Hydrogenation of sugars over supported metal catalyst:

Effect of support

Anup Tathod & Paresh Dhepe*CSIR-National Chemical Laboratory, Pune-411 008, India.

*Tel.No. +91 20 25902024, E-mail: pl.dhepe@ncl.res.in

Introduction

Conclusions

Catalyst preparation & Characterization

Pt/γ-Al2O3+HT catalytic system shows highest activity for hydrogenation of xylose &

glucose.

On basic support metal particles are stabilized and gives higher dispersion as compare

to acidic support.

Combined effect of metal-support interaction and acidic or basic sites governs the

activity of catalyst towards hydrogenation of sugars.

Catalyst shows good recyclability.

In current work, heterogeneous catalysts for the hydrogenation of sugars are developed

which overcome the drawbacks of earlier reported methods, like use of homogeneous

catalyst (enzymes) and deactivation of catalyst during reaction.

Sorbitol and xylitol are named among top twelve value-added chemicals from biomass

(US DOE report).

Sorbitol is used in the production of isosorbide, sorbose, 1,4-sorbitan, glycols, lactic

acid, vitamin C and C5, C6 hydrocarbons.

Sugar alcohols are being used in low calorie sweetener, oral hygiene products,

cosmetics and pharmaceutical industries . It has non-diabetes and anti-caries properties,

also used in osteoporosis treatment.

TEM Images

Pt/HT freshPt/ γ-Al2O3 spent

100 nm

0

10

20

30

40

50

60

70

80

10-20 20-30 30-40 40-50 50-60

No

. o

f p

art

icle

s

Size of particle (nm)

100 nm

Pt/ γ-Al2O3 fresh

20 nm 20 nm

Pt /HT spent

0

10

20

30

40

50

0-1 1-2 2-3 3-4 4-5

No

. o

f p

art

icle

s

Size of particle (nm)

0

10

20

30

40

50

0-1 1-2 2-3 3-4 4-5

No

. o

f p

art

icle

s

Size of particle (nm)

0

10

20

30

40

50

60

70

80

10-20 20-30 30-40 40-50 50-60

No

. o

f p

art

icle

s

Size of particle (nm)

Synthesis of Hydrotalcite

Aq. Solution of

NaOH & Na2CO3

Slow addition under stirring,

pH =8-10

Calcination

(550°C, 8h)

Precipitate obtained was

kept at 60°C for 16 h.

Aq. Solution of

Mg(NO3).6H2O &

Al(NO3)3.9H2O

Catalyst

Surface

areaa

(m2/g)

Acidityb

(mmol/g)

Basicityc

(mmol/g)pHd

γ-Al2O3 154 0.39 - 5.49

Pt/γ-Al2O3 174 0.35 - 5.52

HT 212 - 0.88 9.24

Pt/HT 159 - 0.81 9.30

Pt/γ-Al2O3

+ HT- - - 8.50

XRD Pattern

Structure of

Hydrotalcite

Impregnation method

Support + Water

Stirred, 16h, R.T.

Calcination

&

Reduction

(400°C, 2h)

Drying

Aq. Solution of

metal precursors

Washed & dried at

80°C for 18 h.

Catalyst characterizations

a: Determined by N2 sorption study

b: Acidity calculated from TPD-NH3

c: Basicity calculated from TPD-CO2

d: pH was observed by suspending 0.075 g catalyst

in 30 mL water

10 20 30 40 50 60 70 80 90

Inte

nsity (

a.u

)

2o

10 20 30 40 50 60 70 80 90

Inte

nsity (

a.u

.)

2o

Fresh

Pt/HT

HT

Spent

Pt/HT

HT

(200)

Pt

(111)

HT

(220)

HT

(222)

Pt

(200)

Pt

(220)

Pt

(311)

Spent

Pt/γ-Al2O3

Fresh

Pt/γ-Al2O3

γ-Al2O3

Results and Discussion

Objectives

References

Acknowledgement : A. Tathod thanks UGC, New Delhi for research fellowship.

1. P. L. Dhepe, A. Fukuoka, Angew. Chem., 2006, 118, 5285.

2. H. Kobayashi, Y. Ito, T. Komanoya, Y. Hosaka, P. L. Dhepe, K. Kasai, K. Hara and A. Fukuoka, Green Chem.,

2011, 13, 326.

3. J. P. Mikkola and T. Salmi, Catal. Today, 2001, 64, 271.

4. G.de Wit, C.de Haan, A.P.G. Kieboom, H.van Bekkum, Carbohydr. Res., 1980, 86, 33.

5. A. Tathod, T. Kane, E.S. Sanil, P. L. Dhepe, J. Mol. Catal. A (doi.org/10.1016/j.molcata.2013.09.014)

Reaction scheme

Metal/Support

H2

Metal/Support

H2

Glucose

Xylitol

Sorbitol

Xylose

To convert glucose and xylose into corresponding sugar alcohols using solid base &

supported metal catalyst, with high yield and selectivity for desired product at mild reaction

condition.

To develop stable catalyst for entitled reaction having good recyclability.

Maximum 82% yield of C5 sugar alcohols and 68% yield of C6 sugar alcohols could be

obtained from xylose and glucose respectively using Pt/γ-Al2O3+HT catalytic system.

In alkaline medium sugar molecules tend to be in open chain form, which undergoes

hydrogenation more rapidly. UV spectra of glucose in basic medium shows peak which is

characteristic for carbonyl group.

Isomerization of

glucose

Enolate ion

Enediol

Tautomerization

H2O

H2O OH-

OH-

Glucose

(Open chain form)

Glucose

(Cyclic form)

Fructose

(Open chain form)

H2O

OH-

Effect of base on UV-Vis

spectra of glucose

225 250 275 300 325 350 375 400

0.0

0.2

0.4

0.6

0.8

1.0

310.5

266.2

270

267.8

Ab

so

rb

an

ce

Wavelenth (nm)

a

b

c

a-Glucose+Na2CO3

b-Glucose+NaOH

c-Glucose

~270 nm- carbonyl group

~310 nm- enediol

Xylose 0.15 g, catalyst 0.075 g, water 35 mL,

16 bar H2 at R.T., 60°C, 4 h.

Glucose 0.15 g, catalyst 0.075 g, water 35 mL,

16 bar H2 at R.T., 90°C, 4 h.

0

10

20

30

40

50

60

70

80

90

100

Pro

du

ct

yie

ld (

%)

Catalyst

Hydrogenation of glucose

unidentified products gluconic acid

glycols fructose

xylitol mannitol

sorbitol

0

10

20

30

40

50

60

70

80

90

100

Pro

du

ct

yie

ld (

%)

Catalyst

Hydrogenation of xyloseunidentified products xylonic acid

glycols arabitol

xylitol