Catalytic conversion of biomass-derived levulinic acid into alcohols over nanoporous Ru catalyst

Article abstract of DOI:10.1039/c7cy01838j

Several Ru-based catalysts were investigated under the same reaction conditions for levulinic acid (LA) hydrogenation. All LA conversion was 100% with the catalysts but the selectivity was different. The mina product was ?-valerolactone (GVL) by using powder Ru, Ru/C, and Ru/Al₂O₃ catalysts, yet it was 2-butanol (2-BO) and 2-pentanol (2-PO) with nanoporous Ru (NP-Ru) as catalyst. Several other nanoporous metal, e.g., Ni, Fe, Co, and Cu catalysts have been investigated for LA hydrogenation under the same reaction conditions, but the main product was still GVL with little 2-BO and 2-PO accompanied by serious leaching of catalyst. Results showed that NP-Ru play a positive role in the activation of GVL, which is generally difficult to achieve with mono-metallic catalysts unless under strict reaction ocnditions.

Full text of DOI:10.1039/c7cy01838j

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PAPER
Qingzhu Zhang et al.
Catalytic mechanism of C–F bond cleavage: insights from QM/MM
analysis of fluoroacetate dehalogenase
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Catalytic Conversion of Biomass-derived Levulinic Acid into
Alcohols over Nanoporous Ru Catalyst
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
b
a
a
a
a
Jinkun Lv , Zeming Rong* , Liming Sun , Chengyun Liu , An-Hui Lu , Yue Wang and Jingping Qu
DOI: 10.1039/x0xx00000x
www.rsc.org/
Abstract Several Ru-based catalysts were employed for the increased the selectivity of LA hydrogenation to give PDO in 93%
hydrogenation of levulinic acid and nanoporous Ru showed yield under 130 °C and 3 MPa. Palkovits et al. reported LA
attractive catalytic performance for alcohols production. It can be hydrogenation with Ru/C catalyst and a total 2-BO & 2-PO
found that the total yield of 2-Butanol & 2-pentanol was 78.8% yield of 75%, which is the highest result ever reported to date.
and yield of 1, 4-pentadiol was 74.6%, respectively acquired in However, the process had to be carried out under rigorous
1
40 °C and 100 °C using H
2 2
O as solvent. Thanks to its acid site and conditions with 190 °C and 10 MPa H pressure (Initial
1
lattice plane, nanoporous Ru provided sites for activating the pressure at room temperature). Arias used Ru/C catalyst for
9
lactone group of GVL and C-C/C-O bonds of PDO.
the transformation of MTHF (intermediate of LA
hydrogenation), the yield of 2-BO & 2-PO was 57.2% at 250 °C
2
0
Biomass has been identified as sustainable resource for fuels
and chemicals production which decreases the dependence on
and 4 MPa initial pressure. Li et al. employed Rh-MoO
catalyst for LA hydrogenation under relatively mild conditions
80 °C and 6 MPa), yet the total selectivity of 1-pentanol and 2-
x 2
/SiO
1
-3
fossil resources. Levulinic acid (LA), which has already being
efficiently produced from lignocellulosic biomass in pilot scale,
is originally conducted by the USDOE as key platform
molecules and starting materials to produce value-added
(
1
1
PO was only 15.8%. These previous results indicate that high
temperature and high H pressure are the indispensable
2
conditions for these supported metal catalysts in order to
promote the yield of 2-BO & 2-PO.
4
-6
chemicals.
-Butanol (2-BO) and 2-pentanol (2-PO) are important
monohydric alcohols, as they can be further converted into
2
4
, 7, 8
fuel, fuel additives and solvent.
Substantially, 2-BO/2-PO
can be acquired through removing extra oxygen within LA and
the overall reaction network is described in Scheme 1.
Step-a: LA is converted into γ-valerolactone (GVL) via
9
, 10
hydrogenation and subsequent cyclization.
Step-b, c: GVL is converted into 1, 4-pentadiol (PDO)
1
1-14
1
4-17
and 2-Methyltetrahydrofuran (MTHF)
through ring opening
and dehydration, respectively. Additionally, PDO and MTHF
can be transformed into each other through dehydration or
hydrolysis process.
Step-d, e: PDO undergoes two parallel pathways with C-C
Nanoporous metals are attractive materials with a high
bond scission to produce 2-BO and C-O bond scission to surface-area-to-volume ratio and a large proportion of low-
produce 2-PO. And 2-PO was also obtained by MTHF coordinated surface sites, and they have exhibited excellent
catalytic performance under mild conditions in hydrogenation,
hydrogenation.
2
1
Considering the multi-step activation of lactones, ether dehydrogenation and dehydration reactions.
Herein,
and C-C/C-O bonds, the catalyst for LA transformation ought to nanoporous Ru (NP-Ru) catalyst was used for the
play multiple roles in determining the reaction direction, thus transformation of LA to 2-BO & 2-PO and it showed
affecting the selectivity of PDO and 2-BO & 2-PO. Cao et al. noteworthy catalytic performance, which might derive from its
catalyzed GVL to PDO with Cu/ZrO in 200 °C and 6 MPa initial unique high index crystal surfaces.
2
1
pressure. Kaneda reported that Pt-Mo bimetallic catalyst
8
Firstly, several Ru-based catalysts were investigated
under the same reaction conditions for LA hydrogenation
(Table 1, entries 1-4). Obviously, all LA conversion was 100%
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with these catalysts but the selectivity was different. The main Furthermore, other several nanoporous metal (Ni, Fe, Co, Cu)
product was GVL by using powder Ru, Ru/C and Ru/Al catalysts were investigated for LA hydrogenation under the
catalysts, yet it was 2-BO & 2-PO and the highest productivity same reaction conditions, but the main product was still GVL
2 3
O
-
1 -1
reached 6.09 mmol2-O
g
metal
h
with NP-Ru as catalyst. The with little 2-BO & 2-PO accompanied with serious leaching of
difference illustrates that NP-Ru could more easily activate the catalyst
lactone group of GVL compared with other Ru catalysts.
(Table
S1).
Table 1. Catalytic performance of different catalysts on LA hydrogenation
c
a
Surface area
Particle size
(nm)
Yield (%)
Productivity
Cat.
2
-1 -1
(mmol2-Ogmetal h )
(m /g)
MTHF
2-BO
1.3
0.5
0
2-PO
0
GVL
86.0
93.4
100
4.7
PDO
8.6
5.2
0
Others
5
%Ru/C
796.8
200.3
1.8
2.3
0
0
4.1
1.5
0
2.71
1.04
0.0
5
%Ru/Al
2
O
3
1.9
0
Powder-Ru
NP-Ru
-
-
-
-
-
-
0
0
38.3
58.1
13.2
25.7
10.5
2.5
0.1
0
47.5
0.3
0.1
0
13.7
0.1
0
19.2
0.6
0
12.4
0.1
0.1
0
6.09
0.04
0.01
0.0
NP-Ni
98.8
99.8
NP-Co
b
NP-Fe
0
0
50.4
42.8
0
b
NP-Cu
0
0
0
0
0
0.0
Conditions: 2 mmol LA, 20 mL H
2
O, 0.01 g catalyst, 120 °C, initial hydrogen pressure 6.0 MPa, 24 h a. Productivity= n (2-BO & 2-PO)/(gmetal×t), b. Conversion=Yield, c.
with internal standard method and carbon balance
Yield was calculated
Our experimental results illustrate that NP-Ru seems to
play a positive role for the activation of GVL, which is generally
difficult to achieve with mono-metallic catalyst unless under
1
2, 13, 19, 22
strict reaction conditions
demonstrated that tuning the acidities and active metals of
. Several studies have
11-13, 23, 24
catalysts might be essential for the conversion of GVL.
Therefore, the acid sites of several Ru-based catalysts were
investigated with NH -TPD profiles (Figure S4). For NP-Ru, Ru/C
and Ru/Al samples, a common NH desorption peak
appeared at 197.3 °C, which was attributed to the weak acid
3
2
O
3
3
2
5
sites of Ru species on the surface of catalysts. On the other
hand, it was almost flat for the curve of powder Ru, indicating
the lack of acid sites and inefficiency for GVL transformation.
In addition to the acid sites, electronic effects might also have
influence on the catalytic activity of GVL transformation. XPS
was therefore used for comparing the difference of Ru
electron density between NP-Ru and powder Ru (Figure S5).
The binding energy of Ru metal for two catalysts were same at
catalytic performance for the conversion of GVL and PDO
compared with other Ru catalysts.
280.2 eV for Ru 3d5/2 and 284.4 eV for Ru 3d3/2. It means that
However, powder Ru was completely unable to activate
GVL, although it contained similar high-index planes with steps
and terrace to NP-Ru. According to XRD results, the diffraction
peak of powder Ru seemed much sharper than that of NP-Ru,
meaning powder Ru has high crystallinity and few defect sites,
which could also be confirmed by the comparison of HR-TEM
images (Figure 2a, b). On the contrary, XRD pattern of NP-Ru
indicated a broad and diffuse feature regarding their small
crystalline size and highly disordered structures which derived
from the etching of Ru-Al alloy. As a result, a large fraction of
low coordinated surface atoms could be obtained, and usually
NP-Ru was not modified by electron donator which could
make it more active, thus the influence of electronic effect
2
6-28
could be neglected.
In addition, XRD was used for the structure
characterization of the Ru-based catalysts in Figure 1. XRD
patterns of Ru/AC and Ru/Al
2 3
O showed the typical diffraction
peak at 2θ= 44.0° assigned to the (101) facet of Ru (JCPDS card
No. 65-7646). The broad peak with weak intensity meant the
small sizes of Ru particles mostly corresponding to edge or
corner active sites. NP-Ru and powder Ru gave the typical
diffraction peaks with respect to (101), (100), (002), (102),
2
7, 34
exerted positive influence on catalytic activity.
Thus, NP-
(
110), (103), (200), (112) and (201) facets. (102), (103), (112),
201) are often considered to be high-index planes with more
Ru could effectively provide active sites for the cleavage of C-O
(
and C-C bonds during transformation of GVL
PO under relatively mild conditions
→PDO→2-BO /2-
steps and terrace, which usually serve as active sites for the
2
activation of σ bonds and π bonds, such as C-C or C-O
9
30-33
.
NP-Ru could provide such active sites, so it showed higher
2
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Table 2. The effect of reaction conditions on the hydrogenation of LA
b
Yield (%)
a
Entry
T (°C)
P (MPa)
Catalyst (g)
time (h)
MTHF
2.5
1.9
2-BO
22.9
10.4
60.0
48.6
63.6
45.2
48.6
46.0
2-PO
7.7
GVL
4.1
4.6
0.0
0.5
0.0
4.5
3.1
2.6
PDO
55.3
74.6
4.5
Others
7.5
3.4
1
2
3
4
5
6
7
8
100
100
120
120
140
120
120
120
6
6
6
6
6
5
6
7
0.01
0.03
0.01
0.03
0.01
0.01
0.01
0.01
50
15
50
10
20
25
25
25
5.0
2.7
15.0
19.9
15.2
15.4
13.5
14.7
17.8
14.2
18.3
13.0
13.7
14.2
2.6
14.1
0.9
2.0
2.6
19.4
18.6
19.5
2.5
3.0
2 2
Conditions: 2 mmol LA, 20 mL H O a. H Pressure at room temperature, b. Yield was calculated with internal standard method and carbon balance
From a reaction kinetics viewpoint, GVL could be easily However, the result was exactly reversed and the highest ratio
converted into PDO and corresponding 2-PO/2-BO through the of 2-BO to 2-PO was up to 5.1 (Table S2). On the one hand, Li
3
dissociation of C-O/C-C bonds, which might be attributed to et al. studied the hydrogenation of primary aliphatic alcohols
5
the difference of activation energy between transformation of with Ru/TiO catalyst. Theoretical calculations reveal that C-C
2
GVL and PDO. In order to prove the hypothesis, the bond scission is preferred on flat Ru (0001), while C-O bond
hydrogenation kinetics of GVL and PDO were studied and the scission is preferred on stepped Ru (0001) and Ru (100). NP-Ru
apparent activation energy was calculated according to the with high-index planes contains more terrace, corresponding
reaction rate constants at different temperature (Figure S6- to the flat Ru planes. On the other hand, the solvent which is
S10). The apparent activation energy of Step-b, d, e were 65.88 by-product of dehydration could also exert negative influence
1
9
KJ/mol, 111.67 KJ/mol and 117.66 KJ/mol, respectively (Figure on 2-PO production (Table S3) . As a consequence, the solvent
3).
effect and facet of Ru are factors to determine the selectivity.
According to the reaction mechanism, 2-BO was produced
Because of E (b)<<E (d)<E (e), GVL was easily converted
a
a
a
into PDO, which was relatively stable with the highest 74.6% by the selective scission of C-C bond, simultaneously
yield under the optimum conditions (Table 2, entry 2). generating CO. The control experiments were performed in
Furthermore, PDO could be converted to 2-BO or 2-PO when Figure S11. After NP-Ru was pretreated with CO, the relative
the reaction conditions were promoted. According to the quite ratio of 2-BO to 2-PO decreased, while the production rate of
similar apparent activation energies of Step-d and Step-e, the 2-PO remained nearly unchanged. This demonstrates that the
yield of 2-PO should be slightly higher than that of 2-BO. removal of adsorbed CO on a Ru surface should be a crucial
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step for LA hydrogenation to 2-BO. Moreover, the mixed poisoning effect. So the accumulation of adsorbed CO might
3
6-38
product analysis in the gaseous phase showed the presence of be the major reason for deactivation
CH instead of CO (Figure S12), indicating a direct methanation
of CO over NP-Ru catalyst. The conversion of CO to CH might
be the retarding rate of C-C hydrogenolysis and contribute to
.
4
Table 4. Leaching results of recycling
4
a
Recycling
time
Leaching (ppm)
Leaching (%)
Ru
Al
1
st
0.011
0.0059
0.0028
0.0055
0.0091
0.010
0.053
0.045
0.038
0.033
0.037
0.037
0.034
0.046
0.031
0.036
0.0098
0.0078
0.0080
0.0085
0.0086
0.011
2
nd
3rd
4th
5th
6th
7th
8th
0.017
0.016
the largest energy barrier.
The influence of the reaction temperature, H
2
pressure
and the amount of catalysts were investigated. The results are
listed in Table 2. Evidently, an increase of the reaction
temperature leads to higher catalytic activity. Under the
2
optimum conditions of 140 °C and 6 MPa initial H pressure,
the total yield of 2-BO & 2-PO reached 78.8%, which is higher
than those reported results under relatively mild conditions
1
1, 12, 19, 20
(Table 3).
Table 3. Literature overview of 2-BO & 2-PO production from LA using heterogeneous
a. Ru stands for catalytic metal (ruthenium), Al stands for active metal
(aluminum)
Particle size
Yield (%)
Cat.
T (°C)
P (MPa)
Ref.
(nm)
2-BO
2-PO
37
1
9
In conclusion, NP-Ru catalyst exhibited attractive catalytic
Ru/AC
-
190
250
130
80
10
4
38
a
20
12
Ru/AC
-
37.3
18.9
5
activity for LA hdyrogenation to 2-BO and 2-PO using H O as
2
b
Pt-Mo/HAP
3.2
4.3
3
-
-
solvent. The total yield of 2-BO & 2-PO was 78.8% and yield of
PDO was 74.6%, respectively acquired in 140 °C and 100 °C.
1
1
Rh-Mo/SiO
2
6
15.1
This
Additionally, NH -TPD, XPS, XRD and HR-TEM were used as
3
NP-Ru
-
140
6
63.6
15.2
work
tools to compare the difference of the Ru-based catalysts. Acid
site and lattice plane might be responsible for activating the
lactone group of GVL and C-C/C-O bonds of PDO, thus
a. Substrate is γ-valerolactone; b. HAP is short for hydroxyapatite
The stability of NP-Ru was studied for LA hydrogenation determining the selectivity of product.
Figure 4). It remained relatively stable and the total yield of 2-
(
BO & 2-PO remained over 61% with full conversion of LA at run
-6. Nevertheless, the activity steadily declined with
Acknowledgement
1
continuous recycling and the yield of monohydric alcohols
dropped from 61.2% to 44.6 % at run 6-8, suggesting
significant deactivation. The loss of active sites by leaching or
poisoning was the key of catalyst deactivation. According to
This work was financially supported the Fundamental
Research Funds for the Central Universities (DUT16LK21).
the leaching results of recycling (Table 4) and control Notes and references
experiments (Figure S11), the active sites (Ru and Al) slightly
‡Footnotes relating to the main text should appear here. These
might include comments relevant to but not central to the
dissolved in the reaction liquid and the CO exerted a strong
4
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Catalysis Science & Technology
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DOI: 10.1039/C7CY01838J
Table of contents entry
1
, 4-pentanediol or monohydric alcohol was achieved with high selectivity from levulinic acid
under relatively mild conditions using nanoporous Ru.