Carbon nanosphere supported Ru catalyst for the synthesis of renewable herbicide and chemicals

Article abstract of DOI:10.1016/j.catcom.2017.07.005

A carbon nanosphere supported Ru (Ru-CNS) effectively catalyzed the conversion of biorenewable platform chemicals to 5-aminoleulininc acid (ALA), furan alcohols and γ-valerolactone (GVL). The catalyst exhibits high activity for the investigated processes, enabling 76% ALA and > 90% furan alcohols and GVL from their precursors. The effect of solvent polarity on the yield and selectivity of GVL and its ring-opening product has been studied with detailed characterization of the catalyst.

Full text of DOI:10.1016/j.catcom.2017.07.005

CatalysisCommunications100(2017)206–209
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Carbon nanosphere supported Ru catalyst for the synthesis of renewable
herbicide and chemicals
Dinesh Guptaa,b, Basudeb Sahab,c,⁎
a
Department of Chemistry, Indian Institute of Technology Delhi, Delhi, India
Laboratory of Catalysis, Department of Chemistry, University of Delhi, Delhi 110007, India
Catalysis Center for Energy Innovation, Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716, USA
b
c
A R T I C L E I N F O
A B S T R A C T
Keywords:
A carbon nanosphere supported Ru (Ru-CNS) effectively catalyzed the conversion of biorenewable platform
chemicals to 5-aminoleulininc acid (ALA), furan alcohols and γ-valerolactone (GVL). The catalyst exhibits high
activity for the investigated processes, enabling 76% ALA and > 90% furan alcohols and GVL from their pre-
cursors. The effect of solvent polarity on the yield and selectivity of GVL and its ring-opening product has been
studied with detailed characterization of the catalyst.
Carbon sphere
Carbonaceous
Hydrogenation
5-Aminolevulinic acid
γ-valerolactone
1. Introduction
Despite being an active ingredient for many high value applications
and hence significant commercial interests, the potential of ALA has not
Rapid consumption of petrochemical products and the global efforts
to reduce carbon dioxide emissions necessitates the development of
sustainable processes for the production of industrial chemicals, phar-
maceutical ingredients, herbicides, micronutrient chelating agents and
more from biorenewable feedstock [1,2]. While catalytic conversion of
lignocellulose and carbohydrates into platform chemicals, 5-hydro-
xymethylfurfural (HMF), furfural (Ff), and their further transformation
into chemicals and transportation fuels via oxidation, condensation,
esterification, hydrogenation, and hydrodeoxygenation routes have
been studied in the past [3–6], upgrading furfurals into chemicals for
specialty applications, e.g., biodegradable herbicides, insecticides and
micronutrients is less studied. One such chemical is 5-aminolelulinic
acid (ALA) which is a precursor for biosynthesis of tetrapyrroles and an
effective non-toxic biodegradable herbicide and insecticide. ALA is a
plant growth promoter [7–9], which improves dry matter accumulation
in leaves, stems and pods thorough increased chlorophyll content and
photosynthetic CO2 absorption [7]. The growth parameters, pigment
(chlorophyll) contents and nutrition intake for ALA-based Pentakeep-V
micronutrient treated plants were higher than those without ALA [10].
Besides faster growth of Pentakeep treated plants at optimal ALA con-
centration, the results suggested a significant increase of N, Cu and Zn
contents in the leaves of treated plants and higher concentrations of P
and Zn in the soil. Other applications of ALA and its derivative products
include photodynamic therapy for cancer, dermatological disorder
[11], urology and gynecology [12] and heme biosynthesis [13].
been fully utilized, besides its current limited use as an additive in
Pentakeep-V micronutrient and as sensitizer in photodynamic
a
therapy. Low availability of ALA, owing to high production costs, is the
reason for its limited use [14–16]. The microbial processes for ALA
syntheses are slow and expensive, and generally not suited to produce
on larger scale to meet agrochemical demand. Among the recent pro-
cesses, Nudelman et al. reported an overall 50% yield of ALA from a
three step reaction involving ethyl succinyl chloride and imidazole as
starting reactants, and highly explosive methyl nitrate as a nitrating
agent [17]. Another report disclosed about 51% ALA yield via homo-
genous catalyzed conversion of phthalimide and epichlorohydrin in
four-steps [18]. Mascal et al. reported a three-step synthesis method for
the conversion of 5-chloromethylfurfural (CMF) into ALA with an
overall 68% yield (Scheme S1) [19].
γ-valerolactone (GVL) is another bio-renewable chemical for many
promising applications such as solvent, fuel additive and precursor for
high value chemicals (HVCs). The catalytic reduction of LA to GVL has
been reported with Ru/C Ru/Al2O3 and Ru/SiO2 catalysts in dioxane,
methanol and ethanol/water [20,21]. These reactions at varying tem-
peratures and PH2 ranging from 130 °C to 150 °C and 12 bar to 55 bar,
respectively, have achieved 72–89% GVL yields. Ir/C, Rh/C, Pd/C, Pt/
C, Re/C, MgO/Al2O3, MgO/ZrO2, CeZrOx and ZrO2 catalysts have also
been used for LA hydrogenation with molecular H2 or in-situ H2 gen-
erated via Catalytic Transfer Hydrogenation (CTH) using 2-butanol (2-
BuOH) or iso-propyl alcohol (IPA) [22,23]. The latter reactions yielded
⁎
Corresponding author at: Catalysis Center for Energy Innovation, University of Delaware, USA.
E-mail address: bsaha@udel.edu (B. Saha).
http://dx.doi.org/10.1016/j.catcom.2017.07.005
Received 16 April 2017; Received in revised form 5 July 2017; Accepted 8 July 2017
Availableonline10July2017
1566-7367/©2017ElsevierB.V.Allrightsreserved.

D. Gupta, B. Saha
CatalysisCommunications100(2017)206–209
Fig. 1. TEM and HRTEM images of Ru/CNS with different
magnifications showing (a) uniform particle size of CNS, (b)
wave-like flakes at the edge of CNS, and (c,d) Ru particles
on the surface of CNS.
lower GVL (8–47%), except the ZrO2 catalyzed hydrogenation in 2-
BuOH and IPA, which yielded 80–85% GVL for 4 h at 150 °C and 20 bar
He in which 2-BuOH and IPA formed H2 in-situ via CTH [23].
of Ru/CNS (Fig. S9) identifies several surface oxygen functional groups;
~1390 cm−1 for carboxyl group, ~3450 cm−1 for eOeH of inter-
calated water, 1740 cm−1 and 1620 cm−1 for eC]O and eC]Ce,
2920 cm−1 and 1630 cm−1 for eCeH of eCH2 and eCH3 groups. The
peaks between 1000 and 1300 cm−1 contains stretching and bending
vibrational modes for surface eCeOH groups, consistent with prior
report [27]. The oxygen functional groups make the CNS surface hy-
drophilic for adsorption of reactants and bind strongly with metals. In
addition, prior report demonstrated that CNS materials are stable in
aqueous systems [27].
In this paper, we report a method for the synthesis of ALA from
methyl levulinate (ML), which can be derived from biomass, via a three-
step process using a carbon nanosphere (CNS) supported Ru catalyst,
Ru-CNS. CNS is formed by pentagonal, hexagonal and heptagonal ar-
rangement of carbon rings [24]. The spherical arrangement of CNS with
C60 wave-like flakes and surface with curvature and open edges makes
this as an excellent support for metal binding and catalytic applications
[25,26]. In addition, hydrophilic surface of CNS is advantageous for
adsorption of reactants rendering beneficial catalysis. We found Ru-
CNS, prepared using our CNS support, is an effective catalyst for ALA
synthesis and hydrogenation of levulinic acid (LA) in different solvents,
Raman spectral analysis shows a strong G band at 1580 cm−1 and a
weak D band at 1365 cm−1 (Fig. S10a) in Ru/CNS. These bands cor-
respond to in-plane vibration associated with sp2 carbon (G band) and
sp3 carbon (D band). The high intensity of G band indicates that the
material contains high graphitic carbons. The XRD pattern (Fig. S10b)
shows a broad peak between 2θ = 19–25°, suggesting the presence of
amorphous carbon.
2. Experimental section
The morphologies of CNS and Ru-CNS were first characterized by
FESEM (Fig. S11). It shows spherical morphology for CNS (Fig. S11a)
with an average diameter of 400–600 nm. Notably, the size of the
carbon sphere depends on the synthesis conditions, e.g., glucose con-
centration, temperature and hydrothermal time. The full width at half
maximum (FWHM) of the CNS is 32 nm. Fig. S11d shows that Ru-na-
noparticles are tightly bound to CNS. The images of different magnifi-
cation also show Ru particles of about 10–20 nm sizes (Figs. S11c and
d) are present on CNS support with a wide particle size distribution
(Fig. S12, TEM image). SEM-EDX image (Fig. S13) further confirms that
Ru is present in the catalyst.
The spherical morphology of Ru-CNS was further investigated by
TEM and HRTEM (Fig. 1). Fig. 1a shows spherical shape for CNS of sizes
ranging between 400 nm and 500 nm. These particles are randomly
stacked on the edge and have wave-flake like edges (Fig. 1b). Magnified
HRTEM images (Fig. 1c and d) evidence the presence of Ru particles on
the CNS surface. N2-sorption isotherm of Ru-CNS (Fig. S14) reveals type
IV hysteresis with a BET surface area of 28 m2 g−1, obtained from BET
plot using multipoint BET equation, and porosity of about
0.38 cm3 g−1. Lower surface area of Ru-CNS than the traditional
carbon material could be due to the agglomeration of CNS particles via
π-π stacking of sp2 carbons as reported in prior study [24]. The surface
properties of Ru-CNS agree well with Fe0-CS, which exhibited high
activity for the oxidation organic pollutants [28,29].
2.1. Materials
Glucose, levulinic acid, methyllevulinate, 5-hydroxymethylfurfural,
furfural, RuCl3·3H2O, NaN3 were purchased from Sigma-Aldrich
(India). THF, acetonitrile, ethyl acetate, bromine, and NaBH4 were
purchased from Spectrochem. All chemicals were used as received.
Catalyst was prepared by a two-step process as discussed in the
Supporting information. Detailed characterization of the catalyst, ALA
synthesis procedure, hydrogenation of LA, HMF and Ff, and analysis of
reaction products by NMR (Figs. S1–S8) are in the Supporting in-
formation. Ru-CNS catalyst was prepared in two steps. First, carbon
nanosphere (CNS) was prepared via hydrothermal treatment of glucose
(5 g) in 25 mL water in a 100 mL stainless steel Parr reactor with teflon
lining at 180 °C for 24 h with continuous stirring at 500 rpm. As-syn-
thesized CNS, upon drying, was impregnated with RuCl3·3H2O and then
reduced with NaBH4 to obtain Ru-CNS. Detailed synthesis procedure for
Ru-CNS is in the Supporting information.
3. Results and discussions
3.1. Catalyst characterization
As-synthesized Ru-CNS was characterized by FE-SEM, XRD, HR-
TEM, BET, FT-IR and Raman spectroscopic techniques. FTIR spectrum
207

D. Gupta, B. Saha
CatalysisCommunications100(2017)206–209
Scheme 1. Synthesis of 5-aminolevulinic acid from me-
O
thyllevulinate.
O
O
Step1
Br2
O
O
Br
2
Step
N3
O
O
O
Step 3
H2 Ru-CNS
H2N
OH
3
NaN3
O
O
,
O
3.2. Catalysis
polar solvent, CS2. In the latter case, we observed no ring-opening
product and GVL is formed with 100% selectivity at 35% conversion
(entry 9). A reaction in non-polar solvent, hexane, yields GVL with high
selectivity (entry 10).
A reaction using reused catalyst yields comparable GVL in hexane.
Higher activity of Ru-CNS over Ru/C in EtOH could be due to the un-
ique structure of the carbon sphere of the former catalyst as reported in
prior report [29] as well as porous and oxygen functionalities of the
carbon sphere as observed from the FTIR and HRTEM analysis. Prior
reports on the structural effect of supports for Ru and Pt catalyzed
hydrogenation of LA to GVL, [34] including the beneficial effect of
immobilized metal loaded CNS catalysts are consistent with our ob-
servation [28,29].
In addition to the high activity of the Ru-CNS catalyst for LA hy-
drogenation, we found that this catalyst is also effective for Ff and HMF
hydrogenation to the corresponding furfural alcohols. The hydrogena-
tion of Ff and HMF (2 mmol) with 20 mg Ru-CNS at 4 bar H2 and 150 °C
enables quantitative conversion of substrates with 94% and 95% iso-
lated yields of mono hydroxymethyl furan (MHMF) and bis-hydro-
xymethylfuran (BHMF), respectively, for 3 h (Scheme S2). Because of
high use of MHMF and BHMF as monomers for the synthesis of variety
of polymeric materials such as resins and artificial fibers for high-value
uses, the current global annual consumption of furfural alcohols ex-
ceeds 300,000 MT which is projected to reach about 550,000 MT by
2020. Thus, development of effective catalytic hydrogenation routes for
the conversion of furfurals to furfural alcohols has received significant
attention in recent years. In this context, high yield of furfural alcohols
using the investigated Ru-CNS catalyst is significant.
The catalytic effectiveness of Ru-CNS was tested for the hydro-
genation of compound 3 (5-azide methyllevulinate; AML), LA, HMF and
Ff. First, we used AML as a substrate which was derived from methyl
levulinate (ML) via bromination followed by a reaction with NaN3
(Scheme 1). The yields of the brominated intermediate and AML are
72% and 71%, respectively. The resultant AML (1 mmol) was hydro-
genated with Ru-CNS (20 mg) with maximum 76% yield of ALA in THF.
Overall yield of ALA from the present method is higher compared to
those obtained from microbial processes [14,30]. The yield is lower
than the Mascal's method using CMF as a starting substrate [19] in
which high amount of expensive Pd/C catalyst (60 mg for 1.5 mmol
substrate) with high Pd loading (10 wt% Pd) was used for the hydro-
genation step. Thus, the present method achieving 76% ALA yield in the
hydrogenation step using less expensive Ru metal at lower catalyst
loading (20 mg with 5.2 wt% Ru loading for 1 mmol 3) could be ben-
eficial for ALA process economics.
To test the effectiveness of the Ru-CNS catalyst further, the hydro-
genation of LA was conducted at 20 bar H2 and 140 °C (Scheme 2).
Quantitative conversion of LA with 92% isolated yield of GVL and 1,4-
pentanediol (PDO) (82% and 18% selectivity, respectively) was ob-
tained in ethanol (Table 1, entry 1). To understand the effect of solvent
on the conversion of HMF to GVL, we investigated the reactions in polar
and non-polar solvents. These results are shown in Table 1. The cor-
responding 1H NMR spectra are in the Supporting information.
PDO yield is significant in solvent with high polarity, e.g., EtOH,
indicating ring-opening occurs in this solvent [31]. Less polar solvent,
acetonitrile, yields less PDO (entries 2–3). Based on prior reports sug-
gesting homogeneous metal salts (RuCl3, PdCl2) [32,33] formed metal
nanoparticulates under the hydrogenation conditions, which effectively
catalyzed LA hydrogenation, we used homogeneous RuCl3 as a catalyst.
This reaction achieved 56% LA conversion in acetonitrile; however
selectivity to PDO is high (65%; entry 4) when compared with Ru/CNS.
A controlled experiment in THF using GVL as a starting substrate re-
veals a very little conversion (2%) of GVL to PDO for 8 h (entry 5),
which is consistent with the results of LA conversion in THF (entry 6)
and suggest that GVL is stable in this solvent. PDO yield is less in CHCl3
even after 24 h of reaction with majority of products is GVL (83%)
(entry 7). Comparison of our results using Ru/CNS in EtOH with the
literature results using commercial Ru/C in EtOH (entry 8) [21] sug-
gests that the Ru/CNS catalyst, at higher substrate loading (moles of
LA/gRu = 3.84) than the literature Ru loading (moles of LA/
gRu = 2.1), is more effective in terms of GVL yield and selectivity as
well as its ring-opening to PDO. The effect of solvent polarity on ring-
opening and GVL selectivity becomes clear when we used a very less
4. Conclusions
We reported the synthesis of a Ru-CNS catalyst under hydrothermal
condition from glucose, and its morphological and structural char-
acterization using BET, FESEM, PXRD, HRTEM, FTIR and Raman
spectroscopic techniques. The catalytic effectiveness of Ru-CNS is in-
vestigated for the synthesis of 5-aminolevulinic acid from methyllevu-
linate (ML) and for the hydrogenation of 5-hydroxymethylfurfural,
furfural and levulinic acid to the corresponding furan alcohols and γ-
valerolactone. The results show high activity of the catalyst, enabling
76% 5-aminolevulinic acid yield from 5-azidemethyllevulinate and >
90% furfural alcohols and γ-valerolactone from their respective pre-
cursors, which can be derived from biomass. In addition, we elucidated
the effect of solvent polarity on the yield and selectivity of γ-valer-
olactone and its ring-opening product, and compared the results with
commercial Ru/C catalyst.
Acknowledgements
BS acknowledges Department of Science and Technology (DST),
New Delhi for funding this research (award number SR/S1/IC-61B/
2012). BS also acknowledges the financial support from the Catalysis
Center for Energy Innovation, an Energy Frontier Research Center
funded by the U.S. Department of Energy, Office of Science, Office of
Basic Energy Sciences under Award number DE-SC0001004 for the later
Scheme 2. Ru-CNS catalyzed conversion of levulinic acid to γ-valerolactone and 1,4-
pentanediol (PDO).
208

D. Gupta, B. Saha
CatalysisCommunications100(2017)206–209
Table 1
Comparison of levulinic acid conversion to γ-valerolactone and other products with Ru-CNS and commercial Ru/C in polar and non-polar solvents.
Entry
Substrates
Catalysts
P(H2)
bar
t (h)
Solvents
Conv. (%)
Selectivity (%)
GVL
Isolated yield (%)
Refs
PDO
1
2
LA
LA
LA
LA
GVL
LA
LA
LA
LA
LA
LA
Ru/CNS
Ru/CNS
Ru/CNS
RuCl3
Ru/CNS
Ru/CNS
Ru/CNS
Ru/C
20
20
20
20
20
20
20
12
20
20
20
6
2
6
6
8
6
24
2.7
6
EtOH
CH3CN
CH3CN
CH3CN
THF
> 99
40
> 99
56
82
100
88
35
–
100
83
81
100
100
100
18
–
12
65
100
–
17
–
–
92
–
91
–
–
92
–
61
–
94
92
CW
CW
CW
CW
CW
CW
CW
[21]
CW
CW
CW
3
4a
5
2
6
THF
> 99
48
75
35
> 99
> 99
7
CHCl3
EtOH
CS2
Hexane
Hexane
8b
9
Ru/CNS
Ru/CNS
Reused Ru/CNS
10
6
6
–
–
11c
a
RuCl3·3H2O = 10 mg
b
c
Commercial Ru/C with 5 wt% Ru loading (moles of LA/gRu = 2.1)
Reused Ru/CNS. Ru/CNS = 20 mg, solvent = 10 mL, 140 °C, all reactions were conducted in a Parr reactor, CW = current work. Moles of LA/gRu = 3.84.
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