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Catalysis Today 185 (2012) 104– 108

Contents lists available at SciVerse ScienceDirect

Catalysis Today

j ourna l ho me p ag e: www.elsev ier .com/ lo cate /ca t tod

iquid phase hydrogenation of d-glucose to d-sorbitol over the catalystRu/NiO–TiO2) of ruthenium on a NiO-modified TiO2 support

inesh Kumar Mishra, Jong-Min Lee, Jong-San Chang, Jin-Soo Hwang ∗

iorefinery Research Center, Korea Research Institute of Chemical Technology (KRICT), Daejeon 305-600, Republic of Korea

r t i c l e i n f o

rticle history:eceived 31 May 2011eceived in revised form 6 October 2011ccepted 18 November 2011vailable online 24 December 2011

eywords:ydrogenation-Glucose

a b s t r a c t

The catalyst of ruthenium (Ru) on a new class of NiO-modified TiO2 support material, that is,Ru/(NiO–TiO2) was employed especially for selective hydrogenation of d-glucose to d-sorbitol. The mod-ification of the TiO2 support was carried out with a nickel precursor by a simple impregnation method.After calcinations, the stable NiO-modified TiO2 support was re-impregnated with ruthenium (III) chlo-ride hydrate aqueous solution. An additive effect of NiO in its corresponding catalyst of ruthenium ona NiO-modified TiO2 support exhibits the enhancement in the selectivity to d-sorbitol by minimizingthe d-fructose and d-mannitol. To develop our understanding for the activity of the catalysts, the hydro-genation of d-glucose was investigated with the effect of (1.0 wt.% and 5.0 wt.%) ruthenium loading and

-SorbitolutheniumiO-modified TiO2 support

(2.0–10 wt.%) NiO loading followed by the pretreatment of the catalysts. The reaction condition was opti-mized by varying the concentrations of d-glucose (from 10 to 30 wt.%) and temperatures (from 90 ◦C to120 ◦C) to reach up to the highest product selectivity to d-sorbitol. These catalysts were characterizedby using energy dispersive X-ray (EDX) analysis, temperature-programmed reduction (TPR), inductivelycoupled plasma atomic emission spectrometry (ICP-AES), transmission electron microscopy (TEM), X-ray

and

powder diffraction (XRD)

. Introduction

The catalytic hydrogenation of d-glucose (dextrose) to d-orbitol (glucitol) is of great industrial importance because-sorbitol is widely used as an additive in foods, drugs, and cosmet-

cs [1–5], and it is also used as an intermediate in l-ascorbic acidvitamin C) synthesis [6]. While, only a small amount of d-sorbitolan be obtained naturally from red seaweed and some fruits, com-ercial large scale production of d-sorbitol has always relied on the

ydrogenation of d-glucose in which Raney Ni catalyst is frequentlysed [7,8]. Although, Raney nickel has advantages such as lowost, excellent settling, and high activity, it suffers from its leach-ng properties rendering the process economically less attractive9–12]. Therefore, many scientists and researchers have focused oneveloping catalysts based on other active metals including cobalt,latinum, palladium, rhodium and ruthenium [13–15]. Catalystsased on ruthenium have potential for the hydrogenation of d-lucose; however, high cost poses a problem. To reduce the cost,ifferent supports, such as SiO2, MCM-41, and carbon are used.

atalyst ruthenium supported on carbon has been recognized asn alternative because of non-leaching and high activity [14–18].etal-metalloid amorphous alloy catalysts have also attracted

∗ Corresponding author. Tel.: +82 42 860 7382; fax: +82 42 860 7676.E-mail address: jshwang@krict.re.kr (J.-S. Hwang).

920-5861/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.cattod.2011.11.020

CO chemisorption.© 2011 Elsevier B.V. All rights reserved.

much attention due to their high activity and better selectivityduring hydrogenation [19–22]. Traditionally, those materials wereusually prepared in the form of ultrafine particles by chemicalreduction. An ultrafine Ru-B amorphous alloy catalyst in partic-ular has become more effective in the liquid phase hydrogenationof d-glucose [23,24]. However, its application in industrial cataly-sis seemed almost impossible because of its poor thermal stabilityor/and low surface area. One of the most promising methods isto deposit those ultrafine amorphous alloy particles on a supportwith a high surface area [24–29]. Researchers have reported theuse of amorphous ruthenium catalyst Ru-B alloy in combinationwith a different loading of alumina (�-Al2O3) support used forhydrogenation of ethyl lactate [30] and benzene [31], respectively.Therefore, in this study, an attempt has been made to develop ahitherto unreported catalyst of ruthenium and a new class of NiO-modified TiO2 support which could show much better performancetowards the liquid phase hydrogenation of d-glucose to d-sorbitolthan the catalyst of ruthenium on TiO2 support under the samereaction conditions.

2. Experimental

2.1. Materials

Ruthenium (III) chloride hydrate (RuCl3·xH2O) containing(99.9% Ru) was purchased from Strem Chemicals, Newburyport,

D.K. Mishra et al. / Catalysis Today 185 (2012) 104– 108 105

Table 1Characteristic properties of the catalysts.

Catalysts Precursor SBETa (m2/g) [Vmicropore] ×102 (cm3/g) SRu

b (m2/g catalyst) Dispersion (%) Particle sizec (nm)

Ru (1.0%)/NiO (5.0%)–TiO2

(passid + rede)RuCl3·xH2O – – –

Ru (1.0%)/NiO (5.0%)–TiO2 rede – 42.5 0.31 1.9 63.2 2.0Ru (1%)/TiO2 rede – 57.6 0.43 4.3 97.8 2.5

a Determined by N2 adsorption–desorption at 77 K.b Determined by CO adsorption–desorption.c Obtained by transmission electron microscopy (TEM).d Passivation with (5%) O2/N2 at room temperature.

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2

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2

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3

escMriAs(m

e Reduction under H2/Ar (5%) at 200 ◦C.

A, USA. Nickel chloride was purchased from Sigma–Aldrich com-any, Inc., (U.S.A.). The support titanium (IV) oxide (rutile-type)TiO2), 99.9%-purity, shape fine powder of about 1 to −2 �m parti-le size was purchased from Degussa and was used after drying at10 ◦C. For the solution, de-ionized water was used as a solvent.

.2. Preparation of the catalysts

The catalyst of ruthenium on a NiO-modified TiO2 support wasrepared by the following procedure. The preweighed amount4.8 g) of TiO2 support was impregnated with the nickel chlo-ide (0.55 g) aqueous solution and was kept in an oven at 110 ◦Cvernight. After being dried completely, the sample was oxidized inir at 500 ◦C. The calculated amount of NiO-modified TiO2 supportNiO–TiO2) was re-impregnated with the ruthenium (III) chlorideydrate (0.52 g) aqueous solution and was kept in an oven at 110 ◦Cvernight. The as-prepared catalyst was reduced with a flow of (5%)2/Ar at 200 ◦C for 3 h and used immediately for the hydrogenationf d-glucose. The reduced catalyst was then passivated with (5%)2/N2 at room temperature.

.3. Hydrogenation of d-glucose

The hydrogenation of d-glucose was performed in a 200 mLtainless autoclave. The catalyst was screened with 20 wt.% d-lucose solution prepared in water at approximately 65 ◦C. Toeoxygenate the reaction mixture, the hydrogen gas was purged

nto the reactor at a low pressure of 2.0 MPa and stirred at 400 rpmor 30 min and then pressure was released. The hydrogenation of-glucose was started by stirring the reaction mixture at 1200 rpm

mpeller speed and 120 ◦C for 120 min at 5.5 MPa. The product dis-ribution was analyzed by HPLC/RI detection (column: Sugar-Pakperated at 70 ◦C, eluent water with flow rate of 0.4 mL/min).

Before starting the TPR experiments, the as-prepared samplesere dried with an argon (Ar) flow at 120 ◦C for 1 h and then allowed

o cool down to the room temperature. The (10%) H2/Ar was useds a reducing gas at a continuous flow rate of 10 mL/min. The rate ofemperature rise in the TPR experiments up to 500 ◦C was 5 ◦C/min.

. Catalysts characterization

The amount of ruthenium (% loading of Ru) was observed bynergy dispersive X-ray (EDX, Bruker, Quantax 200 Energy Disper-ive X-ray Spectrometer). The supports and their correspondingatalysts were characterized by X-ray diffraction (XRD, Rigaku,iniflex Instruments). The amount of metal ions present in the

eaction mixture after hydrogenation reactions was analyzed bynductively coupled plasma-atomic emission spectrometry (ICP-

ES, Thermo Scientific ICAP 6500 duo). Morphology and particleize both were determined by transmission electron microscopyTEM, Maker FEI, Model Technai G2). For transmission electron

icroscopy examination, the catalyst samples were dissolved in

2-propanol, dispersed carefully in an ultrasonic bath and thendeposited on carbon-coated copper grids. BET surface area wasdetermined by N2 adsorption–desorption at 77 K with a Microw-metrics, Tristar II analyzer. For each measurement, the sample wasdegassed at 250 ◦C for 3–4 h, then analyzed at 77 K (liquid N2 tem-perature) with N2 analysis gas at relative pressures (P/P0) from0.005 to 1.0 (adsorption) and 1.0 to 0.1 (desorption). CO chemisorp-tion was carried out by using an Instrument Model ASAP 2020CV1.09 G. The samples weighed approximately 0.12 g. Before adsorp-tion of CO, the catalysts were pretreated in He for 35 min and, in O2for 15 min, and then reduced for 30 min in a (5%) H2/Ar gas flow of50 mL/min, and in He for 15 min at 400 ◦C K in a reaction chamber.After this pretreatment, the samples were cooled down to 50 ◦Cunder He gas flow and CO pulse measurements were carried outusing a (5%) CO/He gas flow of 50 mL/min. Finally, the surface con-centration and dispersion of metallic Ru were obtained from theCO pulse analysis data.

4. Results and discussion

4.1. Characteristic properties of the catalysts

The catalysts of ruthenium on NiO-modified TiO2 and TiO2supports were prepared by a simple impregnation method. The per-cent (%) loading of ruthenium, NiO with TiO2 and characterizationresults are summarized in Table 1. Even though the dispersion ofmetallic ruthenium over NiO-modified TiO2 support with BET sur-face area is lower than that of metallic ruthenium over TiO2 support.The catalyst of ruthenium on a NiO-modified TiO2 support showedgood results towards selective hydrogenation of d-glucose to d-sorbitol. To study the leaching properties of ruthenium, the productsolution was analyzed and results are summarized in Table 2. Theresults with Ru/NiO–TiO2 show that Ru leached lesser extent withNi than Ru/TiO2. The data reveal that the catalyst of rutheniumon NiO-modified TiO2 is stable and capable of minimizing the by-products of d-fructose and d-mannitol.

As shown in Fig. 1, the XRD pattern (a) of NiO is given as forreference. On comparing the XRD patterns of TiO2 (b) and thecorresponding NiO-modified TiO2 (c) supports, both have obviousdifferences. There are the characteristic peaks of NiO assigned at2� = 37◦, 43◦, 62◦, 75◦ and 79◦ in the sample of NiO–TiO2, indicat-ing that the TiO2 support was successfully modified with nickelchloride. However, the XRD patterns of NiO-modified TiO2 support(c) and the corresponding catalyst Ru (1.0%)/NiO (5.0%)–TiO2 (d)show very similar diffraction patterns. The peaks attributed to themetallic ruthenium could not be appeared because the rutheniumcontent of less than (5.0 wt.%) was covered by the NiO-modified

TiO2 support as determined by XRD [32]. The XRD pattern of the cat-alyst Ru (1.0%)/NiO (5.0%)–TiO2 separated after reaction (e) is alsosimilar to that of the catalyst Ru (1.0%)/NiO (5.0%)–TiO2. This indi-cates that the catalyst of ruthenium on a NiO-modified TiO2 support

106 D.K. Mishra et al. / Catalysis Today 185 (2012) 104– 108

Table 2Ruthenium content and study of leaching property.

Catalysts Precursors Ru contenta (wt.%) Ru loadingb (wt.%) Leachingc (mg/L)

Ru Ti Ni

Ru (1.0%)/NiO (5.0%)–TiO2 (passid + rede) RuCl3·xH2O 1.0 1.2 N.D. N.D. 35.0Ru (1.0%)/NiO (5.0%)–TiO2 rede – 1.0 1.2 0.31 N.D. 11.0Ru (1%)/TiO2 rede – 1.0 0.9 0.34 N.D. 0.0

ND, not detecteda Ru content (1.0) wt.% loaded on NiO modified TiO2 support experimentally.b Obtained by energy dispersive X-ray (EDX) analysis.c Obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES).d Passivation with (5%) O2/N2 at room temperature.e Reduction under H2/Ar (5%) at 200 ◦C.

Fa

is

Tmhidn

ig. 1. XRD patterns of (a) NiO as reference, (b) TiO2, (c) NiO–TiO2, (d) Ru/NiO–TiO2,nd (e) Ru/NiO–TiO2 after reaction.

s stable towards the liquid phase hydrogenation of d-glucose andhows higher selectivity to the main product d-sorbitol.

Fig. 2 shows the TEM images of the catalysts of ruthenium oniO2 and a NiO-modified TiO2 supports. Image (a) shows that theetallic ruthenium (dark black) particles of diameter (2.5 nm) were

ighly dispersed on TiO2 support (large gray flakes). In the nextmage (b), the particles in the range of (10–12 nm) of NiO (largeark black) are dispersed on TiO2 support. Even though the ruthe-ium particles were smaller in size (2.0 nm) and dispersed over

Fig. 2. TEM images of (a) Ru/TiO2, (b) Ru/Ni

Fig. 3. H2-TPR profile of (a) TiO2, (b) Ru/TiO2, (c) NiO–TiO2 and (d) Ru/NiO–TiO2.

NiO-modified TiO2 support, may not be seen clearly in image (b).The existence of all these three components of ruthenium, NiO, andTiO2 support can also be recognized in EDX analysis and the EDXspectrum of the same sample was shown in image (c).

Fig. 3 shows the H2-TPR profile of the TiO2 support, cata-

lyst Ru/TiO2, NiO-modified TiO2 support (NiO–TiO2), and catalystRu/NiO–TiO2. The TPR curve (a) of TiO2 support is given as for a ref-erence. In curve b, there is a set of two TPR peaks at about 170 ◦C as aresult reduction of Ru3+ → Ru0 and at 320 ◦C as a result of ruthenium

O–TiO2 and (c) EDAX of Ru/NiO–TiO2.

D.K. Mishra et al. / Catalysis Tod

igarTtdt(bftNttt

4r

isgr

Fsr(

Fig. 4. A schematic daigram of catalysts pretreatment.

nteracted with TiO2 support, respectively. In curve (c), a hydro-en reduction peak occurring at approximately 378 ◦C might bettributed to the Ni2+ converted into Ni0 as Richardson et al. [33]eported that NiO needs to reduce into Ni at higher temperature.he reduction of NiO at high temperature is due to strong interac-ion with the TiO2 support. On the other hand, Ru/NiO–TiO2 (curve) shows a peak at about 150 ◦C, which is attributed to the reduc-ion of Ru3+ → Ru0 appearing at nearly the same position in curveb). An additional peak appearing at approximately 425 ◦C mighte a delayed reduction of Ni2+ → Ni0 deposited bulky on the sur-ace of the TiO2 support. The H2-TPR data reveals that the sufficientemperature for the reduction of Ru3+ → Ru0 without affecting theiO-modified TiO2 support is approximately 200 ◦C. The shifting of

hese two peaks, which occurred at 170 ◦C and 320 ◦C also revealshat particles of Ru dispersed on the NiO strongly interacted withhe TiO2 support.

.2. The effect of catalysts pretreatment and the percentuthenium loading in the catalyst

Before hydrogenation of d-glucose, the catalysts were treated

n various ways. All the routes 1a and b, and 2a are shown in achematic diagram of catalysts pretreatment (Fig. 4). The hydro-enation of d-glucose was performed with different catalysts ofuthenium on TiO2 and a NiO-modified TiO2 supports, respectively.

ig. 5. Conversion (%Con.) of d-glucose, yield (%Yield) and selectivity (%Sel.) to D-orbitol of (A) Ru (1.0%)/TiO2 after reduction, (B) Ru (1.0%)/NiO (5.0%)–TiO2 aftereduction, (C) Ru (5.0%)/NiO(5.0%)–TiO2 after reduction, and (D) Ru (1.0%)/NiO5.0%)–TiO2 after passivation and reduction.

ay 185 (2012) 104– 108 107

The reaction results (a set of columns A in Fig. 5) as obtainedwith Ru (1.0%)/TiO2 show low d-glucose conversion (92.5%) withselectivity to d-sorbitol (93.7%), whereas the results obtained withthe catalyst of ruthenium on a NiO-modified TiO2 support, i.e.Ru (1.0%)/NiO (5.0%)–TiO2 show that the d-glucose conversionremained unchanged while the selectivity to d-sorbitol increasedinterestingly up to (96.6%). Comparing the selectivity to d-sorbitol,the catalyst of ruthenium on a NiO-modified TiO2 support Ru(1.0%)/NiO (5.0%)–TiO2 showed higher selectivity than the cata-lyst of ruthenium of TiO2 because NiO modified TiO2 support isvery stable, and this suppresses the isomerization of d-glucose tod-fructose [34,35].

The catalyst of ruthenium on a NiO-modified TiO2 supportwith a high percentage loading (5.0 wt.%) of ruthenium, i.e. Ru(5.0%)/NiO (5.0%)–TiO2 is not much more effective towards thehigh selectivity to d-sorbitol. Comparing the two sets (b and c)of columns in Fig. 5, the results show that the selectivity tod-sorbitol remained unchanged whereas the conversion of d-glucose (from 92.2 to 94.9%) and the yield (from 89.0 to 91.8%)increased.

The hydrogenation of d-glucose was performed with the cat-alyst of ruthenium on a NiO-modified TiO2 support by followingroutes 1a and b as shown in Fig. 4. The route (1b) includingpassivation and subsequent reduction is more effective to route(1a). The results show the highest conversion of d-glucose up to(95.1%) and the selectivity to d-sorbitol up to (97.2%), respectively.It has been observed that the passivation plays important rolesin increasing the selectivity to d-sorbitol by minimizing other by-products such as d-fructose and d-mannitol, as described by Lobryde Bruyn-Alberda van Ekenstein in a reaction network for d-glucosehydrogenation [36]. The catalyst of ruthenium on a NiO-modifiedTiO2 support, i.e. Ru (1.0%)/NiO (5.0%)–TiO2 minimizes the forma-tion of these two by-products of d-fructose and d-mannitol andshows high selectivity to d-sorbitol and d-glucose conversion underthe same hydrogenation condition.

4.3. Effect of d-glucose concentrations, temperatures and percentNiO loading on the conversion of d-glucose and the selectivity tod-sorbitol

The effect of d-glucose concentrations (from 10 to 30 wt.%) onconversion of d-glucose and selectivity to d-sorbitol have beenstudied and the results are given in Fig. 6a. With 10% d-glucose con-centration, the conversion of d-glucose is highest (96.5%) becausethe d-glucose molecules are strongly adsorbed during hydrogena-tion, it reaches saturated adsorption rapidly. The conversion ofd-glucose decreases down to (92.2%) with 20 wt.% d-glucose con-centration and thereafter, is almost same (92.4%) with 30 wt.%d-glucose concentration. This is due to the relatively weak strengthof adsorption of d-glucose molecules at its high concentration dur-ing hydrogenation [23]. On other hand, the selectivity to d-sorbitoldecreased down (from 98.5 to 93.0%) continuously. The resultsreveal that the low concentration of d-glucose might be effectivefor high conversion of d-glucose and the selectivity to d-sorbitol ina selective hydrogenation of d-glucose.

The results of d-glucose hydrogenation investigated in the tem-perature ranges from 90 ◦C to 120 ◦C are presented in Fig. 6b. It canbe seen that the conversion of d-glucose as a function of temper-ature increased from 90.1% to 95.5% continuously. On increasingthe temperature from 90 ◦C to 120 ◦C, the selectivity to d-sorbitolimproved and increased from 96.2 to 96.6%. The results with 150 ◦Cshow the selectivity to d-sorbitol tremendously decreased down

to (87.0%) due to the formation of many by-products such asd-fructose (4.8%), mannitol (2.5%), d-mannose (1.4%) and otherby-products (4.4%) [37]. Based on results, it can be seen that theappropriate temperature for d-gluocse hydrogenation is 120 ◦C.

108 D.K. Mishra et al. / Catalysis Today 185 (2012) 104– 108

t NiO l

eoirtTostoilrtfp

5

ossihlmtTfTcuta

A

otS

[[[

[[[

[[[

[[[[[

[

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[[[[[

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Fig. 6. Effect of d-glucose concentrations (a), temperatures (b) and percen

The hydrogenation of d-glucose has been performed with differ-nt percentages loading (from 2.0 to 10 wt.%) of NiO in the catalystf ruthenium on NiO-modified TiO2 and the results are presentedn the Fig. 6c. It can be seen that the conversion of d-glucoseemains unchanged with different percentages loading (from 2.0o 10 wt.%) of NiO in the catalyst of ruthenium on NiO-modifiediO2. While, the results with 2.0 wt.% NiO loading in the catalystf ruthenium on NiO-modified TiO2, i.e. Ru (1.0%)/NiO (2.0%)–TiO2hows low the selectivity to d-sorbitol, i.e. (92.5%). On increasinghe percentage loading of NiO up to the 5.0 wt.% in the catalystf ruthenium on NiO-modified TiO2, the selectivity to d-sorbitolncreased from 92.6 to 96.6% interestingly. Beyond 5.0 wt.% NiOoading, there is no change in the selectivity to d-sorbitol and alsoemains unchanged. The results reveal that 5.0 wt.% NiO loading inhe catalyst of ruthenium on NiO-modified TiO2 is more effectiveor the highest selectivity to d-sorbitol by minimizing the other byroducts d-fructose and d-mannitol.

. Conclusion

Additive effect of NiO (5.0 wt.%) in the catalyst of rutheniumn a NiO-modified TiO2 support exhibits the enhancement in theelectivity to d-sorbitol (96.6%) interestingly. The passivation andubsequent reduction of the catalyst also plays important roles inncreasing the selectivity to d-sorbitol (97.2%). The liquid phaseydrogenation of d-glucose over the hitherto unreported cata-

yst of ruthenium on a new class of NiO-modified TiO2 supportaterial, i.e. Ru (1.0%)/NiO (5.0%)–TiO2 achieves highest selec-

ivity to d-sorbitol (98.5%) with 10% d-glucose concentration.he catalyst of ruthenium on a NiO-modified TiO2 support wasound to be more effective than the catalyst of ruthenium oniO2 support, Ru (1.0%)/TiO2. Overall, it is concluded that theatalyst of ruthenium on a NiO-modified TiO2 support can besed as an alternative to Ru (1.0%)/TiO2 for selective hydrogena-ion of d-glucose to d-sorbitol, and it is suitable for industrialpplication.

cknowledgements

This work was supported by the Institutional Research Programf KRICT and by a grant (B551179-10-03-00) from the coopera-ive R&D Program funded by the Korea Research Council Industrialcience and Technology, Republic of Korea.

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oading (c) on the conversion of d-glucose and the selectivity to d-sorbitol.

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