Active ruthenium catalysts prepared by Cacumen Platycladi leaf extract for selective hydrogenation of maleic anhydride

Accepted Manuscript Title: Active ruthenium catalysts prepared by Cacumen Platycladi leaf extract for selective hydrogenation of maleic anhydride Author: Yangqiang Huang Yao Ma Youwei Cheng Lijun Wang Xi Li. PII: DOI: Reference:

S0926-860X(15)00106-4 http://dx.doi.org/doi:10.1016/j.apcata.2015.02.014 APCATA 15251

To appear in:

Applied Catalysis A: General

Received date: Revised date: Accepted date:

15-12-2014 4-2-2015 11-2-2015

Please cite this article as: Y. Huang, Y. Ma, Y. Cheng, L. Wang, X. Li., Active ruthenium catalysts prepared by Cacumen Platycladi leaf extract for selective hydrogenation of maleic anhydride, Applied Catalysis A, General (2015), http://dx.doi.org/10.1016/j.apcata.2015.02.014 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.

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*Graphical Abstract (for review)

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*Highlights (for review)

Highlights: A green process for preparation ruthenium-based catalysts.

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Maleic anhydride can be selectively hydrogenated to succinic anhydride.

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The biosynthesized Ru-based catalysts showed excellent stability.

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Active ruthenium catalysts prepared by Cacumen Platycladi leaf extract for selective hydrogenation of maleic anhydride Yangqiang Huang, Yao Ma, Youwei Cheng, Lijun Wang and Xi Li. Department of Chemical and Biological Engineering, Zhejiang University,

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Hangzhou 310027, PR China

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Abstract:

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Ruthenium-based catalysts were prepared by a biogenic method via Cacumen Platycladi leaf extract and tested in the liquid phase hydrogenation of maleic

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anhydride to the corresponding succinic anhydride. The reaction conditions were optimized by varying the Ru loading, reaction temperature, hydrogen pressure, reaction

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time and organic solvents to achieve the superb catalytic performance. Reusability tests and comparison with commercial catalysts were also studied on the biosynthesized

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Ru-based catalysts. Furthermore, a variety of characterization techniques, such as TEM, HRTEM, EDS and XPS showed the effectively introduction of ruthenium

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nanoparticles into the carbon supports. The analyses of FTIR and TG confirmed that the plant extract served as both reducing and protecting agents.

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Keywords:

Maleic anhydride; Selective hydrogenation; Succinic anhydride; Ruthenium

nanoparticles

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Corresponding author. E-mail address: [email protected] (Y. Cheng) 1

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1. Introduction Maleic esters, anhydrides and acids hydrogenation is a widely applied chemical process as all its products, such as succinic anhydride (SA), γ-butyrolactone (GBL),

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1,4-butanediol (BDO) and tetrahydrofuran (THF) are important chemicals used as solvents or raw materials to produce polymers like polyurethanes [1-3]. In particular, SA is required as an intermediate to undergo various reactions in the area of polymers,

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agrochemicals, pharmaceuticals, and food industrial [4, 5]. The market potential of

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the products based on succinic acid and anhydride is evaluated to be 270 000 tons per year [6]. These products are synthesized by the following four processes: (I) Reppe

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process [7] in which acetylene is reacted with formaldehyde; (II) Acro process [8] in which propylene oxide is isomerized first to allyl alcohol and then hydroformylation;

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(III) Mitsubishi Kasei process (MKC) [9] in which maleic anhydride is hydrogenated on Ru complexes; (IV) Davy McKee process [10] which focused on hydrogenation of dialkyl maleates on Cu-based catalysts or ion-exchange resins. Among them, direct

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hydrogenation of maleic anhydride (MA) is reckoned to be the most clean and economical process to produce SA. MA is a convenient feedstock for its availability

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and low price due to the construction of large fluidized-bed plants based on Alusuisse-Lummus, BP/UCB, and DuPont technologies [1, 11]. The reaction pathway of MA hydrogenation is illustrated in Fig. 1 [11].

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It is reported that the gas-phase hydrogenation of MA is carried out with the presence of the copper-based catalysts [12-14], while the liquid-phase hydrogenation of MA is performed mainly on the noble metal catalysts containing Ru, Pd, or Rh [15-18]. The drawback of the reported efficient catalysts is the deactivation problem because of the coke deposition during the hydrogenation process. This clearly indicates that new catalysts are needed to overcome the problems of complicated synthesis of catalyst, high consumption of metal, relatively low activity, high reaction temperature and long reaction time. Transition metal nanoparticles (NPs) have been widely recognized in catalysis 2

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due to their novel chemical and physical properties in recent years [19, 20]. Ascribed to the quantum size effect and surface effect, metal NPs can exhibit fascinating activity and selectivity, which radically distinguish themselves from their bulk counterparts [21]. Ru NPs, among the most efficient and also economical (its price is one third to fifth of that for Pd) noble metals, are attractive and have been adopted in

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many hydrogenation processes, such as hydrogenation of benzene to cyclohexane [22, 23], selective hydrogenation of D-glucose [24], xylose [25], and α,β-unsaturated

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aldehydes [26]. We have previously investigated the Ru-based catalysts for the

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selective hydrogenation of dimethyl terephthalate. In fact, the carbon nanotubes supported Ru NPs with low loading (0.4 wt%) could exhibit both desirable activity and stability [27]. Furthermore, some findings have been reported regarding the

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hydrogenation of maleic anhydride using Ru complexes [15]. Likewise, a series of ruthenium-carbon catalysts were synthesized by Hong et al. using a single-step

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surfactant-templating method and showed excellent catalytic performance for the hydrogenation of succinic acid [28]. In summary, the Ru based catalytic system is

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believed to be a promising candidate for the hydrogenation of MA. Generally speaking, solution-based chemical synthetic strategies, which are

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effective and powerful ways to nanomaterials, are turned out to be more economical and simpler compared to that in the solid or gaseous state [20]. Recently, researchers have made great progress in controllable synthesis of noble NPs. However, these conventional chemical methods will inevitably encounter the problems of using

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various capping agents or auxiliary surfactants; moreover during the synthesis, numerous conditions and parameters will result in poor reproducibility. Recently, an effective system for preparation of noble metal NPs, namely the biosynthesis methods using biological organisms or plants, has attracted intensive research interest. The biosynthesis methods can be applied to produce stable noble NPs with a narrow size distribution in a simple way. Zhan et al. provided two novel modes, namely sol-immobilization (SI) and adsorption-reduction (AR) methods [29]. Their biosynthesized Au NPs supported on TS-1 showed high activity and efficiency for the epoxidation of propylene [30]. In a previous study, we examined the possibility of 3

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synthesizing Ru NPs by the use of Cacumen Platycladi (CP) leaf extract. The bioreduction catalysts exhibited excellent catalytic activity compared with the commercial Ru/C catalysts in the hydrogenation of benzene to cyclohexane [31]. These inspiring results give us more confidence that the eco-friendly bioreduction approach of synthesizing Ru NPs will provide a new direction in the near future.

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The present paper includes the preparation of Ru catalysts by the SI method

through immobilizing the reduced Ru nanoparticles on the supports. Several analysis

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techniques, such as low temperature N2 physisorption, X-ray diffraction (XRD)，

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transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), and thermogravimetric (TG), are adopted to offer insights of the

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intrinsic structure-property relationship of the catalysts. The bioreduction catalysts are probed in the liquid phase hydrogenation of maleic anhydride. Furthermore, in order

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to optimize the hydrogenation process, the effect of various preparation and reaction

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conditions on the catalytic performance is also studied.

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2. Experimental details 2.1 Materials

Carbon (Activated charcoal, LOT-242276) was purchased from Sigma-Aldrich,

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Cacumen Platycladi (CP) leaf was obtained from Zhejiang university hospital. Maleic anhydride (AR, >99.0%) was purchased from Aladdin Chemical Co. Ltd. Other chemical reagents mentioned were all of A.R grade from Sinopharm Chemical Reagent Co. Ltd. and used without further purification. The deionized water with a conductance below 10-6 S/cm was used in all synthesis and washing processes.

2.2 Catalyst preparation The bioreduction Ru-based catalysts were prepared through immobilizing the 4

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biosynthesized Ru nanoparticles (Ru NPs) onto the carbon supports. In a typical synthesis procedure, milled powder CP leaf of 1 g dosage was added to 100 mL of deionized water under stirring for 4 h. The mixture was then filtrated to get filtrate (10 g/L) and used for further preparation of Ru NPs. Then, Ru NPs were biosynthesized through a simple procedure by reducing the aqueous RuCl3 (50 mL, 2.2 mM) with the

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CP extract (30 mL). After 0.5 h, an appropriate amount of dried activated carbon was

added immediately into the solution at the same temperature. After another 5 h, the

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solids were collected by filtration and thoroughly washed with deionized water. The

resulting solid was dried in a vacuum oven at 60 oC for 12 h, and the X wt% Ru/AC

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catalysts were obtained after calcination at 500 oC for 3 h in the atmosphere of

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nitrogen (X was the nominal Ru loading).

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2.3 Catalysts characterization

The Micromeritics ASAP 2020 instrument was applied for monitoring the

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low-temperature N2 adsorption-desorption behaviors, and the Barrett-Joyner-Halenda (BJH) method was used to calculate the textural properties including pore size distribution and total pore volume. XRD patterns were collected on a XRD-6000

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X-ray diffractometer (Shimadzu) with Cu Kα radiation (λ = 0.154 nm) at 40 kV and 30 mA, in a 2θ angle ranging from 10 to 90 º with a scanning rate of 2 º/min and a step size of 0.02 º/s. TEM and HRTEM images of samples were taken with a FEI

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Tecnai G2 F20 S-TWIN microscope operating at an accelerating voltage of 200kV. EDS analysis was used to determine the elemental composition of the colloidal particles. XPS analyses were performed on a VG ESCALAB MARK II equipment with focused monochromic Mg Kα (BE=1253.6 eV). The binding energy (BE) values were calculated with respect to C1s peak at 284.6 eV with an uncertainly of ±0.2 eV. A Nicolet 5700 FTIR infrared spectrometer was used to collect the Fourier transform infrared (FTIR) spectra. TG profiles were measured with a Pyris 1 TGA (Perkin-Elmer).

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2.4 Catalytic Activity Measurement All experiments were performed in a 100 mL stainless steel (SS-316) reactor. In each test, the reactor was charged with 10 mmol of maleic anhydride, 5 mL of tetrahydrofuran, and 50 mg of catalyst. The reactor was pressurized with nitrogen to

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remove air and heated up to the desired temperature. Then, the autoclave was pressurized with H2 to the designed pressure. Analysis of liquid reactants was

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performed by gas chromatograph (Kexiao, GC-1690 with flame ionization detector).

The gas chromatograph was equipped with an OV-1 column and the acetic anhydride

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was chosen as the internal standard substance. The conversion rate was defined as the ratio of consumed maleic anhydride to supplied maleic anhydride. The selectivity was

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calculated by dividing moles of a product by total moles of maleic anhydride consumed. To ensure reproducibility of the results, repeated experiments were carried

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out under identical conditions and data were found to be reproducible within ±2 %

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variation.

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3. Results and discussion Hydrogenation

of

maleic

anhydride

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succinic

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anhydride.

3.1.1 Effect of Ru loading. The effect of various Ru loading (0.25-5.0 wt%) on the hydrogenation of MA

was shown in Fig.2. It could be noticed that Ru loading had a remarkable effect on MA conversion while the SA selectivity was well preserved in the experiment. The conversion of MA increased monotonously with the increase of Ru content from 0.25 to 2.0 wt% while the SA selectivity maintained at a relatively high level around 99.0 %. The inferior performance with the low Ru loading (0.25 and 0.50 wt%) might 6

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be attributed to the insufficient presence of active ruthenium sites, which lowered down the activity of MA hydrogenation. The conversion of MA reached 99.4 % at a Ru loading of 2.0 wt%. When we continuously increased the Ru loading to 5.0 wt%, the catalytic performance was slightly changed; however, we had lower Ru capture efficiency, which could be inferred from the results of ICP-AAS shown in Table 2. In

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addition, the experimental results indicated that incomplete Ru loading would occur in the case of high Ru loading (≥3.0 wt%). Consequently, the optimum Ru loading was

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2.0 wt % since the catalysts showed a higher MA conversion (99.4 %) and had almost

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100 % Ru capture efficiency, which was important from an economic point of view during the process.

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3.1.2 Effect of Reaction Temperature and Hydrogen Pressure.

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It is well known that the reaction temperature is vital in obtaining the desired product [5, 32, 33]. The effect of reaction temperature on MA hydrogenation (Fig. 3)

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led to almost 100 % MA conversion and more than 99.5 % selectivity of SA at 150 oC. Increasing the reaction temperature, MA conversion increased largely, however, the selectivity of SA decreased significantly. The conversion of MA increased from 40.3

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to 99.4 % when the reaction temperature increased from 100 to 150 oC. The unsatisfactory MA conversion rate under low reaction temperature might be caused by the thermal effect on the kinetics. Nevertheless, further hydrogenation of SA to GBL

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along with the hydrogenolysis to propionic acid and n-butanol at higher temperature would inevitably lead to lower SA selectivity. The selectivity of SA decreased from 99.6 % at 150 oC to 83.5 % at 200 oC. For this reason, 150 oC was selected as the proper reaction temperature for MA hydrogenation to SA. Fig. 4 illustrated the catalytic performance of liquid phase hydrogenation of MA at different hydrogen pressures. The influence of the hydrogen pressure on the MA hydrogenation showed that 99.4 % MA conversion with 99.6 % selectivity of SA could be obtained at a pressure of 6 MPa. The conversion of MA increased steadily with the increase of pressure, while the selectivity of SA was almost 100 % under our 7

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present experimental conditions. It was seen that MA conversion increased from 55.1 to 99.4 % when the hydrogen pressure was raised from 1 to 6 MPa. Similar results were reported by other applied metallic nickel catalysts in the MA hydrogenation [34]. The results suggested that under proper reaction conditions, the biosynthesis Ru

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catalysts could selectively hydrogenate MA to SA.

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3.1.3 Effect of Reaction Time and Solvent.

Furthermore, in order to get more insights into the turnover frequency values of

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the hydrogenation reaction, the catalytic behaviors versus reaction time on the biosynthesized catalysts were investigated, and relevant results were given in Fig. 5. It

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could be noted that the reaction time was critical in obtaining the desired MA conversion accompanied with moderate TOF values. As seen in Fig. 5, MA

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conversion increased from 81.2 to 99.4% with the increase of reaction time from 10 to 30 min and then stayed at around 100 % as the reaction time increasing from 30 to

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120 min. However, the TOF values, defined as molar of MA substrate converted per molar of Ru loading, decreased monotonously with the reaction time increasing from 10 to 120 min. Moreover, a longer reaction time would lead to the synthesis of

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overhydrogenation products such as GBL or THF, which would be detrimental to the SA selectivity. As a consequence, it could be speculated that the reaction at about 30 min was preferable considering the tradeoff between SA yield and TOF values.

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Choosing a proper solvent to facilitate the MA hydrogenation process is important because MA is in the solid state at room temperature (mp 52.8 oC). Gao et al. suggested coupling two contradictory hydrogenation and dehydrogenation reaction processes over a single catalyst. In their reaction system, the ethanol not only served as a solvent but also acted as a hydrogen feedstock for MA hydrogenation [35]. MA conversion and products selectivity in different employed solvents at 150 oC and 6 MPa were listed in Table S1. Solvent effect might play a crucial role in the hydrogenation of MA. Meanwhile, in choosing the solvent, several points should be taken into consideration, such as good solubility, easy separability, thermal stability 8

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and resistance to reduction. The conclusion drawn from Table S1 showed that the reaction without solvent was inert to catalytic activity which could be caused by the difficult interaction between the reactants and the catalysts. After reaction for 30 min, the conversion of MA for the solvent of acetic anhydride, methylbenzene, tetrahydrofuran and acetone stood at 91.2 %, 98.5 %, 99.4 % and 99.7 % respectively.

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The conversion of MA increased when the polarities of solvent decreased, which was

in contradiction with those reported by Feng et al. [34]. Moreover, the selectivity of

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SA was not affected when we used various solvents except for acetic anhydride.

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Therefore, a proper solvent should easily dissolve MA, companied with a desired yield of SA.

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3.1.4 Catalyst reusability and comparison with commercial catalysts.

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Since the stability of heterogeneous catalysts was an important parameter, the catalytic recycling tests were conducted to assess the biosynthesized Ru-based

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catalysts. The catalysts were carefully recollected and reused in subsequent cycles as the same conditions as the fresh catalysts. As shown in Table 1, the MA conversion, SA selectivity and TOF values showed minor variation during the consecutive five

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cycles, suggesting the remarkable stability of the Ru based catalysts. For comparison, blank experiment was carried out in the identical manner by replacing the Cacumen Platycladi extract with deionized water. Interestingly, an induction period could be

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observed for the ruthenium catalyst in the blank test. In addition, Ru could be detected by atomic absorption spectroscopy (AAS) analysis in the filtrate obtained from the reusability experiments. The results indicated that the leaching of Ru nanoparticles from the catalysts occurred in the blank test and Cacumen Platycladi extract played a pivotal role in the catalyst preparation. Furthermore, it is of interest to compare the bioreduction catalysts with the conventional 5.0 wt% Ru supported on carbon (purchased from Aladdin Industrial Corporation, China). As shown in Table 1, the conventional 5.0 wt% Ru/C catalysts had a MA conversion of 94.6 % with a SA selectivity of 99.5 % and a TOF value of 9

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1965.3 h-1. Evidently, the catalytic performance of the biosynthesized catalysts was comparable in term of selectivity of SA and superior in term of MA conversion and TOF value to that of the conventional impregnation catalysts, even with a lower Ru loading.

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3.2 Catalysts characterization

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In order to confirm the existence of Ru nanoparticles and its interaction with the supports, a variety of methods were adopted to characterize the structure of the

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biosynthesized Ru catalysts.

N2 physisorption was adopted to detect the mesoporous structure of the supports

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and catalysts. As shown in Table 2, both the SBET and Vp decreased slightly after introducing Ru nanoparticles, exhibiting the immobilization of the Ru nanoparticles

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into the channels of the activated carbon. Nevertheless, no significant changes in the average pore diameter of the catalysts were observed which might be a result of low

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amount of ruthenium. Moreover, when Ru loading was lower than 2 wt%, the ICP-AAS results indicated that the authentic value in the as-synthesized catalysts was the same as the nominal metal loading, thus achieving 100 % Ru capture efficiency.

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Nevertheless, the catalysts with a relative heavy loading of Ru (for example, 5 wt%) showed an inferior capture efficiency of around 70 %. The XRD patterns were recorded for the fresh supports and the bioreduction

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Ru-based catalysts (Fig. S1 of Supplementary Information). It could be noticed that the XRD pattern of 2.0 wt% Ru/AC was similar to that of activated carbon, exhibiting a weak shoulder peak at around 2θ=25o, which was assigned to the diffraction of the graphite phase (JCPDS File, no.41–1487). Only the intensity of the peaks was attenuated after introducing Ru nanoparticles into the supports [36]. That diffraction signals of the Ru nanoparticles could not be observed in Fig. S1 might be due to the low concentration and small particle size. TEM and EDS characterization have been introduced to get information on the morphology of Ru nanoparticles. The images of the bioreduction Ru catalysts clearly 10

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showed high and homogeneous dispersion of spherical metal nanoparticles throughout the surface of activated carbon, giving an average particle size of 2.17 nm (Fig. 6 a-c). Specifically, the HRTEM image in Fig. 6 (d) showed d-spacing of 2.06 Å and 2.14 Å, corresponding to (101), and (002) facets of Ru, respectively (JCPDS File, no. 65-7645). TEM-EDS further confirmed the presence of ruthenium at different

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micrographs spots (Fig. 7; Cu was from the copper grid). The morphological properties and particle size of the recycling catalysts did not show any obvious change

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after being recycled for five times (Fig. S2 of Supplementary Information).

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The surface element and electronic state of the 2.0 wt% Ru/AC catalysts were evaluated by using an XPS apparatus (Fig. S3 of Supplementary Information). The peaks corresponding to chlorine, carbon, ruthenium, oxygen and chlorine were

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distinctly detected (the Cl was from the residue plant biomass). The Ru3d lines were deconvoluted to two peaks which was attributed to Ru(0) and Ru(IV), respectively.

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The XPS measurements could confirm the presence of Ru metal particles on the

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surface of carbon supports.

3.3 The functionality of Cacumen Platycladi extract.

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The conventional chemical methods of synthesizing metal nanoparticles will inevitably suffer from the problems of using different stabilizer and reducer. However, these auxiliary materials would be not only energy intensive but also hostile to

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environment. Thus, in the bioreduction approach, without adding auxiliary organic substance, we should further specify the functionalities presented in the residual plant biomass.

FTIR analyses were used to monitor the chemical structure variation of the

Cacumen Platycladi extract before and after bioreduction. Representative FTIR spectra of Cacumen Platycladi leaf extract before and after the reaction were presented in Fig. 8. The spectra of the plant extract before the reaction (curve a) showed a number of vibration bands at 2921, 1626, 1375, 1256, 1050, and 775 cm-1. These six notable band might be assigned to several functional groups, such as C=C–H or –C–OH. The 11

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absorbance bands at 2921, 1626 and 1050 cm-1 were weakened after the reaction. The intensive bands at 2921 and 1626 cm-1 were associated with the stretching vibration of v(=C–H) and v(–C=C), respectively while the band at 1050 cm-1 may be assigned to the stretching vibration of v(–C–O) [37]. Therefore, this comparison provided information that the reductive groups of C=C or–OH in the Cacumen Platycladi extract were

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responsible for the chemical transformation of ruthenium ions.

Intensive studies show that the major components of the Cacumen Platycladi

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extract are flavonoids, reducing sugars, polysaccharides, and proteins, and other

reducing sugars

were

important

reductants

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substances (amino acids or polyphenols) [38, 39]. Among them, flavonoids and responsible

for

the

chemical

transformation of ruthenium ions. Zhan reported the synthesis of gold nanoparticles

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with different shapes using Cacumen Platycladi extract [38]. Zhang demonstrated the green synthesis of Au-Ag alloy nanoparticles using Cacumen Platycladi extract [40].

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Chen explored the size controllable synthesis of Ni nanoparticles by the plant-mediated method using the alfalfa extract [41]. These previous results reached the same

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conclusion that the flavonoids and reducing sugars were the main categories of the ingredients in the plant extract which affected the chemical transformation of the noble

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metals. The decrease in intensity at 2921 and 1626 cm-1, which is ascribed to C=C or–OH, indicated the component change of flavonoids and reducing sugars [42]. Hence, these flavonoids and reducing sugars in the extract were responsible for the reduction of Ru ions.

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Moreover, the new band centered at 1740 cm-1 in the Cacumen Platycladi leaf

extract after bioreduction could be contributed by the stretch vibration of the carbonyl groups [v(–C=O)] [40], which might be the oxidation product of polyols. This freshly band could play a pivotal role in protecting the Ru nanoparticles. As in the chemical routes of synthesizing noble nanoparticles, the stabilization of the particles using stabilizer, such as PVP, was resulted from the adsorption of the PVP –C=O group to the particles surface [43]. The evolution of the peaks indicated the existence of –C=C and –C=O group which could act as capping ligands for the nanoparticles. Meanwhile, XPS spectra of 2.0 wt% Ru/AC (vide supra) indicated the present of large amount of C 12

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and O on the surface of Ru nanoparticles. The C and O have a probability of binding to the Ru nanoparticles via the functional groups. Simultaneously, TG analysis confirmed the presence of some residual plant biomass around the Ru nanoparticles (Fig. S4 of Supplementary Information). Thus, it was reasonable to speculate that these plant biomass were responsible for stabilization of the nanoparticles. On the basis of the

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results of the above FTIR and TG techniques, we believed that polyols such as flavonoids and reducing sugars containing C=C–H and C–O–H functional groups were

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responsible for the reduction of Ru precursors while the components containing –C=O

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functional groups served as the protecting agents.

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4. Conclusions

The ruthenium based catalysts prepared by Cacumen Platycladi leaf extract

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could be served as effective catalysts in selective hydrogenation of maleic anhydride. The optimized conditions, Ru loading of 2 wt%, reaction temperature of 150 oC,

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hydrogen pressure of 6 MPa, and the time length of 30 min with the choice of tetrahydrofuran as solvent, could lead to succinic anhydride selectivity of 99.6 % with

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almost 100% conversion of maleic anhydride. The biosynthesized Ru-based catalysts could be reused for five cycles and the activity was also comparable to the commercial Ru/C catalysts, even with a lower Ru loading. Based on the characterization analyses, the successfully introduction of Ru nanoparticles was

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achieved by the means of the bioreduction method, while the main components containing C=C–H, C–O–H and –C=O in the plant leaf extract served as both reducing and protecting agents. We believed that this research would open up new opportunities for the preparation of bioreduction catalysts and their application in MA hydrogenation.

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Acknowledgments We gratefully acknowledge the key program (No. U1361112) of the National Natural Sciences Foundation of China, and the Fundamental Research Funds for the

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Central Universities (2013QNA4035) for the financial support.

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[24] D.K. Mishra, A.A. Dabbawala, J.J. Park, S.H. Jhung, J.-S. Hwang, Catal. Today 232 (2014) 99-107. [25] D.K. Mishra, A.A. Dabbawala, J.-S. Hwang, J. Mol. Catal. A: Chem. 376 (2013) 63-70. [26] B. Bachiller-Baeza, I. Rodrıguez-Ramos, A. Guerrero-Ruiz, Appl. Catal. A: Gen. 205 (2001) 227-237. [27] Y. Huang, Y. Ma, Y. Cheng, L. Wang, X. Li, Ind. Eng. Chem. Res. 53 (2014) 4604-4613. [28] U.G. Hong, J.K. Kim, J. Lee, J.K. Lee, J.H. Song, J. Yi, I.K. Song, Appl. Catal. A: Gen. 469 (2014) 466-471. [29] G. Zhan, M. Du, J. Huang, Q. Li, Catal. Commun. 12 (2011) 830-833. [30] G. Zhan, M. Du, D. Sun, J. Huang, X. Yang, Y. Ma, A.-R. Ibrahim, Q. Li, Ind. Eng. Chem. Res. 50 (2011) 9019-9026. [31] Y. Ma, Y. Huang, Y. Cheng, L. Wang, X. Li, Appl. Catal. A: Gen. 484 (2014) 154-160. [32] U.R. Pillai, E. Sahle-Demessie, D. Young, Appl. Catal. B: Environ. 43 (2003) 131-138. [33] Y. Yu, Y. Guo, W. Zhan, Y. Guo, Y. Wang, Y. Wang, Z. Zhang, G. Lu, J. Mol. Catal. A: Chem. 337 (2011) 77-81. [34] Y. Feng, H. Yin, A. Wang, T. Xie, T. Jiang, Appl. Catal. A: Gen. 425 (2012) 205-212. [35] D. Gao, Y. Feng, H. Yin, A. Wang, T. Jiang, Chem. Eng. J. 233 (2013) 349-359. [36] W. Wang, H. Liu, T. Wu, P. Zhang, G. Ding, S. Liang, T. Jiang, B. Han, J. Mol. Catal. A: Chem. 355 (2012) 174-179. [37] X. Yang, Q. Li, H. Wang, J. Huang, L. Lin, W. Wang, D. Sun, Y. Su, J.B. Opiyo, L. Hong, J. Nanopart. Res. 12 (2010) 1589-1598. [38] G. Zhan, J. Huang, L. Lin, W. Lin, K. Emmanuel, Q. Li, J. Nanopart. Res. 13 (2011) 4957-4968. [39] Y. Zhou, W. Lin, J. Huang, W. Wang, Y. Gao, L. Lin, Q. Li, L. Lin, M. Du, Nanoscale Res. Lett. 5 (2010) 1351-1359. [40] G. Zhang, M. Du, Q. Li, X. Li, J. Huang, X. Jiang, D. Sun, RSC Adv. 3 (2013) 1878-1884. [41] H. Chen, J. Wang, D. Huang, X. Chen, J. Zhu, D. Sun, J. Huang, Q. Li, Mater. Lett. 122 (2014) 166-169. [42] H. Chen, D. Huang, X. Su, J. Huang, X. Jing, M. Du, D. Sun, L. Jia, Q. Li, Chem. Eng. J. 262 (2015) 356-363. [43] A. Nemamcha, J.-L. Rehspringer, D. Khatmi, J. Phys. Chem. B, 110 (2006) 383-387.

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Table

Table captions in sequence Table 1 Catalyst reusability studies during MA hydrogenation and comparison with commercial catalysts.

Ac

ce pt

ed

M

an

us

cr

ip t

Table 2 Textural properties of the supports and synthesized catalysts

1

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Table 1 Catalyst reusability studies during MA hydrogenation and comparison with commercial catalysts. Entry

Conversion of MA (%)

Selectivity of SA (%)

TOF (h-1)

Ru/AC a

Fresh 1 recycle 2nd recycle 3rd recycle 4th recycle 5th recycle

99.4 99.5 99.2 99.1 99.1 98.9

99.6 99.5 99.6 99.4 99.5 99.6

2084.9 2073.6 2054.8 2049.5 2038.6 2039.3

Ru/C b

Fresh

94.6

99.5

1965.32

cr

st

ip t

Catalyst

Ac

ce pt

ed

M

an

us

Reaction conditions: MA concentration 2 mol/L (18 wt%), catalyst 50 mg, reaction temperature 150 o C, hydrogen pressure 6 MPa. a Ruthenium catalysts (2.0 wt%) prepared by Cacumen Platycladi leaf extract. b Conventional 5.0 wt% Ru/C catalyst from Aladdin Industrial Corporation, China.

2

Page 19 of 29

Table 2 Textural properties of the supports and synthesized catalysts Ru loading (wt %)b

SBET (m2·g-1)

Vp (cm3·g-1)c

Dp (nm)d

actived carbon(AC) 0.25 % Ru/AC 0.5 % Ru/AC 1.0 % Ru/AC 2.0 % Ru/AC 3.0 % Ru/AC 5.0 % Ru/AC

0.25 0.5 1.0 2.0 2.4 3.6

995 991 964 959 949 865 862

1.08 1.01 0.95 0.95 0.94 0.84 0.87

3.7 4.0 4.1 3.9 4.0 4.0 3.9

cr

ip t

Samplea

Preparation conditions: preparation temperature 60 oC, calcination temperature 500 oC.

b

Determined by ICP-AAS. c Pore volume. d Average pore diameter.

Ac

ce pt

ed

M

an

us

a

3

Page 20 of 29

Figure

Figure captions in sequence Fig. 1. Reaction pathway of the hydrogenation of maleic anhydride. Fig. 2. Effect of Ru loading on MA conversion and SA selectivity. Reaction conditions: MA

ip t

concentration 2 mol/L (18 wt%), catalyst 50 mg, reaction temperature 150 oC, hydrogen pressure 6 MPa, reaction time 30 min.

cr

Fig. 3. Catalytic performance of bioreduction catalysts (2.0 wt% Ru/AC) as a function of reaction

us

temperature. Reaction conditions: MA concentration 2 mol/L (18 wt%), catalyst 50 mg, hydrogen pressure 6 MPa, reaction time 30 min.

an

Fig. 4. Catalytic performance of bioreduction catalysts (2.0 wt% Ru/AC) as a function of

M

hydrogen pressure. Reaction conditions: MA concentration 2 mol/L (18 wt%), catalyst 50 mg, reaction temperature 150 oC, reaction time 30 min.

ed

Fig. 5. Catalytic performance of bioreduction catalysts (2.0 wt% Ru/AC) as a function of reaction time. Reaction conditions: MA concentration 2 mol/L (18 wt%), catalyst 50 mg, reaction

ce pt

temperature 150 oC, hydrogen pressure 6 MPa.

Fig. 6. TEM and HRTEM images of 2.0 wt% Ru/AC.

Ac

Fig. 7. EDS spectrum and its elemental analysis of 2.0 wt% Ru/AC. Fig. 8. FTIR spectra of Cacumen Platycladi extract (a) before bioreaction and (b) after bioreaction.

1

Page 21 of 29

ip t cr us

Ac

ce pt

ed

M

an

Fig. 1. Reaction pathway of the hydrogenation of maleic anhydride.

2

Page 22 of 29

GBL

SA

80

80

60

60

ip t 40

cr

40 20

20

0.25

0.50

1.0

2.0

3.0

5.0

0

an

0

Selectivity (%)

100

us

Conversion of MA (%)

Conversion of MA

100

Ruthenium loading (wt%)

Ac

ce pt

ed

M

Fig. 2. Effect of Ru loading on MA conversion and SA selectivity. Reaction conditions: MA concentration 2 mol/L (18 wt%), catalyst 50 mg, reaction temperature 150 oC, hydrogen pressure 6 MPa, reaction time 30 min.

3

Page 23 of 29

SA

PA+n-butanol

GBL

TOF

100

2000

ip t

1500 60

1000

cr

40

500

100

125

150

us

20 0

TOF (h-1)

80

175

200

0

an

Conversion or Selectivity (%)

MA

Reation temperature (oC)

Ac

ce pt

ed

M

Fig. 3. Catalytic performance of bioreduction catalysts (2.0 wt% Ru/AC) as a function of reaction temperature. Reaction conditions: MA concentration 2 mol/L (18 wt%), catalyst 50 mg, hydrogen pressure 6 MPa, reaction time 30 min.

4

Page 24 of 29

GBL

TOF

100

2000

80 1500

ip t

60

1000

cr

40

500

2

3

4

5

6

7

0

an

1

us

20 0

TOF (h-1)

Conversion or Selectivity (%)

SA

MA

Hydrogen pressure (MPa)

Ac

ce pt

ed

M

Fig. 4. Catalytic performance of bioreduction catalysts (2.0 wt% Ru/AC) as a function of hydrogen pressure. Reaction conditions: MA concentration 2 mol/L (18 wt%), catalyst 50 mg, reaction temperature 150 oC, reaction time 30 min.

5

Page 25 of 29

GBL

TOF

5000

80

4000

ip t

100

3000

60

2000

cr

40

1000

20

30

60

120

0

an

10

us

20 0

TOF (h-1)

Conversion or Selectivity (%)

SA

MA

Reaction time (min)

Ac

ce pt

ed

M

Fig. 5. Catalytic performance of bioreduction catalysts (2.0 wt% Ru/AC) as a function of reaction time. Reaction conditions: MA concentration 2 mol/L (18 wt%), catalyst 50 mg, reaction temperature 150 oC, hydrogen pressure 6 MPa.

6

Page 26 of 29

ip t cr us an M ed

Ac

ce pt

Fig. 6. TEM and HRTEM images of 2.0 wt% Ru/AC.

7

Page 27 of 29

ip t cr us

Ac

ce pt

ed

M

an

Fig. 7. EDS spectrum and its elemental analysis of 2.0 wt% Ru/AC.

8

Page 28 of 29

2000

1050

1256

1500

a

cr

1626 2500

an

3000

us

1375

775

ip t

1740

2921

Transmittance(a.u.)

b

1000

500

Wavenumber (cm-1)

Ac

ce pt

ed

M

Fig. 8. FTIR spectra of Cacumen Platycladi extract (a) before bioreaction and (b) after bioreaction.

9

Page 29 of 29