Efficient Catalytic Hydrogenation of Butyl ... - ACS Publications

‡Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, No.2 ... Guangdong Provincial Key Laboratory of New and Renewable Energy ...
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Catalysis and Kinetics

Efficient Catalytic Hydrogenation of Butyl Levulinate to #-Valerolactone over a Stable and Magnetic CuNiCoB Amorphous Alloy Catalyst Bo Chen, Haijun Guo, Zhe Wan, Xiaocheng Xu, Hairong Zhang, Dan Zhao, Xin-De Chen, and Ning Zhang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b00378 • Publication Date (Web): 27 Mar 2018 Downloaded from http://pubs.acs.org on March 29, 2018

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Energy & Fuels

Efficient Catalytic Hydrogenation of Butyl Levulinate to γ-Valerolactone over a Stable and Magnetic CuNiCoB Amorphous Alloy Catalyst Bo Chen, † Haijun Guo, ‡, §, # Zhe Wan, † Xiaocheng Xu, † Hairong Zhang, ‡, §, # Dan Zhao, †,* Xinde Chen, ‡, §, #,** Ning Zhang, † †

Institute of Applied Chemistry, College of Chemistry, Nanchang University, No.999 Xuefu Road, Nanchang 330031, PR China



Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, No.2 Nengyuan Road, Guangzhou 510640, PR China

§

CAS Key Laboratory of Renewable Energy, No.2 Nengyuan Road, Guangzhou 510640, PR China

#

Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development, No.2 Nengyuan Road, Guangzhou 510640, PR China

S Supporting Information ○

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 Abstract graphic

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ABSTRACT: A series of low-cost, magnetic and high-efficiency CuNiCoB amorphous alloy

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catalysts were developed by chemical reduction method for selective hydrogenation of butyl

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levulinate (BL) to γ-valerolactone (GVL). The catalysts were characterized by ICP-OES, BET,

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XRD, FE-SEM, TEM, XPS, H2-TPD techniques. The results indicated that the CuNiCoB

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amorphous alloy nanosheets with well-dispersed Cu nanoparticles played an important role in

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enhancing the hydrogenation activity. Reaction temperature, pressure, time and substrate

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concentration were optimized. The maximum GVL yield of 89.5% with BL conversion of 99.7%

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was achieved over the best Cu0.5Ni1Co3B catalyst using 3wt% dosage relative to BL at 473 K

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under 3.0 MPa H2 after 3 h. The considerable stability of Cu0.5Ni1Co3B during catalytic recovery

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and reuse experiments (5 cycles) was exhibited, because of the transformation of CuNiCoB

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amorphous alloy active sites to Cu-Ni-Co ternary alloy. The stable and magnetic catalyst was

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demonstrated to be a promising candidate to produce more value-added compounds from biomass

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derived raw materials.

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KEYWORDS: Catalytic hydrogenation, Butyl levulinate, CuNiCoB amorphous alloy,

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Magnetic catalyst, γ-valerolactone

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Energy & Fuels

1

 INTRODUCTION

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Renewable

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environmental-benign resource for fuel industry in view of the serious issues on depleted

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reservation of oil resources and increased emission of greenhouse gases.1 As an important

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platform molecule in the bio-refinery field, levulinic acid (LA) (4-oxypentanoic acid) and its

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transformation drew great interests in producing numerous biofuels and biochemicals.2

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Deoxygenation and C-C coupling are the main reactions involving in the conversion of LA into

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biofuels, such as liquid hydrocarbons and higher alcohols.3 Biochemical, for example, typically

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γ-valerolactone (GVL) and levulinate esters (LE), can be produced by hydrogenation or

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esterification reactions of LA.4-7 Furfural (FUR), another important platform intermediate, can be

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hydrogenated into furfuryl alcohol (FA) and then converted into LA8 or LE9-10. Among these

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compounds, GVL has attracted a lot of attention since it has been identified as a renewable and

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versatile medium molecule. It can be used as an excellent solvent and fuel additive due to its

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outstanding solubility in water and the notable capacity to mix with gasoline as ethanol.4, 11 More

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important, many high value-added chemicals, such as 1,4-pentanediol (1,4-PDO), methyl

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pentenoate, ethylvalerate (EV), are able to be synthesized from GVL.12-14

lignocellulosic

biomass

has

been

investigated

as

an

inexpensive

and

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Obtaining GVL from LA or LE always involved the catalytic hydrogenation process over a

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heterogeneous or homogeneous catalyst.15-18 Some supported precious metal catalysts, such as

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Ru/C15, Ru/TiO219, Rh/SiO220, Ru/ZrO221-22, Ru/Al2O323, Au-Pd/TiO224, etc. have displayed

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superior activity and operation convenience for the catalytic process. However, the high cost and

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low stability restrict the application of noble metal-based catalyst in the large-scale production of

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GVL.15, 25 In view of the shortage of noble metal catalysts, recently, many efforts have been

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devoted to the development of cheap, active, stable and recyclable catalysts for the reaction.26-31

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Yan et al.27 found that a Cu-based catalyst derived from hydrotalcite-like compounds (HTlcs) (9.8

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wt% relative to LA) could achieve high GVL yield (91%) from LA at 473 K with 7.0 MPa H2 after

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10 h. To avoid using high pressure H2, the catalytic transfer hydrogenation (CTH) using organic

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molecules as the hydrogen donors was demonstrated to be a feasible method to convert LA or LE

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to GVL.17, 26-31 A magnetic and recyclable Ni4.59Cu1Mg1.58Al1.96Fe0.70 catalyst prepared from HTlcs

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by Zhang et al.26 could yield 98.1% of GVL from LA through the CTH reaction in methanol at 415

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K after 3 h with 25 wt% catalyst usage percentage to LA. Tang et al.30 reported a nano-copper

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catalyst could serve as a dual-functional CTH catalyst for quantitatively converting methyl

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levulinate (ML) to GVL with a selectivity of 87.6% at 513 K after 1 h in methanol, but the high

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amount of catalyst exceeding 28 wt% relative to ML was required. Cai et al.31 employed a

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bimetallic Cu-Ni catalyst for CTH of ethyl levulinate (EL) to GVL with 2-buthanol as H-donor,

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and 97% yield of GVL was achieved over 10Cu-5Ni/Al2O3 (69.4 wt% relative to EL) at 423 K

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after 12 h. Notably, Cu-based catalysts were also successfully employed for some derived

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hydrogenation reactions.32-34 Du et al.33 discovered that a 30%Cu/ZrO2-OG catalyst (20 wt%

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relative to GVL) could show high 1,4-pentanediol (1,4-PDO) yield (93.1%) from the

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transformation of GVL at 473 K in 6 h. A Cu/SiO2 catalyst carrying highly-dispersed spherical Cu

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nanoparticles could efficiently transform GVL to pentyl valerate (PV) in 91% conversion and 92%

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selectivity.34 These reports indicated that Cu-based catalyst was a kind of attractive candidate to

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replace noble metal catalyst for the successive conversion of levulinate esters, however, there still

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some limitations such as high amount of catalyst and long reaction time for the catalytic system

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should be concerned. Therefore, further improvement on the catalyst composition and structure

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was still highly aspired.

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To address the issue, the inexpensive amorphous alloy catalyst prepared by chemical reduction

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method, for example Ni(Co)-(M)-B (M= Fe, Co, La, Ce, Mo)35-42 used in the hydrogenation

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reactions of furfural could be an alternative due to their virtues: the unique chemical and structural

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properties including broadly adjustable composition, structural homogeneity, and high

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concentration of coordinately unsaturated sites.43 In our previous study, the Ni1Co3B amorphous

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alloy catalyst (Ni/Co molar ratio = 1/3) showed a high yield (90.3%) of tetrahydrofurfuryl alcohol

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(THFA) with a furfural conversion of 99.9% at 373 K in 6 h.42 The excellent activity to the tandem

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hydrogenation of C═O bond and C═C bond on the molecule structure of furfural was due to

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more isolated Co-B active sites in catalyst. Compared to aldehydes, acids and esters are more

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difficult to be hydrogenated because of the steric hindrance of C═O bond and weak polarity.

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Confronting the problem, introducing a third metal into NiCoB structure to form a

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multi-functional amorphous alloy could be a valuable attempt. Therefore, in this work, a series of

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low-cost and magnetic CuNiCoB amorphous alloy catalyst were obtained by the introduction of

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Cu into Ni1Co3B catalyst and applied for butyl levulinate (BL) hydrogenation, since Cu

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component was testified as the main active composition for mimic reactions in references as

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mentioned. Effects of varied experiment parameters were investigated and a detailed

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characterization of the fresh and used catalysts was conducted. The results showed that BL was

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efficiently converted to GVL under the optimized conditions in short reaction time over the

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Cu0.5Ni1Co3B catalyst with a usage of only 3 wt% relative to BL, the feature together with the

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excellent stability in recovery and reuse experiments indicated the well manipulated CuNiCoB

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amorphous alloy could be noteworthy as an efficient catalyst for corresponding lignocellulosic

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biomass transformations.

3

 EXPERIMENTAL SECTION

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Sections including Materials, Catalyst preparation and characterizations, and Product analysis are

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described in detail in the Supporting Information.

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Catalytic Reaction. The catalytic measurements for hydrogenation of butyl levulinate were

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carried out in a 100 mL YZPR-100 (M) stainless steel autoclave reactor equipped with an

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electrical heating jacket and a mechanical stirrer. Before catalytic activity testing, the catalyst was

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took out from absolute ethyl alcohol and dried for 1 h under vacuum at 50 oC, and then was

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levigated and sieved to ˃ 100 mesh. In a typical catalytic reaction, butyl levulinate (1 mL, 0.974 g,

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5.66 mmol), CuxNi1Co3B catalyst powder (0.0292 g) and cyclohexane solvent (24 mL) were

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mixed in the reactor. After the air in the autoclave was excluded completely by repetitively filling

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N2 for four times and H2 for three times, the autoclave was filled by hydrogen to 3.0 Mpa and was

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heated to 200 oC in defined time. When the pressure reached a steady state, the reaction was

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started by adjusting the stirring rate to 800 rpm to eliminate the diffusion effect. After 3 h, the

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product and catalyst was seperated by magnet. Three duplicate runs were performed to ensure the

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experimental errors for the catalytic performances within 5% and the mean values were presented.

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 RESULTS AND DISCUSSION

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Catalyst Characterizations. Table 1 summarizes the specific surface area of these catalysts

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by Brunauer-Emmett-Teller (BET) measurements. Generally, the addition of Cu into Ni1Co3B

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composition increased the BET surface area (SBET) and total pore volume (VP) of samples except

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for Cu1.0Ni1Co3B, meanwhile, the average pore size (Dp) was decreased (Figure S1, Supporting

3

Information). The Cu0.3Ni1Co3B catalyst showed the highest SBET of 32.8 m2/g and the lowest Dp

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of 15.1 nm. From the bulk composition, the slight decrease in Ni/Co ratio was accompanied by the

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increase in Cu/Ni ratio via increasing Cu composition among CuNiCoB samples, suggesting an

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interaction could be present between Cu and Ni1Co3B amorphous alloy structure. For CuB sample,

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the content of B was undetected, implying that B was difficult to be combined with the sole Cu to

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form the amorphous alloy structure like NiCoB.

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Insert Table 1 Here

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X-ray diffraction (XRD) patterns of fresh CuxNi1Co3B catalysts are shown in Figure 1. As

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shown, a typical amorphous alloy structure around 2θ = 45º present on Ni1Co3B catalyst.42, 44 By

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gradually increasing Cu dosage for CuNiCoB samples, in general, the amorphous feature like

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Ni1Co3B was observed on these samples, indicating that the amorphous alloy structure was not

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obviously changed by integrating Cu to form CuNiCoB samples. With the increase of Cu/Ni molar

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ratio to 2/1, a peak raised at 43.4o ascribed to (111) lattice plane of the elementary Cu (Cu0)

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appeared among samples33, indicating that Cu precursor can be reduced to metallic Cu under the

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condition employed for getting CuNiCoB catalysts in this work. In contrast, the sharp crystal

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characteristic diffraction peaks of Cu2O were observed on CuB sample, which confirmed ICP

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analysis that the entire loss of B for the sample. When the Cu/Ni molar ratio was manipulated

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below 0.5/1, the diffractions of metallic Cu was not observed, which could be attributed to the

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little content of Cu (Table 1) or the formation of CuNiCoB amorphous alloy.

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Field Emission-Scanning Electron Microscope (FE-SEM) images of fresh CuxNi1Co3B catalysts 7

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are shown in Figure 2. Ni1Co3B amorphous alloy catalyst shows some irregular sheets which were

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aggregated from a large amount of small particles. The sheet structure can be ascribed to NiCoB

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amorphous alloy. In addition, some spherical particles attributed to the isolated CoB amorphous

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alloy particles are agglomerated upon the surface of catalyst.42 With the introduction of Cu, the

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nanosheets became smaller and their boundary present fuzzier in comparison with Ni1Co3B, which

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implied that amorphous extent could be further enhanced due to the combination of Cu into

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NiCoB structure. The further increase of Cu promotes the electron transfer and the optimization of

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CuNiCoB amorphous alloy structure. Selected area electron diffraction (SAED) image with

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typical diffraction halo of the Cu0.5Ni1Co3B catalyst (Figure S2a, Supporting Information)

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provides evidence for the presence of amorphous alloy structure. In addition, as can be seen from

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the High-Resolution Transmission Electron Microscope (HRTEM) image (Figure S2b and S2c,

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Supporting Information), a large amount of well-dispersed spherical Cu nanoparticles with particle

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size centered at about 5.1 nm are displayed on these nanosheets. Therefore, HRTEM analysis

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clearly shows the presence of well dispersed metallic phase with well formed, highly defective

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metal nanoparticle on the Cu0.5Ni1Co3B catalyst. When the Cu/Ni molar ratio increases to 2/1,

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these nanosheets of CuNiCoB amorphous alloy cannot be found due to the coverage by the

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isolated spherical particles, thus restricting the contact of reactants with CuNiCoB hydrogenation

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active sites. The CuB catalyst displays uniformly distributed spherical particles which are

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belonged to bulk metal Cu particles (average size ca. 50 nm).

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To further explore the effect of Cu addition into Ni1Co3B on the chemical state of the metal

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species, X-ray photoelectron spectroscopy (XPS) analysis of the representative catalysts Ni1Co3B

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and Cu0.5Ni1Co3B was carried out, and the results are present in Figure 3 and Figure 4. Figure 3

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shows the XPS spectra of Ni 2p, Co 2p and B 1s. For Ni 2p, the peaks at 852.6±0.1 and at

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869.8±0.2 eV are ascribed to metallic nickle (Ni0) in Ni02p3/2/ Ni02p1/2 level, respectively.45 The

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peaks at 856.1±0.1 and at 873.7±0.1 eV are assigned to oxidized nickle (Ni2+) in Ni2+2p3/2/

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Ni2+2p1/2 level, accompanying with two satellite peaks around 862.1±0.1 eV and 880.8±0.2 eV,

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respectively. For Co 2p, the peaks at 778.1±0.1 and at 793.1±0.1 eV are ascribed to metallic cobalt

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(Co0) in Co02p3/2/Co02p1/2 level, respectively.46 Meanwhile, the oxidized cobalt (Co2+) in

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Co2+2p3/2/Co2+2p1/2 level are also observed corresponding to the binding energy (BE) of

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781.0±0.1eV and 797.0±0.1eV, respectively, accompanying with their satellite peaks. In addition,

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the peaks around 187.8±0.1 and 191.8±0.1 eV are ascribed to the elemental boron (Be) and the

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oxidized boron (Bo), respectively.45 The BE of Be in the Ni1Co3B catalyst shifted positively by 0.6

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eV in comparison with the standard BE of the pure B (187.1 eV), indicating partial electrons

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transferred from B to Ni and Co in the NiCoB amorphous alloy, making the Ni and Co

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electron-enriched while the B electron-deficient.35 Notably, Cu0.5Ni1Co3B catalyst had lower

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surface concentration of Ni0, Co0 and Be but obviously higher surface concentration of Ni2+, Co2+

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and Bo compared to the Ni1Co3B catalyst, meanwhile, both the BE of Ni0 and Co0 signals on

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Cu0.5Ni1Co3B positively shifted by 0.2 eV relative to those on Ni1Co3B. This phenomenon

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indicated the electron transferring from B to Ni and Co was suppressed by combination of Cu into

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Ni1Co3B structure, which could be attributed to the decreased B content (Table 1) or Cu occupied

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partial electrons donated from B in Cu0.5Ni1Co3B structure. Cu 2p spectra together with Cu LMM

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Auger spectra for Cu0.5Ni1Co3B catalyst were given in Figure 4. In Cu 2p spectra, two peaks at

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932.3 eV and 952.2 eV are corresponded to Cu0/Cu+2p3/2 and Cu0/Cu+2p1/2, respectively;31 two

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species were further identified from Auger spectra. It is worth noting that there are not main peaks

9

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and satellite peaks of CuO species. Above spectra observations, especially the co-existence of

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metallic species clearly indicated the outcoming of CuNiCoB amorphous alloy with

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well-dispersed Cu nanoparticles from our preparation.

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In order to investigate the catalytic hydrogenation active sites, the hydrogen temperature

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programmed desorption (H2-TPD) of the representative catalysts Ni1Co3B and Cu0.5Ni1Co3B was

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carried out, as shown in Figure 5. The Ni1Co3B catalyst only exhibits one desorption peak at 455

7

K, implying that there is only one kind of adsorption site on the catalyst. The Cu0.5Ni1Co3B

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catalyst shows one similar desorption peak at 458 K and another desorption peak at 576 K,

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indicating that a new adsorption site present on the catalyst. In addition, the low-temperature

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hydrogen desorption peak is much smaller than that of Ni1Co3B catalyst. These results indicate

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that the introduction of Cu could decrease the number of hydrogenation active site on Ni1Co3B

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structure but favor to create new hydrogenation active site. It might be ascribed to the

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well-dispersed Cu nanoparticles on the CuNiCoB amorphous alloy nanosheets as above mentioned

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HRTEM observation.

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Catalyst Screening. The screening of the catalysts for the conversion of BL to GVL was

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carried out in cyclohexane (CH) solvent as a substitute for the frequently-used 1,4-dioxane and

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alcohols in liquid-phase hydrogenation.15 The good solubility of BL in CH solvent that is

18

beneficial for the mass transfer during reaction. CH is low cost and low toxicity, which is more

19

economic, safer and more environmental friendly than 1,4-dioxane for large scale production.

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However, when using alcohols such as methanol and ethanol as solvent, they are possible to react

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with levulinic acid (LA) to generate levulinate esters (LE).47 Considering these facts, CH was

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selected as the solvent for BL hydrogenation reaction.

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When Ni1Co3B catalyst was subjected to the model reaction at 200 °C, the reaction gave a 100%

2

conversion of BL but only 64% selectivity to GVL in 3 h (Table 2, entry 1). The introduction of

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Cu slightly decreased the conversion of BL with an obvious increase of GVL selectivity by 17.3%.

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As the weight percentage of Cu increased in the CuxNi1Co3B catalysts, higher GVL yield was

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obtained, 80.3% and 89.5% for Cu0.3Ni1Co3B and Cu0.5Ni1Co3B catalyst, respectively (Table 2,

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entries 3 and 4). These results indicated that increase of Cu addition may bring two advantages: (1)

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the new hydrogenation active site from well-dispersed Cu nanoparticles (Figure S2, Supporting

8

Information) could promote the transformation of the reaction intermediate for GVL formation

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(Figure 5); (2) more Cu would cooperate with NiCoB to form CuNiCoB amorphous alloy (Figure

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3 and 4), which could inhibit the aggregation of nanosheets to exhibit smaller size (Figure 2) that

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is beneficial to enhance the activity.31, 48 However, the further increase of Cu led to a lower GVL

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yield of 68.9% at BL conversion of 99% (Table 2, entry 6). It was probably caused by excessive

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addition of Cu that resulting in the coverage of CuNiCoB hydrogenation active sites by enlarged

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metallic Cu species and thereby decreased the GVL selectivity. For the CuB catalyst, the BL

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conversion decreased sharply to 18.7% with 77.1% selectivity of GVL, further confirmed that

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isolated bulk Cu species was not efficient for selective hydrogenation of GVL. Scotti et al.

17

found that very small metal Cu particles (less than 5 nm) could exhibit catalytically relevant Lewis

18

acidity to promote the esterification between the C=O double bond of GVL molecule and

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1-Pentanol. However, the CuB catalyst displayed bigger size of Cu particles (about 50 nm)

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calculated by the Scherrer equation from the XRD pattern which is consistent with the statistical

21

result of SEM, thus inhibiting the BL hydrogenation conversion.33 These results demonstrated that

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the Cu0.5Ni1Co3B catalyst was the optimum catalyst for BL hydrogenation to GVL, which showed

11

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89.5% yield of GVL in 3 h at 473 K using the dosage of 3 wt% relative to BL. In addition, the

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well-dispersed Cu nanoparticles cooperating with the CuNiCoB amorphous alloy active sites were

3

crucial to the high activity of the Cu-modified Ni1Co3B catalyst.

4

Insert Table 2 Here

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Reaction conditions optimization. The reaction temperature, initial hydrogen pressure

6

and concentration of substrate have a large effect on the reaction rate. Thus, the catalytic

7

hydrogenation of BL was carried out at different reaction temperature (ranging from 393 to 513 K)

8

(Figure 6a), different hydrogen pressure (ranging from 1.0 to 5.0 MPa) (Figure 6b) and different

9

volume ratio of BL feedstock to CH solvent (ranging from 1/24 to 5/20, mL/mL) (Figure 6c).

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When the reaction proceeded at a milder temperature (393 K), only 14.4%yield of GVL with a

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BL conversion of 71.7% was achieved. The BL conversion obviously increased to 99% when the

12

reaction temperature was increased to 413 K. With the further increase of the reaction temperature,

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the BL conversion and GVL yield continuously increased until a maximum GVL yield of 89.5%

14

was obtained at 473 K. This could be possibly attributed to the increase of the reaction rate at

15

higher reaction temperature.31 Further increasing the reaction temperature to 513 K led to the

16

decrease of GVL yield to 75.4% but almost unchanged BL conversion. It was likely that the GVL

17

product might undergo some side reactions and generate unknown products at higher reaction

18

temperature.31 Therefore, the reaction temperature was kept at 473 K for the following reaction.

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Meanwhile, the reaction was also performed to investigate the influence of the initial hydrogen

20

pressure on the BL hydrogenation reaction (Figure 6b). With the increase of hydrogen pressure

21

from 1 MPa to 3 MPa, the BL conversion increased from 88.5% to 99.7%, accompanying with the

22

increase of GVL selectivity from 85.8% to 89.8%. The higher hydrogen pressure enhanced the 12

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dissolved hydrogen concentration in CH solvent, so much more hydrogen molecules could easily

2

access CuNiCoB amorphous alloy active sites, which accounted for the increased reaction rate at

3

elevated pressure from 1 to 3 MPa. At 3 MPa, the yield of GVL reached the highest value.

4

Increase of initial hydrogen pressure to 5 MPa led to the further hydrogenation of little GVL to

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produce some byproducts. According to the GC-MS analysis result (Figure S3 and S4a,

6

Supporting Information), the generated byproduct could be attributed to 1,4-PDO and few butyl

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valerate (BV) from GVL.33 Therefore, a desired initial H2 pressure of 3 MPa for reducing the

8

practical cost and promoting the yield of GVL from BL hydrogenation was employed for the

9

catalytic measurements in this work.

10

Furthermore, the effect of volume ratio of BL feedstock to CH solvent on the BL hydrogenation

11

performances was also investigated (Figure 6c). As can be seen, under the dosage of catalyst was

12

kept 3 wt% of mass of BL unchanged, no matter what the volume ratio of BL to CH was, BL

13

conversion almost was close to 100%. However, the selectivity of GVL showed a decrease,

14

especially for the obtained product at VBL/CH= 2/23. This can be due to the further transformation

15

of GVL to 1,4-PDO (Figure S3 and S4a, Supporting Information). Du et al.

16

1,4-PDO and 2-methyltetrahydrofuran (2-MTHF) could be selectively produced from the

17

hydrogenation of GVL over the Cu/ZrO2 catalyst. Moreover, depending on the reaction conditions,

18

it was feasible to convert GVL to 2-MTHF in excellent yields using the same catalyst system with

19

a slight modification of the preparation conditions via one-step direct carbonyl reduction of the

20

GVL molecule. From this point of view, 1,4-PDO may be generated with high yield from GVL

21

over some materials supported Cu0.5Ni1Co3B catalyst. In the present work, the ideal volume ratio

22

of BL to CH for GVL production is 1/24 (mL/mL).

13

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33

reported that

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1

Effect of Reaction Time. In order to provide convenience for sampling on time during the

2

reaction and avoid the influence of sampling on the character of reaction system, the volume of

3

overall material was increased to 60 mL, in which the volume ratio of BL/CH was 1/11. The

4

effects of reaction time on the reaction conversion and selectivity over Cu0.5Ni1Co3B catalyst were

5

investigated as shown in Figure 7. The reaction reached rapidly the maximum 84.3% yield of

6

GVL in 1 h and the BL conversion gradually increased to 100% as the reaction proceeded to 4 h.

7

However, further prolonging the reaction time resulted in the obvious decrease of GVL yield,

8

which was correlated to that GVL could be further hydrogenated to 1,4-PDO as mentioned above.

9

These results highlight that the Cu0.5Ni1Co3B catalyst could be efficient for one-pot catalytic

10

conversion of BL to 1,4-PDO through the GVL intermediate under suitable reaction conditions.

11

Furthermore, the maximum GVL yield was obtained in 1 h over Cu0.5Ni1Co3B catalyst with 3 wt%

12

relative to BL, which is faster but using much less catalyst than those reported in literatures.26-27, 31

13

Based on the above experiments, the BL hydrogenation rate and product composition over

14

Cu0.5Ni1Co3B catalyst can be adjusted easily by manipulating the concentration of BL and the

15

reaction time.

16

Stability of the Catalyst. To investigate further the stability of the Cu0.5Ni1Co3B catalyst,

17

catalyst recovery and reuse test for the BL hydrogenation to GVL was performed under the

18

optimized reaction condition (VBL/CH= 1/24, BL 5.66 mmol, catalyst 0.0292 g, 473 K, H2 3 MPa,

19

800 rpm, 3 h). After each run, the catalyst was separated by a magnet (Figure S5, Supporting

20

Information), washed with absolute ethyl alcohol and then applied in the next run by adding little

21

once catalyst with the lost amount. The results are presented in Figure 8. As can be seen that,

22

though the catalyst activity showed a slow decrease, the BL conversion were all above 93% in five

14

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cycles, with a maximum GVL yield of 93.2% in the third run. Meanwhile, the GVL selectivity

2

showed a gradual increase from 89.8% to 95%. These results indicated that the Cu0.5Ni1Co3B

3

catalyst was stable and convenient to be separated for repeating use.

4

To figure out the change of the catalyst during the hydrogenation reaction, the used catalyst

5

Cu0.5Ni1Co3B catalyst after five catalytic cycles was collected and characterized. TEM

6

characterization of the used Cu0.5Ni1Co3B catalyst showed that main crystalline particles were

7

formed with interconnected edges (Figure S2d, Supporting Information). The bright dots over the

8

diffraction loop on the inserted SAED image indicated the crystallization of some CuNiCoB

9

amorphous alloy to Cu-Ni-Co ternary alloy with particle size centered at about 45.8 nm due to the

10

loss of B and electron transfer. It can be proved by the newly generated Cu-Ni-Co ternary alloy

11

phase which is observed on the XRD pattern (Figure 9) of used Cu0.5Ni1Co3B catalyst with higher

12

SBET and VP but smaller Dp than the fresh catalyst, suggesting the destroy of amorphous alloy

13

structure. Different groups of lattice fringes are displayed on the magnified views of Cu-Ni-Co

14

ternary alloy particle (Figure S2f, Supporting Information). In addition, the used catalyst particle

15

was easily separated by a magnet due to its magnetism feature, while the fresh catalyst powder

16

was still distributed in ethanol within the same separation period (Figure S5, Supporting

17

Information). It can be concluded that the CuNiCoB amorphous alloy active sites had been

18

transformed into CuNiCo ternary alloy active sites which plays an important role in maintaining

19

the GVL production ability during the recovery and reuse tests.

20

Another factor that caused the loss of activity of the catalyst could be the changes of metallic

21

species. XPS spectra of the fresh and used Cu0.5Ni1Co3B catalysts for five times were employed to

22

investigate the nature of metal species. The Ni 2p and Co 2p spectra intensity of used catalyst was

15

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1

similar with that of fresh Cu0.5Ni1Co3B catalyst (Figure 3), but compared to fresh Ni1Co3B catalyst,

2

the BE of Ni0 and Co0 obviously shifted to higher values. Meanwhile, the peaks belonged to Be

3

and Bo was almost disappeared, which indicating the strong loss of B species. The ICP test result

4

(Table S1, Supporting Information) of the used catalyst provided evidence. The loss of B species

5

of catalyst during the recyclability tests is likely to bring some environmental issues when boracic

6

waste water was generated. As mentioned above, the recycled catalyst was washed with absolute

7

ethyl alcohol before the next reuse. It was implied that the lost B species existed only in the

8

washing liquid or the product solution. For the GVL production in large scale, the lost B species

9

could be recycled by the distillation method from the washing liquid or the product solution due to

10

different boiling point. Therefore, in the present work where no waste water was discharged, the

11

loss of B species did not have an effect on the environment.

12

In our previous study, the similar transformation of NiCoB amorphous alloy to Co-Ni alloy was

13

happened in the selective hydrogenation of furfural to FA over the supported NiCoB amorphous

14

alloy catalyst.49 Furthermore, the loss of B species was effectively improved by loading the NiCoB

15

amorphous alloy on an acid activated attapulgite (H+-ATP) support. Therefore, it is essential to

16

optimize the preparation method of Cu0.5Ni1Co3B catalyst for the purpose of alleviating the loss of

17

B species and maintain its hydrogenation ability in the future. From Cu 2p and Cu LMM Auger

18

spectra (Figure 4), it can be seen that the concentration of Cu species on surface of used catalyst

19

was obviously increased compared to fresh catalyst. The major valent state of Cu remained

20

Cu0/Cu+, while CuO was obtained after the reaction. The decrease in surface atomic ratio of

21

Cu0/Cu+ (Cu LMM spectra) might be a factor that influencing the activity of the used catalysts.

22

CuO might be formed in the reaction or partial oxidation of Cu exposed to the air.50

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Comparing the Cu0.5Ni1Co3B amorphous alloy catalyst with other catalysts (Table S2,

2

Supporting Information), Cu0.5Ni1Co3B presented the lowest catalyst dosage relative to substrate

3

and comparable hydrogenation efficiency for producing GVL from BL hydrogenation in short

4

reaction time. Particularly, the outstanding selectivity and yield to GVL were achieved over the

5

Cu0.5Ni1Co3B catalyst, which was comparable with that of Ru/C.51 However, a significant

6

decrease in the activity of reused Ru/C from 95% to 83% after 4th reuse was observed. According

7

to above comprehensive measurements, magnetic Cu0.5Ni1Co3B amorphous alloy catalyst could be

8

an efficient candidate for catalytic conversion of BL into GVL. In addition, through optimizing the

9

reaction conditions and preparation method of the catalyst, BL could be directly converted into

10

1,4-PDO over mimic amorphous alloy structures.

11

 CONCLUSION

12

A series of cheap and magnetic CuNiCoB amorphous alloy catalysts were developed through

13

chemical reduction method. The optimized composition was manipulated as Cu0.5Ni1Co3B to

14

obtain the highest GVL yield of 89.5% with BL conversion of 99.7% at 473 K, 3.0 MPa H2 using

15

3wt% catalyst dosage relative to BL in 3 h. Characterization of the fresh and spent catalyst showed

16

that the CuNiCoB amorphous alloy nanosheets with well-dispersed Cu nanoparticles were

17

responsible for the superior catalytic performance on the structure. The transformation of

18

CuNiCoB active center to Cu-Ni-Co ternary alloy active center allowed the considerable stability

19

such as enabling repeating use of catalyst in at least five cycles. These features together with the

20

convenience in magnetic separation of used catalyst from liquid reaction systems gifted CuNiCoB

21

amorphous alloy structures a potential as efficient candidate catalyst for producing value-added

17

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1

chemicals from levulinic compound mediated biomass transformations.

2

 ASSOCIATED CONTENT

3

S Supporting Information ○

4

The Supporting Information is available free of charge on the ACS Publications website at

5

DOI:XXXXXXXXXX.

6

Materials, preparation and characterization of catalysts and product analysis; Additional

7

details on the characterization of the catalysts, GC-MS analysis results and catalytic performances

8

comparison.

9

 AUTHOR INFORMATION

10

Corresponding Authors

11

* Tel. /fax: +86 79183969332. E-mail: [email protected] (D. Zhao);

12

** Tel. /fax: +86 20 37213916. E-mail: [email protected] (X. Chen).

13

Notes

14

The authors declare no competing financial interest.

15

 ACKNOWLEDGMENTS

16

This work was supported by the project of National Natural Science Foundation of China

17

(21003071, 21406229, and 21563018), the project of Guangdong Provincial Key Laboratory of

18

New and Renewable Energy Research and Development (Y709jh1001), the Project of Jiangsu

19

Province Science and Technology (BE2014101), and the Science and Technology Program of

18

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Guangzhou, China (201707010240).

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transfer

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49. Guo, H.; Zhang, H.; Zhang, L.; Wang, C.; Peng, F.; Huang, Q.; Xiong, L.; Huang, C.; Ouyang,

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X.; Chen, X.; Qiu, X., Selective hydrogenation of furfural to furfuryl alcohol over acid activated

5

attapulgite-supported NiCoB amorphous alloy catalyst. Ind. Eng. Chem. Res. 2018, 57 (2),

6

498-511.

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50. Guo, J. H.; Xu, G. Y.; Han, Z.; Zhang, Y.; Fu, Y.; Guo, Q. X., Selective conversion of furfural

8

to cyclopentanone with CuZnAl catalysts. ACS Sustain. Chem. Eng. 2014, 2 (10), 2259-2266.

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51. Hengne, A. M.; Biradar, N. S.; Rode, C. V., Surface species of supported Ruthenium catalysts

10

in selective hydrogenation of levulinic esters for bio-refinery application. Catal. Lett. 2012, 142

11

(6), 779-787.

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1

 Table of Contents (TOC) graphic

2

3

Butyl levulinate was efficiently hydrogenated to gamma-valerolactone in short time

4

over a stable and magnetic Cu0.5Ni1Co3B amorphous alloy catalyst with lower dosage.

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Page 26 of 38

Page 27 of 38 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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1

2 3

 Synopsis

Gamma-valerolactone (GVL) was efficiently synthesized from butyl levulinate (BL) in short time over a stable and magnetic Cu0.5Ni1Co3B amorphous alloy catalyst.

27

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Page 28 of 38

1

 Tables

2

Table 1 Textural Properties and Bulk Composition of the Catalysts bulk comp. (wt%)d

SBETa (m2/g)

VPb (cm3/g)

DP c (nm)

Cu

Ni

Co

B

Ni1Co3B

18.0

0.124

27.6

0.0

24.3

66.5

9.2

Ni1Co2.7B2.1

Cu0.1Ni1Co3B

24.4

0.131

21.4

2.4

22.6

66.0

9.1

Cu0.1Ni1Co2.9B2.2

Cu0.3Ni1Co3B

32.8

0.124

15.1

6.7

21.7

62.7

9.0

Cu0.3Ni1Co2.9B2.2

theoretical catalyst

actual catalyst

Cu0.5Ni1Co3B 20.7 0.131 25.3 10.8 20.6 60.3 8.4 Cu0.5Ni1Co2.9B2.2 Cu1.0Ni1Co3B 17.3 0.103 23.7 19.1 19.0 54.3 7.7 Cu0.9Ni1Co2.9B2.2 Cu2.0Ni1Co3B 29.5 0.123 16.7 31.3 16.0 45.9 6.8 Cu1.8Ni1Co2.9B2.3 CuB 18.8 0.113 24.0 100.0 0.0 0.0 0.0 Cu1.0 a b c d BET surface area. Total pore volume. Average pore size. Determined by ICP-OES.

3

Table 2 Screening of the Catalysts for BL Hydrogenation to GVLa catalyst GVL sel. (%) BL conv. (%) Ni1Co3B 64.0 100 Cu0.1Ni1Co3B 81.3 97.1 Cu0.3Ni1Co3B 81.9 98.1 Cu0.5Ni1Co3B 89.8 99.7 Cu1Ni1Co3B 81.4 99.0 Cu2Ni1Co3B 69.6 99.0 CuB 77.1 18.7 a Reaction conditions: VBL/CH= 1/24 (mL/mL), catalyst 0.0292 g (3 wt%), 200 oC, 3 MPa H2, 800 rpm, 3 h.

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 Figure captions

2

Figure 1. XRD patterns of fresh catalysts.

3

Figure 2. FE-SEM images of fresh catalysts with magnification of 100,000X.

4

Figure 3. Ni 2p, Co 2p, and B 1s XPS spectra of fresh Ni1Co3B catalyst (a), fresh (b) and used (c)

5

Cu0.5Ni1Co3B catalyst after five times recovery and reuse.

6

Figure 4. Cu 2p and Cu LMM XPS spectra of fresh (a) and used (b) Cu0.5Ni1Co3B catalyst after

7

five times recovery and reuse.

8

Figure 5. H2-TPD profiles of fresh (a) Ni1Co3B catalyst and (b) Cu0.5Ni1Co3B catalyst.

9

Figure 6. Influences of (a) reaction temperature, (b) initial hydrogen pressure and (c) volume ratio

10

of BL to CH on BL hydrogenation performances over Cu0.5Ni1Co3B catalyst.

11

Figure 7. Influences of reaction time on BL hydrogenation performances over Cu0.5Ni1Co3B

12

catalyst.

13

Figure 8. Effect of Cu0.5Ni1Co3B catalyst recovery and reuse on BL hydrogenation performances.

14

Figure 9. XRD patterns of (a) fresh and (b) used Cu0.5Ni1Co3B catalyst after five times recovery

15

and reuse.

29

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Energy & Fuels

Cu Cu2O

(a) (b) (c)

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 30 of 38

(d) (e) (f)

(g)

5

15

25

35

45

o

55

65

75

2 Theta ( ) Figure 1. XRD patterns of fresh catalysts. (a) Ni1Co3B; (b) Cu0.1Ni1Co3B; (c) Cu0.3Ni1Co3B; (d) Cu0.5Ni1Co3B; (e) Cu1.0Ni1Co3B; (f) Cu2.0Ni1Co3B; (g) CuB.

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Figure 2. FE-SEM images of fresh catalysts with magnification of 100,000X. (a) Ni1Co3B; (b) Cu0.1Ni1Co3B; (c) Cu0.3Ni1Co3B; (d) Cu0.5Ni1Co3B; (e) Cu1.0Ni1Co3B; (f) Cu2.0Ni1Co3B; (g) CuB.

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Ni 2p Ni02p 3/2 0

852.5

Ni 2p1/2

2+

Intensity (a.u)

Ni 2p3/2

2+

Ni 2p1/2

satellite

(a)

satellite 869.7

(b) 870.0

852.7

(c)

870.3 853.0

845

850

855

860

865

870

875

880

885

Binding Energy (eV)

Co 2p Co02p3/2 778.0 2+

2+

Intensity (a.u)

Co 2p3/2

0

Co 2p1/2

Co 2p1/2

satellite

satellite 793.0

(a)

793.2

(b)

793.5

(c)

778.2 778.6

770

775

780

785

790

795

800

805

810

815

Binding Energy (eV)

Bo

Be

B 1s

191.9

191.7

187.7

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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(a) 187.9

(b) (c) 180

182

184

186

188

190

192

194

196

Binding Energy (eV)

Figure 3. Ni 2p, Co 2p, and B 1s XPS spectra of fresh Ni1Co3B catalyst (a), fresh (b) and used (c) Cu0.5Ni1Co3B catalyst after five times recovery and reuse.

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Cu 2p 2+

Cu 2p3/2

Intensity (a.u)

932.9

2+

Cu 2p1/2 satallite

953.0 satallite 0

(b)

+

Cu /Cu 2p3/2 932.3 0

+

Cu /Cu 2p1/2 952.2

925

930

935

940

945

950

(a)

955

960

965

Binding Energy (eV) +

0

Cu LMM

Cu

2+

Cu /Cu

570.6

568.6

(b)

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

Energy & Fuels

0

Cu

+

Cu

569.8 567.9 (a)

564

568

572

576

580

Binding Energy (eV)

Figure 4. Cu 2p and Cu LMM XPS spectra of fresh (a) and used (b) Cu0.5Ni1Co3B catalyst after five times recovery and reuse.

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Energy & Fuels

458

Hydrogen desorption (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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455

576

(b)

(a) 323

423

523

623

723

823

923

1023

Temperature ( K )

Figure 5. H2-TPD profiles of fresh (a) Ni1Co3B catalyst and (b) Cu0.5Ni1Co3B catalyst.

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100

(a)

80

BL GVL

60

VBL/CH= 1/24 (mL/mL), mcat.= 3 wt%

40

3 MPa H2, 800 rpm, 3 h 20

0 373

393

413

433

453

473

493

513

533

o

BL conversion or GVL selectivity (%)

Reaction temperature ( C )

100

(b)

90

80 BL GVL

VBL/CH= 1/24 (mL/mL), mcat.= 3 wt% 473 K, 800 rpm, 3 h

70

60

1

2

3

4

5

Reaction pressure (MPa)

BL conversion or GVL 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

Energy & Fuels

BL conversion or GVL selectivity (%)

Page 35 of 38

100

(c)

BL GVL

90

80

mcat.= 3 wt%

70

60

473 K, 3 MPa H2, 800 rpm, 3 h

1/24

2/23

3/22

5/20

Volume ratio of BL to CH (mL/mL)

Figure 6. Influences of (a) reaction temperature, (b) initial hydrogen pressure and (c) volume ratio of BL to CH on BL hydrogenation performances over Cu0.5Ni1Co3B catalyst.

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

BL conversion or GVL selectivity (%)

Energy & Fuels

Page 36 of 38

100 90 BL GVL

80 70 60 50 40 30

VBL/CH= 1/24 (mL/mL), mcat.= 3 wt%

20

473 K, 3 MPa H2, 800 rpm

10 0

0

1

2

3

4

5

6

Reaction time (h) Figure 7. Influences of reaction time on BL hydrogenation performances over Cu0.5Ni1Co3B catalyst.

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Page 37 of 38

BL conversion

GVL yield

GVL selectivity

100

100

90

90

80

80

70

70

60

60

50

1

2

3

4

5

Yield (%)

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

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Run Figure 8. Effect of Cu0.5Ni1Co3B catalyst recovery and reuse on BL hydrogenation performances. Condition: VBL/CH= 1/24 (mL/mL), mcat.= 3 wt%, 473 K, 3 MPa H2, 800 rpm, 3 h.

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Cu Cu-Ni-Co alloy

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 38 of 38

(b)

(a)

5

15

25

35

45

55

65

75

o

2 Theta ( )

Figure 9. XRD patterns of (a) fresh and (b) used Cu0.5Ni1Co3B catalyst after five times recovery and reuse.

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