Ni3P as a high-performance catalytic phase for the hydrodeoxygenation of phenolic compounds

Article abstract of DOI:10.1039/c7gc03262e

The catalytic performance of an unsupported Ni₂P in the aqueous phase hydrodeoxygenation (HDO) of phenol was investigated. It was found that the unsupported Ni₂P was water-sensitive, being transformed stepwise, first to an amorphous phase and then to Ni₅P₂ and Ni₁₂P₅, and finally to Ni₃P in the presence of water at elevated temperatures. Nonetheless, the generated Ni₃P phase exhibited extraordinary hydrogenation activity at low temperatures and high HDO activity at high temperatures. The unsupported Ni₃P was more active for the hydrogenation of the aromatic ring in the phenol molecule than Pd/SiO₂ (1.0 wt%). The unsupported Ni₃P was catalytically active and stable in phenol HDO in both the aqueous phase and the organic phase. In addition to phenol, catechol and o-cresol were investigated in the HDO catalyzed by the unsupported Ni₃P in both aqueous solution and decalin solution. The HDO reactivity decreased in the order of phenol > catechol > o-cresol in the aqueous phase, and in the order of phenol > o-cresol in the organic phase (catechol is insoluble in decalin). In the oil phase HDOs of phenol and o-cresol, the unsupported Ni₃P exhibited superior hydrogenation activity to that of the unsupported Ni₂P at low temperatures.

Full text of DOI:10.1039/c7gc03262e

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: Z. Yu, Y. Wang, Z.
Sun, X. Li, A. Wang, D. Camaioni and J. A. Lercher, Green Chem., 2018, DOI: 10.1039/C7GC03262E.
This is an Accepted Manuscript, which has been through the
Volume 18 Number
7 7 April 2016 Pages 1821–2242
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Accepted Manuscripts are published online shortly after
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Please do not adjust margins
Green Chemistry
Page 1 of 11
View Article Online
DOI: 10.1039/C7GC03262E
Green Chemistry
ARTICLE
Ni3P as a High-Performance Catalytic Phase for
Hydrodeoxygenation of Phenolic Compounds
Zhiquan Yu,a Yao Wang,a Zhichao Sun,a Xiang Li,a Anjie Wang,a* Donald M. Camaionib and
Johannes A. Lercherb
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
The catalytic performance of an unsupported Ni2P in aqueous phase hydrodeoxygenatio (HDO) of phenol was investigated.
It was found that the unsupported Ni2P was water-sensitive, being transformed stepwise, first to an amorphous phase and
then to Ni5P2 and Ni12P5, and finally to Ni3P in the presence of water at elevated temperatures. Nontheless, the generated
Ni3P phase exhibted extraordinary hydrogenation activity at low temperatures and high HDO activity at high temperatures.
The unsupported Ni3P was more active for hydrogenation of the aromatic ring in phenol molecule than Pd/SiO2(1.0 wt%).
The unsupported Ni3P was catalytically active and stable in phenol HDO in both aqueous phase and organic phase. In
addition to phenol, catechol and o-cresol were investigated in the HDO catalyzed by the unsupported Ni3P in both aqueous
solution and in decalin solution. The HDO reactivity decreased in the order: phenol > catechol > o-cresol in aqueous phase,
and was: phenol > o-cresol in organic phase (catechol is insoluble in decalin). In the oil phase HDOs of phenol and o-cresol,
the unsupported Ni3P exhibited superior hydrogenation activity to the unsupported Ni2P at low temperatures.
www.rsc.org/
but Ni2P supported on MCM-41 showed also excellent activity
in HDO of phenol.20-24 Zhao et al. investigated the gas-phase
HDO of guaiacol on a series of transition metal phosphides,
Introduction
Bio-oils produced by pyrolysis or liquefaction of lignocellulosic
biomass are promising alternative sources for the production
of fuels. Bio-oils have a high oxygen content (45~50 wt%),1
which leads to undesired properties such as high viscosity, low
thermal stability, low heating value and immiscibility with
petroleum fractions. Converting bio-oils to fuels requires the
reduction of the oxygen content. Hydrodeoxygenation (HDO) is
regarded as the most promising route for this task.2
and found that the turnover frequency decreased in the order:
Ni2P/SiO2 > Co2P/SiO2 > Fe2P/SiO2 MoP/SiO2
WP/SiO2.16
≈
≈
Xue et al. reported that Ni2P/SiO2 was more active than Ni/SiO2
in HDO of methyl palmitate.25 Nevertheless, it was reported
that crystalline metal phosphides were not stable and
transformed into an amorphous phase during the
hydrogenation of cellulose into sorbitol.26 In situ EXAFS
measurements showed that the presence of phenol or water
led to the surface oxidation of Ni2P/SiO2.22 Since a large
fraction of water is present in bio-oils and water is also the by-
product in HDO of bio-oils, it is of significant importance to
investigate the effects of water on the structure and
performance of catalytic phases under HDO conditions.
Mo- or W-based sulfide catalysts, which are industrially
important hydrotreating catalysts in refineries, are active for
HDO, showing high performance in removing oxygen from bio-
oils.3,4 However, these metal sulfide catalysts suffer from
progressive deactivation during HDO of bio-oils, due to the loss
of sulfur in the catalytic phase.5 On the other hand, the lost
sulfur species will contaminate the hydrotreated products. As
a result, non-sulfide catalysts, including precious metals,6-9
base metals,10-12 metal carbides,13,14 metal nitrides,15 and
metal phosphides,16-19 have been considered as potential HDO
catalysts for upgrading bio-oils.
Phenolic compounds are among the major oxygen-
containing components in bio-oils. In addition, the Ar-OH bond
in phenolic compounds is the strongest in the representative
O-attached bonds in bio-oils,27 which is evidenced by the fact
that phenolic intermediates were frequently detected in the
HDO products of the refractory O-containing compounds (such
as guaiacol, benzofuran, and dibenzofuran). Therefore, three
phenolic compounds, including phenol, catechol, and o-cresol,
were investigated in the HDO catalyzed by unsupported Ni3P
and unsupported Ni2P in water and in decalin.
Metal phosphides exhibit not only high catalytic activity in
hydrodesulfurization (HDS) and hydrodenitrogenation (HDN),
Experimental
All reagents were of analytical grade, and purchased from
Sinopharm Group CO. LTD., China. They were used as
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 2 of 11
View Article Online
DOI: 10.1039/C7GC03262E
ARTICLE
Journal Name
provided: Ni(NO3)2·6H2O, (NH4)2HPO4, PdCl2, SiO2, decalin,
H2 chemical adsorption was measured to measure the active
quartz sand, dichloromethane, anhydrous MgSO4, phenol, sites of Pd/SiO2. 0.2 g passivated and air-exposed sample was
cyclohexanol, catechol and o-cresol.
re-reduced in a H2 flow to remove the passivation layer (50
mL·min-1 flow rate, heating from 20 to 300
C at a rate of 10
C·min-1, and then holding at the final temperature for 1 h).
°
Catalyst preparation
°
The reactor was then cooled to 30 °C in a flow of He. A He flow
Unsupported Ni2P or Ni3P was prepared from the oxide
precursor by in situ H2 temperature programmed reduction
(TPR) method.28 The oxide precursor was prepared as follows.
Ni(NO3)2·6H2O was dissolved in deionized water under stirring
to form a clear solution, and the aqueous solution of
(NH4)2HPO4 was then added dropwise under stirring, to form a
slurry. The resultant slurry was heated to evaporate water to
at 50 mL·min-1 was used to flush the catalyst for 30 min to
achieve an adsorbate-free catalyst surface. After
pretreatment, a pulse of calibrated volume of H2 was injected
into the flow of He, and the uptake was measured using a TCD.
Pulses were repeatedly injected until the response from the
detector showed no further uptake.
NH3-TPD profile was obtained on a Chembet-3000 analyzer.
Before measurement, 0.2 g passivated Ni3P or Ni2P sample
obtain a solid product. The product was dried at 120 °C for 12
h and calcined at 500 C for 3 h. The initial mole ratios of Ni/P
°
was re-reduced in H2 for 1 h at 500
40 C and exposed to NH3 for 30 min. In a He flow, the
temperature was raised to 500 C at 10
C·min-1. The
°C, and was then cooled to
for unsupported Ni2P and Ni3P were 1 and 3, respectively.
Unsupported Ni was obtained by reduction of NiO precursors,
which was obtained by calcination of Ni(NO3)2·6H2O. The oxide
precursor of Pd/SiO2 (1 wt%) was prepared by the incipient
wetness impregnation method. A PdCl2 solution was dropwise
added onto SiO2 powder. The mixture was aged at ambient
°
°
°
desorption signal was recorded by a TCD. A standard (zeolite
HZSM-5) sample with known acid site concentration was used
to calibrate the acid amount of the catlaysts.
temperature for 12 h, followed by drying at 120
and calcination at 500 C for 3 h.
°C for 12 h
Catalytic HDO
°
The catalysts were obtained in situ by reducing the oxide HDO of phenol was carried out in a stainless-steel tubular
precursors in hydrogen, in the reactor prior to the HDO reactor (10.0 mm i.d.). The oxide precursor of unsupported
reaction.
Ni2P, Ni3P, Ni, or Pd/SiO2 was pelleted, crushed, and sieved to
0.4-0.8 mm. Prior to HDO reaction, the precursor was
transformed into metal phosphide by in situ H2 TPR procedure.
The oxide precursor of unsupported Ni2P, Ni3P or Ni was
reduced in a 150 mL·min-1 H2 flow by heating from room
Catalyst characterization
For characterization, the reduced samples were passivated in a
20 mL·min-1 O2/Ar (0.5 vol%) flow for 2 h at ambient
temperature before exposure to air.
temperature to 400
temperature (500 C) at 1
Pd/SiO2, the oxide precursor was reduced in a 100 mL·min-1 H2
flow by heating from room temperature to 300 C at 10
C·min-1 and kept for 1 h. Then the reactor was cooled to the
°
C at 2
°
C·min-1, then to the final
°
°
C·min-1 and kept for 2 h. For
X-ray diffraction (XRD) patterns were measured on a Rigaku
D/Max 2400 diffractometer with nickel-filtered Cu-Kα
radiation at 40 kV and 100 mA. X-ray photoelectron
spectroscopy (XPS) analysis was conducted on a Multilab 2000
X-ray photoelectron spectrometer, using an Mg-Kα source. The
BET surface area was calculated from the N2 adsorption
°
°
reaction temperature (150-350
°C), and the total pressure was
kept at 4.0 MPa.
Initially, in the aqueous HDO of phenol catalyzed by the
unsupported Ni2P, two temperature programs were used: (1)
the reactor was directly cooled to the reaction temperature
isotherms measured at -196
3020 model.
°C on a Micrometritics Tristar II
Transmission electron microscope (TEM) observation was
conducted on a FEI Tecnai G2 F30 transmission microscope
operated at 300 kV. The sample for TEM observation was
prepared by depositing a drop of an ultrasonic-treated ethanol
suspension of the solid material onto a carbon-coated Cu grid.
CO chemical adsorption was measured to determine the
active sites of unsupported Ni3P. 0.2 g passivated and air-
exposed sample was re-reduced in a H2 flow to remove the
passivation layer (50 mL·min-1 flow rate, heating from 20 to
(Program 1); (2) the reactor was cooled to 150
2.5 h (when reaction temperature T=150 C), then heated to
200 C at 2 C), and heated
C·min-1 and kept for 2.5 h (T=200
to 250 (T=250 C), 300 (T=300 C), and 350 C (T=350 C) and
°C and kept for
°
°
°
°
°
°
°
°
kept for 2.5 h consecutively (Program 2). Both Program 1 and
Program 2 were used to investigate the transformation of Ni2P
to Ni3P, while Program 2 was used in the investigation of HDO
activity in both phases.
500
°C at a rate of 10 °
C·min-1, and then holding at the final
C in a
In the aqueous HDO of phenol catalyzed by Ni3P, Ni and
Pd/SiO2 (1.0 wt% Pd), the HDO reactions were as follows: 0.2 g
catalyst precursor, 5.0 wt% phenol in water as the feed, and a
flowrate of 100 mL·min-1 H2 and 0.1 mL·min-1 liquid feed. After
the reaction system had achieved a steady state (2 h), liquid
product was sampled from the gas-liquid separator. The
organic products in the sample were extracted by
dichloromethane and dehydrated by anhydrous magnesium
temperature for 1 h). The reactor was then cooled to 30
°
flow of He. A He flow at 50 mL·min-1 was used to flush the
catalyst for 30 min to achieve an adsorbate-free catalyst
surface. After pretreatment, a pulse of CO was injected into a
flow of He, and the uptake was measured using a thermal
conductivity detector(TCD). Pulses were repeatedly injected
until the response from the detector showed no further
uptake.
sulfate. The dried products were analyzed by
a gas
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 3 of 11
View Article Online
DOI: 10.1039/C7GC03262E
Journal Name
ARTICLE
hydrogenation to generate cyclohexene and cyclohexane
(Scheme 1).6 As a result, it is possible to determine the major
route in HDO by the selectivities of the oxygen-free products
and the intermediates.
Transformation of Ni2P to Ni3P
Fig. 1a compares the variations of phenol conversion as a
function of temperature in the aqueous HDO catalyzed initially
by Ni2P, using two different temperature programs (see the
chromatograph (GC, Agilent 6890, flame ionization detector)
with a HP-INNOWax capillary column (30 mꢀ320 µmꢀ0.5 µm).
Experimental). No difference was observed at 150
Program 2 gave slightly higher conversion than Program 1 at
200 C. Noticeably, there were marked differences in the
temperature range of 250 to 350 C for the two programs. The
°C, and
For HDO of phenol or o-cresol in decalin over Ni3P and Ni2P,
the procedure was analogous to aqueous HDO, but without
extraction and drying in the product analysis section.
°
°
phenol conversion increased significantly with reaction
temperature in Program 2, whereas extremely low conversion
was obtained in Program 1. The XRD characterization of the
spent catalysts showed that the crystalline phase of the
Results and discussion
Generally, HDO of phenolic compound proceeds in two parallel
routes: (1) the direct deoxygenation (DDO) route to form
benzene; (2) the hydrogenation (HYD) route to form
cyclohexanone and cyclohexanol followed by dehydration and
unsupported Ni2P collapsed after HDO at 350 °C for 2.5 h for
both programs (Fig. 1b), indicating that Ni2P is not stable in the
aqueous HDO at elevated temperatures. In Program 1, Ni2P
was transformed into a mixture of Ni5P2, Ni12P5, and Ni(PO3)2.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 4 of 11
View Article Online
DOI: 10.1039/C7GC03262E
ARTICLE
Journal Name
These mixed phases showed very low catalytic activity in leaching of P species by water and/or steam.29 The resulted
aqueous HDO of phenol (Fig. 1a). In contrast, in Program 2, amorphous phase with decreased P/Ni ratio is then reduced by
Ni2P was transformed mainly to Ni3P, which showed hydrogen to Ni12P5 and Ni5P2, and finally to Ni3P at elevated
considerably high activity in the aqueous HDO of phenol.
temperatures.30 The theoretical calculation indicated that Ni3P
The phase changes in Program 1 and in Program 2 were is thermodynamically more stable than Ni2P.31
monitored by measuring the XRD patterns of the samples
obtained at various temperatures (Fig. 2a and 2b). The Ni2P Aqueous-phase HDO over Ni3P
phase survived in HDO at 150
undetectable after HDO reaction at 200
In both cases, the two broad diffraction peaks around 2
°
C for 2.5 h, but was
Unsupported Ni3P can also be synthesized directly from an
oxide precursor with reduced P/Ni ratio in a similar procedure
°C for both programs.
θ
=
42.2 and 47.2
Ni12P5. At 250
into two peaks for both programs, indicating the formation of
°
indicated the possible formation of Ni5P2 and
°
C, the broad peak around 2 = 47.2 was split
θ
°
a mixture of Ni5P2 and Ni12P5. At 300 °C, the diffraction peaks
of Ni5P2 and Ni12P5 were well resolved in Program 1, whereas
the ones characteristic of Ni3P were predominant in Program
2. At 350 °C, a mixture of distinctive Ni5P2, Ni12P5, and Ni(PO3)2
was formed in Program 1, while the major phase of Ni3P and a
minor fraction of Ni3(PO4)2 were generated in Program 2.
In the investigated HDO reaction conditions, the partial
pressure of water was calculated to be 2.18 MPa, which
corresponds to a boiling point of 217
became steam above 217 C in the reactor, and the reaction
system shifted from gas-liquid-solid phases to gas-solid phases
above 217 C. In the gas-liquid-solid phase at 150 C, the Ni2P
°C. In other words, water
°
°
°
was stable in the first 2.5 h and showed similar catalytic
activity in phenol conversion for Program 1 and Program 2.
However, at 200
°C, the Ni2P crystal structure collapsed in 2.5
h, and an amorphous phase was generated. At 250
°C, water
was in the form of steam, and the disappearance of liquid
phase on the outer surface facilitates the growth of crystalline
Ni5P2 and Ni12P5, which were presumed to grow from the
resultant amorphous phase by hydrogen reduction, for both
programs. However, the direct contact of the fresh Ni2P
catalyst with steam in Program 1 led to the complete activity
loss, whereas the gradual evaporation of water during the
slow heating-up from 200 to 250
severe interaction of Ni2P with steam and thus suppressing the
surface oxidation of metal phosphides in Program 2. At 300 C,
°C might slow down the
°
large particles of Ni5P2 and Ni12P5 were obtained in Program 1,
but the catalyst was not catalytically active. On the other hand,
a major phase of Ni3P was generated at the expense of Ni5P2
and Ni12P5 and a minor fraction of Ni3(PO4)2 was also
detectable in the spent catalyst in Program 2, and the catalyst
was significantly active in hydrogenation. At higher
temperature (350 °C), the crystallinities of Ni5P2 and Ni12P5 in
Program 1 and that of Ni3P in Program 2 were further
improved.
To verify the role of water in the transformation of
unsupported Ni2P to Ni3P in Program 2, the feed was replaced
by pure water, and Ni2P was treated in a similar way. The XRD
patterns of the samples obtained at various temperatures (Fig.
S1) were in accordance with those of the spent catalysts after
the aqueous phase HDO reaction. It is clear that both
temperature program and water played the vital role in the
transformation from Ni2P to Ni3P. The collapse of Ni2P crystal
might be related with the surface oxidation and subsequent
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 5 of 11
View Article Online
DOI: 10.1039/C7GC03262E
Journal Name
ARTICLE
to the synthesis of unsupported Ni2P, and the detail is
described in the ESI. XRD measurement and transmission
electron microscope observation revealed that Ni3P crystal
phase was obtained by the temperature-programmed
reduction procedure (Fig. 3a and 3b). The XRD pattern of
synthesized Ni3P is compared with that of the spent catalyst
after treatment in water in program 2 at 350 °C initially with
Ni2P (Fig. S2). It is indicated that a pure Ni3P phase was
obtained by the temperature-programmed reduction whereas
a minor fraction of Ni3(PO4)2 was present in the spent catalyst.
The BET surface area of unsupported Ni3P was 3.2 m2 g-1. It has
⋅
the hydrogenation pathway, in agreement with the results of
Pd/C and H3PO4 bifunctional catalysts.6 Moon et al. reported
that the major oxygen-free product in the HDO of guaiacol on
Ni2P/SiO2 was benzene at 0.1 MPa whereas cyclohexane at 0.8
MPa.33 The dependences of the conversion and product
selectivities on reaction temperature are illustrated in Fig. 5a.
Ni3P showed high hydrogenation activity at low temperatures
been reported that metal phosphides are of bi-functional
nature, and the acidity is originated from P-OH on the
oxygenated surface and/or phosphates.32 The NH3-TPD profiles
of the unsupported Ni3P and Ni2P indicate that the surface
acidity of the unsupported Ni2P was stronger than that of the
unsupported Ni3P but both were considerably weaker than
that of HZSM-5 zeolite (Fig. 4).
(150-250 °C), converting phenol to cyclohexanol and a trace
In the HDO of phenol catalysed by the unsupported Ni3P or
Pd/SiO2 under the investigated reaction conditions, the
amount of cyclohexanone. The variation of equilibrium
conversion from phenol to cyclohexanol as a function of
temperature was calculated using the Aspen Plus 2006 V8.4
(Fig. S4). It is shown that the equilibrium conversion is 100% at
following
products
were
detected:
cyclohexanol,
cyclohexanone, cyclohexene and cyclohexane (Fig. S3).
Benzene was undetectable in the GC analysis. The absence of
benzene in the HDO product suggests that the aqueous phase
HDO of phenol over Ni3P or Pd/SiO2 proceeded exclusively via
temperatures of < 250
°C. Because cyclohexanol underwent
the subsequent reactions markedly above 250
°
C, there is no
equilibrium limitation under the investigated reaction
conditions. The removal of oxygen groups took place at higher
temperatures. For comparison, the variation of conversion and
product selectivities in phenol HDO catalyzed by Pd/SiO2 is
shown in Fig. 5b. In the low temperature range, lower phenol
conversion over Pd/SiO2 was obtained, and much more
cyclohexanone was detected in the product, indicating that
Ni3P exhibited higher low-temperature hydrogenation activity
than Pd/SiO2. The TOFs for the unsupported Ni3P and Pd/SiO2
at two different temperatures (Table 1) also suggest that Ni3P
was highly active in hydrogenation of aromatic ring in phenol
molecule.
Hydrogenation of aromatic ring in phenol molecule is a
prerequisite, and, as a result, high hydrogenation activity is
required in phenol HDO. Zhou et al. studied the structural and
electronic properties of Ni3P surface by first-principles
calculations.34 They concluded that Ni3P adopts the tetragonal
ꢁ
crystal structure belonging to space group I4 with lattice
constants of a=8.95 Å and c=4.39 Å, and that the Ni3P surfaces
with different terminations are all metallic. A comparative
study showed that the unsupported Ni3P showed much higher
HDO activity than the unsupported Ni (Fig. S5).
The stability of the unsupported Ni3P catalyst was
investigated in aqueous phase HDO of phenol both at high
conversion (300 °C) and at low conversion (150 °C) (Fig. S6). It
is shown that the phenol conversion and the product
selectivities were kept constant in the 50-h runs. The XRD
pattern of the spent catalyst indicated that the Ni3P phase
hardly changed after the 50-h run (Fig. S7).
Catechol, an important constituent from lignin
depolymerization and an intermediate in the conversion of
guaiacol or syringol,16,35,36 was chosen to investigate the
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 6 of 11
View Article Online
DOI: 10.1039/C7GC03262E
ARTICLE
Journal Name
stepwise aqueous phase conversion. As seen in Fig. 6a, over In the HDO of catechol over unsupported Ni3P, the absence of
unsupported Ni3P, the reactivity of catechol was slightly lower phenol and an abundant amount of cyclohexane-1,2-diol
than that of phenol. Similarly, in the low temperature range indicated that catechol HDO mainly proceeded in the
(150-250 °C), the saturation of aromatic ring predominated, hydrogenation and dehydration route. Ni3P serves as the
yielding mainly cyclohexane-1,2-diol and cyclohexanol. It is catalytically active site for hydrogenation, while the surface P-
apparent that Ni3P was highly active in catalyzing the OH groups catalyze the dehydration.
hydrogenation of aromatic ring. The deoxygenated products
(cyclohexene and cyclohexane) were detected in the high upgrading. Fig. 6b shows the variation of o-cresol conversion
temperature range. and product selectivities in the HDO catalyzed by the
Zhou et al.36 reported that, over Ni/HZSM-5, catechol was unsupported Ni3P. The conversion of o-cresol was markedly
hydrogenated to cyclohexane-1,2-diol (major) and lower than those of phenol and catechol, probably due to the
O-Cresol is another important intermediate in bio-oil
hydrogenolyzed to phenol (minor) in parallel routes. steric hindrance and electronic effect of the methyl group.38,39
Subsequently, cyclohexane-1,2-diol was further converted Similarly, in the low temperature range, the major reaction
through dehydration or hydrogenolysis to cleave the aliphatic was the saturation of the aromatic ring, yielding 2-methyl-
C-O bonds, while phenol was hydrodeoxygenated following cyclohexanol. On increasing the temperature, the yield of the
the conventional hydrogenation-dehydration route. However, hydrodeoxygenated product (methyl-cyclohexane) was
Zhao et al. found that, when catalyzed by Pd/C and H3PO4, the increased markedly at the expense of 2-methyl-cyclohexanol.
catechol conversion proceeded in the following route: metal- 2-methyl-cyclohexanone and methyl-cyclohexene were
catalyzed partial aromatic hydrogenation to form 2- present in trace amount.
hydroxycyclohexanone followed by hydrogenation to
Li et al. investigated the hydrogenation of o-cresol over a
cyclohexane-1,2-diol, and then converted to cyclohexanone supported Pt catalyst in batch reactions analyzed with an in
followed by hydrogenation to cyclohexanol.35 Over copper situ ATR IR probe.40 In combination with the calculation
chromite catalyst, hydrogenation of catechol took place in an according to ab initio density-functional theory, they
analogous route where the aromatic ring was hydrogenated suggested that o-cresol was hydrogenated to form 2-methyl-
to form cyclohexane-1,2-diol, followed by subsequent cyclohexanol,
with
2-methyl-cyclohexanone
as
the
dehydration and hydrogenation steps to form cyclohexane.37 intermediate. Thus, it could be concluded that the Ni3P-
catalyzed HDO of o-cresol might also occur through the
hydrogenation route: o-cresol → 2-methyl-cyclohexanone →
2-methyl-cyclohexanol
cyclohexane.
→ methyl-cyclohexene → methyl-
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 7 of 11
View Article Online
DOI: 10.1039/C7GC03262E
Journal Name
ARTICLE
To sum up, the Ni3P-catalyzed HDO of the phenolic result was obtained and the conversion at low temperatures
compounds (phenol, catechol, and o-cresol) in aqueous phase (<250 C) was lower than 100% (Fig. S9). It implies that the
°
proceeded exclusively in the hydrogenation route to form dissolution of H2 might be rate-limiting in the aqueous phase
cyclohexanes, indicating that Ni3P possessed significantly high HDO at low temperatures.
activity in hydrogenation in aqueous phase, suggesting that At low temperature (200 °C), the selectivity of cyclohexanol
Ni3P would be a widely-used catalytic phase in aqueous-phase was 98.5%, and those of cyclohexene and cyclohexane were
HDO of lignocellulosic biomass.
0.2% and 0.1%, respectively, in aqueous phase HDO. In
contrast, the selectivity of cyclohexanol was 67.6%, whereas
those of oxygen-free products (cyclohexene and cyclohexane)
were 20.5% and 11.3%, respectively. It suggests that Ni3P
showed higher dehydration activity in oil phase.
P-OH could bond with water to form H-bond (P-OH…Hw),43,44
thus suppressing the acid-catalyzed dehydration of
cyclohexanol in the aqueous phase. On the other hand, the H-
bond donating ability (Kamlet-Taft α) of water decreases as
water is heated,45,46 leading to increased dehydration activity
at elevated temperatures. Since P-OH…Hw could not be formed
in decalin, Ni3P presented moderate acidity to catalyze the
dehydration of cyclohexanol at low temperatures. The
selectivity of either cyclohexene or cyclohexane in the aqueous
phase HDO was negligible, whereas those of both cyclohexene
and cyclohexane became significant in the oil phase HDO at
Oil-phase HDO over Ni3P and Ni2P
In addition to aqueous phase HDO, the unsupported Ni3P was
also tested in HDO in an organic solvent (decalin), in
comparison with the unsupported Ni2P (Fig. 7). The XRD
patterns of spent Ni3P and Ni2P (Fig. S8) illustrated that, unlike
in aqueous phase HDO, both Ni3P and Ni2P were stable in the
oil phase HDO.
Fig. 7a showed that the unsupported Ni3P catalyzed the
phenol HDO to proceed in a similar reaction route, with
cyclohexanol, cyclohexene and cyclohexane as the main
oxygen-free products. Again, Ni3P exhibited high low-
temperature hydrogenation activity. In addition, Ni3P showed
higher activity in oil phase HDO than in aqueous phase HDS,
because the conversion was 100% in the investigated
temperature range (Fig. 7a). The lower reactivity of phenol in
aqueous phase might be ascribed to the lower solubility of H2
in water.41,42 When the concentration of phenol in the
aqueous solution was reduced from 5 wt% to 1 wt%, similar
low temperatures (200-250 °C). The increased selectivities of
cyclohexene and cyclohexane in the product suggest that the
acid-catalyzed dehydration was significantly enhanced in the
oil phase HDO. A large fraction of cyclohexene in the oxygen-
free product might be related to the polarity of the solvent.
Generally, solvent effects can influence the kinetics of
competitive hydrogenation reactions of polar and non-polar
substrates.47 A polar solvent enhances adsorption of the non-
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 8 of 11
View Article Online
DOI: 10.1039/C7GC03262E
ARTICLE
Journal Name
polar reactant and vice versa. When non-polar decalin was bonding capability between Ni atom and adatom was
used as the solvent, the weak-polar cyclohexene hardly enhanced, resulting in higher hydrogenation activity.
adsorbed on the surface of the catalyst, suppressing further
hydrogenation to form cyclohexane.
At the lowest temperature (150 °C), the selectivity of
cyclohexanol was 97.5% over the unsupported Ni3P, and 8.3%
Fig. 7b shows that, over the unsupported Ni2P, the over the unsupported Ni2P. On the other hand, the selectivity
conversion of phenol was much lower at low temperatures of cyclohexene was only 1.0% over Ni3P, whereas 90.8% over
than that over unsupported Ni3P, and the major product was Ni2P (Fig. 7). It suggests that Ni2P manifested higher
cyclohexene, indicating that the unsupported Ni2P exhibited dehydration activity of cyclohexanol. To verify the significant
poor hydrogenation activity at low temperatures.
difference in dehydration activity for Ni3P and Ni2P, the HDO of
The XPS spectra in the Ni 2p and P 2p regions for the cyclohexanol in decalin was comparatively conducted. Fig. S10
passivated Ni3P and Ni2P are shown in Fig. 8. Ni 2p core level shows that the HDO conversion to cyclohexene was 5.6% for
spectrum consists of two contributions, in which the first one Ni3P and 92.4% for Ni2P at 150 °C, proving that Ni2P was
is assigned to Niδ+ (partially reduced) in nickel phosphide phase superior to Ni3P in dehydration activity. The difference might
at 852.0-852.8 eV and the second one at 855.6-856.6 eV be ascribed to the different acidity of the two catalysts (Fig. 4).
corresponds to the possible interaction of Ni2+ ions with It was reported that metal phosphides were of bi-functional
phosphate ions, as a consequence of superficial passivation.48- nature. The acidity is originated from P-OH on the oxygenated
51 The ratio of the reduced Niδ+ to the oxidized Ni2+ in the XPS surface and/or phosphates.32 The more P-OH groups on the
spectra for Ni3P catalyst was higher than that for the Ni2P, surface of Ni2P catalyst might lead to higher acidity, which
suggesting that surficial Ni3P was more resistant to air enhanced the catalytic dehydration of cyclohexanol to form
exposure than Ni2P during the passivation and exposure to air. cyclohexene.
For Ni2P, the peak at 129.6 eV is assigned to the P 2p binding
To check if the acid-catalyzed cracking took place over
energy of the reduced Pδ-, and the one at 134.6 eV for P5+ in unsupported Ni2P and Ni3P, the outlet gas was analyzed by
metal phosphate generated by the superficial oxidation during means of gas chromatograph (Agilent, HP-AL/S capillary
passivation.52 For Ni3P, two peaks at 129.1 and 129.8 eV column and FID). It is shown that no gaseous hydrocarbons
appeared, and both were lower than elemental phosphorus were detectable, indicating that the acidity on Ni2P or Ni3P was
(130.2 eV). The two peaks are assigned to the reduced Pδ1- and not strong enough to catalyze the cracking reaction.
Pδ2- (δ1>δ2), respectively, while the peak centered at 132.8 eV
-
was ascribed to H2PO3 in the passivated layer of Ni3P
catalyst.53 Similarly, the total peak intensity of the two reduced
P species was higher than that of the oxidized P species,
suggesting that Ni3P catalyst was present at a more reduced
state. Moreover, the fact that the binding energy of Niδ+ in
Ni3P (852.6 eV) was slightly lower than that in Ni2P (852.7 eV)
while binding energy of Pδ- in Ni3P was higher (129.9 vs 129.6
eV) is an evidence for less transfer of electron density from Ni
to P atoms.54 Landau et al.55 studied the densities of states
(DOS) for Ni and P atoms in three nickel phosphide phases:
Ni2P, Ni12P5, and Ni3P. They concluded that the densities of p
states (Np) per P atom and the densities of d states (Nd) per Ni
atom at Fermi energy in the primitive cells for each phase
decreased in the following order: Ni2P > Ni12P5 > Ni3P. The ratio
of Nd/Np clearly showed that the relative fraction of the
directed d bonds increased from Ni2P to Ni3P by a factor of
1.43. It implies that the relative part of d electrons belonging
to Ni and participating in bonding with p electrons of P in NixP
phases decreased with the Ni/P ratio. As a result, in Ni3P, the
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 9 of 11
View Article Online
DOI: 10.1039/C7GC03262E
Journal Name
ARTICLE
Since catechol is insoluble in decalin, only the HDO of o- In aqueous phase, unsupported Ni2P was not stable and
cresol as the substituted phenol in decalin over the transferred stepwise into Ni3P at elevated temperature by an
unsupported Ni3P and the unsupported Ni2P were investigated appropriate temperature program. The unsupported Ni3P
(Fig. 9). For Ni3P, the conversion of o-cresol was lower than presented high and stable HDO activity, and was more active
that of phenol at low temperatures (150-250
probably due to the increased steric hindrance of the methyl Pd/SiO2(1.0 wt%).
group in o-cresol. At low temperatures, the major product was In decalin solution, the unsupported Ni3P showed higher
2-methylcyclohexanol, and slight fraction of 2- hydrogenation activity of the aromatic ring but lower
°C) (Fig. 9a), for the hydrogenation of the aromatic ring in phenol than
a
methylcyclohexene and methylcyclohexane were also present dehydration activity than the unsupported Ni2P in HDO at low
in the product. The low production of oxygen-free products temperatures, due to lower surface acidity of the unsupported
might be related with the low dehydration activity of the Ni3P. The XPS analysis revealed that the ratio of the reduced
unsupported Ni3P. The unsupported Ni2P showed much lower Niδ+ to the oxidized Ni2+ for Ni3P catalyst was higher than that
activity than the unsupported Ni3P, because Ni2P was less for the Ni2P, suggesting that surficial Ni3P was more resistant
active than Ni3P in the hydrogenation of the aromatic ring in o- to air exposure than Ni2P. Similarly, the total peak intensity of
cresol. Similarly, the adjacent methyl group also had a negative the two reduced P species was higher than that of the oxidized
effect on the hydrogenation of the aromatic ring. The low P species, suggesting that Ni3P catalyst existed at a more
activity and high selectivity to 2-methylcyclohexene at low reduced state. In addition, the binding energy of Niδ+ in Ni3P
temperature range in Ni2P-catalyzed HDO of o-cresol was slightly lower than that in Ni2P while binding energy of Pδ-
suggested that Ni2P was inferior in hydrogenation but superior in Ni3P was higher, indicating the less transfer of electron
in dehydration to Ni3P.
density from Ni to P atoms in Ni3P.
In addition, no toluene was detected in the product of HDO
In the aqueous HDO catalyzed by unsupported Ni3P, the
catalyzed by Ni3P or Ni2P, indicating that the HDO of o-cresol reactivity of phenols decreased in the order: phenol >
proceeded exclusively via the hydrogenation route. catechol > o-cresol. When decalin was used as the solvent,
Table summarizes the catalytic performance of phenol was also much more active than o-cresol over the
unsupported Ni3P in aqueous and oil phase HDO of phenols unsupported Ni3P. It may suggest that catechol and o-cresol
(phenol, catechol, and o-cresol) at 300 C and 4.0 MPa. It is was less active than phenol, probably due to the increased
2
°
indicated that the unsupported Ni3P exhibited higher HDO steric hindrance. In the oil phase HDOs of phenol and cresol,
activity in decalin than in water. In aqueous phase, the the unsupported Ni3P also exhibited superior hydrogenation
reactivity of phenols decreased in the order: phenol > catechol activity to the unsupported Ni2P.
> o-cresol, and the reactivity order in oil phase was: phenol >
o-cresol. It seems that the adjacent hydroxyl group in catechol
Conflicts of interest
and methyl group in o-cresol suppressed the hydrogenation of
the aromatic ring, probably due to the steric and electronic
effects. For all the phenolic compounds, no oxygen-free
aromatic compound (benzene or toluene) was produced in the
investigated conditions, suggesting that the hydrogenation-
dehydration-hydrogenation route is the exclusive route for the
HDO of the investigated phenolic compounds. In addition, the
unsupported Ni3P showed superior hydrogenation activity of
the aromatic ring in the phenolic compounds at low
temperatures in both aqueous and oil phases.
There are no conflicts to declare.
Acknowledgements
This work was financially supported by NSFC (21073022,
21173033, 21473017, 21603024, U1162203, U1508205) and
The Ph.D. Programs Foundation (MOE, 20100041110016). J.A.L
and D.M.C. acknowledge support by the U.S. Department of
Energy (DOE), Office of Science, Office of Basic Energy
Sciences, Division of Chemical Sciences, Geosciences
&
Biosciences. Pacific Northwest National Laboratory is operated
for DOE by Battelle Memorial Institute.
Conclusions
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 10 of 11
View Article Online
DOI: 10.1039/C7GC03262E
ARTICLE
Journal Name
32.
A. Infantes-Molina, E. Gralberg, J. A. Cecilia, E. Finocchio
References
and E. Rodriguez-Castellon, Catal. Sci. Technol., 2015,
5
,
1.
2.
3.
A. Corma, S. Iborra and A. Velty, Chem. Rev., 2007, 107
2411.
P. M. Mortensen, J. D. Grunwaldt, P. A. Jensen, K. G.
Knudsen and A. D. Jensen, Appl. Catal., A, 2011, 407, 1.
E. Laurent and B. Delmon, Ind. Eng. Chem. Res., 1993, 32
2516.
,
3403.
33.
34.
35.
36.
37.
38.
39.
J. S. Moon, E. G. Kim and Y. K. Lee, J. Catal., 2014, 311
,
144.
L. Zhou, Y. Kong, Y. Du, J. Wang and Y. Zhou, Appl. Surf.
Sci., 2010, 256, 7692.
C. Zhao, J. He, A. A. Lemonidou, X. Li and J. A. Lercher, J.
Catal., 2011, 280, 8.
W. J. Song, Y. S. Liu, E. Barath, C. Zhao and J. A. Lercher,
Green Chem., 2015, 17, 1204.
,
4.
5.
D. C. Elliott, Energy Fuels, 2007, 21, 1792.
T. R. Viljava, R. S. Komulainen and A. O. I. Krause, Catal.
Today, 2000, 60, 83.
6.
C. Zhao, Y. Kou, A. A. Lemonidou, X. Li and J. A. Lercher,
Angew. Chem., Int. Ed., 2009, 48, 3987.
M. Wang, H. Shi, D. M. Camaioni and J. A. Lercher, Angew.
Chem., Int. Ed., 2017, 56, 2110.
K. L. Deutsch and B. H. Shanks, Appl. Catal., A, 2012, 447
,
144.
7.
V. O. O. Gonçalves, P. M. de Souza, V. T. da Silva, F. B.
Noronha and F. Richard, Appl. Catal., B, 2017, 205, 357.
F. E. Massoth, P. Politzer, M. C. Concha, J. S. Murray, J.
8.
X. Xu, Y. Li, Y. Gong, P. Zhang, H. Li and Y. Wang, J. Am.
Chem. Soc., 2012, 134, 16987.
Jakowski and J. Simons, J. Phys. Chem. B, 2006, 110
,
9.
S. Crossley, J. Faria, M. Shen and D. E. Resasco, Science,
2010, 327, 68.
14283.
40.
41.
Y. Li, Z. Liu, W. Xue, S. P. Crossley, F. C. Jentoft and S.
Wang, Appl. Surf. Sci., 2017, 393, 212.
J. He, C. Zhao and J. A. Lercher, J Catal, 2014, 309, 362-
375.
L. R. Snyder, J. Chromatogr. A, 1974, 92, 223.
R. Costard, T. Tyborski, B. P. Fingerhut and T. Elsaesser, J.
Chem. Phys., 2015, 142, 212406.
E. Tang, D. D. Tommaso and N. H. d. Leeuw, J. Chem.
Phys., 2009, 130, 234502.
Y. Marcus, Chem. Soc. Rev., 1993, 22, 409.
J. Lu, J. S. Brown, C. L. Liotta and C. A. Eckert, Chem.
Commun., 2001, 7, 665.
E. Willinger, Y. Yi, A. Tarasov, R. Blume, C. Massué, F.
Girgsdies, C. Querner, E. Schwab, R. Schlögl and M. G.
Willinger, ChemCatChem, 2016, 8, 1575.
10.
11.
A. Aqsha, L. Katta and N. Mahinpey, Catal. Lett., 2015,
145, 1351.
V. A. Yakovlev, S. A. Khromova, O. V. Sherstyuk, V. O.
Dundich, D. Y. Ermakov, V. M. Novopashina, M. Y.
Lebedev, O. Bulavchenko and V. N. Parmon, Catal. Today,
2009, 144, 362.
42.
43.
12.
13.
J. Y. He, C. Zhao and J. A. Lercher, J. Am. Chem. Soc., 2012,
134, 20768.
J. Han, J. Duan, P. Chen, H. Lou, X. Zheng and H. Hong,
Green Chem., 2011, 13, 2561.
44.
45.
46.
14.
15.
C. J. Chen and A. Bhan, ACS Catal., 2017, 7, 1113.
I. T. Ghampson, C. Sepúlveda, R. Garcia, L. R. Radovic, J. L.
G. Fierro, W. J. DeSisto and N. Escalona, Appl. Catal., A,
2012, 439-440, 111.
47.
16.
17.
H. Y. Zhao, D. Li, P. Bui and S. T. Oyama, Appl. Catal., A,
2011, 391, 305.
S. Ted Oyama, T. Onkawa, A. Takagaki, R. Kikuchi, S.
48.
49.
S. Oyama, J. Catal., 2002, 210, 207.
J. A. Cecilia, A. Infantes-Molina, E. Rodríguez-Castellón
and A. Jiménez-López, J. Catal., 2009, 263, 4.
S. J. Sawhill, K. A. Layman, D. R. Van Wyk, M. H.
Hosokai, Y. Suzuki and K. Bando, Top. Catal., 2015, 58
201.
,
50.
Engelhard, C. Wang and M. E. Bussell, J. Catal., 2005, 231
,
18.
19.
Y. Li, J. Fu and B. Chen, RSC Adv., 2017,
S. K. Wu, P. C. Lai, Y. C. Lin, H. P. Wan, H. T. Lee and Y. H.
Chang, ACS Sustainable Chem. Eng., 2013, , 349.
7, 15272.
300.
51.
52.
53.
54.
55.
X. Liu, J. Chen and J. Zhang, Ind. Eng. Chem. Res., 2008, 47
,
1
5362.
20.
21.
22.
S. T. Oyama and Y. Lee, J. Catal., 2008, 258, 393.
R. Prins and M. E. Bussell, Catal. Lett., 2012, 142, 1413.
T. I. Koranyi, A. E. Coumans, E. J. M. Hensen, R. Ryoo, H. S.
Kim, E. Pfeifer and Z. Kasztovszky, Appl. Catal., A, 2009,
365, 48.
H. Song, M. Dai, Y. T. Guo and Y. J. Zhang, Fuel Process
Technol., 2012, 96, 228.
J. F. Li, Y. M. Chai, B. Liu, Y. L. Wu, X. H. Li, Z. Tang, Y. Q.
Liu and C. G. Liu, Appl. Catal., A, 2014, 469, 434.
D. Fuks, D. Vingurt, M. V. Landau and M. Herskowitz, J.
Phys. Chem. C, 2010, 114, 13313.
M. V. Landau, M. Herskowitz, T. Hoffman, D. Fuks, E.
Liverts, D. Vingurt and N. Froumin, Ind. Eng. Chem. Res.,
2009, 48, 5239.
23.
24.
Q. Guan, X. Cheng, R. Li and W. Li, J. Catal., 2013, 299, 1.
X. Duan, Y. Teng, A. Wang, V. Kogan, X. Li and Y. Wang, J.
Catal., 2009, 261, 232.
25.
26.
Y. Xue, Q. Guan and W. Li, RSC Adv., 2015,
P. F. Yang, H. Kobayashi, K. Hara and A. Fukuoka,
ChemSusChem, 2012, , 920.
5, 53623.
5
27.
28.
29.
E. Furimsky, Appl. Catal., A, 2000, 199, 147.
S. T. Oyama, J. Catal., 2003, 216, 343.
K. L. Li, R. J. Wang and J. X. Chen, Energy Fuels, 2011, 25
854.
,
30.
31.
Y. Suzuki, S. Arai, I. Shohji and E. Kobayashi, J.
Electrochem. Soc., 2009, 156, 283.
J. Ren, J. Wang, J. Li and Y. Li, J. Fuel Chem. Technol., 2007,
35, 458.
10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 11 of 11
Green Chemistry
View Article Online
DOI: 10.1039/C7GC03262E
Ni3P as a High-Performance Catalytic Phase for Hydrodeoxygenation
of Phenolic Compounds
Ni3P shows extremely high activity and stability in phenol hydrodeoxygenation both in aqueous
phase and in organic phase.