Pt/Ferric Hydroxyphosphate: An Effective Catalyst for the Selective Hydrogenation of Α,Β-Unsaturated Aldehydes (Ketones) into Α,Β-Unsaturated Alcohols

Article abstract of DOI:10.1007/s10562-017-2280-5

Abstract: Four micro (nano)-sized mesoporous ferric hydroxyphosphates (FHP) are synthesized by a reverse microemulsion-solvothermal method, and then are used as supports to prepare supported Pt catalysts. The mean particle diameter of Pt nanoparticles (NPs) was 4.5–4.6?nm. When the four different Pt/FHP catalysts were used into the hydrogenation of α,β-unsaturated aldehydes (ketones) to their corresponding unsaturated alcohols, Pt/FHP (c) catalyst showed better catalytic performance than the other three partners. Under the optimal experimental conditions, several tested α,β-unsaturated aldehydes could be effectively transformed into corresponding unsaturated alcohols over Pt/FHP (c) catalyst. The catalyst could be recycled and reused several times without activity loss. We propose the stronger interaction between the Pt NPs and ferric ions of the FHP (c) are responsible for its good catalytic performance, and this stronger interaction should be rooted in its enhanced Lewis acid strength.

Full text of DOI:10.1007/s10562-017-2280-5

Catalysis Letters
https://doi.org/10.1007/s10562-017-2280-5
Pt/Ferric Hydroxyphosphate: An Effective Catalyst for the Selective
Hydrogenation of α,β-Unsaturated Aldehydes (Ketones) into α,β-
Unsaturated Alcohols
1
1
1
1
1
1
2
3
3
Cheng Liu · Wei Luo · Junhua Liu · Lei Sun · Yue Yang · Gui Liu · Fang Wang · Wei Zhong · Curtis Guild ·
Steven L. Suib3
Received: 1 August 2017 / Accepted: 18 December 2017
©
Springer Science+Business Media, LLC, part of Springer Nature 2017
Abstract
Four micro (nano)-sized mesoporous ferric hydroxyphosphates (FHP) are synthesized by a reverse microemulsion-solvo-
thermal method, and then are used as supports to prepare supported Pt catalysts. The mean particle diameter of Pt nanopar-
ticles (NPs) was 4.5–4.6 nm. When the four different Pt/FHP catalysts were used into the hydrogenation of α,β-unsaturated
aldehydes (ketones) to their corresponding unsaturated alcohols, Pt/FHP (c) catalyst showed better catalytic performance
than the other three partners. Under the optimal experimental conditions, several tested α,β-unsaturated aldehydes could
be effectively transformed into corresponding unsaturated alcohols over Pt/FHP (c) catalyst. The catalyst could be recycled
and reused several times without activity loss. We propose the stronger interaction between the Pt NPs and ferric ions of the
FHP (c) are responsible for its good catalytic performance, and this stronger interaction should be rooted in its enhanced
Lewis acid strength.
Graphical Abstract
Keywords α,β-Unsaturated aldehydes (ketones) · Ferric hydroxyphosphates · Lewis acid · Pt nanoparticles · Selective
hydrogenation
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-017-2280-5) contains
supplementary material, which is available to authorized users.
2
*
Junhua Liu
College of Chemistry and Molecular Engineering, Nanjing
Tech University, Nanjing 211816, China
liujh2007@aliyun.com
3
*
Fang Wang
Department of Chemistry, University of Connecticut, Storrs,
CT 06269, USA
wangfang2012@njtech.edu.cn
1
College of Chemistry and Materials Science, Nanjing
Normal University, Nanjing 210023, China
Vol.:(0
1
123456789)
3

C. Liu et al.
1
Introduction
2 Experimental
Selective hydrogenation of α,β-unsaturated aldehydes
ketones) is of great importance, both from an academic
2.1 Preparation of FHP Materials
(
and industrial point of view [1]. In such compounds,
hydrogenation can occur either at the olefinic (C=C) or
carbonyl (C=O) groups. The hydrogenation of the olefinic
group leads to saturated aldehydes, while reaction of the
carbonyl group yields unsaturated alcohols. Allylic alco-
hols represent key building blocks in the pharmaceutical,
agrochemical, fine-chemical, and fragrance industries
All the reagents were all obtained from commercial
sources without any further purification. For the prepara-
tion of catalyst supports FHP (a–d), aqueous solutions of
Fe(NO ) ·9H O (0.025 mol) and either NaH PO ·2H O (mol
3
3
2
2
4
2
ratio 1:1) (FHPa), Na PO ·12H O (mol ratio 1:1) (FHPb),
3
4
2
Na PO ·12H O (mol ratio 1:1) (FHPc), or (NH ) PO ·3H O
3
4
2
4 3
4
2
(mol ratio 1:1) (FHPd) were prepared to give solution A
(15 ml). 4 g Cetyl trimethyl ammonium bromide (CTAB),
2 g poly(oxyethylene)-10-nonylphenol ether (NP-10) and
5 ml butanol were added to cyclohexane to make an organic
solution (solution B, 75 ml). Then solutions A and B were
mixed, the pH value was adjusted to 8–10 for the prepara-
tion of FHP (a) and FHP (d) using 4 mol/l NaOH solutions
and aqueous ammonia, respectively. The mixture was aged
at 200 °C for 48 h in an autoclave, and then the mixture was
centrifuged and washed with absolute ethanol and water.
After drying overnight in a vacuum oven at 80 °C, the prod-
uct was calcined at 500 °C for 4 h.
[
2]. However, the reduction of the C=C double bond is
thermodynamically more favorable, and hence the selec-
tive hydrogenation of the carbonyl in high yields are very
difficult.
A large number of supported Ir, Pt, Ph, Ru and Au cat-
alysts have been reported for this transformation [3–7],
where Pt is most commonly used for the reaction. Several
parameters, such as support, metal particle size, addi-
tives/promoters/composition, preparation method, cata-
lyst precursor, etc., have been proposed to influence the
intramolecular hydrogenation selectivity [8, 9]. However,
the key factors that control the activity and selectivity in
the hydrogenation of α,β-unsaturated aldehydes (ketones)
remain unclear. Among these, Pt nanoparticles modified
with Fe, Sn, Ga, or Co are demonstrated as effective cata-
lysts and achieve high selectivity because of electronic and
structural effects [9, 10]. Mechanistically, the selectivity
for unsaturated alcohols can be enhanced by the polariza-
tion of the C=O group or by hindering the adsorption of
the substrate through the C=C group. This can be accom-
plished by modulating the interaction between the ionic
metal species and the oxygen of carbonyl group [11].
Proper selection of support is a facile way to influence
the activity of Pt in the reaction. Using reducible “active”
supports is a common method as the variable valency of
the metals facilitates the generation of electron deficient
centers on the catalyst surface [12]. Ferric hydroxyphos-
phate draws our attention due to the “reducible” struc-
tural features and rich surface hydroxyl concentration.
Recently, we reported a sodium iron hydroxyphosphate
2.2 Preparation of Pt/FHP Catalyst
A series of FHP supported platinum catalysts were prepared
by impregnation method (3 wt%). Typical procedures are
−
6
as follows: H PtCl ·6H O (3.8 × 10 M) and poly(vinyl
2
6
2
pyrrolidone) (0.142 g) in a mixed solvent of water-ethanol-
isopropanol was aged at 110 °C for 5 h. To this 0.5 g of four
different FHP (0.5 g) materials were suspended for 24 h,
respectively. The FHP supported platinum nanoparticles
were filtered and washed with distilled water. ICP analysis
indicated that all platinum particles were adsorbed on the
supports. The catalysts were dried under vacuum at 338 K.
The obtained catalysts were labeled Pt/FHP (a), Pt/FHP (b),
Pt/FHP (c) and Pt/FHP (d), respectively.
2.3 Catalyst Characterization
The morphologies of obtained Pt/FHP catalysts were
examined by transmission electron microscope (HRTEM)
(JEM-2010) and scanning electron microscopy (SEM)
(JSM-7600F). The crystalline aspects of the catalysts were
studied by X-ray diffraction (XRD) (X’Pert PRO PANalyti-
cal). X-ray photoelectron spectroscopy (XPS) was performed
using a K-Alpha-surface Analysis system with X-Ray Mono-
chromatisation. The fourier transformed-infrared spectros-
copy (FT-IR) and pyridine-IR spectra of samples were
obtained on a Bruker Tensor 27 spectrometer, the spectrom-
eter was equipped with MCT detector cooled by liquid nitro-
gen, the amount of acid sites on the sample was calculated
(
SIHP, Na Fe(PO ) H O) supported gold catalyst
4.55 4 2 0.45
showing excellent catalytic activity for the oxidations of
sulfides to sulfoxides [13]. To overcome their low surface
area, this material was constructed with a mesoporous
structure. In this article, four kinds of different structural
ferric hydroxyphosphates (FHPa–d) are synthesized by
the same procedure then used to prepare supported Pt
catalysts. Interestingly, the Pt/Fe (PO ) (OH) catalyst
3
4 2
2
showed excellent catalytic activity for the hydrogenation
of α,β-unsaturated aldehydes to corresponding unsaturated
alcohols.
1
3

Pt/Ferric Hydroxyphosphate: An Effective Catalyst for the Selective Hydrogenation of…
by measuring the IR peak area of pyridine adsorbed. Specific
possesses a single crystalline phase. The phases for each
catalyst respectively are (a) Na Fe (PO ) H O (JCPDS
surface areas were measured by N adsorption–desorption at
2
4.55
4 2 0.45
7
7 K with an ASAP 2010 instrument. Inductively coupled
no. 52-1393), (b) Fe (PO ) (OH) ·2H O (JCPDS no.
5 4 4 3 2
plasma optical emission spectroscopy (ICP-OES) analyses
were carried out using a Varian ICP-OES 720ES apparatus.
Temperature-programmed reduction (TPR) of catalysts was
conducted in a programmable tube furnace equipped with
a gas analyzer MKS coupled with a quadruple mass selec-
tive detector, about 100 mg of materials were packed in a
quartz tube reactor mounted into the tube furnace, tests were
performed from room temperature to 800 °C with a heating
ramp rate of 10 °C/min.
45-1436), (c) Fe (PO ) (OH) (JCPDS no. 36-0045) and
3 4 2 2
(d) Fe (PO ) (OH) (JCPDS no. 42-0429). This indi-
4
4 3
3
cates the formation of four different FHP under the pre-
sent experimental conditions. Diffraction peaks at 39.7,
46.1 and 67.7° are corresponding to the reflections from
(111), (200) and (220) planes of metallic platinum [9].
However in our Pt/FHP catalysts, no obvious diffraction
peaks assigned to platinum are observed. Figure 1b shows
the FT-IR spectra for the four Pt/FHP catalysts showing
typical peaks for phosphates at ca. 465, 582, 736 and
−
1
2.4 Catalyst Test
1019 cm , along with two hydroxide absorption bands at
−
1
about 1644 and 3411 cm [14].
Hydrogenation of α,β-unsaturated aldehydes (ketones) was
performed with magnetic stirring in a stainless autoclave.
Typically, the autoclave was charged with 0.05 g of Pt/FHP
catalyst, 1 ml of α,β-unsaturated aldehydes, and 5 ml of iso-
propanol. Air was removed by sweeping the system three
times with hydrogen before it was pressurized to the desired
Figure 2 presents representative TEM images of the
four Pt/FHP catalysts. Although the order of surface
2
area of the supports was FHP (a) (41.8 m /g) ≈ FHP (c)
2
2
2
(41.2 m /g) > FHP (d) (18.2 m /g) > FHP (b) (8.6 m /g),
all the Pt NPs are well distributed on the FHP supports and
have diameters of 4.5–4.6 nm, the size of Pt NPs has noth-
ing to do with surface area. Fig. S1 (Supporting Informa-
tion) shows the nitrogen adsorption–desorption isotherms
of the four catalysts, all of which are Type H3 hysteresis
loops, which are attributed to the aggregation of nanopar-
ticles giving rise to slit-shaped pores [15].
H pressure, then the reaction was started by immersing the
2
flask in the oil bath kept at the reaction temperature. The
products were analyzed by gas chromatography (GC 9560)
with a DB-1 capillary column.
Figure 3 presents SEM images of the four Pt/FHP
catalysts, which have different morphologies. Pt/FHP
3
Results and Discussion
(
a) and Pt/FHP (c) catalysts are formed by the clusters
3.1 Catalyst Characterization
of nanospheres, with the particle size of the former
(
300–500 nm) being larger than that of the Pt/FHP (c)
Figure 1a shows the XRD patterns of the four Pt-FHP
catalysts. The diffractions indicate that each catalyst
(100–200 nm). The Pt/FHP (b) catalyst is composed of a
number of sheets with length about 5–8 μm. The Pt/FHP
Fig. 1 XRD and FT-IR patterns of (a) Pt/Na Fe (PO ) H O, (b) Pt/Fe (PO ) (OH) ·2H O, (c) Pt/Fe (PO ) (OH) , (d) Pt/Fe (PO ) (OH)
3
4
.55
4 2 0.45
5
4 4
3
2
3
4 2
2
4
4 3
catalysts
1
3

C. Liu et al.
Fig. 2 TEM pictures of (a) Pt/Na Fe (PO4) H O, (b) Pt/Fe (PO ) (OH) ·2H O, (c) Pt/Fe (PO ) (OH) , (d) Pt/Fe (PO ) (OH) catalysts
4
.55
2
0.45
5
4 4
3
2
3
4 2
2
4
4 3
3
and (e–h) corresponding Pt particle size distribution
Fig. 3 SEM images of (a) Pt/Na4.55Fe (PO ) H O, (b) Pt/Fe (PO ) (OH) ·2H O, (c) Pt/Fe (PO ) (OH) , (d) Pt/Fe (PO ) (OH) catalysts
4 2
0.45
5
4 4
3
2
3
4 2
2
4
4 3
3
1
3

Pt/Ferric Hydroxyphosphate: An Effective Catalyst for the Selective Hydrogenation of…
Fig. 4 XPS spectra of (A) Fe 2p and (B) Pt 4f for (a) Pt/Na Fe (PO ) H O, (b) Pt/Fe (PO ) (OH) ·2H O, (c) Pt/Fe (PO ) (OH) , (d) Pt/Fe
4.55
4 2 0.45
5
4 4
3
2
3
4 2
2
4
(
PO ) (OH) catalysts
4 3 3
HO
(
d) catalyst is formed by brick-like particles, with lengths
R
1
H
of about 3–5 μm. No platinum aggregation was observed
by microscopy.
O
R
2
OH
R1
UA
R
1
H
H
The XPS of Fe 2p and Pt 4f of four Pt/FHP catalysts
are shown in Fig. 4. Generally speaking, the binding
energy (BE) of Fe 2p is about 709 eV for Fe(II) and
O
R
2
R2
R1
SA
H
3
/2
R
2
7
11 eV for Fe(III) [16]. As can be seen from Fig. 4A,
SD
all the peaks for Fe 2p of these four Pt/FHP catalysts
3
/2
appear at 710.2–710.9 eV. Considering the iron source
Scheme 1 Proposed schemes on the hydrogenation of α,β-
(
ferric nitrate) and preparation procedures, all samples
unsaturated aldehydes (ketones)
should be mainly Fe(III) valence; however, all of them
have a negative shift than the values reported in the litera-
ture (711 eV). Pt/FHP (c) catalyst is significantly lower
than the other three catalysts, with a negative shift of
3.2 Catalyst Activity
0
.8 eV. The satellite peak at about 717 eV is a charac-
The hydrogenation of α,β-unsaturated aldehydes (ketones)
involves the parallel and consecutive reduction of C=C and
C=O bonds functional groups in the molecule. The products
obtained were unsaturated alcohols (UA), saturated alde-
hydes/ketones (SD), and saturated alcohols (SA). The reac-
tion pathways involved are shown in Scheme 1.
teristic of Fe(III) in γ-Fe O [17]. This result shows all
2
3
of the four compounds are mixed with a small amount of
Fe O phase.
2
3
0
2+
4+
It is known that the Pt 4f BE of Pt , Pt and Pt is
7
/2
around 71.6, 72.4–74.0 and 75.9–76.1 eV, respectively
[
18]. According to previous literature, Pt species should
The hydrogenation of cinnamaldehyde (CAL) was exam-
ined as a model reaction over Pt/FHP catalysts and the reac-
tion conditions were optimized (Table 1). When the reac-
tions are carried on the four different Pt/FHP catalysts, the
Pt/FHP (c) catalyst exhibits high activity, with the conver-
sion and selectivity to cinnamyl alcohol at 94.2 and 90.2%,
respectively (entries 1–4, Table 1). Different solvents were
used under the same reaction conditions. Obviously, solvent
interaction with metal surface could enhance or hamper the
hydrogenation rate of CAL, it was found that the hydrogena-
tion rate of CAL depends on the solvent as it follows: isopro-
panol>cyclohexanol>ethanol>hexanol>benzene (entries
be reduced to zero-valent state when the temperature is
over 350 °C using H -reduction method [19]. XPS spec-
2
tra of Pt 4f for our four catalysts situates the peak at
7
/2
7
2.0–72.8 eV, the Pt 4f7/2 BEs of these four Pt/FHP cata-
lysts have positive shifts (0.4–1.2 eV). Especially for Pt/
FHP (c) catalyst, there is a 1.2 eV positive shift. Con-
sidering there is a negative shift of 0.8 eV for the Fe
2
p
species, it can be concluded that there is an electron
3/2
transfer from the platinum species to iron. The detailed
Bes of Fe 2p and O 1s are given in Table S1 (Support-
3
/2
ing Information).
1
3

C. Liu et al.
Table 1 Selective
Conv.%b
Product sel. (%)b
Entry
Catalyst
Solvents
Tempera-
hydrogenation of CAL over Pt/
ture/℃
a
FHP catalysts
UA
SD
SA
Others
1
2
3
4
5
6
7
8
9
Pt/FHP (a)
Pt/FHP (b)
Pt/FHP (c)
Pt/FHP (d)
Pt/FHP (c)
Pt/FHP (c)
Pt/FHP (c)
Pt/FHP (c)
Pt/FHP (c)
Pt/FHP (c)
Pt/FHP (c)
FHP (c)
Isopropanol
Isopropanol
Isopropanol
Isopropanol
Ethanol
Hexanol
Cyclohexanol
Toluene
Isopropanol
Isopropanol
Isopropanol
Isopropanol
Isopropanol
Isopropanol
Isopropanol
Isopropanol
60
60
60
60
60
60
60
60
25
40
80
60
60
60
60
80
37.6
17.6
94.2
67.2
20.5
6.4
30.4
1.1
56.8
74.9
100
1.3
23.1
69.2
90.2
42.0
96.7
57.5
83.1
15.2
80.9
84.7
82.2
70.0
–
62.5
24.4
1.6
38.4
1.6
22.0
6.6
–
8.3
4.8
0
3.8
–
14.4
6.4
8.2
19.6
1.7
10.0
6.0
84.8
10.8
10.5
17.1
27.2
–
–
–
–
–
–
10.5
4.3
–
–
–
0.7
–
–
–
3.3
–
10
11
12
13
14
15
16
c
Pt/FHP (c)
Pt/Fe O
–
28.5
30.0
11.6
91.5
89.3
32.7
4.6
4.7
49.2
3.9
2.7
18.1
2
3
Pt/Fe(OH)3
Pt/CNTs
d
a
Reaction conditions: catalyst 0.05 g (Pt: 0.8% mmol), substrate 8 mmol, solvent 5 ml, H 2 Mpa, 60 min
Determined by GC
2
b
c
d
N 2 Mpa, without H , 10 h
2
2
Ref. [22]
5
–8, Table 1). Overall, the hydrogenation rate of CAL
and H adsorption on platinum is crucial for this reaction.
2
increased gradually with polarity of solvents except ethanol,
and the affinity of the aromatic solvent for the metal surface
hampers this reaction [20]. The polarity of solvent was deter-
mined by dielectric constant ε: ethanol (ε: 24.3) > isopro-
panol (ε: 18.3)>cyclohexanol (ε: 15.0)>hexanol (ε: 13.3).
However, alcoholic solvents are able to interact with CAL
through hydrogen bond, which strongly solvate the CAL
molecule. The carbon chain length and type of alcohols
have significant effect on solvation, and the hydrogenation
rate of substrate should be opposite to their solvation, that
is to say, the adsorption of reactant on the catalyst becomes
more difficult due to the increasing solvation. As the solva-
tion could be in the order as follows: isopropanol<ethanol
In addition, Fe O , Fe(OH) and carbon nanotubes (CNTs)
2
3
3
supported Pt catalysts were used for comparison on the
hydrogenation of CAL (entries 14–16, Table 1), obviously,
FHP(c) are far superior to these partners.
Next, various different α,β-unsaturated aldehydes
(ketones) were hydrogenated to corresponding enols over
the Pt/FHP (c) catalyst and the results can be seen in
Table 2. Cinnamaldehyde, but-2-enal and hex-2-enal were
hydrogenated to corresponding unsaturated aldehydes at
short times, all in good yields (higher than 83.3%). Obvi-
ously, the reaction time needs to be extended with the
increase of the carbon chain (Table 2, entries 1, 3–5).
Several kinds of cycloenones and heterocyclic aldehydes,
such as 2-cyclohexen-1-one, furan-2-carbaldehyde and
thiophene-2-carbaldehyde were effectively transferred to
corresponding enols, and the catalytic performance for
2-cyclohexen-1-one are higher than for heterocyclic alde-
hydes (Table 2, entries 6–8). Moreover, carvone can be
effectively hydrogenated to enols at relatively long reac-
tion times, 91.2% conversion of carvone and 100% enol
selectivity at 24 h (Table 2, entry 9). We also investigated
reusability, with very good results obtained the catalyst
was recycled five times (Table 2, entry 2) (detailed data
can be seen in Table S2). ICP analysis indicated that the
amount of Pt species leaching after five cycles from the
initial catalyst was negligible (lower than the detection
limit).
[
21], this is why the isopropanol solvent shows best catalytic
performance.
The experiments also showed appropriate temperature
was important for this reaction, as high or low tempera-
tures could not give good product selectivity (entries
9
–11, Table 1). Therefore, the optimal solvent and reac-
tion temperature for this system is isopropanol and 60 °C.
Moreover, an experiment was performed over FHP (c)
material without platinum under the same reaction condi-
tions yielded 1.3% conversion of cinnamaldehyde (entry
1
2
1
2, Table 1), meanwhile, another test was performed with
MPa of N instead of H over Pt/FHP (c) catalyst (entry
2
2
3, Table 1) and no reaction at all was observed. The
results show that no H-transfer of protic solvent takes place
1
3

Pt/Ferric Hydroxyphosphate: An Effective Catalyst for the Selective Hydrogenation of…
Table 2 Selective
Conv.%b
b
Entry
Substrate
Product
Time (h)
Product sel. (%)
hydrogenation of different
α,β-unsaturated carbonyl
compounds over Pt/FHP (c)
UA
83.3
92.0
96.2
SD
2.4
SA
14.3
6.9
1
2
3
O
OH
1.5
1.5
7
100
98.9
100
c
1.1
1.8
a
catalysts
O
O
OH
2.0
H
H
H
OH
4
5
6
6
9
3
98.7
96.0
97.5
93.6
97.3
63.5
2.1
1.0
–
4.3
H
O
OH
1.7
O
OH
36.5
7
8
9
9
97.3
100
100
100
97.2
–
–
–
–
CHO
CH
2
OH
OH
O
S
O
S
12
24
–
CHO
CH
2
O
OH
91.2
2.8
aReaction conditions: catalyst 0.05 g (Pt: 0.8% mmol), cinnamaldehyde 8 mmol, solvent 5 ml, H
2
2
MPa, 60 °C
b
Determined by GC
Recycled test (5th)
c
Fig. 5 (A) Pyridine-IR and (B) H -TPR spectra of (a) Na Fe (PO ) H0.45O, (b) Fe5 (PO ) (OH) ·2H O, (c) Fe (PO ) (OH) , (d) Fe
2
4.55
4 2
4 4
3
2
3
4 2
2
4
(
PO ) (OH) materials
4 3 3
3
.3 Discussion
FHP (d) have certain of Brønsted acid sites. Combing with
the NH -TPD data, FHP (c) have more Lewis strong acid
3
In four different Pt/FHP catalysts, Pt/FHP (c) catalyst
showed excellent catalytic activity for the hydrogenation
of α,β-unsaturated aldehydes to corresponding unsaturated
alcohols. In order to find this reason, pyridine-IR analysis of
four FHP materials were performed (Fig. 5A). Absorbance
than others.
TEM showed all the Pt NPs are well distributed on the
FHP supports and the size of Pt NPs is well distributed
(4.5–4.6 nm). The BET surface area of FHP (a) and FHP (c)
is almost the same, and the catalytic results suggest the Pt NPs
and BET surface area is not the root of the different catalytic
performances. XPS inferred the occurrence of electron transfer
from the platinum species to iron for these four Pt/FHP cata-
lysts, with the intensity of Pt/FHP (c) catalyst stronger than the
other three tested candidates. Moreover, the FHP (c) has more
Lewis strong acid than the other three partners; the existence
−
1
band at 1445 cm can be attributed to pyridine adsorbed
−
1
on Lewis acid sites, the peaks at 1587 and 1440 cm are
corresponding to hydrogen-bonded pyridine, the absorbance
−
1
bands at 1641 cm belong to Brønsted acid sites [23, 24].
Other three materials have Lewis acid sites except FHP (a)
and the FHP (c) has more Lewis acid sites. FHP (b) and
1
3

C. Liu et al.
of Lewis acid sites on the catalyst surface has been found to
promote the formation of the unsaturated alcohol because they
provide suitable adsorption sites for the carbonyl [10]. Moreo-
ver, since the FHP (c) has more Lewis acid strength, elec-
tron transfer from the platinum species to iron ones are more
significant, which results in a stronger support-Pt interaction
and the stronger interaction leads to the easier polarization of
the C=O group and decreases the adsorption of the substrate
through the C=C group [11].
platinum-based catalysts. The mean particle diameter of Pt
NPs was 4.5–4.6 nm. When the four different Pt/FHP cata-
lysts were used into the hydrogenation of α,β-unsaturated
aldehydes to corresponding unsaturated alcohols, Pt/FHP
(c) catalyst showed the better catalytic performance than the
other three partners, and this catalyst could be reused several
times without any activity loss. The interaction between the
Pt NPs and ferric ions of the hydroxyphosphates promotes
the positive-charged platinum atoms, then they lead to the
polarization of the C=O group and decrease the adsorption
of the substrate through the C=C group, so the better cata-
lytic performance is obtained. Work is ongoing to explore
other reactions using these materials as catalyst supports
in our group. This reverse microemulsion-hydrothermal
synthesis method can be used in the synthesis of other
mesoporous metal hydroxyphosphates and they will be
reported in later artic.
This conclusion also can be drawn from the TPR data
(
Fig. 5B). There are three reduction peaks for all of sam-
ples, the first at 509–576 °C, the second at 637–709 °C and
the third at 787–925 °C. According to previous literatures,
two main reduction peaks at 380 and 684℃ are attributed
to the reduction from Fe O to Fe O and then to Fe [25],
2
3
3
4
meanwhile, bulk-phase wustite (FeO) is thermodynamically
metastable and can hardly be detected during the reduction
of Fe O to Fe [26]. However, a reduction peak at 628 °C is
2
3
Acknowledgements This work is financially supported by the National
Natural Science Foundation of China (21703101, 21303085), the
Natural Science Foundation of Jiangsu Province (BK20130901,
BK20130930), the Program to Cultivate Outstanding Young Key
Teachers of Nanjing Normal University (Qinglan Project), Postgradu-
ate Research & Practice Innovation Program of Jiangsu Province
assigned to the reduction from FePO to Fe P O , that is to
4
2
2
7
2
+
say, the phase containing Fe can be stably present in the
phosphates [27]. So, the last two peaks could be due to the
3
+
2+
transformation from Fe (PO ) (OH) to Fe (PO ) (OH)
x
4 y
z
x
4 y
z
and then to Fe, respectively, and the first peak is attributed
to the reduction of Pt species [28]. Of course, the reduction
temperatures of our Pt–Fe–P–O samples are significantly
higher than those for pure Fe O and related Pt-based cata-
(
KYCX17-1087) and the Priority Academic Program Development of
Jiangsu Higher Education Institutions. SLS acknowledges the support
of the US Department of Energy, Office of Basic Energy Sciences,
Division of Chemical, Biological and Geological Sciences under Grant
DE-FG02-86ER13622.A000.
2
3
lysts, which are due to the stronger interactions among the
deferent components, similar situations can be seen in the
Mg–Fe–Al–O samples [28, 29]. It is worth noting that the
reduction temperature of Pt/FHP (c) are higher than those of
other three samples, as the stronger the interaction between
the metal and supports, the higher the initial temperature of
reduction [30, 31]. This can further testify that a stronger
metal–support interaction (SMSI) exists between the Pt spe-
cies and FHP (c).
References
1
2
.
.
Bauer K, Garbe D (1985) Common fragrance and flavor materials.
VCH, Weinheim
Berger RG (2007) Flavors and fragrance Ingredients. Springer,
Berlin
3
4
.
.
Lenz J, Campo BC, Alvarez M, Volpe MA (2009) J Catal 267:50
Wu B, Huang H, Yang J, Zheng N, Fu G (2012) Angew Chem Int
Ed 51:3440
Recently, B. Qiao et al. have found that the strong
metal–support interaction (SMSI) in their Au/hydroxyapa-
tite catalyst, and they claimed that it was the first time to
discover that SMSI could be formed between metal NPs
and non-oxide supports [32]. However, they could not give
the source of this effect. Based on the above analysis, we
consider that different Lewis acid strengths are responsible
for the distinct catalytic properties of these four catalysts,
and the strong Lewis acid sites lead to obvious SMSI effect.
We believe that this discovery can provide clues for related
studies.
5
6
.
.
Bruyn M, De Coman S, Bota R, Parvulescu VI, De Vos DE,
Jacobs PA (2003) Angew Chem Int Ed 42:5333
Mercadante L, Neri G, Milone C, Donato A, Galvagno S (1996)
J Mol Catal A Chem 105:93
7. Melean LG, Rodriguez M, González A, González B, Rosales M,
Baricelli PJ (2011) Catal Lett 141:709
8
.
Prakash MG, Mahalakshmy R, Krishnamurthya KR, Viswanathan
B (2015) Catal Sci Technol 5:3313
9
.
Bhogeswararao S, Srinivas D (2012) J Catal 285:31
10. Stassi JP, Zgolicz PD, Rodríguez VI, de Miguel SR, Scelza OA
(
2015) Appl Catal A Gen 497:58
1
1
1
1
1. Stassi JP, Zgolicz PD, de Miguel SR, Scelza OA (2013) J Catal
3
06:11
2. Mahata F, Gonçalves N, Pereira MFR, Figueiredo JL (2008) Appl
Catal A Gen 339:159
4
Conclusion
3. Liu J, Liu G, Liu C, Li W, Wang F (2016) Catal Sci Technol
6
:2055
We have synthesized four kinds of different structural micro
nano)-sized mesoporous FHP by a reverse microemulsion-
solvothermal synthesis method and used them to prepare
4. Wu X, Song X, Li D, Liu J, Zhang P, Chen X (2012) J Bionic Eng
:224
15. Sing KSW (1982) Pure Appl Chem 54:2201
(
9
1
3

Pt/Ferric Hydroxyphosphate: An Effective Catalyst for the Selective Hydrogenation of…
1
1
1
1
6. Wu G, Chen Z, Artyushkova K, Garzon FH, Zelenay P (2008)
ECS Trans 16:159
24. Sun J, Zhu K, Gao F, Wang C, Liu J, Peden CHF, Wang Y (2011)
J Am Chem Soc 133:11096
7. Kendelewicz T, Liu P, Doyle CS, Brown GE Jr (2000) Surf Sci
25. Chang FW, Roselin LS, Ou TC (2008) Appl Catal A Gen 334:147
26. Koch AJH, Koch M, Fortuin HM, Geos JW (1985) J Catal 96:261
27. Lin R, Ding Y, Wang R (2014) J Energy Chem 23:29
28. Yu C, Ge Q, Xu H, Li W (2006) Appl Catal A Gen 315:58
29. Ge X, Li M, Shen J (2001) J Solid State Chem 161:38
30. Ji Y, Zhao Z, Duan A, Jiang G. Liu J (2009) J Phys Chem C
113:7186
4
69:144
8. Hanks TW, Ekeland RA, Emerson K, Larsen RD, Jennings PW
(
1987) Organometallics 6:28
9. de Miguel SR, Scelza OA, Román-Martínez MC, de Lecea CSM,
Cazorla-Amorós D, Linares-Solano A (1998) Appl Catal A Gen
1
70:93
2
2
0. Trasarti AF, Bertero NM, Apesteguía CR, Marchi AJ (2014) Appl
Catal A Gen 475:282
31. Sankaranarayanan TM, Berenguer A, Ochoa-Hernándeza C,
Moreno I, Jana P, Coronado JM, Serranoa DP, Pizarro P (2015)
Catal Today 243:163
1. Bertero NM, Trasarti AF, Apesteguía CR, Marchi AJ (2011) Appl
Catal A Gen 394:228
32. Tang H, Wei J, Liu F, Qiao B, Pan X, Li L, Liu J, Wang J, Zhang
T (2016) J Am Chem Soc 138:56
2
2
2. Liu Z, Wang C, Liu Z, Lu J (2008) Appl Catal A Gen 344:114
3. Zhou G, Pei Y, Jiang Z, Fan K, Qiao M, Sun B, Zong B (2014) J
Catal 311:393
1
3