B2O3 was changed
after the catalyst was recycled 6 times. It means that the inter-
action of Ru and B was changed. This may be another reason
for that the activity of the catalyst increased after recycled 6
times. It has been reported that boron-doped Pd nanocata-
lyst boost the generation of hydrogen from formic acid-for-
The peaks with higher binding energies located at 285.8
and 287.0 eV can be attributed to C–N and C=O structures of
PVP, respectively. The peaks at 282.2 and 280.9 eV prove the
existence of Ru nanoparticles in the fresh catalyst and recy-
cled catalyst. The peaks at 188.4 and 189.6 eV belong to B(0)

Liu et al. Sci China Chem October (2016) Vol.59 No.10
1347
mate solutions [21]. That is the reason why the activity of
Ru-B-PVP is higher than that of Ru-F-PVP.
Electrochem Soc, 2001, 148: A11–A23; (b) Zhu QL, Tsumori N, Xu
Q. Chem Sci, 2014, 5: 195–199; (c) Qin Y, Wang J, Meng F, Wang
L, Zhang X. Chem Commun, 2013, 49: 10028–10030
9
(a) Jiangꢀ HL, Singhꢀ SK, Yanꢀ JM, Zhang XB, Xu Q. ChemSusChem,
2010, 3: 541–549; (b) Fellay C, Dyson PJ, Laurenczy G. Angew
Chem Int Ed, 2008, 47: 3966–3968; (c) Ojeda M, Iglesia E. Angew
Chem Int Ed, 2009, 48: 4800–4803; (d) Loges B, Boddien A,
Gärtner F, Junge H, Beller M. Top Catal, 2010, 53: 902–914;
(e) Boddien A, Mellmann D, Gartner F, Jackstell R, Junge H,
Dyson PJ, Laurenczy G, Ludwig R, Beller M. Science, 2011, 333:
1733–1736; (f) Hull JF, Himeda Y, Wang WH, Hashiguchi B,
Periana R, Szalda DJ, Muckerman JT, Fujita E. Nat Chem, 2012,
4: 383–388; (g) Grasemann M, Laurenczy G. Energy Environ Sci,
2012, 5: 8171–8181; (h) Martis M, Mori K, Fujiwara K, Ahn
WS, Yamashita H. J Phys Chem C, 2013, 117: 22805–22810;
(i) Moret S, Dyson PJ, Laurenczy G. Nat Commun, 2014, 5: 4017
4 Conclusions
In summary, the soluble Ru nanoparticles stabilized by PVP
are efficient catalyst for the dehydrogenation of formic acid in
water. The activity of the catalyst synthesized using NaBH4
as the reducing agent is higher than that of the catalyst re-
duced by formic acid, and one of the reasons is the existence
of B in the catalyst reduced by NaBH4. The active compo-
nent of this catalyst is Ru(0). The Ru catalysts are more ac-
tive than the other metal catalysts, including Pt and Pd. The
NVP, which is monomer of PVP, promoted the dehydrogena-
tion of formic acid. 26113 h–1 of TOF can be achieved after
the catalyst was recycled 6 times at 80 °C. The high activi-
ties of Ru-B-PVP-8 may result from the coordination effect
of NVP with Ru NPs. We believe that the effective catalysts
have promising potential of application in hydrogen storage
by fomic acid method.
10 (a) Sato S, Morikawa T, Saeki S, Kajino T, Motohiro T. Angew
Chem Int Ed, 2010, 49: 5101–5105; (b) Sato S, Arai T, Morikawa T,
Uemura K, Suzuki TM, Tanaka H, Kajino T. J Am Chem Soc, 2011,
133: 15240–15243; (c) Yadav M, Xu Q. Energy Environ Sci, 2012,
5: 9698–9725
11 (a) Fukuzumi S, Kobayashi T, Suenobu T. J Am Chem Soc,
2010, 132: 1496–1497; (b) Boddien A, Loges B, Ga
F, Torborg C, Fumino K, Junge H, Ludwig R, Beller M.
Am Chem Soc, 2010, 132: 8924–8934; (c) Fukuzumi S,
̈rtner
J
Acknowledgments This work was supported by the Recruitment Pro-
gram of Global Youth Experts of China, Chinese Academy of Sciences
(KJCX2.YW.H30), the National Natural Science Foundation of China
(21533011, 21321063). The measurements of TEM and XPS were per-
formed at the Centre for Physicochemical Analysis and Measurements in
ICCAS.
Kobayashi T, Suenobu T. ChemSusChem, 2008, 1: 827–834;
(d) Loges BÃ, Boddien A, Junge H, Beller M. Angew Chem Int
Ed, 2008, 47: 3962–3965; (e) Himeda Y. Green Chem, 2009,
11: 2018–2022; (f) Sponholz P, Mellmann D, Junge H, Beller M.
ChemSusChem, 2013, 6: 1172–1176; (g) Gan W, Snelders DJM,
Dyson PJ, Laurenczy G. ChemCatChem, 2013, 5: 1126–1132;
(h) Thevenon A, Frost-Pennington E, Weijia G, Dalebrook AF,
Laurenczy G. ChemCatChem, 2014, 6: 3146–3152
Conflict of interest
The authors declare that they have no conflict of
interest.
12 (a) Huang Y, Zhou X, Yin M, Liu C, Xing W. Chem Mater, 2010,
22: 5122–5128; (b) Zhou X, Huang Y, Liu C, Liao J, Lu T, Xing W.
ChemSusChem, 2010, 3: 1379–1382; (c) Zhou X, Huang Y, Xing W,
Liu C, Liao J, Lu T. Chem Commun, 2008, 48: 3540–3542; (d) Ojeda
M, Iglesia E. Angew Chem, 2009, 121: 4894–4897; (e) Ting SW,
Cheng S, Tsang KY, van der Laak N, Chan KY. Chem Commun, 2009,
47: 7333
1
2
(a) Leitao EM, Jurca T, Manners I. Nat Chem, 2013, 5: 817–829;
(b) Dalebrook AF, Gan W, Grasemann M, Moret S, Laurenczy G.
Chem Commun, 2013, 49: 8735–8751; (c) Yang J, Sudik A,
Wolverton C, Siegel DJ. Chem Soc Rev, 2010, 39: 656–675;
(d) Ma S, Zhou HC. Chem Commun, 2010, 46: 44–53
(a) Schlapbach L, Züttel A. Nature, 2001, 414: 353–358;
(b) Chen P, Xiong Z, Luo J, Lin J, Tan KL. Nature, 2002, 420:
302–304; (c) Orimo S, Nakamori Y, Eliseo JR, Züttel A, Jensen CM.
Chem Rev, 2007, 107: 4111–4132
13 Xiao C, Cai Z, Wang T, Kou Y, Yan N. Angew Chem Int Ed, 2008, 47:
746–749
14 Xiao C, Wang H, Mu X, Kou Y. J Catal, 2007, 250: 25–32
15 Zhu JF, Tao GH, Liu HY, He L, Sun QH, Liu HC. Green Chem, 2014,
16: 2664–2669
3
4
Graetz J. Chem Soc Rev, 2009, 38: 73–82
Suh MP, Park HJ, Prasad TK, Lim DW. Chem Rev, 2012, 112:
782–835
16 Hou Z, Theyssen N, Brinkmann A, Leitner W. Angew Chem Int Ed,
2005, 117: 1370–1373
5
6
7
Staubitz A, Robertson APM, Manners I. Chem Rev, 2010, 110:
4079–4124
17 Zhao D, Wu M, Kou Y, Min E. Catal Today, 2002, 74: 157–189
18 Li Z, Zhang J, Mu T, Du J, Liu Z, Han B, Chen J. Colloid Surfaces A,
2004, 243: 63–66
Tedsree K, Li T, Jones S, Chan CWA, Yu KMK, Bagot PAJ, Marquis
EA, Smith GDW, Tsang SCE. Nat Nanotech, 2011, 6: 302–307
(a) Gu X, Lu ZH, Jiang HL, Akita T, Xu Q. J Am Chem Soc, 2011, 133:
11822–11825; (b) Bulushev DA, Jia L, Beloshapkin S, Ross JRH.
Chem Commun, 2012, 48: 4184–4186; (c) Enthaler S, von
Langermann J, Schmidt T. Energy Environ Sci, 2010, 3: 1207–1217
(a) Springer TE, Rockward T, Zawodzinski TA, Gottesfeld S. J
19 Yan N, Yuan Y, Dyson PJ. Chem Commun, 2011, 47: 2529–2531
20 Umpierre AP, de Jesús E, Dupont J. ChemCatChem, 2011, 3:
1413–1418
21 Jiang K, Xu K, Zou S, Cai WB. J Am Chem Soc, 2014, 136:
4861–4864
8