Aerobic Oxidation of Biomass-Derived 5-(Hydroxymethyl)furfural into 2

Article pubs.acs.org/IECR

Aerobic Oxidation of Biomass-Derived 5‑(Hydroxymethyl)furfural into 2,5-Diformylfuran Catalyzed by the Trimetallic Mixed Oxide (Co−Ce−Ru) Yimei Wang, Bing Liu,* Kecheng Huang, and Zehui Zhang* Key Laboratory of Catalysis and Materials Sciences of the State Ethnic Affairs Commission & Ministry of Education, College of Chemistry and Material Science, South-Central University for Nationalities, Wuhan 430074, People’s Republic of China ABSTRACT: The paper deals with oxidation of the biomass-derived model molecule 5-(hydroxymethyl)furfural (HMF) catalyzed by the trimetallic mixed oxide RuCo(OH)2CeO2. The catalyst RuCo(OH)2CeO2 was prepared through alkali hydrolysis of RuCl3, Co(NO3)2, and Ce(NO3)2 and characterized by X-ray diffraction and transmission electron microscopy techniques. RuCo(OH)2CeO2 showed high catalytic activity for aerobic oxidation of HMF under mild conditions (in the case of atmospheric oxygen pressure). Various reaction parameters such as the reaction temperature, catalyst amount, solvent, and oxidant were explored. Results demonstrated that the oxidant and solvent showed a remarkable effect on the aerobic oxidation of HMF to 2,5-diformylfuran (DFF). Under optimal conditions, DFF was obtained in a high yield of 82.6% with HMF conversion of 96.5% after 12 h at 120 °C. More importantly, the catalyst could be reused several times without significant loss of its catalytic activity.

■

of poly(vinyl alcohol) for battery separations.23−25 In the early reports, DFF has primarily been synthesized from the oxidation of HMF by use of stoichiometric oxidants, including NaOCl,26 BaMnO4,27 and pyridinium chlorochromate.28 These methods not only required stoichiometric oxidants but also produced large amounts of waste. Recently, some new methods have been developed for the synthesis of DFF from HMF. Krystof et al. reported that silica-based 2,2,6,6-tetramethylpiperidine-1oxyl could effectively oxidize the hydroxymethyl group of HMF to afford DFF with high selectivity.29 In recent years, there is growing attention on the synthesis of DFF from the oxidation of HMF with molecular oxygen catalyzed by heterogeneous catalysts. The supported ruthenium-based catalysts generally showed high HMF conversion and DFF selectivity.30−32 The vanadium-based catalysts also have been attracting much attention for aerobic oxidation of HMF to DFF.33,34 However, some of the developed methods for aerobic oxidation of HMF to DFF either required harsh reaction conditions (e.g., high pressure) or suffered leaching of the active component. Therefore, it is strongly demanded to design stable heterogeneous catalysts with high catalytic activity for aerobic oxidation of HMF under mild reaction conditions. Ebitani et al. prepared a trimetallic compound, namely, ruthenium cation combined with microcrystals of cobalt hydroxide and cerium oxide, by a coprecipitation method, and it showed high activity and selectivity in the oxidation of primary alcohols to aldehydes.35 Motivated by the promising results of Ebitani et al., herein the trimetallic compound was prepared and used to catalyze the oxidation of HMF with molecular oxygen.

INTRODUCTION Rapidly depleting fossil fuels and escalating energy consumption coupled with rising environmental awareness among nations have led to increased focus on alternate, viable, ecofriendly, and renewable energy sources.1 In this context, it is strongly demanded to develop new routes for the production of fuels and bulk chemicals from renewable resources. Biomass is becoming more attractive as a logical alternative to petroleum because it is the only available carbon source apart from fossil resources.2−5 Therefore, chemical industries are shifting their focus to the development of sustainable manufacturing processes for the conversion of biomass into bulk chemicals and liquid fuels.6 Recently, there is growing interest in the synthesis of biomass-derived 5-(hydroxymethyl)furfural (HMF), which is a dehydration product of C6-based carbohydrates.7−10 HMF is regarded as one of the most promising platform chemicals and can be used as a versatile precursor for the production of fine chemicals, plastics, pharmaceuticals, and liquid fuels.11−13 Selective oxidation of HMF is one of the most pivotal functional group transformations in biorefinery.14 The fully oxidized HMF adduct, 2,5-furandicarboxylic acid (FDCA), has received significant attention in recent years. FDCA has been regarded as a possible polymer building block, and therefore a potential replacement, for terephthalic acid in the plastics industry.15 In recent years, there is overwhelming research on the synthesis of FDCA from HMF.16−21 For most cases, a strong alkaline condition was required to achieve an effective oxidation of HMF to FDCA. 2,5-Diformylfuran (DFF), as another oxidation product of HMF, can also be used in various fields. It can be used for the synthesis of furan-containing polymers and materials with special properties.22 It can also be used as a starting material for the synthesis of various poly-Schiff bases, pharmaceuticals, antifungal agents, organic conductors, and cross-linking agents © XXXX American Chemical Society

Received: October 12, 2013 Revised: January 11, 2014 Accepted: January 13, 2014

A

dx.doi.org/10.1021/ie4034363 | Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Industrial & Engineering Chemistry Research

■

Article

MATERIALS AND METHODS Materials. RuCl3·xH2O (38.0−42.0% ruthenium basis), Co(NO3)2·6H2O, and Ce(NO3)3·6H2O were purchased from Aladdin Chemicals Co. Ltd. (Beijing, China). 5(Hydroxymethyl)furfural (HMF; 98%) was supplied by Beijing Chemicals Co. Ltd. (Beijing, China). 2,5-Diformylfuran (DFF) was purchased from the J&K Chemical Co. Ltd. (Beijing, China). Na2CO3, NaOH, and all of the solvents were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Acetonitrile [MeCN; high-performance liquid chromatography (HPLC) grade] was purchased from Tedia Co. (Fairfield, OH). Catalyst Preparation and Characterization. The trimetallic Co−Ce−Ru catalyst was prepared according to the known procedures.35 Na2CO3 (13.3 mmol) and NaOH (46.4 mmol) were first dissolved in 30 mL of deionized water, and then the mixed solution of Na2CO3 and NaOH was added dropwise to a mixed solution of Co(NO3)2·6H2O (10.2 mmol), Ce(NO3)3·6H2O (5.1 mmol), and RuCl3·nH2O (ruthenium: 1.53 mmol) in deionized water (20 mL). Then the reaction mixture was vigorously stirred at 65 °C for 18 h. After the reaction, the resulting dark-brown slurry was filtered, washed with deionized water, and dried at 110 °C for 12 h to yield 2.15 g of a black powder, which was abbreviated as a Co6.6Ce3.3Ru1.1 catalyst according to the molar ratio of the metals. Other catalysts were also prepared by a similar method with the corresponding amount of the precursors. Powder X-ray diffraction (XRD) patterns of the samples were determined with a Bruker advanced D8 powder diffractometer (Cu Kα). The scan ranges were 10−80° with 0.016° steps, respectively. X-ray photoelectron spectroscopy (XPS) was conducted on a Thermo VG scientific ESCA MultiLab-2000 spectrometer with a monochromatized Al Kα source (1486.6 eV) at a constant analyzer pass energy of 25 eV. The binding energy (BE) was estimated to be accurate within 0.2 eV. All BEs were corrected by referencing to the C 1s (284.6 eV) peak of the contamination carbon as an internal standard. Elemental analysis was determined by inductively coupled plasma atomic emission spectrometry (ICP/AES) on an IRIS Intrepid II XSP instrument (Thermo Electron Corp., Waltham, MA). HMF Oxidation under Atmospheric Pressure. Aerobic oxidation of HMF was performed on a laboratory scale in a 25 mL round-bottomed glass flask equipped with a reflux condenser, a magnetic stirrer, and a gas inlet, allowing a flow rate of oxygen (20 mL min−1) to bubble through the reaction mixture. HMF (1 mmol, 126 mg) was added to methyl isobutyl ketone (MIBK; 7 mL), and the mixture was stirred vigorously to give a clear solution. Then trimetallic Co6.6Ce3.3Ru1.1 catalyst (160 mg) was added to the reaction system and flushed with pure oxygen for 5 min to dispel the remaining air in the system. Thereafter, the reactor was placed in a preheated oil bath (set to a fixed temperature) to start the reaction. After the reaction, the products in the reaction mixture were analyzed by a HPLC method. Determination of the Products. HMF and DFF were quantified by a HPLC system using an external standard calibration curve method. Samples were separated by a reversed-phase C18 column (200 × 4.6 mm) at a wavelength of 280 nm. MeCN and a 0.1 wt % acetic acid aqueous solution, volume ratio of 15:85, were used as the mobile phase, and the samples were eluted at a rate of 1.0 mL min−1 at 25 °C. Under

our analytical conditions, the retention times of HMF and DFF were 3.0 and 3.5 min, respectively. The contents of HMF and DFF in the samples were obtained directly by interpolation from calibration curves, which were constructed based on the pure compounds. To calculate the yield of DFF from HMF, eq 1 was used. HMF conversion = (moles of HMF added − moles of unreacted HMF) /moles of HMF added × 100%

(1)

One molecule of HMF gave rise to one molecule of DFF. The DFF yield can be calculated using eq 2. DFF yield = moles of DFF/moles of HMF added × 100% (2)

Catalyst Recycling and Stability Experiments. Recycling of the trimetallic Co6.6Ce3.3Ru1.1 catalyst was tested, maintaining the same reaction conditions as those described above, except using a recovered catalyst. Each time, the catalyst was separated from the reaction mixture by filtration. The recovered catalyst was then washed with water and ethanol and dried at 100 °C overnight, prior to its reuse in another run. The recovered catalyst was used for the next circle, and other steps were the same as those described above.

■

RESULTS AND DISCUSSION Catalyst Synthesis and Characterization. The elemental content of each metal in the Co6.6Ce3.3Ru1.1 catalyst was first determined by ICP/AES on an IRIS Intrepid II XSP instrument, and the weight percent of each element was shown as follows: Co, 33.6 wt %; Ce, 25.7 wt %; Ru, 6.4 wt %. The elemental content of each metal in the trimetallic Co6.6Ce3.3Ru1.1 was almost consistent with the precursors used for synthesis of the catalyst. The XRD patterns of the prepared Co6.6Ce3.3Ru1.1 catalyst are shown in Figure 1. For the

Figure 1. XRD pattern of the trimetallic Co6.6Ce3.3Ru1.1 catalyst.

layered structures of hydrotalcite-like material, the characteristic XRD peaks are 11°, 22°, 35°, 61°, and 63°.36 Therefore, the XRD measurement indicated that the layered structure of hydrotalcites was not formed in the Co6.6Ce3.3Ru1.1 catalyst. The reflections observed at 2θ of 20° and 39° are for the diffraction of CoO(OH), and the three reflection peaks at 28°, 48°, and 57° are identified as the CeO2 phase (JCPDS no. of cart: 34-0394). In addition, no peaks were detected for the ruthenium species. B



Article

Aerobic Oxidation of HMF in Various Solvents. It is known that the solvent is an important factor that affects the reaction efficiency. Thus, we have carried out aerobic oxidation of HMF to DFF in a variety of common solvents. Table 1 summarizes the effect of the solvent on the aerobic oxidation of HMF to DFF. It is noted that the solvent showed a remarkable effect on both HMF conversion and DFF yield. DFF was found to be the major product in all of the solvents except tetrahydrofuran (THF; Table 1, entry 1). The reaction in MeCN gave a poor HMF conversion of 9.1% (Table 1, entry 2). Moderate DFF yield and selectivity were obtained when reactions were carried out in the strong polar and high-boilingpoint solvents dimethyl sulfoxide (DMSO) and dimethylformamide (DMF; Table 1, entries 3 and 4). The structures of the aromatic solvents also showed a remarkable effect on the catalytic activity and DFF selectivity (Table 1, entries 5−7). Aerobic oxidation in toluene occurred sluggishly with 17.8% HMF conversion and 11.4% DFF yield after 12 h (Table 1, entry 5). However, aerobic oxidation of HMF proceeded fast with HMF conversion of 100% in 4-chlorotoluene and trifluorotoluene (TFT) after a short reaction time of 4 h (Table 1, entry 6 vs entry 7) compared with the reaction carried out in toluene (Table 1, entries 6 and 7 vs entry 5). Furthermore, the selectivity of DFF in TFT was much lower than that in 4-chlorotoluene (Table 1, entry 6 vs entry 7), and much more FDCA was observed in TFT. MIBK was found to be the best solvent for aerobic oxidation of HMF to DFF with the trimetallic Co6.6Ce3.3Ru1.1 catalyst. A DFF yield of 82.6% and a HMF conversion of 96.5% were obtained after 12 h in MIBK. A control experiment was also carried out in the absence of catalyst; HMF conversion was only 1.4% after 12 h in MIBK with no oxidation products. In order to give deep insight into the aerobic oxidation of HMF in MIBK, the concentration of HMF and the oxidation products at different reaction time points were recorded. As shown in Figure 5, other oxidation products such as FDCA and 5-(hydroxymethyl)-2-furancarboxylic acid (HMFCA) were also detected with little content. The concentration of HMF decreased gradually during the reaction process. The content of DFF increased with an increase in the reaction time. The highest HMF conversion of 96.5% and DFF yield of 82.6% were obtained after 12 h. In addition, FDCA and HMFCA as the byproducts also increased with an increase in the reaction time, but the increasing trend was low. FDCA and HFMCA yields reached 2.2% and 6.9% after 12 h, respectively. Because the HMFCA yield was much lower than that of DFF, we can conclude that oxidation of the aldehyde group in HMF to a carboxyl group was much more difficult than that of the hydroxyl group in HMF to an aldehyde group. Upon a further increase in the reaction time to 15 h, HMF conversion reached 100% and DFF yield was 83.4%. Catalytic Oxidation of HMF to DFF Using Various Oxidants. Oxidation of HMF using other common oxidants such as t-BuOOH and H2O2 was also studied, and the results are summarized in Table 2. Although HMF conversion reached 100% after 12 h with t-BuOOH as the oxidant, all of the detected furan compounds including DFF and FDCA were only 4.6% and 18.0% by HPLC (Table 2, entry 1). No other furan compounds except DFF and FDCA were detected. In addition, no other insoluble byproducts such as humins were formed. On the basis of the large gap between the HMF conversion and yield of furan compounds, we can conclude that the furan ring of HMF would be destroyed during the oxidation

The surface state of the trimetallic Co6.6Ce3.3Ru1.1 catalyst was characterized by XPS technology. The spectra of the Ru 3p, Ce 3d, and Co 2p regions are shown in Figures 2−4,

Figure 2. XPS spectra of the Ru 3p region.

Figure 3. XPS spectra of the Ce 3d region.

Figure 4. XPS spectra of the Co 2p region.

respectively. In Figure 2, Ru 3p doublets are present at 463 and 485 eV, which corresponded to Ru 3p3/2 and Ru 3p1/2, respectively. Ru 3p3/2 at 463 eV and Ru 3p1/2 at 485 eV confirm that the oxidation state of ruthenium in the catalyst is Ru4+, which is consistent with the previous report.37 As shown in Figure 3, the oxidation state of cerium analyzed by XPS technology is compatible with the presence of Ce4+ in CeO2.38 The Co 2p peaks at 780.3 and 781.8 eV (Figure 4) indicate a significant amount of Co2+ or Co3+.37 C



Article

Table 1. Effect of the Solvents on the Aerobic Oxidation of HMFa entry

solvent

1 2 3 4 5 6b 7b 8

THF MeCN DMSO DMF toluene TFT 4-chlorotoluene MIBK

HMF conversion (%) 48.7 9.1 80.2 79.6 17.8 100 100 96.5

± ± ± ± ± ± ± ±

DFF yield (%)

0.4 0.6 0.4 0.5 0.3 0 0 0.1

8.1 5.8 54.6 42.2 11.4 65.1 80.3 82.6

± ± ± ± ± ± ± ±

0.5 0.5 0.3 0.4 0.6 0.3 0.2 0.5

DFF selectivity (%) 16.6 63.7 68.0 53.0 64.0 65.1 80.3 85.6

± ± ± ± ± ± ± ±

0.5 0.5 0.3 0.4 0.6 0.3 0.2 0.5

FDCA yield (%) 32.1 1.9 21.7 13.5 4.0 29.4 11.0 8.9

± ± ± ± ± ± ± ±

0.4 0.2 0.5 0.5 0.3 0.4 0.3 0.3

a

Reaction conditions: HMF (1 mmol, 126 mg) and the Co6.6Ce3.3Ru1.1 catalyst (160 mg) were added to the solvent (7 mL), and the reaction was carried out at 120 °C for 12 h with an oxygen flow rate at 20 mL min−1. bThe reaction time was 4 h.

carried out in air, and HMF conversion of 45.3% and DFF yield of 37.9% were obtained (Table 2, entry 5). The low DFF yield in air was due to the low concentration of oxygen. However, the selectively of DFF was almost the same using oxygen as the oxidant in the three cases (Table 2, entries 3−5). Effect of the Catalyst Amount on the Aerobic Oxidation of HMF. Aerobic oxidation of HMF to DFF was also carried out with various amounts of Co6.6Ce3.3Ru1.1 in order to study the effect of catalyst loading. As shown in Figure 6, catalyst loading showed a remarkable effect on the

Figure 5. Time course of HMF recovery and product distributions during the process of aerobic oxidation of HMF. Reaction conditions: HMF (126 mg, 1 mmol) and the Co6.6Ce3.3Ru1.1 catalyst (160 mg) were added to 7 mL of MIBK, and the reaction was carried out at 120 °C with an oxygen flow rate at 20 mL min−1.

process by t-BuOOH. When we used H2O2 as the oxidant, we observed that oxygen was bubbled from the reaction mixture, which indicated that H2O2 decomposed to oxygen. As a fact, it is reported that ruthenium species had the ability to catalyze the decomposition of H2O2.39 Therefore, the oxidation of HMF occurred difficultly due to the decomposition of H2O (Table 2, entry 2). The catalyst showed an excellent catalytic ability of the activation of molecular oxygen for the oxidation of HMF to DFF. High HMF conversion of 96.5% and DFF yield of 82.6% were obtained after 12 h with the flush of oxygen (Table 2, entry 3). The high activity of the trimetallic Co6.6Ce3.3Ru1.1 catalyst under the flush of oxygen prompted us to further carry out aerobic oxidation of HMF under facile and simple reaction conditions. To our delight, DFF was stilled obtained in a high yield of 71.9% after 12 h, when reaction was carried out under an oxygen atmosphere by use of an oxygen balloon (Table 2, entry 4). Furthermore, the oxidation of HMF was further

Figure 6. Effect of the catalyst loading on the aerobic oxidation of HMF to DFF. Reaction conditions: HMF (1 mmol, 126 mg) and a set amount of the Co6.6Ce3.3Ru1.1 catalyst were added to MIBK (7 mL), and the reaction was carried out at 120 °C for 12 h with an oxygen flow rate at 20 mL min−1.

conversion of HMF and yield of DFF. HMF conversion of 46.3% and DFF yield of 39.8% were obtained after 12 h with 40 mg of the Co6.6Ce3.3Ru1.1 catalyst. DFF yields increased to 57.9% and 70.1% after 12 h for the catalyst loading of 80 and 120 mg, respectively, corresponding to HMF conversions of 68.5% and 82.3%, respectively. Maximum HMF conversion of

Table 2. Effect of Different Oxidants on the Oxidation of HMFa entry

oxidant

1b 2b 3c 4d 5e

t-BuOOH 30% H2O2(aq) O2 O2 air

HMF conversion (%) 100 16.5 96.5 83.5 45.3

± ± ± ± ±

DFF yield (%)

0 0.2 0.3 0.4 0.9

4.6 6.8 82.6 71.9 37.8

± ± ± ± ±

0.7 0.5 0.5 0.3 0.6

DFF selectivity (%) 4.6 41.2 85.6 86.1 84.3

± ± ± ± ±

0.7 0.5 0.5 0.3 0.6

FDCA yield (%) 18.0 8.1 8.4 7.3 4.9

± ± ± ± ±

0.6 0.7 0.3 0.7 0.8

a

Reaction conditions: HMF (1 mmol, 126 mg) and the Co6.6Ce3.3Ru1.1 catalyst (160 mg) were added into MIBK (7 mL), and the reaction was carried out for 12 h. bA total of 7 mmol of H2O2 and t-BuOOH were used, and the reaction temperature was 90 °C. cOxygen was flushed at a rate of 20 mL min−1 at 120 °C. dUnder the oxygen balloon at 120 °C. eThe reactor was directly opened in air without the flush at 120 °C. D



Article

Table 3. Catalytic Conversion of HMF to DFF at Different Reaction Temperaturesa entry

temperature (°C)

1 2 3 4b

50 80 120 120

HMF conversion (%) 47.5 68.5 96.5 4.9

± ± ± ±

DFF yield (%)

0.5 0.4 0.1 0.5

42.3 60.8 82.6 0

± ± ± ±

DFF selectivity (%)

0.3 0.5 0.3 0

88.5 88.8 85.6 0

± ± ± ±

0.3 0.5 0.3 0

FDCA yield (%) 3.7 4.0 8.9 0

± ± ± ±

0.2 0.5 0.4 0

a

Reaction conditions: HMF (1 mmol, 126 mg) and the Co6.6Ce3.3Ru1.1 catalyst (160 mg) were added to MIBK (7 mL), and the reaction was carried out at 120 °C for 12 h with an oxygen flow rate at 20 mL min−1. bReaction was carried out in the absence of the catalyst.

Table 4. Catalytic Conversion of HMF to DFF over Different Catalystsa entry

catalyst

catalyst amount (mg)

1 2 3 4 5 6b

Co6.6Ce3.3 Co9.9Ru1.1 Ce9.9Ru1.1 Co6.6Ce3.3Ru1.1 Co3.3Ce3.3Ru3.3 Co3.3Ce3.3Ru3.3

160 160 160 160 40 20

HMF conversion (%) 5.4 42.1 100 96.5 97.1 98.7

± ± ± ± ± ±

0.2 0.5 0 0.6 0.4 0.3

DFF yield (%) 0 36.2 58.1 82.6 80.8 79.2

± ± ± ± ± ±

0 0.4 0.5 0.4 0.6 0.5

DFF selectivity (%) 0 85.9 58.1 85.6 83.2 80.2

± ± ± ± ± ±

0 0.4 0.5 0.4 0.6 0.5

FDCA yield (%) 0 3.8 35.6 8.9 9.3 11.7

± ± ± ± ± ±

0 0.3 0.3 0.3 0.6 0.2

a

Reaction conditions: HMF (1 mmol, 126 mg) and a set amount of the catalyst (160 mg) were added to MIBK (7 mL), and the reaction was carried out at 120 °C for 12 h with an oxygen flow rate at 20 mL min−1. bReaction was carried out at 10 bar of oxygen.

catalysts were used to catalyze aerobic oxidation of HMF (Table 4). The bimetallic oxide Co6.6Ce3.3 almost showed no catalytic activity, which indicated that ruthenium was the active species for oxidation of HMF (Table 4, entry 1). The absence of cerium produced much lower HMF conversion but with similar selectivity (Table 4, entry 2 vs entry 4). However, the absence of cobalt gave high HMF conversion but poor selectivity (Table 4, entry 3 vs entry 4). The results indicated that the element cerium accelerated aerobic oxidation of HMF, and cobalt played a key role in the selectivity of DFF. Our results were consistent with the previous results.32 It was reported that oxidation involved the formation of a ruthenium alcoholate species, which underwent β-elimination to produce an aldehyde catalyzed by a cerium species and a ruthenium hydride species.32 Oxidation of a ruthenium hydride species by oxygen regenerated a ruthenium species. Further reducing the cobalt content and increasing the ruthenium content resulted in Co3.3Ce3.3Ru3.3. It was found that it showed higher catalytic activity than Co6.6Ce3.3Ru1.1 (Table 4, entry 4 vs entry 5). A DFF yield of 80.8% was obtained with use of 40 mg of Co3.3Ce3.3Ru3.3. The amount of Co3.3Ce3.3Ru3.3 could be further reduced to 20 mg with similar results when the reaction was carried out at 10 bar of oxygen (Table 4, entry 6). In order to provide useful information for practical application for the synthesis of DFF from HMF, a large-scale experiment was carried out. The reaction conditions were as follows: 1 g of HMF, 30 mL of MIBK, 300 mg of the Co3.3Ce3.3Ru3.3 catalyst, at 100 °C, and an oxygen flow rate at 20 mL min−1. During different reaction time points, small aliquots were withdrawn (ca. 50 μL) and analyzed by the HPLC method. It was found that HMF was completely converted after 24 h, and DFF was obtained in an isolated yield of 80.2%. The results were close to the previous results using 126 mg of HMF as the starting material. Catalyst Recycling Experiments. The catalytic stability of the Co6.6Ce3.3Ru1.1 catalyst was studied, and aerobic oxidation of HMF to DFF was used as a model reaction. As shown in Figure 7, the selectively of DFF remained stable, while HMF conversion and DFF yield showed a slight decrease. In order to investigate loss of the catalytic activity, a hot filtration experiment was conducted to ascertain the truly heterogeneous

96.5% and DFF yield of 82.6% were achieved after 12 h when 160 mg of the Co6.6Ce3.3Ru1.1 catalyst was used. Thus, a general rule of the effect of the catalyst amount on the aerobic oxidation of HMF could be concluded as follows. The more the catalyst amount was, the higher the HMF conversion and DFF yield were at the same reaction time. This should be attributed to an increase in the availability and number of catalytically active sites, leading to a high oxidation rate under otherwise the same reaction conditions, and a similar phenomenon was also observed for the oxidation of benzyl alcohol.40 However, it was noted that the selectivity of DFF was almost the same, around 85%, for all of the different catalyst loadings. These results indicated that catalyst loading had little influence on the selectivity of HMF, and the selectivity probably mainly depended on other reaction conditions such as the reaction temperature, solvents, and oxidants. Effect of the Reaction Temperature on the Aerobic Oxidation of HMF. In order to study the effect of the reaction temperature on the aerobic oxidation of HMF, reactions were carried out at 50, 80, and 120 °C, respectively. As shown in Table 2, it is clearly noted that the reaction temperature showed a remarkable effect on the oxidation of HMF to DFF. HMF conversion was elevated from 47.5% to 68.5% when the reaction temperature increased from 50 to 80 °C (Table 3, entries 1 and 2). Upon a further increase of the reaction temperature to 120 °C, a high HMF conversion of 96.5% was obtained after 12 h (Table 3, entry 3). The yield of DFF was also elevated with an increase in the reaction temperature, and the DFF yield reached 42.3%, 60.8%, and 82.6% after 12 h at 50, 80, and 120 °C, respectively (Table 3, entries 1−3). It was observed that the selectivity of DFF at 120 °C was a little lower than those at 50 and 80 °C (Table 3, entries 1−3). These results indicated that HMF was not stable at high reaction temperature.41 A control experiment was also carried out by the treatment of HMF in MIBK without the catalyst at 120 °C for 12 h, and 4.9% HMF was degraded into other products (Table 3, entry 4). Aerobic Oxidation of HMF over Various Catalysts. In order to give more insight into aerobic oxidation of HMF to DFF catalyzed by the trimetallic oxide and the development of a more effective method for aerobic oxidation of HMF, various E



Article

reaction parameters have been investigated, and MIBK was found to be the best solvent for aerobic oxidation of HMF. Under the optimal reaction conditions, HMF conversion of 96.5% and DFF yield of 82.6% were obtained after 12 h at 120 °C. In addition, the preparative procedure of the catalyst is simple, and the catalyst also showed good properties in recovery and stability. In this regard, our developed method showed the potential feasibility for the industrial-scale production of DFF under the crises of fossil resources.

■

AUTHOR INFORMATION

Corresponding Authors

*Tel.: +86-27-67842572. Fax: +86-27-67842572. E-mail: [email protected]. *E-mail: [email protected]. Figure 7. Reusability of the catalyst on aerobic oxidation of HMF. Reaction conditions: HMF (126 mg, 1 mmol) and the Co6.6Ce3.3Ru1.1 catalyst (160 mg) were added to 7 mL of MIBK, and the reaction was carried out at 120 °C with the flush of oxygen at 20 mL min−1.

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The project was supported by the National Natural Science Foundation of China (Grants 21203252 and 21206200) and the Special Fund for Basic Scientific Research of Central Colleges, South-Central University for Nationalities (Grant CYZ2012005).

nature of the Co6.6Ce3.3Ru1.1 catalyst. The catalyst was removed from the reaction mixture after 4 h, and the filtrate was left to react under the same reaction temperature for a certain period of time. As shown in Figure 8, the DFF yield after removal of

■

REFERENCES

(1) Ragauskas, A. J.; Williams, C. K.; Davison, B. H.; Britovsek, G.; Cairney, J.; Eckert, C. A.; Frederick, W. J.; Pallett, J. P., Jr.; Leak, D. J.; Liotta, C. L.; Mielenz, J. R.; Murphy, R.; Templer, R.; Tschaplinski, T. The path forward for biofuels and biomaterials. Science 2006, 311, 484. (2) Modenbach, A. A.; Nokes, S. E. Enzymatic hydrolysis of biomass at high-solids loadingsA review. Biomass Bioenergy 2013, 56, 526. (3) Liu, B.; Zhang, Z. H.; Huang, K. C.; Fang, Z. F. Efficient conversion of carbohydrates into 5-ethoxymethylfurfural in ethanol catalyzed by AlCl3. Fuel 2013, 113, 625. (4) Agirrezabal-Telleria, I.; Gandarias, I.; Arias, P. L. Production of furfural from pentosan-rich biomass: Analysis of process parameters during simultaneous furfural stripping. Bioresour. Technol. 2013, 143, 258. (5) Kantarelis, E.; Yang, W.; Blasiak, W. Production of liquid feedstock from biomass via steam pyrolysis in a fluidized bed reactor. Energy Fuels 2013, 8, 4748. (6) Dutta, S.; De, S.; Saha, B. A brief summary of the synthesis of polyester building-block chemicals and biofuels from 5-hydroxymethylfurfural. ChemPlusChem 2012, 77, 259. (7) Zhang, Z. H.; Wang, Q.; Xie, H. B.; Liu, W. J.; Zhao, Z. K. Catalytic conversion of carbohydrates into 5-hydroxymethylfurfural by germanium(IV) chloride in ionic liquids. ChemSusChem 2011, 4, 131. (8) Binder, J. B.; Raines, R. T. Simple chemical transformation of lignocellulosic biomass into furans for fuels and chemicals. J. Am. Chem. Soc. 2009, 131, 1979. (9) Qu, Y. S.; Song, Y. L.; Huang, C. P.; Zhang, J.; Chen, B. H. Alkaline ionic liquids as catalysts: A novel and green process for the dehydration of carbohydrates to give 5-hydroxymethylfurfural. Ind. Eng. Chem. Res. 2012, 51, 13008. (10) Liu, B.; Zhang, Z. H.; Zhao, Z. K. Microwave-assisted catalytic conversion of cellulose into 5-hydroxymethylfurfural in ionic liquids. Chem. Eng. J. 2013, 215−216, 517. (11) Rosatella, A. A.; Simeonov, S. P.; Frade, R. F. M.; Afonso, C. A. M. 5-Hydroxymethylfurfural (HMF) as a building block platform: biological properties, synthesis and synthetic applications. Green Chem. 2011, 13, 754. (12) Buntara, T.; Noel, S.; Phua, P. H.; Melian-Cabrera, I.; De Vries, J. G.; Heeres, H. J. Caprolactam from renewable Resources: catalytic conversion of 5-hydroxymethylfurfural into caprolactone. Angew. Chem., Int. Ed. 2011, 50, 7083.

Figure 8. Results of the control experiments after hot filtration for aerobic oxidation of HMF to DFF. Reaction conditions: HMF (126 mg, 1 mmol) and the Co6.6Ce3.3Ru1.1 catalyst (160 mg) were added to 7 mL of MIBK, and the reaction was carried out at 120 °C with the flush of oxygen at 20 mL min−1.

the catalyst remained stable, which indicated that there was no leaching of metal during the recycling experiments. In addition, the liquid solution was also analyzed by ICP/AES technology, and the elements of ruthnium, cobalt, and cerium were not detected in the liquid solution. These results once again indicated that there was no leaching of metal during the reaction process. It is reported that some humins were often formed via aldol addition and condensation from HMF.39 Thus, one possible reason for the slight decrease of the catalyst activity might be that some insoluble humins deposited on the surface of the catalyst sites, resulting in the loss of its catalytic activity.

■

CONCLUSION In conclusion, the trimetallic Co−Ce−Ru catalyst acted as an excellent heterogeneous catalyst for aerobic oxidation of HMF to DFF under mild reaction conditions. Various important F



Article

sulfonated resin and hydrotalcite-supported ruthenium catalysts. ACS Catal. 2011, 1, 1562. (33) Grasset, F. L.; Katryniok, B.; Paul, S.; Nardello-Rataj, V.; PeraTitus, M.; Clacens, J. M.; De Campo, F.; Dumeignil, F. Selective oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran over intercalated vanadium phosphate oxides. RSC Adv. 2013, 3, 9942. (34) Sádaba, I.; Gorbanev, Y. Y.; Kegnæs, S.; Putluru, S. S. R.; Berg, R. W.; Riisager, A. Catalytic performance of zeolite-supported vanadia in the aerobic oxidation of 5-hydroxymethylfurfural to 2,5diformylfuran. ChemCatChem 2013, 5, 284. (35) Ebitani, K.; Ji, H. B.; Mizugaki, T.; Kaneda, K. Highly active trimetallic Ru/CeO2/CoO(OH) catalyst for oxidation of alcohols in the presence of molecular oxygen. J. Mol. Catal. A: Chem. 2004, 212, 161. (36) Jiang, Z.; Kong, L.; Chu, Z. Y.; France, L. J.; Xiao, T. C.; Edwards, P. P. Catalytic combustion of propane over mixed oxides derived from CuxMg3−xAl hydrotalcites. Fuel 2012, 96, 257. (37) Ghiacia, M.; Aghabararia, B.; do Rego, A. M. B.; Ferraria, A. M.; Habibollahi, S. Efficient allylic oxidation of cyclohexene catalyzed by trimetallic hybrid nano-mixed oxide (Ru/Co/Ce). Appl. Catal., A 2011, 393, 225. (38) Stuchinskaya, T. L.; Musawir, M.; Kozhevnikova, E. F.; Kozhevnikov, I. V. Liquid-phase oxidation of alcohols by oxygen and nitrous oxide catalysed by Ru−Co oxide. J. Catal. 2005, 231, 41. (39) Selvaraj, P. C.; Mahadevan, V. The decomposition of H2O2 catalyzed by polymer supported transition metal complexes. J. Mol. Catal. A: Chem. 1997, 120, 47. (40) Namboodiri, V. V.; Polshettiwar, V.; Varma, R. S. Expeditious oxidation of alcohols to carbonyl compounds using iron(III) nitrate. Tetrahedron Lett. 2007, 48, 8839. (41) Patil, S. K. R.; Lund, C. R. F. Formation and growth of humins via aldol addition and condensation during acid-catalyzed conversion of 5-hydroxymethylfurfural. Energy Fuels 2011, 25, 4745.

(13) Subbiah, S.; Simeonov, S. P.; Esperanca, J. M. S. S.; Rebelo, L. P. N.; Afonso, C. A. M. Direct transformation of 5-hydroxymethylfurfural to the building blocks 2,5-dihydroxymethylfurfural (DHMF) and 5hydroxymethyl furanoic acid (HMFA) via Cannizzaro reaction. Green Chem. 2013, 15, 2849. (14) Moreau, C.; Belgacem, M. N.; Gandini, A. Recent catalytic advances in the chemistry of substituted furans from carbohydrates and in the ensuing polymers. Top. Catal. 2004, 27, 11. (15) Gandini, A. The irruption of polymers from renewable resources on the scene of macromolecular science and technology. Green Chem. 2011, 13, 1061. (16) Pasini, T.; Piccinini, M.; Blosi, M.; Bonelli, R.; Albonetti, S.; Dimitratos, N.; Lopez- Sanchez, J. A.; Sankar, M.; He, Q.; Kiely, C. J.; Hutchings, G. J.; Cavani, F. Selective oxidation of 5-hydroxymethyl-2furfural using supported gold−copper nanoparticles. Green Chem. 2011, 13, 2091. (17) Davis, S. E.; Houk, L. R.; Tamargo, E. C.; Datye, A. K.; Davis, R. J. Oxidation of 5-hydroxymethylfurfural over supported Pt, Pd and Au catalysts. Catal. Today 2011, 160, 55. (18) Carlini, C.; Patrono, P.; Galletti, A. M. R.; Sbrana, G.; Zima, V. Selective oxidation of 5-hydroxymethyl-2-furaldehyde to furan-2,5dicarboxaldehyde by catalytic systems based on vanadyl phosphate. Appl. Catal., A 2005, 289, 197. (19) Casanova, O.; Iborra, S.; Corma, A. Biomass into chemicals: aerobic oxidation of 5-hydroxymethyl-2-furfural into 2,5-furandicarboxylic acid with gold nanoparticle catalysts. ChemSusChem 2009, 2, 1138. (20) Saha, B.; Dutta, S.; Abu-Omar, M. M. Aerobic oxidation of 5hydroxylmethylfurfural with homogeneous and nanoparticulate catalysts. Catal. Sci. Technol. 2012, 2, 79. (21) Saha, B.; Gupta, D.; Abu-Omar, M. M.; Modak, A.; Bhaumik, A. Porphyrin-based porous organic polymer-supported iron(III) catalyst for efficient aerobic oxidation of 5-hydroxymethylfurfural into 2,5furandicarboxylic acid. J. Catal. 2013, 299, 316. (22) Ma, J. P.; Du, Z. T.; Xu, J.; Chu, Q.; Pang, Y. Efficient aerobic oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran, and synthesis of a fluorescent material. ChemSusChem 2011, 4, 51. (23) Adams, H.; Bastida, R.; deBlas, A.; Carnota, M.; Fenton, D. E.; Macias, A.; Rodriguez, A.; Rodriguez Blas, T. Complexes of lead(II) and lanthanide(III) ions with a macrocyclic ligand containing a furan head unit. Crystal structure of a methanol inclusion compound of a novel macrocycle. Polyhedron 2007, 16, 567. (24) Amarasekara, A. S.; Green, D.; Williams, L. D. Renewable resources based polymers: Synthesis and characterization of 2,5diformylfuran−urea resin. Eur. Polym. J. 2009, 45, 595. (25) Ma, J. P.; Wang, M.; Du, Z. T.; Chen, C.; Gao, J.; Xu, J. Synthesis and properties of furan-based imine-linked porous organic frameworks. Polym. Chem. 2009, 3, 2346. (26) Amarasekara, A. S.; Green, D.; McMillan, E. Efficient oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran using Mn(III)-salen catalysts. Catal. Commun. 2008, 9, 286. (27) Lichtenthaler, F. W. Unsaturated O- and N-heterocycles from carbohydrate feedstocks. Acc. Chem. Res. 2002, 35, 728. (28) Cottier, L.; Descotes, G.; Viollet, E.; Lewkowski, J.; Skowroński, R. Oxidation of 5-hydroxymethylfurfural and derivatives to furanaldehydes with 2,2,6,6-tetramethylpiperidine oxide radical−co-oxidant pairs. J. Heterocycl. Chem. 1995, 32, 927. (29) Krystof, M.; Perez-Sanchez, M.; de Maria, P. D. LipaseMediated Selective Oxidation of Furfural and 5-Hydroxymethylfurfural. ChemSusChem 2013, 6, 826. (30) Nie, J. F.; Xie, J. H.; Liu, H. C. Activated carbon-supported ruthenium as an efficient catalyst for selective aerobic oxidation of 5hydroxymethylfurfural to 2,5-diformylfuran. Chinese J. Catal. 2013, 34, 871. (31) Nie, J. F.; Xie, J. H.; Liu, H. C. Efficient aerobic oxidation of 5hydroxymethylfurfural to 2,5-diformylfuran on supported Ru catalysts. J. Catal. 2013, 301, 83. (32) Takagaki, A.; Takahashi, M.; Nishimura, S.; Ebitani, K. One-pot synthesis of 2,5-diformylfuran from carbohydrate derivatives by G


Aerobic Oxidation of Biomass-Derived 5-(Hydroxymethyl)furfural into 2

Recommend Documents