Selective Hydrogenation of Furfural to Furfuryl Alcohol over Acid

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Selective Hydrogenation of Furfural to Furfuryl Alcohol over Acid Activated Attapulgite-Supported NiCoB Amorphous Alloy Catalyst Haijun Guo, Hairong Zhang, Liquan Zhang, Can Wang, Fen Peng, Qianlin Huang, Lian Xiong, Chao Huang, Xinping Ouyang, Xinde Chen, and Xueqing Qiu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b03699 • Publication Date (Web): 04 Dec 2017 Downloaded from http://pubs.acs.org on December 9, 2017

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Industrial & Engineering Chemistry Research

Selective Hydrogenation of Furfural in Liquid-Phase over Acid Activated Attapulgite-Supported NiCoB Amorphous Alloy Catalyst Haijun Guo, †, ‡, §, ‖, # Hairong Zhang, ‡, §, ‖, # Liquan Zhang, ‡, §, ‖, #, £ Can Wang, ‡, §, ‖, # Fen Peng, ‡, §, ‖, # Qianlin Huang, ‡, §, ‖, #, £ Lian Xiong, ‡, §, ‖, # Chao Huang, ‡, §, ‖, # Xinping Ouyang, †, * Xinde Chen, ‡, §, ‖, #, ** Xueqing Qiu, †

†

School of Chemistry & Chemical Engineering, South China University of Technology, Guangzhou 510640, P. R. China;

‡

Key Laboratory of Renewable Energy, Chinese Academy of Sciences, Guangzhou 510640, P. R. China;

§

Guangdong Key Laboratory of New and Renewable Energy Research and Development, Guangzhou 510640, P. R. China;

‖

Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, P. R. China;

#

R&D Center of Xuyi Attapulgite Applied Technology, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Xuyi 211700, P. R. China;

£

University of Chinese Academy of Science, Beijing 100049, P. R. China.

S ○

Supporting Information

1

ACS Paragon Plus Environment

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ABSTRACT: Acid activated attapulgite (H+-ATP)-supported NiCoB amorphous alloy catalysts were applied to the selective hydrogenation of furfural (FUR) in liquid-phase. The reduction process between metallic ions impregnated in/on H+-ATP-A and BH4

－

is important to adjust the textural properties of catalyst due to the secondary activation of H+-ATP-A. The

enhancement of interaction between H+-ATP-A and NiCoB particles promotes the dispersion of NiCoB amorphous alloy. Under the optimal conditions (140 oC, 3MPa H2, 800 rpm, 3.8 wt% of NiCoB active component with respect to FUR), FUR conversion of 91.3% and furfuryl alcohol (FA) selectivity of 82.0% were achieved over the H +-ATP-A supported 20wt%NiCoB amorphous alloy catalyst (20NCB/H+-ATP-A) catalyst. Moreover, the catalyst was recycled six times for the hydrogenation of FUR with an increase of 3.9 % in FUR conversion and 8.2% in FA selectivity which might be due to the newly generated Co-Ni alloy active site.

KEYWORDS: Ni-Co-B amorphous alloy, acid activated attapulgite, selective hydrogenation, furfural, secondary activation, Co-Ni alloy

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

INTRODUCTION

Lignocellulosic biomass with low-cost, great availability, and renewable characteristics

1-2

, has been attracting worldwide

attention to produce fuels and chemicals for relieving the climate change and energy crisis derived from the usage of traditional non-renewable fossil fuels 3-4. Furfuryl alcohol (FA) is an important chemical compound, which is widely used in the production of resins, liquid resins for strengthening ceramics, fine chemicals, lysine, vitamin C, lubricants, dispersing agents, plasticizers and in the synthesis of fiber

5-6

. FA can be produced by the selective hydrogenation of furfural (FUR) in gas-phase or liquid-

phase according to Scheme 1 7, an important chemical platform for the production of lignocellulosic chemicals and biofuels. Recently, catalytic transfer hydrogenation (CTH) of FUR into FA has also received great interest

8-10

. In addition, one-pot

production of FA via xylose dehydration to furfural followed by furfural hydrogenation was also achieved over a dual catalyst system composed of Pt/SiO2 and sulfated ZrO2 11, a catalyst combining Hβ zeolite and Cu/ZnO/Al2O3 12, and a single ordered mesoporous SBA-15 bearing SO3H acid groups supported Pt catalysts 13. Industrially, FA is produced over the copper chromite (Cu-Cr) based catalysts at high temperature (130−200 °C) and high H2 pressure (30 bar), which is moderately active for the selective FUR hydrogenation but can cause severe environmental pollution due to the high toxicity of Cr6+ ion

7, 14

. For this

reason, different research groups have performed a great effort to develop the Cr-free based catalysts for hydrogenation of FUR to FA, such as supported Ni, Cu, Co, Au, Ru, Pt, Pd and their bimetallic based catalysts

6, 15-23

, Al, Fe, Mn modified Cu-Zn

mixed oxide catalysts 10, 24, Cu-MgO based catalysts 25-26 and Ni(Co)-(M)-B (M= Fe, Co, La, Ce, Mo) amorphous alloy catalysts 27-33

.

Since 1980s, the metal-metalloid amorphous alloys with unique short-range ordered and long-range disordered atomic arrangement have attracted growing attention from both academia and industry 34.

They are important catalytic materials due

to the unique chemical and structural properties including broadly adjustable composition, structural homogeneity, and high concentration of coordinately unsaturated sites 35. Li et al. developed several amorphous alloy catalysts for hydrogenation of

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FUR to FA, such as Ni-B modified with different metallic promoter (Fe 30, Co 31, Ce 27, etc.), Co-B 14, 36 and Co-Mo-B 37. They showed high catalytic efficiency and low environmental pollution, especially for the NiCoB amorphous alloy catalyst with Co/(Co+Ni) mole ratio of 0.5

29, 31-32

. Nevertheless, because of the poor thermal stability or/and low surface area of these

amorphous alloy catalysts, an improvement scenario by depositing them on a support with high surface area has been applied in different hydrogenation field 35. The most commonly used support is SiO2 24, 38-43 and γ-Al2O3 44-47. Bai et al. 48 compared the selective hydrogenation performances of cinnamic acid over different supported NiCoB amorphous alloys and the γ-Al2O3 supported NiCoB catalyst showed particularly good activity. Bai et al.

49

also investigated the liquid phase selective

hydrogenation of benzophenone over Ni-La-B amorphous alloys supported on SiO2 and γ-Al2O3, respectively. The results indicated that a SiO2 supported catalyst showed better initial activity and selectivity, while a γ-Al2O3 supported catalyst showed better stability. Based on these results, in order to improve simultaneously the activity and stability of NiCoB amorphous catalyst for FUR hydrogenation to FA, a support by combining SiO2 and γ-Al2O3 is expected to be one of promising candidates for supporting the NiCoB amorphous alloy. Attapulgite (ATP, also known as palygorskite) with an ideal molecular formula of [Si8Mg5O20(OH)2(H2O)4·4H2O] is a natural hydrated magnesium aluminum silicate nonmetallic mineral, having 1-D fibrous morphology, diameter in nanometers and porous crystalline structure containing tetrahedral layers 50. Due to the excellent colloidal, adsorption, reinforcing properties, and thermal/mechanical stability, ATP has been applied in different yield, including colloidal or stabilizing agents, adsorbents, catalyst or catalyst support, polymer nanocomposites, organic–inorganic hybrid pigments, drug delivery carriers, biosensing materials, antibacterial material, electrorheological materials, thermal energy storage materials and sealing materials, etc. 51-55. In addition, ATP constitutes abundant of SiO2, Al2O3, MgO and Fe2O3 components, of which proportion can be adjusted effectively by acid-activation process 56. Silicon is the dominant constituent in the tetrahedral sheets and Mg, Al and Fe are the main constituents of the octahedral sheets of ATP clay. The acid-activation can decrease the crystallinity of ATP clay due to

4


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octahedral cations (Mg2+, Al3+ and Fe3+) removal and the formation of amorphous silica 57. Recently, we have reported that the mixed alcohols synthesis from syngas over sulfuric acid-activated ATP supported Cu-Fe-Co based catalyst for the first time 5859

. By changing the concentration of sulfuric acid solution and Cu/Fe molar ratio, the CO conversion of around 70% and

selectivity towards mixed alcohols of 12.4% could be accomplished. Wu et al.

60

developed a palygorskite supported Pd-B

amorphous alloy for the selective hydrogenation of o-chloronitrobenzene (o-CNB) to o-chloroaniline (o-CAN) which exhibited a ultra-high selectivity (100%) and good stability for three times recycled use. Notably, the acid-activated ATP can be used as a promising catalyst support for the application in various catalytic reactions due to the unique property and the feature of much low cost and easy availability. Herein, we report the selective catalytic hydrogenation of FUR to FA in liquid-phase over a novel acid activated attapulgitesupported NiCoB amorphous alloy catalyst. Different natural attapulgite were activated by sulfuric acid and applied to support the NiCoB amorphous alloy catalysts. They were systematically tested in order to obtain the optimum support and reaction solvent. The effects of NiCoB amorphous alloy loading on physicochemical properties and hydrogenation activity of catalyst were evaluated. In addition, various parameters such as reaction temperature, speed of stirring, initial hydrogen pressure and reaction time were studied to optimize the furfural conversion and furfuryl alcohol selectivity. Finally, catalyst stability will also be evaluated by the cycle testing and some characterizations.



EXPERIMENTAL SECTION Materials. Furfural (99%), furfuryl alcohol (98%), NaBH4 (98%) were purchased from Aladdin Reagent Co. Ltd. (Shanghai,

China). Tetrahydrofurfuryl alcohol (99%) was purchased from Adamas-beta Co. Ltd. (Shanghai, China). 2-methylfuran (98%) was purchased from TCI Co. Ltd. (Shanghai, China). Nickel chloride (NiCl2·6H2O), Cobalt chloride (CoCl2·6H2O) and Absolute ethyl alcohol (EtOH) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Natural ATPA, ATP-B and ATP-C, named as Crude-ATP-A, Crude-ATP-B and Crude-ATP-C, were provided by ZHONGKE New Energy

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Technological Development Co., Ltd (Huai-An, China). The three natural ATPs were activated according to the previous reported procedure using 12 wt% sulfuric acid without the calcination process 58. The obtained acid-activated ATPs were named as H+-ATP-A, H+-ATP-B and H+-ATP-C, respectively. All other reagents, including methanol, n-propanol, isobutanol, ethanediol, acetic acid and cyclohexane, were commercially available, and they were all analytically pure and used without any further purification. Catalyst Preparation. The NiCoB amorphous alloy catalyst with Ni/Co molar ratio of 1/1 was prepared by the conventional chemical reduction method with NaBH4 as the reduction agent 31, and it was named as NCB. Other supported NiCoB amorphous alloy catalysts were prepared by an impregnation-reductive method. Typically, a catalyst with 10% NiCoB supported on H+-ATP-A was prepared as the following procedure: 12.7 g H +-ATP-A powder (>100 mesh) was equivalentvolume impregnated with an aqueous solution of 2.852 g NiCl2·6H2O and 2.855 g CoCl2·6H2O (molar ratio of Ni:Co = 1:1) under vacuum for 24 h at room temperature. It was then dried at 120 oC for 1 h to exclude most of water, and then dried at 80 o

C for 6 h to remove thoroughly the water. The precursor powder (>100 mesh) was reduced by adding 44.4 mL 2.0 M NaBH4

aqueous solution containing 0.2 M NaOH dropwise with vigorous stirring in an ice-water bath under consecutive Nitrogen flow of 50 mL/min. The reaction was lasted for 3.0 h to ensure the complete reduction of metallic ions on the carrier. The resulting precipitate was washed with deionized water several times until neutral, followed by washing with absolute ethyl alcohol three times to remove the residual water and water-soluble impurities. Finally, the obtained catalyst was named as 10NCB/H+-ATPA and kept in absolute ethyl alcohol for future use. For the comparison purpose, the 10NCB/H+-ATP-B and 10NCB/H+-ATPC catalysts were also prepared according to the above procedure. Results showed that the H +-ATP-A was the better support (Supporting Information). Furthermore, in order to investigate the effects of loading of NiCoB particle on the structure and properties of H+-ATP-A supported NiCoB amorphous alloy catalysts, the xNiCoB/H+-ATP-A (x= 5, 10, 20, 30 and 40) catalysts were also prepared by the same method, where x is the theoretical loading of NiCoB particle. In addition, for the purpose of

6


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indicating the superiority of H+-ATP-A support, the commercial amorphous porous silica gel (SiO2, 40-100 mesh) and active γ-Al2O3 (>100 mesh) were first calcined at 500 oC for 4 h and then applied to prepare the 20NCB/SiO2 and 20NCB/γ-Al2O3 catalysts according to the same method as the 20NiCoB/H+-ATP-A catalyst. Catalyst Characterization. The bulk composition and NiCoB loading of the catalysts were detected by the OPTIMA 8000 Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES, PerkinElmer). The Brunauer-Emmet-Teller surface area (SBET), total pore volume (Vp), and average pore diameter (Dp) of the supports and corresponding catalysts were determined by the N2 adsorption/desorption isotherms at 77 K using a ASIQMO002-2 analyzer (Quantachrome, US). The samples were degassed at 80 oC for 6 h prior to measurement. Powder X-ray diffraction (XRD) patterns of the supports and corresponding catalysts were measured using a D/max-RA X-ray diffractometer (Rigaku, Japan) with Cu Kα radiation (λ = 0.154 nm) operated at 40 kV and 100 mA on a scanning range of 5-80

o

(2θ). X-ray photoelectron spectroscopy (XPS)

measurement was carried out on an ESCALAB 250Xi spectrometer (Thermo Fisher Scientific Inc, US) with Al Kα radiation to determine the surface atomic ratios and valence states of elements of the fresh and used samples. In order to subtract the surface charging effect, the C1s peak has been fixed at binding energy (BE) of 284.6 eV. The morphology of catalyst was observed by a Hitachi S-4800 high resolution Field Emission Scanning Electron Microscope (FE-SEM, Hitachi, Japan) operated at 2.0 kV and 10 μA. High Resolution Transmission Electron Microscope (HRTEM) analysis and selected area electron diffraction (SEAD) were performed on a JEM-2100F microscope (JEOL, Japan) operating at 200 kV. Sample for TEM was prepared by dispersing the sample in ethanol under ultrasonication. Several droplets of dispersion were placed on carboncoated cooper grids. H2-Temperature programmed reduction (H2-TPR) experiment was carried out in a U-shape tube quartz reactor using a ChemBET/Pulsar-1 automated chemisorptions analyzer (Quantachrome, US) with 5.0 vol%H2/Ar as the reductive gas. The samples (～ 30 mg) were flushed with a He flow of 110 mL/min at 80 oC to remove adsorbed water, and then reduced in a flow of reductive gas at a rate of 10 oC/min from 50 oC to 750 oC. The consumed gas was monitored by a

7



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thermal conductivity detector (TCD). Activity Test. Liquid phase furfural hydrogenation was carried out in a 100 mL YZPR-100 (M) stainless steel autoclave equipped with an electrical heating jacket and a mechanical stirrer. In a typical catalytic test, the furfural (5 mL, 0.06 mol), catalyst (0.2 g NiCoB or 1.0g supported NiCoB) and ethanol solvent (25 mL) were introduced into the reactor. The air in the autoclave was excluded completely by repetitively filling N2 four times and H2 three times. Then the autoclave was filled with an initial hydrogen pressure of 3.0 MPa. Then, the reactor was heated to 100 oC with a stirring rate of 200 rpm. When the hydrogen pressure reached a steady state, the hydrogenation reaction was started immediately by adjusting the stirring rate to 800 rpm. According to the drop of H 2 pressure within the first 0.5 h, the average hydrogenation rate (the H2 uptake rate per m

gram of Ni and Co, RH in mmol·h-1·gM-1) was calculated according to the ideal gas equation 14. The areal activity (the H2 S

uptake rate per m2 of the surface area, RH in mmol·h-1·m-2) was also calculated 14. After reaction for 2 h, the liquid product was measured by a gas chromatographic analysis (GC 9900, Jiafen, Beijing in China; Column: FFAP, 30 m × 0.25 mm × 0.25 μm) equipped with a flame ionization detector (FID). The conditions for the analysis were as following: 30 mL/min N2 flow as a carrier gas, injector temperature 230 oC, detector temperature 250 oC, and the oven temperature programmed from 70 to 230 o

C at the speed of 10 oC/min. The FUR conversion and the selectivity to different product was calculated accoding to the study

of Sharma et al. 61. The turnover frequency (TOF) values of FUR hydrogenation to FA are calculated according to the equation (1) 62:

TOF=

V  (d / M )  C  6.02 1023  S N t

(1)

Here V is the volume of furfural used in the hydrogenation, d the density of furfural, M the molecular mass of furfural, C the furfural conversion, S the selectivity to furfuryl alcohol, N the number of surface Ni and Co atoms, t the reaction time, and 6.02 × 1023 the Avogadro’s number. The unit of TOF is per hour (h−1). N can be calculated by the equation (2) 63:

N=

SM ,SM  6/(ρ  d M ) s

(2)

8


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Here SM is the surface area of NiCoB alloy, ρ the density of NiCoB alloy, dM the statistical particle size of NiCoB alloy obtained from HRTEM (Table 1), s the surface area of 6.5 × 10−20 m2 per Ni 38 or Co atom 64.

Table 1. Textural properties and composition of the support and corresponding supported amorphous alloy catalysts. SBET

VP

DP

SM

dM a

(m2/g)

(cm3/g)

(nm)

(m2/g)

(nm)

Ni

Co

B

Total

SiO2

294.2

0.996

13.5

-

-

-

-

-

-

γ-Al2O3

213.3

0.448

8.4

-

-

-

-

-

-

268.0

0.374

5.6

-

-

-

-

-

-

190.7

0.563

11.8

-

-

-

-

-

-

NCB

32.5

0.137

16.8

18.18

39.6

46.9

44.4

8.7

100

5NCB/H+-ATP-A

197.5

0.526

10.7

24.49

28.6

1.9

1.8

0.2

3.9

10NCB/H+-ATP-A

Support/Catalyst

+

H -ATP-A －

BH4 -ATP-A

c

176.3

0.458

10.4

23.49

30.2

4.9

4.7

0.7

10.3

+

161.3

0.480

11.9

23.89

29.7

10.4

10.1

1.5

22.0

+

147.5

0.403

10.9

26.43

26.9

15.3

14.8

2.3

32.4

+

40NCB/H -ATP-A

113.8

0.368

12.9

24.39

29.3

19.5

18.6

3.2

41.3

20NCB/SiO2

251.4

0.785

12.5

-

-

4.9

4.9

0.7

10.5

20NCB/γ-Al2O3

194.1

0.272

5.6

-

-

9.4

9.2

1.9

20.5

20NCB/H -ATP-A 30NCB/H -ATP-A

a

Bulk comp. (wt%) b

b

c

Determined by HRTEM. Determined by ICP-OES. Prepared by chemical reduction method using H+-ATP-A as feedstock

with an equal amount of NaBH4 aqueous solution as the 5NCB/H+-ATP-A catalyst used.



RESULTS AND DISCUSSION Characterization of Catalysts with Different NiCoB Loading. As mentioned in Supporting Information (Tables S1-

S3, Figures S1-S4), the H+-ATP-A supported NiCoB amorphous alloy allowed the highest activity during FUR hydrogenation due to the biggest surface area and total pore volume. One of the main goals of this paper is focused on optimizing the loading of NiCoB amorphous alloy to selectively produce FA. The textural properties and bulk composition of the support and corresponding supported NiCoB catalysts are shown in Table 1. It can be seen that the mass of NiCoB amorphous alloy is in accordance with the theoretical value of 100%. With the increase of NiCoB loading onto H+-ATP-A support, the actual total content of NiCoB particle shows a weak change with the theoretical value. Generally speaking, the surface area and pore volume of catalyst will decrease compared with the support itself due to the occupation of some pores of this carrier by small amorphous alloy particles 9


. When 5 wt% NiCoB was

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supported on H+-ATP-A, the SBET showed a significant decrease, on the contrary, the Vp and Dp enlarged obviously. It was estimated that the reduction process between metallic ions (Ni2+ and Co2+) impregnated in/on the H+-ATP-A support and BH4 －

played an important role in adjusting the pore structure due to the secondary activation by the generated H+ and OH

－

according to the reaction mechanism as the following equations (4) and (5) 65:

BH 4  2H 2 O = BO2 +4H 2 

(3)

BH 4  2Ni 2+ (Co2+ )  2H 2O = 2Ni(Co)   BO 2 +4H   2H 2 

(4)

BH 4  H 2O = B  +OH  +2.5H 2 

(5)

In order to demonstrate this point, the H+-ATP-A was reduced by the same amount of NaBH4 aqueous solution as the －

5NCB/H+-ATP-A catalyst used. The SBET of obtained BH4 -ATP-A showed an obvious decrease by 77.3 m2/g compared to H+ATP-A, while the Vp and Dp prominently increased by 0.189 cm3/g and 6.2 nm, respectively (Table 1). Wang et al. 66 reported that the SBET and Vp of alkali-activated palygorskite (PAL) decreased with the increase of concentration of NaOH solution, while the Dp showed an increase. In addition, the acidic sites didn’t be neutralized by the NaBH 4/NaOH aqueous solution (Figure S4). Therefore, the secondary activation of H+-ATP-A by H+ or OH

－

during the reduction process of NiCoB particle

was indeed happened. The NCB catalyst showed the lowest SBET and Vp. With the increase of NiCoB loading, the SBET and Vp decreased, which could be attributed to the deposition of more and more NiCoB particles. From the N2 adsorption/desorption isotherms showed in Figure 1(a), it can be seen that all samples show type IV isotherm according to the IUPAC classification 67

. At the very start, the N2 adsorption for H+-ATP-A support showed a rapid increase. However, H+-ATP-A supported NiCoB

catalysts rallentando increased at lower relative pressure (P/P0< 0.40), implying that the presence of a little amount of small pores. The N2 adsorption sharply increased and displayed a H3-type hysteresis loop at higher P/P0 (> 0.80) due to the capillary condensation and its multilayer adsorption of N2, indicating the existence of mesopores and/or macropores 66. The pore size distributions (PSDs) of mesopores for the H+-ATP-A support and corresponding supported NiCoB catalysts were calculated by

10


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Barret–Joyner–Halenda (BJH) method from the desorption branches (Figure 1(b)). Apparently, the pore structure of H+-ATPA has been changed by the loading of NiCoB particle due to the secondary activation as mentioned above. The formation of some small mesopores (～ 3.8 nm ), the number increase of those intrinsic mesopores with a size enlargement from 9.6 nm to －

17.0-28.5 nm attributed to the tight stacking of NiCoB particles can be observed from the PSD curve of BH4 -ATP-A. The 5NCB/H+-ATP-A catalyst showed the highest intensity of second peak, which provided an evidence for its largest pore volume. With the increase of NiCoB loading, the strongest secondary activation of H+-ATP-A on 30NCB/H+-ATP-A catalyst leaded to the highest intensity of first peak, while the most serious deposition of NiCoB particles resulted in the lowest intensity of second peak. The XRD patterns of fresh NiCoB catalyst, H+-ATP-A support and corresponding supported NiCoB catalysts are shown in Figure 2. The NCB catalyst exhibits two broad peaks around 2θ = 25º and 45º, respectively. The former is attributed to the amorphous boron oxides 68 and the latter indicates the presence of a typical amorphous alloy structure 34. The H+-ATP-A support shows the characteristic diffraction peaks of palygorskite (JCPDS, No. 31-0783) at 2θ of 8.5°, 13.9°, 16.4°, 19.8°, 20.8°, 24.2°, and 28.8° and quartz (JCPDS, No. 46-1045) at 2θ of 20.9°, 26.6° and 50.1°

59

. With the increase of NiCoB loading, the

diffraction peaks intensity of palygorskite and quartz showed a gradual decrease and an abrupt drop when the loading was higher than 20%. On the contrary, the broad diffraction peaks intensity at 2θ = 16-30º and 45º was enhanced. This phenomenon provides a convincing evidence for the successful loading of NiCoB amorphous alloy onto H+-ATP-A. Generally speaking, the activation of attapulgite by H+ or OH

－

will lead to the decrease of diffraction peak intensity of palygorskite due to the partial

leaching of metal ions from the octahedron sheets

56, 66

. During the process of catalyst preparation, the usage of H+-ATP-A

support was kept unchanged and the reaction system was alkaline. Therefore, the diminution of crystalline H+-ATP-A phase resulted from the secondary activation of ATP-A as mentioned above was further proved to be happened. The morphology and particle size distribution of NiCoB and supported NiCoB catalysts are shown in Figure 3. The statistical

11



Page 12 of 46

mean particle size (dM) from 100 varisized particles and calculated surface area of NiCoB alloy (SM) are shown in Table 1. The NiCoB catalyst shows interconnected spherical particles with a dM of 39.6 nm. According to the inserted selected-area electrondiffraction (SAED) image (Figure 3), the halo diffraction pattern rather than distinct dots indicates that the NiCoB particles has a typical amorphous character 28, which is conformed to the XRD result. When 5 wt% NiCoB was supported on H+-ATP-A, the dM was sharply decreased and the SM was obviously increased. With the further increase of NiCoB loading to 40 wt%, the dM and SM firstly show an opposite change over 10NCB/H+-ATP-A and then continue to decrease and increase, respectively. The obtained results indicated that the dispersion of NiCoB amorphous alloy particle was effectively improved over the H+ATP-A supported NiCoB amorphous alloy catalysts. However, the 30NCB/H+-ATP-A catalyst shows the biggest SM of 26.43 m2/g, which might be related with the most serious deposition of NiCoB particles as above-mentioned (Figure 1(b)). In order to investigate the chemical states of NiCoB and supported NiCoB amorphous alloy catalysts, the XPS characterization of NCB and 20NCB/H+-ATP-A catalysts stored in absolute ethyl alcohol was conducted, of which the spectra are showed in Figure 4. According to the standard BE from the database developed by Thermo Fisher Scientific Inc. 69, for the Ni 2p spectra of NCB catalyst, the peaks at 852.3/869.4 eV and 855.7/873.4 eV are ascribed to metallic Ni and oxidized Ni in Ni2p3/2/Ni2p1/2 level, respectively 70. For the Co 2p spectra, the peaks at 777.8/792.7 eV and 780.8/796.7 eV are ascribed to metallic Co and oxidized Co in Co2p3/2/Co2p1/2 level, respectively

14, 69

. Meanwhile, the peaks around 187.6/191.7 eV are

assigned to the metalloid B and the oxidized B, respectively 70. During the process of catalyst preparation by the conventional －

chemical reduction method, the occurrence of BH4

hydrolysis (Equation (1)) to oxidized B species was unavoidable 71. For

the NCB catalyst, the atomic ratios of metallic Ni to oxidized Ni, metallic Co to oxidized Co and metalloid B to oxidized B, are 0.64, 0.43 and 0.36, respectively. In addition, in comparison with the standard BE of the pure B (187.1 eV) 27, the BE of metalloid B positively shifts about 0.5 eV. On the contrary, it is noted that the BE of metallic Ni and Co all shift negatively compared with the standard BE of pure Ni (853.1 eV)

70

and pure Co (778.4 eV)

12


14

, which is different from the failure in

Page 13 of 46 1 2 3 4 5 1 6 7 8 2 9 10 3 11 12 13 4 14 15 16 5 17 18 6 19 20 21 7 22 23 8 24 25 26 9 27 28 2910 30 3111 32 33 3412 35 36 13 37 38 3914 40 41 4215 43 4416 45 46 4717 48 49 18 50 51 5219 53 54 5520 56 5721 58 59 60


observing the BE shift of the metallic Ni and Co in most other reports 14, 70, 72. These results showed that partial electrons were transferred from B to Ni and Co in the NiCoB amorphous alloy, making Ni and Co electron-enriched while B electron-deficient. For the 20NCB/H+-ATP-A catalyst, it’s evident that the peak intensity of most spectrum bands except for the oxidized Co in Co2p3/2/Co2p1/2 level shows a sharp decrease due to the decrease of bulk NiCoB content (Table 1). The atomic ratios of metallic Ni to oxidized Ni, metallic Co to oxidized Co and metalloid B to oxidized B, are also drop obviously to 0.15, 0.04 and 0.26, respectively, which might be caused by the exchange of Ni2+ and Co2+ with Mg2+ and Al3+ of H+-ATP-A 60. However, the peak position of all spectrum bands shows a positive shift about 0.5 eV in comparison with the shift of NCB catalyst. The results mean that the electron density of Ni and Co atoms decreased despite the electron transfer from B to Ni and Co. H+-ATP-A contains a large amount of acid sites 60. Therefore, the results might be caused by the electron adsorption of the acid cites of H+-ATP-A support from well-dispersed Ni and Co atoms, thus promoting the interaction between H+-ATP-A and NiCoB amorphous alloy particle and was also beneficial to improve the hydrogenation activity of the catalyst. H2-TPR was applied to compare the reduction properties of NCB and 20NCB/H+-ATP-A catalysts as shown in Figure 5. The NCB catalyst showed a group of peaks in the range of 200～370 oC, which was corresponding to the two-step process of Co3O4 reduction, Co3O4→CoO→Co 73. The other peaks at 426 oC and 481 oC were assigned to the reduction of NiO to Ni0 74. For 20NCB/H+-ATP-A catalyst, since SiO2, MgO and Al2O3 in H+-ATP-A could not be reduced in the studied temperature range 20 and little Fe2O3 in H+-ATP-A (Table S1) only showed a very broad and short peak from 500 oC to 650 °C 75, the present reduction peaks were attributed to the reduction process of different Ni and Co species existed in the catalyst. These peaks at 200～350 o

C were attributed to the two-step reduction of Co3O4, including two much stronger low-temperature peaks at 245 oC and 263 C and one significantly weaker high-temperature peak at 312 oC than those observed in NCB catalyst. It was worth noting that

o

the 20NCB/H+-ATP-A also showed a sharp peak of NiO reduction at 403 oC, and a broad peak in the range of 540～640 oC assigned to the reduction of NiCo2O4 to Ni-Co alloy 73. Therefore, the abruptly decreased peak at 312 oC might be due to the

13



Page 14 of 46

formation of NiCo2O4 from some reductive intermediate Co species. It’s reasonable to conclude that the reduction of oxidized Ni and Co species in the NiCoB amorphous alloy particles was improved by the loading of NiCoB particles on H+-ATP-A support. Furfural Hydrogenation Properties of Different Catalysts. Table 2 summaries the hydrogenation results of furfural over different catalysts in ethanol solvent. The unsupported NiCoB amorphous alloy catalyst showed a low average m

S

hydrogenation rate ( RH ) and intrinsic activity ( RH ) with a furfural conversion of 58.1%. For the 5NCB/H+-ATP-A catalyst, the well dispersion of NiCoB amorphous alloy particles improved the average hydrogenation rate during the first 0.5 h of reaction, however, the final furfural conversion after reaction 2 h decresed slightly. On the one hand, the sharp decrease of the number of surface Ni and Co atoms which was resulted from the decrease of actual NiCoB active components to 0.05 g might lead to the decrease of adsorbed H2, thereby decreasing the furfural conversion and restraining the further hydrogention of FA to tetrahydrofurfuryl alcohol (THFA). On the other hand, Ni and Co showed a similar content with the Ni/Co molar ratio of near 1.0 (Table 1) that was beneficial to enhance the synergistic effect between Ni and Co

31

, thus increasing the average m

S

hydrogenation rate and the TOF for FA prodcution. When the NiCoB loading increased to 10 wt%, the RH and RH all doubled, and the conversion of furfural also showed an increse by 11.6%. However, the TOF for FA prodcution fell by more than half from the 5NCB/H+-ATP-A catalyst due to the increase of actual NiCoB active components to 0.1 g. Apparently, the hydrogenation activity was effectively improved by using only half the quantity of NiCoB active components belonged to the m

S

NCB catalyst. With the gradual increase of NiCoB loading from 10 wt% to 40 wt% except for 30 wt%, the RH and RH all showed the same downtrend due to the continuous decease of SBET (Table 1). In addition, the TOF for FA prodcution also decrease manyfold to 80.5 h-1 and the conversion of furfural showed a gradual increase to 81.9%. It’s well known that welldispersed active sites with small particle size on the surface of support are much liable to contact with reactant molecules to improve the reaction activity 76. Lee et al. 33 reported that the gas-liquid mass-transfer limitation over Ni-P-B amorphous alloy

14


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catalyst can be eliminated by the proper stirring speed because the initial rate of hydrogenation of furfural is linearly dependent on the catalyst loading with a zero intercept. During the evaluation process of FUR hydrogenation performance in this work, the catalyst loading is unchanged. According to the change trend of SM and dM in those catalysts, the percentage conversion of furfural to FA increased with an increase in the catalyst loading can be due to a proportional increase in the NiCoB active site of the catalyst and the improvement of dispersion of NiCoB particles 61. However, the reaction activity of furfural hydrogenation m

S

( RH , RH and conversion of furfural) over the 30NCB/H+-ATP-A catalyst wasn’t between 20NCB/H+-ATP-A and 40NCB/H+-ATP-A but lower than both. This could be attributed to the most serious deposition of NiCoB particles and the strongest secondary activation of H+-ATP-A in the 30NCB/H+-ATP-A catalyst as-above mentioned, which would restrain the adsorption of hydrogen and furfural molecules to decrease the conversion of furfural and TOF for FA prodcution.

Table 2. Hydrogenation results of furfural over different catalysts in ethanol solvent a. Catalysts b NCB +

5NCB/H -ATP-A

c

RHS

( mmol•h-1•gM-1) 3.5

(mmol•h-1•m-2) 0.19

Selectivity (%)

Yield (%)

TOF d (h-1)

Conversion (%)

MF

THFA

FA

THFA

FA

164.6

58.1

0.0

19.9

80.1

11.6

46.5

17.4

0.71

670.5

57.4

1.5

8.4

90.1

4.8

51.8

+

33.6

1.43

306.0

69.0

0.5

14.3

85.2

9.9

58.8

+

28.3

1.18

151.3

76.5

2.8

14.8

82.4

11.3

63.1

+

19.3

0.73

88.7

72.6

1.6

15.6

82.8

11.3

60.1

+

40NCB/H -ATP-A

25.4

1.04

80.5

81.9

0.5

21.4

78.1

17.5

63.7

20NCB/SiO2

19.7

-

-

54.4

0.0

17.5

82.5

9.5

44.8

20NCB/γ-Al2O3

10.4

-

-

52.2

0.0

9.5

90.5

4.9

47.3

10NCB/H -ATP-A 20NCB/H -ATP-A 30NCB/H -ATP-A

a

RHm

o

Reaction condition: Furfural (5 mL, 0.06 mol), ethanol (25 mL), supported catalyst (1.0 g); T= 100 C, p(H2)= 3.0 MPa, stirring

rate= 800 rpm, reaction time= 2 h. b0.2 g NCB catalyst and 1.0 g other catalysts. cThe average hydrogenation rate within the first 0.5 h reaction. dTOF is defined as the mole number of FA generated per hour per metal site, metal sites refer to the total amount of Ni and Co sites determined by ICP-OES.

In terms of the products selectivity and yield, the supported NiCoB catalysts showed much higher FA selectivity and yield than the unsupported NiCoB amorphous alloy catalyst. With the increase of NiCoB loading, the FA selectivity showed a gradual decrease and the THFA selectivity showed an opposite change. According to the scheme of FUR hydrogenation to different chemicals (Scheme 1), the high selectivity and yield of FA can determine that the hydrogenation activity of C=O bond is much 15



Page 16 of 46

higher than C=C bond. However, the hydrogenation of C=C bond to form THFA is always easier than hydrogenation of C=O bond

77

. Consequently, the byproduct THFA is always inevitable during the process of FUR hydrogenation to FA. In our

previous study 78, the isolated Ni-B active sites showed better hydrogenation activity of C=C bond on the furan ring of furfural molecule than the isolated Co-B active sites. The increase of surface metallic active site in those Ni-Co-B catalysts promoted the further hydrogenation of FA to THFA. Therefore, the slight increase of THFA selectivity at the cost of the decrease of FA selectivity with the increase of NiCoB loading on the H+-ATP-A support can be due to the increased content of NiCoB active site. Comprehensively considering the catalytic activity, FA selectivity and catalyst cost, the preferred catalyst was 20NCB/H+ATP-A catalyst in the selective liquid-phase hydrogenation of FUR to FA. Activity Comparison with Commercial Support. The commercial SiO2 (40-100 mesh) and γ-Al2O3 (>100 mesh) supported 20 wt% NiCoB amorphous alloy catalyst were applied to compare their FUR hydrogenation properties with the screened 20NCB/H+-ATP-A catalyst as shown in Table 2. Under the same reaction conditions, the 20NCB/SiO2 and 20NCB/γAl2O3 catalysts showed much lower activity than 20NCB/H+-ATP-A catalyst, and even the unsupported NiCoB amorphous alloy catalyst. However, the FA selectivity of 20NCB/γ-Al2O3 catalyst was much higher than 20NCB/H+-ATP-A catalyst. The elevated background, declined peak intensity and unchanged phase composition on the XRD patterns (Figure S5) of those catalysts compared with the corresponding supports themselves confirmed that the presence of NiCoB amorphous alloy. According to the textural properties and composition of 20NCB/SiO2 and 20NCB/γ-Al2O3 catalysts (Table 1), the SBET and Vp of the catalysts supported on SiO2 and γ-Al2O3 decreased obviously compared with SiO2 and γ-Al2O3 themselves, which can be due to the occupation of some pores of these supports by small amorphous alloy particles. This phenomenon was opposite －

to 20NCB/H+-ATP-A catalyst, further indicating the occurrence of secondary activation of ATP-A by H+ or OH . In addition, the NiCoB bulk content of 20NCB/SiO2 catalyst showed only one half of 20NCB/H+-ATP-A catalyst which might be due to the loss of NiCoB component on granular SiO2. Similarly, the 20NCB/γ-Al2O3 catalyst also showed slightly decreased NiCoB

16


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bulk content than that of 20NCB/H+-ATP-A catalyst. Li et al.

79

revealed that the pore structure of supports profoundly

influenced the particle size, location and dispersion degree of Co-B amorphous alloys. Therefore, the increased pore volume and pore size (Table 1) indicated that the NiCoB amorphous alloy was more liable to load and disperse on the H+-ATP-A support to improve the adsorption and hydrogenation ability. Reaction Conditions Optimization of Furfural Hydrogenation. The reactions were carried out using 20NCB/H+ATP-A catalyst with a variation of temperature from 80 to 160 oC using an initial hydrogen pressure of 3.0 MPa to investigate its effect on the furfural conversion, selectivity and yield of different products. As can be seen from Figure 6, the furfural conversion increased rapidly from 48.2% to 91.3% with the increase of reaction temperature to 140 oC and showed a continuously weak increase when the temperature rose to 160 oC. At low temperature (80 oC), FA (46.2 % yield), the hydrogenation compound of C=O bond at carbonyl group of furfural, was the major product with a selectivity of 95.8%. When the reaction temperature was 100 oC, a large amount of FA was converted into THFA and 2-methylfuran (MF) according to Scheme 1. The yield of THFA reached its summit at 100 oC. With the further rise of temperature to 140 oC, the production of THFA was restrained and partial FA was converted to MF. The yield of FA reached its summit of 74.9 % at 140 oC. However, with the rise of temperature to 160 oC, the undesired dehydration-condensation reaction of FA to hydrocarbons (48.0% selectivity) due to the surface acidity of H+-ATP-A support (Figure S5) would significantly lower the FA selectivity (37.0%) and yield (34.9%) 80. Consequently, the color of hydrogenation products gradually turned to be deeper (the insert in Figure 6) with the increase of reaction temperature. The reactions were carried out in a batch reactor with a stirring rate in the range of 200, 400, 600 and 800 rpm at reaction temperature of 140 oC to investigate the feasibility of a pilot technology under slow-speed of stirring. The experimental results are reported in Figure 7. When the stirring rate was 200 rpm, the furfural conversion was up to 88.7% with a FA selectivity of 81.3% due to the accessibility between the feedstock and catalyst in ethanol solvent. With the increase of stirring rate, the

17



Page 18 of 46

furfural conversion first decreased and then slightly increased. The maximum conversion of furfural was found to be 91.3 % with the selectivity of 82.0% at 800 rpm. Sharma et al.

61

reported that 1000 rpm is sufficient to eliminate mass transfer

resistance for the liquid phase hydrogenation of FUR to FA. However, in our experiments, the 1000 rpm could not be achieved due to the restriction of mechanical stirrer. For the purpose of further pilot demonstration, the speed of agitation was kept at 200 rpm for further experiments for the assessment of the effect of reaction pressure on the reaction and investigation of the catalyst stability. The conversion of furfural and selectivity of different product were also investigated by varying the initial hydrogen pressure from 1.0 to 4.0 MPa. Autogenous pressure of the reaction was generated at 140 oC. Total pressure of the reaction was maintained at 1.6-5.0 MPa. It was observed that with the increase in the hydrogen pressure, the conversion of furfural gradually increased with a weak decrease of the selectivity of FA (Figure 8). However, when the initial hydrogen pressure was less than 2.5 MPa, the selectivity of THFA showed a gradual increase from 4.3% to 10.7% at the cost of a decrease of the selectivity of MF from 15.7% to 8.4%. It was indicated that the increased hydrogen pressure promoted the generation of tetrahydrofurfural and further hydrogenation to THFA according to the reaction (2) in the Scheme 1, while inhibited the further hydrogenolysis of FA to MF according to the reaction (3) in Scheme 1. When the initial hydrogen pressure further increased to 4.0 MPa from 2.5 MPa, about 2.4% of FA was converted into MF and THFA, thus slightly increasing their selectivity. Therefore, one can conclude that the increased hydrogen pressure is beneficial to the C═C band on the furan ring of furfural. In addition, the increased solubility of hydrogen in the reaction mixture at increased hydrogen pressure can account for the increased conversion 61. The effects of reaction time on catalytic activity, product distribution and yield over NCB and 20NCB/H+-ATP-A catalysts have been investigated at 140 oC, 3.0 MPa hydrogen and 200 rpm (Figure 9). For the NCB catalyst, the conversion of furfural gradually increased during the reaction process. It is observed that the trend of the furfural conversion rate was sharper at an early reaction of 2 h than that at the latter reaction of 4 h. This is due to the higher concentration of furfural at an early reaction

18


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stage, thus with a higher reaction rate. During the whole reaction process, the MF generated from the hydrogenolysis of FA was started to form and increase after 2 h reaction (Figure 9(a)). However, the FA was transformed into THFA with a sharply decreased selectivity by 10.4% in the first 0.5 h of reaction and kept a slightly gradual decrease until 6 h of reaction. These results indicated that FA was not enough stable under our reaction conditions using the NCB catalyst, which might be due to the poor thermal stability of NiCoB amorphous alloy with a weight loss of 46.1 wt% (Table S5) and the generation of cobaltous oxide in the used NCB catalyst (Figure S6 (b)) which showed petaloid shape embedded in some clusters (Figure S7 (a)). The HRTEM image of the used NCB catalyst also displayed many petaloid nanoflakes (Figure S8 (a)) and the SAED image showed some light spots that were ascribed to the single crystal of CoO. Furthermore, the unchanged peak intensity of oxidized Ni and prominently increased peak intensity of oxidized Co in the used NCB catalyst (Table S5 and Figure S9) provided an evidence for the presence of Ni-CoO 81. Since the reaction condition was reductive, the generation of CoO might be happened during the process of product/catalyst separation in air. For the 20NCB/H+-ATP-A catalyst, the much higher FUR conversion than that of NCB catalyst showed similar change trend with it. The FUR conversion was improved by 12.6% after 6 h reaction. However, the selectivity of FA was much lower than NCB catalyst due to the generation of increased MF from the hydrogenolysis of FA (Figure 9(b)) which might be promoted by the synergistic effect of NiCoB alloy and surface acid sites of H+-ATP-A support 8283

. In addition, the selectivity of THFA was also slightly lower than that of NCB catalyst, indicating that the hydrogenation of

C═C band on the furan ring of furfural was restricted. During the whole reaction process, the selectivity of FA and THFA all firstly decreased and then increased, reaching the minimum of 79.7% and 7.4% at 2 h reaction, respectively, when the selectivity of MF was the summit of 12.9%. These results indicated that the 20NCB/H+-ATP-A catalyst has long-term activity and selectivity of FA due to its improved stability with a little weight loss of 2.0 wt% (Table S5). The used catalyst after 6 h reaction still showed the same crystalline phase composition (Figure S6 (d)) as the fresh catalyst and had well-dispersed particles with uniform size (Figure S7 (b)). The HRTEM image (Figure S8 (b)) also indicated that the amorphous alloy structure of supported

19



Page 20 of 46

NiCoB particles kept intact even if the product/catalyst separation was also conducted in air. Therefore, the NiCoB amorphous alloy catalyst supported on acid activated attapulgite is expected to be industrially applied in the furfural hydrogenation due to the improved stability of NiCoB active site. Stability Tests and Characterizations of Used Catalyst. Recovery capability and stability are important properties of practical heterogeneous catalysts 84. In this section, the reusability in FUR hydrogenation reaction of the used 20NCB/H+ATP-A catalyst after 6 h reaction was studied, and the results are shown in Figure 10. After each hydrogenation run, the reaction mixture was separated by vacuum filtration. The used catalyst was washed by solvent and was applied in the next run by adding little fresh catalyst with the lost amount under the same reaction conditions as the first run. The volume ratio of fresh FUR added to ethanol was always 1/5. The amount of FUR was not adjusted during the recycling process. As shown in Figure 10, the conversion of furfural dropped to 75.7% from 80.3% after the first two cycles, oppositely, it showed a sustainable growth to 84.2% after six cycles. Satisfyingly, the selectivity of FA also showed a similar change trend with the conversion of furfural which achieved an increase of 8.2% after six cycles with an increase of 10% of the yield. It was also reasonably to conclude that the selectivity of MF showed an antipodal change with FA because MF was generated from the conversion of FA according to the reaction (3) in Scheme 1. This might be caused by the decrease of the interaction between NiCoB alloy and H+-ATP-A support. In addition, the selectivity and yield of THFA showed a decrease from 7.4% and 5.9% to 3.0% and 2.6%, respectively, indicating that the hydrogenation activity of C═C band on the furan ring of furfural or furfuryl alcohol was dropped due to the content decrease of NiCoB active site in the used catalyst according to the ICP-OES detection (Table S5). Generally speaking, the leaching of active metals will lead to the decrease of reaction activity in heterogeneous catalysis 13, 20, 85

. In this work, though the used 20NCB/H+-ATP-A catalyst showed a decrease of total NiCoB content by 5.2 wt% (Table

S5), the entire hydrogenation activity through all recycling tests increased by 3.9%. According to the XRD pattern of the used catalyst after reaction for six recycles (Figure S6 (f)), a new sharp diffraction peak was presented at 2θ= 44.4o, an intermediate

20


Page 21 of 46 1 2 3 4 5 1 6 7 8 2 9 10 3 11 12 13 4 14 15 16 5 17 18 6 19 20 21 7 22 23 8 24 25 26 9 27 28 2910 30 3111 32 33 3412 35 36 13 37 38 3914 40 41 4215 43 4416 45 46 4717 48 49 5018 51 52 53 54 55 56 57 58 59 60


position between metallic Co (2θ= 44.2o) and metallic Ni (2θ= 44.5o), indicating the formation of a Co-Ni alloy. The FE-SEM image of the used catalyst after reaction for six recycles (Figure S7 (c)) showed the uniform distribution of a large amount of small particles belonged to Co-Ni alloy on the surface of H+-ATP-A support. The HRTEM image also indicated the well dispersion of those Co-Ni alloy particles with a typical SAED pattern of single crystal (Figure S8 (c)). Luisetto et al. 73 reported that the intrinsic nature of the Co-Ni alloy contributed to the high catalytic activity, selectivity and stability of a bimetallic CoNi/CeO2 catalyst for the syngas production by methane dry reforming under high reaction temperature. Therefore, the generated Co-Ni alloy in the used 20NCB/H+-ATP-A catalyst after six cycles was likely to be a new active site to maintain the high furfural hydrogenation activity. Much more characterization and investigation need to be conducted to prove it in future. Under the optimization conditions (140 oC, 3MPa H2, 800 rpm, 3.8 wt% of NiCoB active component with respect to FUR), FUR conversion of 91.3% and FA selectivity of 82.0% were achieved over the 20NCB/H+-ATP-A catalyst. Table 3 summarizes the liquid-phase hydrogenation properties over different supported metallic catalysts. Comparing to other supported metallic catalysts, the superiority of acid activated attapulgite supported NiCoB amorphous alloy catalyst in this work is not remarkable due to the complex composition (Table S1) and ill-fitted surface acidity of H+-ATP (Figure S4). However, the cheap and abundant attapulgite is expected to a promising support material for reducing the entire cost for industrial production of FUR hydrogenation to FA and improving the catalyst stability. Considering the significance of kinetics study for investigating the reaction mechanism of a catalyst, the kinetics of 20NCB/H+-ATP-A catalyst such as reaction orders with respect to furfural and H2, and apparent activation energy of the reaction will be presented in our future work.

Table 3. Liquid-phase hydrogenation of FUR to FA over different supported metallic catalysts. Solvent

T (oC)

H2 pressure (MPa)

FUR Conversion (%)

FA selectivity (%)

Ref.

Cu−Co/SBA-15

isopropanol

170

2

99.4

80.1

86

Co/SBA-15

ethanol

150

2

92

95

87

Ni−Mo−B/γ-Al2O3

methanol

80

5

99.1

91.0

88

Cu/SiO2(I)

2-propanol

110

1

4.8

0.8

24

Cu/SiO2(PD)

2-propanol

110

1

66.3

21.4

24

Catalyst

21



Ni−Sn/TiO2 +

Ni−Co−B/H -ATP



Page 22 of 46

isopropanol

110

3

>99

>99

89

ethanol

140

3

91.3

82.0

This work

CONCLUSIONS

In summary, we have developed a novel highly dispersed and stable NiCoB amorphous alloy supported catalysts via an impregnation-reductive method using the acid activated attapulgite as support. The screened acid activated attapulgite A (H+ATP-A), which owned the highest pore volume and much more amorphous silica on its surface, supported NiCoB alloy catalyst showed excellent catalytic activity for the hydrogenation of FUR to FA in the best ethanol solvent. The systematic investigation of the effects of NiCoB loading on physicochemical properties and hydrogenation activity of catalyst indicated that the －

reduction process between metallic ions (Ni 2+ and Co2+) impregnated in/on the H+-ATP-A support and BH4

to form NiCoB

amorphous alloy played an important role in enlarging the pore volume and adjusting the pore diameter due to the secondary －

activation of H+-ATP-A by the generated H+ and OH . The dispersion of NiCoB amorphous alloy had also been effectively improved due to the enhancement of interaction between H+-ATP-A and NiCoB particles, thus achieving excellent catalytic performances. Under the optimal conditions (140 ◦C, 3 MPa of initial hydrogen pressure, 800 rpm of stirring rate, 3.8 wt% of NiCoB active component in catalyst with respect to furfural), furfural conversion about 91.3% and 82.0 mol% furfuryl alcohol selectivity were obtained throughout 2 h of reaction over the 20NCB/H+-ATP-A catalyst which has long-term activity and selectivity. Moreover, the acid activated attapulgite supported NiCoB amorphous alloy catalyst showed good stability for FUR hydrogenation to FA during the consecutive six catalytic runs which might be due to the newly generated Co-Ni alloy active site. The acid activated attapulgite-supported NiCoB amorphous alloy catalysts are not only the promising candidates for effective upgrading of biomass-derived furfural, but also provide useful guidance for rational design of metal-metalloid amorphous alloy nanocatalysts for hydrogenation transformation.



ASSOCIATED CONTENT

22


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S ○


Supporting Information

The Supporting Information is available free of charge on the ACS Publications website at DOI: XXXXXXXXXX. The characterizations including XRF, N2 adsorption/desorption, XRD, FE-SEM, NH3-TPD, etc. and analysis of crude and acid-activated attapulgite A, B and C and corresponding supported catalysts, the furfural hydrogenation results and analysis of supported catalysts on acid-activated attapulgite A, B and C and in different reaction solvents, the characterizations including ICP, FE-SEM, HRTEM and XPS etc. and analysis of used catalysts can be found in the Supporting Information. The original data presented in this manuscript can be accessed at XXXXXXXXXX.



AUTHOR INFORMATION

Corresponding Authors * E-mail: [email protected] (X. Ouyang). Tel. /Fax: +86-20-87114722. * E-mail: [email protected] (X. Chen). Tel. /Fax: +86-20-37213916. Notes The authors declare no competing financial interest.



ACKNOWLEDGMENTS

This work was supported by the project of National Natural Science Foundation of China (21406229), the Project of Jiangsu Province Science and Technology (BE2014101), the project of Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development (Y709jh1001), and the Science and Technology Program of Guangzhou, China (201707010240).



REFERENCES

1.

Huang, C.; Chen, X. F.; Xiong, L.; Chen, X. D.; Ma, L. L.; Chen, Y., Single cell oil production from low-cost substrates:

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Page 24 of 46

The possibility and potential of its industrialization. Biotechnol. Adv. 2013, 31, 129-139. 2.

Lin, Y. C.; Huber, G. W., The critical role of heterogeneous catalysis in lignocellulosic biomass conversion. Energy

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


Schemes

Scheme 1. Simplified reaction schemes for the furfural conversion into main chemicals.

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Page 34 of 46

Figure captions

Figure 1. (a) N2 adsorption/desorption isotherms and (b) BJH pore size distribution (PSD) curves of H+-ATP-A and fresh supported NiCoB amorphous alloy catalysts. Figure 2. XRD patterns of fresh NCB amorphous alloy catalyst (a), H+-ATP-A (b) and its supported NiCoB amorphous alloy catalysts: (c) 5NCB/H+-ATP-A; (d) 10NCB/H+-ATP-A; (e) 20NCB/H+-ATP-A; (f) 30NCB/H+-ATP-A; (g) 40NCB/H+-ATP-A. Figure 3. HRTEM images and the corresponding particle size distribution of fresh NCB amorphous alloy catalyst (a) and H+ATP-A supported NiCoB amorphous alloy catalysts (b→f): (b) 5NCB/H+-ATP-A; (c) 10NCB/H+-ATP-A; (d) 20NCB/H+-ATPA; (e) 30NCB/H+-ATP-A; (f) 40NCB/H+-ATP-A. Figure 4. Ni 2p, Co 2p, and B 1s XPS spectras of fresh NCB amorphous alloy catalyst (a) and 20NCB/H+-ATP-A catalyst (b). Figure 5. H2-TPR curves of fresh NCB amorphous alloy catalyst (a) and 20NCB/H+-ATP-A catalyst (b). Figure 6. Furfural hydrogenation results over the 20NCB/H+-ATP-A catalyst at different reaction temperature. Figure 7. Furfural hydrogenation results over the 20NCB/H+-ATP-A catalyst at different stirring rate. Figure 8. Furfural hydrogenation results over the 20NCB/H+-ATP-A catalyst at different initial hydrogen pressure. Figure 9. Furfural hydrogenation properties as a function of time-on-stream over (a) NCB amorphous alloy catalyst and (b) 20NCB/H+-ATP-A catalyst. Figure 10. Reusability of 20NCB/H+-ATP-A catalyst for selective hydrogenation of furfural.

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Table of Contents (TOC)

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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

Scheme 1. Simplified reaction schemes for furfural conversion into main chemicals.


Page 36 of 46

Page 37 of 46

400

(a)

+

H -ATP-A － BH4 -ATP-A

3

Quantity adsorbed (cm /g)

350

NCB + 5NCB/H -ATP-A + 10NCB/H -ATP-A + 20NCB/H -ATP-A + 30NCB/H -ATP-A + 40NCB/H -ATP-A

300 250 200 150 100 50 0

0.0

0.2

0.4

0.6

0.8

1.0

Relative pressure (P/P0) 0.7

(b)

+

H -ATP-A － BH4 -ATP-A

0.6

NCB + 5NCB/H -ATP-A + 10NCB/H -ATP-A + 20NCB/H -ATP-A + 30NCB/H -ATP-A + 40NCB/H -ATP-A

0.5

dV(logd) (cc/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


0.4 0.3 0.2 0.1 0.0

2

10

100

1000

Diameter (nm) Figure 1. (a) N2 adsorption/desorption isotherms and (b) BJH pore size distribution (PSD) curves of H+-ATP-A and fresh NCB and supported NCB catalysts.



(a) Palygorskite Quartz (g) (f)

Intensity (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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(e) (d) (c) (b) 5

15

25

35

45

55

65

75

o

2 Theta ( ) Figure 2. XRD patterns of fresh NCB catalyst (a), H+-ATP-A (b) and its supported NCB catalysts: (c) 5NCB/H+-ATP-A; (d) 10NCB/H+-ATP-A; (e) 20NCB/H+-ATP-A; (f) 30NCB/H+-ATP-A; (g) 40NCB/H+-ATP-A.


25

NCB 39.6 25 nm

Frequency (%)

20 15 10 5 0 10

20

30

40

50

60

Particle size (nm) 25 +

5NCB/H -ATP-A 28.6 18.1 nm

Frequency (%)

20 15 10 5 0 10

20

30

40

50

60


10NCB/H -ATP-A 30.2 23.7 nm

Frequency (%)

20 15 10 5 0

15

25

35

45

55


20NCB/H -ATP-A 29.7 39.9 nm

Frequency (%)

25 20 15 10 5 0

15

25

35

45

55

65

75


30NCB/H -ATP-A 26.9 35.9 nm

25

Frequency (%)

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


20 15 10 5 0

15

25

35

45

55

65

75


Frequency (%)

Page 39 of 46

40NCB/H -ATP-A 29.3 19.4 nm

15

10

5

0 15

25

35

45

Particle size (nm)

Figure 3. HRTEM images and particle size distribution of fresh NCB catalyst (a) and H+-ATP-A supported NCB catalysts (b→f): (b) 5NCB/H+-ATP-A; (c) 10NCB/H+-ATP-A; (d) 20NCB/H+-ATP-A; (e) 30NCB/H+-ATP-A; (f) 40NCB/H+-ATP-A. The insert is the SAED picture of the catalyst.



Ni 2p

Intensity (a.u)

Co2p

Intensity (a.u)

(a)

(a)

(b)

(b)

845

850

855

860

865

870

875

880

885

770

775

780

785

Binding Energy (eV)

790

795

800

805

810

815

Binding Energy (eV)

191.7

B1s

187.6

Intensity (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

Page 40 of 46

(a) 192.3 188.1

180

182

184

186

188

(b) 190

192

194

196

Binding Energy (eV)

Figure 4. Ni 2p, Co 2p, and B 1s XPS spectra of fresh NCB catalyst (a) and 20NCB/H+-ATP-A catalyst (b).


Page 41 of 46

-15

-5 0

264

247

-10

H2 consumption

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


245

328 342 426 481

263

(a)

403 312

5 (b) 10 15

569

20

587 615

25 30 50

150

250

350

450

550

650

750

o

Temperature ( C) Figure 5. H2-TPR curves of fresh NCB catalyst (a) and 20NCB/H+-ATP-A catalyst (b).



FUR THFA Others

MF FA

100 Others

80 OH

O

60

60

FA OH

40

O

40

THFA

20 0

O

MF

80

100

120

140

160

20

Conversion & Yield (%)

100

80

Selectivity (%)

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 42 of 46

0 180

o

Reaction temperature ( C) Figure 6. Furfural hydrogenation results over the 20NCB/H+-ATP-A catalyst at different reaction temperature. Other reaction conditions: Furfural (5 mL, 0.06 mol), ethanol (25 mL), catalyst (1.0 g); p(H2)= 3.0 MPa, stirring rate= 800 rpm, reaction time= 2 h.


FUR MF THFA FA

100

100

80 80

Selectivity (%)

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


60

OH O

40

FA

10 OH

20

O

O

MF

0

200

5


Page 43 of 46

THFA

400

600

800

0

Stirring rate (rpm) Figure 7. Furfural hydrogenation results over the 20NCB/H+-ATP-A catalyst at different stirring rate. Other reaction conditions: Furfural (5 mL, 0.06 mol), ethanol (25 mL), catalyst (1.0 g); T= 140 oC, p(H2)= 3.0 MPa, reaction time= 2 h.



FUR MF THFA FA

100

100 80

80

70 OH

60

60

O

FA

50

OH O

40

THFA

10 20 0

5

O

MF

1.0

1.5

2.0

2.5

3.0

3.5

4.0


90

Selectivity (%)

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 44 of 46

0

Reaction pressure (MPa) Figure 8. Furfural hydrogenation results over the 20NCB/H+-ATP-A catalyst at different initial hydrogen pressure. Other reaction conditions: Furfural (5 mL, 0.06 mol), ethanol (25 mL), catalyst (1.0 g); T= 140 oC, stirring rate= 200 rpm, reaction time= 2 h.


Page 45 of 46

100

100

(a)

90

80

80

70

70

60

60

50

50 FUR MF THFA FA

40

40

MF THFA FA

10

0

Yield (%)

Conversion & Selectivity (%)

90

10

0

1

2

3

4

5

6

0

Reaction time (h)

100

100

(b)

90

80

80

70

70

60

60

FUR MF THFA FA

50 40

MF THFA FA

50 40

10

10

0

Yield (%)

90

Conversion & Selectivity (%)

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

1

2

3

4

5

6

0

Reaction time (h) Figure 9. Furfural hydrogenation properties as a function of time-on-stream over (a) NCB amorphous alloy catalyst and (b) 20NCB/H+-ATP-A catalyst. Reaction conditions: Furfural (10 mL, 0.12 mol), ethanol (50 mL), catalyst (2.0 g); T= 140 oC, p(H2)= 3.0 MPa, stirring rate= 200 rpm.



MF

THFA

FA

100

80

80

FA

60

THFA

20

10

0

60

20

10

MF

0

1

2

3

4

5

6


FUR

100

Selectivity (%)

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 46 of 46

0

Run Figure 10. Reusability of 20NCB/H+-ATP-A catalyst for selective hydrogenation of furfural. Reaction conditions: Furfural (5 mL, 0.06 mol), ethanol (25 mL), catalyst (1.0 g); T= 140 oC, p(H2)= 2.5 MPa, stirring rate= 200 rpm, reaction time= 2 h.


Selective Hydrogenation of Furfural to Furfuryl Alcohol over Acid

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