- Email: [email protected]
Highly selective hydrogenation of levulinic acid catalyzed by Ru on TiO2-SiO2 hybrid support
Accepted Manuscript Title: Highly selective hydrogenation of levulinic acid catalyzed by Ru on TiO2 -SiO2 hybrid support Authors: Leandro D. Almeida, Ana Luiza A. Rocha, Thenner S. Rodrigues, Patricia A. Robles-Azocar PII: DOI: Reference:
S0920-5861(18)30347-X https://doi.org/10.1016/j.cattod.2018.12.022 CATTOD 11839
To appear in:
Catalysis Today
Received date: Revised date: Accepted date:
1 May 2018 21 November 2018 11 December 2018
Please cite this article as: Almeida LD, Rocha ALA, Rodrigues TS, Robles-Azocar PA, Highly selective hydrogenation of levulinic acid catalyzed by Ru on TiO2 -SiO2 hybrid support, Catalysis Today (2018), https://doi.org/10.1016/j.cattod.2018.12.022 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Highly selective hydrogenation of levulinic acid catalyzed by Ru on TiO2SiO2 hybrid support
Leandro D. Almeida a; Ana Luiza A. Rocha a; Thenner S. Rodrigues b; Patricia
aDepartamento
IP T
A. Robles-Azocar a *
de Química, Universidade Federal de Minas Gerais, Belo Horizonte
bInstituto
SC R
31270-901, MG, Brasil de Química- Universidade de São Paulo, São Paulo, Brasil
N
U
*Corresponding author: [email protected]
M
A
Graphical abstract
Have been developed an efficient catalyst for the catalytic conversion of LA into
A
CC E
PT
ED
GVL, ruthenium based catalyst in silica, titania and a silica-titania hybrid material.
IP T SC R U N A M
ED
Highlights
Ru-based catalysts were prepared in TiO2, SiO2 and TiO2-SiO2 supports
PT
using surfactant
The liquid-phase catalytic hydrogenation of levulinic acid reaction was
CC E
performed by the rutenium-based heterogeneous catalytis
High conversion for levulinic acid hydrogenation and selectivity to gammavalerolactone were obtained under mild reaction conditions
A
The catalyst prepared Ru-TS was more active and selective than either the Ru-SiO2 and Ru-TiO2catalysts.
It was obtained a high efficiency for Ru-TS and Ru-SiO2 after three cycles
Abstract Levulinic acid is an important molecule of biomass and the gammavalerolactone (GVL) is one of the most promising compound from levulinic acid. We have developed an efficient catalyst for the catalytic conversion of LA into GVL, ruthenium based catalyst in silica, titania and a silica-titania hybrid support The prepared catalysts were characterized by TEM, XRD, TPR and nitrogen
IP T
adsorption analysis. The results have shown higher catalytic activity of Ru/TiO2SiO2 than Ru/TiO2 either Ru/SiO2. Herein, we report that yields higher than 90% were obtained for gamma-valerolactone from levulinic acid hydrogenation
SC R
catalyzed by Ru/TiO2-SiO2 at 100°C and 20 atm of hydrogen without additives.
Keywords: Levulinic acid, hydrogenation, biomass, ruthenium catalyst, hybrid
1.
Introduction
ED
M
A
N
U
support
PT
Different categories of renewable sources of energy include solar, geothermal, wind, waves, hydric and biomass has been already used in several countries,
CC E
according the U.S. Energy Information Administration. Biomass has being studied exhaustively in the recent years, and it is considered one of the most promising substituent of the fossils fuels [1]. Lignocellulosic biomass (LB) is originated from agricultural residues (wheat straw, sugar cane bagasse, corn
A
bran), wood and plants [2]. LB is composed of cellulose (30-50%), hemicellulose (15-30%) and lignin (15-30%) [3–5]. Cellulose and hemicellulose are organic polymers; their monomeric units are composed of glucose and xylose, respectively [3,5]. These organic polymers can be cleaved by acid hydrolysis [4]. Glucose and xylose, can produce several industrial products like 5-hydroxymethyl furfural (5-HMF), lactic acid, formic
acid, acetic acid, ethylene, propylene, glycol, sorbitol, mannitol, furfural and levulinic acid (LA) [6,7]. Levulinic acid (LA) was considered one of the 12 most important molecules from biomass by the U.S. Department of Energy (US-DOE) [8]. Its importance is because it can be used in different segments of the industry such as ingredient for personal care, adsorbents, electronics, photography, batteries, drug delivery
IP T
system, lubricants and chemical intermediates [8,9]. The value-added chemicals which can be obtained from levulinic acid
transformations are 1,4-petanediol (PD), 2-methyl-tetrahydrofuran (MTHF) and
SC R
gamma-valerolactone [9].
Gamma-valerolactone (GVL) is a very interesting and important molecule for the industry, as it can be used as food additive, solvent, fuel additives,
U
insecticides, adhesives and chemical intermediates for the production of 2‐
N
methyltetrahydrofuran (MTHF), pentanoic acid, etc [7,9-11].
A
Extensive research has been performed on the hydrogenation of LA to GVL
M
using homogeneous and heterogeneous catalysts.that operate under milder reactions, give higher selectivities and can be recycled continuously are
ED
attracting considerable attention. GVL can be obtained from the hydrogenation of levulinic acid, over heterogeneous catalysts using different metals [7,12–17],
PT
supports [11,18–20], , co-catalyst [21], bimetallic catalyst [22,23].
CC E
(Figure 1. Levulinic acid hydrogenation to γ-Valerolactone)
Ruthenium-based catalysts are widely applied to this reaction [12,13,15]. Further,
A
the influence of support has been shown to significantly affect GVL yield [12,18,19] and to evaluate the deactivation of the catalyst is also of interest. One interesting support for catalytic reactions is the mixture of titanium and silica oxides. This support can increase the surface area and preserve the ntype semiconductor site of TiO2, while maintaining the characteristics of SiO2 (high surface area, mechanical and thermal stability) [24,25].
This paper presents the influence of supports SiO2, TiO2 and a hybrid of TiO2– SiO2 (TS) using CTAB as a surfactant in their preparation for to obtain ruthenium-based catalysts for the selective hydrogenation of LA to GVL under mild reaction conditions. Different reactions conditions like pressure,
2.
Experimental
2.1
Materials
IP T
temperature, solvent, time, and and recyclability were studied.
SC R
All the reagents were used as received without any purification procedure. For the catalyst synthesis hexadecyltrimethylammonium bromide (CTAB) (SigmaAldrich), titanium (IV) isopropoxide (TIOT) (Aldrich), tetraethyl orthosilicate
(TEOS) (Aldrich), ethanol absolute (Sigma-Aldrich), RuCl3 hydrate (Aldrich) and
U
deionized water. For the catalytic tests, levulinic acid >97% (Sigma), ethanol PA
Catalysts preparation
M
2.2
A
N
(Synth) and hydrogen (H2) (Air Products – UHP grade).
The synthesis of supports materials started from 25 mmol of TEOS, 3.37 mmol
ED
TIOT and 1.5 mL of ethanol for the hybrid material (TS) and other solution of 2.5 g of CTAB and 10 mL of ethanol. The solutions containing TEOS was slowly
PT
added to the CTAB solution and stirred for 30 minutes and were add in a Teflon reactor and stirred for 30 minutes. For the SiO2, 28.3 mmol of TEOS was used,
CC E
without TIOT. For TiO2 28.3 mmol of TIOT was used, without TEOS. The reactor was sealed and stirred at 40°C for 24 hours. After this, the reactor was placed in the oven at 90°C for 48 hours. The reactor was opened to dry the material at 110°C. The materials were heated in an opened tubular oven without
A
gas flow at 550°C for 3 hours with 10°C min-1 rate. The supports TiO2-SiO2 denominate TS, SiO2 and TiO2 were impregnated with an aqueous solution of RuCl3 (5% wt/wt) by wetness impregnation. After the water evaporation, the catalyst was dried at 110°C. The catalysts were reduced prior to use. The reduction of ruthenium was performed in a tubular oven using a mixture of H2/N2 (8%) with 50 mL min-1 flow, at 300°C for 2 hours with a heat
rate of 10°C min-1. The catalysts were denominated Ru-TS,5% Ru-SiO2 and 5%Ru-TiO2(5%Ru wt/wt).
2.3
Characterization of catalysts
2.3.1. Ru content
IP T
Total 5% of Ru content was determined by inductively-coupled plasma atomicemission spectrometry (ICP-AES) in a analytical instrument system, Spectro
2.3.2. Temperature Programmed Reduction (TPR)
SC R
Ciros CCD.
Temperature-Programmed Reduction (TPR) analysis was made in a Quantachrome – Chembet 3000 instrument equipped with a thermal
U
conductivity detector. The experiments were performed between 30 and 900 °C
.
A
1
N
in a flow of 8 % H2/N2, the temperature increasing linearly at a rate of 10 °C.min-
M
2.3.3. X ray diffraction (XRD)
Powder X ray diffraction (XRD) patterns were recorded on a Shimadzu XRD-
ED
7000 with cooper anode (CuKα1), scans from 7° to 80° 2θ and velocity of 4θ min-1 was utilized. The x ray diffraction patterns were identified using the
PT
Search-Match by Crystallographica software. 2.3.4. Adsorption/desorption of N2
CC E
The textural properties of catalysts were measured from nitrogen adsorption isotherms, in a Quantachrome NOVA equipment at 77 K. Specific surface areas were determined by the Brunauer-Emmett-Teller equation (BET method) from
A
adsorption isotherm generated in a relative pressure range 0.07 < P/Po < 0.3.. The average pore diameter was determined by the Barrett-Joyner-Halenda (BJH) method from the N2 desorption isotherms. 2.3.5. Transmission Electronic Microscope (TEM) Transmission electron microscope (TEM) images were taken with a Tecnai-G220 (FEI) electron microscope with an acceleration potential of 200 kV.
2.3.6. Fourier transform infrared spectroscopy (FTIR) The infrared spectrum was recorded in a Perkin Elmer FTIR RXI equipment. with a range of 400 – 4000 cm-1 with 64 scans. The samples were dilluted in KBr, previously dried at 110°C.
Levulinic acid hydrogenation
IP T
2.4.
The catalytic tests were carried out in a stainless steel reactor (100 mL). A 700 rpm stirring was used in all experiments. A 30 mL volume of a 0.5 mol L-1 of
SC R
levulinic acid and 0.05 g catalyst (5%wt Ru) was utilized, unless otherwise
stated. The reactor was purged three times with H2 to remove atmospheric air before being pressurized with H2. Catalyst recycling experiments were
U
performed as follows: after the reaction, the catalyst was centrifuged and washed with ethanol (25 mL) three times. The catalyst was dried at room
N
temperature.
A
The reactions were followed by gas chromatography (GC) (Shimadzu GC-2010
M
Plus instrument, Rtw®-wax capillary column and a flame ionization detector (FID). Periodically aliquots were analyzed at appropriate time intervals.
ED
The products identification was made by gas chromatography coupled with mass spectrometry (GC-MS) GC2010/QP2010-GC/MS equipment, using an
PT
electron impact detector at 70 eV.
The major product (GVL) was isolated by vacuum distillation and analyzed by H-Nuclear Magnetic Resonance (1H-NMR), 13C-Nuclear Magnetic Resonance
CC E
1
(13C-NMR) and DEPT-Nuclear Magnetic Resonance (DEPT-NMR) in a Bruker 200 MHz AVANCE DPX 200 spectrometer using acetone-d as solvent (see
A
Supporting Information). Spectroscopic data of γ-valerolactone: 1H NMR (200 MHz, acetone-d6): δ = 4.85 ppm (sex, Ha, CH), δ = 2.62 ppm (m, Hb, CH2), 2.04 ppm (m, Hc, CH2), δ = 1.58 ppm (d, Hd, CH3). 13C NMR (100 MHz, acetone-d6): δ = 177.76 ppm (Ce), δ = 77.96 ppm (Ca), δ = 30.73 ppm (Cb), δ = 29.85 ppm), δ = 21.68 ppm (Cd). MS (70 eV, EI): m/z 101 (0.4%), 100 (6%), 99 (4%), 85 (70%), 71 (2%), 57 (16%), 56 (100%), 39 (11%).
3. Results
3.1.
Catalyst characterization
The powder XRD patterns of the catalysts are shown in the Fig. 2. The Ru-TiO2
IP T
presented reflections patterns relative of rutile and mainly anatase crystalline structure. The silica supported catalyst (Ru-SiO2) showed a broad reflection in 23°, which is due to the amorphous silica support [28]. The hybrid Ru-TS has
SC R
the broad diffraction in 23° relative to silica structure, and diffractions of anatase phase of TiO2. It is not possible to observe the rutile phase in the hybrid
material, just the anatase phase, although not as pronounced as the TiO2
U
material.
N
(Figure 2. XRD patterns of ruthenium-supported materials (Ru-TiO2, Ru-SiO2,
M
A
Ru-TS and the TS support) ; α – Anatase, ρ – Rutile.)
The specific surface area BET and average pore diameter BJH are shown in
ED
the Table 1. It was observed that the ruthenium containing pure silica showed the highest specific area, the addition of TiO2 in the SiO2 structure showed decreases the specific surface area value (740 to 289 m2 g-1), probably the
PT
amorphous SiO2 phase delays the formation of the anatase/rutile TiO2 phases in the pore walls of SiO2 contributing to maintain a specific area higher than
CC E
TiO2. Further, the Ru-TiO2 exhibited the drastic drop in the specific surface area, which is inherent TiO2-based materials. The Ru-TS material have the highest pore volume value, this suggests that the
A
presence of TiO2 forming a hybrid support contributes to a slight improvement in the pore volume of the material. The increase of pore volume and average pore diameter in the impregnated catalyst Ru-TS is probably due to an intraparticules formation.
(Table 1)
Adsorption isotherms in the Figure 3 are type IV according to the IUPAC classification, it is characteristically of mesoporous materials (2 – 50 nm), implying that the catalysts have cylindrical shaped mesopores, as expected for materials obtained using surfactant, except for the Ru-TiO2, this presents an isotherm type II, characteristics of a non-porous material, which is in agreement
IP T
with the low pore volume (Table 1). The Figure 4 shows the pore distribution of the catalysts, it was observed that the silica-supported catalyst has a narrow distribution pore, centered in ~4
SC R
nm. The insertion of TiO2 in the SiO2 structure changes the porous
characteristics of the material. The Ru-TS catalyst has a wide pore distribution, as previously mentioned due to the formation of intraparticulate pores, which
U
probably prevents the formation of anatase /rutile phases.
A
N
Figure 3 – Nitrogen adsorption–desorption isotherms of Ru-based catalysts.
ED
M
Figure 4. Pore distribution of ruthenium- based catalysts.
3.1.1. Temperature Programmed Reduction
PT
The TPR profiles are shown in the Figure 5 and are characteristics for ruthenium supported catalyst [26,27]. It is possible note the presence of two
CC E
reduction events close to 169°C for all materials, these events are assigned to ruthenium reduction from chlorine and oxychlorine species, respectively (as represented in Figure 6) [26]. Ru-TS and Ru-TiO2 can be completely reduced until 200°C, while Ru-
A
SiO2 has a broadening reduction profile; this is an indication of a higher interaction between support/ruthenium. The reduction events in the Ru-TiO2 in temperatures higher than 400°C, are probably the reduction of exposed titanium in the catalyst surface. The absence of reduction peaks corresponding to TiO2 and indicates this are non-reducible under TPR analysis conditions
(Figure 5. TPR profiles of the catalysts before de reduction process)
(Figure 6. The proposed ruthenium surface reduction under hydrogen atmosphere)
IP T
The FTIR results (Figure S.9, Supplementary Information) of support, showed two peaks referents to the Ti-O-Si (960 cm-1) and Si-O-Si (1260 cm-1) vibrations [25]. This is an indicative of the titania doped silica structure.
SC R
The transmission electronic microscope (TEM) of all materials are
presented in the Figures 7 – 9, in SI can be found other TEM images (Figure S.10) and the element map of TS support (Figure S.11). The element map of
U
TS support, showed the dispersion of titanium in the doped silica structure.
N
The catalysts showed an average particle size of 2 – 3 nm for ruthenium.
A
It is possible to see a good dispersion of the ruthenium nanoparticles over all the supports. The TS and SiO2 supported catalyst, showed an amorphous
M
structure organization, which agrees with the XRD analysis. The Ru-TiO2 material has an organized structure that can be seen in the TEM images, this
PT
ED
structural organization agrees with the XRD analysis.
CC E
(Figure 7. TEM images and particle size histogram of Ru-TS catalyst)
(Figure 8. TEM images and particle size histogram of Ru-SiO2 catalyst)
A
(Figure 9. TEM images and particle size histogram of Ru-TiO2 catalyst)
3.2.
Catalytic hydrogenation of levulinic acid
The initial levulinic acid hydrogenation experiments were performed in order to verify the behavior of the Ru-TS catalyst in various solvents to evaluate the influence in the γ-valerolactone selectivity (Table 2). The use of aprotic solvents THF and 1,4-dioxane (Table 2, entries 4 and 5, respectively) resulted in a low conversion of levulinic acid furthermore, the reactions were not selective for GVL. In the polar solvents, as the alcohols (Table 2, entries 1-3) the conversion of LA increased (>80%) with a good selectivity for GVL. In methanol and
IP T
ethanol, the conversions were similar, but the selectivity for GVL is favored in ethanol.
SC R
(Table 2)
Tan and coworkers [29], evaluated the hydrogen solubility in different
U
solvents in the levulinic acid hydrogenation and verified that ethanol guarantee
N
a better solubility of hydrogen, which is agreement with the obtained yield for
A
different alcohols (Table 2, entry 2).
M
As can be seen in Fig. 10, in the methanol solvent the conversion can achieve 89% of LA in 3 h, however the selectivity for GVL is low. In n-butanol the selectivity is 70%, nevertheless after 8h, a satisfactory conversion of LA is
ED
achieved (80%). In the ethanol solvent, the LA hydrogenation presents high selectivity for GVL, after 6 hours is 80% (84% in 8 h) with high conversion.
PT
Probably the solvent leads to polarization of the carboxylic acid group in addition to maintaining the higher solubility of H2.
CC E
(Figure 10. Kinect curves for GVL obtaining from LA hydrogenation in alcohols
(a) LA conversion and (b) GVL selectivity.) The temperature influence for GVL production is presented in the Table 3. At
A
70°C, the maximum GVL yield obtained in 6 h was 62% (Table 3, entry 3), similar results were obtained in a shorter reactional time at 100°C (Table 3, entry 5) and 130°C (Table 3, entry 7). This suggests that over 100oC, using RuTS, the conversion of LA is most favored, without loss of selectivity.
(Table 3)
The effect of hydrogen pressure is illustrated in the Figure 11. In general, for liquid-phase hydrogenation, it is highly likely that the reaction can be rate limited by mass transfer. The increase in pressure has a significant improvement in conversion values and selectivity for GVL. Probably, in pressures higher than 20 atm of H2 the gas diffusion is efficient, ensuring an improvement in the
IP T
levulinic acid conversion and selectivity for γ-valerolactone. (Fig. 11). Similar yield for GVL was obtained at 20 and 30 atm. With the increase of the hydrogen pressure to 40 atm, the GVL selectivity decreased significantly, this can be
SC R
attributed to the formation of ethyl levulinate.
(Figure 11. Pressure effect in the catalytic hydrogenation of levulinic acid.
U
(Ethanol; 130°C; 6 h; 100 mg of 5%Ru-TS; [LA]=0.5 mol L-1))
N
To investigate the effect of reaction temperature and hydrogen pressure were
A
conducted experiments on different combinations of temperatura/pressure
M
(Table 4). It was observed, that the conversion was improved in temperatures higher than 100°C, as previously evaluated (Table 4). The highest yield of GVL is achieved at 100°C and 40 atm of H2 (Table 4, entry 8). However, a significant
ED
result is obtained at 100°C and 20 atm (Table 4, entry 2), the yield was 89%. at temperatures higher than 100°C may contribute to the increase of the AL
PT
hydrogenation rate with 100% conversion and maximum selectivity to GVL, however, probably under drastic conditions of high temperatures and pressure,
CC E
lead to the formation of their respective ester.
(Table 4)
A
processes are known for their high activity and selectivity for the desired product, for this reason this system was compared with the heterogeneous RuTS catalyst versus homogeneous catalytic systems to evaluate GVL yield [30]. The results are shown in Table 5.
(Table 5.)
(Figure 12. Levulinic acid hydrogenation catalyzed by homogeneous Ru-based.) The Ru-TS heterogeneous catalyst showed higher yields for GVL than the homogeneous system (Table 5, entry 1). After 24 h of reaction was not possible to achieve elevated yield for GVL in catalytic homogeneous systems (Table 5,
IP T
entries 3, 5), probably due the ester product is favored, ethyl levulinate (Figure 12). These results suggest that the hybrid inorganic support of TiO2-SiO2
SC R
contributes to the activation and diffusion of hydrogen on its surface, resulting in better adsorption of H2 and levulinic acid on the metal surface.
N
U
(Figure 13. Levulinic acid esterification to ethyl levulinate.)
A
The TON of Ru-TS was 108 times greater and 45 times greater than RuCl3 and
M
RuCl3/4PPh3 in 6 h reaction, respectively (Table 5, entries 1, 2 and 4). The Table 6 shows the results about the support influence in the selective
ED
hydrogenation of LA. The supported ruthenium catalysts Ru-TS, Ru-TiO2 and Ru-SiO2 (Table 6, entries 1-3) presented yields higher than 80% in 6 h reaction. The TiO2 based material presented a great selectivity for GVL, compared with
PT
the SiO2 material. While the SiO2 presented a higher conversion for LA, compared with the TiO2 material. However, the Ru-TS (Table 6, entry 1)
CC E
showed high conversion (similar the SiO2 catalyst) and high selectivity (similar the TiO2 catalyst). The hybrid TiO2-SiO2 support contributes with high ruthenium catalyst activity, due their characteristics: specific surface area, metal dispersion
A
and accessibility to metallic centers. The ruthenium reduction step was very important for the AL hydrogenation whereas unreduced ruthenium was not selective for LA hydrogenation (yield decreased to 20% for GVL), while the reduced catalyst showed a yield of 89% (entries 4 and 1, respectively). The non-reduced catalyst favored the selectivity for the esterification product (ethyl levulinate).
(Table 6)
A reason for the low yield for GVL, in the non-reduced catalyst, is the ruthenium chloride lixiviation, once it has a slight interaction with the support. Other hypothesis is the oxidation state of ruthenium species are not able to activate
IP T
the hydrogen molecule.
The Ru/C is often described as one of the best catalyst in the literature
SC R
[12,15,21,31-33]. Their activity was compared with the catalysts in this paper. The Ru/C was prepared with the same ruthenium percentage in mass by the wetness impregnation as described in the experimental section. The yield for
U
GVL is significantly higher when using Ru-TS (Table 6, entries 1 vs 5).
Probably, the pore channels of the Ru/C material are not as accessible as those
N
of the Ru-TS material.
A
The recyclability of a catalyst is one of the most important characteristics for
M
heterogeneous liquid phase catalysis. Catalyst deactivation can be caused by leaching of the active species or because of metal sintering. We have been
ED
studied the reuse of the catalysts. It was obtained a high efficiency for Ru-TS and Ru-SiO2 after three cycles (Figure 14).
CC E
PT
(Figure 14. Reuse of catalysts for levulinic acid hydrogenation.)
The Ru-TiO2 loses their activity during the reuse test, probably due a metal leaching; which it is based on a coloration change in the reaction medium. The selectivity of reuse remained constant around 90% for Ru-TS and 85% for Ru-
A
SiO2 cycles.
With the objective of evaluating the catalytic activity of the best catalysts of this work, were compared according to the specific surface area, equaling the area values per m2 of the Ru-TS and Ru-SiO2 catalysts (Table 7). The Ru-TS (289 m2 g-1) showed an activity greater than Ru-SiO2 (740 m2 g-1) using equal values of specific surface area (Table 7).
(Table 7)
Comparatively, this indicates that TS support contributes with ruthenium catalytic performance rather than silica in the selective hydrogenation of Al to GVL by specific surface area. In this case, the yield for GVL using of Ru-SiO2
IP T
(Table 7, entry 2) is similar to the reaction in the absence of catalyst. (Table 6,
SC R
entry 6).
.4. Conclusion
Ruthenium based catalysts, supported in matrices of silica, titania and a hybrid
U
titania-silica supports. The Ru-TS catalyst is proven to be an efficient catalyst for the levulinic acid hydrogenation with high selectivity for g- valerolactone. The
N
prepared Ru-TS presented high yield (89%) for GVL production in mild reaction
A
conditions. The Ru-TS and Ru-SIO2 catalysts were reused without loss of
ED
to be the most efficient.
M
catalytic activity. Comparing the catalyst load per m2, the Ru-TS catalyst proved
Acknowledgements
PT
The authors would like to acknowledge the Center of Microscopy at the Universidade Federal de Minas Gerais (http://www.microscopia.ufmg.br)
CC E
experiments involving electron microscopy and for their financial support. National Council for Scientific and Technological Development (CNPq). National Council for the Improvement of Higher Education (CAPES) and the authors
A
thank Minas Gerais State Foundation for Research Development FAPEMIG.
Supplementary material In the supplementary material can be found the N2 adsorption/desorption equations, NMRs spectrum, and GC-MS spectrum.
References [1]
A. Demirbas, Prog. Energy Combust. Sci. 31 (2005) 171–192.
[2]
P. Kumar, P., D.M. Barrett, M.J. Delwiche, M, P. Stroeve, P., Ind. Eng. Chem. (Analytical Ed. 48 (2009) 3713–3729. F. Liguori, C. Moreno-Marrodan, P. Barbaro, ACS Catal. 5 (2015) 1882–
IP T
[3]
1894.
W.R.H. Wright, R. Palkovits, ChemSusChem 5 (2012) 1657–1667.
[5]
D.M. Alonso, S.G. Wettstein, J.A. Dumesic, Green Chem. 15 (2013) 584.
[6]
J. Song, H. Fan, J. Ma, B. Han, Green Chem. 15 (2013) 2619–2635.
[7]
V. Mohan, C. Raghavendra, C.V. Pramod, B.D. Raju, K.S. Rama Rao,
SC R
[4]
A. Mukherjee, M.J. Dumont, V. Raghavan, Biomass and Bioenergy 72
N
[8]
U
RSC Adv. 4 (2014) 9660–9668.
C. Ortiz-Cervantes, J.J. García, Inorganica Chim. Acta 397 (2013) 124–
M
[9]
A
(2015) 143–183.
128.
ED
[10] W. Luo, U. Deka, A.M. Beale, E.R.H. Van Eck, P.C. a Bruijnincx, B.M. Weckhuysen, J. Catal. 301 (2013) 175–186.
PT
[11] J.Q. Bond, D.M. Alonso, D. Wang, R.M., West, J.A.Dumesic, Science, 327 (2010), pp. 1110-1114.
CC E
[12] L.E. Manzer, Appl. Catal. A Gen. 272 (2004) 249–256. [13] P.P. Upare, J.M. Lee, D.W. Hwang, S.B. Halligudi, Y.K. Hwang, J.S. Chang, J. Ind. Eng. Chem. 17 (2011) 287–292.
A
[14] K. Yan, T. Lafleur, G. Wu, J. Liao, C. Ceng, X. Xie, Appl. Catal. A Gen. 468 (2013) 52–58.
[15] Z. Yan, L. Lin, S. Liu, Energy & Fuels 23 (2009) 3853–3858. [16] K. Shimizu, S. Kanno, K. Kon, Green Chem. 16 (2014) 3899. [17] M. Sudhakar, M. Lakshmi Kantam, V. Swarna Jaya, R. Kishore, K. V. Ramanujachary, a. Venugopal, Catal. Commun. 50 (2014) 101–104.
[18] M. Chia, J. a. Dumesic, Chem. Commun. 47 (2011) 12233. [19]
a. M. Ruppert, J. Grams, M. Jdrzejczyk, J. Matras-Michalska, N. Keller, K. Ostojska, P. Sautet, ChemSusChem 8 (2015) 1538–1547.
[20] J. Ftouni, A. Muñoz-Murillo, A. Goryachev, J.P. Hofmann, E.J.M. Hensen, L. Lu, C.J. Kiely, P.C. a Bruijnincx, B.M. Weckhuysen, ACS Catal. 6 (2016) 5462–5472.
IP T
[21] A.M.R. Galletti, C. Antonetti, V. De Luise, M. Martinelli, Green Chem. 14 (2012) 688–694.
SC R
[22] D.J. Braden, C. a. Henao, J. Heltzel, C.C. Maravelias, J. a. Dumesic, Green Chem. 13 (2011) 1755.
[23] S.G. Wettstein, J.Q. Bond, D.M. Alonso, H.N. Pham, A.K. Datye, J. a.
U
Dumesic, Appl. Catal. B Environ. 117–118 (2012) 321–329.
[24] F. Boccuzzi, S. Coluccia, G. Martra, N. Ravasio, J. Catal. 184 (1999)
N
316–326.
A
[25] X. Gao, I.E. Wachs, Catal. Today 51 (1999) 233–254.
(2010) 269–272.
M
[26] V. a Mazzieri, M.R. Sad, C.R. Vera, C.L. Pieck, R. Grau, Quim. Nova 33
3658–3666.
ED
[27] G. Peng, F. Gramm, C. Ludwig, F. Vogel, Catal. Sci. Technol. 5 (2015)
PT
[28] X. Chen, J. Jiang, F. Yan, S. Tian, K. Li, RSC Adv. 4 (2014) 8703. [29] J. Tan, J. Cui, T. Deng, X. Cui, G. Ding, Y. Zhu, Y. Li, ChemCatChem 7
CC E
(2015) 508–512.
[30] Mehdi, H., Fábos, .V, Tuba, R. ,Bodor, A., Mika, L.T., Horváth, I. T. Topics in Catalysis 48 (2008) 49–54.
A
[31] M.G. Al-Shaal, W.R.H. Wright, R. Palkovits, Green Chem. 14 (2012)
[32]
1260. A. Phanopoulos, A.J.P. White, N.J. Long, P.W. Miller, ACS Catal. 5
(2015) 2500–2512. [33]
F.M.A. Geilen, B. Engendahl, A. Harwardt, W. Marquardt, J.
Klankermayer, W. Leitner, Angew. Chemie - Int. Ed. 49 (2010) 5510–5514.
SC R
IP T
Figure 1. Levulinic acid hydrogenation to γ-Valerolactone
U
TS
N
Ru-SiO2
ED PT
CC E
10
20
30
Ru-TS
M
A
Intensity (a.u.)
Ru-TiO2
40
50
60
70
80
2(°)
Figure 2. XRD patterns of ruthenium-supported materials (Ru-TiO2, Ru-SiO2, Ru-
A
TS and the TS support) ; α – Anatase, ρ – Rutile
500
3
-1
400
TS Ru-TS Ru-SiO2 Ru-TiO2
IP T
300
200
SC R
Adsorbed volume (cm g )
600
100
0 0,4
0,6
N
P/P0
0,8
1,0
U
0,2
A
CC E
PT
ED
M
A
Figure 3 – Nitrogen adsorption–desorption isotherms of Ru-based catalysts.
60
TS Ru-TS Ru-SiO2 Ru-TiO2
40
3
-1
-1
Pore Volume (cm g )
50
30
IP T
20
10
0 4
6
8
10
12
14
16
18
20
SC R
2
Pore diameter (nm)
M
A
N
U
Figure 4. Pore distribution of ruthenium- based catalysts
Ru-TS
ED PT
Ru-SiO2
CC E
Signal (a.u.)
169°C
A
Ru-TiO2
100
200
300
400
500
600
700
Temperature (°C)
Figure 5. TPR profiles of the catalysts before de reduction process
800
IP T
PT
ED
M
A
N
U
SC R
Figure 6. The proposed ruthenium surface reduction under hydrogen atmosphere
A
CC E
Figure 7. TEM images and particle size histogram of Ru-TS catalyst
IP T
M
A
N
U
SC R
Figure 8.TEM images and particle size histogram of Ru-SiO2 catalyst
A
CC E
PT
ED
Figure 9. TEM images and particle size histogram of Ru-TiO2 catalyst
Figure 10. Kinect curves for GVL obtaining from LA hydrogenation in alcohols (a) LA conversion and (b) GVL selectivity.
100
Conversion GVL selectivity GVL yield
80
IP T
%
60
20 0 20
30
40
U
10
SC R
40
N
Pressure (atm)
A
Figure 11. Pressure effect in the catalytic hydrogenation of levulinic acid.
CC E
PT
ED
M
(Ethanol; 130°C; 6 h; 100 mg of 5%Ru-TS; [LA]=0.5 mol L-1)
A
Figure 12. Levulinic acid hydrogenation catalyzed by homogeneous Ru-based
Figure 13. Levulinic acid esterification to ethyl levulinate
Cycle 1 Cycle 2 Cycle 3
100
80
IP T
Yield (%)
60
40
SC R
20
0
Ru-SiO2
Ru-TiO2
N
U
Ru-TS
A
CC E
PT
ED
M
A
Figure 14. Reuse of catalysts for levulinic acid hydrogenation.
Table 1 Catalysts specifics surface area BET and pore characteristics BJH Specific surface area
Pore volume
Average pore
BET (m2 g-1)
(cm3 g-1)
diameter (nm)
TS
389
0.7
7
Ru-TS
289
0.9
12
Ru-SiO2
740
0.8
4
Ru-TiO2
40
0.1
14
IP T
Catalyst
SC R
Table 2. Solvent influence in the LA hydrogenation catalyzed by Ru -TSa Solvent
Conversion (%)
Selectivity b (%)
Yield (%)
1
Methanol
95
62
59
2
Ethanol
98
86
3
n-Butanol
80
4
THF
61
5
1,4-dioxane
21
PT CC E A
N b
84
76
61
0
0
5
1
A M
130°C; 20 atm; 5%Ru-TS; 8 h; 0.5 mol L-1 LA
ED
a
U
Entry
Selectivity = mol GVL/ mol products*100
Table 3. Effect of the temperature on conversion and selectivity in AL hydrogenation catalyzed by Ru-TS a Selectivity b
Yield c
(%)
(%)
(%)
2
27
69
19
4
61
68
41
3
6
79
79
4
2
43
83
4
74
89
6
6
90
7
2
69
4
84
6
96
2
70
5
100
8
130
62 36 66
90
81
89
61
89
75
88
84
N
9
SC R
1
U
(°C)
Time (h)
IP T
Conversion
Temperature
Entry
Ethanol; 30 atm H2; 100 mg of 5% Ru-TS; 0.5 mol L-1 LA, bSelectivity = mol GVL/ mol products*100, cYield = conv. x sel./100
M
A
a
Table 4. Temperature and pressure effect in the levulinic acid hydrogenation a
(atm)
2
20
5 6
30
A
7
CC E
3 4
Conversion
Selectivity b
Yield c
(°C)
(%)
(%)
(%)
70
24
74
18
100
96
93
89
130
94
85
80
70
79
79
62
100
90
90
81
130
96
88
84
70
85
87
74
100
>99
95
95
130
>99
48
48
PT
1
Temperature
ED
Entry
Pressure
8 9
a c
40
Ethanol; 6 h; 100 mg of 5%Ru-TS; 0.5 mol L-1 LA Yield = conv. x sel./100
b
Selectivity = mol GVL/ mol products*100
Table 5. Comparison between homogeneous and heterogeneous catalytic system in GVL production from LA hydrogenation a Entry Catalyst
Conversion Selectivity GVLb
Yield GVcd
(%)
(%)
(%)
TON d
Ru-TS
96
93
89
542
2
RuCl3
61
4
2
5
3
RuCl3 b
92
41
38
4
RuCl3/4PPh3
74
8
6
5
RuCl3/4PPh3 b
89
19
17
IP T
1
75
SC R
12
Ethanol; 100 °C; 20 atm H2; 0.5 mol L-1; 6 h; 100 mg of 5% Ru-TS; 0,5% mol Ru in homogeneous reaction b Selectivity = mol GVL/ mol products*100 c Yield = conv. x sel./100 TON= total number of moles transformed into the GVL by one mole of active substrate consumption/TOF= site per hour
d
U
a
34
Catalyst
Conversion (%)
Selectivity
Yield
(%)
(%)
93
89
A
Entry
N
Table 6. Ru-based heterogenous catalysts: levulinic acid hydrogenation a
Ru-TS
96
2
Ru-SiO2
97
87
84
3
Ru-TiO2
91
92
84
4
Ru-TS b
71
29
21
5
Ru/C
28
70
20
6
No catalyst
37
56
21
ED
PT
Ethanol; 6 h; 100°C; 20 atm H2; 0.5 mol L-1 LA; 100 mg of catalyst Selectivity = mol GVL/ mol products*100 dYield = conv. x sel./100
b
Non-reduced catalyst
c
CC E
a
M
1
A
Table 7. Performance evaluation per m2 of ruthenium-based catalysts a
Entry Catalyst
Mass
Conversion Selectivity b Yield Activity d
catalyst (g)
(%)
(%)
c
(%) (mmol GVL m-2)
1
Ru-TS
0.050
96
93
89
1,94
2
Ru-SiO2
0.020
35
71
25
0,54
a c
–Ethanol; 100°C; 20 atm H2; 6 h; 0.5 mol L-1 LA
Yield = conv. x sel./100
d
b
Selectivity = mol GVL/ mol products*100
mmol of GVL/specific area BET
S0920-5861(18)30347-X https://doi.org/10.1016/j.cattod.2018.12.022 CATTOD 11839
To appear in:
Catalysis Today
Received date: Revised date: Accepted date:
1 May 2018 21 November 2018 11 December 2018
Please cite this article as: Almeida LD, Rocha ALA, Rodrigues TS, Robles-Azocar PA, Highly selective hydrogenation of levulinic acid catalyzed by Ru on TiO2 -SiO2 hybrid support, Catalysis Today (2018), https://doi.org/10.1016/j.cattod.2018.12.022 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Highly selective hydrogenation of levulinic acid catalyzed by Ru on TiO2SiO2 hybrid support
Leandro D. Almeida a; Ana Luiza A. Rocha a; Thenner S. Rodrigues b; Patricia
aDepartamento
IP T
A. Robles-Azocar a *
de Química, Universidade Federal de Minas Gerais, Belo Horizonte
bInstituto
SC R
31270-901, MG, Brasil de Química- Universidade de São Paulo, São Paulo, Brasil
N
U
*Corresponding author: [email protected]
M
A
Graphical abstract
Have been developed an efficient catalyst for the catalytic conversion of LA into
A
CC E
PT
ED
GVL, ruthenium based catalyst in silica, titania and a silica-titania hybrid material.
IP T SC R U N A M
ED
Highlights
Ru-based catalysts were prepared in TiO2, SiO2 and TiO2-SiO2 supports
PT
using surfactant
The liquid-phase catalytic hydrogenation of levulinic acid reaction was
CC E
performed by the rutenium-based heterogeneous catalytis
High conversion for levulinic acid hydrogenation and selectivity to gammavalerolactone were obtained under mild reaction conditions
A
The catalyst prepared Ru-TS was more active and selective than either the Ru-SiO2 and Ru-TiO2catalysts.
It was obtained a high efficiency for Ru-TS and Ru-SiO2 after three cycles
Abstract Levulinic acid is an important molecule of biomass and the gammavalerolactone (GVL) is one of the most promising compound from levulinic acid. We have developed an efficient catalyst for the catalytic conversion of LA into GVL, ruthenium based catalyst in silica, titania and a silica-titania hybrid support The prepared catalysts were characterized by TEM, XRD, TPR and nitrogen
IP T
adsorption analysis. The results have shown higher catalytic activity of Ru/TiO2SiO2 than Ru/TiO2 either Ru/SiO2. Herein, we report that yields higher than 90% were obtained for gamma-valerolactone from levulinic acid hydrogenation
SC R
catalyzed by Ru/TiO2-SiO2 at 100°C and 20 atm of hydrogen without additives.
Keywords: Levulinic acid, hydrogenation, biomass, ruthenium catalyst, hybrid
1.
Introduction
ED
M
A
N
U
support
PT
Different categories of renewable sources of energy include solar, geothermal, wind, waves, hydric and biomass has been already used in several countries,
CC E
according the U.S. Energy Information Administration. Biomass has being studied exhaustively in the recent years, and it is considered one of the most promising substituent of the fossils fuels [1]. Lignocellulosic biomass (LB) is originated from agricultural residues (wheat straw, sugar cane bagasse, corn
A
bran), wood and plants [2]. LB is composed of cellulose (30-50%), hemicellulose (15-30%) and lignin (15-30%) [3–5]. Cellulose and hemicellulose are organic polymers; their monomeric units are composed of glucose and xylose, respectively [3,5]. These organic polymers can be cleaved by acid hydrolysis [4]. Glucose and xylose, can produce several industrial products like 5-hydroxymethyl furfural (5-HMF), lactic acid, formic
acid, acetic acid, ethylene, propylene, glycol, sorbitol, mannitol, furfural and levulinic acid (LA) [6,7]. Levulinic acid (LA) was considered one of the 12 most important molecules from biomass by the U.S. Department of Energy (US-DOE) [8]. Its importance is because it can be used in different segments of the industry such as ingredient for personal care, adsorbents, electronics, photography, batteries, drug delivery
IP T
system, lubricants and chemical intermediates [8,9]. The value-added chemicals which can be obtained from levulinic acid
transformations are 1,4-petanediol (PD), 2-methyl-tetrahydrofuran (MTHF) and
SC R
gamma-valerolactone [9].
Gamma-valerolactone (GVL) is a very interesting and important molecule for the industry, as it can be used as food additive, solvent, fuel additives,
U
insecticides, adhesives and chemical intermediates for the production of 2‐
N
methyltetrahydrofuran (MTHF), pentanoic acid, etc [7,9-11].
A
Extensive research has been performed on the hydrogenation of LA to GVL
M
using homogeneous and heterogeneous catalysts.that operate under milder reactions, give higher selectivities and can be recycled continuously are
ED
attracting considerable attention. GVL can be obtained from the hydrogenation of levulinic acid, over heterogeneous catalysts using different metals [7,12–17],
PT
supports [11,18–20], , co-catalyst [21], bimetallic catalyst [22,23].
CC E
(Figure 1. Levulinic acid hydrogenation to γ-Valerolactone)
Ruthenium-based catalysts are widely applied to this reaction [12,13,15]. Further,
A
the influence of support has been shown to significantly affect GVL yield [12,18,19] and to evaluate the deactivation of the catalyst is also of interest. One interesting support for catalytic reactions is the mixture of titanium and silica oxides. This support can increase the surface area and preserve the ntype semiconductor site of TiO2, while maintaining the characteristics of SiO2 (high surface area, mechanical and thermal stability) [24,25].
This paper presents the influence of supports SiO2, TiO2 and a hybrid of TiO2– SiO2 (TS) using CTAB as a surfactant in their preparation for to obtain ruthenium-based catalysts for the selective hydrogenation of LA to GVL under mild reaction conditions. Different reactions conditions like pressure,
2.
Experimental
2.1
Materials
IP T
temperature, solvent, time, and and recyclability were studied.
SC R
All the reagents were used as received without any purification procedure. For the catalyst synthesis hexadecyltrimethylammonium bromide (CTAB) (SigmaAldrich), titanium (IV) isopropoxide (TIOT) (Aldrich), tetraethyl orthosilicate
(TEOS) (Aldrich), ethanol absolute (Sigma-Aldrich), RuCl3 hydrate (Aldrich) and
U
deionized water. For the catalytic tests, levulinic acid >97% (Sigma), ethanol PA
Catalysts preparation
M
2.2
A
N
(Synth) and hydrogen (H2) (Air Products – UHP grade).
The synthesis of supports materials started from 25 mmol of TEOS, 3.37 mmol
ED
TIOT and 1.5 mL of ethanol for the hybrid material (TS) and other solution of 2.5 g of CTAB and 10 mL of ethanol. The solutions containing TEOS was slowly
PT
added to the CTAB solution and stirred for 30 minutes and were add in a Teflon reactor and stirred for 30 minutes. For the SiO2, 28.3 mmol of TEOS was used,
CC E
without TIOT. For TiO2 28.3 mmol of TIOT was used, without TEOS. The reactor was sealed and stirred at 40°C for 24 hours. After this, the reactor was placed in the oven at 90°C for 48 hours. The reactor was opened to dry the material at 110°C. The materials were heated in an opened tubular oven without
A
gas flow at 550°C for 3 hours with 10°C min-1 rate. The supports TiO2-SiO2 denominate TS, SiO2 and TiO2 were impregnated with an aqueous solution of RuCl3 (5% wt/wt) by wetness impregnation. After the water evaporation, the catalyst was dried at 110°C. The catalysts were reduced prior to use. The reduction of ruthenium was performed in a tubular oven using a mixture of H2/N2 (8%) with 50 mL min-1 flow, at 300°C for 2 hours with a heat
rate of 10°C min-1. The catalysts were denominated Ru-TS,5% Ru-SiO2 and 5%Ru-TiO2(5%Ru wt/wt).
2.3
Characterization of catalysts
2.3.1. Ru content
IP T
Total 5% of Ru content was determined by inductively-coupled plasma atomicemission spectrometry (ICP-AES) in a analytical instrument system, Spectro
2.3.2. Temperature Programmed Reduction (TPR)
SC R
Ciros CCD.
Temperature-Programmed Reduction (TPR) analysis was made in a Quantachrome – Chembet 3000 instrument equipped with a thermal
U
conductivity detector. The experiments were performed between 30 and 900 °C
.
A
1
N
in a flow of 8 % H2/N2, the temperature increasing linearly at a rate of 10 °C.min-
M
2.3.3. X ray diffraction (XRD)
Powder X ray diffraction (XRD) patterns were recorded on a Shimadzu XRD-
ED
7000 with cooper anode (CuKα1), scans from 7° to 80° 2θ and velocity of 4θ min-1 was utilized. The x ray diffraction patterns were identified using the
PT
Search-Match by Crystallographica software. 2.3.4. Adsorption/desorption of N2
CC E
The textural properties of catalysts were measured from nitrogen adsorption isotherms, in a Quantachrome NOVA equipment at 77 K. Specific surface areas were determined by the Brunauer-Emmett-Teller equation (BET method) from
A
adsorption isotherm generated in a relative pressure range 0.07 < P/Po < 0.3.. The average pore diameter was determined by the Barrett-Joyner-Halenda (BJH) method from the N2 desorption isotherms. 2.3.5. Transmission Electronic Microscope (TEM) Transmission electron microscope (TEM) images were taken with a Tecnai-G220 (FEI) electron microscope with an acceleration potential of 200 kV.
2.3.6. Fourier transform infrared spectroscopy (FTIR) The infrared spectrum was recorded in a Perkin Elmer FTIR RXI equipment. with a range of 400 – 4000 cm-1 with 64 scans. The samples were dilluted in KBr, previously dried at 110°C.
Levulinic acid hydrogenation
IP T
2.4.
The catalytic tests were carried out in a stainless steel reactor (100 mL). A 700 rpm stirring was used in all experiments. A 30 mL volume of a 0.5 mol L-1 of
SC R
levulinic acid and 0.05 g catalyst (5%wt Ru) was utilized, unless otherwise
stated. The reactor was purged three times with H2 to remove atmospheric air before being pressurized with H2. Catalyst recycling experiments were
U
performed as follows: after the reaction, the catalyst was centrifuged and washed with ethanol (25 mL) three times. The catalyst was dried at room
N
temperature.
A
The reactions were followed by gas chromatography (GC) (Shimadzu GC-2010
M
Plus instrument, Rtw®-wax capillary column and a flame ionization detector (FID). Periodically aliquots were analyzed at appropriate time intervals.
ED
The products identification was made by gas chromatography coupled with mass spectrometry (GC-MS) GC2010/QP2010-GC/MS equipment, using an
PT
electron impact detector at 70 eV.
The major product (GVL) was isolated by vacuum distillation and analyzed by H-Nuclear Magnetic Resonance (1H-NMR), 13C-Nuclear Magnetic Resonance
CC E
1
(13C-NMR) and DEPT-Nuclear Magnetic Resonance (DEPT-NMR) in a Bruker 200 MHz AVANCE DPX 200 spectrometer using acetone-d as solvent (see
A
Supporting Information). Spectroscopic data of γ-valerolactone: 1H NMR (200 MHz, acetone-d6): δ = 4.85 ppm (sex, Ha, CH), δ = 2.62 ppm (m, Hb, CH2), 2.04 ppm (m, Hc, CH2), δ = 1.58 ppm (d, Hd, CH3). 13C NMR (100 MHz, acetone-d6): δ = 177.76 ppm (Ce), δ = 77.96 ppm (Ca), δ = 30.73 ppm (Cb), δ = 29.85 ppm), δ = 21.68 ppm (Cd). MS (70 eV, EI): m/z 101 (0.4%), 100 (6%), 99 (4%), 85 (70%), 71 (2%), 57 (16%), 56 (100%), 39 (11%).
3. Results
3.1.
Catalyst characterization
The powder XRD patterns of the catalysts are shown in the Fig. 2. The Ru-TiO2
IP T
presented reflections patterns relative of rutile and mainly anatase crystalline structure. The silica supported catalyst (Ru-SiO2) showed a broad reflection in 23°, which is due to the amorphous silica support [28]. The hybrid Ru-TS has
SC R
the broad diffraction in 23° relative to silica structure, and diffractions of anatase phase of TiO2. It is not possible to observe the rutile phase in the hybrid
material, just the anatase phase, although not as pronounced as the TiO2
U
material.
N
(Figure 2. XRD patterns of ruthenium-supported materials (Ru-TiO2, Ru-SiO2,
M
A
Ru-TS and the TS support) ; α – Anatase, ρ – Rutile.)
The specific surface area BET and average pore diameter BJH are shown in
ED
the Table 1. It was observed that the ruthenium containing pure silica showed the highest specific area, the addition of TiO2 in the SiO2 structure showed decreases the specific surface area value (740 to 289 m2 g-1), probably the
PT
amorphous SiO2 phase delays the formation of the anatase/rutile TiO2 phases in the pore walls of SiO2 contributing to maintain a specific area higher than
CC E
TiO2. Further, the Ru-TiO2 exhibited the drastic drop in the specific surface area, which is inherent TiO2-based materials. The Ru-TS material have the highest pore volume value, this suggests that the
A
presence of TiO2 forming a hybrid support contributes to a slight improvement in the pore volume of the material. The increase of pore volume and average pore diameter in the impregnated catalyst Ru-TS is probably due to an intraparticules formation.
(Table 1)
Adsorption isotherms in the Figure 3 are type IV according to the IUPAC classification, it is characteristically of mesoporous materials (2 – 50 nm), implying that the catalysts have cylindrical shaped mesopores, as expected for materials obtained using surfactant, except for the Ru-TiO2, this presents an isotherm type II, characteristics of a non-porous material, which is in agreement
IP T
with the low pore volume (Table 1). The Figure 4 shows the pore distribution of the catalysts, it was observed that the silica-supported catalyst has a narrow distribution pore, centered in ~4
SC R
nm. The insertion of TiO2 in the SiO2 structure changes the porous
characteristics of the material. The Ru-TS catalyst has a wide pore distribution, as previously mentioned due to the formation of intraparticulate pores, which
U
probably prevents the formation of anatase /rutile phases.
A
N
Figure 3 – Nitrogen adsorption–desorption isotherms of Ru-based catalysts.
ED
M
Figure 4. Pore distribution of ruthenium- based catalysts.
3.1.1. Temperature Programmed Reduction
PT
The TPR profiles are shown in the Figure 5 and are characteristics for ruthenium supported catalyst [26,27]. It is possible note the presence of two
CC E
reduction events close to 169°C for all materials, these events are assigned to ruthenium reduction from chlorine and oxychlorine species, respectively (as represented in Figure 6) [26]. Ru-TS and Ru-TiO2 can be completely reduced until 200°C, while Ru-
A
SiO2 has a broadening reduction profile; this is an indication of a higher interaction between support/ruthenium. The reduction events in the Ru-TiO2 in temperatures higher than 400°C, are probably the reduction of exposed titanium in the catalyst surface. The absence of reduction peaks corresponding to TiO2 and indicates this are non-reducible under TPR analysis conditions
(Figure 5. TPR profiles of the catalysts before de reduction process)
(Figure 6. The proposed ruthenium surface reduction under hydrogen atmosphere)
IP T
The FTIR results (Figure S.9, Supplementary Information) of support, showed two peaks referents to the Ti-O-Si (960 cm-1) and Si-O-Si (1260 cm-1) vibrations [25]. This is an indicative of the titania doped silica structure.
SC R
The transmission electronic microscope (TEM) of all materials are
presented in the Figures 7 – 9, in SI can be found other TEM images (Figure S.10) and the element map of TS support (Figure S.11). The element map of
U
TS support, showed the dispersion of titanium in the doped silica structure.
N
The catalysts showed an average particle size of 2 – 3 nm for ruthenium.
A
It is possible to see a good dispersion of the ruthenium nanoparticles over all the supports. The TS and SiO2 supported catalyst, showed an amorphous
M
structure organization, which agrees with the XRD analysis. The Ru-TiO2 material has an organized structure that can be seen in the TEM images, this
PT
ED
structural organization agrees with the XRD analysis.
CC E
(Figure 7. TEM images and particle size histogram of Ru-TS catalyst)
(Figure 8. TEM images and particle size histogram of Ru-SiO2 catalyst)
A
(Figure 9. TEM images and particle size histogram of Ru-TiO2 catalyst)
3.2.
Catalytic hydrogenation of levulinic acid
The initial levulinic acid hydrogenation experiments were performed in order to verify the behavior of the Ru-TS catalyst in various solvents to evaluate the influence in the γ-valerolactone selectivity (Table 2). The use of aprotic solvents THF and 1,4-dioxane (Table 2, entries 4 and 5, respectively) resulted in a low conversion of levulinic acid furthermore, the reactions were not selective for GVL. In the polar solvents, as the alcohols (Table 2, entries 1-3) the conversion of LA increased (>80%) with a good selectivity for GVL. In methanol and
IP T
ethanol, the conversions were similar, but the selectivity for GVL is favored in ethanol.
SC R
(Table 2)
Tan and coworkers [29], evaluated the hydrogen solubility in different
U
solvents in the levulinic acid hydrogenation and verified that ethanol guarantee
N
a better solubility of hydrogen, which is agreement with the obtained yield for
A
different alcohols (Table 2, entry 2).
M
As can be seen in Fig. 10, in the methanol solvent the conversion can achieve 89% of LA in 3 h, however the selectivity for GVL is low. In n-butanol the selectivity is 70%, nevertheless after 8h, a satisfactory conversion of LA is
ED
achieved (80%). In the ethanol solvent, the LA hydrogenation presents high selectivity for GVL, after 6 hours is 80% (84% in 8 h) with high conversion.
PT
Probably the solvent leads to polarization of the carboxylic acid group in addition to maintaining the higher solubility of H2.
CC E
(Figure 10. Kinect curves for GVL obtaining from LA hydrogenation in alcohols
(a) LA conversion and (b) GVL selectivity.) The temperature influence for GVL production is presented in the Table 3. At
A
70°C, the maximum GVL yield obtained in 6 h was 62% (Table 3, entry 3), similar results were obtained in a shorter reactional time at 100°C (Table 3, entry 5) and 130°C (Table 3, entry 7). This suggests that over 100oC, using RuTS, the conversion of LA is most favored, without loss of selectivity.
(Table 3)
The effect of hydrogen pressure is illustrated in the Figure 11. In general, for liquid-phase hydrogenation, it is highly likely that the reaction can be rate limited by mass transfer. The increase in pressure has a significant improvement in conversion values and selectivity for GVL. Probably, in pressures higher than 20 atm of H2 the gas diffusion is efficient, ensuring an improvement in the
IP T
levulinic acid conversion and selectivity for γ-valerolactone. (Fig. 11). Similar yield for GVL was obtained at 20 and 30 atm. With the increase of the hydrogen pressure to 40 atm, the GVL selectivity decreased significantly, this can be
SC R
attributed to the formation of ethyl levulinate.
(Figure 11. Pressure effect in the catalytic hydrogenation of levulinic acid.
U
(Ethanol; 130°C; 6 h; 100 mg of 5%Ru-TS; [LA]=0.5 mol L-1))
N
To investigate the effect of reaction temperature and hydrogen pressure were
A
conducted experiments on different combinations of temperatura/pressure
M
(Table 4). It was observed, that the conversion was improved in temperatures higher than 100°C, as previously evaluated (Table 4). The highest yield of GVL is achieved at 100°C and 40 atm of H2 (Table 4, entry 8). However, a significant
ED
result is obtained at 100°C and 20 atm (Table 4, entry 2), the yield was 89%. at temperatures higher than 100°C may contribute to the increase of the AL
PT
hydrogenation rate with 100% conversion and maximum selectivity to GVL, however, probably under drastic conditions of high temperatures and pressure,
CC E
lead to the formation of their respective ester.
(Table 4)
A
processes are known for their high activity and selectivity for the desired product, for this reason this system was compared with the heterogeneous RuTS catalyst versus homogeneous catalytic systems to evaluate GVL yield [30]. The results are shown in Table 5.
(Table 5.)
(Figure 12. Levulinic acid hydrogenation catalyzed by homogeneous Ru-based.) The Ru-TS heterogeneous catalyst showed higher yields for GVL than the homogeneous system (Table 5, entry 1). After 24 h of reaction was not possible to achieve elevated yield for GVL in catalytic homogeneous systems (Table 5,
IP T
entries 3, 5), probably due the ester product is favored, ethyl levulinate (Figure 12). These results suggest that the hybrid inorganic support of TiO2-SiO2
SC R
contributes to the activation and diffusion of hydrogen on its surface, resulting in better adsorption of H2 and levulinic acid on the metal surface.
N
U
(Figure 13. Levulinic acid esterification to ethyl levulinate.)
A
The TON of Ru-TS was 108 times greater and 45 times greater than RuCl3 and
M
RuCl3/4PPh3 in 6 h reaction, respectively (Table 5, entries 1, 2 and 4). The Table 6 shows the results about the support influence in the selective
ED
hydrogenation of LA. The supported ruthenium catalysts Ru-TS, Ru-TiO2 and Ru-SiO2 (Table 6, entries 1-3) presented yields higher than 80% in 6 h reaction. The TiO2 based material presented a great selectivity for GVL, compared with
PT
the SiO2 material. While the SiO2 presented a higher conversion for LA, compared with the TiO2 material. However, the Ru-TS (Table 6, entry 1)
CC E
showed high conversion (similar the SiO2 catalyst) and high selectivity (similar the TiO2 catalyst). The hybrid TiO2-SiO2 support contributes with high ruthenium catalyst activity, due their characteristics: specific surface area, metal dispersion
A
and accessibility to metallic centers. The ruthenium reduction step was very important for the AL hydrogenation whereas unreduced ruthenium was not selective for LA hydrogenation (yield decreased to 20% for GVL), while the reduced catalyst showed a yield of 89% (entries 4 and 1, respectively). The non-reduced catalyst favored the selectivity for the esterification product (ethyl levulinate).
(Table 6)
A reason for the low yield for GVL, in the non-reduced catalyst, is the ruthenium chloride lixiviation, once it has a slight interaction with the support. Other hypothesis is the oxidation state of ruthenium species are not able to activate
IP T
the hydrogen molecule.
The Ru/C is often described as one of the best catalyst in the literature
SC R
[12,15,21,31-33]. Their activity was compared with the catalysts in this paper. The Ru/C was prepared with the same ruthenium percentage in mass by the wetness impregnation as described in the experimental section. The yield for
U
GVL is significantly higher when using Ru-TS (Table 6, entries 1 vs 5).
Probably, the pore channels of the Ru/C material are not as accessible as those
N
of the Ru-TS material.
A
The recyclability of a catalyst is one of the most important characteristics for
M
heterogeneous liquid phase catalysis. Catalyst deactivation can be caused by leaching of the active species or because of metal sintering. We have been
ED
studied the reuse of the catalysts. It was obtained a high efficiency for Ru-TS and Ru-SiO2 after three cycles (Figure 14).
CC E
PT
(Figure 14. Reuse of catalysts for levulinic acid hydrogenation.)
The Ru-TiO2 loses their activity during the reuse test, probably due a metal leaching; which it is based on a coloration change in the reaction medium. The selectivity of reuse remained constant around 90% for Ru-TS and 85% for Ru-
A
SiO2 cycles.
With the objective of evaluating the catalytic activity of the best catalysts of this work, were compared according to the specific surface area, equaling the area values per m2 of the Ru-TS and Ru-SiO2 catalysts (Table 7). The Ru-TS (289 m2 g-1) showed an activity greater than Ru-SiO2 (740 m2 g-1) using equal values of specific surface area (Table 7).
(Table 7)
Comparatively, this indicates that TS support contributes with ruthenium catalytic performance rather than silica in the selective hydrogenation of Al to GVL by specific surface area. In this case, the yield for GVL using of Ru-SiO2
IP T
(Table 7, entry 2) is similar to the reaction in the absence of catalyst. (Table 6,
SC R
entry 6).
.4. Conclusion
Ruthenium based catalysts, supported in matrices of silica, titania and a hybrid
U
titania-silica supports. The Ru-TS catalyst is proven to be an efficient catalyst for the levulinic acid hydrogenation with high selectivity for g- valerolactone. The
N
prepared Ru-TS presented high yield (89%) for GVL production in mild reaction
A
conditions. The Ru-TS and Ru-SIO2 catalysts were reused without loss of
ED
to be the most efficient.
M
catalytic activity. Comparing the catalyst load per m2, the Ru-TS catalyst proved
Acknowledgements
PT
The authors would like to acknowledge the Center of Microscopy at the Universidade Federal de Minas Gerais (http://www.microscopia.ufmg.br)
CC E
experiments involving electron microscopy and for their financial support. National Council for Scientific and Technological Development (CNPq). National Council for the Improvement of Higher Education (CAPES) and the authors
A
thank Minas Gerais State Foundation for Research Development FAPEMIG.
Supplementary material In the supplementary material can be found the N2 adsorption/desorption equations, NMRs spectrum, and GC-MS spectrum.
References [1]
A. Demirbas, Prog. Energy Combust. Sci. 31 (2005) 171–192.
[2]
P. Kumar, P., D.M. Barrett, M.J. Delwiche, M, P. Stroeve, P., Ind. Eng. Chem. (Analytical Ed. 48 (2009) 3713–3729. F. Liguori, C. Moreno-Marrodan, P. Barbaro, ACS Catal. 5 (2015) 1882–
IP T
[3]
1894.
W.R.H. Wright, R. Palkovits, ChemSusChem 5 (2012) 1657–1667.
[5]
D.M. Alonso, S.G. Wettstein, J.A. Dumesic, Green Chem. 15 (2013) 584.
[6]
J. Song, H. Fan, J. Ma, B. Han, Green Chem. 15 (2013) 2619–2635.
[7]
V. Mohan, C. Raghavendra, C.V. Pramod, B.D. Raju, K.S. Rama Rao,
SC R
[4]
A. Mukherjee, M.J. Dumont, V. Raghavan, Biomass and Bioenergy 72
N
[8]
U
RSC Adv. 4 (2014) 9660–9668.
C. Ortiz-Cervantes, J.J. García, Inorganica Chim. Acta 397 (2013) 124–
M
[9]
A
(2015) 143–183.
128.
ED
[10] W. Luo, U. Deka, A.M. Beale, E.R.H. Van Eck, P.C. a Bruijnincx, B.M. Weckhuysen, J. Catal. 301 (2013) 175–186.
PT
[11] J.Q. Bond, D.M. Alonso, D. Wang, R.M., West, J.A.Dumesic, Science, 327 (2010), pp. 1110-1114.
CC E
[12] L.E. Manzer, Appl. Catal. A Gen. 272 (2004) 249–256. [13] P.P. Upare, J.M. Lee, D.W. Hwang, S.B. Halligudi, Y.K. Hwang, J.S. Chang, J. Ind. Eng. Chem. 17 (2011) 287–292.
A
[14] K. Yan, T. Lafleur, G. Wu, J. Liao, C. Ceng, X. Xie, Appl. Catal. A Gen. 468 (2013) 52–58.
[15] Z. Yan, L. Lin, S. Liu, Energy & Fuels 23 (2009) 3853–3858. [16] K. Shimizu, S. Kanno, K. Kon, Green Chem. 16 (2014) 3899. [17] M. Sudhakar, M. Lakshmi Kantam, V. Swarna Jaya, R. Kishore, K. V. Ramanujachary, a. Venugopal, Catal. Commun. 50 (2014) 101–104.
[18] M. Chia, J. a. Dumesic, Chem. Commun. 47 (2011) 12233. [19]
a. M. Ruppert, J. Grams, M. Jdrzejczyk, J. Matras-Michalska, N. Keller, K. Ostojska, P. Sautet, ChemSusChem 8 (2015) 1538–1547.
[20] J. Ftouni, A. Muñoz-Murillo, A. Goryachev, J.P. Hofmann, E.J.M. Hensen, L. Lu, C.J. Kiely, P.C. a Bruijnincx, B.M. Weckhuysen, ACS Catal. 6 (2016) 5462–5472.
IP T
[21] A.M.R. Galletti, C. Antonetti, V. De Luise, M. Martinelli, Green Chem. 14 (2012) 688–694.
SC R
[22] D.J. Braden, C. a. Henao, J. Heltzel, C.C. Maravelias, J. a. Dumesic, Green Chem. 13 (2011) 1755.
[23] S.G. Wettstein, J.Q. Bond, D.M. Alonso, H.N. Pham, A.K. Datye, J. a.
U
Dumesic, Appl. Catal. B Environ. 117–118 (2012) 321–329.
[24] F. Boccuzzi, S. Coluccia, G. Martra, N. Ravasio, J. Catal. 184 (1999)
N
316–326.
A
[25] X. Gao, I.E. Wachs, Catal. Today 51 (1999) 233–254.
(2010) 269–272.
M
[26] V. a Mazzieri, M.R. Sad, C.R. Vera, C.L. Pieck, R. Grau, Quim. Nova 33
3658–3666.
ED
[27] G. Peng, F. Gramm, C. Ludwig, F. Vogel, Catal. Sci. Technol. 5 (2015)
PT
[28] X. Chen, J. Jiang, F. Yan, S. Tian, K. Li, RSC Adv. 4 (2014) 8703. [29] J. Tan, J. Cui, T. Deng, X. Cui, G. Ding, Y. Zhu, Y. Li, ChemCatChem 7
CC E
(2015) 508–512.
[30] Mehdi, H., Fábos, .V, Tuba, R. ,Bodor, A., Mika, L.T., Horváth, I. T. Topics in Catalysis 48 (2008) 49–54.
A
[31] M.G. Al-Shaal, W.R.H. Wright, R. Palkovits, Green Chem. 14 (2012)
[32]
1260. A. Phanopoulos, A.J.P. White, N.J. Long, P.W. Miller, ACS Catal. 5
(2015) 2500–2512. [33]
F.M.A. Geilen, B. Engendahl, A. Harwardt, W. Marquardt, J.
Klankermayer, W. Leitner, Angew. Chemie - Int. Ed. 49 (2010) 5510–5514.
SC R
IP T
Figure 1. Levulinic acid hydrogenation to γ-Valerolactone
U
TS
N
Ru-SiO2
ED PT
CC E
10
20
30
Ru-TS
M
A
Intensity (a.u.)
Ru-TiO2
40
50
60
70
80
2(°)
Figure 2. XRD patterns of ruthenium-supported materials (Ru-TiO2, Ru-SiO2, Ru-
A
TS and the TS support) ; α – Anatase, ρ – Rutile
500
3
-1
400
TS Ru-TS Ru-SiO2 Ru-TiO2
IP T
300
200
SC R
Adsorbed volume (cm g )
600
100
0 0,4
0,6
N
P/P0
0,8
1,0
U
0,2
A
CC E
PT
ED
M
A
Figure 3 – Nitrogen adsorption–desorption isotherms of Ru-based catalysts.
60
TS Ru-TS Ru-SiO2 Ru-TiO2
40
3
-1
-1
Pore Volume (cm g )
50
30
IP T
20
10
0 4
6
8
10
12
14
16
18
20
SC R
2
Pore diameter (nm)
M
A
N
U
Figure 4. Pore distribution of ruthenium- based catalysts
Ru-TS
ED PT
Ru-SiO2
CC E
Signal (a.u.)
169°C
A
Ru-TiO2
100
200
300
400
500
600
700
Temperature (°C)
Figure 5. TPR profiles of the catalysts before de reduction process
800
IP T
PT
ED
M
A
N
U
SC R
Figure 6. The proposed ruthenium surface reduction under hydrogen atmosphere
A
CC E
Figure 7. TEM images and particle size histogram of Ru-TS catalyst
IP T
M
A
N
U
SC R
Figure 8.TEM images and particle size histogram of Ru-SiO2 catalyst
A
CC E
PT
ED
Figure 9. TEM images and particle size histogram of Ru-TiO2 catalyst
Figure 10. Kinect curves for GVL obtaining from LA hydrogenation in alcohols (a) LA conversion and (b) GVL selectivity.
100
Conversion GVL selectivity GVL yield
80
IP T
%
60
20 0 20
30
40
U
10
SC R
40
N
Pressure (atm)
A
Figure 11. Pressure effect in the catalytic hydrogenation of levulinic acid.
CC E
PT
ED
M
(Ethanol; 130°C; 6 h; 100 mg of 5%Ru-TS; [LA]=0.5 mol L-1)
A
Figure 12. Levulinic acid hydrogenation catalyzed by homogeneous Ru-based
Figure 13. Levulinic acid esterification to ethyl levulinate
Cycle 1 Cycle 2 Cycle 3
100
80
IP T
Yield (%)
60
40
SC R
20
0
Ru-SiO2
Ru-TiO2
N
U
Ru-TS
A
CC E
PT
ED
M
A
Figure 14. Reuse of catalysts for levulinic acid hydrogenation.
Table 1 Catalysts specifics surface area BET and pore characteristics BJH Specific surface area
Pore volume
Average pore
BET (m2 g-1)
(cm3 g-1)
diameter (nm)
TS
389
0.7
7
Ru-TS
289
0.9
12
Ru-SiO2
740
0.8
4
Ru-TiO2
40
0.1
14
IP T
Catalyst
SC R
Table 2. Solvent influence in the LA hydrogenation catalyzed by Ru -TSa Solvent
Conversion (%)
Selectivity b (%)
Yield (%)
1
Methanol
95
62
59
2
Ethanol
98
86
3
n-Butanol
80
4
THF
61
5
1,4-dioxane
21
PT CC E A
N b
84
76
61
0
0
5
1
A M
130°C; 20 atm; 5%Ru-TS; 8 h; 0.5 mol L-1 LA
ED
a
U
Entry
Selectivity = mol GVL/ mol products*100
Table 3. Effect of the temperature on conversion and selectivity in AL hydrogenation catalyzed by Ru-TS a Selectivity b
Yield c
(%)
(%)
(%)
2
27
69
19
4
61
68
41
3
6
79
79
4
2
43
83
4
74
89
6
6
90
7
2
69
4
84
6
96
2
70
5
100
8
130
62 36 66
90
81
89
61
89
75
88
84
N
9
SC R
1
U
(°C)
Time (h)
IP T
Conversion
Temperature
Entry
Ethanol; 30 atm H2; 100 mg of 5% Ru-TS; 0.5 mol L-1 LA, bSelectivity = mol GVL/ mol products*100, cYield = conv. x sel./100
M
A
a
Table 4. Temperature and pressure effect in the levulinic acid hydrogenation a
(atm)
2
20
5 6
30
A
7
CC E
3 4
Conversion
Selectivity b
Yield c
(°C)
(%)
(%)
(%)
70
24
74
18
100
96
93
89
130
94
85
80
70
79
79
62
100
90
90
81
130
96
88
84
70
85
87
74
100
>99
95
95
130
>99
48
48
PT
1
Temperature
ED
Entry
Pressure
8 9
a c
40
Ethanol; 6 h; 100 mg of 5%Ru-TS; 0.5 mol L-1 LA Yield = conv. x sel./100
b
Selectivity = mol GVL/ mol products*100
Table 5. Comparison between homogeneous and heterogeneous catalytic system in GVL production from LA hydrogenation a Entry Catalyst
Conversion Selectivity GVLb
Yield GVcd
(%)
(%)
(%)
TON d
Ru-TS
96
93
89
542
2
RuCl3
61
4
2
5
3
RuCl3 b
92
41
38
4
RuCl3/4PPh3
74
8
6
5
RuCl3/4PPh3 b
89
19
17
IP T
1
75
SC R
12
Ethanol; 100 °C; 20 atm H2; 0.5 mol L-1; 6 h; 100 mg of 5% Ru-TS; 0,5% mol Ru in homogeneous reaction b Selectivity = mol GVL/ mol products*100 c Yield = conv. x sel./100 TON= total number of moles transformed into the GVL by one mole of active substrate consumption/TOF= site per hour
d
U
a
34
Catalyst
Conversion (%)
Selectivity
Yield
(%)
(%)
93
89
A
Entry
N
Table 6. Ru-based heterogenous catalysts: levulinic acid hydrogenation a
Ru-TS
96
2
Ru-SiO2
97
87
84
3
Ru-TiO2
91
92
84
4
Ru-TS b
71
29
21
5
Ru/C
28
70
20
6
No catalyst
37
56
21
ED
PT
Ethanol; 6 h; 100°C; 20 atm H2; 0.5 mol L-1 LA; 100 mg of catalyst Selectivity = mol GVL/ mol products*100 dYield = conv. x sel./100
b
Non-reduced catalyst
c
CC E
a
M
1
A
Table 7. Performance evaluation per m2 of ruthenium-based catalysts a
Entry Catalyst
Mass
Conversion Selectivity b Yield Activity d
catalyst (g)
(%)
(%)
c
(%) (mmol GVL m-2)
1
Ru-TS
0.050
96
93
89
1,94
2
Ru-SiO2
0.020
35
71
25
0,54
a c
–Ethanol; 100°C; 20 atm H2; 6 h; 0.5 mol L-1 LA
Yield = conv. x sel./100
d
b
Selectivity = mol GVL/ mol products*100
mmol of GVL/specific area BET