Subscriber access provided by FLORIDA ATLANTIC UNIV
Article
Hydrogenation of biomass-derived furfural to tetrahydrofurfuryl alcohol over hydroxyapatite supported Pd catalyst under mild conditions Chuang Li, Guangyue Xu, Xiaohao Liu, Ying Zhang, and Yao Fu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b02046 • Publication Date (Web): 17 Jul 2017 Downloaded from http://pubs.acs.org on July 18, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 22
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
Industrial & Engineering Chemistry Research
Hydrogenation of biomass-derived furfural to tetrahydrofurfuryl alcohol over hydroxyapatite supported Pd catalyst under mild conditions Chuang Li, Guangyue Xu, Xiaohao Liu, Ying Zhang*, Yao Fu iChEM, CAS Key Laboratory of Urban Pollutant Conversion, Anhui Province Key Laboratory for Biomass Clean Energy and Department of Chemistry, University of Science and Technology of China, Hefei 230026, P. R. China. * E-mail:
[email protected] ABSTRACT: Tetrahydrofurfuryl alcohol (THFAL), as green industrial solvent, can be obtained directly from biomass-derived furfural with 100% conversion and 100% yield over hydroxyapatite supported Pd catalyst (Pd-HAP) under relatively mild conditions (40 °C, 1 MPa H2 and 3 h) in 2-propanol. At room temperature and reacting for 8 h, the yield of THFAL was more than 99%. By capturing the intermediates, two pathways were proposed as follows: (1) furfural was partially hydrogenated to furfuryl alcohol, and then furfuryl alcohol was further hydrogenated to THFAL; (2) furfural and 2-propanol firstly formed 2-(isopropoxymethyl)furan (2-IPMF) via etherification and then 2-IPMF was ultimately converted to THFAL. The Pd-HAP catalyst was characterized by various techniques including XRD, SEM, TEM, HAADF-STEM, XPS and ICP-AAS. The results revealed that the outstanding catalytic performance of Pd-HAP was attributed to the quasicoordination effect between Pd and HAP, which not only contributed to highly dispersed and stable Pd nanoclusters, but also led to better activation of hydrogen. The recyclability of Pd-HAP catalyst was also investigated and proved its stability in the conversion of furfural and high selectivity towards THFAL.
1. INTRODUCTION Diminishing fossil fuel resources and increasing global warming issues require the development and implementation of sustainable biorefinery technology for the production of renewable fuels and chemicals.1-3 Furfural, which can be produced
ACS Paragon Plus Environment
Industrial & Engineering Chemistry Research
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 2 of 22
from renewable biomass resources by acid-catalyzed dehydration of pentoses, is an important platform compound in biorefinery.4-6 It can be selectively hydrogenated to various useful products such as furfuryl alcohol, tetrahydrofurfuryl alcohol (THFAL), 2-methylfuran, 2-methyl tetrahydrofuran and cyclopentanone. 7 - 11 Among these products, THFAL is a green industrial solvent, because it is degradable, less toxic, and more stable than unsaturated furan compounds.3,12-13 It can also be used to produce dihydropyran, pyridine, and tetrahydrofuran.14,15 Moreover, recent researches have indicated that THFAL can also be converted to useful straight-chain polyols such as 1,5-pentanediol and 1,2-pentanediol in high yield which are important monomers in the plastics industry.16-19 First, the process for the efficient production of THFAL from furfural on nickel-chromium catalyst in the liquid phase was patented. However, it requires a temperature above 110 °C and hydrogen pressure exceeding 10 MPa. Furthermore, it is noted that the systems containing chromium are strongly hazards for the environment.9,20 Previous studies proved that various Cr-free supported Pd, Ru, Rh and Ni catalysts modified with a second metal, e.g. Cu, Bi, etc., can operate selectively towards either furfuryl alcohol (FA) or the THFAL.3,21-23 As for non-noble catalyst systems, mainly Ni-based catalysts such as Raney Ni, 24 Ni/SiO2, 25 Ni/Al2O3,26 CuNi/MgAlO,27 are known to be effective in total hydrogenation of furfural to THFAL. However, Ni catalysts leached easily in liquid-phase systems and their supports stability still need to be improved.27 More stable noble metal catalysts, mainly supported Pd catalysts, have been widely investigated. Noble metal catalyst systems reported for vapor phase hydrogenation of furfural under severe temperature and pressure conditions (200-300 °C and 10 MPa H2) yield not only the desired products but also various byproducts including furan, tetrahydrofuran, and even ring-opening products, such as pentanol and pentanediols. 28 Recently, direct liquid-phase hydrogenation of furfural to THFAL has been achieved over Ni-Pd/SiO2,
29
Pd-Ir/SiO2,
30
Ni-Pd/TiO2-ZrO2,
31
Pd/MFI,
32
Pd/M-AC,
33
and
Pd/Al2O3 catalysts.34 Tomoshige et al. prepared Ni-Pd/SiO2 alloy catalyst for the hydrogenation of furfural and yielded 94% of THFAL under 8 MPa hydrogen pressure
ACS Paragon Plus Environment
Page 3 of 22
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
Industrial & Engineering Chemistry Research
and 40 °C for 2 h with acetic acid as solvent.30 They also found that the Pd and Ir alloy over SiO2 support showed high activity for total hydrogenation of furfural to THFAL.31 However, higher hydrogen pressure (8 MPa H2) and lower reaction temperature (2 °C) were needed to suppress the side reactions. Chen et al. found that the coexistence of small proportion of palladium with supported nickel species greatly improves the catalytic reduction of furfural into THFAL.31 The yield of tetrahydrofurfuryl alcohol (THFAL) reached 93.4% in the case of catalyst with Ni-Pd mole ratio of 5:1 supported on TiO2-ZrO2 binary oxides under 130 °C, 5 MPa H2 and 8 h. Rode et al. designed a Si-MFI molecular sieve supported Pd catalyst to catalyze furfural with 95% selectivity of THFAL under 200 °C, 3.45 MPa H2 and 5 h.32 Bhogeswararao et al. reported that 5%Pd/Al2O3, at 25 °C and 6 MPa H2, showed furfural conversion of 79.5% with THFAL selectivity of 100%.34 The above facts reveal that the catalyst’s support markedly influence its performance for liquid-phase catalytic hydrogenation of furfural. Moreover, achieving furfural selective hydrogenation with highly selective catalyst under mild conditions is still a challenge due to the difficulty in controlling the reaction route and hydrogenation degree. Hydroxyapatite (HAP), Ca10(PO4)6(OH)2, is a calcium orthophosphate with apatite structure and its Ca2+ sites surrounded by a PO43- tetrahedron parallel to the hexagonal axis. HAP is green, nontoxic, highly substrate-tolerant, almost no damage in the solvent and easy to be recycled, and its flexible and special structure results in the strong ion-exchange ability and thermal stability which allows a well-dispersed noble-metal loading leading to high reactivity. 35 The catalytic systems based on palladium are friendly to the environment and allow the reaction to proceed in milder conditions. Our previous investigation found hydroxyapatite supported Pd catalyst (Pd-HAP) exhibited excellent performance on 100% selective hydrogenation of phenol to cyclohexanone at room temperature and 1 bar H2. 36 It could also be advantages to achieve the selective hydrogenation of furfural to tetrahydrofurfuryl alcohol. Herein, we prepared Pd nanoclusters bonded onto commercial HAP (Pd-HAP) by a green and simple ion-exchange route for total hydrogenation of furfural to
ACS Paragon Plus Environment
Industrial & Engineering Chemistry Research
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
THFAL. Other Pd catalysts loaded on different supports were also synthesized and explored for furfural conversion. The Pd-HAP catalyst was characterized in detail by XRD, SEM, TEM, HAADF-STEM, XPS and ICP-AAS. The effects of temperature, hydrogen pressure and reaction time on the reaction were investigated. The possible pathways were also investigated and proposed. The stability of the catalyst was measured.
2. EXPERIMENTAL SECTION 2.1. Materials and Chemicals. Hydroxylapatite (HAP), palladium acetate (Pd(OAc)2), High-pure H2 and high-pure N2 were purchased from Nanjing Special Gas Factory Co. Ltd. Furfural (AR, >99%) was purified by vacuum distillation and stored at -15 °C. Furfuryl alcohol (AR, >99%), tetrahydrofurfuryl alcohol (AR, >97%) and n-hexanol were from Sinopharm Chemical Reagent Co., Ltd. MgO, SiO2, Al2O3, CeO2, ZrO2 were purchased from Aladdin Chemical Reagent Co., Ltd. TiO2 was purchased from Sigma-Aldrich Chemical Reagent Co., Ltd. Furfuryl alcohol were not purified. 2.2. Catalysts Preparation. The Pd-HAP catalyst was synthesized by the ion-exchange method. 1.00 g of HAP powder was added into round-bottom flask with 100 mL of acetone and then the mixture was heated to 55 °C with magnetic stirring at 1000 rpm. 45.6 mg of palladium acetate was dissolved in 10 mL of acetone and was then dropwise added to the above HAP/acetone suspension in 15 min. The mixture was kept at 55 °C with magnetic stirring at 1000 rpm for 24 h, filtered, and dried at 40 °C overnight. The catalysts based on MgO, CeO2, ZrO2, TiO2, Al2O3 and SiO2 were prepared by impregnation method. 1.00 g of support (MgO, CeO2, ZrO2, TiO2, Al2O3 or SiO2) was added into round-bottom flask with 100 mL of acetone and then the mixture was heated to 55 °C with magnetic stirring at 1000 rpm. 45.6 mg of palladium acetate was dissolved in 10 mL of acetone and was then dropwise added to the above support/acetone suspension in 15 min. The mixture was kept at 55 °C with magnetic stirring at 1000 rpm for 24 h, rotary evaporation, and dried at 40 °C overnight. The Pd
ACS Paragon Plus Environment
Page 4 of 22
Page 5 of 22
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
Industrial & Engineering Chemistry Research
loading is 1%. The catalysts precursor were reduced in a quartz tube furnace at 280 °C under a forming gas mixture of 10%/90% H2/N2 flowing at approximately 100 ml·min-1. The temperature reduction program of the tube furnace was raised from 20 °C to 120 °C by 3 °C· min-1, kept for 20 min at 120 °C and then raised again from 120 °C to 280 °C with 1 °C· min-1 and kept for another 3 h. 2.3. Catalyst characterization. The powder X-ray diffraction (XRD) patterns of the catalysts were measured by an X’pert (PANalytical) diffractometer, using CuKα radiation at 40 kV and 40 mA, 2θ ranges were 10°-70°. The crystal sizes were calculated by Scherrer equation through the Pd (111) diffraction peak:
=
Kλ β cos θ
, where K is a constant and equal to 0.89,
λ is the X-ray wavelength and equal to 0.154056 nm, β is the full width at half maximum (rad) and θ is the diffraction angle (rad). The scanning electron microscopy (SEM) images were taken by a field-emitting scanning electron microscope (FESEM, JEOL-JSM-6700F). The characterization paramters were as follows: EHT=5.0 kV, WD=6.0 mm, Signal A=InLense, Mag=105.00 KX. Before the test, the samples were deposited on Cu grids after ultrasonic dispersion of the milled catalyst samples in ethanol. The transmission electron microscopy (TEM) image was taken with a JEOL JEM-2010 LaB6 transmission electron microscope. The accelerating voltage was 200 kV, and the spot size was 1.0 nm. Before being transferred into the TEM chamber, the samples dispersed with ethanol were deposited onto a carbon-coated copper grid and then quickly moved into the vacuum evaporator. The size distribution of the metal particles was determined by measuring about 200 random particles on the images. The high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images were taken with a JEM-ARM200F atomic resolution analytical microscope. The accelerating voltage was 200 kV, and the nominal electron probe size was about 1.0 nm in diameter. Before the test, the samples were deposited on Cu grids after ultrasonic dispersion of the milled catalyst samples in ethanol. The X-ray photoelectron spectroscopy (XPS) spectra was obtained with an X-ray
ACS Paragon Plus Environment
Industrial & Engineering Chemistry Research
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
photoelectron spectrometer (ESCALAB250, Thermo-VG Scientific, USA) at room temperature under a vacuum of 10-8-10-9 Torr using monochromated Al Kα radiation (1486.92 eV). The binding energies (BE) were calibrated to carbon with a C 1s band at 284.6 eV. The chemical composition of catalysts was analyzed by an Optima 7300 DV ICP-AAS. ICP-AAS was performed on a PerkinElmer Corporation Analyst 800 instrument. The catalyst sample handling process is as follows: 10 mg of catalyst was added into a 10 mL round-bottom flask with 4 mL of aqua regia and stirred at 80 °C for 24 h until metal is completely dissolved. Then the mixture was diluted to 25 mL in a volumetric flask for characterization. 2.4. Catalyst Test. All catalytic reactions for total hydrogenation of furfural to THFAL were performed in a 25 mL Parr reactor. In a typical experiment, 100 mg of furfural, 30 mg of the reduced Pd-HAP catalyst and solvent (10 mL of 2-propanol) were added into the reactor. After purged for 6 times, H2 was filled to corresponding pressure at ambient temperature. The reaction temperature and the reaction time were kept at certain values with magnetic stirring. After the reaction, when the reactor was cooled to room temperature, the products were separated from the catalyst by centrifugation and then diluted with 2-propanol. Finally, the collected sample solution was identified by a gas chromatograph-mass spectrometer combination (GC-MS, Agilent 5975C) and quantified by a gas chromatograph (Kexiao 1690) with HP-INNOWAX capillary column (30 m*0.250 mm*0.25 µm). The GC detecting conditions were as follows: nitrogen as carrier gas; injection port temperature: 280 °C; detector (FID) temperature: 280 °C; column temperature: 40 °C, heating up to 250 °C with a heating rate of 10 °C/min. Hexanol was used as internal standard to quantify the products. In this paper, the experiments were repeated for three times and the data were the average value with experimental error less than 1%. The conversion and yield were calculated by mol%.
molar amount of furfural after reaction Conv. (%) = 1 × 100% molar amount of furfural in the starting material
ACS Paragon Plus Environment
Page 6 of 22
Page 7 of 22
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
Industrial & Engineering Chemistry Research
Yield (%) =
molar amount of THFAL product × 100% molar amount of furfural in the starting material
3. RESULTS AND DISCUSSION 3.1. Hydrogenation of furfural to tetrahydrofurfuryl alcohol. Table 1. Catalytic conversion of furfural to THFAL over various Pd-based catalysts. Entry
Catalyst
Conv. Furfural (%)
Yield THFAL(%)
Yield2-IPMF(%) Others
1
Pd-HAP
100
100
0
0
2
Pd-MgO
100
52
47
1
3
Pd-CeO2
100
54
44
2
4
Pd-ZrO2
100
65
26
9a
5
Pd-TiO2
100
89
9
2
6
Pd-Al2O3
100
44
51
5
7
Pd-SiO2
100
43
54
3
Reaction conditions: 30 mg 1% Pd-based catalyst; 100 mg furfural; 10 mL 2-propanol as solvent; 40 °C; 1 MPa H2; 4 h; 800 rpm. Others are condensation products. a. It also includes another by-product hard to be identified. THFAL: tetrahydrofurfuryl alcohol, 2-IPMF: 2-(isopropoxymethyl)furan. In order to investigate whether the supports would have a significant effect on the selective hydrogenation of furfural to THFAL, Pd catalysts loaded on various supports such as Pd-HAP, Pd-MgO, Pd-CeO2, Pd-ZrO2, Pd-TiO2, Pd-Al2O3 and Pd-SiO2 were screened at 40 °C, 1 MPa H2 and 4 h and the results are given in Table 1. The conversion of furfural with all the Pd catalysts is 100%. Pd-HAP showed highest selectivity to THFAL than other catalysts did. Therefore, Pd-HAP was employed to further explore the effect of various parameters on furfural conversion under different reaction conditions.
Table 2 Catalytic performance of Pd-HAP catalyst for the selective hydrogenation of furfural to THFAL under different reaction conditions
Entry Temp. /°C
P(H2) / MPa
Conv. Furfural (%)
YieldTHFAL(%) Yield2-IPMF(%)
ACS Paragon Plus Environment
Industrial & Engineering Chemistry Research
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 8 of 22
1
80
2
100
100
0
2
60
2
100
100
0
3
40
2
100
100
0
4
20
2
100
72
28
5
40
0.1
100
51
49
6
40
0.5
100
88
12
7
40
1
100
100
0
8
40
2
100
100
0
9b
40
1
0
0
0
10c
r.t
1
100
>99
