Hydrogen Generation from Catalytic Reforming of Paraformaldehyde and Water by Polymeric Bifunctional Catalysts Comprising Ruthenium and Sulfonic Acid Units

Article abstract of DOI:10.1002/cplu.202000394

As a clean and sustainable source of energy, hydrogen shows great potential to be the ultimate energy source in future. In this research, paraformaldehyde is used as hydrogen carrier. Several bifunctional catalysts are prepared for the hydrogen generation from paraformaldehyde. The bifunctional catalysts contain two catalytically active sites. One is a sulfonic acid group for paraformaldehyde hydrolysis, and the other is an organometallic group that catalyzes the hydrogen release from formaldehyde. Bifunctional iridium catalysts and bifunctional rhodium catalysts could only generate traces of hydrogen in the initial phase of paraformaldehyde decomposition. Only the bifunctional ruthenium catalyst shows high activity due to its bifunctional catalytically active sites, thus more than 98.0 % of the initially produced gas contains hydrogen. The initial TOF is 685 h^?1 at 363 K when the paraformaldehyde concentration is 20 wt%. A reaction mechanism is proposed for the hydrogen generation from paraformaldehyde in which formaldehyde and formic acid are intermediates Formic acid decomposition is the rate-determining step in the later phase of paraformaldehyde decomposition.

Full text of DOI:10.1002/cplu.202000394

A Multidisciplinary Journal Centering on Chemistry
Accepted Article
Title: Hydrogen Generation from Catalytic Reforming of
Paraformaldehyde and Water by Polymeric Bifunctional Catalysts
Comprising Ruthenium and Sulfonic Acid Units
Authors: Yangbin Shen, Chuang Bai, Yulu Zhan, Fandi Ning, Huihui
Wang, Guojun Lv, and Xiaochun Zhou
This manuscript has been accepted after peer review and appears as an
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the VoR from the journal website shown below when it is published
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content of this Accepted Article.
To be cited as: ChemPlusChem 10.1002/cplu.202000394
Link to VoR: https://doi.org/10.1002/cplu.202000394
01/2020

10.1002/cplu.202000394
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Hydrogen Generation from Catalytic Reforming of Paraformaldehyde
and Water by Polymeric Bifunctional Catalysts Comprising
Ruthenium and Sulfonic Acid Units
Dr.Yangbin Shen,*,a Dr.Chuang Bai,b Dr.Yulu Zhan,c Dr.Fandi Ning,b Dr. Huihui Wang,b Dr.Guojun
Lv,d and Prof.Xiaochun Zhou*,b
aInstitute of Materials Science and Devices, Suzhou University of Science and Technology，
Suzhou 215009, China
bDivision of Advanced Nanomaterials, Suzhou Institute of Nano-tech and Nano-bionics, Chinese
Academy of Sciences, Suzhou 215123, China
cDepartment of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative
Materials, Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China
dSchool of Environmental and Chemical Engineering, Jiangsu University of Science and Technology,
Zhenjiang 212003, China
*Corresponding Author: Yangbin Shen (email:syb1989@126.com);
Xiaochun Zhou (email:xczhou2013@sinano.ac.cn)
Abstract:
As a clean and sustainable source of energy, hydrogen shows great potential to be the ultimate
energy in future. In this research, we employ paraformaldehyde as the hydrogen source. We prepare
several bifunctional catalysts for hydrogen generation from paraformaldehyde decomposition. Every
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bifunctional catalyst contains two catalytic active sites, one is sulfonic acid group for
paraformaldehyde catalytic hydrolysis, and the other is organometallic group for hydrogen
generation from formaldehyde catalytic reforming. The initial evolved gas contain trace hydrogen
when bifunctional iridium catalyst or bifunctional rhodium catalyst is employed for the hydrogen
generation from paraformaldehyde. Only the bifunctional ruthenium catalyst shows high activity due
to its bifunctional catalytic active sites, more than 98.0% of the initial gaseous production is
hydrogen. The initial TOF is up to 685 h-1 at 363K when the paraformaldehyde concentration is 20
wt%. We propose the reaction mechanism of hydrogen generation from paraformaldehyde. The
formaldehyde and the formic acid are the intermediate products during the total reaction. We also
confirm the formic acid decomposition is the rate-determining step in the later stage of the
paraformaldehyde decomposition.
1. Introduction
Hydrogen is considered to be the ultimate energy in future due to its high combustion value.
While hydrogen storage is one of the major barriers for its commercialization. It remains difficult to
store large amount of hydrogen safely. Thus, organic liquid is experiencing increasing popularity for
hydrogen storage research. Growing attention is given to hydrogen generation from methanol, formic
acid and formaldehyde because of their low costs, alternative sources and high gravimetric hydrogen
contents.[1-9] The CO-free hydrogen from organic liquid decomposition has been used in proton
exchange membrane fuel cell (PEMFC) successfully.[10-14] Researchers have put great efforts on
organic liquid for hydrogen storage, but little attention has been paid to the solid organic polymers
despite of their high hydrogen content. It is well known that it is difficult to decompose polymers
into hydrogen under mild condition. The paraformaldehyde might be a promising candidate for
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hydrogen storage and production, and this solid polymer is derived from the formaldehyde
polymerization. The paraformaldehyde could be hydrolyzed into formaldehyde under acid condition.
In aqueous solution, the major species is methanediol with the hydrogen content of 8.4 wt%. The
formaldehyde could decompose into hydrogen and carbon dioxide (Scheme 1).
Scheme 1. Reaction Pathway Using Paraformaldehyde and Water for Hydrogen Generation.
As exhibited in Table 1, the volumetric hydrogen content of paraformaldehyde is 95.34 g/L,
which is slightly lower than 98.75 g/L of methanol. But 1 cm3 paraformaldehyde could produce 2288
cm3 hydrogen if it could be completely decomposed into H2 and CO2 through formaldehyde-water
reforming, 1 cm3 methanol only produces 1782 cm3 hydrogen through methanol-water reforming.
The paraformaldehyde could produce more hydrogen compared with methanol.
Table 1. Representative Organic Molecules for Hydrogen Production.
Hydrogen
carriers
State
at r.t.
Density
[g/cm3]
Volumetric Hydrogen Gravimetric Hydrogen
Evolved H2 volume per cm3
substrate [cm3]
1304
Content[g/L]
Content [wt%]
HCHO
gas
/
54.36
98.75
53.04
95.34
6.67
12.5
4.34
6.67
CH3OH
liquid
liquid
solid
0.79
1.22
1.43
1778
636
HCOOH
(CH2O)n
2288
[a] Refer to the reactions in SI-1 for hydrogen production from the representative organic molecules.
Therefore, paraformaldehyde is a promising solid organic hydrogen carrier, the initial TOF for
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hydrogen generation from paraformaldehyde could be up to 2020 h-1 over the homogeneous
ruthenium catalyst.[15] However, certain technical problems still exist for hydrogen generation from
paraformaldehyde. The paraformaldehyde can’t react with water in solution directly. It should be
hydrolyzed into formaldehyde or methanediol in acid solution firstly,[16] then the formaldehyde could
react with water and generate hydrogen.[17-22] It seems promising to produce hydrogen from
paraformaldehyde through a two-steps reaction under acid condition (Scheme 1). However, the
formaldehyde decomposition prefers alkaline or neutral reaction conditions.[20-23] Few researchers
report the formaldehyde catalytic decomposition in acid solution. Paraformaldehyde hydrolysis and
formaldehyde catalytic decomposition require distinct reaction conditions.
In order to generate hydrogen from paraformaldehyde, for one thing paraformaldehyde
hydrolysis should be performed under strong acidic condition, for another new catalysts have to be
prepared for the hydrogen generation from formaldehyde. It is worth mentioning that the
formaldehyde-water shift reaction is the key step for hydrogen generation from paraformaldehyde.
This reaction could be catalyzed by many heterogeneous noble metal nanoparticles and
homogeneous organometallics in neutral or alkaline solution.[20-23] The catalytic activities are
sensitive to the reaction solution. The acidic condition could reduce the catalytic activity for
hydrogen generation from formaldehyde sharply, which is confirmed by our previous study.[24]
The catalytic microenvironment can be designed on the heterogeneous catalysts, making the
catalysts possess the solvation ability.[25, 26] Hereby we prepare some heterogeneous bifunctional
catalysts based on coordination polymers. The coordination polymers could provide two catalytic
active sites, the sulfonic acid and the organometallics. The sulfonic acid group could catalyze the
paraformaldehyde hydrolysis, which will not change the solution pH, because the two catalytic
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active sites are both fixed on the polymer. Therefore, the organometallics on the catalysts could keep
the high catalytic activity for hydrogen generation from formaldehyde in neutral solution.
Consequently, the paraformaldehyde could produce hydrogen continuously through the synergetic
catalysis of the sulfonic acid and the organometallics on the surface of the bifunctional catalysts.
2. Results and Discussion
2.1 Selectivity and Activity of Bifunctional Catalysts for Hydrogen Generation from
Paraformaldehyde.
The paraformaldehyde is decomposed into hydrogen and carbon dioxide by the synergetic
catalysis of two catalytic active sites on the bifunctional catalysts. The bifunctional catalysts are
coordination polymers that contain sulfonic acid and organometallics. We find the
pyridine-containing polymer is not suitable for immobilizing the ruthenium complex (SI-2).
Therefore, we immobilize the ruthenium complex by imino-containing polymers carriers. The
polymers are prepared through cross-linking polymerization of diallylamine, sodium
p-styrenesulfonate and divinylbenzene. The diallylamine and divinylbenzene are the frequently-used
cross-linking agents, making the catalysts own three-dimensional microstructures and insoluble in
water.
As exhibited in Table 2, the bifunctional catalysts show different catalytic activity and
selectivity for hydrogen generation from paraformaldehyde. The bifunctional iridium catalyst and
bifunctional rhodium catalyst show low catalytic activity and selectivity for the paraformaldehyde
decomposition, and a small amount of gas will be generated when we employ the two catalysts (SI-4,
SI-5). The main gaseous products are carbon dioxide and trace hydrogen after analyzed by GC-TCD.
It implies the formaldehyde disproportionation reactions are carried out when we employ the two
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catalysts for the paraformaldehyde decomposition.[27] Only the bifunctional ruthenium catalyst shows
high activity and selectivity, the main gaseous product is hydrogen. It indicates the
formaldehyde-water shift reaction is carried out during paraformaldehyde decomposition. Hence, this
research focuses on the bifunctional ruthenium catalyst for the paraformaldehyde and water
reforming.
Table 2. The Gas Composition of the Initial Evolved Gas.
Entry
Catalysts
Catalytic Activity
H2
CO2 TOF [h-1]
Ru
Ir
high
low
low
98.0%
trace
trace
trace
91.8%
87.6%
685
0.6
0.2
1
2
3
Rh
2.2 Characterization of Bifunctional Ruthenium Catalyst.
The characteristic of bifunctional ruthenium catalyst is exhibited in Figure 1. This catalyst has
porous structure with the specific surface area of 176.6 m2/g, and the particle size is mainly
distributed from 400 nm to 600 nm. The catalyst does not own any noble metal nanoparticles, which
could be proved by SEM and XRD data (SI-6). This structure provides large surface for the
hydrogen generation from paraformaldehyde and water reforming.
The XPS spectrums show the binding energy of the major elements in bifunctional ruthenium
catalyst (Figure 1b), indicating the catalyst has the N, O, S and Ru. The binding energy of N 1s is
401.6 eV, indicating the N originates from amine. The amine could coordinate with organometallics.
The binding energy of C 1s is 284.6 eV and 291.1 eV, indicating the C originates from benzene ring,
polyethylene and Ru(p-Cymene) group (SI-7). The binding energy of S 2p and O 1s is 168.3 eV and
531.2 eV respectively, which is consistent with the S 2p and O 1s in benzene sulfonic acid. After
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analyzing the catalyst by acid-base titration, we confirm the catalyst own 0.00015mol –SO3H per
gram (SI-8), hence sulfonic acid could catalyze the paraformaldehyde hydrolysis. The binding
energy of Ru 3p in the bifunctional ruthenium catalyst is 463.5 eV and 485.8 eV, and the binding
energy of Ru 3p in [Ru(p-Cymene)Cl2]2 is 462.3 eV and 484.8 eV (SI-7). It reveals the bifunctional
ruthenium catalyst have the Ru(p-Cymene) group, although the binding energy of Ru 3p in the
bifunctional ruthenium catalyst is slightly different from that in the [Ru(p-Cymene)Cl2]2. This
difference is mainly caused by the electron states of ruthenium change to some degree after the
[Ru(p-Cymene)Cl2]2 is immobilized by the N-containing polymer.
Figure 1. Characterization of Bifunctional Ruthenium Catalyst. (a) SEM image of the catalyst. (b)
XPS spectrums of the N, O, S and Ru in the catalyst. (c) FTIR spectrums of the catalysts.
FTIR results show the bifunctional ruthenium catalyst own the characteristic absorption peaks of
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the sulfonic acid and benzene ring. The 3055 cm-1 is the absorption peak of C-H stretching vibration
in benzene ring. The 2963 cm-1 and 2924 cm-1 are the asymmetric stretching vibrations of the –CH3
and –CH2–. The 1631 cm-1and 1451 cm-1 are the vibration absorption peaks of the benzene ring. The
1176 cm-1,1031 cm-1 and 1007cm-1 are the characteristic absorption peaks of sulfonic acid, the S
content is 0.47wt% after analyzed by ICP. 450 cm-1 is the characteristic absorption peak of Ru-Cl in
the catalyst. All these data confirm the bifunctional ruthenium catalyst owns the –SO3H and
Ru(p-Cymene) group, so it has high catalytic activity for hydrogen generation from
paraformaldehyde.
2.3 Catalytic Synergetic Effect and Selectivity of the Bifunctional Ruthenium Catalyst.
Figure 2a shows the gas will be generated from the paraformaldehyde solution catalyzed by
different catalytic systems. The brown and grey line indicate the gas generate through the two-steps
catalysis process in Scheme 1. The paraformaldehyde is hydrolyzed into formaldehyde by
hydrochloric acid or acetic acid firstly. These inorganic and organic acid could favor the
paraformaldehyde hydrolysis, but they will inhibit the catalytic activity of ruthenium complex for
formaldehyde decomposition.[24] Some researchers also find the alkalinity could favor the hydrogen
generation from formaldehyde.[20-23] When we employ the bifunctional ruthenium catalyst for
paraformaldehyde decomposition, the relatively independent acid active sites and the ruthenium
active sites are fixed on the surface of the bifunctional catalyst. The acid active sites will not inhibit
the catalytic activity of ruthenium active sites. Consequently, the blue line indicating bifunctional
ruthenium catalyst shows higher catalytic efficiency compared with brown and grey line in Figure
2a.
We analyze the gas composition of the evolved gas by gas chromatography (GC) during the
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paraformaldehyde and water catalytic reforming. The gas only contains hydrogen and carbon dioxide
(Figure 2b). Little carbon monoxide could be detected by the GC-TCD although the GC-TCD has
been equipped with methanizer.
Figure 2. Gas Evolved from Paraformaldehyde and Water Catalytic Reforming. (a) Gas evolved
under different conditions at 90℃. Blue, brown, grey and yellow lines indicate the bifunctional
ruthenium catalyst, Ru(p-Cymene)(H2O)3SO4 – CH3COOH, Ru(p-Cymene)(H2O)3SO4 – HCl,
polymer support respectively. (b) and (c) GC analysis of the evolved gas. Please refer to SI-9 for
more details.
2.4 The Dependence of Paraformaldehyde Concentration and Reaction Temperature on
Hydrogen Generation from Paraformaldehyde.
The paraformaldehyde concentration has great influence on hydrogen generation from
paraformaldehyde and water catalytic reforming. As exhibited in the Figure 3a, the initial TOF is up
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to 685 h-1 when the paraformaldehyde concentration is 20 wt%. Higher or lower concentration could
reduce the TOF of the bifunctional ruthenium catalyst. Several reasons could account for this. We
consider the paraformaldehyde and water catalytic reforming is a first-order reaction when the
paraformaldehyde concentration is low and the water is sufficient. A fraction of water reacts with the
paraformaldehyde, while most of water mainly act as solvent, thus the effect of water on the reaction
order can be negligible. When the paraformaldehyde concentration is high, the water is not only the
solvent for the paraformaldehyde, but also the reactant which should be taken into reaction order.
The reaction rate equation can be described as follows.
r=k[(CH2O)n]x[H2O]y
Equation 1
When the paraformaldehyde concentration is below 20%, the reaction order x is 1, and y is 0,
which means the water has little influence on the reaction order. If the paraformaldehyde
concentration is higher than 20%, the x is 1, and the y is higher than 1, that means the water shows
more influences on the reaction order than the paraformaldehyde. When we increase the
paraformaldehyde concentration, the water content decreases in the solution, so the reaction rate will
also decrease.
Figure 3. Influence of Reaction Conditions on Catalytic Activity. (a) The concentration dependence
of paraformaldehyde on the initial TOF. (b) The TOF values and Arrhenius plot at different
temperature.
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Figure 3b shows raising temperature could promote the catalytic activity of the hydrogen
generation from paraformaldehyde and water catalytic reforming. The TOF could rise from 49 h-1 to
685 h-1 when the temperature increases from 333 K to 363 K. We could gain the Arrhenius equation
from the temperature-dependent TOF, ln(TOF)=-10517(1/T) + 35.4. The reaction activation energy is
87.4 kJ/mol according to the Arrhenius equation.
2.5 Process of the Hydrogen Generation from Paraformaldehyde.
To propose the catalytic process and mechanism of the hydrogen generation from
paraformaldehyde decomposition, we analyze the gas and liquid products during the reaction. As
showed in Figure 4a, trace CO2 is generated in the initial reaction stage, and more than 98.0% of
gaseous production is hydrogen. We could also detect small amounts of formaldehyde in the reaction
1
solution by H NMR, which is from paraformaldehyde catalytic hydrolysis. Then GC could detect
both hydrogen and carbon dioxide after several hours’ reaction, accompanied with more
formaldehyde and formic acid generation. Therefore, we can confirm the formaldehyde-water shift
reaction and formic acid decomposition are both carried out after several hours. The former reaction
could generate hydrogen and formic acid, and the latter reaction could produce carbon dioxide and
hydrogen.
HCHO+ H2O= HCOOH+H2
HCOOH =CO 2 +H2
Reaction 1
Reaction 2
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Figure 4. The Process during Paraformaldehyde and Water Catalytic Reforming. (a) The components
variation of the evolved gas. (b) The 1H NMR variation of the reaction solution.
1
We analyze the reaction solution by H NMR continuously during the paraformaldehyde
catalytic decomposition in Figure 4b. No formic acid is detected in the reaction solution in the initial
reaction stage, only formaldehyde is generated through paraformaldehyde hydrolysis. Therefore, we
could confirm the paraformaldehyde can’t be converted into formic acid directly. After several hours’
reaction, more formaldehyde is accumulating through paraformaldehyde hydrolysis, and a small
amount of formic acid is generated through the formaldehyde-water shift reaction. Meanwhile we
find the mole ratio of evolved formic acid to formaldehyde (
) drops from 3.13 to 1.52
steadily. We could confirm the formaldehyde can be converted into formic acid quickly attributing to
the high activity of bifunctional ruthenium catalyst for the formaldehyde-water shift reaction. The
formaldehyde is always accumulating during the entire process, but the formic acid is not. We
speculate the bifunctional ruthenium catalyst may prefer formic acid as reaction substrate than the
formaldehyde. Therefore, the formic acid could be decomposed continuously while the formaldehyde
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can’t be converted to formic acid effectively.
2.6 The Dependence of Formic Acid on Hydrogen Generation from Paraformaldehyde.
To prove the speculation, we detect the generated gas continuously. We find the hydrogen
content of the evolved gas is decreasing steadily, accompanied with the carbon dioxide content
increasing. It leads to the mole ratio of hydrogen to carbon dioxide declining continuously (Figure
5a). It is noteworthy this ratio could fall below 2 after 21 hours’ reaction. 2 is the theoretical mole
ratio of the hydrogen to carbon dioxide during the paraformaldehyde and water catalytic reforming.
That means the formic acid could be decomposed into carbon dioxide and hydrogen effectively after
21 hours, but the formaldehyde can’t. In addition, we confirm the hydrogen generation from
paraformaldehyde is characterized by stepwise reaction, and each step has its own reaction rate
constant.
Figure 5. Process of Hydrogen Generation from Paraformaldehyde Decomposition. (a) Components
variation of the evolved gas. (b) The effect of formic acid on gas generation from formaldehyde
solution. The blue, grey, brown and yellow line indicate the
solution respectively.
is 0, 0.025, 0.05 and 0.1 in
We study the effect of formic acid on the gas generation from formaldehyde decomposition. It
will help us to confirm the rate-determining step during hydrogen generation from paraformaldehyde.
As exhibited in Figure 5b, the formic acid has negative effects on the gas generating rate from
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formaldehyde decomposition. The Ru(Cymene) group may prefer formic acid as its reaction
substrate than the formaldehyde, but it has much higher activity for formaldehyde-water shift
reaction compared with formic acid decomposition.[24] Consequently, the bifunctional ruthenium
catalyst prefer to catalyze the formic acid decomposition in the formic acid and formaldehyde mixed
solution. It leads to the
dropping from 3.13 to 1.52 steadily during paraformaldehyde
decomposition in Figure 4b. It can also explain why the gas generating rate could decrease if the
formic acid is added in the reaction solution. The formic acid decomposition will dominate the
hydrogen generation after formic acid accumulation in the reaction solution.
We confirm the formic acid will be generated during the paraformaldehyde. We analyze the
recycled catalysts by FTIR after they are dried at 105℃ for 3 hours. As exhibited in the Figure 6,
both the recycled homogeneous Ru(p-Cymene)Cl2 and the recycled immobilized ruthenium catalyst
have the absorption peaks at 1933 cm-1, 1723 cm-1 and 671 cm-1. 1723 cm-1 and 671 cm-1 are the
characteristic absorptions of the formic acid. It indicates the carboxyl group tend to adsorb on the
ruthenium atom of the Ru(p-Cymene)Cl2, which could lead to the structure change of the ruthenium
complexes. The structure change could account for the gas generating rate decrease after the formic
acid is generated or added in the solution.
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Figure 6. FTIR Spectrums of the Catalysts Before or After the Paraformaldehyde Decomposition.
2.7 Catalytic Mechanism of the Hydrogen Generation from Paraformaldehyde.
We propose the reaction mechanism for the hydrogen generation from the paraformaldehyde
based on the above research. The entire reaction process consists of three reaction steps. Firstly, the
paraformaldehyde could be hydrolyzed into formaldehyde by the sulfonic acid group of the
bifunctional ruthenium catalyst. It’s noteworthy the formaldehyde mainly exists as methanediol in
water. The two hydroxyl hydrogen atoms of the methanediol originate from the water.
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Scheme
2. Catalytic Cycles for Paraformaldehyde and Water Catalytic Reforming. (a)
Paraformaldehyde hydrolysis. (b) Formaldehyde-water shift reaction. (c) Formic acid decomposition.
The atoms of H and O from water are marked with red colour.
Secondly, the formaldehyde reacts with the water over the ruthenium complex in the
bifunctional ruthenium catalyst. We could gain the Ru(p-cymene) hydride complex after the formic
acid released from the catalyst intermediates. The carboxyl-connected hydrogen atoms originate
from paraformaldehyde which have been confirmed by the deuterium isotopic labeling (SI-11). Then
the ruthenium hydride complex will react with H+ to produce hydrogen in solution. One H atom of
hydrogen molecule is from paraformaldehyde, and the other is from water in the solution. This is the
complete catalytic process of the formaldehyde-water shift reaction, and the water act as the oxidant
in this reaction (Scheme 2b).It’s a typical aldehyde-water shift reaction, and the catalytic
mechanism have been reported in the literatures.[28-30]
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At last, the formic acid carries out the β-hydrogen elimination reaction, releasing CO2 and
Ru(p-cymene) hydride complex. The ruthenium hydride complex will react with H+ to produce
hydrogen molecule in the solution (Scheme 2c). The ruthenium complex has high selectivity for
formic acid decomposition.[31-33]
3. Conclusions
This study proposes a hydrogen generation method based on paraformaldehyde. Several
bifunctional catalysts are developed for hydrogen generation from the paraformaldehyde. The
catalysts have two catalytic activity sites, the sulfonic acid and organometallics. We find only the
bifunctional ruthenium catalyst has high catalytic activity and selectivity for paraformaldehyde and
water reforming. The sulfonic acid on the bifunctional ruthenium catalyst could catalyze the
paraformaldehyde hydrolysis into formaldehyde efficiently. Then the formaldehyde-water shift
reaction is carried out by the ruthenium complex on the bifunctional ruthenium catalyst, generating
hydrogen and formic acid. The formic acid could be further decomposed into hydrogen and carbon
dioxide. Attributing to the synergistic effect of the sulfonic acid and Ru(p-Cymene) on the
bifunctional ruthenium catalyst, the catalyst has high activity for hydrogen generation from
paraformaldehyde. The TOF is up to 685 h-1 at 363K. We propose the reaction process and
mechanism during the hydrogen generation from paraformaldehyde. We find the formaldehyde and
formic acid are the intermediate products during the reaction. The carboxyl-connected hydrogen
atoms originate from paraformaldehyde which have been confirmed by the deuterium isotopic
labeling. This research not only puts forward the new scheme for hydrogen generation from the solid
polymer, but also has some potential significance for water-induced conversion of aldehyde to acid
by bifunctional catalyst. It proves various types of reactions could be catalyzed by bifunctional
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catalysts, which makes the catalytic conversion more efficient.
4. Experiments
4.1 Chemicals and Materials
All chemicals were commercial and used without further purification unless otherwise specified.
Paraformaldehydede ((CH2O)n, Shanghai Macklin Biochemical, Co.,Ltd. , 95%), ethanol (C2H5OH,
Tianjing Baishi Chemical Industry, Co.,Ltd., >99.7%), hydrochloric acid (HCl, Sinopharm Chemical
Reagent. Co., Ltd., >37%), formic acid (HCOOH, Sinopharm Chemical Reagent. Co., Ltd., >98%),
methanol (CH3OH, Sinopharm Chemical Reagent, Co., Ltd., >99.7%), azodiisobutyronitrile (AIBN)
(C8H12N4, Shanghai Macklin Biochemical, Co., Ltd., >98%), α-phellandrene (C10H16, Jiangxi
Gannan natural & perfume oil Co.,Ltd., >98%), diallylamine(C6H11N, Shanghai Macklin
Biochemical, Co.,Ltd., >98%), chloroiridic acid (H2IrCl6·6H2O, Shanxi Kaida Chemical Engineer
Co., Ltd., Ir wt%>35%), rhodium trichloride (RhCl3, Shanxi Kaida Chemical Engineer Co., Ltd., Rh
wt%>39.5%), 1,2,3,4,5-pentamethylcyclopentadiene (C10H16, Sun Chemical Technology(Shanghai)
Co., Ltd., 97%), divinylbenzene ( C10H10, Shanghai Macklin Biochemical, Co.,Ltd, 80% mixture of
isomers), sodium p-styrenesulfonate (C8H7NaO3S, Shanghai Macklin Biochemical, Co.,Ltd., 98%),
Ruthenium trichloride (RuCl3, Energy-chemical, Co.,Ltd., Ru wt%>48.2%), ultrapure water was
prepared by Thermo PureLab Ultra Genetic. The [Ru(p-Cymene)Cl2]2, [Cp*IrCl2]2 and [Cp*RhCl2]2
were synthesized according to literature procedures. [24, 34]
4.2 Characterization and Physical Measurements.
1H NMR spectra were recorded on Varian Plus 400 MHz. The evolved gas was analyzed by
GC-G5 (Beijing Persee General Instrument Co., Ltd.), and the gas chromatography was assembled
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with FID, TCD and methanizer. With N2 as carrier gas, the detection limit of CO was below 1 ppm.
Powder X-ray diffraction (XRD) patterns of samples were recorded with Bruker D8 X-ray
diffractometer using Cu-Kα radiation (λ =1.5406 Å, 40 kV and 40 mA). The XPS measurements
were employed via Escalab 250Xi spectrometer. The ruthenium, rhodium and iridium contents of the
catalysts were determined by Agilent 720 ICP-OES. SEM images were recorded on Quanta 400 FEG,
FEI. The FTIR data were detected by Nicolet iS10 (Nicolet Instrument Co. USA). The pore size
distributions and average pore diameter of the catalysts were analyzed by Nano-ZS90 (Malvern), and
the surface areas of the bifunctional catalysts were determined by Malvern Instruments
Zetasizer Nano ZS90.
4.3 Catalysts Preparation.
The [Ru(p-Cymene)Cl2]2 could coordinate with many N-containing ligands, for instance,
2,2’-bipyridine, 2,2’-bipyrimidine, 1,10-phenanthroline, 2,2’-biimidazole. While these ligands will
deactivate the ruthenium complex. Only the amino-coordinated ruthenium complex has high
catalytic for the formaldehyde.[24] In this research, we immobilize the [Ru(p-Cymene)Cl2]2 by the
imino group of the polymer.
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Scheme 3. Detailed Process to Prepare the Bifunctional Catalysts.
The catalysts preparation is illustrated in Scheme 3. 200mg sodium p-styrenesulfonate, 1 mL
diallylamine, and 2 mL divinylbenzene were stirring in ethanol-water solution. Then 100mg AIBN
were added into the solution, acting as the initiator after the flask was heated to 90 ℃. White
polymer powder would be formed after 10 hours’ reaction. The white polymer powder should be
filtered from the solution and washed by the ultrapure water for several times. The polymer powder
was ion-exchanged by 1 M HCl (100 mL) for 6 hours, this process was repeated twice. We could
gain the –SO3H and –NH containing polymers which could coordinate with [Ru(p-cymene)Cl2]2,
[Cp*IrCl2]2 or [Cp*RhCl2]2. At last, 2g polymers were reacted with 100mg organometallics in water
at 60℃ for 12 hours. After being filtered, washed with water and dried under vacuum, the
bifunctional catalysts were prepared. Details are illustrated in SI-3
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4.4 Hydrogen Generation from Paraformaldehyde and Water Catalytic Reforming.
Typically, 10mL 20 wt% paraformaldehyde water solution was stirred by magnetic bar in
25mL flask. Then, 40mg catalysts were added into the solution after the flask been heated to the
preset temperature. The flask was connected to the U-shape tube to measure the volume of the
evolved gas during paraformaldehyde decomposition. The gas was analyzed by gas chromatography.
4.5 TOF Calculations.
Little carbon dioxide was detected by GC during the initial 30 minutes of reaction, so we
calculated the TOF of the paraformaldehyde and water catalytic reforming based on the following
reaction.
(CH2O)n + n H2O → n HCOOH + n H2
The TOF was calculated by Equation 2 when the ruthenium catalyst was employed. The
water vapor was neglected.
TOF=
Equation 2
VH2 was the volume of hydrogen that generated during the initial 0.5 hour, t was 0.5 h. n(Ru) was
the molar number of ruthenium. The ruthenium content of the bifunctional ruthenium catalyst was
0.87 wt%. The Vm,H2 was calculated by van der Waals equation of hydrogen.[35]
Vm,H2
=
+b- ≈ 24 L/mol
R is 8.3145 m³ Pa mol-1 K-1, T is 293.15 K, p is 101325 Pa, b is 26.7ⅹ10-6 m3·mol-1, a is
2.49ⅹ10-10 Pa·m3·mol-2.
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The TOF was calculated by Equation 3 when the rhodium or iridium catalyst was employed.
The water vapor was neglected.
TOF=
Equation 3
3 was the stoichiometric ratio in Reaction 3, VCO2 was the volume of carbon dioxide that
generated during the initial 0.5 hour, t was 0.5 h. The calculation of Vm,CO2 was carried out using van
der Waals of CO2 by Equation 4. The n was the molar number of rhodium or iridium in the
immobilized catalyst. The Ir content of the catalyst is 1.32 wt%, and Rh content of the catalyst is
1.43 wt%.
Vm,CO2
=
+b-
≈ 24 L/mol
Equation 4
R is 8.3145 m³ Pa mol-1 K-1, T is 293.15 K, p is 101325 Pa, b is 42.7ⅹ10-6 m3·mol-1, a is 36.5
ⅹ10-10 Pa·m3·mol-2.
3 (CH2O)n +n H2O→ n CO2 + 2n CH3OH
Reaction 3
Acknowledgments. The authors are grateful for financial support granted by the National Natural
Science Foundation of China (No. 21902115), China Postdoctoral Science Foundation (No.
2018M632406), Ministry of Science and Technology of China (No.2016YFE0105700, No.
2016YFA0200700). We are also thankful to Yang Huang in Suzhou Science and Technology Town
Foreign Language School for her help on polishing the manuscript.
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Keywords: bifunctional catalysts • catalytic reforming • formaldehyde • hydrogen generation •
ruthenium
Author contributions
Y.-B. S. and X.-C. Z. designed and directed the project. Y.-B. S., C.B. and Y.-L. Z. carried out
the experiments and prepared the catalysts, F.-D. N performed NMR analysis and analyzed the data.
H.-H. W. performed the GC and analyzed the data, G.-J. L test element content of all the catalysts.
Y.-B. S. and X.-C. Z. wrote and revised the manuscript.
References
[1] K. I. Fujita, R. Kawahara, T. Aikawa, R. Yamaguchi Angew. Chem. Int. Ed. 2015, 54, 9057-9060.
[2] A. Guerriero, H. Bricout, K. Sordakis, M. Peruzzini, E. Monflier, F. Hapiot, G. Laurenczy, L.
Gonsalvi ACS Catal. 2014, 4, 3002-3012.
[3] T. He, P. Pachfule, H. Wu, Q. Xu, P. Chen Nat. Rev. Mater. 2016, 1, 16059.
[4] L. E. Heim, S. Vallazza, D. van der Waals, M. H. G. Prechtl Green Chem. 2016, 18, 1469-1474.
[5] F. Cai, J. J. Ibrahim, Y. Fu, W. Kong, J. Zhang, Y. Sun Appl. Catal. B-Environ. 2020, 264,
118500.
[6] L. Lin, W. Zhou, R. Gao, S. Yao, X. Zhang, W. Xu, S. Zheng, Z. Jiang, Q. Yu, Y.-W. Li, C. Shi,
X.-D. Wen, D. Ma Nature. 2017, 544, 80-83.
[7] L.-N. Chen, K.-P. Hou, Y.-S. Liu, Z.-Y. Qi, Q. Zheng, Y.-H. Lu, J.-Y. Chen, J.-L. Chen, C.-W. Pao,
S.-B. Wang, Y.-B. Li, S.-H. Xie, F.-D. Liu, D. Prendergast, L. E. Klebanoff, V. Stavila, M. D.
Allendorf, J. Guo, L.-S. Zheng, J. Su, G. A. Somorjai J. Am. Chem. Soc. 2019, 141,
17995-17999.
This article is protected by copyright. All rights reserved.

10.1002/cplu.202000394
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[8] S.-M. Lu, Z. Wang, J. Wang, J. Li, C. Li Green Chem. 2018, 20, 1835-1840.
[9] S. Patra, S. K. Singh Inorg. Chem. 2020, 59, 4234-4243.
[10] F. Ning, X. He, Y. Shen, H. Jin, Q. Li, D. Li, S. Li, Y. Zhan, Y. Du, J. Jiang, H. Yang, X. Zhou
ACS Nano. 2017, 11, 5982-5991.
[11] Y. Du, Y.-B. Shen, Y.-L. Zhan, F.-D. Ning, L.-M. Yan, X.-C. Zhou Chin. Chem. Lett. 2017, 28,
1746-1750.
[12] X. Zhou, Y. Huang, C. Liu, J. Liao, T. Lu, W. Xing Chemsuschem. 2010, 3, 1379-1382.
[13] B. Loges, A. Boddien, H. Junge, M. Beller Angew. Chem. Int. Ed. 2008, 47, 3962-3965.
[14] M. Czaun, J. Kothandaraman, A. Goeppert, B. Yang, S. Greenberg, R. B. May, G. A. Olah, G. K.
S. Prakash ACS Catal. 2016, 6, 7475-7484.
[15] L. Wang, M. Z. Ertem, R. Kanega, K. Murata, D. J. Szalda, J. T. Muckerman, E. Fujita, Y.
Himeda ACS Catal. 2018, 8, 8600-8605.
[16] L. E. Heim, N. E. Schloerer, J.-H. Choi, M. H. G. Prechtl Nat.Commun. 2014, 5.
[17] H. Liu, M. Wang, J. Ma, G. Lu J. Catal. 2019, 375, 493-506.
[18] R. Li, X. Zhu, X. Yan, H. Kobayashi, S. Yoshida, W. Chen, L. Du, K. Qian, B. Wu, S. Zou, L.
Lu, W. Yi, Y. Zhou, J. Fan ACS Catal. 2017, 7, 1478-1484.
[19] Q. Jin, Y. Shen, Y. Cai, L. Chu, Y. Zeng J. Hazard. Mater. 2019, 381, 120934-120934.
[20] H. Gao, J. Zhang, R. Wang, M. Wang Appl. Catal. B-Environ. 2015, 172, 1-6.
[21] M. Trincado, V. Sinha, R. E. Rodriguez-Lugo, B. Pribanic, B. de Bruin, H. Gruetzmacher
Nat.Commun. 2017, 8.
[22] S. Zhang, H. Wang, L. Tang, M. Li, J. Tian, Y. Cui, J. Han, X. Zhu, X. Liu Appl. Catal.
B-Environ. 2018, 220, 303-313.
This article is protected by copyright. All rights reserved.

10.1002/cplu.202000394
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[23] H. Hu, Z. Jiao, J. Ye, G. Lu, Y. Bi Nano Energy. 2014, 8, 103-109.
[24] Y. Shen, F. Ning, C. Bai, Y. Zhan, S. Li, Y. Huang, X. Zhou ACS Appl.Energy Mater. 2018, 1,
4860-4866.
[25] Q. Sun, S. Wang, B. Aguila, X. Meng, S. Ma, F.-S. Xiao Nat.Commun. 2018, 9.
[26] Q. Sun, Y. Tang, B. Aguila, S. Wang, F.-S. Xiao, P. K. Thallapally, A. M. Al-Enizi, A. Nafady, S.
Ma Angew. Chem. Int. Ed. 2019, 58, 8670-8675.
[27] L. Wang, M. Z. Ertem, K. Murata, J. T. Muckerman, E. Fujita, Y. Himeda ACS Catal. 2018, 8,
5233-5239.
[28] T. P. Brewster, W. C. Ou, J. C. Tran, K. I. Goldberg, S. K. Hanson, T. R. Cundari, D. M.
Heinekey ACS Catal. 2014, 4, 3034-3038.
[29] Balaraman, Ekambaram, E. Khaskin, G. Leitus, D. Milstein Nat.Chem. 2013, 5, 122-125.
[30] H. Zhou, H. Xu, X. Wang, Y. Liu Green Chem. 2019, 21, 2923-2927.
[31] J. D. Scholten, M. H. G. Prechtl, J. Dupont ChemCatChem. 2010, 2, 1265-1270.
[32] H. Junge, A. Boddien, F. Capitta, B. Loges, J. R. Noyes, S. Gladiali, M. Beller Tetrahedron Lett.
2009, 50, 1603-1606.
[33] C. Fellay, P. J. Dyson, G. Laurenczy Angew. Chem. Int. Ed. 2008, 47, 3966-3968.
[34] M. A. Bennett, T. N. Huang, T. W. Matheson, A. K. Smith Inorganic Synthesis. 1982, 21, 74-78.
[35] Z. Wang, S. M. Lu, J. Li, J. Wang, C. Li Chem. Eur. J. 2015, 21, 12592-12595.
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Table of Contents
The bifunctional ruthenium catalyst is developed for hydrogen generation from the
paraformaldehyde. Attributing to the synergistic effect of the sulfonic acid and Ru(p-Cymene) on the
bifunctional ruthenium catalyst, the catalyst has high activity for hydrogen generation from
paraformaldehyde. The TOF is up to 685 h-1 at 363K. The formaldehyde and formic acid are the
intermediate products during the reaction. This research put forward the new scheme for hydrogen
generation from the solid polymer.
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