One-pot solvothermal synthesis of graphene nanocomposites for

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One-pot solvothermal synthesis of graphene nanocomposites for catalytic conversion of cellulose to ethylene glycol Kai Zhang, Guihua Yang, Gaojin Lyu, Zhixin Jia, Lucian Lucia, and Jiachuan Chen ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.9b00006 • Publication Date (Web): 09 Jun 2019 Downloaded from http://pubs.acs.org on June 9, 2019

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ACS Sustainable Chemistry & Engineering

One-pot solvothermal synthesis of graphene nanocomposites for catalytic conversion of cellulose to ethylene glycol Kai Zhang†, Guihua Yang*†, Gaojin Lyu†, Zhixin Jia†, Lucian A. Lucia†,‡, Jiachuan Chen*†

†

State Key Laboratory of Bio-based Materials and Green Papermaking/Key Lab of Pulp &

Paper Science and Technology of Education Ministry of China, Qilu University of Technology (Shandong Academy of Sciences), Ji’nan, Shangdong Province, P.R.China, 250353 ‡

Department of Forest Biomaterials/College of Natural Resources, North Carolina State

University, Raleigh, USA, 27606 *Corresponding author: Qilu University of Technology (Shandong Academy of Sciences), China E-mail: [email protected]; Qilu University of Technology (Shandong Academy of Sciences), China E-mail: [email protected];

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Abstract: Three nanocomposite catalysts such as Ru/graphene, WO3/graphene and Ru-W18O49/graphene were synthesized by solvothermolysis to increase the ethylene glycol (EG) yield from the hydrothermal conversion of cellulose. The morphology and composition of the nanocomposites were characterized by XRD, XPS, EDS, BET, SEM, and TEM. The results showed a new nanocomposite made up of graphene nanosheets that supported in situ growth of Ru nanoparticles with an average size of ~ 7 nm and W18O49 nanowires with an average diameter of ~ 5 nm. Compared with Ru/graphene and WO3/graphene nanocomposites, Ru-W18O49/graphene showed nearly unit conversion of cellulose at a yield of 62.5% of EG when the reaction was carried out at 245oC for 60 min. Moreover, it could be used at least three times with the high yield of EG in the range of 48.7% to 62.5%, however, with the increase of recycled runs, the tungsten species on the surface of graphene would be slowly dissolved in the aqueous solution, then the selectivity of this catalyst would gradually decrease. Besides, the one-pot solvothermal synthesis enabled reduction of Ru ions, graphene oxide, and growth of W18O49 nanowires to thus provide a simple approach for the preparation of the graphene-based nanocomposite catalysts. Key words: Graphene; Nanocomposite; Sustainability; Cellulose; Ethylene Glycol


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Introduction Cellulose is among the most abundant renewable carbon sources on earth that can be represented as a syndiotactic polymer composed of glucose units linked by β-1,4-glycosidic bonds. From the perspective of sustainability, it is considered as a strategic alternative to fossil resources for production of fuel and chemicals.1-2 However, cellulose has a relatively high O/C ratio, in order to preserve the majority of the oxygen-functional groups, it is highly atom-economic to transform cellulose to oxygenates.3 Ethylene glycol (EG) is a very important bulk chemical that is mainly produced using petroleum so far.4 Recently, non-petroleum routes for its high yield production from renewable resources have attracted great attention because they will greatly reduce the emission of greenhouse gases and dependence on petroleum.5 To date, catalysts consisting of tungsten species and a transition metal have been deemed as the most active for conversion of cellulose to EG.5-11 At first, Na Ji et al 5 reported that EG can be directly produced from cellulose in such a high yield of 61% by using 2%Ni-30%W2C/AC-973 as catalyst, which opened a new avenue for the production of valuable chemicals from lignocellulose. Ming-Yuan Zheng et al 9 developed a series of transition-tungsten (M-W) metal bimetallic catalysts for the formation of EG from cellulose, they confirmed that W acted as the active metal to selectively catalyze C-C bond cleavage of cellulose-derived sugars, and discovered that transition metals played an important role in the hydrogenation reactions of unsaturated intermediates. Yueling Cao et al10 prepared a 3%Ni-15%WO3/SBA-15 catalyst that was applied to the hydrogenolysis of cellulose, and 70.7% yield of EG was obtained with a 100% conversion of cellulose. Among the reported catalysts so far, various similar catalysts have been developed, although great progress has been



made in the one-pot conversion of cellulose to EG by using those catalysts, the standard procedure of preparing those catalysts is very complex because the impregnation of support materials with solutions of metals, drying and reduction under H2 flow at high temperatures are indispensable. 5-13 In addition to active sites, the support of catalyst is necessary due to its key role in dispersion, accessibility, and stability of active sites.6 For example, when a 3D mesoporous carbon (MC) was used as the support to disperse tungsten carbide, the EG yield reached 75% or 73% with or without the promotion of transition metals. 3D MC support facilitated the dispersion and accessibility of active component and showed preferential adsorption for glycosidic bonds in cellulose.7 Over the past ten years, supports such as active carbon (AC),5, 6, 9 MC,7 Al2O3,8 SBA-15,10 NbOPO4,11 carbon nanofibers (CNF),12 carbon nanotube (CNT),13 and so on have been used in the green synthesis reaction of EG. Among various commercially available supports, carbon materials are preferred due to their high resistance to acid and base attack, their excellent stability and chemical inertia under hydrothermal conditions.14 Graphene is a two-dimensional atomic crystal, which has been widely investigated for catalysis. 15, 16

It consists of a single layer of sp2-hybridized carbons that is the basic structural element for 0

D fullerenes, 1 D carbon nanotubes, and 3 D bulk graphite.17 It possesses physico-chemical features that endow its catalysts with a very high surface area conducive to dispersion of active sites, its mechanical properties have high stability and durability, and high thermal conductivity and electric conductivity.18 In addition, graphene contains some -COOH and -OH groups which can exhibited good catalytic performance for the hydrolysis of cellulose.19 For this work, in order to explore a simple approach to prepare high-performance catalysts for selective conversion of cellulose to EG, graphene oxide (GO) was used as precursor, while Ru


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nanoparticles and tungsten species were loaded onto its surface in a hydrothermal reduction reaction by using EG and water as solvents and reactants. The nanocomposites were characterized and used for catalytic conversion of cellulose in a high-pressure hydrothermal reaction revealing that the RuW18O49/Graphene nanocomposite is highly efficient and promising catalyst for the production of bio-EG.

Experimental Materials Unless otherwise stated, all chemicals and feedstock in this experiment were commercially available and used without further purification. Microcrystalline cellulose (Acros, average size: 50 μm) and tungsten (Ⅵ) chloride (WCl6, 99.9%) were purchased from Beijing Innochem Science & Technology Co. Ltd. Ruthenium (Ⅲ) chloride hydrate (RuCl3·nH2O, Ru 38%) and regents of chromatographically pure ( ≧ 99.5%) were provided by Aladdin Industry Inc. Ethylene glycol (C2H6O2, 99.0%) of chemical pure was obtained from Tianjin Kemiou Chemical Reagent Co. Ltd. GO was made by a modified Hummers method from Institute of coal chemistry (Chinese Academy of Science) in Shanxi Province. Catalysts preparation Preparation of Ru/graphene, WOx/graphene, and Ru-WOx/graphene composites were as follows: EG and deionized water were used as solvents and reactants for the preparation of composites by a one-pot solvothermal process.20 Ruthenium (Ⅲ) chloride hydrate (0.02 g or 0 g) and graphene oxide (0.1 g) were dissolved in a 30 g water solution, tungsten (VI) chloride (0 g or 0.09 g) was dissolved in a 40 mL EG solution, and the solutions were processed at 40 kHz in an SB-100DT bath-type



ultrasonic cleaner for 30 min; the EG solution was added dropwise to the water solution under rapid agitation, and the pH value of the mixed solutions were tested. Then, the mixture was transferred to a Teflon-lined autoclave and heated at 200°C under autogenous pressure for 3 h. The obtained solid products were filtered and washed with distilled water several times. Finally, the composites were vacuum dried at 60°C overnight. Catalysts characterization X-ray diffraction (XRD) pattern of material was recorded on a D8 ADVANCE (Bruker) diffractometer equipped with a Cu Kα radiation source (0.15418 nm), operating at 40 kV and 40 mA, and the step length was 0.02° with a scanning rate of 0.1 s/step. X-ray photoelectron spectra (XPS) was recorded using an X-ray photoelectron spectrometer (ESCALAB 250XI, Thermo Scientific) with non-monochromatized Al Kα radiation as the excitation source. Nitrogen adsorption-desorption measurements were performed at 77 K with a Micromeritics ASAP2010 instrument. Prior to the measurements, the samples were degassed at 523 K for 5 h. The morphology and chemical composition of the composites were determined by scanning electron microscopy (SEM, Merlin, Zeiss) with an energy dispersive X-ray detector (EDX, X-MaxN20), and by transmission electron microscope (TEM, JEM-2100F, JEOL) equipped with a FEG source and an Inca X-ray analysis system. Catalytic conversion of cellulose Hydrothermal conversion of cellulose to EG was carried out in a 100 mL high-pressure stainlesssteel autoclave (Series 5100 HP Compact Reactors, Parr Instrument Company). Briefly, the catalyst (0.05 g), water (50 g) and microcrystalline cellulose (0.5 g) were transferred into the reactor. Then, the reactor was first purged with H2 to remove air from the system at atmospheric pressure and the


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reactor was subsequently pressurized with hydrogen at a pressure of 6 MPa. After sealing the reactor, the mixture was heated up to reaction temperatures of 245 °C and maintained for 60 min at a constant stirring rate of 1000 rpm. After reaction, the reactor was rapidly cooled down to room temperature with cold water. The liquid products were collected after permeation through a membrane filter with an average pore size of 0.45 μm, and the components in the liquid phase were analyzed using a highperformance liquid chromatography (Waters e2695, RI detector, Shodex SC100 column) and an ultra-performance liquid chromatography instrument (Agilent 1290, Agilent Technologies, Agilent 6540 MS, sugar column). In addition, the components of gas phase were detected using gas chromatography (Techcomp GC7890, TCD detector, GDX104 column). Besides, solid residue obtained after filtration was washed with deionized water, followed by drying in a vacuum oven overnight at 105°C. The yields of products were calculated as the ratio of weight of products determined and the weight of cellulose sealed into the reactor. The conversion rate of the cellulose was determined by the weight difference of dry filter cake before and after the reaction. Typical absolute error in the catalytic experiments was within ±3%.

Results and discussion 3.1 Characterization of synthesized composites The crystalline phases of synthesized composites were analyzed by XRD (Fig. 1). The XRD pattern of Ru/graphene (a) showed a strong diffraction peak of graphene (002) at 2θ=26.5°, which indicated the formation of graphene from the thermal reduction of graphite oxide by the solvents. 20,21

Moreover, two peaks at 2θ=38.4°, 44.0° were observed, which could be assigned to the (100),

(101) diffractions of metallic Ru (JCPDS 06-0663),22 and the broadened diffraction peaks of Ru



indicated the formation of nanosized Ru particles on graphene nanosheets. It can be seen that the XRD pattern (b) of WOx/graphene was highly crystalline and all peaks well matched the JCPDS file No.43-1035 corresponding to monoclinic WO3,23 which confirmed the production of WO3 from the hydrolysis of tungsten (Ⅵ) chloride, whereas the diffraction peak of graphene could not be shown clearly in XRD patterns of WO3/graphene duo to interference of overlapping diffraction peaks. Additionally, the XRD pattern of Ru-WOx/graphene (c) exhibited two sharp reflections, matching well with the (010) and (020) reflections of monoclinic W18O49 (JCPDS 71-2450)24 that indicated the formation of W18O49 from the solvothermal reaction of tungsten species. It was noteworthy that the diffraction pattern of Ru-W18O49/graphene contained a weak signal of Ru at 2θ=38.4°, which could be attributed to homogeneous dispersion of Ru nanoparticles on graphene.

Fig. 1 XRD patterns of of Ru/Graphene (a), WOx/Graphene (b) and Ru-WOx/Graphene (c). The surface electronic composition and elemental valence of the Ru/Graphene, WO3/Graphene and Ru-W18O49/Graphene were further studied by XPS. As shown in Fig. 2a, three nanocomposites had two obvious peaks centered at the binding energies of 284.6 and 532.8 eV, which were assigned to C 1s and O 1s XPS signals, respectively. The survey XPS spectrum for the Ru/Graphene showed


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the presence of elemental Ru, for the WO3/Graphene, the existence of W could be revealed, while for the Ru-W18O49/Graphene, elemental Ru and W could be detected simultaneously. Fig. 2b showed high resolution XPS spectra of Ru 3p of Ru/Graphene and Ru-W18O49/Graphene, the Ru 3p spectrum exhibited peaks at 463.36 and 485.08 eV and could be attributed to 3p3/2 and 3p1/2 of the metallic state of Ru, indicating the reduction of RuCl3 in the water-ethylene glycol system.25 The high-resolution tungsten 4f XPS spectrum were shown in Fig. 2c. It can be seen that, for the WO3/Graphene, the symmetric features at binding energies of 37.9 and 35.8 eV were assigned to W 4f5/2 and W 4f7/2 of W6+ oxidation state in WO3, respectively.26,27 While for the RuW18O49/Graphene, the core-level XPS spectrum of W 4f could be seen, two peaks with binding energies of 34.8 and 37.1 eV, which belonged to W 4f7/2 and W 4f5/2 of the W5+ formal oxidation state, and the other two peaks at 37.9 and 35.8 eV corresponding to W6+.26-28 These results agreed well with those found by an XRD measurement (Fig. 1).

Fig. 2 (a) XPS spectra of Ru/Graphene, WO3/Graphene and Ru-W18O49/Graphene; (b) high resolution Ru 3p spectrum of Ru/Graphene and Ru-W18O49/Graphene; (c) high resolution W 4f spectrum of WO3/Graphene and Ru-W18O49/Graphene The SEM images of composites were shown in Fig. 3. It can be seen that three composites had a



similar sponge-type structure with a mass of folds and crimps that consisted of agglomerated and overlapped graphene films without a visible particle on the surface of layered structures after increasing magnification, which may illustrate the production of extremely small particles and homogeneous dispersion of particles. Fig. 3d was the EDX spectrum taken from a random surface on Ru-W18O49/graphene (Fig. 3c). The elementary composition contained C, O, W and Ru, indicating the phase purity of Ru-W18O49/graphene. The average concentrations of Ru and W of RuW18O49/graphene estimated by EDS quantitative analysis software (Oxford Instrument) were 7.35% and 37.06%, respectively, which were little higher than the intended concentrations (5% Ru-30% W18O49/graphene) because the reactive metals mainly dispersed on the surface of graphene nanosheets.

Fig. 3 SEM images showing the surface morphology of Ru/graphene (a), WO3/graphene (b), RuW18O49/graphene (c) and EDX spectrum (d) of Ru-W18O49/graphene composite.


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Fig. 4a-c showed the TEM images of Ru/graphene (a), WO3/graphene (b), Ru-W18O49/graphene (c). It can be seen that there were huge differences in morphology of supported metals among the three samples. For Ru/graphene composite shown in Fig. 4a, Ru nanoparticles were homogeneously deposited on the surface, consistent with XRD characterization with an average size of Ru nanoparticles of ~ 3 nm. The WO3/graphene displayed WO3 platelets with micrometer size that flocculated on the surface of graphene nanosheets in Fig. 4b. Remarkably, Fig. 4c showed a unique surface morphology of Ru-W18O49/graphene composite; more specifically, ultrathin graphene nanosheets (see arrow area) were decorated with Ru nanoparticles and numerous W18O49 nanowires. Specifically, in comparison with the morphology of Ru/graphene in Fig. 4a, the Ru nanoparticles on the Ru-W18O49/graphene nanocomposite were larger and dominated with an average size of ~ 7 nm and good dispersion on graphene nanosheets. While the W18O49 nanowires were uniformly scattered on nanosheets with an average length of ~ 200 nm and an average diameter of ~ 5 nm. Additionally, the crystal growth direction of the W18O49 nanowires was determined by using highresolution TEM (HRTEM) analysis. As shown in Fig. 4d, d-spacing of the lattice fringes is 0.37 nm, corresponding to (010) crystallographic planes of the monoclinic phase W18O49, which confirmed that the W18O49 nanowires were crystalline and grew along the [010] direction.29



Fig. 4 TEM images of Ru/graphene (a), WO3/graphene (b), Ru-W18O49/graphene (c) and HRTEM images of Ru-W18O49/graphene (d). Catalytic conversion of cellulose to EG Three nanocomposites were used as catalysts for the selective conversion of cellulose to EG under hydrothermal reaction. Table 1 showed the results of cellulose conversion and yields of some products. Overall, cellulose degraded at least 73.5% in 60 min, but the final product distribution differed with different nanocomposites under the same reaction conditions. According to the results from HPLC, UPLC-MS and GC, the compositions of the other products are very complex, containing CO, CO2, erythritol, glucose, glycerol, anhydroglucose, oligosaccharide, and so on. For Ru/Graphene catalyst, EG was the main product at a 2.5% yield, and the yields of the other polyols were lower than 1.0%, illustrating the poor catalytic activity of the catalyst. For the WO3/graphene as the catalyst, the main products were 1,2-BG and EG with yields up to 6.4% and 6.0%, respectively, and the cellulose conversion increased to 84.1%, while trace amounts of other polyols were obtained.


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For those two catalysts, a mass of unsaturated compounds is contained in the liquid by Fehling’s tests. Ru-W18O49/graphene catalyst was the most selective for the production of EG and sorbitol having yields up to 61.5% and 7.4%, respectively, at 245°C with complete conversion of cellulose. Ru-W18O49/graphene showed excellent catalytic selectivity among the three catalysts for cellulose conversion into EG, the reason may be Ru-W18O49/graphene resulting more exposure of active surface area and uniform dispersion of active metal nanoparticles. Table 1 Results of cellulose conversion and yields of some products. a,b Composites

Yield

Conv.

[%]

[%]

EG

1,2-PG

1,3-PG

1,2-BG

Sorbitol

Mannitol

5% Ru/Graphene

2.5

0.6

trace

0.7

0.4

trace

73.5

30% WO3/Graphene

6.0

0.1

trace

6.4

trace

trace

84.1

5% Ru-30% W18O49/Graphene

62.5

5.1

5.2

5.0

7.4

2.4

100

[a] EG: Ethylene glycol, 1,2-PG: 1,2-propylene glycol, 1,3-PG: 1,3-propylene glycol, 1,2-BG: 1,2butanediol. [b] Reaction conditions: cellulose 0.5 g, composite 0.08 g, deionized water 50 g, H2 pressure 6 MPa, time 60 min, rotate speed 1000 rpm, temperature 245oC. Catalytic conversion of cellulose into EG is a rather complex process, involving multi-step reactions.14 In combination of this study, the possible reaction steps and the effect of the various catalyst properties were discussed. First, arising both from hot water and from the tungsten species, the acid sites can catalyze the hydrolysis of cellulose to water-soluble oligosaccharides and glucose. Then, oligosaccharides and glucose undergo C-C bond cleavage to form glycolaldehyde with



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catalysis of tungsten species. Finally, hydrogenation of glycolaldehyde by Ru metal on graphene produces the end product EG. Therefore, owing to the absence of tungsten species for Ru/Graphene nanocomposite, the hydrolyzation and hydrogenolysis of cellulose were hindered, then the conversion of cellulose was the lowest among three catalysts. For WO3/Graphene catalyst, the hydrogenation reaction was affected because of lacking of a transition metal catalyst, so the EG yield was lower than Ru-W18O49/graphene. As shown in Table 2, the specific surface area of Ru/Graphene, WO3/Graphene and RuW18O49/Graphene catalysts was determined as 70.83, 43.61 and 214.33 m2/g, meanwhile, the mean pore diameter of the three catalysts was 12.92, 8.10, and 3.59 nm, respectively. Hence, the introduction of different active metals into graphene could highly affect the specific area and the mean pore diameter of nanocomposites. Comparing with Ru/Graphene nanocomposite, the existence of micron-sized WO3 platelets on the surface of graphene nanosheets could obviously decrease the specific area, the pore volume and the average pore diameter of WO3/Graphene catalyst. However, the production of W18O49 nanowires could highly increase the specific area of composite material, which would enhance the reactant accessibility and promote the reaction efficiency. Table 2 The texture properties of prepared catalysts. Surface area a

Pore volume

Pore diameter b

m2/g

cm3/g

nm

Ru/Graphene

70.83

0.23

12.92

WO3/Graphene

43.61

0.11

8.10

Ru-W18O49/Graphene

214.33

0.22

3.59

Sample

[a] The specific surface areas were calculated with BET equation.


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[b] The average pore diameters were estimated with desorption branches based on BJH model. Catalytic performance of the Ru-W18O49/graphene As shown in Fig.5, the catalytic performance of the Ru-W18O49/graphene for cellulose conversion under different conditions were studied. Fig. 5a showed the effect of temperature on the catalytic performance of conversion of cellulose. With the temperature increased from 215 to 255ºC, the EG yield exhibited a gradual increase until its maximum value at 245ºC, and then decreased about 2.14% at 255ºC. The result indicates that the formation of EG is sensitive to the changes in reaction temperature, a small amount of EG would undergo further decomposition into smaller molecules at a higher temperature. Besides, the other polyols showed slight changes with the similar trend. Fig. 5b showed the time course of catalytic performance of the Ru-W18O49/graphene for EG production under optimal reaction temperature. The EG yield initially increased with increasing the reaction time and then reached a maximum EG yield of 62.5% at 60 min.

Fig. 5 Catalytic performance of the Ru-W18O49/graphene nanocomposite for conversion of cellulose under different reaction conditions. Reaction conditions: (a) microcrystalline cellulose 0.5 g, deionized water 50 g, nanocomposite 0.08 g, H2 pressure 6 MPa, rotate speed 1000 rpm, time 90 min; (b) microcrystalline cellulose 0.5 g, deionized water 50 g, nanocomposite 0.08 g, H2 pressure 6 MPa, rotate speed 1000 rpm, temperature 245ºC.



Reusability of the catalysts The ability for recycling is always important for metal-catalyzed liquid-phase reactions, especially for precious-metal catalysts. The catalysts used in the compressed hot water medium are required to be resistant to hydrothermal and acid attack. Therefore, we recycled Ru-W18O49/graphene catalyst over three runs. From Fig. 6, one can see that the yield of EG over the Ru-W18O49 /graphene catalyst slightly decreased from 62.5% to 57.5% in the second run, the subsequent recycling test showed distinct loss in EG yield which is dropping down from 57.5% to 48.7%. The result suggests that the Ru-W18O49/graphene catalyst could be used at least three times with the yield of EG in the range of 48.7% to 62.5%. However, the deactivation of the Ru-W18O49/graphene catalyst gradually exhibited with the increase of recycled runs. It is reported that no matter what tungsten compounds were used in the reaction, tungsten bronze (HxWO3) was always formed.14 Therefore, the W18O49 nanowires on the surface of graphene would be slowly transformed into HxWO3 by H2, then dissolved in the aqueous solution during the reaction. That maybe cause the deactivation of the Ru-W18O49/graphene catalyst.

Fig. 6 The reusability of the Ru-W18O49/Graphene nanocomposite in cellulose conversion to EG. Proposed synthesis mechanism for the formation of Ru-W18O49 /graphene nanocomposite


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Fig. 7 Schematically illustration of growth mechanism of the Ru-W18O49/Graphene nanocomposite. The possible formation process of Ru-W18O49/graphene nanocomposite is schematically illustrated in Fig. 7. The GO nanosheets contained numerous oxygenated functional groups including epoxy, carboxyl functional, and hydroxyl,30 which could easily interact with metal ions because they were negatively charged in water. Therefore, during the dissolution of ruthenium chloride hydrate in an aqueous solution of GO, ruthenium (Ⅲ) ions were adsorbed on the surface of GO nanosheets. Alternatively, the GO nanosheets acted as favorable templates or supports for tungsten oxide (WOx) nuclei produced by the hydrolysis of WCl6. Subsequently, during the hydrothermal reaction, simultaneous reduction of graphene oxide and ruthenium (Ⅲ) ions were achieved in the waterethylene glycol system;20 meanwhile, the WOx nuclei grew along the [010] direction to form W18O49 nanowires. It is reported that the morphologies and formation of substoichiometric W18O49 were controlled by the pH of precursor solutions and inorganic additives.31 While, the pH values of precursor solutions of WO3/graphene and Ru-W18O49/graphene are 1.52 and 1.51, respectively, without obvious differences. According to the specific preparation processes of WO3/graphene and Ru-W18O49/graphene, there is no difference between them except for the addition of ruthenium chloride hydrate, we can conclude that ruthenium chloride hydrate plays an important role in the formation of W18O49 nanowires. Besides, the oxygenated functional groups of GO act as favorable



nucleation and anchor sites for the WOx nano-crystals, however, those functional groups would gradually decrease during the hydrothermal reduction reaction.32 Hence, the production of W18O49 nanowires grown on the graphene may be affected.

Conclusions The Ru/graphene, WO3/graphene and Ru-W18O49/graphene nanocomposites were synthesized, respectively, by a one-pot solvothermal reduction reaction employing two-dimensional graphene nanosheets as supports. Then, they were used as the catalyst in turn for the conversion of cellulose into polyols. Compared with Ru/graphene and WO3/graphene, the Ru-W18O49/graphene nanocomposite has a unique surface morphology that ultrathin graphene nanosheets are decorated with Ru nanoparticles and numerous W18O49 nanowires, which provides abundant active sites for selective conversion of cellulose to EG. Moreover, it possesses the highest specific area that would increase the quantity of active sites and enhance the reaction efficiency. Hence, the RuW18O49/graphene nanocomposite showed excellent catalytic activity in selectively converting cellulose to EG as catalyst. The highest yield of EG was 62.5% at complete conversion of cellulose. However, the yield of EG would gradually decrease with the increase of recycled runs duo to the slowly dissolving of tungsten species on the surface of graphene. Besides, the one-pot solvothermal synthesis was a simple approach to prepare the graphene-based nanocomposite catalysts for the production of valuable chemicals from renewable resources. During the solvothermal process, the addition of ruthenium chloride hydrate to the reaction system and oxygenated functional groups on GO significantly promoted WOx nucleation on the support with simultaneous reduction of graphene oxide and ruthenium (Ⅲ) ions, and enhanced the formation of W18O49 nanowires in the water-


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ethylene glycol system.

Acknowledgements The authors are grateful for financial support from the Provincial Key Research and Development Program of Shandong (Grant No. 2016CYJS07A01), the National Natural Science Foundation of China (Grant No. 31770628, 31770630), the Natural Science Foundation of Shandong (Grant No. ZR2018BC042), the Excellent Young Scientist Fund of Shandong (Grant No. ZR2018JL015), the Taishan Scholars Program.

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Synopsis This paper provides a nonpetroleum route for the sustainable production of ethylene glycol from cellulose over graphene-supported catalysts.


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One-pot solvothermal synthesis of graphene nanocomposites for

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