Solid base supported metal catalysts for the oxidation and hydrogenation of sugars

Article abstract of DOI:10.1016/j.molcata.2013.09.014

Pt impregnated on γ-Al₂O₃ (acidic support) and hydrotalcite (basic support) catalysts were synthesized, characterized and used in the oxidation and hydrogenation reactions of C5 and C6 sugars. In the absence of homogeneous base, 83% yield for gluconic acid; an oxidation product of glucose can be achieved over Pt/hydrotalcite (HT) catalyst at 50 °C under atmospheric oxygen pressure. Similarly, 57% yield for xylonic acid, an oxidation product of xylose is also possible over Pt/HT catalyst. Hydrogenation of glucose conducted using Pt/γ-Al₂O₃ + HT catalytic system showed 68% sugar alcohols (sorbitol + mannitol) formation. The 82% yield for C5 sugar alcohols (xylitol + arabitol) was obtained by subjecting xylose to hydrogenation over Pt/γ-Al₂O₃ + HT at 60 °C. UV analysis helped to establish the fact that under alkaline conditions sugars prefer to remain in open chain form in the solution and thus exposes CHO group which further undergoes oxidation and hydrogenation reactions to yield acids and alcohols.

Full text of DOI:10.1016/j.molcata.2013.09.014

GModel
MOLCAA-8868; No. of Pages10
ARTICLE IN PRESS
Journal of Molecular Catalysis A: Chemical xxx (2013) xxx–xxx
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Solid base supported metal catalysts for the oxidation and
hydrogenation of sugars
Anup Tathod, Tanushree Kane, E.S. Sanil, Paresh L. Dhepe∗
Catalysis and Inorganic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 April 2013
Received in revised form 21 August 2013
Accepted 11 September 2013
Available online xxx
Pt impregnated on ␥-Al2O3 (acidic support) and hydrotalcite (basic support) catalysts were synthesized,
characterized and used in the oxidation and hydrogenation reactions of C5 and C6 sugars. In the absence
of homogeneous base, 83% yield for gluconic acid; an oxidation product of glucose can be achieved over
Pt/hydrotalcite (HT) catalyst at 50 ◦C under atmospheric oxygen pressure. Similarly, 57% yield for xylonic
acid, an oxidation product of xylose is also possible over Pt/HT catalyst. Hydrogenation of glucose con-
ducted using Pt/␥-Al2O3 + HT catalytic system showed 68% sugar alcohols (sorbitol + mannitol) formation.
The 82% yield for C5 sugar alcohols (xylitol + arabitol) was obtained by subjecting xylose to hydrogena-
tion over Pt/␥-Al2O3 + HT at 60 ◦C. UV analysis helped to establish the fact that under alkaline conditions
sugars prefer to remain in open chain form in the solution and thus exposes CHO group which further
undergoes oxidation and hydrogenation reactions to yield acids and alcohols.
Keywords:
Solid base
Supported metal catalysts
Oxidation
Hydrogenation
Sugars
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
water soluble cleansing agent, an ingredient for concrete and as an
intermediate in the food and pharmaceutical industries [13]. Cal-
The requirement for alternate resources for obtaining chem-
icals which are presently derived from non-renewable (in short
cycle), fossil feedstocks have attracted researchers across the world
to work on the renewable resource, viz., biomass. Among biomass
non-edible to humans, lignocellulosic materials (cellulose, hemi-
celluloses, and lignin), which can be derived from agricultural
wastes have dominated the research domain for chemical synthe-
sis. In an acidic medium, cellulose undergoes hydrolysis reaction
to yield glucose which upon further dehydrocyclization gives 5-
hydroxymethyl furfural (HMF). Similarly, hemicelluloses (xylans)
can yield xylose, arabinose and furfural under the acidic conditions.
Once these sugars and furans are obtained, those can act as plat-
form chemicals to synthesize value added chemicals by undergoing
oxidation (acids), hydrogenation (sugar alcohols), isomerization,
hydrogenolysis (glycols), and reforming (alkanes, hydrogen) reac-
tions.
Glucose, derived from cellulose is used as a food additive
but it can also be converted to many useful chemicals such as
ethanol (fermentation) [1], sorbitol and mannitol (hydrogenation)
[2,3], 5-hydroxymethyl furfural (dehydrocyclization) [4], hydro-
gen (hydrogenolysis/cracking/reforming) [5–7] and gluconic and
glucaric acid (oxidation) [8–12]. Gluconic acid has many diverse
industrial applications such as, biodegradable chelating agent,
cium gluconate is used as a detoxifying agent after exposure to HF
[14]. Gluconic acid has an annual estimated market of 6 × 104 ton
and on industrial scale is currently prepared by fermentation of glu-
cose by Aspergillus niger [10,15]. However, fermentation method
has many drawbacks such as slow reaction rate and disposal of
dead microbes and excretory substances of microbes [16,17]. To
overcome these drawbacks, replacement of enzymes with hetero-
geneous catalysts is a viable option.
There have been few reports on the aerobic oxidation of glucose
to gluconic acid carried over supported transition metals catalysts
including Pd, Pt, Rh and Au supported on various supports like TiO2,
Al2O3 and activated carbon (AC) [8,10,11,18–27]. Among those,
gold catalysts have been extensively studied by various research
groups [10,18,19,23–27]. It is claimed that gold nanoparticles (NP)
supported on activated carbon show good catalytic activity in the
oxidation of glucose to gluconic acid done at 50 ◦C [22]. Another
report claims better turnover frequency (TOF) values per surface
Au atom of 45 s−1 at 50 ◦C, pH 9.0 and 56 s−1 at 50 ◦C, pH 9.5 in
the case of gold catalyst supported on ZrO2 [28]. In most of these
studies metals suffer from over oxidation and thus they eventually
deactivate [22–24,27]. Study on particle size effect shows that rate
of reaction is inversely proportional to Au size indicating that reac-
tion is structure-sensitive. In Au/C catalyst, Au with 1.9 nm particle
size gives maximum yield [29]. It is also observed that these metals
undergo sintering during the reaction and thus drop in activity is
reported [30]. Moreover, in all these reactions, homogeneous base
(1–20 equiv.) is used to maintain the reaction solution pH between
∗
Corresponding author. Tel.: +91 20 25902024; fax: +91 20 25902633.
E-mail address: pl.dhepe@ncl.res.in (P.L. Dhepe).
1381-1169/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2013.09.014
Please cite this article in press as: A. Tathod, et al., J. Mol. Catal. A: Chem. (2013), http://dx.doi.org/10.1016/j.molcata.2013.09.014

GModel
MOLCAA-8868; No. of Pages10
ARTICLE IN PRESS
2
A. Tathod et al. / Journal of Molecular Catalysis A: Chemical xxx (2013) xxx–xxx
disadvantages associated with nickel based catalysts by synthe-
sizing Fe, Mo, Sn, Cr promoted nickel, and nickel supported on
ZrO2, TiO2 and ZrO2/TiO2 catalysts [3,43]. Hydrogenation of glu-
cose over supported metal catalysts has been extensively studied
by the researchers in the last few decades [2,46–50]. Ru cata-
lysts are expansively used for the glucose hydrogenation, but the
catalysts are observed to be deactivating during the continuous
use [51]. Typically, neutral (AC, SiO2) [2,46,47] or mildly acidic
(Al2O3) [3] supports have been used in the study. Enzymatic con-
version of glucose is another route for the production of sorbitol
but enzymes, soluble in water are difficult to separate after use and
hence intricate to recycle [52]. Xylose hydrogenation using sup-
ported metal catalysts and enzymes is well known [39,53–58]. It is
shown that hydrogenation of xylose is possible over Ru/C catalyst
[59]. Recently, it is reported that the reduced Ni/Cu/Al hydrotalcite
catalyst at 125 ◦C and 30 bar H2 pressure can convert glucose to
yield ca.70% sorbitol [60].
In the current work we have studied glucose and xylose hydro-
genation using Pt supported on acidic, ␥-Al2O3 and basic, HT
supports under mild reaction conditions (Scheme 1). Good yield
and selectivity has been achieved at optimum reaction conditions.
Even though solid base catalysts have been used in several
industries, extensive catalytic studies on them are scanty compared
to the solid acid catalysts [61]. Application of homogeneous bases
in reactions such as isomerization, addition, alkylation and cycliza-
tion is well documented. But the homogeneous nature makes their
separation and recycling very tricky. Beside this, use of homoge-
neous bases makes the overall process corrosive and most of the
times it needs to be added in the stoichiometric amount. On the
other hand solid bases are easily separable from reaction mix-
ture, safe to handle and can be recycled. In recent past, solid base
catalysts such as, basic zeolites, hydrotalcites, apatites, chrysotile,
sepiolite, basic metal oxides like MgO, CaO and mixed oxide like
SiO2-MgO, SiO2-CaO, Al2O3-MgO, etc. have been used instead of
homogeneous bases [61–67]. It is understood that in solid base cat-
alysts like metal oxides, surface O2− species form the Lewis base site
[61,64].
Scheme 1. Conversion of sugars to corresponding acids and sugar alcohols.
9 and 11. The increase in pH (>11) typically leads to degradation
reactions and hence it is required to charge the homogeneous base
in continuous mode to maintain the pH [22]. Additionally, handling
of corrosive homogeneous base is also a major problem. It is known
that glucose oxidation carried out in a media other than alkaline is
a very slow process. Under acidic conditions, AC supported Au–Pt
bimetallic catalysts show 64% conversion and turnover frequency
(TOF) of 295 h−1 [8]. Most of the reports use high pressures of oxy-
gen in the reactions. There are only few reports available in the
literature on the oxidation of xylose to xylonic acid using heteroge-
neous catalysts [31]. Electro-catalytic oxidation of xylose to xylonic
acid using Au and Pt electrodes in alkaline medium is known [32].
To avoid the use of homogeneous base and to develop a method
which is environmentally friendly and harmless, we have employed
Pt-supported on solid acid and basic supports. In this paper, we
report the liquid phase aerobic oxidation of glucose to gluconic
acid (Scheme 1) using Pt/hydrotalcites (HT). To compare the results
we have also carried out reactions with Pt/␥-Al2O3 catalysts with
the addition of homogeneous base (Na2CO3) and solid base (HT).
Oxidation of xylose to xylonic acid is also performed.
In the US DOE report, sugar alcohols, sorbitol and xylitol
obtained by hydrogenation of glucose and xylose, respectively are
named among the 12 value added chemicals obtained from biomass
[33]. These sugar alcohols are low calorie sweeteners and find
application in oral hygiene products. Sorbitol is used as humectant
and utilization of xylitol is known in cosmetics and pharmaceu-
tical industries. Moreover, sugar alcohols have non-diabetes and
anti-caries properties because of low amount of lactic acid forma-
tion [34,35]. Recently, exploitation of sorbitol for the production
of hydrogen and C5, C6 hydrocarbons has been investigated [6,36].
Additionally, a spectrum of other functional chemicals such as, 1,4-
sorbitan, sorbose, isosorbide, glycols, lactic acid, vitamin C etc. are
produced from sugar alcohols [37,38]. Due to widespread applica-
tions of sugar alcohols demand for those is increasing day by day
[39,40].
Hydrotalcites (HT) are anioni−c clays having a double layered
structure with OH− and HCO3 groups. They have the gen-
eral formula, [Me2+1−xMe3+x(OH)2]x+(An−
x/n·mH2O and naturally
)
occurring hydrotalcite is hydroxycarbonate of magnesium and alu-
minum having formula Mg6Al2(OH)16CO3·4H2O. They are known
to show catalytic activity in numerous base catalyzed reactions
such as, aldol condensation, Knoevenagel and transesterification
[68–70]. HT supported metal catalysts are applied in the oxidation
reactions of alcohols [71]. This class of catalysts shows applications
in chemical synthesis, in isomerization reactions and as additive
in polymer and in medicine [72–74]. Layered double hydroxides of
Mg and Fe have been used in catalysis; water purification and anion
exchange [75–77]. Basic nature of hydrotalcites has been studied
extensively to use them in few other reactions [78,79].
In this work, our aim of using basic support like HT is to shun
the use of homogeneous base in oxidation reactions and to make
the overall process environmentally benign and safe. It is thought
that properties pertaining to strong interaction between metal and
basic support may help us in achieving higher activities in oxidation
and hydrogenation reactions.
2. Experimental
Sorbitol (annual production: 6.5 × 105 ton) and xylitol (annual
production: 2.4 × 104 ton) are commercially prepared by hydro-
genation of glucose and xylose using (Raney) nickel catalyst
[41,42]. However, catalyst deactivation is a major problem in
these reactions [43–45]. Efforts have been taken to rise above the
2.1. Materials
Magnesium nitrate hexahydrate (Mg(NO3)2·6H2O) was pur-
chased from Merck, India (99%), Aluminum nitrate nonahydrate
(Al(NO3)3·9H2O) was purchased from Thomas Baker, Germany.
Please cite this article in press as: A. Tathod, et al., J. Mol. Catal. A: Chem. (2013), http://dx.doi.org/10.1016/j.molcata.2013.09.014

GModel
MOLCAA-8868; No. of Pages10
ARTICLE IN PRESS
A. Tathod et al. / Journal of Molecular Catalysis A: Chemical xxx (2013) xxx–xxx
3
Tetraamine platinum nitrate (99.99%) was purchased from Alfa
Aesar, UK. Sodium carbonate (Na2CO3) (99.5%), sodium hydroxide
(NaOH) (98%) and xylose were purchased from Loba Chemicals,
India. Sorbitol and levulinic acid were purchased from Aldrich
Chemicals, USA. Glucose, arabitol, arabinose, xylitol, mannitol,
gluconic acid, glycerol, ethylene glycol, 1,2-propanediol were pur-
chased from S.D. Fine Chemicals Limited, India. All the chemicals
were used as received.
2.5. Catalytic reactions and analysis
2.5.1. Glucose and xylose oxidation reactions and analysis
Glucose and xylose oxidation reactions were carried out in a
batch mode reactor (Parr autoclave, USA) with a teflon beaker. The
reactor was charged with 3.9 mmol of glucose or 4.7 mmol of xylose
in 30 mL water. Subsequently supported metal catalyst was added.
While reactions were conducted using Pt/␥-Al2O3 catalyst, either
0.2 g of Na2CO3 or 0.3 g HT was added in the reaction mixture. In
this work during the course of reaction (intermediate addition) to
maintain the pH of the solution, no base was added. The reactor
was flushed 3 times with oxygen and then environment of oxygen
was maintained (atmospheric oxygen pressure). The autoclave was
then heated to desired temperature under slow stirring (100 rpm).
After attaining the reaction temperature, stirring was increased to
700 rpm Reaction mixture was analyzed using HPLC (Shimadzu,
Japan) equipped with HC-75 H+ (9 ␮m, 7.8 mm × 305 mm) column
while succinic acid (0.5 mmol) is used as an eluent (0.5 mL/min).
The refractive index detector (model no. RID-6A) was used for the
detection and calibration of compounds. The calibration of com-
pounds was done using commercially available standards.
2.2. Synthesis of hydrotalcite
Hydrotalcite was synthesized by co-precipitation method.
NaOH was used to maintain the pH, while Na2CO3 was used as a
carbonate source. For the synthesis of catalyst by co-precipitation
method, an aqueous solution ‘A’ (37.5 mL) of Mg(NO3)·6H2O
(0.279 mol) and Al(NO3)3·9H2O (0.093 mol) were slowly added into
aqueous solution ‘B’ (37.5 mL) of NaOH (0.4375 mol) and Na2CO3
(0.1125 mol) under vigorous stirring over a period of 2 h. Solution
pH was maintained between 8 and 10. The white precipitate thus
obtained was kept in autoclave at 60 ◦C for 16 h. Precipitate was
then washed with deionised water until pH becomes neutral. Solid
thus obtained was then dried at 80 ◦C for 18 h. Sample was calcined
at 550 ◦C in the presence of air for 8 h. Mg/Al ratio in hydrotalcite
obtained was 3.
2.5.2. Glucose and xylose hydrogenation reactions and analysis
Glucose and xylose hydrogenation reactions were carried out in
a batch reactor (Amar equipments, India). The reactor was charged
with 0.83 mmol of glucose or 1.00 mmol of xylose in 35 mL water.
During reactions catalyst/substrate ratio was kept constant at 1:2
(wt/wt). When reactions were conducted using HT, 0.075 g of HT
was added. Experiments were conducted at temperatures ranging
between 60 ◦C and 190 ◦C under 8–24 bar of hydrogen pressure.
The reactions were conducted for 2–6 h. Reaction mixture was ana-
lyzed using HPLC (Agilent, USA) equipped with HC-75 Pb++ (9 ␮m,
7.8 mm × 300 mm) column. Water was used as an eluent, at the flow
rate of 0.6 mL/min, and RID (model no. 1260 infinity) was used to
detect the compounds. The products which are poorly separable by
using HC-75 Pb++ column, were analyzed using HPLC (Shimadzu,
Japan) equipped with HC-75 H+ (9 ␮m, 7.8 mm × 305 mm) col-
umn. Succinic acid (0.5 mmol) is used as an eluent (0.5 mL/min).
The refractive index detector (Model no. RID-6A) was used for the
detection and calibration of compounds. The calibration of all the
compounds was done using commercially available standards.
Calculations of selectivity and yield (%),
2.3. Preparation of supported platinum catalysts
Before the synthesis of supported metal catalysts, supports were
evacuated at 150 ◦C for 6 h. An aqueous solution of platinum precur-
sor, tetrammine platinum nitrate (quantity used corresponding to
3.5 wt% loading on support) was added to the support suspended in
water. The solution was stirred for 16 h at room temperature. Next,
water was removed by rotary evaporator and powder obtained was
dried in oven at 60 ◦C for 16 h. The powder was later dried under
vacuum at 150 ◦C for 6 h. This dry powder was subjected for calci-
nation in air flow (20 mL/min) and was reduced in hydrogen flow
(20 mL/min) at 400 ◦C for 2 h each.
2.4. Characterization of catalysts
The powder X-ray diffraction (XRD) patterns of all samples were
ꢀ
ꢁ
mole of gluconic acid formed (HPLC)
mole of glucose converted (HPLC)
recorded on a Philips Powder XRD, operated at Cu K␣ radiation
Selectivity (%) =
× 100
˚
(ꢀ = 1.540598 A) as a primary beam. The patterns were recorded
with a scanning rate of 2◦/min. Nitrogen sorption analysis at
low temperature was performed using Dona Quantachrome Nova
4200e instrument. The surface areas of catalysts were calculated by
the BET method. The temperature programmed desorption (TPD) of
CO2 was done using the Micromeritics AutoChem 2910 instrument.
Prior to measurement, samples were activated at 350 ◦C for 15 min
The adsorption of CO2 was done at 50 ◦C and then the sample was
kept at 100 ◦C under He flow. Next, sample was heated from 100 ◦C
to 600 ◦C with a ramping rate of 4 ◦C/min. The TPD-NH3 analysis
was done using Micrometrics Autochem-2910 model, instrument;
USA. Catalyst was activated at a temperature of 500 ◦C in He gas
flow (25 mL/min). NH3 adsorption (30 mL/min) was done at 100 ◦C
and desorption was started from 100 ◦C to 823 ◦C at the rate of
10 ◦C/min. Metal contents in the prepared catalysts were ana-
lyzed by inductive coupled plasma atomic emission spectroscopy
(ICP-AES) using SPECTRO ARCOS Germany, FHS 12 instrument.
Transmission electron microscopy (TEM) was done using FEI Tec-
nai TF-30 instrument. UV absorbance spectras were recorded using
PerkinElmer spectrophotometer (model-Lambda 650). Tempera-
ture programmed reduction (TPR) was done using Micromeritics
AutoChem chemisorptions analyzer.
ꢀ
ꢁ
mole of product formed (HPLC)
theoretical mole of product
Yield (%) =
× 100
3. Results and discussion
3.1. Catalysis
3.1.1. Results
3.1.1.1. Oxidation reactions. Oxidation of glucose was carried out
over Pt supported on ␥-Al2O3 and HT catalysts in water medium
at 50 ◦C under atmospheric oxygen pressure (Table 1). The Pt/HT
and Pt/␥-Al2O3 + Na2CO3 catalysts gave similar oxidation results
(entry 1 and 2). Pt/HT catalytic system without addition of any
homogeneous base gave good performance for the oxidation of
glucose showing 83% gluconic acid yield after 12 h reaction time
(entry 1). Along with gluconic acid ca. 8% fructose formation was
also observed. Whereas in conventional system in which homoge-
neous base, Na2CO3 was used along with the Pt/␥-Al2O3 catalyst
82% gluconic acid yield was observed (entry 2). In this reaction ca.
Please cite this article in press as: A. Tathod, et al., J. Mol. Catal. A: Chem. (2013), http://dx.doi.org/10.1016/j.molcata.2013.09.014

GModel
MOLCAA-8868; No. of Pages10
ARTICLE IN PRESS
4
A. Tathod et al. / Journal of Molecular Catalysis A: Chemical xxx (2013) xxx–xxx
Table 1
Comparison of gluconic acid yield with different catalyst at various time intervals.
Entry
Catalyst
Gluconic acid yield (%)
(Glucose conversion (%))
TOFa
pH
6 h
8 h
10 h
12 h
Before reaction
After reaction
1
2
3
4
5
6
Pt/HT
73
65
55 (94)
76
82 (98)
56 (99)
81 (95)
83 (99)
55
83 (99)
–
54
0.252
5.278
5.485
9.31
11.06
8.76
9.24
10.95
7.96
9.36
7.02
9.16
10.84
Pt/␥-Al2O3 + Na2CO3
Pt/␥-Al2O3 + HT
HT
␥-Al2O3 + Na2CO3
Non catalytic
Isomerization
Isomerization
–
–
–
–
Reaction conditions: glucose 0.7 g, catalyst 0.3 g, Na2CO3 0.2 g, HT 0.3 g, water 30 mL, 1 bar O2 at R.T., 50 ◦C. During the course of reaction pH was not maintained.
a
Turn over frequency in min−1. TOF is calculated at initial stage of reaction at almost similar conversion levels ( 5% difference) in all the reactions.
5% fructose formation also was observed. Careful inspection reveals
that actually after 6 h, higher gluconic acid yield was observed with
Pt/HT catalyst (73%) than Pt/␥-Al2O3 + Na2CO3 catalyst (65%). The
Pt/␥-Al2O3 + HT catalytic system afforded maximum gluconic acid
yield of 56% after 8 h of reaction. In all these experiments, almost
complete conversion of glucose was achieved. It is important to
note here that in all the reactions besides desired products, we also
observed formation of oxalic acid, malonic acid, lactic acid etc. in
minor amount (4–5%). Blank run (non catalytic, entry 6) did not
show any activity under the reaction conditions. Bare HT could
not convert glucose to oxidation products; however, 20% yield of
fructose was observed (entry 4), which is in line with the liter-
ature wherein it is reported that basic catalysts are capable of
isomerizing glucose [80–82]. Similarly, reactions done using only
␥-Al2O3 + Na2CO3 (entry 5) did not yield any oxidation product
but formation of fructose was observed (19%). These results clearly
indicate that not only basicity but metal also is necessary to obtain
oxidation products.
To check the stability of gluconic acid under the reaction con-
ditions, catalytic runs with gluconic acid as substrate over HT,
␥-Al2O3, Pt/HT, Pt/␥-Al2O3 + Na2CO3 and Pt/␥-Al2O3 + HT were car-
ried out and we did not observe any conversions. This clearly
implies that gluconic acid is stable and does not participate in any
further reactions or undergoes any degradation reactions under our
reaction conditions.
Table 2 summarizes the results for xylose oxidation reaction.
As seen, maximum yield of 65% was attainable with Pt/␥-
Al2O3 + Na2CO3 catalytic system (entry 2). On the other hand,
Pt/␥-Al2O3 + HT (entry 3) showed maximum yield of 53% and Pt/HT
catalyst showed 57% yield (entry 1). Xylose oxidation carried out
in the absence of catalyst did not show any conversions (entry
6). Along with oxidation products, arabinose, lactic acid, tartaric
acid formation and some other unidentified products were also
observed. Formation of the minor products (ca. 5%) arises due to
isomerization reaction of xylose when reactions were done using
bare HT and ␥-Al2O3 + Na2CO3 catalytic systems at 50 ◦C.
catalyst in the presence of homogeneous base, showed that increase
in oxygen partial pressure gives poor FDCA yields [83]. This might
be due to the presence of higher concentration of oxygen in water
at elevated pressures which causes oxidation of active metal [84].
In this work we did reactions over Pt/HT with varying pressure
(1 bar, 5 bar) and we achieved marginally less gluconic acid yield at
5 bar (51%, 24 h). The catalysts could be recycled effectively at least
for 3 times with a loss of ca. 10% activity after each catalytic run.
This loss of activity might be due to the leaching of Pt in the solu-
tion which was confirmed by ICP-OES analysis (please refer catalyst
characterization section).
3.1.1.2. Hydrogenation reactions. Hydrogenation of glucose was
studied over Pt/␥-Al2O3, Pt/HT and Pt/␥-Al2O3 + HT catalysts at
90 ◦C using 16 bar hydrogen pressure. Amongst all the catalytic
systems, Pt/␥-Al2O3 + HT catalytic system gave the best result
(Table 3). As observed, Pt/␥-Al2O3 + HT showed 68% sugar alco-
hols yield with 92% conversion (entry 4). Under similar reaction
conditions, Pt/HT (entry 3) showed 39% sugar alcohol yield (80%
conversion) and the lowest activity was observed for Pt/␥-Al2O3
catalyst (8.4% yield, 15% conversion, entry 2). In the absence of
any catalyst only 2% conversion with 0.5% sugar alcohol yields is
observed (entry 1). Besides C6-sugar alcohols, formation of C5-
sugar alcohol (xylitol), ethylene glycol, 1,2-propanediol, glycerol,
gluconic acid and levulinic acid is observed. The results clearly indi-
cate that Pt/␥-Al2O3 + HT catalytic system gives maximum yield
(68%) of C6-sugar alcohols compared to any other catalysts.
The results imply that change in support affects the activity of
catalyst and hence reactions with only supports were carried out. It
is interesting to note here that without catalyst (†ESI Table S1, entry
1) and with ␥-Al2O3 (†ESI Table S1, entry 2) as a catalyst maximum
of 4% conversion is possible after 6 h. However, when basic cata-
lyst is introduced the conversion increased to 80% (†ESI Table S1,
entry 3) yielding 39% fructose and 16% sugar alcohols. As explained
earlier (Section 3.1.1.1), isomerization of glucose is possible under
the alkaline medium. It is also evidenced that the HT in hydroxide
form has the most basic properties which may help achieve higher
isomerization activity [85]. Reaction with ␥-Al2O3 + HT (entry 4)
Our earlier work on the oxidation of 5-hydroxymethyl fur-
fural to yield 2,5-furandicarboxylic acid (FDCA) using Pt/␥-Al2O3
Table 2
Comparison of xylonic acid yield with different catalysts at various time intervals.
Entry
Catalyst
Xylonic acid yield (%)
(Xylose conversion (%))
TOFa
pH
6 h
12 h
18 h
24 h
Before reaction
After reaction
1
2
3
4
5
6
Pt/HT
24
27
18
–
30
20
52
54
21
57 (90)
65 (84)
53 (86)
0.124
1.119
0.726
9.28
11.02
8.62
9.24
10.93
9.01
9.87
8.09
9.36
10.80
Pt/␥-Al2O3 + Na2CO3
Pt/␥-Al2O3 + HT
HT
␥-Al2O3 + Na2CO3
Non catalytic
Isomerization
Isomerization
–
–
–
–
Reaction conditions: xylose 0.7 g, catalyst 0.3 g, Na2CO3 0.2 g, HT 0.3 g, water 30 mL, 1 bar O2 at R.T., 50 ◦C. During the course of reaction pH was not maintained.
a
Turn over frequency in min−1. TOF is calculated at initial stage of reaction at almost similar conversion levels ( 5% difference) in all the reactions.
Please cite this article in press as: A. Tathod, et al., J. Mol. Catal. A: Chem. (2013), http://dx.doi.org/10.1016/j.molcata.2013.09.014

GModel
MOLCAA-8868; No. of Pages10
ARTICLE IN PRESS
A. Tathod et al. / Journal of Molecular Catalysis A: Chemical xxx (2013) xxx–xxx
5
Table 3
Effect of different catalysts on the hydrogenation of glucose.
Entry
Catalyst
Time (h)
Conversion (%)
Product yield (%)
Sugar alcohols
TOFa
pH
Fructose
Glycols
–
Gluconic
acid
Before
reaction
After
reaction
Sorbitol
Mannitol
Xylitol
1
2
3
4
Without catalyst
Pt/␥-Al2O3
2
4
6
–
2
4
–
–
–
–
–
–
–
–
–
–
–
–
–
–
0.5
1.5
–
0.5
2
4
6
8
15
25
5.7
8.4
9.8
–
–
–
–
–
1
–
–
–
–
–
–
0.91
0.98
10.21
5.51
9.29
8.42
5.69
9.64
9.19
1.5
3.5
Pt/HT
2
4
6
60
80
85
12
19.4
26
13.3
19.6
19.5
2
4.5
5
15
16
14
3.7
6.5
9
5
5.5
5.5
Pt/␥-Al2O3 +HT
2
4
6
80
92
98
42
54
53
16
14
12
4
4
4
3
–
–
6.5
7
8
4
5
5
Reaction conditions: glucose 0.15 g, catalyst 0.075 g, HT 0.075 g, water 35 mL, 16 bar H2 at R.T., 90 ◦C.
a
Turn over frequency in min−1. TOF is calculated at initial stage of reaction at almost similar conversion levels ( 5% difference) in all the reactions.
also showed higher glucose conversions (72%) with 42% fructose
and 18.6% sugar alcohol formation. Contrary to the recent report
wherein it is shown that alkaline medium (NaOH) yields less sor-
bitol compared to acidic or neutral medium [60], we observed that
better yields are possible in alkaline medium (solid base).
in 2 h of reaction time and 92% conversion with 68% yield of C6-
sugar alcohols could be obtained in 4 h (Table 3, entry 4). From the
figure it is clear that we could achieve very high carbon balance
since there is typically only 5–7% difference between conversion
and total product yields.
Fig. 1 depicts the effect of temperature on the catalytic activity
over Pt/␥-Al2O3 + HT catalyst. As seen, increase in temperature to
130 ◦C does not necessarily increase the sugar alcohols yield even
though conversion was increased to 99% in 2 h. This in fact lowers
the yield for C6-sugar alcohols formation (56%) at the expense of
increase in the yield for glycols (1,2-propane diol, glycerol, ethyl-
ene glycol) and other products like levulinic acid and xylitol (39%).
On the other hand decrease in temperature to 60 ◦C reduced the
conversion levels to 28% with 21% yield of C6-sugar alcohols. In
view of above results, 90 ◦C reaction temperature is optimum to
obtain higher conversions (80%) and 58% C6-sugar alcohols yield
It is known from the literature that hydrogen solubility follows
Henry’s law which means that solubility of hydrogen in water is
directly proportional to pressure and temperature [84]. To under-
stand how these factors would play role in our catalytic system we
altered the pressures. The increase in pressure from 16 to 24 bar did
not alter the catalytic results (16 bar: 68% yield with 92% conver-
sion; 24 bar: 67% yield with 93% conversion, 4 h). However, if 8 bar
hydrogen pressure is used then activity was decreased (54% yield
with 93% conversion, 8 h).
Hydrogenation of xylose is studied over catalysts, Pt/␥-Al2O3,
Pt/HT and Pt/␥-Al2O3 + HT at 60 ◦C with 16 bar hydrogen pressure
(Table 4). In these reactions also Pt/␥-Al2O3 + HT catalytic system
showed the best activity (82% yield with 99% conversion) among
all the catalysts evaluated. It can be seen that highest TOF was
observed for Pt/␥-Al2O3 + HT system.
The effect of temperature was studied and it was found out that
60 and 90 ◦C reaction temperatures are the best (Fig. 2). Although
At 60 ◦C conversion is less (82%) than other temperatures, the selec-
tivity for sugar alcohols is highest, i.e. 87.8%. Maximum 82% yield
of xylitol + arabitol could be obtained from xylose at 60 ◦C within
4 h.
Effect of supports on the yields of sugar alcohols has been stud-
ied by conducting reactions with bare supports (†ESI Table S2).
Similar to glucose hydrogenation, xylose hydrogenation has
been studied by applying various H2 pressures. Yield of sugar alco-
hols obtained after complete conversion, at any pressure, seems
to be similar (ca. 80%). But the noteworthy point is that the time
required for total conversion of xylose is different. Xylose conver-
sion was 95% at 24 bar (80% yield of sugar alcohols), 82% at 16 bar
(72% yield) and 63% at 8 bar (58% yield) after 2 h. Complete conver-
sion with 82% yield occurs after 4 h at higher pressure but it takes
6 h for complete conversion at 8 bar
Recycle study has been done for Pt/␥-Al2O3 + HT catalytic sys-
tem for glucose and xylose hydrogenation. In case of glucose
hydrogenation, activity decreases by 20% after 1st cycle and 12%
after 2nd cycle. However, in xylose hydrogenation, catalyst shows
good recyclability up to 3rd cycle with negligible decrease in the
yield after each run (1st run: 82%; 2nd run: 80%; 3rd run: 74%).
These results can be correlated to the fact that during reactions Pt
Fig. 1. Results for the conversion of glucose to sugar alcohols at various reaction
temperatures using Pt/␥-Al2O3 + HT. Reaction conditions: glucose 0.15 g, Pt/␥-Al2O3
0.075 g, HT 0.075 g, water 35 mL, 16 bar H2 at R.T., 2 h.
Please cite this article in press as: A. Tathod, et al., J. Mol. Catal. A: Chem. (2013), http://dx.doi.org/10.1016/j.molcata.2013.09.014

GModel
MOLCAA-8868; No. of Pages10
ARTICLE IN PRESS
6
A. Tathod et al. / Journal of Molecular Catalysis A: Chemical xxx (2013) xxx–xxx
Table 4
Effect of different catalysts on the hydrogenation of xylose.
Entry
Catalyst
Time (h)
Conversion (%)
Product yield (%)
Sugar alcohols
TOFa
pH
Glycols
Xylonic
acid
Before
reaction
After
reaction
Xylitol
Arabitol
1
2
3
4
Without catalyst
Pt/␥-Al2O3
2
4
6
–
–
2
–
–
0.5
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
2
4
6
4
6
9
3.3
3
4.5
–
–
–
–
1
1.5
–
0.38
–
–
5.31
–
5.47
–
Pt/HT
2
4
6
41.5
59
72
36
50
55
6
6
4
–
1.5
3.5
–
–
2
0.42
9.20
–
–
9.57
–
–
Pt/␥-Al2O3 + HT
2
4
6
82
99
99
68
79
78
4
3
3
4
6
6
2
2.5
2.5
13.01
8.31
–
–
9.29
–
–
Reaction conditions: xylose 0.15 g, catalyst 0.075 g, HT 0.075 g, water 35 mL, 16 bar H2 at R.T., 60 ◦C.
a
Turn over frequency in min−1. TOF is calculated at initial stage of reaction at almost similar conversion levels ( 5% difference) in all the reactions.
is not leached out in the solution (refer catalyst characterization
section).
adsorption of sorbitol on HT and ␥-Al2O3. The results presented in
Table S3 (†ESI) however shows that there is no considerable differ-
ence in the adsorption of sorbitol on either HT or ␥-Al2O3. This may
imply that to obtained enhanced activity over Pt/HT catalyst com-
pared to Pt/␥-Al2O3 catalyst weak or strong adsorption of product
may not be the reason.
3.1.2. Discussion
It is well documented that solid base can suppress the crack-
ing reaction, which generally occur on acidic catalysts (␥-Al2O3)
[86]. It is suggested that over solid bases no strong adsorption of
complexes (through ‘O’ of the product) is possible which means
that the products formed will be readily removed from the sur-
face to avoid undergoing further reactions (glycols, coke). This can
improve the yield for sugar alcohols and acids derived from C5
and C6 sugars (glucose and xylose) by suppressing further reac-
tions of acids/alcohols and formation of coke. This may indicate the
reason for the better results on Pt/HT compared with Pt/␥-Al2O3
catalysts. To prove this we conducted the experiments to check the
It is known from the literature that at the surface of a basic sup-
port typically, oxide ions form ion pairs with low coordinated metal
ions [87]. Usually, hydrogen molecule is split heterolytically over
supported metal (Pt) to give rise to hydrogen ions (H+ and H−).
In case of base support, there is a possibility of retention of the
molecular identity of H atoms during a reaction as is reported ear-
lier [87]. It is possible that hydrogen ions are immobilized on the
set of active sites (O2− – metal cation pair) and that these sites are
separated from each other and hence migration and recombination
of hydrogen ions to form hydrogen molecule is not possible. This
ultimately may give rise to rich environment of hydrogen ions on
the support. This pool of hydrogen ions then may be available for
the hydrogenation reaction thus increasing the activity of a catalyst.
The other possibility for increased activity in case of Pt sup-
ported on basic support is that the basic support can give rise
to electron-rich metallic particles. In fact it is reported that elec-
tron rich Pd particles are possibly formed when MgO is used as
a support [88]. A similar phenomenon is also reported for Pt par-
ticles supported on hydrotalcites [89,90]. In yet another report it
is evidenced that since Pt particle size is almost same in all the
tested catalysts, it is the electronic ligand effect produced by basic
support that enhances the hydrogenation activity [91]. The strong
metal-support interaction (SMSI) is first reported for Pt/MgO cat-
alyst and it was showed that higher metal dispersion achieved by
SMSI enhances the hydrogenation activity [92]. In case of our cat-
alysts, better hydrogenation activity with Pt/HT may arise due to
SMSI in Pt/HT compared to Pt/␥-Al2O3 catalyst as we observed that
over HT support Pt is well dispersed to give rise to average parti-
cle size of 1.9 nm while in case of Pt supported on ␥-Al2O3 average
particle size of Pt was 20–30 nm (TEM study, refer Section 3.2). In
oxidation reactions metal in zero oxidation state is most active [93]
and as discussed above when Pt is present on basic support (HT,
MgO) it may have more electron rich environment. This may be the
reason for higher oxidation activity for Pt/HT catalyst. Moreover, Pt
particle size decreases if there is a strong metal support interaction
and thus in Pt/HT catalyst particle size of Pt was observed to be
much less than Pt supported on ␥-Al2O3. This again will improve
the oxidation activity on Pt/HT catalyst. An attempt was made to
Fig. 2. Results for the conversion of xylose to sugar alcohols, at various reaction
temperatures using Pt/␥-Al2O3 + HT. Reaction conditions: xylose 0.15 g, Pt/␥-Al2O3
0.075 g, HT 0.075 g, water 35 mL, 16 bar H2 at R.T., 2 h.
Please cite this article in press as: A. Tathod, et al., J. Mol. Catal. A: Chem. (2013), http://dx.doi.org/10.1016/j.molcata.2013.09.014

GModel
MOLCAA-8868; No. of Pages10
ARTICLE IN PRESS
A. Tathod et al. / Journal of Molecular Catalysis A: Chemical xxx (2013) xxx–xxx
7
Fig. 3. Proposed changes in the structures of glucose under alkaline conditions.
carefully look at the Pt(4f) core level using XPS as any electronic
perturbation associated with Pt can result in changes in the binding
energy values Figure S1 (†ESI). Unfortunately, this was not success-
ful as Pt (4f) binding energy values (71 eV) falls almost at the same
energy for Al (2p) (73 eV) making it extremely difficult to get any
meaningful binding energy shifts. However, we believe that from
earlier reports Pt might present in more electron rich state on HT
[89–92]. Besides this we performed TPR studies to know the hydro-
gen consumption by both Pt/HT and Pt/␥-Al2O3 catalyst. The data is
plotted in Figure S2 (†ESI). It is evident from the figure that in case
of Pt/HT catalyst higher amount of hydrogen (22.9 cm3/g) is con-
sumed as compared to Pt/␥-Al2O3 catalyst (18.8 cm3/g). This may
imply that Pt present on HT is in more electron rich environment;
however, it is essential to prove this point beyond doubt.
difference in activity/selectictivity for Pt/␥-Al2O3, Pt/HT and Pt/␥-
Al2O3 + HT catalysts. Careful observation of the data from Table 3
reveals that when Pt/␥-Al2O3 is used (entry 2) no fructose forma-
tion is observed. However, when Pt/HT catalyst is used (entry 3),
fructose (isomerization product of substrate, glucose) is obtained in
high quantity (14%, 6 h). In comparison over Pt/␥-Al2O3 + HT cata-
lyst (entry 4, 3%, 2 h) fructose formation was seen. As shown in Table
S1 (†ESI) when bare HT is used for the reaction (entry 3) almost
39% fructose formation was possible. Compared to this if bare ␥-
Al2O3 is used in the reaction no fructose formation was seen (†ESI
Table S1, entry 2). Considering this, it is obvious to expect that if a
basic support is used to impregnate Pt then higher concentrations
of mannitol should form in the reaction (via fructose formation
and its further hydrogenation). Now, again looking at sugar alco-
hols formation data from Table 3, with Pt/HT catalyst sorbitol is
formed with 26% yield while mannitol (a hydrogenation product of
fructose) has 19.5% yield (entry 3). Whereas with Pt/␥-Al2O3 + HT
system, 53% sorbitol yield is obtained with only 12% mannitol yield.
Moreover, when Pt/␥-Al2O3 catalyst is used (without addition of
any base) formation of mannitol was not observed. These results
indicate that higher the fructose formation, higher the mannitol
yield and lower is the sorbitol yield (Table 3, entry 3 and 4). We
would like to bring to notice that pH of the reaction solution in case
of Pt/HT catalyst was observed to be 9.3 while with Pt/␥-Al2O3 + HT
catalyst it was 8.4 and with Pt/␥-Al2O3 it was 5.5 (Table 3). This dif-
ference in pH makes the variation in products yield, since higher
pH enhances the concentration of glucose in the enolate form (open
chain) which ultimately leads to fructose formation.
There is a possibility of catalytic transfer hydrogenation of alde-
hydes while solid base is used as a support (catalyst). However, this
possibility is ruled out in our study as with only HT as a catalyst (in
absence of Pt) minor sugar alcohols formation was observed (†ESI
Tables S1 and S2).
The best hydrogenation activity for Pt/␥-Al2O3 + HT catalytic
system can be attributed to the fact that presence of HT may influ-
ence the isomerization of glucose to make it available in open chain
form. It is proved that concentration of open-chain glucose in water
at equilibrium is very small. Dissolving glucose in alkaline medium
yields fructose by undergoing keto-enol tautomerizations reactions
as known by Lobry de Bruyn-Albeda van Ekenstein transformation.
The enolate ion thus formed as an intermediate is present in an
open-chain form (in water) and this higher concentration of ion is
available for hydrogenation reactions. It is not possible to obtain
similar concentration of glucose in an open chain form under neu-
tral and acidic reaction conditions and hence it is suggested that
higher yields are possible when Pt/␥-Al2O3 + HT catalyst is used
for the reaction (Table 3). It is interesting to point out here the
The above explanation about presence of glucose in higher con-
centration in open chain form under alkaline conditions also holds
true for oxidation reactions. In oxidation reactions, gluconic acid
can be formed in high yields if higher concentration of glucose in
open chain form is available in solution. Moreover in Pt/HT catalytic
Please cite this article in press as: A. Tathod, et al., J. Mol. Catal. A: Chem. (2013), http://dx.doi.org/10.1016/j.molcata.2013.09.014

GModel
MOLCAA-8868; No. of Pages10
ARTICLE IN PRESS
8
A. Tathod et al. / Journal of Molecular Catalysis A: Chemical xxx (2013) xxx–xxx
1.0
out additional studies on using NaOH instead of Na2CO3 as a base.
With the addition of NaOH with same mole as that like Na2CO3,
we observed additional peak appearing at ꢀmax = 310.5 nm, which
can be assigned to enediol anion as reported earlier [94]. Along with
this peak we also observed peak at ꢀmax = 270 nm ascribed to CHO
group. To understand why after addition of NaOH additional peak
appears, we checked the pH of the solution and found out that with
the addition of NaOH, pH was 13.84 while after addition of Na2CO3,
pH of the solution was 11.48. It is hence understood that with high
pH values (due to NaOH) glucose is converted from cyclic form to
open chain form to yield, enolate ion and subsequently gives rise
to enediol formation. We could not perform the experiments with
the addition of HT since it is a solid base and after adding the same
it is difficult to do UV analysis.
a-Glucose+Na CO
2
b-Glucose+NaOH
c-Glucose
3
0.8
267.8
a
0.6
0.4
b
c
270
0.2
0.0
266.2
3.2. Characterizations
225
250
275
300
325
350
375
400
Wavelenth (nm)
Fig. 5 shows the XRD patterns of fresh and spent catalysts used in
hydrogenation reactions. It can be observed that most of the peaks
are retained in the spent catalyst. However, careful observation
suggests that in Pt/HT catalyst Pt peaks are very small indicating
that Pt particle size may be very small and Pt might be well dis-
persed on the support. The peaks appeared at 35.23◦, 43.34◦ and
62.63◦ correspond to the lattice plane (1 1 1), (2 0 0), and (2 2 0) are
characteristic peak for the hydrotalcite (JCPDF file No. 45-0946).
On the contrary in Pt/␥-Al2O3 catalyst, sharp peaks for Pt could
be seen at characteristic peak positions. Diffraction through lattice
plane (1 1 1) gives peak at 39.70◦, similarly peak at 46.20◦, 67.22◦,
81.22◦ and 85.67◦ correspond to lattice plan (2 0 0), (2 2 0), (3 1 1)
and (2 2 2). These sharp peaks imply that Pt has agglomerated to
form big particles. The additional peak at 24.5◦ in spent catalyst
can originate from absorbed carbon species.
The TEM images and particle size distribution of fresh Pt/HT cat-
alyst (Fig. 6) indicate that Pt nanoparticles of average size of 1.9 nm
are highly dispersed on HT support. On the other hand, in case of
Pt/␥-Al2O3 catalyst, Pt nanoparticles with average size of 20–30 nm
are present. This information points out that the Pt has a strong
interaction with basic support (HT) which helps to have higher
dispersions and stabilization of metal particles (Section 3.1.2). The
oxidation reactions are structure sensitive [29], and thus smaller
particle size of Pt obtained over Pt/HT catalysts are naturally more
active than the Pt/␥-Al2O3 catalyst.
Fig. 4. UV absorption spectra of glucose.
system, reaction solution pH is about 9.3 (Table 1) which means
that it falls in the exact range of pH 8–10 at which maximum oxi-
dation activity is reported to be possible [28]. At the same time
Pt/␥-Al2O3 + HT system shows pH of 8.7 (Table 1) which is on the
lower marginal side of best pH range to obtain higher oxidation
results and hence shows slightly less activity than Pt/HT catalyst.
As discussed above glucose may undergo Lobry de Bruyn-
Alberda van Ekenstein transformation (Fig. 3) under alkaline
medium to yield enolate ions, enediol and fructose formation.
To prove that the higher concentrations of open chain form glu-
cose is possible under alkaline conditions we performed UV studies.
From the literature it is very well known that glucose is UV active
if it is present in open chain form due to exposure of CHO group.
Based on this fact we performed UV of glucose (0.233 g) dissolved in
only water (10 mL) under neutral conditions (pH = 6.7). The peak at
ꢀmax = 266.2 nm was visible as a small hump (Fig. 4). However, after
addition of mineral base (Na2CO3, 0.066 g) in the glucose solution
(glucose, 0.233 g in 10 mL water: same glucose concentration solu-
tion as was used for oxidation reaction) the peak at ꢀmax = 267.8 nm
was increased many folds. This proves that under alkaline condi-
tions, glucose is present in open chain form. Moreover, we carried
Pt
(111)
HT
(200)
Pt
(200)
Pt
(220)
Spent
HT
(220)
Pt/γ-Al2O3
Spent
Pt/HT
Pt
(311)
HT
(222)
Fresh
Pt/γ-Al2O3
Fresh
Pt/HT
γ-Al2O3
HT
10
20
30
40
50
θo
60
70
80
90
10
20
30
40
50
θo
60
70
80
90
2
2
Fig. 5. XRD patterns of fresh and spent catalysts used in hydrogenation reaction.
Please cite this article in press as: A. Tathod, et al., J. Mol. Catal. A: Chem. (2013), http://dx.doi.org/10.1016/j.molcata.2013.09.014

GModel
MOLCAA-8868; No. of Pages10
ARTICLE IN PRESS
A. Tathod et al. / Journal of Molecular Catalysis A: Chemical xxx (2013) xxx–xxx
9
Fig. 6. TEM images of fresh and spent Pt/␥-Al2O3 and Pt/HT catalysts.
Table 5
Summary on catalyst characterizations.
Entry
Catalyst
Surface area, m2/g
Basicity, mmol/ga
Acidity, mmol/gb
pHc
1
2
3
4
5
6
7
HT
212
159
73
154
174
132
–
0.88
0.81
1.02
–
–
–
–
–
–
0.39
0.35
–
9.24
9.30
–
–
5.52
–
Pt/HT-Fresh
Pt/HT-Spentd
␥-Al2O3
Pt/␥-Al2O3-Fresh
Pt/␥-Al2O3-Spentd
Pt/␥-Al2O3 + HT
–
–
8.50
a
Basicity calculated from TPD-CO2.
Acidity calculated from TPD-NH3.
pH was observed by suspending 0.075 g catalyst in 30 mL water.
Spent catalyst from glucose oxidation reaction.
b
c
d
Table 5 summarizes the results on the characterization of fresh
from oxidation reaction showed loss of only 0.03% of Pt in the
solution in the case of Pt/␥-Al2O3 and 0.018% in the case of Pt/HT
catalyst.
and spent catalysts. It can be noticed that surface area of bare
HT decreases to 159 m2/g after loading of Pt when used in oxida-
tion reaction. However, after the oxidation reaction, surface area
decreases to 73 m2/g. This implies that catalyst may undergo some
structural changes during the reaction. In Pt/␥-Al2O3-spent catalyst
marginal decrease in surface area was seen.
4. Conclusion
The temperature programmed desorption study done with car-
bon dioxide as a probe molecule gave 0.88 mmol/g as basicity value
for bare HT catalyst (Table 5). The basicity remains almost constant
after Pt loading (0.81 mmol/g). The TPD-NH3 was done to check the
acidity of ␥-Al2O3 and Pt/␥-Al2O3 catalysts (Table 5). The pH val-
ues for Pt/HT, Pt/␥-Al2O3 are 9.30 and 5.52, respectively (Table 5).
However addition of HT to Pt/␥-Al2O3 changes the pH to 8.5. This
is natural since HT has basicity (pH 9.24).
The possibility of leaching of Pt during reactions was studied
by ICP-OES technique. In case of Pt/␥-Al2O3 catalysts 3.3% and in
Pt/HT 3.2% Pt loading in fresh catalysts was found which is in line
with the actual loading (3.5%). The spent catalyst used for hydro-
genation reactions shows similar concentration of Pt implying that
there is no leaching of Pt in the solution. This result is corroborated
by not observing any Pt in the reaction solution. Spent catalyst
Catalytic oxidation and hydrogenation over Pt supported on
basic supports can offer a convenient way to advance the valoriza-
tion of glucose and xylose to yield acids and alcohols. The oxidation
carried out at 50 ◦C is a feasible way to achieve as high as 83% glu-
conic acid yield by suppressing the side reactions. Sugar alcohols
yield of 68% could be achieved with Pt/␥-Al2O3 catalyst suspended
with basic support (HT). The basicity of support might be helpful
in stabilizing metal particles to give higher dispersions and make
them electron rich which helps in attaining higher yields. The alka-
line medium is useful to build higher concentration of glucose in
open chain form which readily gets converted to corresponding
acids and alcohols. Hence a combined effect of metal as well as
acidic and basic sites renders these multifunctional catalysts ideal
for both hydrogenation and oxidation of substrates like glucose and
xylose.
Please cite this article in press as: A. Tathod, et al., J. Mol. Catal. A: Chem. (2013), http://dx.doi.org/10.1016/j.molcata.2013.09.014

GModel
MOLCAA-8868; No. of Pages10
ARTICLE IN PRESS
10
A. Tathod et al. / Journal of Molecular Catalysis A: Chemical xxx (2013) xxx–xxx
Acknowledgment
[45] R. Albert, A. Strätz, G. Vollheim, Chem. Ing. Tech. 52 (1980) 582–587.
[46] B.W. Hoffer, E. Crezee, P.R.M. Mooijman, A.D. van Langeveld, F. Kapteijn, J.A.
Moulijn, Catal. Today 79–80 (2003) 35–41.
[47] B. Kusserow, S. Schimpf, P. Claus, Adv. Synth. Catal. 345 (2003) 289–299.
[48] K.V. Gorp, E. Boerman, C.V. Cavenaghi, P.H. Berben, Catal. Today 52 (1999)
349–361.
[49] J. Wisniak, R. Simon, Ind. Eng. Chem. Prod. Res. Dev. 18 (1979) 50–57.
[50] A. Perrard, P. Gallezot, J.P. Joly, R. Durand, C. Baljou, B. Coq, P. Trens, Appl. Catal.,
A 331 (2007) 100–104.
Author, A. T. thanks UGC for senior research fellowship.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.molcata.2013.09.014.
[51] B.J. Arena, Appl. Catal., A 87 (1992) 219–229.
[52] M. Makkee, A.P.G. Kieboom, H. van Bekkum, Starch 37 (1985) 232–241.
[53] J.H. Kim, K.C. Han, Y.H. Koh, Y.W. Ryu, J.H. Seo, J. Ind. Microbiol. Biotechnol. 29
(2002) 16–19.
[54] D.K. Oh, S.Y. Kim, J.H. Kim, Biotechnol. Bioeng. 58 (1998) 440–444.
[55] J. Zhang, A. Geng, C. Yao, Y. Lu, Q. Li, Bioresour. Technol. 105 (2011) 134–141.
[56] M.G.A. Felipe, M. Vitolo, I.M. Mancilha, S.S. Silva, Biomass Bioenergy 13 (1997)
11–14.
[57] S. Kumar, S. Singh, I. Mishra, D. Adhikari, J. Ind. Microbiol. Biotechnol. 36 (2009)
1483–1489.
References
[1] Y. Lin, S. Tanaka, Appl. Microbiol. Biotechnol. 69 (2006) 627–642.
[2] P. Gallezot, N. Nicolaus, G. Fleche, P. Fuertes, A. Perrard, J. Catal. 180 (1998)
51–55.
[3] R. Geyer, P. Kraak, A. Pachulski, R. Schödel, Chem. Ing. Tech. 84 (2011) 513–516.
[4] J.N. Chheda, Y. Roman-Leshkov, J.A. Dumesic, Green Chem. 9 (2007) 342–350.
[5] R.D. Cortright, R.R. Davda, J.A. Dumesic, Nature 418 (2002) 964–967.
[6] R.R. Davda, J.A. Dumesic, Chem. Commun. (2004) 36–37.
[7] R.R. Davda, J.W. Shabaker, G.W. Huber, R.D. Cortright, J.A. Dumesic, Appl. Catal.,
B 56 (2005) 171–186.
[58] J.P. Mikkola, T. Salmi, A. Villela, H. Vainio, P. Maki Arvela, A. Kalantar, T. Ollon-
qvist, J. Vayrynen, R. Sjoholm, Braz. J. Chem. Eng. 20 (2003) 263–271.
[59] H.M. Baudel, C.A.M.D. Abreu, C.Z. Zaror, J. Chem. Technol. Biotechnol. 80 (2005)
230–233.
[60] J. Zhang, S. Wu, Y. Liu, B. Li, Catal. Commun. 35 (2013) 23–26.
[61] H. Hattori, Chem. Rev. 95 (1995) 537–558.
[8] M. Comotti, C.D. Pina, M. Rossi, J. Mol. Catal. A: Chem. 251 (2006) 89–92.
[9] M. Wenkin, R. Touillaux, P. Ruiz, B. Delmon, M. Devillers, Appl. Catal., A 148
(1996) 181–199.
[62] C.B. Dartt, M.E. Davis, Catal. Today 19 (1994) 151–186.
[63] K. Ebitani, K. Motokura, K. Mori, T. Mizugaki, K. Kaneda, J. Org. Chem. 71 (2006)
5440–5447.
[10] Y. Önal, S. Schimpf, P. Claus, J. Catal. 223 (2004) 122–133.
[11] A. Abbadi, H. van Bekkum, J. Mol. Catal. A: Chem. 97 (1995) 111–118.
[12] S. Karski, T. Paryjczak, I. Witonnska, Kinet. Catal. 44 (2003) 618–622.
[13] S. Ramchandran, Food Technol. Biotechnol. 44 (2006) 185–195.
[14] K. Matsuno, Occup. Med. 46 (1996) 313–317.
[15] J.Z. Liu, L.P. Weng, Q.L. Zhang, H. Xu, L.N. Ji, Biochem. Eng. J. 14 (2003) 137–141.
[16] P. Beltrame, M. Comotti, C.D. Pina, M. Rossi, J. Catal. 228 (2004) 282–287.
[17] J. Bao, K. Furumoto, K. Fukunaga, K. Nakao, Biochem. Eng. J. 8 (2001) 91–102.
[18] C. Baatz, B. Thielecke, Y. Pru␤e, Appl. Catal., B 70 (2007) 653–660.
[19] C. Baatz, U. Pru␤e, J. Catal. 249 (2007) 34–40.
[20] M. Wenkin, P. Ruiz, B. Delmon, M. Devillers, J. Mol. Catal. A: Chem. 180 (2002)
141–159.
[21] S. Hermans, M. Devillers, Appl. Catal., A 235 (2002) 253–264.
[22] S. Biella, L. Prati, M. Rossi, J. Catal. 206 (2002) 242–247.
[23] M. Comotti, C. Della Pina, E. Falletta, M. Rossi, Adv. Synth. Catal. 348 (2006)
313–316.
[64] Y. Ono, T. Baba, Catal. Today 38 (1997) 321–337.
[65] Y. Duan, D. Xia, Y. Xiang, X. Zhang, J. Colloid Interface Sci. 281 (2005) 197–200.
[66] Z. Gao, J. Zhou, F. Cui, Y. Zhu, Z. Hua, J. Shi, Dalton Trans. 39 (2010)
11132–11135.
[67] B. Veldurthy, J.M. Clacens, F. Figueras, Adv. Synth. Catal. 347 (2005) 767–771.
[68] J.M. Fraile, J.I. Garcia, J.A. Mayoral, F. Figueras, Tetrahedron Lett. 37 (1996)
5995–5996.
[69] K. Motokura, N. Fujita, K. Mori, T. Mizugaki, K. Ebitani, K. Kaneda, J. Am. Chem.
Soc. 127 (2005) 9674–9675.
[70] M. Lakshmi Kantam, B.M. Choudary, C. Venkat Reddy, K. Koteswara Rao, F.
Figueras, Chem. Commun. (1998) 1033–1034.
[71] P. Liu, Y. Guan, R.A.V. Santen, C. Li, E.J.M. Hensen, Chem. Commun. 47 (2013)
11540–11542.
[72] L.B. Kunde, S.M. Gade, V.S. Kalyani, S.P. Gupte, Catal. Commun. 10 (2009)
1881–1888.
[73] D.G. Evans, X. Duan, Chem. Commun. 0 (2006) 485–496.
[74] C.M. Jinesh, C.A. Antonyraj, S. Kannan, Appl. Clay Sci. 48 (2010) 243–249.
[75] P.S. Kumbhar, J. Sanchez-Valente, J.M.M. Millet, F.O. Figueras, J. Catal. 191 (2000)
467–473.
[76] R. Chitrakar, S. Tezuka, A. Sonoda, K. Sakane, T. Hirotsu, Ind. Eng. Chem. Res. 47
(2008) 4905–4908.
[24] M. Comotti, C. Della Pina, R. Matarrese, M. Rossi, Angew. Chem. 116 (2004)
5936–5939.
[25] N. Thielecke, K.D. Vorlop, U. Pru␤e, Catal. Today 122 (2007) 266–269.
[26] M. Comotti, C. Della Pina, E. Falletta, M. Rossi, J. Catal. 244 (2006) 122–125.
[27] P. Beltrame, M. Comotti, C. Della Pina, M. Rossi, Appl. Catal., A 297 (2006) 1–7.
[28] T. Ishida, N. Kinoshita, H. Okatsu, T. Akita, T. Takei, M. Haruta, Angew. Chem.
120 (2008) 9405–9408.
[29] H. Okatsu, N. Kinoshita, T. Akita, T. Ishida, M. Haruta, Appl. Catal., A 369 (2009)
8–14.
[30] I. Nikov, K. Paev, Catal. Today 24 (1995) 41–47.
[77] W. Meng, F. Li, D.G. Evans, X. Duan, Mater. Res. Bull. 39 (2004) 1185–1193.
[78] D.P. Debecker, E.M. Gaigneaux, G. Busca, Chem. Eur. J. 15 (2009) 3920–3935.
[79] V. Choudhary, R. Jha, P. Choudhari, J. Chem. Sci. 117 (2005) 635–639.
[80] C. Moreau, R. Durand, A. Roux, D. Tichit, Appl. Catal., A 193 (2000) 257–264.
[81] S. Lima, A.S. Dias, Z. Lin, P. Brandao, P. Ferreira, M. Pillinger, J. Rocha, V. Calvino-
Casilda, A.A. Valente, Appl. Catal., A 339 (2008) 21–27.
[31] A. Mirescu, U. Pru␤e, Appl. Catal., B 70 (2007) 644–652.
[32] A.T. Governo, L. Proenca, P. Parpot, M.I.S. Lopes, I.T.E. Fonseca, Electrochim. Acta
49 (2004) 1535–1545.
[82] R.O.L. Souza, D.P. Fabiano, C. Feche, F. Rataboul, D. Cardoso, N. Essayem, Catal.
Today 195 (2012) 114–119.
[33] US Department of Energy, Energy Efficiency and Renewable Energy, Top Value
Added Chemicals From Biomass, Vol. 1: Results of Screening for Potential
Candidates from Sugars and Synthesis Gas, 2004 http://eereweb.ee.doe.gov/
biomass/pdfs/35523.pdf
[83] R. Sahu, P.L. Dhepe, 2013 (submitted for publication).
[84] H.A. Pary, C.E. Schweickert, B.H. Minnich, Ind. Eng. Chem. 44 (1952) 1146–1151.
[85] C. Moreau, J. Lecomte, A. Roux, Catal. Commun. 7 (2006) 941–944.
[86] F. King, G.J. Kelly, Catal. Today 73 (2002) 75–81.
[34] J.P. Mikkola, T. Salmi, Chem. Eng. Sci. 54 (1999) 1583–1588.
[35] J.P. Mikkola, T. Salmi, Catal. Today 64 (2001) 271–277.
[36] L. He, D. Chen, ChemSusChem 5 (2011) 587–595.
[87] S. Coluccia, A.J. Tench, Proceeding of the 7th International Congress on Catalysis,
Tokyo, 1980, p. 1160.
[88] M. Kappers, C. Dossi, R. Psaro, S. Recchia, A. Fusi, Catal. Lett. 39 (1996) 183–189.
[89] F. Humblot, F. Lepeltier, J.P. Candy, J. Corker, O. Clause, F. Bayard, J.M. Basset, J.
Am. Chem. Soc. 120 (1998) 137–146.
[90] Z. Gandao, B. Coq, L.C. de Menorval, D. Tichit, Appl. Catal. A 147 (1996) 395–406.
[91] S. Recchia, C. Dossi, N. Poli, A. Fusi, L. Sordelli, R. Psaro, J. Catal. 184 (1999) 1–4.
[92] J. Adamiec, R.M.J. Fiederow, S.E. Wanke, 74th Annual A.I.Ch.E. Meeting, vol. 59,
New Orleans, Paper 13A, Fiche, 1981.
[93] J.M.H. Dirkx, H.S. van der Baan, J. Catal. 67 (1981) 1–13.
[94] G. de Wit, C. de Haan, A.P.G. Kieboom, H. van Bekkum, Carbohydr. Res. 86 (1980)
33–41.
[37] J. Sun, H. Liu, Green Chem. 13 (2011) 135–142.
[38] P. De Wulf, W. Soetaert, E.J. Vandamme, Biotechnol. Bioeng. 69 (2000) 339–343.
[39] M. Yadav, D.K. Mishra, J.S. Hwang, Appl. Catal., A 425–426 (2012) 110–116.
[40] J. Zhang, A. Geng, C. Yao, Y. Lu, Q. Li, Bioresour. Technol. 105 (2013) 134–141.
[41] F.W. Lichtenthaler, Acc. Chem. Res. 35 (2002) 728–737.
[42] T. GranstrÖm, K. Izumori, M. Leisola, Appl. Microbiol. Biotechnol. 74 (2007)
273–276.
[43] P. Gallezot, P.J. Cerino, B. Blanc, G. Fleche, P. Fuertes, J. Catal. 146 (1994) 93–102.
[44] M. Herskowitz, Chem. Eng. Sci. 40 (1985) 1309–1311.
Please cite this article in press as: A. Tathod, et al., J. Mol. Catal. A: Chem. (2013), http://dx.doi.org/10.1016/j.molcata.2013.09.014