Tandem catalyzing the hydrodeoxygenation of 5-hydroxymethylfurfural over a Ni3Fe intermetallic supported Pt single-atom site catalyst

Article abstract of DOI:10.1039/d0sc05983h

Single-atom site catalysts (SACs) have been used in multitudinous reactions delivering ultrahigh atom utilization and enhanced performance, but it is challenging for one single atom site to catalyze an intricate tandem reaction needing different reactive sites. Herein, we report a robust SAC with dual reactive sites of isolated Pt single atoms and the Ni₃Fe intermetallic support (Pt₁/Ni₃Fe IMC) for tandem catalyzing the hydrodeoxygenation of 5-hydroxymethylfurfural (5-HMF). It delivers a high catalytic performance with 99.0% 5-HMF conversion in 30 min and a 2, 5-dimethylfuran (DMF) yield of 98.1% in 90 min at a low reaction temperature of 160 °C, as well as good recyclability. These results place Pt₁/Ni₃Fe IMC among the most active catalysts for the 5-HMF hydrodeoxygenation reaction reported to date. Rational control experiments and first-principles calculations confirm that Pt₁/Ni₃Fe IMC can readily facilitate the hydrodeoxygenation reaction by a tandem mechanism, where the single Pt site accounts for C-O group hydrogenation and the Ni₃Fe interface promotes the C-OH bond cleavage. This interfacial tandem catalysis over the Pt single-atom site and Ni₃Fe IMC support may develop new opportunities for the rational structural design of SACs applied in other heterogeneous tandem reactions.

Full text of DOI:10.1039/d0sc05983h

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Tandem catalyzing the hydrodeoxygenation of 5-
hydroxymethylfurfural over a Ni3Fe intermetallic
supported Pt single-atom site catalyst†
Cite this: Chem. Sci., 2021, 12, 4139
All publication charges for this article
have been paid for by the Royal Society
of Chemistry
b
b
c
d
Ge Meng,‡a Kaiyue Ji,‡a Wei Zhang, ‡ Yiran Kang, Yu Wang, Ping Zhang,
*
b
a
Yang-Gang Wang,
Dingsheng Wang
Jun Li,
and Yadong Li
Tingting Cui,a Xiaohui Sun,a Tianwei Tan,e
*
a
a
*
Single-atom site catalysts (SACs) have been used in multitudinous reactions delivering ultrahigh atom
utilization and enhanced performance, but it is challenging for one single atom site to catalyze an
intricate tandem reaction needing different reactive sites. Herein, we report a robust SAC with dual
reactive sites of isolated Pt single atoms and the Ni3Fe intermetallic support (Pt1/Ni3Fe IMC) for tandem
catalyzing the hydrodeoxygenation of 5-hydroxymethylfurfural (5-HMF). It delivers a high catalytic
performance with 99.0% 5-HMF conversion in 30 min and a 2, 5-dimethylfuran (DMF) yield of 98.1% in
90 min at a low reaction temperature of 160 ꢀC, as well as good recyclability. These results place Pt1/
Ni3Fe IMC among the most active catalysts for the 5-HMF hydrodeoxygenation reaction reported to
date. Rational control experiments and first-principles calculations confirm that Pt1/Ni3Fe IMC can readily
facilitate the hydrodeoxygenation reaction by a tandem mechanism, where the single Pt site accounts
for C]O group hydrogenation and the Ni3Fe interface promotes the C–OH bond cleavage. This
interfacial tandem catalysis over the Pt single-atom site and Ni3Fe IMC support may develop new
opportunities for the rational structural design of SACs applied in other heterogeneous tandem reactions.
Received 31st October 2020
Accepted 29th January 2021
DOI: 10.1039/d0sc05983h
rsc.li/chemical-science
groups.8–12 Numerous noble (Pt, Ru, Pd, etc.) and non-noble (Ni,
Fe, Cu, Co, etc.) metal based catalysts have been designed to
boost the reaction, and much progress has been made.8,13–17
Introduction
Upgrading of renewable biomass and its derivatives to fuels and
ne chemicals through green catalytic processes is an effective
strategy to reduce our dependence on fossil fuels.1–7 Among
them, 2,5-dimethylfuran (DMF) has been regarded as an
important biomass-derived “platform” chemical, which is
widely applied in the perfume and pharmaceutical industries
and as a promising alternative biofuel.8 For DMF production,
one of the most favorable approaches is the hydro-
deoxygenation of biomass-derived 5-hydroxymethylfurfural (5-
HMF), which is a typical tandem reaction involving the hydro-
genation of the –CHO group and hydrogenolysis of –CH2OH
Nevertheless, it is still challenging for one catalyst to simulta-
neously have high reaction kinetics for both the hydrogenation
and dehydroxylation processes, and thus achieve high reaction
efficiency and DMF selectivity without side-reactions (furan ring
hydrogenation, ring opening, condensation reactions, etc.).18–20
Recently, single-atom site catalysts (SACs) have been of major
interest in heterogeneous catalysis with high atom utilization
and enhanced catalytic performance,21–38 which provide a great
opportunity for efficient catalyst exploration towards the 5-HMF
hydrodeoxygenation reaction. However, when applying SACs to
catalyze the intricate tandem reactions needing multiple steps
and catalytic sites, theoretically it is difficult for one single-atom
site to cover all the catalytic steps with high efficiencies
simultaneously.
aDepartment of Chemistry, Tsinghua University, Beijing 100084, China. E-mail:
wangdingsheng@mail.tsinghua.edu.cn
bDepartment of Chemistry, Southern University of Science and Technology, Shenzhen,
Tandem or synergistic catalysis, in which the reactants are
simultaneously activated by judiciously designed two or more
distinct active sites, has been developed as a powerful strategy
to improve the efficiency and selectivity of numerous homoge-
neous and heterogeneous reactions that cannot be easily cata-
lyzed by a single active species.39–45 Thus, construction of
multiple catalytic sites is a signicant strategy to overcome the
drawback of single reactive sites in SACs for multitudinous
tandem reactions, such as dual single-atom site design.46–48
Guangdong 518055, China. E-mail: wangyg@sustech.edu.cn
cShanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute,
Chinese Academy of Sciences, Shanghai 201204, China. E-mail: wangyu@sinap.ac.cn
dCollege of Civil Engineering & Mechanics, Xiangtan University, Xiangtan 411105,
China
eBeijing Key Laboratory of Bioprocess, College of Life Science and Technology, Beijing
University of Chemical Technology, Beijing 100029, China
† Electronic supplementary information (ESI) available: Experimental details and
supplementary characterization. See DOI: 10.1039/d0sc05983h
‡ G. M., K. J., and W. Z. contributed equally.
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Besides, one of the crucial endeavors should be developing obtained PtCl62ꢁ/NiFe-LDHs show an irregular nanosheet
functional support systems to introduce single atom/support morphology with an average diameter of 27.4 nm and thickness
tandem catalysis. Taking this concept to the reaction of 5- of 2.3 nm. The X-ray diffraction (XRD) pattern (Fig. S1c†) of
HMF hydrodeoxygenation to DMF, the rational choice of the PtCl62ꢁ/NiFe-LDHs presents the characteristic diffraction peaks
single-atom species and the unique support is crucial to realize of LDHs around 11.5ꢀ, 22.5ꢀ, 34.5ꢀ and 60ꢀ, which originate
the tandem catalysis of sequential –CHO hydrogenation and from the in-plane (003), (006), (100) and (110) reections and
–CH2OH hydrogenolysis reactions. Currently, Ni–Fe bimetallic conrm the formation of two-dimensional LDH nanosheets.
alloy catalysts have been demonstrated to have high selectivity Aer being reduced in a 5% H2/N2 atmosphere at 300 ꢀC,
in this reaction because of the oxyphilic Fe sites favoring the PtCl62ꢁ/NiFe-LDHs were transformed into Pt1/Ni3Fe IMC
selective C–OH bond cleavage.8,49–51 However, their hydrogena- nanoparticles, as shown in Fig. S2.† For comparison, Ni3Fe IMC
tion abilities are still unsatisfactory compared to that of many was also prepared (Fig. S3†), which shows morphological
noble metal catalysts. In contrast, noble Pt-based nanocatalysts similarity to the Pt1/Ni3Fe IMC sample. As shown in Fig. 1a, the
have exhibited superior activity in the hydrogenation of C]O typical XRD patterns of Ni3Fe and Pt1/Ni3Fe IMC conform to the
ꢀ
bonds, but are prone to break the C]C bonds or furan ring, standard peaks of Pm3m (221) Ni3Fe (JCPDS le no. 38-0419),
resulting in a loss of DMF selectivity.52–54 Recently, the single- with a face-centered cubic (fcc) structure, where the eight
atom design of Pt catalysts has been proved to be an effective vertices of an individual unit cell are occupied by Fe atoms, and
strategy to tune their selectivity in hydrogenation reactions.55–58 the centers of the six faces bear Ni atoms. To further conrm the
Inspired by the above facts, a unique Ni–Fe nanocrystalline atomic-scale geometrical structure of the as-prepared Pt1/Ni3Fe
supported Pt SAC can be an ideal model to tandem catalyze the IMC, the atomic resolution aberration-corrected high-angle
5-HMF hydrodeoxygenation to DMF, where the hydrogenation annular dark-eld scanning TEM (AC-HAADF-STEM) image
of the C]O group can mainly be catalyzed by the single-atom Pt (Fig. 1b), high-resolution TEM (HRTEM) image (Fig. S4†) and
site, and the C–OH bond rupture processes can occur on the Ni– the fast Fourier transform (FFT) pattern (Fig. 1c) of Pt1/Ni3Fe
Fe interface, and thus both the activity and selectivity would be IMC oriented along the [220] zone axis are presented. The AC-
guaranteed simultaneously.
HAADF-STEM image exhibits an ordered crystalline atomic
ꢁ
ꢁ
Herein, to construct the Pt/Ni–Fe dual interface tandem arrangement. The lattice spacings of 2.04 A and 1.77 A corre-
ꢀ
catalyst, we develop a novel approach to accomplish synthesis of spond to the (111) and (200) planes of Pm3m Ni3Fe, respectively,
Pt1/Ni3Fe IMC SACs derived from the PtCl62ꢁ adsorbed ultrathin as also characterized by HRTEM analysis. The FFT pattern
NiFe layered double hydroxide (NiFe-LDH) precursor. The Pt1/ reveals a simple cubic (sc) structure of Pt1/Ni3Fe IMC, which
Ni3Fe IMC sample exhibited remarkable 5-HMF hydro- agrees with the XRD result. Moreover, as shown in Fig. 1d, the
deoxygenation activity (99.0% conversion within 30 min) and ideal crystal structure model of Ni3Fe along the [220] zone axis
optimal selectivity (98.1% yield of DMF in 90 min) at a low coincides exactly with the experimental STEM image (Fig. 1b),
reaction temperature of 160 ꢀC, which is among the best results conrming the formation of Ni3Fe IMC. As shown in the low-
for DMF production from 5-HMF as reported in the literature. magnied HAADF-STEM image in Fig. 1e, no obvious brighter
Moreover, in the sixth cycle, the Pt1/Ni3Fe IMC catalyst still Pt nanoparticles can be observed. Energy-dispersive X-ray
maintained robust reactivity, further indicating its great spectroscopy analysis (EDXA) (Fig. 1e and S5†) reveals that Pt,
potential as a candidate for industrial applications. Subse- Fe and Ni elements are uniformly distributed. The Pt content in
quently, a series of catalytic control experiments and density Pt1/Ni3Fe IMC is 2.1 wt% as shown by inductively coupled
functional theory (DFT) calculations indicated that the excellent plasma optical emission spectrometry (ICP-OES). This value is
reactivity of the Pt1/Ni3Fe IMC SAC arises from the tandem similar with the EDXA result (2.2 wt%, Table S1†), further
catalysis over Pt and Ni3Fe interfacial sites, where the single- indicating that Pt is homogeneously dispersed in the Ni3Fe
atom Pt site lowers the hydrogenation energy barrier of the matrix. In another AC-HAADF-STEM image of Pt1/Ni3Fe IMC
aldehyde group, and the Ni3Fe interface accelerates the C–OH (Fig. 1f) with a different observation direction, many isolated
bond rupture process. Therefore, this work illustrates bright dots can be observed, demonstrating that the isolated Pt
a successful paradigm for the rational design of SACs with atoms are uniformly embedded in the surface of the Ni3Fe IMC
multiple catalytic sites towards boosting the tandem hydro- nanocrystals.
deoxygenation reactions, which also shows potential applica-
tion in other heterogeneous reactions.
To further verify the electronic and geometrical structure of
Pt1/Ni3Fe IMCs, X-ray absorption spectrometric (XAS) studies at
the Pt L3-edge, Fe K-edge and Ni K-edge were conducted (Fig. 2).
As shown in Fig. 2a, for Pt in Pt1/Ni3Fe IMCs, the white line
intensity, which reect the Pt oxidation state, is lower than that
Results and discussion
Pt1/Ni3Fe IMC was synthesized by a LDH transformation of Pt foil, revealing the electron-richness of Pt atoms in Pt1/
2ꢁ
2ꢁ
method. Firstly, PtCl6 adsorbed NiFe-LDHs (named PtCl6
/
Ni3Fe IMC compared to metallic Pt0. This phenomenon
NiFe-LDHs) were prepared by a co-precipitation process. Then, demonstrates the electron transfer from Ni or Fe to Pt atoms
a thermal reduction treatment was applied to transform due to the higher electronegativity of Pt (2.20) than Ni (1.91) and
PtCl62ꢁ/NiFe-LDHs into Pt1/Ni3Fe IMC. As revealed by the Fe (1.83). The electron transfer characteristics were further
transmission electron microscopy (TEM) image and corre- demonstrated by X-ray photoelectron spectroscopy (XPS)
sponding particle size histogram in Fig. S1a and b,† the measurements. For comparison, Pt nanoparticles supported on
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Fig. 1 Structural characterization of the Pt1/Ni3Fe IMC catalyst. (a) XRD patterns of Ni3Fe and Pt1/Ni3Fe IMC. Atomic resolution AC-HAADF-STEM
image (b) and FFT pattern (c) of Pt1/Ni3Fe IMC nanocrystals oriented along the [220] zone axis. (d) Ideal crystal structure models along the [220]
zone axis. Blue and orange spheres show Ni and Fe atoms, respectively. (e) HAADF-STEM image and the corresponding elemental maps, Pt
(green), Fe (red), Ni and (blue), respectively. (f) AC-HAADF-STEM image of Pt1/Ni3Fe IMC.
ꢁ
from Pt–Pt scattering paths (ꢂ2.6 A) compared with Pt foil. This
reveals that the Pt atoms are isolated and no aggregations exist
in Pt1/Ni3Fe IMC. Specially, the tting results show that the
coordination number (CN) of Pt–Ni/Fe in Pt1/Ni3Fe IMC is
ꢂ10.6. The unsaturated coordination of the Pt site testies the
enriched Pt element on the surface, agreeing well with the XPS
result (Table S1†) that the Pt content on the surface of Pt1/Ni3Fe
IMC (5.12 wt%) is much higher than the total content observed
from ICP-OES (2.1 wt%) and EDXA (2.2 wt%). The single-atom Pt
structure was further demonstrated by wavelet transform (WT)
analysis of Pt L3-edge EXAFS as shown in Fig. S10.† Compared to
Fig. 2 X-ray absorption spectroscopy characterization of the Pt1/ the WT contour plots of Pt foil (Fig. S10a†), the intensity
ꢁꢁ1
Ni3Fe IMC catalyst. Pt L3-edge (a), Fe K-edge (b) and Ni K-edge (c)
XANES profiles of Pt1/Ni3Fe IMC as well as the reference samples. The
Fourier transform (FT) of Pt L3-edge (d), Fe K-edge (e) and Ni K-edge (f)
EXAFS spectra and fitting curves of the samples. The plots are not
corrected for phase shift.
maximum of Pt1/Ni3Fe IMC (Fig. S10b†) arises at ꢂ8.0 A from
the contribution of the Pt–Ni/Fe path and no intensity
ꢁꢁ1
maximum of the Pt–Pt path (ꢂ10.8 A ) is detected. Evidenced
by AC-HAADF-STEM, XANES, EXAFS and WT analysis, we can
draw a conclusion that Pt atoms are isolated, dispersed in Pt1/
Ni3Fe IMCs and stabilized by Pt–Ni/Fe bonds with a feature of
Ni3Fe IMC (noted as Pt NPs/Ni3Fe IMC; Pt content of 2.23 wt%) electron-richness (Ptdꢁ).
were also prepared and characterised (Fig. S6–S8†). As shown in
Fig. 2b shows the normalized Fe K-edge XANES spectra of
Fig. S9,† the Pt 4f peaks of Pt1/Ni3Fe IMC show slightly lower Pt1/Ni3Fe IMC and Fe foil, in which Pt1/Ni3Fe IMC exhibits
binding energies than Pt NPs/Ni3Fe IMC with characteristic a similar near-edge absorption energy compared to Fe foil,
peaks of metallic Pt (Pt0), indicating the electronegative feature revealing the metallic state of Fe atoms in Pt1/Ni3Fe IMC.
of Pt atoms in Pt1/Ni3Fe IMC. Pt isolated single atoms in Pt1/ Specically, from the Fe K-edge EXAFS spectra and the curve
Ni3Fe IMC were identied from the EXAFS spectra and the tting results (Fig. 2e and Table S3†), it can be found that the Fe
theoretical tting results (Fig. 2d, Table S2†), and only the Pt– atoms in Pt1/Ni3Fe IMC are present in an fcc packing form with
ꢁ
Ni/Fe shell at ꢂ2.2 A was observed without any contribution a CN of 10.7 ꢃ 2.1, rather than the body-centered cubic (bcc)
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structure as Fe foil. Besides, the intensity enhancement and hydrodeoxygenation reaction catalyzed by the Pt1/Ni3Fe IMC
ꢁꢁ1
ꢀ
location shi (from ꢂ7.9 to ꢂ8.2 A ) in the K-edge WT contour sample was rstly investigated at a temperature of 160 C and
plots of Pt1/Ni3Fe IMCs (Fig. S11†) compared to that of Fe foil H2 pressure of 1.0 MPa. As shown in Fig. 3b and Table S5,† Pt1/
also demonstrate the coordination environment difference of Ni3Fe IMC exhibited an extraordinary catalytic performance, in
Fe atoms in these two samples. These results conform to the which 99.0% conversion of 5-HMF was achieved within 30 min
XRD and AC-HAADF-STEM analysis that the intermetallic and the DMF yield reached 98.1% aer 90 min. As shown in
structure of fcc Ni3Fe was formed without the existence of Fe Table S6,† the lower reaction temperature, higher reaction rate
clusters or nanoparticles. For the Ni K-edge, XANES (Fig. 2c), and DMF selectivity, and low noble metal consumption of Pt1/
EXAFS oscillations (Fig. 2f and Table S4†) and WT analysis Ni3Fe IMC make it one of the best catalysts compared to the
(Fig. S12†) of Pt1/Ni3Fe IMCs are very similar to those of Ni foil, results reported in the literature. In addition, during the whole
indicating the metallic and fcc structure of Ni in Pt1/Ni3Fe IMC. reaction process, except for DMF, the intermediates of DHMF,
The smaller CN of 10.1 for Ni in Pt1/Ni3Fe IMC than Ni foil can 2-methyl-5-hydroxymethylfuran (MFA) and trace amounts of
be attributed to the nite size effect. All these results agree well MFF, no signs of other compounds were observed. These results
with the XRD, AC-HAADF-STEM and HRTEM analysis as dis- reveal the superior effectiveness of Pt1/Ni3Fe IMC for the fast
cussed above.
and highly selective hydrodeoxygenation of the oxygenic group
Typically, as depicted in Fig. 3a, the tandem hydro- (–CHO, –OH) in 5-HMF, without C]C group hydrogenation or
deoxygenation of 5-HMF to DMF can occur through two reac- furan-ring-opening reactions. Moreover, it is also suggested that
tion pathways.10,15 For one pathway (Path 1), 2,5- the hydrodeoxygenation reaction mainly follows Path 1 on the
di(hydroxymethyl)furan (DHMF) appears as the primary Pt1/Ni3Fe IMC catalyst. To further evaluate its cycling stability,
product through the hydrogenation of the formyl group (–CHO) the reaction was recycled six times (160 ꢀC/2 h), and both the 5-
in 5-HMF. For Path 2,5-HMF is rstly converted to methyl HMF conversion and DMF yield remained at >99% (Fig. 3c).
furfural (MFF) by the hydrogenolysis of the hydroxyl group. Both Aer the sixth cycle, the spent Pt1/Ni3Fe IMC catalyst was fully
of them are then followed by further hydrogenation or hydro- characterized (Fig. S13–S17†) and the results reveal that the
genolysis processes and DMF can be obtained. The morphology and intermetallic structure were well preserved and
the Pt atoms were maintained atomically dispersed, indicating
the outstanding structural stability of the Pt1/Ni3Fe IMC
catalyst.
Subsequently, to understand the roles of the Pt single-atom
site and Ni3Fe interface in the Pt1/Ni3Fe IMC catalyst for the
hydrodeoxygenation reaction, a series of control experiments
were performed. Accordingly, the reaction was rstly carried out
over Pt NPs/Ni3Fe IMC. It is worth noting that, Fig. 3d, aer
120 min of reaction, the conversion of 5-HMF attained 90.9%,
wherein the corresponding DMF yield was 51.1% and remain-
ing products distributed over MFA (19.9%), DHMF (7.1%) and
some by-products (ꢂ12.0%). Such inferior performance on Pt
NPs/Ni3Fe IMC demonstrates that the Pt nanoparticle surface
suffers from poor reactivity and selectivity sparking an assort-
ment of side reactions (furan ring hydrogenation, ring-opening
reactions, etc.), which conforms to previous reports.8,52,59 To
further conrm the catalytic behavior of Pt single-atom sites,
the Pt1/NiFe-LDHs SAC with the catalytically inactive NiFe-LDHs
as the support was also synthesized and tested. The structure of
Pt1/NiFe-LDHs was well characterized as shown in Fig. S18–S21†
and the Pt content in Pt1/NiFe-LDHs is 1.3 wt% as determined
by ICP-OES. As shown in Fig. S22,† Pt1/NiFe-LDHs exhibit
Fig. 3 Performance evaluation for the hydrodeoxygenation reaction
over different catalysts. (a) Schematic paths for the conversion of 5- obvious activity for 5-HMF hydrogenation to DHMF, with a 5-
HMF to DMF. (b) 5-HMF conversion and product yields as a function of
reaction time over Pt1/Ni3Fe IMC with the 5-HMF/Pt molar ratio of
100/1. (c) 5-HMF conversion and DMF selectivity as a function of
catalytic cycles (run time: 2 h). 5-HMF conversion and product yields
as a function of reaction time over Pt NPs/Ni3Fe IMC (d) and Ni3Fe IMC
(e). Reaction conditions: All reactions were run at 160 ꢀC and 1.0 MPa strate that, compared to Pt nanoparticles, the single-atom
H2. The loading of 5-HMF was 0.5 wt% in 60 ml THF solvent. The
catalyst dosage was introduced according to the 5-HMF/Pt molar ratio
of 100/1 for Pt1/Ni3Fe IMC (196.0 mg) and Pt NPs/Ni3Fe IMC (184.6
mg). The mass dosage of Ni3Fe IMC (196.0 mg) was the same as that of
Pt1/Ni3Fe IMC for comparison. All the error bars were evaluated from
>3 times of independent measurements.
HMF conversion of 50.8% and DHMF yield of 42.4% aer 2 h of
reaction. However, this catalyst exhibits extremely weak activity
for the hydrogenolysis of –OH groups with only trace DMF and
other intermediate products presented. These results demon-
design of Pt catalysts can suppress their catalytic activity for
furan ring hydrogenation and ring-opening side reactions to
a large extent, with specicity in high –C]O hydrogenation
ability but low –OH hydrogenolysis capacity. Thus, it can be
inferred that the Pt single-atom site in the Pt1/Ni3Fe IMC
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catalyst can take responsibility for the –C]O group hydroge- also suggested that on Nickel and Platinum catalysts the furyl
nation in the 5-HMF hydrodeoxygenation reaction. To study the ring of the furanic derivatives can strongly interact with the
role of the Ni3Fe interface in the hydrodeoxygenation catalysis, metal d orbitals and the carbonyl group mostly interacts with
the catalytic behavior of the Ni3Fe IMC sample was also studied. the pre-adsorbed hydrogen.60–62 Generally, the conversion of 5-
As presented in Fig. 3e, aer 120 min of reaction, the conversion HMF to DMF can be divided into two tandem parts: the rst is
of 5-HMF reaches only 42.8% and gives a poor DMF yield of the hydrogenation of 5-HMF to DHMF; and the second is the
15.7%, indicating the slow kinetics of the hydrodeoxygenation hydrogenolysis of DHMF to DMF. On a pure Pt catalyst, the rate-
reaction over the pure Ni3Fe IMC surface. More importantly, the limiting steps are found to be the dehydroxylation of DHMF
MFF intermediate with a high yield of 19.8% was detected, (vi/vii) and MFA (xii/xiii). The calculated barriers (TS-a and
which reveals that C–OH dehydroxylation is preferred over TS-b, as marked in green areas) are 1.79 eV and 2.20 eV,
hydrogenation of the –C]O group in 5-HMF on the Ni3Fe IMC respectively, which indicates that the dehydroxylation of DHMF
catalyst (Path 2). Therefore, we can infer that the Ni3Fe interface and MFA is kinetically unfavorable over the pure Pt surface.
in the Pt1/Ni3Fe IMC catalyst mainly accounts for the dehy- However, the low hydrogenation barriers (TS-1 ¼ 0.52 eV and
droxylation of –OH groups in the reaction of 5-HMF hydro- TS-2 ¼ 0.54 eV) have suggested that the Pt catalyst should
deoxygenation. The raw data of GC-MS analysis of Pt NPs/Ni3Fe exhibit high hydrogenation performance, which agrees well
IMC, Pt1/NiFe-LDHs and Ni3Fe IMC in 120 min reaction dura- with previous observations.59,63 In contrast, we nd that on the
tion are provided in Fig. S23–S25.† Summarizing the catalytic Ni3Fe catalyst the rate-limiting step is the rst hydrogenation
results (Table S5†) elucidates that the excellent performance of step of 5-HMF (iii/iv) with a high barrier of 1.25 eV (TS-1, as
Pt1/Ni3Fe IMC for the 5-HMF hydrodeoxygenation reaction can marked in blue area), suggesting the difficult conversion of 5-
arise from tandem catalysis over Pt and Ni3Fe interfacial sites, HMF to DHMF. However, for the selective cleavage of the C–OH
where the –C]O group in 5-HMF was rstly hydrogenated to bond, the Ni3Fe catalyst shows very low barriers of 0.73 eV and
DHMF on single Pt sites, and then, the C–OH bonds of DHMF 0.93 eV for TS-a and TS-b, respectively.
ruptured on the Ni3Fe interface to form DMF.
Comparing Pt and Ni3Fe catalysts, we can nd that the
To further understand the tandem catalysis process and the former is effective for the hydrogenation step and the latter is
excellent activity of the Pt1/Ni3Fe IMC catalyst, we performed signicant for the dehydroxylation step. Without surprise, Pt1/
DFT calculations to explore the hydrodeoxygenation mecha- Ni3Fe, which combines Pt and Ni3Fe catalysts, shows signi-
nisms on different substrates including Pt, Ni3Fe IMC and Pt1/ cantly improved catalytic performance for the hydro-
Ni3Fe IMC surfaces. The calculated reaction pathways as well as deoxygenation of 5-HMF. The barrier for the rst hydrogenation
reaction energetics are shown in Fig. 4, and the corresponding step on Pt1/Ni3Fe decreases from 1.25 eV to 0.55 eV compared to
reaction equations are shown in Scheme S1.† For the hydroge- that of Ni3Fe, and the barrier for the dehydroxylation of MFA
nation process, the hydrogen atom is considered to be located decreases from 2.20 eV to 0.64 eV compared to that of Pt. The
at the adjacent site to the carbonyl group. Recent studies have congurations for the rst hydrogenation of 5-HMF and the
Fig. 4 Calculated reaction pathways for the hydrodeoxygenation of 5-HMF to DMF over Pt, Ni3Fe and Pt1/Ni3Fe catalysts. The elementary steps
were numbered with i–xviii; “TS-1”, “TS-2”, “TS-3” and “TS-4” represent the transition states of the hydrogenation steps, “TS-a” and “TS-b”
represent the transition states of dehydroxylation steps, and “TS-H2O” denotes the transition state of water formation.
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Fig. 5 The tandem mechanism of Pt and the Ni3Fe interface. Optimized structures of reaction intermediates for the first hydrogenation step (a)
and the dehydroxylation of MFA (b) over Pt, Ni3Fe and the Pt1/Ni3Fe surface. (c) Tandem mechanism on Pt/Ni3Fe, combing the catalytic
performance of both Pt and Ni3Fe catalysts. The light blue, orange, blue, grey, red and white spheres represent Ni, Fe, Pt, C, O and H atoms,
respectively.
dehydroxylation of DHMF on each catalyst are also shown in SACs in the hydrodeoxygenation reaction, in which the single-
Fig. 5a and b. It is demonstrated that the aldehyde group on Pt1/ atom Pt site accelerates the hydrogenation of the aldehyde
Ni3Fe directly correlates with the single Pt sites, which accounts group, and the Ni3Fe interface facilitates the C–OH bond
for the high activity for the hydrogenation step. For the dehy- cleavage. These results provide not only an efficient synthetic
droxylation of DHMF, the cleavage of C–OH occurs at the Ni3Fe strategy for a new type of IMC supported SAC, but also guide-
interface and the produced hydroxyl exhibits a strong interac- lines for the tandem catalysis design of SACs by constructing
tion with the Fe site. This is conrmed by the cleavage energies functional support systems for numerous intricate tandem
of the C–OH bond (ꢁ0.36 eV on Ni3Fe vs. 0.85 eV on Pt). Our reactions.
results suggest that the prepared Pt1/Ni3Fe IMC has combined
the advantages of Pt and Ni3Fe catalysts and the tandem
mechanism results in the high catalytic reactivity for the
Conflicts of interest
hydrodeoxygenation of 5-HMF, as schematically shown in
Fig. 5c.
There are no conicts to declare.
Acknowledgements
Conclusions
This work was supported by the National Key R&D Program of
In summary, a Ni3Fe intermetallic compound supported Pt China (2018YFA0702003), National Natural Science Foundation
single-atom site catalyst (Pt1/Ni3Fe IMC) was designed through of China (21890383, and 21871159), Science and Technology
an efficient LDH transformation strategy for tandem catalyzing Key Project of Guangdong Province of China (2020B010188002)
the hydrodeoxygenation of 5-HMF to DMF, where the aldehyde and Beijing Municipal Science & Technology Com-mission No.
hydrogenation and C–OH bond cleavage processes can be Z191100007219003. We thank the BL14W1 station in the
respectively promoted by the single-atom Pt site and Ni3Fe Shanghai Synchrotron Radiation Facility (SSRF) for use of the
interface. Therefore, it delivered a robust catalytic performance instruments. W. Z. and Y. G. W. were nancially supported by
with a 99.0% conversion of 5-HMF in 30 min and a DMF yield of NSFC (22022504, and 22003022) of China, the Guangdong
ꢀ
98.1% within 90 min at 160 C, as well as an excellent cycling “Pearl River” Talent Plan (2019QN01L353), and the Guangdong
stability. Experimental and DFT calculation studies support our Provincial Key Laboratory of Catalysis (2020B121201002). The
hypothesis that the tandem catalysis over Pt and Ni3Fe inter- computational resource was provided by the Center for
facial sites accounts for the excellent reactivity of Pt1/Ni3Fe IMC Computational Science and Engineering at SUSTech.
4144 | Chem. Sci., 2021, 12, 4139–4146
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