A gas-phase coupling process for simultaneous production of γ-butyrolactone and furfuryl alcohol without external hydrogen over bifunctional base-metal heterogeneous catalysts

Article abstract of DOI:10.1039/c5gc02924d

A solvent-free gas-phase coupling process through hydrogen transfer without external hydrogen supply over novel bifunctional base-metal heterogeneous catalysts was developed for the simultaneous production of γ-butyrolactone and furfuryl alcohol with high yields of 95.0% from biomass-derived compounds. Such a practical, unparallely efficient and environmentally benign process makes it promising in terms of both green sustainable chemistry and industrial perspective.

Full text of DOI:10.1039/c5gc02924d

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G
asꢀphase coupling process for simultaneous production of γꢀ
butyrolactone and furfuryl alcohol without external hydrogen
over bifunctional baseꢀmetal heterogeneous catalysts
Received 00th January 20xx,
Qi Hua, Guoli Fana, Lan Yanga, Xinzhong Caob, Peng Zhangb, Baoyi Wangb and Feng Lia*
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
A solventꢀfree gasꢀphase coupling process through hydrogen external hydrogen produced by nonꢀrenewable substances such
transfer without external hydrogen supply over novel as coal and other natural gas. Very recently, liquidꢀphase
bifunctional baseꢀmetal heterogeneous catalysts was developed hydrogenation of FL using different alcohols as hydrogen
for the simultaneous production of γꢀbutyrolactone and sources has been investigated. 7 The demand for large amounts
furfuryl alcohol with high yields of 95.0 % from bimassꢀderived of hydrogen donators and solvents, however, limits its practical
compounds. Such practical, unparalleledly efficient and application. Therefore, gasꢀphase solventꢀfree hydrogenation
environmentꢀbenign process make it promising in terms of both using equal moles of organic hydrogen donators would be
green sustainable chemistry and industrial perspective.
greener alternative.8 Due to low efficiency of catalysts, external
hydrogen supply or hydrogen recycle is still prerequisite to
With the increasing concern about energy and environment issues achieve products with high yields, which renders hydrogen
originating from increasing greenhouse gas emission and the transfer process economically and environmentally undesirable.
shortage of fossil resources, the conversion from sustainable and
As an important chemical intermediate, γꢀbutyrolactone (GBL)
renewable raw biomass to fuel and chemicals is attracting more and has been employed widely for the production of pyrrolidone
more attention.1 As one of the most promising biomassꢀderived derivatives, herbicides, and rubber additives in fine and petroleum
platform chemicals, furfuryl alcohol (FOL), which is widely industries 9
In industry, the major production route for GBL
.
transformed into various useful chemicals including functional involves gasꢀphase dehydrogenation of 1, 4ꢀbutanediol (1,4ꢀBDO)
resins, lysine, lubricants, and plasticizers,2 can be produced over supported metal catalysts, especially copper chromite
industrially by gasꢀphase hydrogenation of furfural (FL) over catalysts.10 Recently, supported Cu/SiO2 catalyst with 80 wt %
copper chromite catalysts.3 However, Cr6+ species with the high metal loadings has been reported to exhibit excellent catalytic
toxicity can cause severe environmental pollution. Therefore, performance with a 98 % yield of GBL.11 However, decreasing Cu
exploring environmentally friendly Crꢀfree metal catalysts for FL loadings to 12 wt % led to a rapid deactivation, due to the sintering
hydrogenation is attracting enormous concerns. For example, a large of active species. And, it was found that surface acid sites on
number of supported noble metal catalysts (i.e. Pt, Pd, Ru) can show catalysts could induce the formation of tetrahydrofuran (THF) in the
excellent catalytic hydrogenation performance.4 Further, electronic 1,4ꢀBDO dehydrogenation.12 Therefore, high selectivity to GBL can
or structural promoters like Re also are incorporated into catalysts to be achieved on alkaline metals modified Cuꢀbased catalyst.13
improve the affinity toward carbonyl group.5 Their high cost,
At present, 1,4ꢀBDO can be easily obtained on a large scale
however, limits practical application. Recently, heterogeneous nonꢀ by highly efficient, lowꢀcost, commercially realized fermentation of
nobleꢀmetal catalysts (i.e. Ni, Co, Cu) have been employed for FL renewable biomass (i.e. glucose).14 Recently, combining 1,4ꢀBDO
hydrogenation.6 The main disadvantage is that these catalysts are lactonization with transfer hydrogenation of FL has been reported
less active compared with nobleꢀmetalꢀbased catalysts.
over a Cuꢀbased catalyst. However, the whole reaction system still
rom the
Conventionally, hydrogenating FL always consumes was operated under external hydrogen (16 bar) 15
.
F
viewpoint of sustainable development of resources and economy, if
equal moles of 1,4ꢀBDO and FL can be converted
simultaneously to GBL and FOL via in situ the coupling
between hydrogenation and dehydrogenation over recyclable
and selective catalysts in the absence of any external hydrogen,
such synthetic route would become the most sustainable and
a State key laboratory of Chemical Resource Engineering, Beijing University of
Chemical Technology, P.O.BOX 98, Beijing, 100029, P. R. China.
b Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Institute of
High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
Email: lifeng@mail.buct.edu.cn; Fax:+8610 64425385 ; Tel : +8610 64451226
†Electronic Supplementary Information (ESI) available. See
DOI: 10.1039/x0xx00000x
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economical process. In this regard, designing nonꢀtoxic and metal NPs and support, 17 thus enhancing the dispersion of Cu NPs.
Moreover, as the Ca content increases, the diffractions for
metallic copper become broader and weaker (Fig.S1),
indicating the dispersion effect of CaAlO component in
samples, leading to the reduced particle size of Cu NPs (Table
1).
highly efficient heterogeneous catalysts is quite crucial for the
simultaneous production of GBL and FOL with high yields.
Herein, we reported new CaꢀAl mixed metal oxide supported
copper catalysts prepared via a twoꢀstep procedure based on layered
double hydroxide precursors
(
LDHs, [M1−x2+Mx3+(OH)2]x+
n−
[Ax/n
] ·
mH2O),16 and then employed them as bifunctional baseꢀ
metal heterogenous catalysts for gasꢀphase solventꢀfree coupling
between dehydrogenation and hydrogenation without external
hydrogen to produce GBL and FOL from bimassꢀderived 1,4 BDO
Table 1 The structural data of Cuꢀbased catalysts
b
c
Specific SLB
sites d
Ca/Al
ratio
Cu a
SCu
Dav
Cu+/(Cu0+Cu+)
ratio e
and FL (Fig.1). It was found that the surface Lewis base (LB)
(wt %) (m2/g) (nm)
Samples
sites, defective Cu nanoparticles (NPs) and Cu+ species on
catalysts could create a cooperative nanoenvironment for
holding the dehydrogenation of hydroxyl group in 1,4 BDO and
the hydrogenation of carbonyl group in FL. More importantly, asꢀ
synthesized bifunctional baseꢀmetal catalyst achieved lasting high
yields of GBL and FOL (> 95.0 %) up to 100 hours under the
mild reaction conditions. To the best our knowledge, such
practical, unparalleledly efficient and environmentꢀbenign gasꢀ
phase coupling between 1,4ꢀBDO dehydrogenation and FL
hydrogenation for simultaneous production of GBL and FOL
without the use of any solvent and external hydrogen supply or
recycle has not been reported until now.
(mmol CO2/g)
Cuꢀ3
Cuꢀ4
3:1
4:1
27.6
24.3
7.9
19.8
1.58
2.61
0.38
0.52
10.8 11.7
11.0 10.9
0.37
Cuꢀ5
5:1
25.6
2.82
a
b
c
Determined by ICPꢀAES. Copper surface area. Average crystal size of
d
e
Cu NPs determined by XRD patterns.
Determined by XPS.
Determined by CO2ꢀTPD.
In the case of Ca/Al atom ratio of 3.0, a broad reduction region
for Cu2+ species in H2ꢀTPR profiles of calcined precursors can be
fitted into three peaks at about 200, 237 and 288 C (Fig.S2), which
o
are assigned to the reduction of isolated highlyꢀdispersed CuO
(CuA2+), small CuO particles (CuB2+) and large bulk CuO species
(CuC2+), respectively.18 With increasing Ca/Al molar ratio to 4.0, two
2+
2+
reduction peaks for CuA and CuB species shift to lower
2+
temperatures, and the reduction peak for CuC species disappears.
In the case of Ca/Al atom ratio of 5.0, in turn, the reduction peaks
slightly shift to higher temperatures, due to strong metalꢀsupport
interaction. It demonstrates that the addition of an appropriate
amount of Ca2+ can greatly improve the reducibility of Cu2+ species.
Further, Cu XAES analysis was performed to determine the
chemical states of copper species on Cuꢀx catalysts (Fig.S3).
Obviously, broad and asymmetric Auger kinetic energy peak can be
fitted into two peaks around 916.6 eV and 918.8 eV, corresponding
to Cu+ and Cu0 species, respectively.19 The surface Cu+/(Cu0+Cu+)
ratio can be quantitatively calculated by the ratio of the peak area of
Cu+ to total peak area.20 Notably, Cuꢀ4 sample possesses the
largest Cu+/(Cu0+Cu+) ratio (0.52).
The morphology and microstructure of Cuꢀ4 sample were
characterized by TEM. It is interesting to note that a large
number of highly dispersed cuboctahedron or truncated
octahedron Cu NPs of around 11 nm in size are embedded in
the support matrix (Fig 2b,c), suggestive of the presence of
strong metalꢀsupport interaction (SMSI). This result is in good
agreement with the HAADFꢀSTEMꢀEDS observation showing
relatively homogenous distributions of Cu, Ca and Al elements
on the sample (Fig.S4). As the best approximations for the
geometry of a metallic particle, both cuboctahedron and
octahedron may bring about the surface to intrinsically contain
a large number of steps, thereby leading to the formation of
defects.21 In addition, in the case, the fast Fourier transform
(FFT) latticeꢀfringe image of an individual copper particle (Fig.
2d) depicts spots at 2.0 and 1.8 Å, which correspond to the (111)
and (200) planes of metallic copper, respectively, further
reflecting the presence of cuboctahedron Cu NPs in a fcc
structure.22
Fig. 1 Reaction coupling for the production of GBL and FOL from biomass.
The preparation of supported copperꢀbased catalysts over
CaꢀAl mixed metal oxide (CaAlO) (Table 1) includes the
preparation of CaAlO from CaAlꢀLDH precursors, followed by
further impregnation, calcination and reduction (see ESI†). As
shown in Fig 2a, XRD patterns of representative CaAlꢀLDH
precursor with the Ca/Al atom ratio of 4.0 exhibit the
characteristic diffractions of hydrotalciteꢀlike materials (JCPDS
no. 37ꢀ0630) with good crystallinity. However, a small amount
of calcium carbonate phase (JCPDS no. 47ꢀ1743) can be
observed, due to the reaction between Ca2+ cations in the
bruciteꢀlike layers of CaAlꢀLDH precursor and interlayer
carbonate anions upon heating. In the case of reduced Cuꢀ4
sample, a major diffraction at 2
θ
of about 43.07o can be
indexed to the (111) plane of face cubic centered (fcc) metallic
copper (JCPDS 04ꢀ0836), besides CaCO3 phase. No
diffractions related to crystalline CaO and Al2O3 are observed,
implying that CaAlO or Al2O3 may exist in the amorphous form.
In the present catalyst system, this kind of Al3+ꢀcontaining
amorphous phase as a support can improve the interaction between
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NPs and CaAlO support. As a result, a large number of SLB
sites and highly dispersed defective Cu NPs intimately
contacting with SLB sites can be formed on the catalyst surface
after reduction. Moreover, according to the CO2ꢀTPD results,
the density of SLB sites in Cuꢀx samples presents an increasing
trend with the Ca content (Table 1). In addition, FTꢀIR spectra
of CO2 adsorption depict the presence of unidentate carbonate
species at 1360 and 1590 cmꢀ1 (Fig.S5), which are associated
with high strength basic absorption formed on surface CaꢀO2+
pairs and Oδꢀ species, further reflecting the existence of a large
amount of SLB sites on asꢀformed catalysts.28
Fig. 2 XRD patterns of different samples (a), TEM (b), HRTEM (c), and FFT (d)
images of Cuꢀ4 sample.
Fig. 3 CO2ꢀTPD curve (A) and O 1s XPS (B) for Cuꢀ4 sample.
Table 2 Catalytic performance of different catalysts a
As an extremely sensitive probe of defects in solids,
positron annihilation spectroscopy (PAS) can provide an
excellent means to investigate relative density of various
defects. Positron lifetime components and relative intensities of
components for Cuꢀ4 and pristine CaAlO support are listed in
Table S1.It is wellꢀknown that the shortestꢀsurvived component
(τ1) of sample is usually ascribed to small size defects mostly in
the bulk section of NPs,23 while the moderate one (τ2) results
from positrons trapped by large size defects located on the
surface, boundary, or interface of NPs.24 Correspondingly, the
higher relative intensity of τ2 to τ1 for Cuꢀ4 (0.48) than that for
CaAlO support (0.42) indicates that the concentration of defect
sites is higher in the Cuꢀ4 than in the CaAlO, which is in good
accordance with the HRTEM results. Therefore, it can be
deduced that the SMSI can promote the formation of a large
number of wellꢀdispersed defective Cu NPs on the CaAlO
support.
CO2ꢀTPD measurement was used to probe the surface
basicity of copper catalysts. In the case of Cuꢀ4, there are four
kinds of CO2 desorption peaks (Fig.3A). A tiny peak at about
100 °C is assigned to weak Brønsted base sites, while a small
peak in the range from 440 °C to 580°C is associated with
moderate strength LB sites. Noticeably, large desorption peak
above 580 °C can be assigned to strong LB (SLB) sites.25 To
gain a deeper insight into SLB sites, the O 1s XPS was further
TOF b
(hꢀ1)
Conversion (%)
Selectivity (%)
Catalysts
FL
BDO
FOL
100
100
100
100
100
99 c
99 c
100
GBL
100
100
100
100
100
99 d
99 d
100
Cuꢀ3
Cuꢀ4
63.0
96.0
90.1
30.3
23.2
14.3
10.4
1.0
63.1
95.3
91.2
30.6
22.4
14.7
12.6
2.1
43.8
50.9
47.2
16.2
14.7
9.2
Cuꢀ5
Cu/CaO
Cu/MgO
Cu/Al2O3
Cu/SiO2
CaAlO
5.5
ꢀꢀ
a
Reaction condition: LHSV(FL+1,4ꢀBDO)=1.8hꢀ1, n(FL):n(1,4ꢀBDO)=1,
n(N2):n(FL+1,4ꢀBDO) = 13, temperature = 210 oC and reaction pressure = 1 atm.
b
Calculated based on the moles of FL converted per mole surface metallic
copper in the initial 1 h. c 2ꢀMF as by products. c THF as by products.
Under nitrogen atmosphere, the hydrogen transfer goes
through
a
consecutive twoꢀstep reaction pathway:
dehydrogenation of 1,4ꢀBDO to produce hydrogen and GBL
and hydrogenation of FL to produce FOL using the hydrogen
produced by dehydrogenation. Table 2 summarizes the results
of catalytic hydrogenation of FL and dehydrogenation of 1,4ꢀ
BDO over different Cuꢀbased catalysts without external
hydrogen supply or recycle. And, gas chromatogram spectra of
some typical experiments are shown in Figs.S6ꢀS9. It is found
that the yields of GBL and FOL decrease in the following order for
catalysts: Cuꢀ4 > Cuꢀ5 > Cuꢀ3. Especially, high GBL and FOL
yields (> 95.0%) are achieved over the Cuꢀ4 under the high LHSV
analyzed (Fig.3B). Obviously, four fitted XPS peaks should
correspond to different surface oxygen species. The small peak
at about 531.0 eV can be attributed to oxygen species in
hydroxyl groups, while another small peak at 530.2 eV is
related to MꢀOꢀM groups in the CaAlO structure.26 Notably,
two large peaks at 529.3 and 528.1 eV belong to CaꢀO2+ pairs
and coordinatively unsaturated O2ꢀ species bound to Ca2+
cations (Oδꢀ), respectively. Specially, Oδꢀ species are probably
formed by the reduction of Cu2+ꢀOꢀCa2+ parts upon activation.27 value. For comparison, such coupling process was also conducted
It demonstrates that strong interfacial contact exists between Cu
over other oxides (CaO, MgO, Al2O3, SiO2)ꢀsupported Cu
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catalysts with the similar Cu loadings to Cuꢀ4, which were
synthesized by conventional impregnation method. Noticeably, these
catalysts exhibit remarkably lower catalytic performance, compared
with the present Cuꢀ4. Among these comparison catalysts, basic
oxidesꢀsupported catalysts (Cu/CaO and Cu/MgO) are more
active than neutral and acidic oxidesꢀsupported ones (Cu/Al2O3
and Cu/SiO2), indicating the significant promotional effect of
LB sites on the couple between dehydrogenation and
defective Cu NPs may capture another hydrogen atom from the
αꢀCꢀH bond, thus facilitating hydrogen transfer and activating
CꢀO bond in adsorbed alkoxide intermediate. As a result, more
active hydrogen atoms can be abstracted from alcohol by a
larger amount of surface strong base sites and defective Cu
NPs.
hydrogenation
. Notably, Cuꢀ4 attains a highest turnover
frequency (TOF) value of 50.9 hꢀ1, demonstrating the excellent
catalytic efficiency of Cuꢀ4 catalyst. On the other hand, such
excellent catalytic performance of Cuꢀ4 stays nearly unchanged
over 100 hours (Fig.S10). And, TEM image (Fig.S11) gives the
evidence that no aggregation or growth of Cu NPs is found
after reaction, arising from the stabilization effect of CaAlO
support on Cu NPs.
Further, NH3ꢀTPD profiles of Cuꢀx samples (Fig.S12) only
reveal one broad peak at 113 °C, which originates from desorption
of NH3 from weak Brønsted acid sites.29 In addition, FTꢀIR spectra
of pyridine adsorption (Fig.S13) present two weak bands at 1450 and
1584 cmꢀ1 associated with adsorption of pyridine by Hꢀbonding,
besides a weak band at 1435 cmꢀ1 assigned to physical adsorption of
pyridine.30 As it was reported, surface Lewis acid sites could
facilitate the formation of 2ꢀmethyl furan (2ꢀMF) in the FL
hydrogenation or the formation of THF in the 1,4ꢀBDO
dehydrogenation.12,31 Therefore, the high selectivities to both FOL
and GBL over Cuꢀx catalysts also are related to the lack of surface
Lewis acid sites.
Fig. 4 FTꢀIR spectra of butanol absorption on CaAlO and Cuꢀ4 samples.
In addition, 1,4ꢀBDO dehydrogenation under N2 atmosphere was
conducted over Cuꢀx, Cu/CaO and CaAlO samples (Table S2). A
relatively high 1,4ꢀBDO conversion of 89.2% can be achieved over
the Cuꢀ4 catalyst. However, compared with the results in Table 2,
the conversions of 1,4ꢀBDO over catalysts are reduced, indicating
that FL hydrogenation can drive reaction equilibrium of 1,4ꢀBDO
dehydrogenation toward GBL. Further, FL hydrogenation and 1,4ꢀ
BDO dehydrogenation over different catalysts was simultaneously
conducted under 50% H2/N2 mixture atmosphere (Table S3).
Noticeably, with the introduction of external hydrogen, the FL
conversion is increased in each case, whereas the FOL selectivity is
greatly decreased due to the formation of 2ꢀMF. However, the
conversion of 1,4ꢀBDO is significantly decreased, because external
hydrogen can inhibit the dehydrogenation reaction.
Previously, it was reported that the surface basicity of
catalysts imposes a significant effect on the dehydrogenation of
alcohols.32 In the course of dehydrogenation, a negatively
charged alkoxide intermediate can form through the abstraction
of hydroxyl group in alcohols by surface nucleophilic base
sites.33 To further investigate the effect of surface basicity on
the dehydrogenation, FTꢀIR spectra of butanol adsorption on
Cuꢀ4 and CaAlO samples were obtained (Fig.4). As for pristine
CaAlO, the band at 1032 cmꢀ1 is associated with alkoxide
species (CaꢀOꢀCH2ꢀR) formed through the interaction between
basic CaꢀO pairs on the catalyst surface and hydroxyl group in
butanol.34 Interestingly, after loading Cu NPs, the band related
to CaꢀOꢀCH2ꢀR species disappears, but another new band at
1072 cmꢀ1 representing CuꢀOꢀCH2ꢀR like species can be
observed.35 Meanwhile, the stretching bands of ꢀCH2 groups
blueꢀshifts by about 5 cm−1. The above results demonstrate that
CaAlO support may activate hydroxyl group in butanol, while
According to the above results, it can be concluded that
surface SLB sites in intimate contact with defective Cu NPs can
interact strongly with the hydroxyl group in 1,4ꢀBDO for
abstracting hydrogen, while the highly dispersed defective Cu
NPs can further abstract and transfer hydrogen. Cuꢀ3 catalyst
with smaller specific SLB sites and copper surface area shows a
lower catalytic performance than other Cuꢀx catalysts, due to
the insufficiency of catalytically active sites supplying for
transfer hydrogenation. However, the catalytic activity does not
change monotonically with the copper surface area or the
amount of SLB sites. Specially, compared with Cuꢀ4, Cuꢀ5
exhibits a lower catalytic activity, in spite of the larger number
of SLB sites or slightly higher copper surface area. Therefore,
there should be other factors affecting the catalytic process. As
it is well reported, surface electrophilic Cu+ species may
promote the hydrogenation of carbonyl compounds to some
extent by polarizing the C=O bond via the interaction with the
lone pair electron on the O atom.36 Thus, Cu+ species on
catalysts also may play an important role in further enhancing
the catalytic efficiency during the FL hydrogenation, thus
promoting the reaction equilibrium toward the production of
GBL (Table 1).
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Acknowledgment
We gratefully thank the financial support from National
Natural Science Foundation of China (21325624) and the
Fundamental Research Funds for the Central Universities
(buctrc201528).
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a cooperative nanoenvironment
composed of surface SLB sites, defective Cu NPs and Cu+
species, which efficiently hold the dehydrogenation of hydroxyl
group in 1,4 BDO and the hydrogenation of carbonyl group in
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Conclusions
5
In summary, we reported the fabrication of CaAlOꢀsupported
copper catalysts with strong base sites via a twoꢀstep procedure
based on CaAlꢀLDH precursor route. The resulting catalyst exhibited
superior catalytic performance for gasꢀphase solventꢀfree coupling
between dehydrogenation and hydrogenation without external
hydrogen supply or recycle to simultaneously produce GBL and
FOL. The HRTEM, PAS, XPS, CO2ꢀTPD, in situ IR of butanol
adsorption confirmed the existence of defective Cu NPs, abundant
SLB sites and Cu+ species on the catalyst surface, which created
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a
cooperative nanoenvironment for the highly efficient
dehydrogenation of hydroxyl group in 1,4 BDO and
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good stability with a lasting 100 h for the high yields of GBL
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Graphical and textual abstract
A solvent-free gas-phase coupling process through hydrogen transfer without external
hydrogen was conducted over novel bifunctional base-metal heterogeneous catalysts.