Elucidating the effect of solid base on the hydrogenation of C5 and C6 sugars over Pt–Sn bimetallic catalyst at room temperature

Article abstract of DOI:10.1016/j.carres.2021.108341

Conversion of sugars into sugar alcohols at room temperature with exceedingly high yields are achieved over Pt–Sn/γ-Al₂O₃ catalyst in the presence of calcined hydrotalcite. pH of the reaction mixture significantly affects the conversion and selectivity for sugar alcohols. Selection of a suitable base is the key to achieve optimum yields. Various solid bases in combination with Pt–Sn/γ-Al₂O₃ catalysts were evaluated for hydrogenation of sugars. Amongst all combinations, the mixture (1:1 wt/wt) of Pt–Sn/γ-Al₂O₃ and calcined hydrotalcite showed the best results. Hydrotalcite helps to make the pH of reaction mixture alkaline at which sugar molecules undergo ring opening. The sugar molecule in open chain form has carbonyl group which can be polarized by Sn in Pt–Sn/γ-Al₂O₃ and Pt facilitates the hydrogenation. In the current work, effect of both; solid base and Sn as a promoter has been studied to improve the yields of sugar alcohols from various C5 and C6 sugars at very mild reaction conditions.

Full text of DOI:10.1016/j.carres.2021.108341

Carbohydrate Research 505 (2021) 108341
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Elucidating the effect of solid base on the hydrogenation of C5 and C6
sugars over Pt–Sn bimetallic catalyst at room temperature
a,
b,
*
a,**
Anup P. Tathod
, Paresh L. Dhepe
a
Catalysis and Inorganic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune, 411 008, India
Light Stock Processing Division, CSIR-Indian Institute of Petroleum, Dehradun, 248 005, India
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Conversion of sugars into sugar alcohols at room temperature with exceedingly high yields are achieved over
Sugar
Pt–Sn/γ-Al
the conversion and selectivity for sugar alcohols. Selection of a suitable base is the key to achieve optimum
yields. Various solid bases in combination with Pt–Sn/γ-Al catalysts were evaluated for hydrogenation of
and calcined hydrotalcite showed
2 3
O catalyst in the presence of calcined hydrotalcite. pH of the reaction mixture significantly affects
Sugar alcohols
Bimetallic catalyst
Hydrogenation
Hydrotalcites
2 3
O
sugars. Amongst all combinations, the mixture (1:1 wt/wt) of Pt–Sn/γ-Al
2 3
O
the best results. Hydrotalcite helps to make the pH of reaction mixture alkaline at which sugar molecules undergo
ring opening. The sugar molecule in open chain form has carbonyl group which can be polarized by Sn in Pt–Sn/
γ-Al
2 3
O and Pt facilitates the hydrogenation. In the current work, effect of both; solid base and Sn as a promoter
has been studied to improve the yields of sugar alcohols from various C5 and C6 sugars at very mild reaction
conditions.
1
. Introduction
Environmental concern and exhausting fossil carbon sources caused
17–21]. Many other catalysts including noble metal-based catalysts also
have been explored for the conversion of sugars to sugar alcohols
[22–35]. But these catalysts have some obvious drawbacks like catalyst
deactivation, requisite of harsh reaction condition or low yields of sugar
alcohols [36–38]. In current work, the conversion of C5-sugars (xylose,
arabinose) and C6-sugars (glucose, galactose) into respective sugar al-
paradigm shift towards the processing of biomass for the production of
fuels and chemicals in the recent decades. Development of efficient
catalysts and processes is the need of time to meet the requirement in a
sustainable and economical way. Lignocellulosic biomass can serve as
renewable source for chemicals and fuels. It consists of cellulose,
hemicellulose and lignin in various amounts depend on its origin. Cel-
lulose is homo-polysaccharide made up of glucose while hemicelluloses
are hetero-polysaccharide made up of various C5 and C6-sugars
depending upon its origin. Lignin is highly branched polymer of aro-
matic compounds. Conversion of cellulose and hemicellulose into sugars
and further conversion of sugars to furans, sugar alcohols, glycols, etc. is
well known [1–8]. Sugar alcohols are considered as important biomass
derived compounds because of its wide spread applications in various
fields like, oral hygiene products, pharmaceutical industry, in cosmetics,
cohols at room temperature is studied over Sn promoted Pt/γ-Al
catalyst in presence of solid base (Scheme 1). Sn is known to promote the
catalyst toward the hydrogenation reaction
2 3
O
activity of Pt/γ-Al
2 3
O
[39–41]. Recently hydrogenation of xylose to xylitol at milder reaction
◦
condition (130 C, 16 bar H
2
) over Pt–Sn/γ-Al
2 3
O is reported with high
yield (93%) [6]. In yet another report, increment in the yield of sugar
alcohols from sugars, polysaccharide (xylan, arabinogalactan, inulin)
and agricultural wastes was achieved over Pt–Sn/γ-Al
larly, the effect of solid base (C-HT) in the conversion of sugars to sugar
catalyst is studied and high yield of sugar al-
2 3
O [42]. Simi-
alcohols over Pt/γ-Al
2 3
O
cohols (82% xylitol from xylose) was achieved [5].
for production of various chemicals and H
2
generation, therefore its
In the view of this, it is interesting to explore the effect of hydro-
demand is escalating continuously [9–16]. Conventionally sugar alco-
hols such as sorbitol and xylitol are prepared over supported metal
catalysts and nickel-based catalysts are used more extensively [9,10,
talcite in the conversion of sugars over Pt–Sn/γ-Al
lyst. The combined effect of Sn and hydrotalcite is anticipated to
enhance the hydrogenation activity of Pt/γ-Al . Although, the effect
2 3
O bimetallic cata-
2 3
O
*
Corresponding author. Catalysis and Inorganic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune, 411 008, India.
** Corresponding author.
E-mail addresses: anup.tathod@gmail.com (A.P. Tathod), pl.dhepe@ncl.res.in (P.L. Dhepe).
https://doi.org/10.1016/j.carres.2021.108341
Received 18 March 2021; Received in revised form 5 May 2021; Accepted 5 May 2021
Available online 9 May 2021
0
008-6215/© 2021 Elsevier Ltd. All rights reserved.

A.P. Tathod and P.L. Dhepe
Carbohydrate Research 505 (2021) 108341
and powder was washed with deionized water till pH becomes neutral.
◦
The white powder thus obtained was dried at 80 C for 16 h followed by
◦
calcinations at 550 C for 8 h in the flow of air (20 mL/min). Calcined
hydrotalcite was used as a support material to prepare catalyst or added
as a solid base along with catalyst.
2
.3. Catalyst preparation
Supported metal catalysts were prepared by co-impregnation
method using γ-Al
2
O
3
(AL) or calcined hydrotalcite (C-HT) supports.
◦
Prior to catalyst preparation, supports were evacuated at 150 C for 6 h
under vacuum (ꢀ 700 Torr). Mixture of the support and water (1 gm
support in 10 mL water) was stirred for 1 h at room temperature.
Required amount of metal precursor solution was added drop wise to the
support suspension under stirring (10 wt% aqueous solution of Pt
(
NH
3
)
4
(NO
3
)
2
and 10 wt% solution of SnCl
2
⋅2H
2
O in 3 M HCl). The
◦
mixture was stirred for 16 h at room temperature (30±3 C), after this
solvent was removed by rotary vacuum evaporator. Powder was dried at
◦
◦
6
0
C overnight in oven and at 150 C for 3 h under vacuum. Dried
◦
powder was calcined at 400 C for 2 h in a flow of oxygen (20 mL/min)
◦
and reduced in a hydrogen flow (20 mL/min) at 400 C for 2 h. Pt/AL,
Pt–Sn/AL, Pt/C-HT and Pt–Sn/C-HT catalysts were prepared by keeping
Pt loading of 2 wt% and Sn loading of 0.25 wt% i.e. Pt(2)/AL (2 wt%Pt/
γ-Al
2
O
3
), Pt(2)Sn(0.25)/AL (2 wt%Pt-0.25 wt%Sn/γ-Al
2 3
O ), Pt(2)/C-HT
(
2 wt%Pt/C-HT) and Pt(2)Sn(0.25)/C-HT (2 wt%Pt-0.25 wt%Sn/C-HT).
Scheme 1. Conversion of sugars to sugar alcohols at room temperature.
2
.4. Catalyst characterization
Characterization of the catalysts was performed using various tech-
of base in ring opening of sugars and its role in keto-enol tautomeriza-
tion (known as Lobry de Bruyn-Albeda van Ekenstein transformation) is
well known, the systematic studies correlating the activity with pH/
basicity are missing. There is enough scope to establish a relation be-
tween catalytic activity and pH of the reaction mixture. Therefore, in
present work solid bases with various basicity were used in combination
with the catalyst, which results into varying pH of the reaction mixtures.
Effect of pH of the reaction mixture on the yield and selectivity is studied
in systematic way. Moreover, solid bases were used for the study to
maintain heterogeneity of the catalytic systems.
niques. Dona Quantachrome Nova 4200e instrument was used for the
nitrogen sorption study and TPD was performed using Micrometrics
Autochem-2910. Inductively coupled plasma atomic emission spec-
troscopy (ICP-AES) was performed using SPECTRO ARCOS Germany,
FHS12 instrument. The X-ray diffraction patters of the catalysts were
recorded using Philips Powder XRD machine, operated at Cu K radia-
α
tion (λ = 1.540598 Å). Transmission electron microscopy (TEM) was
done using FEI Tecnai TF-30 instrument. X-Ray photoelectron spec-
troscopy (XPS) study was performed using VG Micro Tech ESCA-3000
instrument (operating under ultrahigh vacuum).
2
. Experimental
.1. Materials
γ-Al (AL), sorbitol (99.9%), hydroxyapatite (99.9%), calcium
2
.5. Catalytic test
2
Reactions were conducted in a batch mode autoclave of 50 mL ca-
2 3
O
pacity (Amar Equipments, India). Substrate/catalyst ratio was kept
constant as 2 wt/wt i.e. 0.15 g substrate and 0.075 g catalyst were taken
in 35 mL of water. 0.075 g of C-HT was added wherever effect of solid
oxide (99.9%) and magnesium oxide (98%) were purchased from
Aldrich Chemicals, USA. Glucose (99%), galactose (98%), galactitol
(
99%), mannitol (99.5%), xylitol (99%), arabitol (99%), glycerol (98%),
2
base was studied. After adding water, substrate and catalyst, H was
ethylene glycol (99%), 1,2-propanediol (99.5%), were procured from s.
d. fine chemicals, India. Tetraamine platinum nitrate (99.9%) was ob-
tained from Alfa Aesar, UK. Stannus chloride dihydrate (98%), xylose
charged into the reactor with required pressure (16 or 24 bar at room
temperature). Experiments were carried out in a temperature range of
◦
room temperature (32 ± 3) to 80 C, for various reaction times. Reaction
(
99%), arabinose (99%) and sodium hydroxide (98%), Sodium cor-
mixture was stirred at 150 rpm until desired temperature is reached then
stirring was increased to 900 rpm and this was considered as starting
time of the reaction. For room temperature experiments, reaction
mixture was stirred at 900 rpm since beginning. After reaction, auto-
clave was cooled down to room temperature under the flow of air. The
catalyst was separated from reaction mixture by centrifugation and the
bonate (99.9%) were purchased from Loba Chemicals, India. Magne-
sium nitrate hexahydrate (99%) was purchased from Merk, India.
Aluminum nitrate nonahydrate (99%) was procured from Thomas
Baker, Germany.
2
.2. Synthesis of hydrotalcite
liquid was filtered through 0.22
μ
m syringe filter. The products were
analyzed using HPLC (Agilent Technologies, 1200 infinity series, USA)
+
+
Mg–Al hydrotalcite was prepared by co-precipitation method with
equipped with HC-75 Pb
(Hamilton, 7.8 mm × 300 mm) column
◦
Mg/Al ratio 3. Na
2
CO
3
was used as a source of carbonate and NaOH was
maintained at 80 C. Deionized water (flow rate 0.6 mL) was used as an
eluent. Refractive index detector (RID, Agilent Technologies, 1200 in-
used to maintain the pH of the solution. 37.5 mL aqueous solution of Mg
NO O (0.279 mol) and Al(NO ⋅9H O (0.093 mol) was added
⋅6H
drop wise into the 37.5 mL aqueous solution of NaOH (0.4375 mol) and
Na CO (0.1125 mol) under stirring. During addition pH of the solution
◦
(
3
)
2
2
3
)
3
2
finity series, cell temperature, 40 C) was used for the detection of
compounds. Another HPLC system (Agilent Technologies, 1200 infinity
+
2
3
series, USA) equipped with HC-75H (Phenomenex, 7.8 × 300 mm)
◦
was maintained between 8 and 10. The white precipitate obtained was
column (at 60 C) with sulfuric acid (0.5 mmol) as an eluent (0.6 mL/
◦
kept for digestion in autoclave for 16 h at 60 C. The slurry was filtered
min flow rate) was also used to quantify the products. RID (Agilent
2

A.P. Tathod and P.L. Dhepe
Carbohydrate Research 505 (2021) 108341
◦
Technologies, 1200 infinity series, cell temperature, 40 C) was used for
detection of compounds.
the better support metal interaction of the metals with C-HT than that
with AL. The oxidation state of Sn was determined by XPS study. On
γ-Al
2 3
O support, Sn cannot be reduced to (0) oxidation state even when
◦
◦
3
. Results and discussion
reduced at 500 C [45]. In this study, catalysts were reduced at 400 C so
Sn may present in (II) or (IV) oxidation state. XPS spectra showed peak at
486.5 eV which is characteristic for Sn (II) or (IV) (Fig. S3, †ESI). It is
difficult to distinguish between Sn (II) and (IV) by XPS as the difference
in binding energy is very low [6].
3
.1. Catalyst characterizations
All synthesized catalysts were characterized using various tech-
niques i.e. ICP-AES, N
tained from various characterizations are summarized in Table 1. The
surface area for AL determined by N sorption technique was found to be
74 m /g, while after metal impregnation it was slightly decreased
Table 1 entry 1,2,3). Similarly, the surface area of C-HT was decreased
after metal impregnation (Table 1, entry 4,5,6). The acid and base
amounts of the samples were determined by NH -TPD and CO -TPD
respectively. NH -TPD profiles for AL, Pt(2)/AL and Pt(2)Sn(0.25)/AL
2
sorption, TPD, XRD, TEM, XPS, etc. Results ob-
3.2. Hydrogenation of C5-Sugars
2
2
1
Hydrogenation reactions of xylose were carried out at room tem-
(
2
perature under 24 bar H pressure to evaluate the catalytic activity of
various catalysts (Table 2). Conversion of xylose was only 20% after 28 h
over monometallic Pt(2)/AL catalyst and 18% yield of sugar alcohols
(xylitol + arabitol) was obtained. The conversion was doubled (40%)
and 38.5% yield of sugar alcohols was obtained when bimetallic Pt(2)Sn
(0.25)/AL was used. Further improvement in the conversion and yield
was observed when Pt(2)/C-HT and Pt(2)Sn(0.25)/C-HT catalysts were
employed at similar reaction condition. Highest yield of sugar alcohols
(96%) was obtained with almost complete conversion (97%) over (Pt(2)
Sn(0.25)/AL + C-HT catalytic system i.e. the physical mixture of Pt(2)Sn
(0.25)/AL and C-HT. Other than sugar alcohols, side products like gly-
cols (glycerol + ethylene glycol + 1,2-propanediol) were formed but in
negligible quantity.
3
2
3
are shown in Figs. S1–A (†ESI). The profile for AL showed a broad peak
◦
nearly at 200 C indicating presence of weak acid sites. The decrease in
total acidity of AL after metal impregnation is pointing towards the
interaction of metals with acid sites. In the profile of Pt(2)Sn(0.25)/AL
◦
small hump at 400-500 C was observed which was not observed for AL
and Pt(2)/AL indicates the acid sites arose due to Sn with positive
charge. It is well known fact that Sn forms tin-aluminate on the surface
of AL, therefore complete amount of Sn can’t be reduced to Sn (0) if
supported on AL [43–45]. The Sn species with positive charge can
◦
generate new type of acid sites and the peak observed at 400-500 C in
To check the possibility of conducting reactions at lower pressure,
reaction of xylose over Pt(2)Sn(0.25)/AL + C-HT was conducted at 16
this study might be due such acid sites (Table 1, entry 1,2,3). The
CO
2
-TPD profiles for C-HT, Pt(2)/C-HT and Pt(2)Sn(0.25)/C-HT are
2
bar H keeping other parameters same. But, the yield of sugar alcohols
shown in Figs. S1–B (†ESI). The slight decrease in the base amount of
C-HT was observed after impregnation of metals (Table 1. Entry 4,5,6).
The metal contents of the samples were determined using ICP-AES.
Expected metal loadings and actual metal loadings determined by
ICP-AES are very much similar (Table 1).
was observed to be decreased to 85% (87% conversion), indicating that
16 bar pressure is not enough to achieve complete conversion within 28
h at room temperature. Further, hydrogenation reactions of arabinose
(another C5 sugar) were conducted at 24 bar pressure at room tem-
perature for 28 h (Table 3). The catalytic activity of various catalysts
towards the hydrogenation of arabinose follows the same trend as that
for xylose hydrogenation. Maximum 97.5% yield of sugar alcohols
(arabitol + xylitol) was achieved using Pt(2)Sn(0.25)/AL + C-HT cata-
lytic system at room temperature. Highest yield of sugar alcohols was
achieved over Pt(2)Sn(0.25)/AL + C-HT catalyst. This is because of the
combined effect of Sn (in ionic form) and presence of C-HT. Ionic Sn
XRD patterns for various catalysts are shown in Fig. S2 (†ESI). Both
Pt(2)/AL and Pt(2)Sn(0.25)/AL catalysts showed sharp peaks for Pt
(
Joint Committee on Powder Diffraction Standards, JCPDS file no. 01-
88- 2343). From XRD pattern of Pt(2)Sn(0.25)/AL it can be
0
concluded that no alloy or inter metallic species was formed in bulk
quantity (concentration must be very less, hence not detected by XRD).
Because of high dispersion of Pt, peak intensity was lower in Pt(2)Sn
–
helps to polarize the C O bond in carbonyl group of sugars and hy-
–
–
drogenation of polarized C O bond is easier [6]. C-HT is a solid base by
(
0.25)/AL than in Pt(2)/AL. In Pt(2)/C-HT and Pt(2)Sn(0.25)/C-HT
–
peak intensity for Pt was very low because of highly dispersed Pt on
C-HT support compare to AL support (Fig. S2, †ESI). TEM analysis
showed that the particle size of Pt in Pt(2)/AL and Pt(2)Sn(0.25)/AL was
addition of which pH of the reaction medium becomes alkaline (Approx.
9). As reported elsewhere, UV absorption study proves that more num-
ber of sugar molecules are present in open chain form in alkaline me-
dium than that of in neutral medium [5]. In addition, at basic pH
keto-enol tautomerization can occur which might result in isomer-
isation/epimerization of sugar (Fig. S4, †ESI). This is the reason for
formation of sugar isomers and the respective alcohols in present study.
For an instance; in xylose hydrogenation arabitol was observed along
with xylitol while in glucose hydrogenation mannitol was observed
along with sorbitol.
2
0–30 nm and 10–20 nm respectively (Fig. 1). Better dispersion in Pt(2)
Sn(0.25)/AL catalyst compare to Pt(2)/AL catalyst, is because of inter-
action of Sn with support (AL). Sn interacts with alumina to form tin-
aluminate type structure [43]. Hence, Sn forms surface shell with
alumina which prevents mobility of Pt particle during calcinations and
reduction [43,44]. In case of C-HT based catalyst, in both Pt(2)/C-HT
and Pt(2)Sn(0.25)/C-HT particle size was 2–3 nm (Fig. 1). This shows
Table 1
Properties of catalysts.
a
b
c
2
Entry
Catalyst
Acidity (mmol/g)
Basicity (mmol/g)
Surface area (m /g)
Pt content (wt%)
Sn content (wt%)
d
d
Actual
Expected
Actual
Expected
1
2
3
4
5
6
AL
0.42
0.24
0.22
–
–
174
157
164
210
148
134
–
–
–
–
Pt(2)/AL
–
2.13
2.16
–
2.00
2.00
–
–
–
Pt(2)Sn(0.25)/AL
C-HT
–
0.87
0.78
0.61
0.22
–
0.25
–
Pt(2)/C-HT
Pt(2)Sn(0.25)/C-HT
–
2.19
2.17
2.00
2.00
–
–
–
0.21
0.25
a
Determined by NH
3
-TPD.
-TPD.
sorption.
Determined by ICP-AES.
b
c
Determined by CO
Determined by N
2
2
d
3

A.P. Tathod and P.L. Dhepe
Carbohydrate Research 505 (2021) 108341
Fig. 1. TEM images of various catalysts.
Table 2
Table 3
Conversion of xylose over various catalysts at room temperature.
Conversion of arabinose over various catalysts at room temperature.
Catalyst
Product yield (%)
Conv.
%)
TOF
Catalyst
Product yield (%)
Conv.
(%)
TOF
ꢀ
1
ꢀ 1
(
(h
)
(h
)
Xylitol
Arabitol
Sugar
Xylitol
Arabitol
Sugar
alcohols
alcohols
Pt(2)/AL
17.0
36.0
77.0
80.0
1.0
2.5
3.5
4.0
18.0
38.5
80.5
84.0
20.0
40.0
85.0
89.0
12.2
15.5
8.3
Pt(2)/AL
0.5
0.0
1.0
0.5
33.5
44.0
84.0
89.5
34.0
44.0
85.0
90.0
35.0
46.0
87.0
92.0
22.9
19.1
12.2
13.1
Pt(2)Sn(0.25)/AL
Pt(2)/C-HT
Pt(2)Sn(0.25)/AL
Pt(2)/C-HT
Pt(2)Sn(0.25)/C-
HT
8.7
Pt(2)Sn(0.25)/C-
HT
Pt(2)/AL + C-HT
Pt(2)Sn(0.25)/AL
85.0
94.5
2.5
1.5
87.5
96.0
90.0
97.0
76.6
59.9
Pt(2)/AL + C-HT
Pt(2)Sn(0.25)/AL
+ C-HT
1.0
1.5
92.0
96.0
93.0
97.5
95.0
99.0
110.4
77.4
+
C-HT
Reaction condition: xylose 0.15 g, catalyst 0.075 g, C-HT 0.075 g, H
2
O 35 mL, 32
2
Reaction condition: arabinose 0.15 g, catalyst 0.075 g, C-HT 0.075 g, H O 35
(
±3) ◦C, H
2
24 bar at R.T., 28 h.
mL, 32(±3) ◦C, H
2
24 bar at R.T., 28 h.
◦
The effect of reaction temperature was studied by conducting the
that at 50 C of reaction temperature, 16 bar H
2
pressure and 6 h of
◦
hydrogenation reaction of xylose at 50 C at 24 bar H
2
pressure over Pt
reaction time is enough to achieve complete conversion. This is much
obvious as the solubility of H in water increases with temperature
(
2)Sn(0.25)/AL + C-HT catalyst. At this elevated temperature complete
conversion of xylose was achieved within 6 h with 97% yield of sugar
alcohols. When hydrogenation of xylose was conducted at 16 bar H
2
which facilitated the faster hydrogenation of xylose and complete con-
version could be achieved in shorter reaction time. The results for hy-
2
◦
pressure instead of 24 bar over Pt(2)Sn(0.25)/AL + C-HT catalyst at
drogenation of xylose over various catalysts at 50 C and 16 bar pressure
◦
5
0
C temperature (keeping other parameters same), no significant
of H
2
are represented as Fig. 2. The highest yield of sugar alcohols (96%)
difference was observed in the yield of sugar alcohols. The results show
was obtained over Pt(2)Sn(0.25)/AL + C-HT catalyst with complete
4

A.P. Tathod and P.L. Dhepe
Carbohydrate Research 505 (2021) 108341
conversion) was achieved while 96 and 98% yield (with complete xylose
conversion) could be obtained using C-HT with Pt(2)Sn(0.25)/AL and
MgO with Pt(2)Sn(0.25)/AL, respectively. Complete conversion was
observed over CaO with Pt(2)Sn(0.25)/AL catalytic system but yield of
sugar alcohols was only 64% due to the formation of side products like
glycols. The activity can be correlated with pH of the reaction mixtures
(
after adding xylose, catalyst and base into water). The pH of reaction
mixture in case of only Pt(2)Sn(0.25)/AL catalyst and Pt(2)Sn(0.25)/AL
+
+
HAP was 5.3 and 7.5 respectively, while in case of Pt(2)Sn(0.25)/AL
C-HT and Pt(2)Sn(0.25)/AL + MgO it was 9.2. and 9.4, respectively.
In case of Pt(2)Sn(0.25)/AL + CaO the pH was 12.2. These results show
that pH of the reaction medium has profound effect on the conversion
and selectivity. pH in the range of 9–9.5 is the most suitable to achieve
higher conversion of sugars and better selectivity for sugar alcohols. At
lower pH the ring opening of sugar molecules could not occur up to
significant extend at such a low temperature. This results into lower
conversion of sugar (xylose) despite of having good hydrogenation
catalyst (Pt(2)Sn(0.25)/AL). On the other hand, when pH of the reaction
mixture was very high (as in the case of Pt(2)Sn(0.25)/AL + CaO), other
side reactions like glycol formation by C–C bond breakage were more
provoking. Therefore, mere addition of any base will not work but the
selection of proper solid base with appropriate basicity is the key to
improve conversion of sugar molecules without compromising the
selectivity for sugar alcohols.
Fig. 2. Conversion of xylose over various catalysts.
Reaction condition: xylose 0.15 g, catalyst 0.075 g, C-HT 0.075 g, H
2
O 35 mL,
◦
5
0
C, H
2
16 bar at R.T., 6 h.
3
.3. Hydrogenation of C6-Sugars
conversion of xylose in 6 h.
After achieving very high yield of sugar alcohols from C5 sugars
It is very much clear from the above results that C-HT is plying sig-
nificant role in hydrogenation of sugars. The possibility to recreate the
similar effect using other solid bases was checked by using hydroxyap-
atite (HAP), magnesium oxide (MgO) and calcium oxide (CaO) instead
of C-HT in combination with Pt(2)Sn(0.25)/AL catalyst for xylose hy-
drogenation (Fig. 3). Amongst all the catalytic systems, Pt(2)Sn(0.25)/
AL + C-HT and Pt(2)Sn(0.25)/AL + MgO showed the highest yield for
sugar alcohols. But MgO is soluble in water and hence difficult to reuse.
The Pt(2)Sn(0.25)/AL catalyst without addition of any base showed
(xylose and arabinose), catalyst Pt(2)Sn(0.25)/AL + C-HT was evaluated
for the conversion of C6 sugars (glucose and galactose) at room tem-
perature and 24 bar H . For complete conversion of glucose, the time
2
required was 60 h and 84% yield of C6 sugar alcohols (sorbitol-76%+
mannitol-8%) was obtained. Galactose was converted completely at
room temperature within 48 h to yield 87% galactitol and small amount
of mannitol (3%). To check the effect of temperature in the conversion of
◦
glucose, reaction was conducted at 50 C under 16 bar H . But only 43%
2
conversion was observed with 36% yield of sugar alcohols in 6 h. When
◦
3
4% yield of sugar alcohols with 38% xylose conversion. When HAP was
temperature was switch to 80 C, complete conversion of glucose was
used along with Pt(2)Sn(0.25)/AL, 37% yield of sugar alcohols (40%
achieved in 6 h to yield 88% sugar alcohols (sorbitol + mannitol).
Comparison of catalytic activities of various catalysts to yield sugar al-
cohols from glucose is shown in Fig. 4.
3
.4. Recycle study
Recyclability of Pt(2)Sn(0.25)/AL + C-HT was checked for xylose
conversion up to 4 runs and showed good result with negligible decrease
(
2–4%) in the yield after each run. After completion of reaction, catalyst
was recovered from reaction mixture by centrifugation and used in next
run without drying and without calcination or reduction. The slight
decrease in the yield was due to loss of some catalyst quantity during
separation from reaction mixture.
4
. Conclusions
The pH of reaction mixture has significant effect on the conversion of
sugars and selectivity towards sugar alcohols. Combined effect of Sn (in
ionic form) and solid base furnish the high yield of sugar alcohols from
sugars at room temperature. Solid base help to maintain the pool of
sugar molecules in open chain form. Ionic Sn polarize the C–
–
O bond of
carbonyl group of sugars. In presence of active metal i.e. Pt hydroge-
–
nation of polarized C O bond takes place more rapidly. Very high
–
yields of sugar alcohols i.e. 96%, 97.5%, 84% and 90% were obtained
from xylose, arabinose, glucose and galactose respectively at room
temperature.
Fig. 3. Effect of various bases on xylose hydrogenation.
Reaction condition: xylose 0.15 g, catalyst (Pt(2)Sn(0.25)/AL) 0.075 g, base
◦
0
.075 g, H
2
O 35 mL, 50 C H
2
16 bar at R.T., 6 h.
5

A.P. Tathod and P.L. Dhepe
Carbohydrate Research 505 (2021) 108341
[
13] P. De Wulf, W. Soetaert, E.J. Vandamme, Optimized synthesis of L-sorbose by C5-
dehydrogenation of D-sorbitol with gluconobacter oxydans, Biotechnol. Bioeng. 69
(
2000) 339–343.
[
[
14] R.R. Davda, J.A. Dumesic, Renewable hydrogen by aqueous-phase reforming of
glucose, Chem. Commun. (2004) 36–37, 0.
15] M. Yadav, D.K. Mishra, J.S. Hwang, Catalytic hydrogenation of xylose to xylitol
using ruthenium catalyst on NiO modified TiO2 support, Appl. Catal., A 425–426
(
2012) 110–116.
[
16] J. Zhang, A. Geng, C. Yao, Y. Lu, Q. Li, Xylitol production from d-xylose and
horticultural waste hemicellulosic hydrolysate by a new isolate of Candida
athensensis SB18, Bioresour. Technol. 105 (2011) 134–141.
[
[
[
[
17] J. Wisniak, M. Hershkowitz, R. Leibowitz, S. Stein, Hydrogenation of xylose to
xylitol, Ind. Eng. Chem. Prod. Res. Dev. 13 (1974) 75–79.
18] M. Herskowitz, Modelling of a trickle-bed reactor-the hydrogenation of xylose to
xylitol, Chem. Eng. Sci. 40 (1985) 1309–1311.
19] K. van Gorp, E. Boerman, C.V. Cavenaghi, P.H. Berben, Catalytic hydrogenation of
fine chemicals: sorbitol production, Catal. Today 52 (1999) 349–361.
20] S. Yamaguchi, S. Fujita, K. Nakajima, S. Yamazoe, J. Yamasaki, T. Mizugaki,
T. Mitsudome, Air-stable and reusable nickel phosphide nanoparticle catalyst for
the highly selective hydrogenation of d-glucose to d-sorbitol, Green Chem. 23
(
2021) 2010–2016.
[
[
[
21] H. Xia, L. Zhang, H. Hu, S. Zuo, L. Yang, Efficient hydrogenation of xylose and
hemicellulosic hydrolysate to xylitol over Ni-Re bimetallic nanoparticle catalyst,
Nanomaterials 10 (2020) 73.
22] W.Y. Jeon, B.H. Yoon, W.Y. Shim, J.H. Kim, Reduction of arabitol in xylitol
production by changed substrate preference of xylose reductase in Candida
tropicalis, J. Biotechnol. 150 (2010) 345–346.
23] H. Ling, K. Cheng, J. Ge, W. Ping, Statistical optimization of xylitol production
from corncob hemicellulose hydrolysate by Candida tropicalis HDY-02, N. Biotech.
2
8 (2011) 673–678.
[
[
24] B. Kusserow, S. Schimpf, P. Claus, Hydrogenation of glucose to sorbitol over nickel
and ruthenium catalysts, Adv. Synth. Catal. 345 (2003) 289–299.
Fig. 4. Conversion of glucose over various catalysts.
25] B.W. Hoffer, E. Crezee, P.R.M. Mooijman, A.D. van Langeveld, F. Kapteijn, J.
A. Moulijn, Carbon supported Ru catalysts as promising alternative for Raney-type
Ni in the selective hydrogenation of d-glucose, Catal. Today 79–80 (2003) 35–41.
26] P. Sudarsanam, E. Peeters, E.V. Makshina, V.I. Parvulescu, B.F. Sels, Advances in
porous and nanoscale catalysts for viable biomass conversion, Chem. Soc. Rev. 48
Reaction condition: glucose 0.15 g, catalyst 0.075 g, C-HT 0.075 g, H
2
O 35 mL,
◦
8
0
C, H
2
16 bar at R.T. 6 h.
[
[
Declaration of competing interest
(
2019) 2366–2421.
27] S. Liu, Y. Okuyama, M. Tamura, Y. Nakagawa, A. Imai, K. Tomishige, Selective
transformation of hemicellulose (xylan) into n-pentane, pentanols or xylitol over a
rhenium-modified iridium catalyst combined with acids, Green Chem. 18 (2016)
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
1
65–175.
[
[
[
28] Y. Delgado Arca n˜ o, O.D. Valma n˜ a García, D. Mandelli, W.A. Carvalho, L.
A. Magalh ˜a es Pontes, Xylitol, A review on the progress and challenges of its
production by chemical route, Catal. Today 344 (2020) 2–14.
Appendix A. Supplementary data
29] T.N. Pham, A. Samikannu, A.-R. Rautio, K.L. Juhasz, Z. Konya, J. W ¨a rnå, K. Kordas,
J.-P. Mikkola, Catalytic hydrogenation of d-xylose over Ru decorated carbon foam
catalyst in a Spin Chem® rotating bed reactor, Top. Catal. 59 (2016) 1165–1177.
30] N.P. Tangale, P.S. Niphadkar, P.N. Joshi, P.L. Dhepe, Hierarchical K/LTL zeolite as
solid base for aqueous phase hydrogenation of xylose to xylitol, Microporous
Mesoporous Mater. 278 (2019) 70–80.
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.carres.2021.108341.
References
[31] X. Zhang, L.J. Durndell, M.A. Isaacs, C.M.A. Parlett, A.F. Lee, K. Wilson, Platinum-
catalyzed aqueous-phase hydrogenation of d-glucose to d-sorbitol, ACS Catal. 6
(2016) 7409–7417.
[
[
1] P.L. Dhepe, R. Sahu, A solid-acid-based process for the conversion of hemicellulose,
Green Chem. 12 (2010) 2153–2156.
[32] B. García, J. Moreno, G. Morales, J.A. Melero, J. Iglesias, Production of sorbitol via
catalytic transfer hydrogenation of glucose, Appl. Sci. 10 (2020) 1843.
[33] C. Hernandez-Mejia, E.S. Gnanakumar, A. Olivos-Suarez, J. Gascon, H.F. Greer,
2] R. Sahu, P.L. Dhepe, A one-pot method for the selective conversion of
hemicellulose from crop waste into C5 sugars and furfural by using solid acid
catalysts, ChemSusChem 5 (2012) 751–761.
2
W. Zhou, G. Rothenberg, N. Raveendran Shiju, Ru/TiO -catalysed hydrogenation
[
[
[
[
3] J. Geboers, S. Van de Vyver, K. Carpentier, P. Jacobs, B. Sels, Efficient hydrolytic
hydrogenation of cellulose in the presence of Ru-loaded zeolites and trace amounts
of mineral acid, Chem. Commun. 47 (2011) 5590–5592.
of xylose: the role of the crystal structure of the support, Catal. Sci. Technol. 6
(2016) 577–582.
[34] J. Zhao, X. Yang, W. Wang, J. Liang, Y. Orooji, C. Dai, X. Fu, Y. Yang, W. Xu, J. Zhu,
Efficient sorbitol producing process through glucose hydrogenation catalyzed by
Ru supported amino poly (Styrene-co-Maleic) polymer (ASMA) encapsulated on
γ-Al
[35] M. Audemar, W. Ramdani, T. Junhui, A. Raluca Ifrim, A. Ungureanu, F. J
S. Royer, K. Oliveira Vigier, Selective hydrogenation of xylose to xylitol over Co/
SiO
catalysts, ChemCatChem 12 (2020) 1973–1978.
[36] P. Gallezot, N. Nicolaus, G. Fl
4] J. Sun, H. Liu, Selective hydrogenolysis of biomass-derived xylitol to ethylene
glycol and propylene glycol on supported Ru catalysts, Green Chem. 13 (2011)
1
35–142.
2 3
O , Catalysts 10 (2020) 1068.
´e r oˆ me,
5] A. Tathod, T. Kane, E.S. Sanil, P.L. Dhepe, Solid base supported metal catalysts for
the oxidation and hydrogenation of sugars, J. Mol. Catal. A: Chem. 388–389 (2014)
9
0–99.
2
`
eche, P. Fuertes, A. Perrard, Glucose hydrogenation
6] A.P. Tathod, P.L. Dhepe, Towards efficient synthesis of sugar alcohols from mono-
and poly-saccharides: role of metals, supports & promoters, Green Chem. 16 (2014)
on ruthenium catalysts in a trickle-bed reactor, J. Catal. 180 (1998) 51–55.
[37] J.P. Mikkola, R. Sj
o¨ holm, T. Salmi, P. M a¨ ki-Arvela, Xylose hydrogenation: kinetic
4
944–4954.
[
[
7] A. Shrotri, H. Kobayashi, A. Fukuoka, Cellulose depolymerization over
heterogeneous catalysts, Acc. Chem. Res. 51 (2018) 761–768.
and NMR studies of the reaction mechanisms, Catal. Today 48 (1999) 73–81.
[38] B.J. Arena, Deactivation of ruthenium catalysts in continuous glucose
hydrogenation, Appl. Catal., A 87 (1992) 219–229.
8] K. Dietrich, C. Hernandez-Mejia, P. Verschuren, G. Rothenberg, N.R. Shiju, One-pot
selective conversion of hemicellulose to xylitol, Org. Process Res. Dev. 21 (2017)
[39] G.C. Torres, S.D. Ledesma, E.L. Jablonski, S.R. de Miguel, O.A. Scelza,
1
65–170.
2 3
Hydrogenation of carvone on Pt-Sn/Al O catalysts, Catal. Today 48 (1999) 65–72.
[
9] J.P. Mikkola, T. Salmi, In-situ ultrasonic catalyst rejuvenation in three-phase
[40] A.B. Merlo, V. Vetere, J.F. Ruggera, M.n.L. Casella, Bimetallic PtSn catalyst for the
selective hydrogenation of furfural to furfuryl alcohol in liquid-phase, Catal.
Commun. 10 (2009) 1665–1669.
hydrogenation of xylose, Chem. Eng. Sci. 54 (1999) 1583–1588.
[
[
[
10] J.P. Mikkola, T. Salmi, Three-phase catalytic hydrogenation of xylose to xylitol-
prolonging the catalyst activity by means of on-line ultrasonic treatment, Catal.
Today 64 (2001) 271–277.
[41] M. Englisch, V.S. Ranade, J.A. Lercher, Hydrogenation of crotonaldehyde over Pt
based bimetallic catalysts, J. Mol. Catal. A: Chem. 121 (1997) 69–80.
[42] A.P. Tathod, P.L. Dhepe, Efficient method for the conversion of agricultural waste
into sugar alcohols over supported bimetallic catalysts, Bioresour. Technol. 178
(2014) 36–44.
11] T. Granstrom, K. Izumori, M. Leisola, A rare sugar xylitol. Part II: biotechnological
production and future applications of xylitol, Appl. Microbiol. Biotechnol. 74
(
2007) 273–276.
12] Y. Sun, J. Cheng, Hydrolysis of lignocellulosic materials for ethanol production: a
review, Bioresour. Technol. 83 (2002) 1–11.
6

A.P. Tathod and P.L. Dhepe
Carbohydrate Research 505 (2021) 108341
[
[
43] K. Balakrishnan, J. Schwank, A chemisorption and XPS study of bimetallic Pt-Sn/
Al
44] B.A. Sexton, A.E. Hughes, K. Foger, An X-ray photoelectron spectroscopy and
[45] G.T. Baronetti, S.R. de Miguel, O.A. Scelza, A.A. Castro, State of metallic phase in
O
2 3
catalysts, J. Catal. 127 (1991) 287–306.
PtSn/Al
2 3
O catalysts prepared by different deposition techniques, Appl. Catal. 24
(1986) 109–116.
reaction study of Pt-Sn catalysts, J. Catal. 88 (1984) 466–477.
7