Hydrogenation of sugars over supported metal catalyst - effect of support
1
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: [email protected] Introduction Conclusions Catalyst preparation & Characterization Pt/γ-Al 2 O 3 +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 fresh Pt/ γ-Al 2 O 3 spent 100 nm 0 10 20 30 40 50 60 70 80 10-20 20-30 30-40 40-50 50-60 No. of particles Size of particle (nm) 100 nm Pt/ γ-Al 2 O 3 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. of particles Size of particle (nm) 0 10 20 30 40 50 0-1 1-2 2-3 3-4 4-5 No. of particles Size of particle (nm) 0 10 20 30 40 50 60 70 80 10-20 20-30 30-40 40-50 50-60 No. of particles Size of particle (nm) Synthesis of Hydrotalcite Aq. Solution of NaOH & Na 2 CO 3 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(NO 3 ).6H 2 O & Al(NO 3 ) 3 .9H 2 O Catalyst Surface area a (m 2 /g) Acidity b (mmol/g) Basicity c (mmol/g) pH d γ-Al 2 O 3 154 0.39 - 5.49 Pt/γ-Al 2 O 3 174 0.35 - 5.52 HT 212 - 0.88 9.24 Pt/HT 159 - 0.81 9.30 Pt/γ-Al 2 O 3 + 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 N 2 sorption study b: Acidity calculated from TPD-NH 3 c: Basicity calculated from TPD-CO 2 d: pH was observed by suspending 0.075 g catalyst in 30 mL water 10 20 30 40 50 60 70 80 90 Intensity (a.u) 2 o 10 20 30 40 50 60 70 80 90 Intensity (a.u.) 2 o Fresh Pt/HT HT Spent Pt/HT HT (200) Pt (111) HT (220) HT (222) Pt (200) Pt (220) Pt (311) Spent Pt/γ-Al 2 O 3 Fresh Pt/γ-Al 2 O 3 γ-Al 2 O 3 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. Mikkolaand 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 H 2 Metal/Support H 2 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-Al 2 O 3 +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 H 2 O H 2 O OH - OH - Glucose (Open chain form) Glucose (Cyclic form) Fructose (Open chain form) H 2 O 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 Absorbance Wavelenth (nm) a b c a-Glucose+Na 2 CO 3 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 H 2 at R.T., 60°C, 4 h. Glucose 0.15 g, catalyst 0.075 g, water 35 mL, 16 bar H 2 at R.T., 90°C, 4 h. 0 10 20 30 40 50 60 70 80 90 100 Product yield (%) Catalyst Hydrogenation of glucose unidentified products gluconic acid glycols fructose xylitol mannitol sorbitol 0 10 20 30 40 50 60 70 80 90 100 Product yield (%) Catalyst Hydrogenation of xylose unidentified products xylonic acid glycols arabitol xylitol
description
A process of hydrogenation of sugars into sugar alcohol is described in presence of supported metal catalysts. Influence of support in reaction is also shown.
Transcript of Hydrogenation of sugars over supported metal catalyst - effect of support
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: [email protected]
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
