Pd/C-Catalyzed H2 Evolution from Tetrahydroxydiboron Hydrolysis

Article abstract of DOI:10.1007/s10562-021-03547-2

The production of H₂ from non-fossil sources is a key research challenge to contributing solving the forthcoming energy problem. Aqueous solutions of tetrahydroxydiboron have very recently appeared as a H₂ source, from which both hydrogen atoms are provided by water, in the presence of highly sophisticated nanocatalysts. Herein, commercial and cheap Pd/C is shown to be an efficient and recyclable catalyst for H₂ evolution upon tetrahydroxydiboron hydrolysis. Graphic Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-021-03547-2

Catalysis Letters
https://doi.org/10.1007/s10562-021-03547-2
Pd/C‑Catalyzed H Evolution from Tetrahydroxydiboron Hydrolysis
2
1
1
1
1
Junjie Zhou · Yu Huang · Jialu Shen · Xiang Liu
Received: 30 December 2020 / Accepted: 22 January 2021
©
The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature 2021
Abstract
The production of H from non-fossil sources is a key research challenge to contributing solving the forthcoming energy
2
problem. Aqueous solutions of tetrahydroxydiboron have very recently appeared as a H source, from which both hydrogen
2
atoms are provided by water, in the presence of highly sophisticated nanocatalysts. Herein, commercial and cheap Pd/C is
shown to be an eꢀcient and recyclable catalyst for H evolution upon tetrahydroxydiboron hydrolysis.
2
Graphic Abstract
COMMUNICATION
Pd/C (0.2 mol%)
Pd/C-Catalyzed
H2
Evolution
from
B (OH) + 2 H O H
2 B(OH) + H2
3
2
4
2
o
2
O (0.5 M), 30 C, 2 min
Tetrahydroxydiboron Hydrolysis
Junjie Zhou,Yu Huang, Jialu Shen and Xiang Liu *
Keywords Pd/c · Tetrahydroxydiboron · H evolution · Tandem reaction · Kinetic isotope eꢁect
2
−
1
1
Introduction
vs. 44 kJ/g for petroleum) and the fact that water is the
only by-product during its combustion [2–4]. Therefore,
hydrogen has received a great expectations from the envi-
ronmental and energy research community [5, 6]. How-
ever, the controlled storage and release of hydrogen is still
a key issue for the future “hydrogen economy” [7, 8]. Over
In the twenty-ꢂrst century, the global air pollution and
energy crises have become a critical issue that the Society
is facing [1]. Therefore, the exploration of eꢁective, green
and renewable energy sources, which do not cause further
damage to the environment is a very active research ꢂeld.
the past decades, great eꢁorts have been made to store H
2
Hydrogen (H ) has been considered to be the preference
in chemical hydrogen storage materials that release H
2
2
as the cleanest and highly eꢀcient energy carrier due to its
in situ under ambient conditions [9]. Among them, boron
−
1
high gravimetric energy density (120 kJ/g for hydrogen
compounds, such as NH BH and NaBH have a great
3
3
4
potential to meet transportation requirements [10–17].
Tetrahydroxydiboron, often used as a current borylation
source [18–20], has recently been reported as an active
source for a number of transfer hydrogenation reactions to
various substrates [21–27]. For example, in 2016, Stokes’s
group ꢂrst reported Pd catalyzed transfer hydrogenation
and deuteriation of alkenes and alkynes from water in the
presence of tetrahydroxydiboron [24]. In 2020, Laksh-
man’s group also reported Pd/C catalyzed reduction of
Junjie Zhou and Yu Huang have equally contributed to this work
and should be considered as co-ꢂrst authors.
*
Xiang Liu
xiang.liu@ctgu.edu.cn
1
College of Materials and Chemical Engineering, Key
Laboratory of Inorganic Nonmetallic Crystalline and Energy
Conversion Materials, Analysis and Testing Center, China
Three Gorges University, Yichang 443002, Hubei, China
Vol.:(0
1
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3

J. Zhou et al.
aryl halides in the presence of tetrahydroxydiboron and
2.3 Catalytic H Evolution
2
4
-methylmorpholine, without external hydrogen gas [26].
Standing on the shoulders of giants, in 2020 aqueous solu-
tions of tetrahydroxydiboron have been shown to release
Generally, the evolution of H upon reaction between
2
B (OH) and H O were conducted in water at 30 °C.
2
4
2
H itself upon catalysis by graphene quantum dot-stabi-
B (OH) (1.0 mmol, 89.6 mg) and 0.002 mmol of Pd/C (5%
2
2 4
lized metal nanoparticles [28]. Interestingly, both H atoms
w/w, 4.2 mg) have been added into a round bottom 50 mL
ꢃask. 2 mL water was injected in this round bottom ꢃask,
and timing started. The Pd to B (OH) ratio was ꢂxed at
of H have been shown to come from water upon tetrahy-
2
droxydiboron hydrolysis, as conꢂrmed by D formation
2
2
4
from D O, in contrast with the hydrolysis of NH BH or
0.2 mol %. The ꢃask was ꢂtted with a gas outlet, and a side
arm was sealed with a tight-ꢂtting septum cap. The ꢃask was
connected via the gas outlet to a water-ꢂlled gas burette. Gas
evolution immediately began, and the amount of gas evolved
was determined periodically by measuring the displacement
of water in the burette. A quantitative conversion of B (OH)
2
3
3
NaBH for which one H atom of H formed is provided by
4
2
H O and the other one by the boron compound [28]. It is
2
an important step in H formation research that the source
2
of H is water only, even if the other reagent used in the
2
reaction is not yet catalytic. We report here catalytic stud-
ies of water dehydrogenation using tetrahedroxydiboron
and Ru/C, Pd/C, and Pt/C as heterogeneous catalysts. In
particular, Pd/C, a cheap and commercial catalyst [29],
2
4
produced 1.0 equivalents of H , and occupied ca.22.4 mL
2
at atmospheric pressure. Prior to the reactions, the volumes
were measured at atmospheric pressure and corrected for
water vapor pressure at room temperature.
is shown to be an eꢀcient and recyclable catalyst for H
2
evolution upon tetrahydroxydiboron hydrolysis (Eq. 1).
No ligands are necessary for this heterogeneous catalyst
that, in addition, has been successfully recycled 5 times
by simple ꢂltration.
2.4 Diphenylacetylene and Norbornene
Hydrogenation
Pd∕C (0.2 mol%)
B (OH) + 2H O ����������������������������������������������������� → 2 B(OH) + H
(1)
The tandem reaction was performed in a sealed two-chamber
system. The left tube was used for hydrogen generation, and
2
4
2
3
2
◦
min . 30 C
2
The inꢃuence of B (OH) concentration, Pd/C concentra-
the right one was used for hydrogenation with H gener-
2
4
2
tion and temperature on the reaction eꢀciency are investi-
ated in the left tube. The generated hydrogen in the left tube
transported to the hydrogenation reaction into the right tube
through the connecting glass tube.
gated, as well as kinetic isotope eꢁects (KIEs) using D O
2
instead of H O. Tandem reaction for diphenylacetylene and
2
norbornene hydrogenation have also been conducted, in par-
ticular to conꢂrm the mechanism of tetrahydroxydiboron
hydrolysis.
Hydrogenation of diphenylacetylene: B (OH) (4 mmol,
2
4
–
3
358.6 mg) and 8×10 mmol Pd/C (5% w/w, 16.8 mg) were
added into the left tube. Meanwhile, 10.6 mg (5 mmol % per
diphenylacetylene) Pd/C catalyst was added to the right tube.
Air was removed in vacuo, and 2.0 mL methanol contain-
ing 0.1 mmol diphenylacetylene was injected into the right
tube. Then, 2 mL water was injected into the left tube. After
2
Experimental
5
min, reaction was conducted at 30 °C for 12 h. Hydrogena-
2.1 Chemicals and Reagents
tion of norbornene was carried out using the same method.
All commercial materials were used without further puriꢂca-
tion, unless indicated. The deionized water was prepared in
the laboratory. Pd/C (Pd: 5wt%), Pt/C, Ru/C and B (OH) ,
3
Results and Discussion
2
4
diphenylacetylene and norbornene were purchased from
Aladdin Reagent Co., Ltd. (Shanghai, China, http://www.
aladdin-e.com/).
The H evolution upon tetrahydroxydiboron hydrolysis
2
catalyzed by commercial Pt/C, Pd/C and Ru/C were car-
ried out at 30 °C, respectively. Commercial Pt/C and Pd/C
were shown to undergo the same catalytic activities, with a
−
1
−1
TOF of 286 mol ·mol
·min , while the TOF of Ru/C
2.2 Characterization Techniques
H2
cat
−
1
−1
was only 47 mol ·mol
·min . On the other hand, such
H2
cat
H evolution does not work under neutral conditions in the
Transmission electron microscopy (TEM) measurements
were performed on a TECNAI F-20 electron microscope
2
absence of catalyst (Fig. 1a). Hence, Pd/C has been chosen
as the catalyst for further studies of H evolution from aque-
(
JOEL 2100F, Netherlands) at an accelerating voltage of
2
ous solutions of tetrahydroxydiboron. Then, the size of the
2
00 kV.
1
3

Pd/C-Catalyzed H Evolution from Tetrahydroxydiboron Hydrolysis
2
Fig. 1 a Comparison of the evolution of H catalyzed by 2 mol‰
of the volume of hydrogen generated versus time for the evolution
2
(cat)
Pt/C, Pd/C and Ru/C. Note: TOF=n
/[n
x t], with n : the
of H catalyzed by 0.002 mmol Pd/C (5% w/w) at various amount of
(
H2)
(H2)
2
number of mol generated H , n(cat): the number of mol catalyst, t:
B (OH) . d Plots of the hydrogen volume versus time for evolution of
2
2
4
reaction time; b Time plots of the catalytic evolution of H by various
H catalyzed at various temperatures by 2 mol‰ Pd/C. Reaction con-
2
2
amount of Pd/C. Inset image: Plots of the rates of H generation vs.
ditions: 1 mmol B (OH) , 2 mol‰ catalyst, 2 mL H O, 30 °C
2
2
4
2
the amount of the Pd/C, both on natural logarithmic scales. c Plots
Pd/C catalyst was found to be 3.29 nm (Fig. 2). The inves-
tigation of the inꢃuence of the catalyst concentrations on
tetrahydroxydiboron hydrolysis catalyzed by 0.5 to 4 mol‰
Pd/C (5% w/w) has been evaluated at 30 °C. The slope of the
(Fig. 1d) [30, 31]. Then, the isotopic experiment using D O
2
instead of H O for H evolution upon tetrahydroxydiboron
2
2
hydrolysis has also been investigated (Fig. 3) [32–34]. The
kinetic results using D O exhibited a large kinetic eꢁect of
2
logarithmic H production plot versus Pd/C concentration is
3.51 for Pd/C, indicating that the RDS involves the cleavage
2
0
.42 (Fig. 1b), indicating that the H evolution upon tetrahy-
of a water O–H bond [35–39].
2
droxydiboron hydrolysis was ꢂrst order in Pd/C concentra-
The stability and recyclability of the Pd/C for H evo-
2
tion. The H evolution also was ꢂrst order in the concen-
lution has also been investigated (Fig. 4). Pd/C was re-
2
tration of tetrahydroxydiboron; slope: 0.87 by 0.002 mmol
Pd/C in Fig. 1c, conꢂrming tetrahydroxydiboron activation
in the rate-determining step (RDS). The result of the time
obtained and reused by ꢂltration, washing and drying after
the reaction. The H evolution has been re-initiated by the
2
addition of a fresh solution of B (OH) and H O. In addition,
2
4
2
dependence of H generation at various temperatures (from
the separated catalyst Pd/C after the 5th run of H evolution
2
2
2
73 to 308 K) showed that the activation energy (Ea) of
has been further examined by TEM (Fig. 5a). The 5th used
Pd/C was 32.0 kJ/mol based on the Arrhenius equation
Pd/C (3.75 nm) was found slightly bigger than that of fresh
1
3

J. Zhou et al.
Fig. 2 a The TEM image of Pd/C; b distribution diagram of Pd/C
Fig. 3 H evolution by
2
0
.5 mol‰ Pd/C in H O (black)
2
or D O (red)
2
Pd/C (3.29 nm), conꢂrming the good stability of Pd/C upon
recycling (Fig. 5b). The result showed that Pd/C catalyst
was reused 5 times with slightly decrease in the TOF, with
simple ꢂltration and washing as a means of separation.
achieved in a sealed two-chamber system (Fig. 6). The
left tube was used for hydrogen generation, and the right
one was used for hydrogenation with H generated in the
2
left tube.
The practical utility of H generation upon tetrahy-
Following H evolution, the hydrogenation of dipheny-
2
2
droxydiboron hydrolysis are not only H storage and
lacetylene and norbornene in the presence of generated H
2
2
release but also its direct usage in situ, in tandem reac-
tions, and in the mechanistic studies of the tetrahydroxy-
diboron hydrolysis reaction. The tandem reaction was
occurred quantitatively (99% yield) after 12 h of reaction at
30 °C. In addition, the formation of B(OH) has also been
3
conꢂrmed by the mass spectra (Figure S1).
1
3

Pd/C-Catalyzed H Evolution from Tetrahydroxydiboron Hydrolysis
2
Fig. 4 Plots of H volume
2
versus time for the B (OH)
2
4
hydrolysis during the reusability
test
Fig. 5 a The TEM image and b distribution diagram of 5th reused Pd/C
For the hydrogenation of norbornene with generated D ,
H
H
2
Pd/C (5 mol%)
D
D
derived from the reaction of B OH and D O, the result
2
4
2
+
D2
o
MeOH, 30 C, 12 h
(2)
showed that the desired product was also produced in 99%
yield (Eq. 2), consistent with the fact that both H atoms of
>
99 %
H gas were provided by water.
2
1
3

J. Zhou et al.
Fig. 6 Sealed two-chamber
system for the hydrogenation
of diphenylacetylene and nor-
bornene with H2
Pd/C (5 mol%)
Ph
Ph
Ph + H2
.05 M, 1a
Ph
MeOH (2 mL),
0
o
3
0 C, 12 h
2
a, >99 %
Pd/C
B (OH) + H O
2
4
2
Pd/C
H
Pd/C (5 mol%)
H
H
+
H2
MeOH (2 mL),
o
3
0 C, 12 h
H
0.05 M, 3a
4a, >99 %
4
Conclusion
a primary kinetic isotope eꢁect of 3.51 for Pd/C, indicat-
ing that the RDS involves the cleavage of a water O–H
bond, and conꢂrming the reaction mechanism. Tandem
reactions for diphenylacetylene and norbornene hydrogen-
ation also conꢂrmed that both H atoms of H2 are released
by water, in contrast with the hydrolysis of NH3BH3 or
NaBH4 for which one H atom of H2 formed is provided
by H2O and the other one by the boron compound. Hence,
Pd/C-catalyzed tetrahydroxydiboron hydrolysis in D2O
provides an easy and useful way for D2 synthesis. Con-
cerning large-scale H2 production by this method using
B2(OH)4, however, serious drawbacks remain with the cost
and the diꢀculty to reconvert the product B(OH)3 to the
B2(OH)4 precursor [40].
In summary, following this study of the heterogeneous
catalysis by Ru/C, Pd/C and Pt/C of the hydrolytic H
2
release using tetrahydroxydiboron, the two latter catalysts
are found to be equally active. Thus, Pd/C, a commercial
and cheap product, was disclosed as a remarkable, useful
and eꢀcient heterogeneous catalyst for this reaction. Pd/C
was recycled 5 times with slightly decrease in TOF for this
hydrogen evolution reaction, upon simple ꢂltration and
washing as a means of separation. The temperature plays
a signiꢂcant inꢃuence on the tetrahydroxydiboron hydroly-
sis, the activation energy (Ea) being 32.0 kJ/mol for Pd/C.
The isotopic experiment using D O instead of H O showed
2
2
1
3

Pd/C-Catalyzed H Evolution from Tetrahydroxydiboron Hydrolysis
2
Supplementary Information The online version of this article (https://
doi.org/10.1007/s10562-021-03547-2) contains supplementary mate-
rial, which is available to authorized users.
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Acknowledgements Financial support from the National Natural Sci-
ence Foundation of China (21805166), the 111 Project (D20015), the
Engineering Research Center of Eco-environment in Three Gorges Res-
ervoir Region, Ministry of Education, China Three Gorges University
8. Neeve EC, Geier SJ, Mkhalid IA, Westcott SA, Marder TB (2016)
Chem Rev 116:9091
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