Electrocatalytic hydrogenation of furfural to furfuryl alcohol using platinum supported on activated carbon fibers

Accepted Manuscript Title: Electrocatalytic hydrogenation of furfural to furfuryl alcohol using platinum supported on activated carbon fibers Author: Bo zhao Mengyuan Chen Qingxiang Guo Yao Fu PII: DOI: Reference:

S0013-4686(14)00944-X http://dx.doi.org/doi:10.1016/j.electacta.2014.04.164 EA 22670

To appear in:

Electrochimica Acta

Received date: Revised date: Accepted date:

10-3-2014 25-4-2014 28-4-2014

Please cite this article as: B. zhao, M. Chen, Q. Guo, Y. Fu, Electrocatalytic hydrogenation of furfural to furfuryl alcohol using platinum supported on activated carbon fibers, Electrochimica Acta (2014), http://dx.doi.org/10.1016/j.electacta.2014.04.164 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Electrocatalytic hydrogenation of furfural to furfuryl alcohol using platinum supported on activated carbon fibers

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Bo zhao, Mengyuan Chen, Qingxiang Guo* and Yao Fu* Anhui Province Key Laboratory of Biomass Clean Energy, Department of Chemistry,University of Science and

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Technology of China, Hefei, Anhui 230026, P. R. China

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Abstract

In this work, electrocatalytic hydrogenation (ECH) of furfural to furfuryl alcohol was studied.

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Experiments were run in a H-type cell in aqueous solution with a platinum sheet as anode. Platinum (Pt), nickel (Ni), copper (Cu) and lead (Pb) were used as cathode materials. As expected, the cathode

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material, which serves as the hydrogenation catalyst, was found to have a large effect on the ECH of furfural. Among the cathode materials studied, the Pt gave the best product selectivity. So cathodic

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reduction was catalyzed by platinum supported on activated carbon fibers(Pt/ACF), a novel electrocatalyst. Incipient wetness impregnation and electrodeposition methods were employed to

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prepare the electrocatalyst. Catalysts prepared by impregnation method were more active than prepared using electrodeposition method, presumably because of more active surface area. When using impregnation method, 3%Pt/ACF showed the best activity and current efficiency, followed by 5%Pt/ACF. Effects of electrolyte on product yield and current efficiency were also investigated. The yield of furfuryl alcohol was highest in the 0.1M HCl. The initial furfural concentration and the electrolytic potential also strongly affected the product yield and current efficiency. Key word: furfural; electrocatalytic hydrogenation; activated carbon fibers. 1.Introduction Production of chemicals and fuels from abundant, renewable biomass and its derivatives 1   

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provides a viable route to alleviating the strong dependence worldwide on the depleting fossil fuels[1-3].A wide range of chemicals such as furfural, 5-hydroxymethyl furfural, levulinic acid, xylitol and glucaric acid are obtained from agricultural waste[4]. Furfural has a large spectrum of

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industrial applications and it is a major platform chemical. Furfural is obtained from the dehydration

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of fivecarbon sugars, such as xylose and arabinose, commonly obtained by acidic hydrolysis of

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hemicellulose-rich agricultural wastes [5].

Furfuryl alcohol produced by the hydrogenation of furfural is widely used in fine chemical and

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polymer industries. The major applications of furfuryl alcohol are the production of acid proof bricks, thermostatic resins, corrosion resistant polymer concrete, corrosion resistant fiber glass and liquid

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resins for galvanic bath tub. Furfuryl alcohol is also an important intermediate chemical in the

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alcohol [6,7].

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synthesis of vitamin C, lysine, lubricants, dispersing agents, plasticizer and tetrahydrofurfuryl

The main method for preparation of furfuryl alcohol is vapor-phase catalytic hydrogenation of

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furfural [8,9]. This approach requires high reaction temperature and high pressure of hydrogen. That mean an external hydrogen generation station is required to supply the hydrogen. The hydrogenation at high pressure also creates safety problems such as leakage, pumping, storage and explosiveness. In addition, most catalysts and solvents used for furfural hydrogenation have high toxicity and thus cause severe environmental pollution[10].Therefore, there is an urgent need for a green chemical process with moderate operating conditions for controlling pollution and eliminating safety hazards. Electrocatalytic hydrogenation (ECH) offers a mild alternative to traditional chemical catalytic methods. This approach is not only usually performed at atmospheric pressure and temperatures below 100 ◦C, but also avoids the need for externally supplied, fossil-based hydrogen gas and 2   

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associated handling equipment. Ideally, the needed electricity would come from carbon-free sources such as solar, wind, or even nuclear power［11］. In the ECH process, the chemisorbed hydrogen (Hads) generated in situ on the catalytic electrode

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surface by electroreduction of hydronium ion or water(Reaction 1) reacts with the adsorbed organic

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substrates (Y=Z) (reaction2-4 )under normal pressure and low temperature. These mild conditions

（1）

Y = Z → Y = Z ads

（2）

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H 3O + + ( H 2O) + e − → Hads + H 2O(OH − )

（3）

Y = Z ads + 2H ads → YH − ZHads ads

（4）

→ YH − ZH

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YH − ZH

（5）

H 2 + H 2O ( Heyrovsky step )

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H ads + H 3O + ( H 2O ) + e − →

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2H ads → H 2 (Tafel step)

or

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prevent side reactions usually encountered in chemical catalytic hydrogenation.

（6）

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However the competition between the substrate hydrogenation and the hydrogen evolution reaction (HER)(Tafel 5 or Heyrovsky 6 reactions) can drastically lower the current efficiency or prevent the ECH of substrates.

Previous research on ECH of furfural showed that it is hard to obtain high yield of furfuryl alcohol because of the low conversion of furfural or low selectivity to furfuryl alcohol［12-16］. Nevertheless, research on ECH of phenol［17-19］，guaiacol［11］ and lactic acid［20］ have shown that large cathode surface area are usually necessary to achieve high reaction rates. The conventional metal electrode have been used in many reactions but they have poor surface area. Electrodes made with pressed metallic powder particles have big surface area, but their mechanical strength is weak 3   

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［21］. In order to improve these disadvantages，a well-defined catalytic cathode need to be developed. The use of carbons as catalyst supports is well established and activated carbon is the essential

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support material used by the industry, supporting metal catalysts. Recently, new forms of activated

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carbon, activated carbon fibers(ACF) are being prepared and has been used as electrode in the

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treatment of wastewater［22,23］.This new form of activated carbon materials present noticeable advantageous characteristics in relation to usual activated carbons:(a)The apparent surface area of

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this active carbon is usually high, normally in the range 600-3000m2g-1.The porous network of ACF is mainly formed by deep pores in a narrow range of sizes, especially micropores［24］;(b)ACF can

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be easily processed to all kinds of shapes and easily to bent and rolled. The ACF’s three-dimensional

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particles.

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network of large pores provides electrically conductive host sites to support the metal catalyst

To develop a high-efficiency catalytic cathode, we immobilized platinum onto ACF using

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incipient wetness impregnation and electrodeposition methods. Platinum supported on carbon has been shown to be an efficient catalyst for classical chemical hydrogenation of various organics such as nitrobenzene［24］,phenols［25］, olefin［26］, o-chloronitrobenzene［27］. In this investigation, ECH of furfural was assessed in terms of reactivity, product yield and current efficiency as functions of catalyst parameters (e.g. electrode types, preparation methods, platinum contents) and reaction conditions (temperature and electrolyte).Effect of starting furfural concentration and potential were also investigated. 2. Experimental 2.1. Reagents and electrodes 4   

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Furfural, furfuryl alcohol, H2PtCl6·6H2O, H2SO4, HCl, HClO4, NaOH, which are commercial available, were used without further purification. Activated carbon fibers(ACF) was obtained from Nantong Senyou Carbon Fiber Company Limited. The cathode material, including copper rod(Cu),

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nickel rod(Ni),lead rod(Pb) and platinum sheet(Pt) were obtained from Tianjin Aida Technology

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Development Company.

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2.2. Pt/ACF preparation

ACF was chosen as the support for the platinum catalysts due to good conductivity and high

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surface area. For most of the experiments, ACF was first washed in deionized water, and then boiled in concentrated HCl solution for three days to remove impurity, at last the ACF was thoroughly

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rinsing with deionized water to remove residual HCl, and then drying in the oven at 100 °C［11］. Two methods were used for the catalyst preparation: incipient wetness impregnation and

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electrodeposition. For conventional impregnation method, an aqueous solution of H2PtCl6 was used as precursor and two platinum loadings (3 wt% and 5 wt%) were prepared. Typically, an aqueous

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solution of H2PtCl6 (0.04g H2PtCl6·6H2O in 10mL water, Pt content 0.015g ) was used as precursor for 3 wt% Pt loading. A piece of ACF (1cm × 1.5 cm, about 0.05g) was first soaked in 1ml platinum precursor solution to saturate the ACF pores(Pt metal loading 3 wt%). For 5 wt% Pt loading, an aqueous solution of H2PtCl6 (0.066g H2PtCl6·6H2O in 10mL water, Pt content 0.025g ) was used as precursor. The wet ACF was dried under room conditions, then vacuum dried at room temperature, and finally reduced in a fixed-bed flow reactor with H2 (30 mLmin−1) at 400 °C for 2 h to give Pt/ACF catalyst ［ 25 ］ .For electrodeposition method, 3 wt% platinum loadings were prepared(EDPt/ACF) .Typically, an aqueous solution of H2PtCl6 (0.008g H2PtCl6·6H2O in 10mL water, Pt content 0.003g ) was prepared as catholyte，a piece of ACF(0.1g) was fixed with electrode 5   

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holder as cathode. Thoroughly galvanostatic deposition was run in an undivided cell(volume15ml) with a current of 1 A. A piece of Pt sheet was used as the counter electrode. Working electrode was placed in the middle of the cell and electrolyte was stirred with magnetic stirrer during

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electrodeposition［28］.

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2.3. Apparatus and experimental procedures

All measurements were carried out in a H-type cell(30ml per chamber) with cation exchange

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membrane(DuPont® Nafion-117).The cell was cleaned by employing a standard procedure[29] for

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removing traces of organic and inorganic contaminants. Oxygen was removed by bubbling argon through the solution prior to the voltammetric experiments. Pretreatment of the electrodes was

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carried out to remove the metal oxides, which can deactivate the reaction when existing on the electrode surface. After polishing with sand paper, Ni, Cu,Pb and Pt electrodes were acid washed

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with 1 M HCl solution for 1 h.  After pretreatment, all electrodes were rinsed with deionized water

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[15].The surface area (cm2) of the electrodes, used to calculate the current density (mA cm2) was

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obtained based on geometric area, except for Pt/ACF. In all experiments, a large platinum sheet was used as a counter electrode while a saturated calomel electrode (SCE) was employed as a reference electrode. 

Electrochemical cell potentials were controlled with a potentiostat (DJS-292A ,Shanghai xinrui, China). Catholyte (20 mL) consisted of different concentrations H2SO4,HCl,HClO4 and NaOH depending on the experiments. The whole cell was placed in a water bath for experiments at controlled temperatures.The distance between cathode and anode was 3cm. 2.4. Product analysis The organic products were diluted ten-fold with acetonitrile, filtered through 0.22µm filters and 6   

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analyzed by a gas chromatograph (GC, Shimadzu GC-2014 Series GC System, flame ionization detector) with a Rtx-wax capillary column (30 m×250 µm).A gas chromatograph-mass spectrometer combination (GC-MS, Thermo Scientific AS 3000 Series) was used to identify the organic

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compounds.

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2.5. Calculations

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The conversion, selectivity and electrochemical efficiency were calculated according to the following equations:

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Conversion=(moles furfural consumed ⁄ initial moles furfural)×100 Selectivity=(moles desired product ⁄ total moles products) ×100

 

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3. Results and discussion

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×100

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Current efficiency= (electrons used to generate product(furfuryl alcohol) ⁄ total electrons passed)

3.1. ECH of furfural using different cathode.

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To determine suitable metal to load on the ACF as electrode, copper, lead, nickel and platinum were chosen as electrode materials in this study. Fig.1 shows cyclic voltammograms of the electrochemical reduction of furfural. In the voltammograms the onset potentials are visible, at which the reduction currents increase and hence the reduction reactions commence. In electrochemical reactions the current flow is proportional to the amount of compound converted per time. For the reduction of furfural the onset potential is about -1.1V, -0.9V, -0.8V, -0.2V on Cu,Pb,Ni and Pt respectively. As shown in table 1, on copper electrode in 0.1M NaOH,the electrolysis was performed at -1.2 V. 80% of the initial furfural was consumed only 15% was transformed into furfuryl alcohol. The 7   

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analysis by GC-MS have shown that other products are 2-methylfuran, 1,5-pentanediol(coming from the opening of the furan ring) and hydroxyfuroin(coming from electrohydrodimerization)(Fig.2). This result is consistent with the findings of Parpot［13］. On lead cathode, the applied potential was

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set at -1.1V. Though the conversion of furfural is high(90%) ,the yield of furfuryl alcohol remained

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low (40%). It was found that the main reaction products were also coming from electrodimerization

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processes(Fig.2). On nickel cathode,only 25% of the initial furfural was consumed and 80% were transformed into furfuryl alcohol. With Pt cathode, though the conversion remained very low (8%),

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the selectivity to furfuryl alcohol was very high(99%).  Indicate that there were no other side reactions occur. This result showed that platinum is a suitable cathode material.  Because of lack of

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active surface area with smooth platinum electrode, the conversion of furfural was low.  This result

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load on the ACF as cathode.

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may improved by a large active surface area on platinum［30］. So we choose platinum as catalyst to

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3.2. Characterization of Pt/ACF catalysts

The catalytic cathodes’ BET surface area, micropore area and micropore volume were analyzed (Table 2). In order to assess the underlying support properties of the catalyst supports, blank ACF was pretreated in the same manner as the catalyst, by washing with DI water and reducing with hydrogen.The freshly prepared blank ACF and Pt/ACF catalysts were characterised by SEM. The blank ACF has a BET surface area of 2398m2g-1, very similar to the value reported in the literature ［24］.Compared with other supports used for cathodes［11］,this kind of support has much larger surface area. The majority of the pores are micropores and the volume is 1.13 cm3g-1(Table 2). Upon loading with different content of platinum, the ACF’s micropore volumes decreased, suggesting that 8   

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some of the micropores were filled by platinum or platinum deposition may occured on the mouth of the pore and resulted in the pore blockage. Figure.3(A) gives the SEM image of the blank ACF. It was clearly displayed a network structure with its carbon fibers knitted together. So the conductivity

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of ACF is very high, making it a good electrocatalyst support［24］.

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As shown in Table 2, 3%EDPt/ACF prepared by electrodeposition method, has a very small

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surface area and micropore volume than the other catalysts.This is probably due to drastic electrolysis process and platinum layers covered only on the surface of ACF and the micropore was

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blocked(Fig.3B).

SEM images of the 3% and 5% Pt/ACF prepared by impregnation method are shown in Fig.3 C

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and D. As seen in Fig.3C, most of the platinum was distributed into white spots of nanoscale in 3%Pt/ACF. But SEM images of 5%Pt/ACF indicate partial platinum were agglomerated to bulk

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(Fig.3D). This is probably due to excessive platinum precursor(H2PtCl6). Dispersion of Pt detected by CO adsorption is summarized in Table 3. It is clear that both

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dispersion and metal area per gram of catalyst (or Pt) decrease sharply with increase in Pt loading from 3% to 5%. However, the particle size shows the opposite trend and both in nanoscale(2.1nm and 6.5nm), this result is consistent with SEM images of the 3% and 5% Pt/ACF. In addition, there is a sharply decrease in CO uptake with an increase of Pt loading from 3% to 5%, implying that more active hydrogenation sites are present on 3%Pt/ACF. These results concluded that the dispersion of Pt depends strongly on Pt loading and the preparation method. 3.3. ECH of furfural using different Pt/ACF catalysts ECH of furfural was studied with several different catalysts prepared using two methods (incipient wetness impregnation and electrodeposition).Two platinum loadings (3%,5% for 9   

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impregnation method and 3% for electrodeposition method) were employed. Fig.4 shows cyclic voltammograms of the electrochemical reduction of furfural with three kinds of Pt/ACF electrodes. The onset potential of these Pt/ACF electrodes is -0.35,-0.35V and -0.32V on 3%Pt/ACF,5%Pt/ACF

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electrodes(with potential of -0.5V) were summarized in table 4.

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and 3%EDPt/ACF, respectively. The results of electrocatalytic reduction of furfural with these

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Pt/ACF catalysts prepared from different methods showed different activities toward ECH of furfural. 3%Pt/ACF exhibited the highest activity among the three catalysts, followed by 5%Pt/ACF

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and 3%EDPt/ACF. This result may be attributed to decrease of catalytic activity area caused by pore blockage in 5%Pt/ACF and 3%EDPt/ACF. But all three Pt/ACF electrodes exhibitted better catalytic

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activity than metallic Pt electrode. This may be attributed to high real surface area of Pt/ACF electrodes［31］.

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According to K.Amouzegar and O.Savadogo［32］. The higher activity of Pt/ACF might not be completely due to higher surface area. Another contributing factor may be the interactions between

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Pt and the carbon support. It has been proposed that when Pt(with an electron work function of 5.4eV) is deposited on supports with a lower electron work function such as carbon or gold(4.7 and 4.3eV, respectively), the Pt electron density increases. The increased negative charge on Pt would result in a weakening of Pt-H bond and consequently an activation of reactions on supported Pt. 3.4. Control experiments

A control experiment carried out at room temperature using the blank ACF with no catalyst in 0.1M H2SO4 showed no furfural conversion(Table 4). For this control experiment, there were no metal active sites for atomic hydrogen, and no catalyst for the reaction.Thus, the ACF alone is incapable of hydrogenation. Another control experiment with 3%Pt/ACF catalyst and gaseous 10   

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hydrogen(H2 gas was supplied by bubbling through the solution) run at room temperature similarly showed no reaction, confirming that Pt needs to be in electrical contact for hydrogenation of furfural to occur at the mild conditions of this study.

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3.5. Effect of temperature

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The effect of temperature on furfural ECH was studied with 0.1 M H2SO4 as catholyte under a

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potential of -0.5V. Four different temperatures, 30, 50 ,70and 90 °C, were studied, all much lower than those used in classical catalytic hydrogenation of furfural［10,33］. The current efficiency is a

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function of the competition between electrocatalytic hydrogenation and hydrogen desorption. Relative rates of hydrogenation and hydrogen evolution are thought to depend on the intrinsic

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thermochemistry of the reduction,adsorption modes and energies of the reactants and products, and the activity of chemisorbed hydrogen [17].Raising the temperature from 30 °C to 50 °C increased

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current efficiency from 78% to 85% but further heating to 90 °C dropped it back to 74% (Fig.5). This indicates that electrocatalytic hydrogenation was favored from 30 °C to 50 °C, while hydrogen

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desorption rates accelerated as temperature increased from 50 °C to 90 °C. Similar increases in the conversion and current efficiency with increasing temperature have been previously noted in the ECH of（a）lactic acid to lactaldehyde and propylene glycol［20］ over 5% Ru/C in an RVC electrode using 0.01M H2SO4 as the electrolyte.（b）bio-oil derived phenolic compounds using ruthenium supported on activated carbon cloth studied by Li.et al.［11］ （c）phenol to cyclohexanol on dispersed Pt electrode in 0.05 M H2SO4, studied by Amouzegar and Savadogo［31］. The effects of temperature on the product selectivities are also shown in Fig.5.At 30 °C, product was almost all furfuryl alcohol,while raising the temperature from 30 °C to 90 °C decreased selectivity of furfuryl alcohol from 99% to 85%. It was found that the other reaction products were 11   

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coming from electrodimerization processes(like Cu electrode,see Fig.2). 3.6. Effect of potential Potential, directly related to the total reaction rate, may have an effect on the current efficiency

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and product yield. Several different potentials from -0.4 to -0.7 V were studied. As shown in Fig.6,

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furfural conversion increase when potential is in the range of -0.4V to -0.6V and then decrease at

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-0.7V. Current efficiency are basically invariant when potential is in the range of -0.4V to -0.6V and decrease drastically at -0.7V.An optimum potential usually exists for ECH of organic compounds

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［34］. When potentials are smaller than this optimum value, the surface coverage of the Hads is smaller. The probability of the collision between Hads and (furfural)ads is lower. With more negative

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potentials, the availability of surface Hads atoms increases, the ECH of furfural accelerates. However, the more negative the applied potential is, the unwanted HER step is more competitive, proceeding

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through Tafel or Heyrovsky steps [Eqs. (5) and (6)]. Hydrogen gas bubbles generated on the Pt/ACF electrode surface as the applied potential became higher than -0.6V.Therefore,the measured current

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efficiency reaches a maximum at -0.5 V (85%) and decreases to 72% at -0.7 V. Additionally, product selectivities are only slightly affected by potentials . 3.7. Effect of electrolyte

ECH of furfural was carried out in various electrolytes at 50 ◦C and potential of -0.5V. Previous studies have shown that this reaction was hard to happen in neutral and alkaline medium with Pt electrode［13］,so the study was carried out in the acidic medium. Electrolytes studied were 0.1 M H2SO4, HClO4 , HCl , 0.05 M HCl and 0.2 M HCl.The final yields of the products and current efficiencies are listed in Fig.7. In the concentration of 0.1M electrolytes,the yield of furfuryl alcohol was found to decrease in 12   

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the order HCl,H2SO4 and HClO4.The adsorption of anions on electrode surfaces and their effects on hydrogen adsorption on metal surfaces have been extensively studied. The relative strengths of adsorption of the anions were found by Horanyi to decrease in the order Cl−﹥HSO4−﹥ ClO4− on Pt

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electrode［35］. This was consistent with the experimental results of this study.

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In the HCl electrolytes of  different concentration, the yield of furfuryl alcohol and current

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efficiency decreased in the order 0.1M﹥0.05M﹥0.2M.Controlling the hydrion concentration during the hydrogenation process is important for obtaining a high yield of furfuryl alcohol. Strongly acidic

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conditions lead to increase of H2 and decline of current efficiency .In addition,furfural adsorption onto catalyst sites is a key step in the hydrogenation reaction. The ionization state of furfural varies

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with solution pH, potentially affecting its adsorption characteristics. 3.8. Influence of starting reactant concentration

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Different starting concentrations of furfural were chosen to study their effects on the furfuryl alcohol yield and current efficiency during ECH. As shown in Fig. 8, the current efficiency was

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maximized when the starting concentration was 80mmol.L-1. As the concentration was reduced below 80 mmol.L-1, the hydrogenation of furfural became slower so that hydrogen evolution became more competitive. This is because there were many empty catalyst sites when starting concentration of furfural is low, so the unwanted HER step is more competitive and lead to decline of current efficiency. When the concentration of furfural is large, hydrogenation should be favored relative to the hydrogen evolution reaction. However, when all catalyst sites were occupied by furfural, more reactant needs more reaction time and this lead to more furfuryl alcohol volatilize. 3.9. Catalyst stability Catalyst deactivation is an important concern during hydrogenation process. To evaluate the 13   

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stability of Pt/ACF during ECH of furfural, the catalysts were reused three times. After each reaction, it was washed thoroughly using deionized water, followed by drying in vacuum desiccator. At the beginning of the next experiment, pre-electrolysis was carried out at -0.8V for 10 min. As shown in

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Fig.9, for the ECH of furfural to furfuryl alcohol, the Pt/ACF electrode had a nearly constant activity

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after being reused three times at 50 . The furfuryl alcohol yield and current efficiency remained at

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82% and 78%, respectively, in third reuse, indicating a good stability of the electrode. 4. Conclusions

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Electrocatalytic hydrogenation of furfural to furfuryl alcohol was accomplished with Pt, Ni, Cu, and Pb as cathode materials. The cathode material had a large effect on the electrocatalytic

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hydrogenation of furfural, with Pt giving the best result of product selectivity among those studied.This work shows that Pt/ACF is an efficient catalyst for electrocatalytic hydrogenation of

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furfural to furfuryl alcohol under mild conditions compared to other catalytic reductions, including other ECH schemes. Catalyst comparisons demonstrated that Pt/ACF catalysts prepared via the

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impregnation method show much better activity than that prepared by electrodeposition method. When using incipient wetness impregnation, 3%Pt/ACF showed the highest activity among the two Pt loading studied. With 3%Pt/ACF as catalyst, -0.5V was the best electrolytic potential.The kind of electrolytes also affected product selectivities and current efficiency. Furfuryl alcohol had an best yield when 0.1M HCl as electrolyte. Based on the results from this investigation, electrocatalytic hydrogenation with Pt/ACF is a potential strategy for ambient pressure hydrogenation of furfural to furfuryl alcohol at low temperatures, and it may offer a very promising process for furfuryl alcohol production Acknowledgements 14   

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The authors are grateful to the National Basic Research Program of China (2013CB228103, 2012CB215306),

NSFC(21172209),

FRFCU(WK2060190025),

SRFDP(20123402130008),

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CAS(KJCX2-EW-J02) and Fok Ying Tung Education Foundation for the financial support. Corresponding Author

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Fax: +86-551-63606889 ;Tel: +86-551-63606374.

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*E-mail: [email protected];[email protected]. Reference

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[12] G. Chamoulaud, D. Floner, C. Moinet, C. Lamy, E.M. Belgsir, Biomass conversion II: simultaneous electrosyntheses of furoic acid and furfuryl alcohol on modified graphite felt electrodes, Electrochim. Acta 46 (2001) 2757-2760. [13] P. Parpot, A.P. Bettencourt, G. Chamoulaud, K.B. Kokoh, E.M. Beigsir, Electrochemical investigations of the oxidation–reduction of furfural in aqueous medium-Application to electrosynthesis, Electrochim. Acta 49 (2004) 397-403. [14] D.Chu, Y.Hou, J.He, M. Xu, Y.Wang, S.Wang, J. Wang, L.Zha, Nano TiO2 film electrode for electrocatalytic reduction of furfural in ionic liquids, J. Nanopart. Res. 11 (2009) 1805-1809. [15] Z.Li, S.Kelkar, C.H. Lam, K.Luczek, J.E. Jackson, D.J. Miller, C.M. Saffron,Aqueous 16   

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electrocatalytic hydrogenation of furfural using a sacrificial anode, Electrochim. Acta 64 (2012) 87-93. [16] P.Nilges, U. Schröder, Electrochemistry for biofuel generation: production of furans by

ip t

electrocatalytic hydrogenation of furfurals, Energy Environ. Sci. 6 (2013) 2925-2931.

cr

[17] H. Ilikti, N. Rekik, M. Thomalla, Electrocatalytic hydrogenation of phenol in aqueous solutions

us

at a Raney nickel electrode in the presence of cationic surfactants, J. Appl. Electrochem. 32 (2002) 603-609.

an

[18] H. Ilikti, N. Rekik, M. Thomalla, Electrocatalytic hydrogenation of alkyl-substituted phenols in aqueous solutions at a Raney nickel electrode in the presence of a non-micelle-forming cationic

M

surfactant , J. Appl. Electrochem. 34(2004)127-136.

[19] F.Laplante, L.Brossard, H.Ménard, Considerations about phenol electrohydrogenation on

te

d

electrodes made with reticulated vitreous carbon cathode, Can. J. Chem. 81(2003)258-264. [20] T.S. Dalavoy, J.E. Jackson, G.M. Swain, D.J. Miller, J.Li, J.Lipkowski, Mild electrocatalytic

Ac ce p

hydrogenation of lactic acid to lactaldehyde and propylene glycol, J. Catal. 246 (2007) 15-28. [21] A. Cyr, F. Chiltz, P. Jeanson, A. Martel, L. Brossard, J. Lessard, H.Ménard, Electrocatalytic hydrogenation of lignin models at Raney nickel and palladium-based electrodes, Can. J. Chem. 78(2000)307-315.

[22] P.Liang, L.Yuan, X.Yang, S.Zhou, X.Huang. Coupling ion-exchangers with inexpensive activated carbon fiber electrodes to enhance the performance of capacitive deionization cells for domestic wastewater desalination, Water Res. 47(2013)2523-2530. [23] G.Zhou, X.Wang, Z.Wang, S.Pan, S.Li, Electrosorption Desalination by Activated Carbon Fibers Electrode, Adv. Mater. Res. 610-613(2013) 1710-1717. 17   

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[24] M.C.M. Pérez, C. S.M. Lecea,A. L.Solano, Platinum supported on activated carbon cloths as catalyst for nitrobenzene hydrogenation, Appl. Catal., A 151 (1997) 461-475. [25] H.Ohta, H.Kobayashi, K.Hara,A,Fukuoka, Hydrodeoxygenation of phenols as lignin models

ip t

under acid-free conditions with carbon-supported platinum catalysts, Chem. Commun. 47

cr

(2011)12209-12211.

us

[26] P.Chen, L.M.Chew, W.Xia, The influence of the residual growth catalyst in functionalized carbon nanotubes on supported Pt nanoparticles applied in selective olefin hydrogenation, J. Catal.

an

307 (2013) 84-93.

[27] X.Xu, X.Li, H.Gu, Z.Huang, X.Yan, A highly active and chemoselective assembled Pt/C(Fe)

M

catalyst for hydrogenation of o-chloronitrobenzene, Appl. Catal., A 429-430 (2012) 17-23.

te

43 (1978) 2059-2061.

d

[28] L.L.Miller,L.Christensen, Electrocatalytic hydrogenation of aromatic compounds, J. Org. Chem.

[29] S. C. S. Lai, M. T. M. Koper, Electro-oxidation of ethanol and acetaldehyde on platinum

Ac ce p

single-crystal electrodes, Faraday Discuss. 140(2009)399-416. [30] Y.Kwon, M.T. M. Koper, Electrocatalytic Hydrogenation and Deoxygenation of Glucose on Solid Metal Electrodes , ChemSusChem 6 (2013) 455-462. [31] K.Amouzegar, O.Savadogo, Electrocatalytic hydrogenation of phenol on highly dispersed Pt electrodes, Electrochim. Acta 39 (1994) 557-559. [32] K.Amouzegar, O.Savadogo, Electrocatalytic hydrogenation of phenol on dispersed Pt: reaction mechanism and support effect, Electrochim. Acta 43 (1998) 503-508. [33] R.V. Sharma, U. Das, R. Sammynaiken, A. K. Dalai, Liquid phase chemo-selective catalytic hydrogenation of furfural to furfuryl alcohol, Appl. Catal., A 454 (2013) 127-136. 18   

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[34] L.Xin, Z. Zhang, J. Qi, D. J. Chadderdon, Y.Qiu, K.M. Warsko, W. Li, Electricity Storage in Biofuels: Selective Electrocatalytic Reduction of Levulinic Acid to Valeric Acid or γ-Valerolactone, ChemSusChem 6 (2013) 674-686.

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[35] G. Horanyi, Induced cation adsorption on platinum and modified platinum electrodes,

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te

d

M

an

us

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Electrochim. Acta 36 (1991) 1453-1463.

19   

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Table1. Electrocatalytic reduction of furfural with different electrode E(V)

j(mA cm2)

electrolyte

Cona(%)

Sb(%)

C.Ec (%)

Cu

-1.2

15-20

0.1M NaOH

80

15

10

Pb

-1.1

20-30

0.1M H2SO4

90

45

Ni

-0.9

10-15

0.1M NaOH

25

80

Pt

-0.3

5-10

0.1M H2SO4

8

36

cr

16

7

us

99

Conversion of reactant. bSelectivity of the furfuryl alcohol. cCurrent efficiency

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te

d

M

an

a

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electrode

21   

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Table 2. Structural parameters of blank ACF and the catalysts

Blank ACF

water wash and H2

BET surface

micropore

Micropore

area(m2g-1)

volume(cm3g-1)

Area（m2g-1）

2398

1.13

reduction

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Preparation method

1729

cr

Catalyst

impregnation method

1862

0.94

5%Pt/ACF

impregnation method

1360

0.66

995

3%EDPt/ACF

electrodeposition method

896

0.47

671

1347

an

us

3%Pt/ACF

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te

d

M

 

23   

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CO adsorption

Pt area

Pt area

Dispersion

(µmol g-1)

(m2 g(cat)-1)

(m2 g(Pt)-1)

(%)

3%Pt/ACF

83.4

4.0

134.0

54.2

5%Pt/ACF

44.8

2.2

43.1

17.5

3%EDPt/ACF

n.d.a

n.d.a

n.d.a

cr

Table 3. CO adsorption properties and dispersion of Pt

(nm)

n.d.a

2.1

6.5

n.d.a

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No data can be calculated because of the surface was fully covered with Pt.

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te

d

M

an

a

Particle size

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Catalyst

24   

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Table 4. Electrocatalytic reduction of furfural with different Pt/ACF electrode E (V)

I(mA)

electrolyte

Cona(%)

Sb(%)

C.Ec(%)

3%Pt/ACF

-0.5

20-30

0.1M H2SO4

82

99

78

5%Pt/ACF

-0.5

20-30

0.1M H2SO4

75

99

3%EDPt/ACF

-0.5

20-30

0.1M H2SO4

25

99

Pt sheet

-0.5

20-25

0.1M H2SO4

5

Blank ACF

-0.5

0

0.1M H2SO4

b

0

Selectivity of the furfuryl alcohol formation

21

cr 99

us

Conversion of reactant

72

0

c

3 0

Current efficiency

an

a

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electrode

Ac ce p

te

d

M

 

25   

Page 23 of 32

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d

Figure .1. Cyclic voltammograms of electrocatalytic furfural reduction (80mM) on Cu, Ni(in 0.1M NaOH) and Pb,Pt(in 0.1M H2SO4). Current density profiles with (red line) and without (black line) furfural in the solution

 

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during linear sweep voltammetry with a scan rate of of 50 mV s-1, room temperature, and ambient pressure.

26   

Page 24 of 32

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Fig. 2. Reaction scheme for ECH of furfural to furfuryl alcohol and other compound.

Ac ce p

te

d

M

an

 

27   

Page 25 of 32

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Fig.3. SEM images of (A) blank ACF.(B)SEM images of 3% EDPt/ACF prepared with electrodeposition

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te

 

d

method.(C) and (D) SEM images of 3% and 5% Pt/ACF prepared with impregnation method.

28   

Page 26 of 32

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Figure .4. Cyclic voltammograms of the ECH of furfural on three kinds of Pt/ACF electrodes in 0.1M H2SO4 at a

 

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scan rate of 1 mV s-1, room temperature, and ambient pressure.

29   

Page 27 of 32

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Fig. 5. Product selectivities, furfural conversion and C.E. for ECH of Furfural at different temperatures using 3%Pt/ACF at potential of -0.5V, 0.1 M H2SO4 as catholyte.

Ac ce p

te

d

M

 

30   

Page 28 of 32

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Fig. 6. Product selectivities, furfural conversion and current efficiency for ECH of furfural at different potential using 3%Pt/ACF at 50 , 0.1 M H2SO4 as catholyte.

Ac ce p

te

d

M

 

31   

Page 29 of 32

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Fig.7. Product yield and current efficiency for ECH of furfural in different electrolyte using 3%Pt/ACF as cathode. Potential: -0.5V.Temperature:50 .

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te

d

M

 

32   

Page 30 of 32

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Fig. 8. Effect of different starting concentrations of reactant on ECH of furfural using 3%Pt/ACF in 0.1M HCl. Potential: -0.5V.Temperature:50 .

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te

d

M

 

33   

Page 31 of 32

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Fig.9. Electrode reuse with 80 mmol.L-1 furfural as reactant at temperature of 50

and potential of

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te

 

d

-0.5V.Electrolyte: 0.1M HCl

34   

Page 32 of 32