Catalytic Transfer Hydrogenation of Biomass-Derived Levulinic Acid

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Catalytic transfer hydrogenation of biomass-derived levulinic acid and its esters to #-valerolactone over sulfonic acid-functionalized UiO-66 Yasutaka Kuwahara, Hiroto Kango, and Hiromi Yamashita ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b02464 • Publication Date (Web): 09 Dec 2016 Downloaded from http://pubs.acs.org on December 10, 2016

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ACS Sustainable Chemistry & Engineering

Catalytic transfer hydrogenation of biomass-derived levulinic acid and its esters to γ-valerolactone over sulfonic acid-functionalized UiO-66 Yasutaka Kuwahara,†,‡ Hiroto Kango,† and Hiromi Yamashita*,†,‡ †

Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka

University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan ‡

Unit of Elements Strategy Initiative for Catalysts & Batteries (ESICB), Kyoto University,

Katsura, Kyoto 615-8520, Japan KEYWORDS: Biomass, Heterogeneous catalysis, Metal-organic-framework (MOF), Catalytic transfer hydrogenation, Levulinate esters, γ-valerolactone.

ABSTRACT: Production of γ-valerolactone (GVL) from biomass-derived levulinic acid and its esters via a catalytic transfer hydrogenation (CTH) process over sulfonic acid-functionalized UiO-66, a microporous zirconium-based metal–organic framework (Zr-MOF), is reported herein. Based on comprehensive structural analyses by means of XRD, N2 physisorption, IR, TG, and Zr K-edge XAFS, we show that free sulfonic acid (–SO3H) groups can uniformly be tethered on UiO-66 framework without affecting the coordination state of Zr atoms, while crystallinity and

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surface area decrease along with the functionalization. As a consequence, UiO-66 bearing 60 mol% fraction of sulfonic acid-containing benzene dicarboxylate (BDC) linker and retaining high-surface-area exhibits the highest catalytic activity in the CTH reaction of levulinic acid and its esters to give GVL with the maximum GVL yield of up to 85% at 140 °C. Comparative experiments, together with characterization results, reveal that the high catalytic activity is provided by the cooperative effect between Lewis-basic Zr6O4(OH)4 clusters and Brönsted-acidic –SO3H sites arranged in a confined nanospace adjacently with each other, which catalyse CTH reaction of levulinic acid and its esters and facilitate the successive intramolecular dealcoholization to afford GVL, respectively. The catalyst is reusable during repeated cycles without appreciable loss of activity and selectivity, and shows broad scopes toward substrates and alcohols, and also allows direct synthesis of GVL from furfural, making this material a promising candidate for efficient GVL production from biomass resources.

INTRODUCTION Upgrading of lignocellulosic biomass, an abundant and inexpensive carbon source available worldwide, to biofuels and chemicals has been regarded as a vital technology for easing our strong dependence on non-renewable fossil resources as well as for reducing anthropogenic CO2 emissions.1-10 In order to realize the valorization of low-cost lignocellulosic biomass, catalytic conversion into diverse industrially valuable platform chemicals (so-called “biomass refinery”) is a key. To date, a tremendous number of catalytic strategies have been developed to convert lignocellulosic biomass into platform molecules, among which γ-valerolactone (GVL) has recently attracted increasing attention owing to the promise for future industrial applications.11-13


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GVL has proven to be a fuel additive for gasoline14 and a green solvent especially useful in biomass valorization.15,

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GVL can be converted to butenes through ring-opening and

decarboxylation, and the resulting butenes can be condensed to yield liquid hydrocarbon fuels suitable for gasoline, diesel and aviation kerosene.17, 18 GVL can also be utilized as a low-cost precursor for the production of various polymeric monomers, including α-methylene-γvalerolactone,19 ε-caprolactam and adipic acid,20 as well as for production of commodity chemicals (2-methyltetrahydrofuran etc.)21 and valuable bio-oxygenates (valerate esters, nonanone etc.).22, 23 Biomass-derived GVL is typically produced by the reduction and successive intramolecular dealcoholization of levulinic acid (LA) and its esters,13, 24, 25 which are intermediate molecules produced by acid-catalysed hydrolysis and alcoholysis of various carbohydrate fractions of lignocelluloses, respectively (Scheme 1).26-32 For the reduction of LA to GVL, hydrogenation using molecular H2 catalysed by homogeneous/heterogeneous noble metal catalysts (such as Ru,33-38 Pd,39-40 Ir,41 and Cu42-44) has been the overwhelmingly major approach. Although this approach can provide high GVL yields, high-cost of noble metal catalyst and operational problems associated with the use of high-pressure H2 limit the large-scale implementation. Catalytic transfer hydrogenation (CTH) process using alcohols as H-donors has been proposed as an alternative approach for scalable GVL production with economic competitiveness and sustainability, because the reaction occurs under milder conditions without the need of H 2 or noble metal catalysts, and alcohols are used as low-cost and renewable H-donors.45,

46

Additionally, the alcohol media derived from the former alcoholysis process can potentially be used as H-donors, thereby leading to an energy-saving and cost-effective GVL production process.25, 47, 48


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Scheme 1. Production route of γ-valerolactone (GVL) from lignocellulosic biomass.

Although many catalysts are known to be active for CTH reactions, Zr-based catalysts, such as ZrO2,49 hydrated zirconia (ZrO(OH)2·xH2O),50, 51 Zr-beta,51, 52 and ZrFeOx,53 have been reported as efficient heterogeneous catalysts for the production of GVL from LA and its esters via CTH process due to their amphoteric nature. Our research group also reported that mesoporous silicasupported ZrO2 catalyst having highly-dispersed Zr4+-O2- species exhibits a superior activity compared with bulk ZrO2 under mild reaction conditions (150 °C, 1.0 MPa of Ar).47, 48 Recently, amorphous Zr-complexes such as zirconium 4-hydroxybenzoate (Zr-HBA)54 and porous zirconium-phytic acid hybrid (Zr-PhyA),55 both composed of Zr4+ as metal ions and organic acids as building blocks, have been reported as efficient heterogeneous catalysts for this reaction. The high GVL yields obtained over these catalysts are due to the cooperative effect of Lewisacidic Zr4+ atoms and Lewis-basic carboxylate/phosphate O2- atoms which simultaneously activate carbonyl and alcohol molecules, respectively. Structurally considering, Zr-containing metal-organic-framework (MOF) is expected to work as an alternative to the above-mentioned Zr-based catalysts. As well-known, MOFs are crystalline porous materials assembled from inorganic metal ions (or metal-containing clusters) as nodes and organic moieties as linkers through coordination bonds. Because of their tunable structures, physicochemical properties and the functionality of metal ions and organic ligands,


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they are now finding widespread applications in catalysis, gas sorption, membrane, and energy storage.56-61 Zr-containing MOFs (UiO-66, nominal composition: Zr6O4(OH)4(BDC)6 (BDC = 1,4-benezene dicarboxylate)) is comprised of 12-coordinated Zr6O4(OH)4 clusters that are threedimensionally connected with BDC linkers (Scheme 2).56,

62, 63

In fact, μ3-OH groups and

missing-linker-type defect sites in the Zr oxo cluster have been proven to show Brönsted acidity,63, 64 rendering it to be an active acid catalyst for the esterification of biomass-derived acids with alcohols65 and for the cyclization of citronellal.66 From the viewpoint of catalysis, the porosity and extraordinarily high surface area of MOFs can allow efficient diffusion of reactant molecules and can offer a larger number of accessible active sites, leading to an efficient catalytic reaction. Furthermore, the BDC linker of UiO-66 can be tailored to add functionality by integrally or partially replacing with analogous organic linkers.66-68 With these advantageous properties, UiO-66 is expected to act as an active catalyst for the CTH reaction. Herein, we report a CTH reaction of LA and its esters to produce GVL over sulfonic acidfunctionalized UiO-66 catalysts. The Zr4+-O2- acid-basic pair sites uniformly imbedded in UiO66 framework allow to catalyse CTH reaction of LA and its esters, and the sulfonic acid groups (–SO3H) attached at the BDC linkers facilitate the successive intramolecular dealcoholization to afford GVL with high yield (Scheme 2). In the present study, a series of sulfonic acidfunctionalized UiO-66 with varied –SO3H contents were synthesized, characterized, and examined in the CTH reactions of methyl levulinate using 2-butanol as a H-donor to maximize the catalytic performances. With optimum –SO3H content, the sulfonic acid-functionalized UiO66 could afford GVL with up to 85% yield, which far outperformed bulk ZrO2 and pristine UiO66 catalysts owing to the cooperative effect between Lewis-basic Zr6O4(OH)4 clusters and Brönsted acidic –SO3H sites locating adjacent with each other. The catalyst showed broad scopes


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toward substrates (including LA and furfural) and alcohols, and was readily reusable at least four repeated cycles without significant loss of catalytic performances. In addition, a plausible reaction mechanism was proposed based on the results obtained from characterizations and comparative experiments.

Scheme 2. Illustration of structure of sulfonic acid-functionalized UiO-66 (Zr and O atoms are shown in green and brown, respectively, and sulfonic acid group is represented in pale blue) and reaction pathway for catalytic transfer hydrogenation (CTH) of levulinate esters to produce GVL.

EXPERIMENTAL SECTION Materials. 2-sulfonylterephthalic acid monosodium salt (2-NaSO3-H2BDC, 98%), methyl levulinate (ML, 99%), ethyl levulinate (EL, 99%), butyl levulinate (BL, 99%) were purchased from Tokyo Chemical Industry, Ltd. ZrO2 (98%), ZrCl4 (99%), AlCl3·6H2O (97%), Cr(NO3)3·9H2O (99.5%), terephthalic acid (H2BDC, 98%), levulinic acid (LA, 99%), acetic acid (99%), N,N-dimethylformamide (DMF, 99.5%), methanol (anhydrous, 99.5%), 2-butanol (anhydrous, 99.5%), furfural (Fur, 98%), γ-valerolactone (GVL, 99%), biphenyl (99%), ptoluenesulfonic acid monohydrate (p-TsOH, 99%) and other commercially available chemical


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reagents for material synthesis and catalytic tests were purchased from Nacalai Tesque, Inc. All chemicals were used without further purification. Catalyst preparation. A series of sulfonic acid-functionalized UiO-66 were prepared by the solvothermal method according to the procedure previously reported.69 In a typical synthesis, 4.0 mmol of ZrCl4 and total 4.0 mmol of H2BDC and 2-NaSO3-H2BDC were dissolved in a mixture solution containing 162 mL DMF and 18 mL acetic acid, followed by stirring for 30 min to obtain homogeneous solution. The primary role of acetic acid is to in-situ exchange Na+ ions of 2-NaSO3-H2BDC ligand with H+ in the acidified reaction solution.69 The reaction mixture was transferred to a Teflon-lined high-pressure vessel (45 mL) and thermally reacted at 140 °C for 40 h under static conditions. The obtained solid was separated by centrifugation, washed with DMF and methanol, dried at room temperature under vacuum overnight, and finally thermally treated at 150 °C for 4 h under vacuum to eliminate residual organic ligands. The thus obtained samples were denoted as UiO-66-Sx (x represents the mole fraction of sulfonated ligand), in which x was varied from 0 to 100 (mol%). For comparisons, Cr-based MOF (MIL-101(Cr)) and Al-based MOF (MIL-53(Al)), both comprised of H2BDC as a connecting linker, were also synthesized by the solvothermal method according to the procedures published earlier.70, 71 Characterization. X-ray diffraction (XRD) measurements were carried out on a Rigaku Ultima IV diffractometer with CuKα radiation (λ = 1.54056 Å, 40 kV–40 mA). N2 adsorptiondesorption isotherms were obtained at -196 °C using BELSORP-max system (MicrotracBEL Corp.). The samples were degassed at 150 °C under vacuum for at least 12 h prior to analysis. The surface areas were calculated from the adsorption data using the Brunauer–Emmett–Teller (BET) method, and micropore size distributions were determined by the Saito-Foley (SF)


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method, which is conventionally employed for microporous solids such as zeolite and MOF materials. Field-emission scanning electron microscopy (FE-SEM) images were taken on a JEOL JSM-6500F with an accelerating voltage of 12 kV. The content of Zr and sulfonic acid groups were estimated from the thermogravimetric (TG) analysis data measured on a Rigaku Thermo plus EVO2 under a flow of air (30 mL/min) with a ramping rate of 10 °C/min. Infrared (IR) spectra were recorded on a JASCO FT/IR-6300 instrument in the spectral range 2000–400 cm–1 under vacuum with a resolution of 4 cm–1 using samples diluted with KBr. X-ray absorption fine structure (XAFS) measurement for Zr K-edge was performed in transmission mode at room temperature at the BL01B1 beam line at the SPring-8 (JASRI), Hyogo, Japan. A Si(311) single crystal was used to obtain the monochromated X-ray beam. The fourier transformation of k3-weighted normalized EXAFS data (FT-EXAFS) from k space to r space was performed over the range 2.0 ≤ k (Å−1) ≤ 15.0 to obtain the radial structure function (RDF). For the curve-fitting analysis, the empirical phase shift and amplitude functions for Zr–O and Zr···Zr were extracted from the data for monoclinic ZrO2. The analysis of the XAFS data was performed using Rigaku REX2000 software. Catalytic test. In a typical reaction, catalyst (100 mg), substrate (1 mmol for LA and its esters, 0.2–0.5 mmol for Fur) and alcohol (5 mL) were charged into a 60 mL cylindrical stainless steel high-pressure reactor (EYELA, Inc.) containing an inner lining of Pyrex glass and equipped with a bourdon pressure gauge. The reaction vessel was sealed, purged and pressurized with 0.5 MPa of Ar and then heated to 140 °C to initiate the reaction. During the reaction, magnetic stirring at 600 rpm was continued. After the predetermined reaction time, the reactor was cooled to room temperature and the liquid products collected from the reaction mixture were analysed by a gas chromatograph (GC, Shimadzu GC-14B) with a frame ionization detector equipped with a


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capillary column (Zebron ZB-FFAP; 0.32 mm × 50 m; phenomenex®). Conversion of substrate and yields of products were quantified using biphenyl as an internal standard. To assess the catalyst reusability, the spent catalyst was recovered from the reaction mixture by filtration, washed with methanol, dried at 100 °C and then subjected to multiple catalytic runs.

RESULTS AND DISCUSSION Catalyst characterization. The structures of the series of UiO-66-Sx samples were confirmed by means of XRD, N2 adsorption, and TG analyses. As shown in Figure 1(A), XRD patterns of UiO-66-Sx with x = 20, 40, and 60 were coincided with that of pristine UiO-66 showing two distinct peaks at 2θ = 7.4° and 8.5°, and no impurity phases assignable to Zr oxide compounds were found. The coordination structure of Zr6O4(OH)4(BDC)6 building unit of UiO-66 is shown in Scheme 2, where each Zr oxo cluster is 12-fold connected to adjacent clusters through a BDC linker, resulting in a highly packed fcc structure.62-64, 72 The two distinct diffractions at 2θ = 7.4° and 8.5° can be indexed to (111) and (002) planes, respectively. N2 adsorption isotherms of these samples exhibited type I isotherms (according to IUPAC classification) with steep increases at low pressure region (P/P0 < 1.0×10-3) which are typical of microporous solids (Figure 1(B)). The XRD intensity and the amount of adsorbed N2 apparently decreased with increasing the degree of sulfonic acid ligand substitution. In contrast, UiO-66-S80 and UiO-66-S100 containing larger fractions of sulfonated ligand did not show clear X-ray diffractions, suggesting the significant deterioration of MOF structure at higher ligand exchange levels. Furthermore, these samples exhibited only slight amounts of adsorbed N2. It can be deduced that UiO-66-S80 and UiO-66S100 contain many defects (such as missing-linker defect sites) or irregular connectivities.


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500 x=0 x = 20 x = 40 x = 60 x = 80 x = 100

(A)

(002)

Volume adsorbed / cm (STP) g

-1

(111)

x=0

400

(B)

3

x = 20

Intensity / a.u.

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x = 40

x = 60

x = 80

300

200

100

x = 100

10

20

30

40

50

0 0.0

0.2

0.4

0.6

0.8

1.0

P/P0

2 / degree

Figure 1. (A) XRD patterns of UiO-66-Sx synthesized with varied sulfonated ligand content (x = 0, 20, 40, 60, 80, and 100 mol%). (B) N2 adsorption-desorption isotherms of UiO-66-Sx synthesized with varied fractions of sulfonated BDC linker (x = 0, 20, 40, 60, 80, and 100 mol%). Table 1. Textural properties of a series of UiO-66-Sx samples with varied amounts of sulfonated ligand

Sample

Mole fraction of Zr content a Molar ratio of Acidity b sulfonated ligand in (mmol/g) ligand/Zr a (mmol/g) initial gel (mol%)

N2 physisorption SBET c (m2/g)

Vtotal d (cm3/g)

Dp e (nm)

UiO-66

0

3.00

1.03

0.167

1146

0.57

0.7

UiO-66-S20

20

3.35

1.00

0.316

1126

0.64

0.7

UiO-66-S40

40

3.20

0.88

0.465

787

0.46

0.7

UiO-66-S60

60

3.05

0.83

0.569

502

0.32

0.7

UiO-66-S80

80

3.04

0.80

0.686

138

0.13

0.7

UiO-66-S100

100

3.06

0.78

0.778

22.1

0.04

1.25

a

Determined based on TG data. b Amount of acid sites determined by titration method using phenolphthalein as an indicator. c Surface area determined by BET method. d Total pore volume reported at P/P0 = 0.99. e Average pore size determined by SF method.


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The textural properties of the samples determined from N2 adsorption measurement are summarized in Table 1. The pristine UiO-66 catalyst exhibits a large surface area (1146 m2/g) and total pore volume (0.57 cm3/g), which fairly match the values reported earlier.62 A substantial decrease of textural properties was observed as increasing the amount of SO3H-BDC linker during the catalyst preparation. For example, UiO-66-S60 catalyst bearing 60 mol% fraction of SO3H-BDC linker exhibited SBET of 502 m2/g and Vtotal of 0.32 cm3/g with type I isotherm, which can still be considered as a microporous solid. The pore size distributions determined by SF method showed distinct peaks assignable to the defined micropores of UiO-66 with an average pore size of 0.7 nm, which is similar to the reported aperture size of UiO-66 (approx. 6 Å),62 therefore the reduced textural property might be due to the pore filling effect by –SO3H groups tethered on the framework. However, substitution with excess of sulfonated BDC linker (>80 mol% fraction) caused a considerable loss of textural properties; UiO-66-S100 showed SBET of 22.1 m2/g and Vtotal of 0.04 cm3/g, resulting in the formation of a non-porous solid. Considering the XRD result, this is due to the structure collapse caused by the reduced stability of UiO-66 framework. FE-SEM observation also indicated a substantial aggregation of primary particle size as increasing the fraction of sulfonated BDC linker (see Figure S1 in the Supporting Information (SI)). Overall, the crystallinity of the UiO-66 appears to decrease when more than 80 mol% of BDC ligand is substituted with sulfonated BDC ligand. In TG profiles (Figure S2 in SI) measured in a flow of air, all samples showed steep weight losses of 35-43 wt% in the same range of 400-550 ºC, which are attributed to the structure collapse and the loss of organic linkers,56, 72 suggesting that the ligand exchange with SO3H-BDC has little effect on the thermal stability of the UiO-66 framework. Elemental analysis based on TG measurement revealed that the ligand/Zr molar ratio was around 1.0 for pristine UiO-66 and


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UiO-66-S20, while it was in the range of 0.78–0.88 for UiO-66-Sx (x > 40) samples (Table 1). This result indicates that pristine UiO-66 and UiO-66-S20 are the materials with predetermined stoichiometric ratios (Zr6O4(OH)4(BDC)6), but UiO-66-Sx with more than 40 mol% of sulfonated BDC ligand should possess missing-linker defects and results in materials with the nominal formula of Zr6O4(OH)4–(OH)2(BDC)5, in which one missing-linker defect site is likely be compensated by two –OH groups.64

1710 1658

1372 1250

1176 1025 1078

x=0

Transmittance / a.u.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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x = 20 x = 40 x = 60 x = 80 x = 100 1800

1600

1400

1200

1000

800

600

400

-1

Wavenumber / cm

Figure 2. FT-IR spectra of UiO-66-Sx synthesized with varied fractions of sulfonated BDC linker (x = 0, 20, 40, 60, 80, and 100 mol%).

In addition, no sodium ions were detected by inductively coupled plasma (ICP) analysis, indicating that the Na+ ions of 2-NaSO3-H2BDC ligand were completely exchanged with H+ provided by acetic acid during the preparation. The presence of sulfonic acid groups tethered on UiO-66 framework was also confirmed by FT-IR spectroscopy (Figure 2). The absorption bands


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appeared at 1176/1250 cm-1 and the shoulder peak at around 1372 cm-1 are assigned to the symmetric and asymmetric stretching vibrations of O=S=O bonding, respectively, and the band at 1025 cm-1 can be assigned to the stretching mode of S=O bonding, whereas the band at 1078 cm-1 may correspond to the n-plane skeletal vibration of the benzene rings substituted by a sulfonic acid group.69, 73 As expected, an increasing intensity of these bands was observed as increasing the fraction of sulfonated ligand; however, no shift was observed upon the variation of the amount of sulfonated ligand, suggesting that –SO3H groups are present as “free” sulfonic acid groups. Furthermore, the absorption bands appeared at 1710 and 1658 cm-1 are assignable to the stretching vibrations of C=O bondings of “free” carboxylic acid groups and “coordinated” carboxylates, respectively, where the latter band was dominantly observed in all cases. These results confirm that Zr oxo clusters are solely coordinated with the carboxylate oxygen atoms, not with the sulfonated oxygen atoms. Substantial amount of acid site was quantified by neutralization titration method using NaOH aqueous solution (5 mmol/L) as a base and phenolphthalein as an indicator, because CO2-TPD measurement, a typical method to determine acidic properties of oxides, was not applicable to these materials due to thermal degradation and the associated generation of gaseous species upon the TPD measurement. As tabulated in Table 1, the amount of acid site increased from 0.167 to 0.778 mmol/g linearly with the increase of sulfonated ligand fraction from 0 to 100 mol%. Although missing-linker defect sites (consisting of Zr-OH sites) are also known to act as Brönsted acid sites,63-65 their acidity is much weaker than that of –SO3H sites; therefore the determined acidity is mostly arisen from Brönsted acidic – SO3H sites tethered on UiO-66 framework. This result again confirms that accessible protonic acid sites associated with –SO3H groups are tight attached to the UiO-66 framework.


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The local structure of Zr atoms was investigated by Zr K-edge XAFS measurement. Figure 3(A) shows normalized X-ray absorption near-edge structure (XANES) spectra at the Zr K-edge position of a series of UiO-66-Sx samples, together with monoclinic ZrO2 as a reference sample. The shape and edge positions well corresponded with those of monoclinic ZrO2, and were unchanged upon the ligand substitution with sulfonated BDC ligand, indicating that Zr atoms are present as 4+ oxidation state in all cases. The RDFs obtained from k3-weighted normalized EXAFS data of UiO-66-Sx samples show two distinct peaks (Figure 3(B)); the first peak in the region of r = 1.2–2.0 Å (the phase shift uncorrected) is due to the overlap of two different Zr–O bonds, Zr–O and Zr–Oμ3 bonds comprising Zr6O4(OH)4 cluster with different bond lengths, and the second peak at around r = 3.1 Å is due to Zr…Zr contribution. No appreciable changes were found in the RDFs with the variation of the sulfonated ligand amount. The coordination numbers (C.N.) and the interatomic distance (R) for the Zr–O, Zr–Oμ3 and Zr…Zr shell regions were determined by curve-fitting analysis, which suggested that each Zr atom is 8-fold coordinated with two short Zr–Oμ3 bonds (R = 2.08 Å) and six long Zr–O bonds (R = 2.23 Å) in all cases (for curve-fitting analysis data, see Table S1 in SI). Furthermore, the C.N. and R for the second Zr…Zr shell were determined to be 3.8±0.2 and 3.53±0.01 Å, respectively, in all cases. These results agree well with the crystal structure model and a XAFS analysis data for UiO-66 reported in previous literature.72 Thus, XAFS analysis unravelled that ligand substitution of UiO-66 with sulfonated BDC linker had little effect on the local structure of Zr atoms.


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(A)

(B)

Zr-O Zr…Zr x=0 x = 20

x=0

x = 40

x = 20

x = 60 x = 80 x = 100

Magnitude / a.u.

Normalized absorption / a.u.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


x = 40 x = 60 x = 80

m-ZrO2

x = 100

m-ZrO2 17950 18000 18050 18100 18150 18200

0

1

2

Energy / eV

3

4

5

6

r/Å

Figure 3. (A) Zr K-edge XANES spectra and (B) Zr K-edge radial distribution functions of UiO66-Sx synthesized with varied fractions of sulfonated BDC linker (x = 0, 20, 40, 60, 80, and 100 mol%) and monoclinic ZrO2 as a reference sample.

GVL production via a CTH process. In the initial tests, UiO-66 and its derivatives were used as catalysts in the CTH reaction of methyl levulinate (ML) using 2-BuOH as a hydrogen donor, and were compared with some related catalysts to study the influence of various parameters. Unfunctionalized, pristine UiO-66 as a baseline catalyst afforded 70% conversion of ML and 36% yield of GVL at 140 °C after 9 h of reaction (Table 2, Entry 1). Other types of MOFs containing different metallic centers, Cr-based MOF (MIL-101(Cr))70 and Al-based MOF (MIL53(Al)),71 were both inactive for this reaction (Entry 11 and 12, respectively), and, indeed, the reaction did not proceed in the absence of catalyst (Entry 17). Commercial crystalline ZrO 2 (monoclinic) gave only 13% ML conversion and 6.1% GVL yield under the identical conditions


15


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Page 16 of 40

(Entry 16). These results substantiate that Zr element imbedded in MOF framework is the main active species for the CTH reaction. Over UiO-66 catalyst, transesterified byproduct (sec-butyl levulinate (sBL)) and its hydrogenated derivative (4-hydroxy pentanoate butyl ester (4-HPBE)) were observed as the major byproducts, while hydrogenated product (4-hydroxy pentanoate methyl ester (4-HPME)) was hardly observed. Considering the product distributions and reaction time profile determined by GC analysis (see Figure S3(A) in SI), it appears that i) CTH reaction to reduce ML and ii) transesterification reaction occur simultaneously at the initial stage. In the CTH reaction of ML, carbonyl group of ML is reduced to give 4-HPME intermediate, and 4-HPME easily undergoes intramolecular dealcoholization to afford GVL since this reaction is thermodynamically preferred. Simultaneously, ML also undergoes transesterification to give transesterified product, sBL, which is successively hydrogenated to give 4-HPBE via CTH process. The thus formed 4HPBE can be further converted to GVL via intramolecular dealcoholization, however these reaction rates are significantly slower than ML does (Figure S3(A) in SI). Therefore, CTH reaction of transesterified product and the following intramolecular dealcoholization to produce GVL are likely a key step to attain higher GVL yield.

Table 2. CTH reaction of methyl levulinate with 2-butanol over UiO-66-Sx and the related catalysts a

Entry

Catalyst

Temp. (°C)

Time (h)

1

UiO-66

140

9

Conversion Selectivity (%) (%) 70


51

GVL yield (%) 36

16

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2

UiO-66-S20

140

9

77

56

43

3

UiO-66-S40

140

9

96

64

62

4

UiO-66-S60

140

9

98

82

80

5

140

24

99

86

85

6

160

9

99

91

90

7

180

9

>99.5

93

93

8

UiO-66-S80

140

9

93

78

73

9

UiO-66-S100

140

9

87

80

70

10

UiO-66-NH2

140

9

64

27

17

11

MIL-101(Cr)

140

9

6.4

-

0

12

MIL-53(Al)

140

9

0

-

0

13

UiO-66 + p-TsOH b

140

9

66

0

0

14

ZrCl4 c

140

9

96

58

56

15

ZrCl4 c + p-TsOH b

140

9

96

24

23

16

ZrO2 d

140

9

13

45

6.1

17

None

140

9

0

-

0

a

Reaction conditions: catalyst (ca. 100 mg, corresponding to 0.3 mmol of Zr), ML (1 mmol), 2BuOH (5 mL), Ar 0.5 MPa. b p-TsOH = p-toluenesulfonic acid. 1 equivalent per mole of Zr was added. c Zr 0.3 mmol. d monoclinic ZrO2.

To study the effect of acid/basic properties on GVL production, reaction was examined using UiO-66 derivatives possessing different ligand functionalities. UiO-66 functionalized with basic amine groups (UiO-66-NH2, Entry 10), which was prepared using 2-aminoterephthalic acid as an organic linker according to the earlier report,66-68 gave decreased conversion (64%) and GVL yield (17%) compared to the standard UiO-66, affording sBL as the major product. This is due to the ability of amine-functionality to catalyse the transesterification reaction, of which reaction rate is much faster than the CTH reaction. In contrast, improved catalytic activities were achieved over the series of sulfonic acid-functionalized UiO-66 catalysts; both selectivity and


17


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Page 18 of 40

yield toward GVL after 9 h of reaction at 140 °C increased in the order of UiO-66 < UiO-66-S20 < UiO-66-S40 < UiO-66-S100 < UiO-66-S80 < UiO-66-S60 (Entry 1-4, 8, 9). The highest GVL yield was attained over UiO-66-S60, giving nearly complete conversion of ML and 80% GVL yield after 9 h of reaction at 140 °C (Entry 4). Considering the fact that the production of transesterified products (sBL and 4-HPBE) was apparently suppressed over UiO-66-S60 catalyst (see Figure S3(B) in SI), the increased activity is primarily attributed to the acid-functionality of UiO-66-Sx to promote dealcoholization of 4-HPBE to produce GVL. In addition, the fact that UiO-66-S60 catalyst showed a higher catalytic activity than UiO-66-S40 having a similar defect site density corroborates the predominance of Brönsted acidic –SO3H sites in the catalysis, rather than missing-linker defect sites. Each step in this reaction is reversible, hence the overall GVL production rate is governed by the concentrations and thermodynamic properties of the products and intermediates. Since UiO-66-Sx can facilitate dealcoholization of 4-HPBE to produce GVL due to the presence of Brönsted acidic –SO3H sites, the reaction equilibrium tends to incline to the 4-HPBE formation, thus the GVL yield can be increased. Prolonging reaction time to 24 h resulted in a slight increase of GVL yield (85%, Entry 5) due to a continuous consumption of transesterified products (sBL and 4-HPBE) to yield GVL. Further increased GVL yields were attained at elevated reaction temperatures (Entry 6 and 7), where GVL yield reached the maximum of 93% at 180 °C after 9 h of reaction (Entry 7). This is because CTH reaction of sBL more effectively proceeds at higher temperatures. Nevertheless, UiO-66-S80 and UiO-66-S100 with excess amounts of sulfonated ligand showed moderate activities, giving 87-93% conversions of ML and 70-73% yields of GVL (Entry 8, 9). This is probably due to the loss of defined porous structure and surface area, limiting the access of reactants to the active sites.


18

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To demonstrate the synergistic catalysis of the dual functionalities of UiO-66-Sx, a comparative experiment was carried out by adding p-TsOH as a homogeneous alternative to sulfonated linker. Surprisingly, addition of p-TsOH (1 equiv. per mole of Zr) together with UiO66 resulted in no GVL formation, giving sBL as a sole product (Entry 13). Homogeneous pTsOH is easily accessible to the Zr clusters of UiO-66 via a micropore channels. Sulfonic acid groups of p-TsOH diminished the ability of Zr active sites to catalyse CTH reaction, thereby resulted in a significantly reduced activity. A similar result was also observed in a homogeneous reaction system; ZrCl4 as a homogeneous catalyst for this reaction gave 96% conversion of ML and 56% yield of GVL at 140 °C after 9 h of reaction (Entry 14), however, combined use of ZrCl4 and p-TsOH (1 equiv. per Zr) provided a significantly reduced catalytic activity (Entry 15). These results clearly indicate that spatial isolation of Zr centers and sulfonic acid groups without interrupting their respective catalysis is highly important to demonstrate the cooperative catalysis. UiO-66 is a platform material capable of incorporating two different catalytic sites spatially isolated from each other, enabling the access of organic reactants to both Zr centers and sulfonic acid sites arranged in a confined nanospace, and thus resulting in a high GVL yield. Above all results conclusively indicate that sulfonic acid-functionalized UiO-66 acts as an effective catalyst for the CTH reaction of levulinate esters to GVL, primarily due to acidfunctionality to promote dealcoholization step and secondly due to its high surface area and microporous structure as well as high dispersion of both active centers, which are important for mass transfer and efficient access of reactant molecules.

Reusability of UiO-66-S60 catalyst. The heterogeneous nature of UiO-66-S60 catalyst was examined by removing the catalyst from the reaction mixture after reaction for 2 h, and the


19


resulting reaction solution was subjected to stirring for additional 7 h. No further reaction proceeded, substantiating that UiO-66-S60 acts as a heterogeneous catalyst. Moreover, UiO-66S60 was repeatedly reusable at least four times without significant decrease of catalytic activity under the standard reaction conditions (Figure 4), demonstrating that UiO-66-S60 is durable under the reaction conditions examined in this study.

ML conversion or GVL yield / %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 40

ML conversion

GVL yield

100 80 60 40 20 0

1st

2nd

3rd

4th

Cycles

Figure 4. (A) Reusability tests of UiO-66-S60 in CTH reaction of ML to GVL. Reaction conditions: catalyst (UiO-66-S60, 100 mg), ML (1 mmol), 2-BuOH (5 mL), Ar 0.5 MPa, 140 ºC, 9 h.


20

Page 21 of 40

Fresh

Transmittance / a.u.

Intensity / a.u.

(A)

Fresh

Used

O=S=O S=O

Used 10

20

30

40

50

Wavenumber / cm

-1

250 200

(C) 2

3

SBET = 502 m /g

150 2

SBET = 435 m /g

100

Fresh Used

50 0 0.0

(D)

0

Weight loss / wt.%

-1

(B)

1800 1600 1400 1200 1000 800 600 400

2 / degree

Volume Adsorbed / cm (STP) g

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.2

0.4

0.6

p/p0

0.8

-20 -40

-57.4 wt%

-60 -80

1.0

-40.9 wt%

0

Fresh Used 200

400

600

800

1000

Temperature / ℃

Figure 5. Comparisons of (A) XRD patterns, (B) N2 adsorption-desorption isotherms, (C) FT-IR spectra, and (D) TG profiles of UiO-66-S60 before and after catalytic reaction.

To check the stability of catalyst, UiO-66-S60 recovered after the CTH reaction of ML was characterized by XRD, FT-IR, N2 physisorption, and TG measurements (Figure 5(A)-(D)). No significant crystallographic change was observed for used catalyst (Figure 5(A)), and the IR bands assigned to –SO3H groups were perfectly retained even after the catalytic reactions (Figure 5(B)), being consistent with the high chemical stability reported for UiO-66 in previous literature.56, 72 However, a substantial decrease in the amount of adsorbed N2, together with a decrease of structural properties, was observed upon the catalytic use (BET surface area decreased from 502 to 435 m2/g) (Figure 5(C)). The total weight loss attributed to the organic linkers was about 40.9 wt% for the fresh catalyst, but this value increased to 57.4 wt% for the spent catalyst after the fourth run (Figure 5(D)), indicating a substantial accumulation of


21


carbonaceous species during the catalytic reaction. Based on these characterization results, it is suggested that the accumulation of non-volatile products results in a reduced surface area by blocking the micropore channels, inhibits the access of reactant molecules to the active sites, hence leading to the slightly reduced catalytic activity during repeated cycles. Investigation on reaction mechanism. To obtain insight into the catalytic role of the Zr oxo cluster, comparative experiments were performed by introducing two different external additives, pyridine and benzoic acid. Figure 6 shows the effects of the two additives on the catalytic activity of pristine UiO-66 catalyst in the CTH reaction of ML to GVL. A significant drop of the catalytic activity was observed when benzoic acid was added as a homogeneous acid in the reaction system, being consistent with the case of p-TsOH added together with UiO-66 (Table 1, Entry 13). On the other hand, the addition of pyridine as a homogeneous base showed no negative effect on the activity. This result indicates that the CTH reaction of ML to GVL is primarily dominated by basic property of the Zr-oxide species and acid property have little contribution to the reaction. 50 40

GVL yield / %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 40

pyridine

30 20 10 0

benzoic acid 0

100

200

300

400

500

Amount of additives / mol%

Figure 6. Effect of addition of pyridine and benzoic acid on the catalytic activity of UiO-66 catalyst. Reaction conditions: catalyst (UiO-66, 100 mg), ML (1 mmol), 2-BuOH (5 mL), additive (0–500 mol%), Ar 0.5 MPa, 140 ºC, 9 h.


22

Page 23 of 40

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Scheme 3. Possible reaction mechanism for CTH process of levulinate esters to produce GVL over UiO-66-Sx catalyst.

On the basis of the experimental results and previous reports,47-48, 50, 52, 54-55 a possible reaction mechanism for CTH reaction of levulinate esters over UiO-66-Sx was proposed as schematically illustrated in Scheme 3. First step is adsorption of alcohols on the Zr oxo cluster imbedded in UiO-66 framework, and the subsequent dissociation to the corresponding alkoxide and hydrogen by the Zr4+-O2- acid-base pair sites, in which the deprotonation of alcohol is promoted by basic property of the carboxylate O2- atoms (step 1).50,

54-55

As reported in many GVL formation

processes over Zr-containing catalysts, the carbonyl group of levulinate ester is subsequently activated by acidic Zr4+ sites (step 2).47-48, 50, 52, 54-55 Next, 4-hydroxypentanoate ester is formed by hydrogen transfer between the dissociated alkoxide and the activated levulinate ester via the


23


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Page 24 of 40

formation of a six-membered transition state (step 3). The newly-formed 4-hydroxypentanoate ester and carbonyl byproduct are then released to regenerate the initial active sites (Step 4). Finally, the desorbed 4-hydroxypentanoate is converted to GVL via Brönsted acid-catalysed intramolecular dealcoholization (step 5). Considering the product distribution profile (see Figure S3(B) in SI), it is suggested that the rate-limiting step in this reaction (using 2-BuOH as a Hdonor) is step 3, where the Zr4+-O2- acid-basic pair sites arranged in UiO-66 framework adjacently with each other play a critical role. As aforementioned, each step in this reaction is reversible. Sulfonic acid groups of UiO-66-Sx can facilitate the step 5, which allows the reaction equilibrium to shift to the 4-hydroxypentanoate ester formation, thereby the formation of GVL can be promoted. Thus, the free sulfonic acid moieties present in the frameworks of UiO-66-Sx plays a key role in the selective formation of GVL. Scope of substrates and alcohols. The choice of feedstocks and alcohols provides a significant impact on GVL yield. Table 3 summarizes the results of CTH reaction over UiO-66S60 with different choices of levulinate esters as substrates and alcohols as H-donors. GVL was scarcely obtained when MeOH was employed as a H-donor (Entry 1). Moderate amounts of GVL (26-35% after 9 h of reaction at 140 °C) were obtained from ML when other primary alcohols (EtOH, 1-PrOH and 1-BuOH) were used (Entry 2-4), which afforded the corresponding transesterified products as main products rather than hydrogenated products. On the contrary, secondary alcohols, such as 2-PrOH and 2-BuOH, acted as effective H-donors, giving 78-80% of GVL yields with improved selectivities toward GVL under the identical conditions (Entry 5 and 6; for reaction kinetics data, see Figure S4(A) in SI). Prolonging reaction time resulted in increased GVL yields, and 85-86% GVL yields were attained after 24 h of reaction. Such a


24

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difference in GVL yields is a consequence of the ease of β-Hydride elimination from the intermediate alkoxide species during the CTH reaction.47, 48

Table 3. Scope of substrates and alcohols for the production of GVL over UiO-66-S60 catalyst. a Conversion c Selectivity c GVL yield c,d (%) (%) (%)

Entry

Substrate b

Alcohol

Time (h)

1

ML

MeOH

9

8.1

19

1.5 (4.2)

2

ML

EtOH

9

98

35

34 (58)

3

ML

1-PrOH

9

98

36

35 (55)

4

ML

1-BuOH

9

98

27

26 (47)

5

ML

2-PrOH

9

99

79

78 (86)

6

ML

2-BuOH

9

98

82

80 (85)

7

EL

EtOH

9

49

75

37 (55)

8

EL

2-BuOH

9

66

67

45 (74)

9

BL

2-BuOH

9

46

68

31 (59)

10

LA

2-BuOH

9

69

37

25 (67)

11 e

Fur

2-BuOH

48

100

27

27

12 f

Fur

2-BuOH

48

100

33

33

a

Reaction conditions: catalyst (UiO-66-S60, 100 mg), substrate (1 mmol), alcohol (5 mL), Ar 0.5 MPa, 140 °C. b ML = methyl levulinate, EL = ethyl levulinate, BL = n-butyl levulinate, LA = levulinic acid, Fur = furfural. c Determined by GC using biphenyl as the internal standard. d The values in parenthesis is GVL yield after 24 h of reaction. e 0.5 mmol of Fur was used. f 0.2 mmol of Fur was used.

Other levulinate derivatives, such as ethyl levulinate (EL) and n-butyl levulinate (BL) and levulinic acid (LA), afforded GVL via a CTH process using 2-BuOH as a H-donor (Entries 710); however, a decreased reaction rate was observed along with the elongation of the alkyl chains of levulinate esters (cf. Entry 6, 8, and 9; for reaction kinetics data, see Figure S4(B) in SI), which might be due to the steric hindrance of the alkyl groups. In the confined nanospace of


25


UiO-66, reactant molecules should suffer from the steric effect, i.e. the steric effect of levulinate esters increases with the elongation of the alkyl chains, which retards the mass transfer of more bulky molecules and accordingly results in a reduced reaction rate. Furthermore, GVL could be synthesized from EL using EtOH as a H-donor, giving 37% and 55% GVL yields after 9 h and 24 h of reaction, respectively (Entry 7). EL is a biomass-derived levulinate ester obtained through alcoholysis of sugars in ethanol media. If the resulting ethanol media could directly be utilized as a renewable H-donor in the following CTH reaction of EL, an energy- and cost-saving GVL production route would be achievable. Compared to levulinate esters, LA showed the lowest activity toward GVL formation (25% GVL yield after 9 h of reaction at 140 °C) (Entry 10), which is due to the acidic nature of LA diminishing the ability of basic active sites (O 2-) to catalyse the CTH reaction. This idea can be well corroborated by the abovementioned comparative experimental result using benzoic acid as a homogeneous acid (Figure 6).

100

(B) Yields of products / %

(A) Yields of products / %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 40

80 Fur GVL FA FE LA/LB

60 40 20 0

0

10

20

30

40

50

100 Fur GVL FA FE LA/LB

80 60 40 20 0

0

10

Time / h

20

30

40

50

Time / h

Figure 7. Yields of products over 48 h in the reaction of furfural with 2-BuOH in the presence of (A) UiO-66 and (B) UiO-66-S60 at 140 °C. Reaction conditions: catalyst (ca. 100 mg,


26

Page 27 of 40

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corresponding to 0.3 mmol of Zr), furfural (0.5 mmol), 2-BuOH (5 mL), Ar 0.5 MPa, 140 °C. Fur = furfural, FA = furfuryl alcohol, FE = sec-butyl furfuryl ether, LA = levulinic acid, BL = sec-butyl levulinate, GVL = γ-valerolactone.

Recently, Román-Leshkov et al. demonstrated a domino reaction to produce GVL from furfural (Fur) using microporous zirconosilicate molecular sieve catalyst (Zr-beta),52 in which Zr-related Lewis acid sites simultaneously catalyse the ring-opening of furan ring of Fur to produce LA and its esters and the following CTH reaction to convert them to GVL in a tandem reaction pathway. Since UiO-66-Sx has a similar dual functionality, direct production of GVL from Fur was also examined using UiO-66-S60 as a heterogeneous catalyst. Figure 7(A) and (B) show time profiles of the yields of products in the reaction of Fur with 2-BuOH over pristine UiO-66 and UiO-66-S60 catalysts, respectively. Under the optimized reaction conditions (140 °C, 0.5 MPa Ar), unfunctionalized UiO-66 showed 100% conversion of Fur within 3 h of reaction and gave furfuryl alcohol (FA) as a major product with ~92% selectivity, via a CTH reaction of Fur with 2-BuOH (Figure 7(A)). A small amount of sec-butyl furfuryl ether (FE) was obtained as a result of etherification between FA and 2-BuOH, and thereafter trace of GVL was produced as a result of the acid-catalysed ring-opening of FA (or FE) to produce LA (or sBL)31, 32 followed by a CTH reaction. However, GVL yield obtained over UiO-66 after 48 h of reaction was only 5.1% because of the absence of Brönsted acid sites. On the contrary, acid-functionalized UiO-66S60 exhibited a dramatically improved selectivity toward GVL, affording 27% GVL yield under the identical conditions (Figure 7(B)) (33% GVL yield was attained when 0.2 mmol of Fur was supplied; Table 3, Entry 12). UiO-66-S60 provided FE and GVL as the major products. Since FA and LA (or sBL) intermediates were scarcely observed, the ring-opening of FE must be a rate-


27


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Page 28 of 40

determining step in this reaction. It is obvious from the product distribution profile that this improved GVL selectivity is due to the ability of sulfonic acid sites to catalyse the ring-opening of FA (or FE) to produce LA (or sBL). Although further improvement in catalytic performance/conditions is clearly needed toward the direct GVL production from Fur, this result opens up a possibility of UiO-66-Sx to be a promising heterogeneous catalyst for the selective GVL formation from a variety of biomass feedstocks.

CONCLUSIONS In summary, we have demonstrated that sulfonic acid functionalized UiO-66 acts as an active heterogeneous catalyst for CTH reaction of biomass-derived levulinic acid and its esters to produce GVL using alcohols as H-donors. A higher GVL yield was attained by increasing the content of sulfo-terephthalic acid linkers with a maximum GVL yield of 85% over UiO-66-S60 at 140 °C, which far outperformed those of other MOFs embedding different metallic centers, bulk ZrO2, and pristine UiO-66. This was due to the cooperative effect between Lewis-basic Zr oxo clusters and Brönsted-acidic –SO3H groups uniformly arranged in a confined nanospace of UiO66, which can catalyse CTH reaction of levulinate esters and the successive intramolecular dealcoholization to form GVL, respectively. With this synergistic effect, the dual-functional UiO-66 showed a broad scope for substrates and alcohols for selective GVL formation, and could directly produce GVL from furfuryl alcohol in a tandem reaction pathway. Additionally, UiO-66-S60 catalyst developed in this study was reusable at least four successive cycles under the specified reaction conditions without significant loss of catalytic activity. This research opens up new perspectives of MOF materials as heterogeneous catalysts for the selective transformation of biomass feedstocks in bio-refinery process.


28

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ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.xxxxxxx. SEM, TG, XAFS analysis data of the catalysts and reaction kinetics data.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (H. Yamashita) Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This study was financially supported by the Grant-in-Aid from Frontier Research Base for Global Young Researchers, Osaka University and the Grant-in-Aid for Scientific Research (KAKENHI) from the Japan Society for the Promotion of Science (JSPS) (No. 15K18270). A part of this work was also performed under a management of “Elements Strategy Initiative for Catalysts & Batteries (ESICB)” supported by MEXT. The synchrotron radiation experiments were performed at the BL01B1 beam line in SPring-8 with the approval of JASRI (No. 2016A1057).


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REFERENCES (1)

Corma, A.; Iborra, S.; Velty, A. Chemical routes for the transformation of biomass into

chemicals. Chem. Rev. 2007, 107, 2411-2502. (2)

Chheda, J. N.; Huber, G. W.; Dumesic, J. A. Liquid-phase catalytic processing of

biomass-derived oxygenated hydrocarbons to fuels and chemicals. Angew. Chem. Int. Ed. 2007, 46, 7164-7183. (3)

Alonso, D. M.; Bond, J. Q.; Dumesic, J. A. Catalytic conversion of biomass to biofuels.

Green Chem. 2010, 12, 1493-1513. (4)

Bozell, J. J.; Petersen, G. R. Technology development for the production of biobased

products from biorefinery carbohydrates—the us department of energy’s “top 10” revisited. Green Chem. 2010, 12, 539-554. (5)

Zhou, C.-H.; Xia, X.; Lin, C.-X.; Tong, D.-S.; Beltramini, J. Catalytic conversion of

lignocellulosic biomass to fine chemicals and fuels. Chem. Soc. Rev. 2011, 40, 5588-5617. (6)

Serrano-Ruiz, J. C.; Luque, R.; Sepúlveda-Escribano, A. Transformations of biomass-

derived platform molecules: From high added-value chemicals to fuels via aqueous-phase processing. Chem. Soc. Rev. 2011, 40, 5266-5281. (7)

Climent, M. J.; Corma, A.; Iborra, S. Converting carbohydrates to bulk chemicals and

fine chemicals over heterogeneous catalysts. Green Chem. 2011, 13, 520-540. (8)

Climent, M. J.; Corma, A.; Iborra, S. Conversion of biomass platform molecules into fuel

additives and liquid hydrocarbon fuels. Green Chem. 2014, 16, 516-547.


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(9) Kubička, D.; Kubičková, I.; Čejka, J. Application of molecular sieves in transformations of biomass and biomass-derived feedstocks. Catal. Rev. 2013, 55, 1-78. (10) Resasco, D. E.; Wang, B.; Crossley, S. Zeolite-catalysed C–C bond forming reactions for biomass conversion to fuels and chemicals. Catal. Sci. Technol. 2016, 6, 2543-2559. (11) Alonso, D. M.; Wettstein, S. G.; Dumesic, J. A. Gamma-valerolactone, a sustainable platform molecule derived from lignocellulosic biomass. Green Chem. 2013, 15, 584-595. (12) Han, J.; Sen, S. M.; Alonso, D. M.; Dumesic, J. A.; Maravelias, C. T. A strategy for the simultaneous catalytic conversion of hemicellulose and cellulose from lignocellulosic biomass to liquid transportation fuels. Green Chem. 2014, 16, 653-661 (13) Yan, K.; Yang, Y.; Chai, J.; Lu, Y. Catalytic reactions of gamma-valerolactone: A platform to fuels and value-added chemicals. Appl. Catal. B 2015, 179, 292-304. (14) Horváth, I. T.; Mehdi, H.; Fábos, V.; Boda, L.; Mika, L. T. γ-valerolactone—a sustainable liquid for energy and carbon-based chemicals. Green Chem. 2008, 10, 238-242. (15) Gallo, J. M. R.; Alonso, D. M.; Mellmer, M. A.; Dumesic, J. A. Production and upgrading of 5-hydroxymethylfurfural using heterogeneous catalysts and biomass-derived solvents. Green Chem. 2013, 15, 85-90. (16) Xue, Z.; Zhao, X.; Sun, R.-C.; Mu, T. Biomass-derived γ-valerolactone-based solvent systems for highly efficient dissolution of various lignins: Dissolution behavior and mechanism study. ACS Sustainable Chem. Eng. 2016, 4, 3864-3870.


31


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 40

(17) Bond, J. Q.; Alonso, D. M.; Wang, D.; West, R. M.; Dumesic, J. A. Integrated catalytic conversion of γ-valerolactone to liquid alkenes for transportation fuels. Science 2010, 327, 1110-1114. (18) Bond, J. Q.; Alonso, D. M.; West, R. M.; Dumesic, J. A. γ-valerolactone ring-opening and decarboxylation over SiO2-Al2O3 with water. Langmuir 2010, 26, 16291-16298. (19) Manzer, L. E. Catalytic synthesis of α-methylene-γ-valerolactone: A biomass-derived acrylic monomer. Appl. Catal. A 2004, 272, 249-256. (20) Lange, J.-P.; Vestering, J. Z.; Haan, R. J. Towards ‘bio-based’ nylon: Conversion of γvalerolactone to methyl pentenoate under catalytic distillation conditions. Chem. Commun. 2007, 3488-3490. (21) Geilen, F. M. A.; Engendahl, B.; Harwardt, A.; Marquardt, W.; Klankermayer, J.; Leitner, W. Selective and flexible transformation of biomass-derived platform chemicals by a multifunctional catalytic system. Angew. Chem. Int. Ed. 2010, 49, 5510-5514. (22) Lange, J.-P.; Price, R.; Ayoub, P. M.; Louis, J.; Petrus, L.; Clarke, L.; Gosselink, H. Valeric biofuels: A platform of cellulosic transportation fuels. Angew. Chem. Int. Ed. 2010, 49, 4479-4483. (23) Serrano-Ruiz, J. C.; Wang, D.; Dumesic, J. A. Catalytic upgrading of levulinic acid to 5nonanone. Green Chem. 2010, 12, 574-577. (24) Liguori, F.; Moreno-Marrodan, C.; Barbaro, P. Environmentally friendly synthesis of γ‑ valerolactone by direct catalytic conversion of renewable sources. ACS Catal. 2015, 5, 18821894.


32

Page 33 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(25) Wright, W. R. H.; Palkovits, R. Development of heterogeneous catalysts for the conversion of levulinic acid to γ-valerolactone. ChemSusChem 2012, 5, 1657-1667. (26) Hu, X.; Li, C.-Z. Levulinic esters from the acid-catalysed reactions of sugars and alcohols as part of a bio-refinery. Green Chem. 2011, 13, 1676-1679. (27) Hu, X.; Song, Y.; Wu, L.; Gholizadeh, M.; Li, C.-Z. One-pot synthesis of levulinic acid/ester from C5 carbohydrates in a methanol medium. ACS Sustainable Chem. Eng. 2013, 1, 1593-1599. (28) Démolis, A.; Essayem, N.; Rataboul, F. Synthesis and applications of alkyl levulinates. ACS Sustainable Chem. Eng. 2014, 2, 1338-1352. (29) Kuwahara, Y.; Fujitani, T.; Yamashita, H. Esterification of levulinic acid with ethanol over sulfated mesoporous zirconosilicates: Influences of the preparation conditions on the structural properties and catalytic performances. Catal. Today 2014, 237, 18-28. (30) Kuwahara, Y.; Kaburagi, W.; Nemoto, K.; Fujitani, T. Esterification of levulinic acid with ethanol over sulfated Si-doped ZrO2 solid acid catalyst: Study of the structure–activity relationships. Appl. Catal. A 2014, 476, 186-196. (31) Lange, J.-P.; van de Graaf, W. D.; Haan, R. J. Conversion of furfuryl alcohol into ethyl levulinate using solid acid catalysts. ChemSusChem 2009, 2, 437-441. (32) Neves, P.; Antunes, M. M.; Russo, P. A.; Abrantes, J. P.; Lima, S.; Fernandes, A.; Pillinger, M.; Rocha, S. M.; Ribeiro, M. F.; Valente, A. A. Production of biomass-derived furanic ethers and levulinate esters using heterogeneous acid catalysts. Green Chem. 2013, 15, 3367-3376.


33


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 40

(33) Deng, L.; Li, J.; Lai, D.-M.; Fu, Y.; Guo, Q.-X. Catalytic conversion of biomass-derived carbohydrates into γ-valerolactone without using an external H2 supply. Angew. Chem. Int. Ed. 2009, 48, 6529-6532. (34) Yan, Z.-P.; Lin, L.; Liu, S. Synthesis of γ-valerolactone by hydrogenation of biomassderived levulinic acid over Ru/C catalyst. Energy & Fuels 2009, 23, 3853-3858. (35) Al-Shaal, M. G.; Wright, W. R. H.; Palkovits, R. Exploring the ruthenium catalysed synthesis of γ-valerolactone in alcohols and utilisation of mild solvent-free reaction conditions. Green Chem. 2012, 14, 1260-1263. (36) Galletti, A. M. R.; Antonetti, C.; De Luise, V.; Martinelli, M. A sustainable process for the production of γ-valerolactone by hydrogenation of biomass-derived levulinic acid. Green Chem. 2012, 14, 688-694. (37) Kuwahara, Y.; Magatani, Y.; Yamashita, H. Ru nanoparticles confined in Zr-containing spherical mesoporous silica containers for hydrogenation of levulinic acid and its esters into γvalerolactone at ambient conditions. Catal. Today 2015, 258 Part2, 262-269. (38) Yang, Y.; Sun, C.-J.; Brown, D. E.; Zhang, L.; Yang, F.; Zhao, H.; Wang, Y.; Ma, X.; Zhang, X.; Ren, Y. A smart strategy to fabricate Ru nanoparticle inserted porous carbon nanofibers as highly efficient levulinic acid hydrogenation catalysts. Green Chem. 2016, 18, 3558-3566. (39) Yan, K.; Jarvis, C.; Lafleur, T.; Qiao, Y.; Xie, X. Novel synthesis of Pd nanoparticles for hydrogenation of biomass-derived platform chemicals showing enhanced catalytic performance. RSC Adv. 2013, 3, 25865-25871.


34

Page 35 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(40) Yan, K.; Lafleur, T.; Wu, G.; Liao, J.; Ceng, C.; Xie, X. Highly selective production of value-added γ-valerolactone from biomass-derived levulinic acid using the robust Pd nanoparticles. Appl. Catal. A 2013, 468, 52-58. (41) Deng, J.; Wang, Y.; Pan, T.; Xu, Q.; Guo, Q.-X.; Fu, Y. Conversion of carbohydrate biomass to γ-valerolactone by using water-soluble and reusable iridium complexes in acidic aqueous media. ChemSusChem 2013, 6, 1163-1167. (42) Hengne, A. M.; Rode, C. V. Cu–ZrO2 nanocomposite catalyst for selective hydrogenation of levulinic acid and its ester to γ-valerolactone. Green Chem. 2012, 14, 1064-1072. (43) Yan, K.; Liao, J.; Wu, X.; Xie, X. A noble-metal free Cu-catalyst derived from hydrotalcite for highly efficient hydrogenation of biomass-derived furfural and levulinic acid. RSC Adv. 2013, 3, 3853-3856. (44) Zhang, J.; Chen, J.; Guo, Y.; Chen, L. Effective upgrade of levulinic acid into γvalerolactone over an inexpensive and magnetic catalyst derived from hydrotalcite precursor. ACS Sustainable Chem. Eng. 2015, 3, 1708-1714. (45) Assary, R. S.; Curtiss, L. A.; Dumesic, J. A. Exploring meerwein–ponndorf–verley reduction chemistry for biomass catalysis using a first-principles approach. ACS Catal. 2013, 3, 2694-2704. (46) Kuwahara, Y.; Kaburagi, W.; Fujitani, T. Catalytic transfer hydrogenation of levulinate esters to γ-valerolactone over supported ruthenium hydroxide catalysts. RSC Adv. 2014, 4, 45848-45855.


35


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 40

(47) Kuwahara, Y.; Kaburagi, W.; Fujitani, T. Catalytic conversion of levulinic acid and its esters to γ-valerolactone over silica-supported zirconia catalysts. Bull. Chem. Soc. Jpn. 2014, 87, 1252-1254. (48) Kuwahara, Y.; Kaburagi, W.; Osada, Y.; Fujitani, T.; Yamashita, H. Catalytic transfer hydrogenation of biomass-derived levulinic acid and its esters to γ-valerolactone over ZrO2 catalyst supported on SBA-15 silica. Catal. Today 2017, 281, Part 3, 418-428. (49) Chia, M.; Dumesic, J. A. Liquid-phase catalytic transfer hydrogenation and cyclization of levulinic acid and its esters to γ-valerolactone over metal oxide catalysts. Chem. Commun. 2011, 47, 12233-12235. (50) Tang, X.; Hu, L.; Sun, Y.; Zhao, G.; Hao, W.; Lin, L. Conversion of biomass-derived ethyl levulinate into γ-valerolactone via hydrogen transfer from supercritical ethanol over a ZrO2 catalyst. RSC Adv. 2013, 3, 10277-10284. (51) Wang, J.; Jaenicke, S.; Chuah, G.-K. Zirconium–beta zeolite as a robust catalyst for the transformation of levulinic acid to γ-valerolactone via meerwein–ponndorf–verley reduction. RSC Adv. 2014, 4, 13481-13489. (52) Bui, L.; Luo, H.; Gunther, W. R.; Román-Leshkov, Y. Domino reaction catalyzed by zeolites with brønsted and lewis acid sites for the production of γ-valerolactone from furfural. Angew. Chem. Int. Ed. 2013, 52, 8022-8025. (53) Li, H.; Fang, Z.; Yang, S. Direct conversion of sugars and ethyl levulinate into γvalerolactone with superparamagnetic acid–base bifunctional ZrFeOx nanocatalysts. ACS Sustainable Chem. Eng. 2016, 4, 236-246.


36

Page 37 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(54) Song, J.; Wu, L.; Zhou, B.; Zhou, H.; Fan, H.; Yang, Y.; Meng, Q.; Han, B. A new porous Zr-containing catalyst with a phenate group: An efficient catalyst for the catalytic transfer hydrogenation of ethyl levulinate to γ-valerolactone. Green Chem. 2015, 17, 1626-1632. (55) Song, J.; Zhou, B.; Zhou, H.; Wu, L.; Meng, Q.; Liu, Z.; Han, B. Porous zirconiumphytic acid hybrid: A highly efficient catalyst for meerwein-ponndorf-verley reductions. Angew. Chem. Int. Ed. 2015, 54, 9399-9403. (56) Wiersum, A. D.; Soubeyrand-Lenoir, E.; Yang, Q.; Moulin, B.; Guillerm, V.; Yahia, M. B.; Bourrelly, S.; Vimont, A.; Miller, S.; Vagner, C.; Daturi, M.; Clet, G.; Serre, C.; Maurin, G.; Llewellyn, P. L. An evaluation of UiO-66 for gas-based applications. Chem. Asian J. 2011, 6, 3270-3280. (57) Lee, J. Y.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen, S. T.; Hupp, J. T. Metalorganic framework materials as catalysts. Chem. Soc. Rev. 2009, 38, 1450-1459. (58) Dhakshinamoorthy, A.; Opanasenko, M.; Čejka, J.; Garcia, H. Metal organic frameworks as solid catalysts in condensation reactions of carbonyl groups. Adv. Synth. Catal. 2013, 355, 247-268. (59) Dhakshinamoorthy, A.; Alvaro, M.; Garcia, H. Metal–organic frameworks as heterogeneous catalysts for oxidation reactions. Catal. Sci. Technol. 2011, 1, 856-867.” (60) Dhakshinamoorthy, A.; Opanasenko, M.; Čejka, J.; Garcia, H. Metal organic frameworks as heterogeneous catalysts for the production of fine chemicals. Catal. Sci. Technol., 2013, 3, 2509-2540.”


37


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 40

(61) Wang, C.; Liu, D.; Lin, W. Metal–organic frameworks as a tunable platform for designing functional molecular materials. J. Am. Chem. Soc. 2013, 135, 13222-13234. (62) Cavka, J. H.; Jakobsen, S.; Olsbye, U.; Guillou, N.; Lamberti, C.; Bordiga, S.; Lillerud, K. P. A new zirconium inorganic building brick forming metal organic frameworks with exceptional stability. J. Am. Chem. Soc. 2008, 130, 13850-13851. (63) Ling, S.; Slater, B. Dynamic acidity in defective UiO-66. Chem. Sci. 2016, 7, 4706-4712. (64) Klet, R. C.; Liu, Y.; Wang, T. C.; Hupp, J. T.; Farha, O. K. Evaluation of brønsted acidity and proton topology in Zr- and Hf-based metal–organic frameworks using potentiometric acid– base titration. J. Mater. Chem. A 2016, 4, 1479-1485. (65) Cirujano, F. G.; Corma, A.; Llabrés i Xamena, F. X. Zirconium-containing metal organic frameworks as solid acid catalysts for the esterification of free fatty acids: Synthesis of biodiesel and other compounds of interest. Catal. Today 2015, 257, 213-220. (66) Vermoortele, F.; Vandichel, M.; Van de Voorde, B.; Ameloot, R.; Waroquier, M.; Van Speybroeck, V.; De Vos, D. E. Electronic effects of linker substitution on lewis acid catalysis with metal-organic frameworks. Angew. Chem. Int. Ed. 2012, 51, 4887-4890. (67) Katz, M. J.; Brown, Z. J.; Colón, Y. J.; Siu, P. W.; Scheidt, K. A.; Snurr, R. Q.; Hupp, J. T.; Farha, O. K. A facile synthesis of UiO-66, UiO-67 and their derivatives. Chem. Commun. 2013, 49, 9449-9451. (68) Vermoortele, F.; Ameloot, R.; Vimont, A.; Serre, C.; De Vos, D. An amino-modified Zrterephthalate metal–organic framework as an acid–base catalyst for cross-aldol condensation. Chem. Commun. 2011, 47, 1521-1523.


38

Page 39 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(69) Foo, M. L.; Horike, S.; Fukushima, T.; Hijikata, Y.; Kubota, Y.; Takata, M.; Kitagawa, S. Ligand-based solid solution approach to stabilisation of sulphonic acid groups in porous coordination polymer Zr6O4(OH)4(BDC)6 (UiO-66). Dalton Trans. 2012, 41, 13791-13794. (70) Ferey, G.; Mellot-Draznieks, C.; Serre, C.; Millange, F.; Dutour, J.; Surblé, S.; Margiolaki, I. A chromium terephthalate-based solid with unusually large pore volumes and surface area. Science 2005, 309, 2040-2042. (71) Loiseau, T.; Serre, C.; Huguenard, C.; Fink, G.; Taulelle, F.; Henry, M.; Bataille, T.; Férey, G. A rationale for the large breathing of the porous aluminum terephthalate (MIL-53) upon hydration. Chem. Eur. J. 2004, 10, 1373-1382. (72) Valenzano, L.; Civalleri, B.; Chavan, S.; Bordiga, S.; Nilsen, M. H.; Jakobsen, S.; Lillerud, K. P.; Lamberti, C. Disclosing the complex structure of UiO-66 metal organic framework: A synergic combination of experiment and theory. Chem. Mater. 2011, 23, 17001718. (73) Goesten, M. G.; Juan-Alcañiz, J.; Ramos-Fernandez, E. V.; Sai Sankar Gupta, K. B.; Stavitski, E.; van Bekkum, H.; Gascon, J.; Kapteijn, F. Sulfation of metal–organic frameworks: Opportunities for acid catalysis and proton conductivity. J. Catal. 2011, 281, 177-187.


39


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Table of Contents Graphic

Sulfonic acid functionalized Zr-based metal–organic framework (MOF) efficiently catalyses catalytic transfer hydrogenation of levulinic acid and it esters to produce γ-valerolactone.


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Catalytic Transfer Hydrogenation of Biomass-Derived Levulinic Acid

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