Aqueous phase reforming and hydrodeoxygenation of ethylene glycol on Pt/SiO2-Al2O3: Effects of surface acidity on product distribution

Article abstract of DOI:10.1039/c6ra09522d

Aqueous-phase reforming (APR) and aqueous-phase hydrodeoxygenation (APH) reactions of ethylene glycol (EG) were investigated using platinum supported solid-acid SiO₂-Al₂O₃ catalysts with different Si/Al molar ratios. The molar ratio of Si/Al on the SiO₂-Al₂O₃ mixed metal oxides largely altered the surface area due to changes to the acidity, as well as changing the reduction behavior of the supported platinum nanoparticles. The Pt/SiO₂-Al₂O₃ catalysts with a Si/Al molar ratio of 0.1 showed a higher activity for APR as well as APH. Among the various properties of Pt/SiO₂-Al₂O₃, the amount of acid sites on the SiO₂-Al₂O₃ supports changed the EG conversion and production distribution with different coke depositions. The acidic property was a more dominant factor for the catalytic activity than the affects of the platinum crystallite size on the reduction behavior. The easy and simultaneous cleavages of C-C as well as the C-O bonds in EG on the Bronsted acid sites of Pt/SiO₂-Al₂O₃ catalysts were responsible for a higher EG conversion and hydrocarbon formation. A larger number of weak acid sites was also related to the formation of larger hydrocarbons and a lower coke deposition. Compared with Pt/Al₂O₃, improved catalytic acidity with a low coke deposition was observed for Pt/SiO₂-Al₂O₃ at a Si/Al molar ratio of 0.1. This can mainly be attributed to the easy control of weak and strong acid sites with a high dispersion of platinum crystallites by simply changing the Si/Al molar ratio of the SiO₂-Al₂O₃ mixed metal oxides.

Full text of DOI:10.1039/c6ra09522d

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Submitted to the RSC Advances
Aqueous phase reforming and hydrodeoxygenation of ethylene glycol on
Pt/SiO -Al O : effects of surface acidity to product distribution
2
2
3
a
b
c
a,
Seongho Jeon , Hyun-Seog Roh , Dong Ju Moon , Jong Wook Bae *
a
School of Chemical Engineering, Sungkyunkwan University (SKKU), Suwon, Gyeonggiꢀdo,
4
40ꢀ746, Republic of Korea
b
Department of Environmental Engineering, Yonsei University, 1 Yonseidaeꢀgil, Wonju,
Gangwonꢀdo, 220ꢀ710, Republic of Korea
c
Clean Energy Research Center, Korea Institute of Science and Technology (KIST), 136ꢀ791
Seoul, Republic of Korea
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
*Corresponding author (J.W. Bae); Tel.: +82ꢀ31ꢀ290ꢀ7347; Fax: +82ꢀ31ꢀ290ꢀ7272; Eꢀmail
address: finejw@skku.edu
1

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ABSTRACT
Aqueousꢀphase reforming (APR) and aqueousꢀphase hydrodeoxygenation (APH) reaction of
ethylene glycol (EG) were investigated using the platinum supported solidꢀacid SiO
2
ꢀAl
2
2
O
3
catalysts having different Si/Al molar ratios. The molar ratio of Si/Al on the SiO
2
ꢀAl
O
3
mixed metal oxides largely altered the surface area with its acidity as well as the reduction
behavior of the supported platinum nanoparticles. The Pt/SiO ꢀAl catalysts having a Si/Al
molar ratio of 0.1 showed a higher activity for APR as well as APH reaction. Among the
various properties of Pt/SiO ꢀAl , the amount of acid sites on SiO ꢀAl supports largely
2
2 3
O
2
2
O
3
2
2 3
O
changed EG conversion and production distribution with different coke depositions, and the
acidic property was more dominant factor for catalytic activity than the platinum crystallite
size with its reduction behavior. The easy and simultaneous cleavages of CꢀC as well as CꢀO
bonds in EG on the Bronsted acid sites of Pt/SiO ꢀAl O catalysts were responsible for a
2
2
3
higher EG conversion and hydrocarbon formation. A larger amount of weak acid sites was
also related with a larger hydrocarbon formation and a lower coke deposition. Compared with
2 3 2 2 3
the Pt/Al O , the better catalytic acidity with a low coke deposition on the Pt/SiO ꢀAl O at a
Si/Al molar ratio of 0.1 was observed. It can be mainly attributed to the easy control of weak
and strong acid sites with a high dispersion of platinum crystallites by simply changing a
2 2 3
Si/Al molar ratio of the SiO ꢀAl O mixed metal oxides.
Keywords: Aqueousꢀphase reforming (APR); Aqueousꢀphase hydrodeoxygenation (APH);
Ethylene glycol (EG); Platinum; SiO
2
ꢀAl
2
O
3
mixed metal oxides; Surface acidity.
2

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1. Introduction
Since the utilizations of traditional fossil fuels such as coal, crude oils and natural or shale
gases can generate energy sources with an abundant emission of environmental pollutants,
some renewable energy sources such as biomassꢀderived hydrogen can be one of alternative
candidates to overcome environmental problems of fossil fuels having limited resources. For
a complete carbon recycle, biomassꢀderived fuels have promising characters by some
transformation processes such as gasification, pyrolysis, fermentation or chemical conversion
1
-3
processes and so on.
Among them, an aqueousꢀphase reforming (APR) reaction of
biomassꢀderived intermediates seems to have many advantages due to its lower operating
temperature and a high purity of hydrogen production with a lower concentration of CO.
Generally, some supported novel metals such as Pt, Ru, Ir, Rh, Ni or Pd have been known to
4
be active for the APR reaction with a higher selectivity to hydrogen. Especially, Ptꢀ
2 3 2 2 3 2
supported catalysts on various supports such as Al O , SiO , zeolites and Al O ꢀSiO and so
on have been largely investigated for APR reaction through the characteristic reactions such
as main APR reaction, waterꢀgas shift (WGS) reaction, dehydrogenation, methanation and
decomposition as represented in Eq. 1 to Eq. 4 using a biomassꢀderived model component of
5
-7
ethylene glycol (EG).
(
(
(
(
1) C
2) CO + H
3) C
4) CO + 3H
2
H
6
O
2
+ 2H
2
O → 2CO
+ H
+ (x/2)H
+ H
2
+ 5H
2
(APR)
2
O → CO
2
2
(WGS)
2
H
6
O
2
→ C2H6ꢀx
O
2
2
(dehydrogenation)
(methanation)
2
→ CH
4
2
O
The reaction pathways of APR reaction to generate hydrogen using EG feedstock have been
generally known to proceed by first dehydrogenation reaction step of EG followed by the Cꢀ
C cleavage and WGS reaction simultaneously. The methanation reaction is one of the main
8
,9
side reactions, which can be also strongly related with extents of coke formation. Moreover,
3

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the byproducts such as ethylene, CO and other oxygenates can also cause a severe coke
1
0-13
formation on the catalysts surfaces as well.
The hydrogen and alkanes can be produced by
1
4-17
separate CꢀC and CꢀO bond cleavages during APR reaction.
The oxygenates such as
alcohols and acetaldehydes can be also formed by a simultaneous dehydration on Ruꢀbased
APR catalysts, however these oxygenated intermediates can be easily transformed to
18
hydrogen and CO
cleavages have been generally known to generate various products during APR reaction,
where CꢀC bond cleavage (Eq. 5) can selectively produce hydrogen and CO with a
2
by a facile WGS reaction as well. The selective CꢀC or CꢀO bond
2
combination of WGS reaction, and CꢀO bond cleavage (Eq. 6) can selectively produce
hydrocarbons as well. The simultaneous CꢀO and CꢀC cleavages (Eq. 7) can also happen
easily since these cleavages are very competitive reactions during APR reaction. The
preferential activities of separate CꢀC or CꢀO bond cleavages are strongly depending on the
types of active metals, which seems to be an important catalyst design factor due to a high
19
O/C ratio of the biomassꢀderived intermediates.
(
(
(
5) C
2
2
H
6
6
O
O
2
2
→ 2CO + 3H
2
(CꢀC cleavage)
6) C
H
→ C + C
2
H
4
2
H
6
+ 2H
2
O
(CꢀO cleavage)
7) C H O → CH + CO + CH O + CH OH
(CꢀC with simultaneous CꢀO cleavage)
2
6
2
4
2
3
In addition, aqueousꢀphase hydrodeoxygenation (APH) reaction has been known as an
efficient production method of alkanes and petrochemicals using biomassꢀderived chemicals
2
0-22
with a similar catalytic system as explained for APR catalysts.
However, APH reaction
requires a much higher activity for CꢀC cleavage to remove oxygen atoms by dehydration and
to add hydrogen atoms through hydrogenation and hydrogenolysis as well. In general, the
supported metal catalysts containing active palladium species have been known to be active
23
for C=O and C=C bond cleavages in furfural by hydrogenation, and those of rutheniumꢀ
based catalysts have been reported as the most active catalyst for APH reaction for an
4

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activation of nonꢀfuranic carbonyl groups, which also requires different active sites compared
to APR reaction. Therefore, APH catalysts generally require to possess different active sites
for CꢀC cleavages through a retroꢀaldol condensation with decarbonylation on the metallic
2
4
sites and CꢀO cleavages by selective dehydration on the acidic sites as well. Based on the
15,22,25-30
previous studies,
the CꢀC and CꢀO bond cleavages are competitive reactions at the
very beginning of retroꢀaldol condensation and dehydration step on the metallic sites of the
1
5,22,25,26
novel metals as well as on the acid sites of solidꢀacid surfaces.
alcohols such as methanol during CꢀC and CꢀO bond cleavages can be converted to CO
hydrogen by dehydrogenation followed by WGS reaction, which seems to be competitive
In addition, the formed
2
and
27-30
reactions as well on the metallic platinum sites such as Pt(111) surfaces.
Among the
competitive and complicated reactions during APR and APH reaction, the hydrogenation and
dehydration steps have been known to be essential steps for an easy transformation of the
biomassꢀderived intermediates. Those reactions selectively occur on heterogeneous or
homogeneous catalytic systems by using bimetal or metal complexes with a combination of
31-34
solidꢀacid zeolites and metal oxides as well.
In addition, hydrogenolysis and dehydration
with a subsequent dehydrogenation reaction have been also largely investigated using some
35-40
solidꢀacid catalysts to efficiently remove oxygen atoms in the biomassꢀderived reactants.
In the present investigation, simple and prototype Pt/SiO ꢀAl catalysts having different
2
2 3
O
acidic properties due to different Si/Al ratios were investigated for APR and APH reactions to
verify the roles of the amount and type of acidic sites for a different catalytic activity and
product distribution. Even though some Ptꢀsupported solid acid catalysts have been
extensively reported, the comparative studies for APR and APH reaction using the same
2 2 3
Pt/SiO ꢀAl O catalysts have been scarcely reported till now as far as we know, especially by
comparing different hydrocarbon distribution according to the surface acidic properties.
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2
. Experimental section
.1. Catalyst preparation and activity test of the Pt/SA catalysts
SiO ꢀAl mixed metal oxides (SA) with a different Si/Al molar ratio from 0 to 1.0 were
synthesized by coprecipitaion method. For more detail, the SiO ꢀAl solid acid supports
were prepared using aluminum nitrate nonahydrate (Al(NO •9H O, Daejung) precursor and
tetraethlorthosilicate (TEOS, Si(OC , Alfa) precursor after dissolving separate precursors
2
2
2 3
O
2
2 3
O
3
)
3
2
2
5 4
H )
in a mixed solvent of deionized water and ethanol. The dissolved two separate metal
precursors were vigorously stirred for 15 minutes separately, and the separate metal precursor
solutions were mixed together carefully. For the subsequent coprecipitation of the above two
solutions, 30vol% ammonia solution was dropped slowly into the mixed metal precursor
solutions and it as stirred for 3 h at ambient temperature. Asꢀprepared gelꢀlike slurry was
o
o
dried under a vacuum condition at 60 C for 2 h and followed by drying at 110 C overnight.
o
Finally, the asꢀprepared sample was calcined at 300 C for 4 h to prepare solid acid mixed
40
metal oxide of SiO
2
2
ꢀAl O
3
. For preparing platinum supported catalysts using the previously
prepared SA supports, tetraammineplatinum (II) nitrate (Pt(NO
3
)
4
(NO ) precursor was
3 2
)
loaded over the asꢀprepared SA support by incipient wetness impregnation method at a fixed
platinum metal amount from 1 to 7wt% using a deionized water. The platinum supported SA
o
o
catalysts was further dried overnight at 80 C followed by calcining at 350 C for 4 h. The asꢀ
prepared catalyst was denoted as Pt/SA(x), where SA stands for the solidꢀacid SiO ꢀAl
2
2 3
O
support and x for a different molar ratio of Si/Al. In addition, Pt(y)/SA(0.1) catalysts were
also prepared similarly and y represent weight % of platinum metal on the SA(0.1) support.
APR reaction was carried out in a fixedꢀbed tubular reactor having an outer diameter of 9.5
o
mm at the reaction conditions of T = 250 C, P = 4.5 MPa and weight hourly space velocity
ꢀ1
(
WHSV) = 2.0 h for around 20 h using 0.3 g catalyst. Prior to activity test, the catalyst was
o
reduced at 350 C for 2 h under a flow of 5vol%H
2
2
balanced with N . The reaction
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temperature was adjusted using PID controller with Kꢀtype thermocouple, and the pressure
was controlled by using back pressure regulator as well. The reactant of ethylene glycol (EG)
with 10wt% in an aqueous solution (molar ratio of EG/H
2
O = 0.383) was fed to the reactor at
flow with a flow
a flow rate of 0.1 ml/min using HPLC pump (SP930D, YoungLin) with N
2
rate of 30 ml/min, which was used as a carrier and an internal standard gas. APH reaction
was also carried out at a similar reduction and reaction condition with 0.5 g catalyst using a
mixed gas of 80vol%H balanced with N . The catalytic activity was measured at the reaction
2
2
o
ꢀ1
conditions of T = 260 C, P = 5.0 MPa and WHSV = 0.6 h for around 20 h. The effluent
gases from the reactor were inꢀsitu analyzed by using a gas chromatography (6500GC,
YoungLin) equipped with thermal conductivity detector (TCD) connected with Carboxen
1000 column as well as flame ionization detector (FID) connected with HPꢀPLOT/Q capillary
column. The conversion of EG and product distributions were calculated using the following
equations based on an internal standard gas of N
2 2
, and the production rate of H was also
⋅
calculated using the produced moles of H with a unit of mL/(g h).
2
cat
ꢀ
EG conversion to gaseous products (mol %) = (moles of C atoms in a gasꢀphase / moles
of C atoms in the EG feed) *100
ꢀ
Selectivity of gaseous products (mol %) = (moles of selected product in a gasꢀphase /
total moles of carbons formed in a gasꢀphase) *100
2.2. Catalyst characterizations
Powder Xꢀray diffraction (XRD) patterns of the fresh and used Pt/SA catalysts were
obtained using D8 ADVANCE (Bruker) instrument with a CuꢀKα radiation of wavelength of
o
1
5.406 nm at an operating voltage of 40 kV with a scanning rate of 4 /min in the diffraction
o
range of 2θ = 20 ꢀ 70 to verify the crystalline phases and crystallite sizes. The crystallite
sizes of the supported platinum nanoparticles were calculated using a value of full width at
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half maximum (FWHM) by using DebyeꢀScherrer equation with the most intensive
o
diffraction peak of metallic platinum at 2θ = 40.0 . Thermogravimetric analysis (TGA) of the
used Pt/SA catalysts was carried out by using Seiko Exstar 6000 (TG/DTA6100) to confirm
the quantity of the deposited cokes after APR reaction for 20 h on stream. The Si/Al molar
ratio of the mixed metal oxides was further characterized by Xꢀray fluorescence (XRF)
analysis using Bruker AXS S4 Pioneer that operated at 60 kV and 150 mA.
Specific surface area, pore volume and average pore diameter were measured by N2
adsorptionꢀdesorption analyses using Micromeritics TriStar II instrument working at liquid
o
nitrogen temperature of ꢀ196 C. The specific surface area of the fresh Pt/SA catalysts was
calculated by BrunaureꢀEmmettꢀTeller (BET) method, and average pore diameter and its pore
size distribution were measured by Barrett–Joyner–Halenda (BJH) method from the
desorption isotherm. Prior to analysis, the sample was pretreated by degassing at 90 and 350
o
2
C for 4 h consecutively. In addition, H chemisorption analysis of the Pt/SA catalysts was
also carried out by using Micromeritics ASAP 2020 instrument. The metal surface area and
dispersion of the supported platinum nanoparticles were obtained by using adsorbed amount
o
of hydrogen at 35 C on the reduced Pt/SA catalyst. Prior to analysis, the sample was
o
pretreated under vacuum condition of 10 mmHg at 300 C for 2 h to remove any impurities
o
on the Pt/SA surfaces. The sample was subsequently reduced at 350 C for 2 h, which is the
same condition of the reduction step before APR reaction. The dispersion, metal surface area
and crystallite size of the supported platinum nanoparticles were calculated with an
assumption of a stoichiometry number (H/Pt) of 1.0.
2
Temperatureꢀprogramed reduction with H (TPR) and temperatureꢀprogramed desorption of
ammonia (NH ꢀTPD) were separately measured by suing BelcatꢀM (Bel Japan) instrument
3
equipped with TCD. Prior to TPR analysis, 30 mg of the fresh Pt/SA catalyst was pretreated
o
at 250 C under a flow of argon to remove any impurities and water adsorbed on the surfaces.
8

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o
TPR patterns were obtained with a ramping rate of 10 C/min under a flow of 10vol% H
2
balanced with argon. The formed water from the TPR experiment was selectively removed by
using molecular sieve trap, and the hydrogen consumption was measured by TCD. For the
analysis of NH
3
ꢀTPD, 30 mg of the fresh Pt/SA catalyst was loaded in a quart tube reactor
o
and the sample was pretreated at 250 C for 2 h under a flow of He. After that, ammonia gas
o
was adsorbed at 50 C for 30 minutes and the physisorbed ammonia was removed by flushing
it under He flow at the same temperature for 1 h. Finally, the amount of the desorbed
o
ammonia was measured by TCD under He flow in the temperature range of 100 ꢀ 600 C at a
o
ramping rate of 10 C/min. The surface morphologies and the variation of crystallite sizes on
the fresh and used fresh Pt/SA(0) and fresh Pt/SA(0.1) after APR reaction were characterized
using transmission electron microscopy (TEM) with a TECNAI G2 instrument operated at an
accelerating voltage of 200 kV.
Fourier transformed infrared (FTꢀIR) spectroscopy of the adsorbed pyridine (PyꢀIR) was
applied to characterize the types of acid sites such as Bronsted and Lewis sites on the fresh
2
Pt/SA catalysts. Using inꢀsitu IR cell equipped with CaF window and shelfꢀsupported thin
pellet of the Pt/SA catalyst which was previously mixed and pelletized with an excess KBr
powder with a mass ratio of 100:1, the PyꢀIR experiment was carried out. For a selective
adsorption of pyridine probe molecules on the acid sites, the pyridine were previously flowed
2
on to the pellet using N gas carrier at room temperature for 30 min. After the physisorbed
pyridine was selectively evacuated for 45 min under vacuum condition, the chemically
adsorbed pyridine absorption band spectra were obtained after subtracting background peaks
obtained before an adsorption of pyridine on the fresh Pt/SA catalyst.
3. Results and discussion
3.1. Catalytic activities of the APR and APH reaction
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The catalytic activities for APR reaction of EG on the Pt/SA catalysts at a fixed platinum
metal content of 5wt% are summarized in Table 1 in terms of conversion of EG to gaseous
products and product distributions, where SA(x) represents the solidꢀacid SiO
2 2 3
ꢀAl O for SA
with x digit for a molar ratio of Si/Al, and SA(0) for the Al support. The EG conversions
2
O
3
to gaseous products were maximized on the Pt/SA(0.1) with 43.4% and a maximum H
2
⋅
production rate of 1691 mL/(gcat h), which were the averaged values at a steadyꢀstate after the
reaction of 15 h on stream. A typical volcano pattern of EG conversions and product
distributions was observed on the Pt/SA catalysts. The lowest EG conversion was observed
on the Pt/SA(1.0) with the value of 18.4%, which seems to be responsible for an observed
2
high CO selectivity of 5.2% with a lower CO selectivity due to a suppressed WGS activity
of the intermediates derived from CꢀC bond cleavages of EG. Interestingly, the hydrocarbon
selectivity was decreased with an increase of Si/Al molar ratios of the Pt/SA catalysts from
0.9% on the Pt/SA(0.1) to 2.5% on the Pt/SA(1.0), except for the Pt/SA(0). This observation
seems to be attributed to a higher dehydrogenation activity for the CꢀC bond cleavages on the
8
,9
catalysts having a larger amount of Bronsted acid sites. Most interesting observation is a
significantly different hydrocarbon distributions by showing an increasing trend of CH4
selectivity from 20.5 to 64.5% and vice versa in that of C
increase of Si/Al ratios. This observation can be attributed to a different acidity of the SiO
Al surfaces by largely changing the intrinsic activities of CꢀC and CꢀO bond cleavages.
2 6
H from 79.5 to 35.3% with an
2
ꢀ
2
O
3
Based on these observations, a higher conversion of EG to gaseous products is responsible
for a higher H production rate with a lower selectivity of CO and hydrocarbons with the help
2
of the enhanced WGS activity, except for the Pt/SA(0). Even though the Pt/SA(0) showed a
2
lower conversion of EG around 27.5%, a higher selectivity to H and a lower selectivity to
CO were observed due to a possible coke deposition on the too strong acidic sites with a
higher WGS activity on the largely exposed platinum metal surfaces. Compared to other
1
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Pt/SA catalysts which showed a stable EG conversion to gaseous products even after 15 h on
stream, a significant decrease of EG conversion on the Pt/SA(0) during 15 h on stream can be
possibly attributed to a severe coke deposition as shown in Figure 1. The steady increases of
the EG conversion to gaseous products for 15 h on stream can be due to a possible surface
rearrangement of the supported platinum crystallites and an easy phase transformation of
alumina species. It can be also attributed to a hydrogen gas residue used for reduction step of
Pt/SA catalysts and for a pressure adjustment step at 5.0 MPa before APR reaction. However,
the comparisons of the catalytic activities at steadyꢀstate after 15 h on stream seem to be
reasonable since the similar catalytic activity changes according to a Si/Al ratio on the Pt/SA
catalysts were observed at similar EG conversions as summarized in supplementary Table S1.
The selectivity to hydrocarbons on the Pt/SA catalysts seems to be mainly caused by a
presence of the acidic sites having a proper acid strength, which seems to be increased with
35-39
an increase of the surface acid sites.
The selectivity of hydrocarbons such as C
1 2
and C
paraffinic species seems to increase on the weak acid sites of SiO
2
ꢀAl preferentially by a
2 3
O
possible decomposition of the intermediates derived from EG, which can be dehydration or
retroꢀaldol condensation reactions. To verify the effects of acid sites during the consecutive
reactions of EG conversion, the most active Pt/SA(0.1) catalyst was further examined at
ꢀ1
different space velocities such as 1.0 and 0.5 h and the results are summarized in Table 1.
The conversions of EG to gaseous products at different space velocities are displayed in
ꢀ1
supplementary Figure S1. With a decrease of space velocities from 2.0 to 0.5 h on the
o
Pt/SA(0.1) at T = 250 C and P = 4.5 MPa, the conversion of EG steadily increased from 43.4
to 78.6% without the significant changes of product distributions except for the hydrocarbons
from 0.9 to 2.0% with a significant variation of C
1.9%. These results strongly suggest that the intermediates such as aldehydes and alcohols
formed from the APR reaction of EG can be further reacted to form hydrocarbons, especially
1 2
from 36.2 to 78.1 % and C from 63.8 to
2
1
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4
for CH hydrocarbon at a longer residence time. It also revealed that the Bronsted acidic sites
having weak acid strengths and small metallic platinum crystallites (confirmed by NH ꢀTPD
3
and TPR in next section) are responsible for further transformation of the intermediates to
light hydrocarbons, which seems to be similar effects of longer residence times of the
intermediates formed by simultaneous CꢀO and CꢀC bond cleavages of EG reactant.
Interestingly, the hydrocarbon formation rate on the Pt/SA catalysts having a higher Si/Al
ratio above 0.4 was stabilized after 10 h on stream as shown in supplementary Figure S2,
which can be possibly attributed to the presence of a relatively larger amount of Bronsted
acid sites. As summarized in supplementary Table S2, a higher hydrocarbon formation was
observed on the large amount of Ptꢀcontaining Pt(7)/SA(0.1) catalyst with the value of 5.0%
4
with CH selectivity of 88.6%. The large amount of the metallic platinum content seems to be
responsible for the further reactions of intermediates to hydrocarbons. However, conversion
of EG to gaseous products was not significantly increased on the Pt/SA(0.1) having a large
amount of platinum above 3wt% except for the Pt(1)/SA(0.1) due to an easy aggregation of
the supported platinum crystallites at a high platinum content on the SA(0.1) support with
facile phase transformations of alumina.
To further verify the roles of the acidity of SA supports according to Si/Al ratios to the
hydrocarbon selectivity and EG conversion, APH reaction was further carried out on all
Pt/SA catalysts and the results are summarized in Table 1. The variations of EG conversion
to gaseous products were found to be similar with those of APR reaction with the highest
conversion of 47.9% on the Pt/SA(0.1) and lowest on the Pt/SA(1.0) with 29.0% at steadyꢀ
state. CO selectivity was decreased with an increase of Si/Al ratio from 96.2% on the
2
Pt/SA(0) to 76.3% on the Pt/SA(1.0) due to a lower WGS activity of the intermediated
formed from the CꢀC bond cleavage by the dehydration of EG possibly. However, CO
selectivity was varied inversely by increasing from 1.1% on the Pt/SA(0) to 14.7% on the
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2

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Pt/SA(1.0) with an increase of Si/Al ratio of the Pt/SA catalysts. This observation suggests
that the catalytic activities of APR and WGS reaction are strongly influenced by the amount
of active metal surface area as well as the acid sites during the aqueousꢀphase reaction. At a
higher partial H
2
pressure during APH reaction, hydrogenation activity can be increased by
by WGS reaction.
enhancing the CꢀC bond cleavage of EG due to the additionally formed H
2
Therefore, the increased hydrocarbon selectivity from 2.7 to 9.0% and its production rate
from 1.4 to 3.1 mL/(g ·h) with an increase of Si/Al molar ratio during APH reaction can
cat
support an enhanced hydrogenation activity, which was significantly increased with an
increase of Si/Al ratio on the Pt/SA catalysts. As shown in Figure 2, the catalytic activity for
APH reaction with time on stream seems to be more stable than APR reaction without
1
showing a significant deactivation after 10 h on stream. Interestingly, the variations of C –
C paraffinic hydrocarbon selectivity for APH reaction were found to be similar with those of
3
APR reaction with same trends by showing a higher selectivity of hydrocarbons on the Pt/SA
catalyst having larger Bronsted acid sites. The increase of C
and decrease of C selectivity from 50.9 to 42.8% were observed with an increase of Si/Al
ratio on the Pt/SA catalysts, which suggests that the different acidity of the SiO ꢀAl
1
selectivity from 46.0 to 56.1%
2
2
2 3
O
surfaces and metallic surface area of platinum crystallites can largely alter the CꢀC and CꢀO
bond cleavages as well. The production rates of the hydrocarbons on the Pt/SA catalysts are
displayed in the supplementary Figure S3. At a high Si/Al ratio above 0.4, the significant
stability of the hydrocarbon formation rate with time on stream seems to be attributed to a
lower coke deposition with a large amount of Bronsted acid sites as well. From the observed
catalytic activities for APR as well as APH reaction on the Pt/SA catalysts having a different
Pt loading and space velocity, an optimal Pt/SA(0.1) was found to be proper to obtain a
higher conversion of EG and hydrogen production rate. The product distribution was
significantly affected by the surface properties such as a density and type of acid sites with a
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3

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surface area of the active platinum metal nanoparticles, which can also change hydrocarbon
distributions through CꢀC and CꢀO bond cleavages of intermediates formed from EG reactant.
3.2. Physicochemical surface properties of the Pt/SA catalysts
The physicochemical properties such as specific surface areas, pore volumes and average
2
pore diameters of the Pt/SA catalysts and SA supports measured by N adsorptionꢀdesorption
methods are summarized in Table 2. The Pt/SA catalysts prepared by coprecipitation method
of the SA supports and a subsequent impregnation of platinum metal precursor showed
2
2
2
surface areas above 300 m /g by increasing from 302 m /g on the Pt/SA(0) to 384 m /g on the
Pt/SA(1.0) with an increase of Si/Al molar ratio. An actual molar Si/Al ratio on the SA
supports was found to be 0.12, 0.46 and 0.89 on the SA(0.1), SA(0.4) and SA(1.0),
respectively, which were measured by XRF analysis. From the observed variations of surface
2
areas of the SA supports from 370 to 496 m /g, the decreased surface area of the Pt/SA
catalysts was attributed to a partial pore blockage of the pore mouths through platinum metal
deposition. These aggregation phenomena are the wellꢀknown segregation process by a
deposition of the impregnated metal nanoparticles on the outer mesopores, which can be
18,41
induced during a drying or calcination step.
The pore volumes of the Pt/SA catalysts were
3
increased with an increase of surface area in the range of 0.24 – 0.55 cm /g, and the average
pore diameter was found to be larger on the Pt/SA catalysts with the size of 4.6 – 5.2 nm than
2 2 3
that of the Pt/AS(0) due to possible intraꢀparticular pore formation on the SiO ꢀAl O support.
A pore size distribution on all the Pt/SA catalysts showed a unimodal pore size distributions
as shown in supplementary Figure S4. Since the specific surface area and average pore
diameter were not significantly altered on all fresh Pt/SA catalysts, these physical properties
41
seem to insignificantly change the catalytic activity of APR and APH reaction as well.
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4

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Therefore, the dispersion, surface area and crystallite size of the supported metallic platinum
on the fresh Pt/SA catalysts were further measured by H chemisorption, and the results are
2
summarized in Table 2. The dispersions of metallic platinum crystallites were found to be in
the range of 45.7 – 63.9%, where it was lower on the Pt/SA(0) with the value of 45.7% than
other Pt/SA catalysts having the value of above 60%. In addition, a larger crystallite size of
2
2
.54 nm and smaller surface area of metallic platinum of 5.64 m /gPt were also observed on
the Pt/SA(0), however the values were found to be similar on the other Pt/SA catalysts in the
2
ranges of 1.81 – 1.86 nm and 7.65 – 7.89 m /gPt, respectively. Generally, a larger crystallite
size and smaller surface area of metallic platinum crystallites are known to be responsible for
18,41
a lower hydrogenolysis and WGS activity.
The variations of platinum crystallite sizes can
significantly alter an activity as well as a deactivation rate, and some active metal particles
are preferentially sintered during the reaction, which resulted in altering the catalytic stability
42-48
as well.
4
Therefore, the observed high selectivity of CH on the Pt/SA(0.4) and Pt/SA(1.0)
compared with the Pt/SA(0) can be attributed to a higher surface area of metallic platinum
crystallites by the possible methanation activity after CꢀC and CꢀO bond cleavages of the
5
-9,14-17
intermediates.
However, since there was no direct correlation of EG conversion with
the surface area of metallic platinum crystallites, we believe that the observed different
catalytic activity and product distribution seem be originated preferentially from the other
surface properties of the Pt/SA catalysts such as the density and type of acid site, aggregation
of active metals and coke deposition and so on.
The crystalline structures and phases of the Pt/SA catalysts measured by XRD analyses are
displayed in Figure 3 and the supplementary Figure S5 on the used and fresh Pt/SA catalysts,
respectively. Some crystalline phases of platinum crystallites and boehmiteꢀphase alumina (γꢀ
AlOOH) were clearly observed on the fresh Pt/SA(0), however, only platinum crystallite
phases were observed on the other fresh Pt/SA(0) and Pt/SA(0.1) due to the presence of the
1
5

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amorphous phases of the SiO
2
ꢀAl
A larger characteristic peak intensity of platinum crystallites was observed on
the fresh Pt/SA(0) and Pt/SA(0.1), which strongly suggests larger platinum crystallite
formation compared with other Pt/SA catalysts, and these results were also supported by H
2 3
O mixed metal oxides with highly dispersed platinum
42,49
crystallites.
2
ꢀ
chemisorption and TEM analysis. Interestingly, the fresh Pt/SA(0) showed a characteristic γꢀ
AlOOH and Pt(111) phases at the diffraction peak positions of 2θ = 40.0, 47.5 and 68.0,
which revealed a phase transformation of γꢀalumina to boehmite phase resulted in strongly
42
interacting with a supported platinum nanoparticles. As shown in Figure 3, the aggregation
of platinum crystallites after APR reaction measured by XRD analysis was significant on the
used Pt/SA catalysts with an average platinum crystallite size of 5.8, 2.2, 2.5, and 2.8 nm on
the Pt/SA(0), Pt/SA(0.1), Pt/SA(0.4) and Pt/SA(1.0), respectively. In addition, the extent of
transformation to γꢀAlOOH phases was much significant on the Pt/SA(0) after APR reaction,
and a significant coke deposition was observed only on the Pt/SA(0) by showing the
o
characteristic peak of coke precursor at around 2θ = 23 . The larger aggregation phenomena
of platinum crystallites on the Pt/SA(0) with a large extent seems to be mainly attributed to a
smaller amount of surface acidic sites and its easy transformation to the boehmite phases
through a weak interaction of platinum crystallites compared with other Pt/SA catalysts. In
addition, the observed larger amount of coke deposition on the Pt/SA(0) can be also
2 3
originated from the presence of the strong acid sites on the Al O or boehmite phases, which
can largely altered EG conversion and product distribution during APR and APH reaction as
25-30
well.
The extent of coke deposition on the used Pt/SA catalysts after APR reaction for the
duration of 20 h was further characterized by thermogravimetric analysis (TGA). In general,
a weight loss (%) measured in a temperature range of 300 ꢀ 600 °C can be attributed to an
4
9
oxidation of the deposited graphitic carbons. As shown in Table 2 and supplementary
Figure S6, a significant coke deposition with the amount of 10.0wt% was observed on the
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6

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Pt/SA(0). A relatively smaller amounts of coke deposition in the range of 3.9 ꢀ 5.5wt% were
observed on the other Pt/SA catalysts with the lowest value of 3.9wt% on the Pt/SA(0.1),
which was the most active catalyst for APR and APH reaction. The inactive coke precursors
can be generally formed over strong acidic sites from unstable intermediates during APR
1
2
reaction. However, a facile hydrogen spillover characters on the surfaces can suppress coke
50
formations by hydrogenolysis reaction. The ratio of Bronsted/Lewis acid sites can also
significantly alter the adsorption characters of oxygenates formed, which can also promote
1
0,51
coke depositions with a severe deactivation, especially on the strong Bronsted acidic sites.
A reducibility of platinum crystallites on the Pt/SA catalysts was further verified by TPR
experiments and the reduction behaviors of those catalysts are displayed in Figure 4, and the
consumed amount of hydrogen are summarized in Table 2. The broad reduction peaks on the
o
Pt/SA catalysts were observed at a maximum temperature at around 350 C with a shoulder
o
peak at around 430 C, which suggests a relatively homogeneous distribution of platinum
nanoparticles, except for the Pt/SA(0). However, multiple reduction peaks were observed on
the Pt/SA(0) which suggests the distribution of the various platinum crystallite sizes on the
o
Al
2
O
3
support. A lower reduction temperature peak at around 180 C on the Pt/SA(0) seems
to be responsible for a decomposition of platinum metal precursor with an easy reduction
L
character (assigned to T ). In addition, a medium reduction temperature peak at around 350
o
M
C (assigned to T ) on the Pt/SA catalysts can be assigned to the reduction of wellꢀdispersed
platinum nanoparticles on the SA surfaces. The reduction behaviors of supported platinum
crystallites are strongly affected by the surface properties of silicaꢀalumina mixed oxides by
4
2,52
changing the platinumꢀsupport interactions.
peak (assigned to T ) can be responsible for the strongly interacted platinum nanoparticles
only on the Al support.
to T peak was increased with an increase of Si/Al ratio from 87 to 188 ꢀmol/gcat without a
Therefore, a higher temperature reduction
H
4
1,53
2
O
3
Interestingly, the amount of hydrogen consumption assigned
M
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7

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significant variation of the amount of T
L
peak except for the Pt/SA(0). It seems to be
attributed to the enhanced acidic sites of the bare SA supports by forming strongly interacted
4
2,52
and wellꢀdispersed platinum nanoparticles on strong acidic SiO
2
ꢀAl
2
O
3
supports.
These
characteristic reduction behaviors of the supported platinum nanoparticles also significantly
20-23,27-30
alter the WGS activity and CꢀC and CꢀO bond cleavages
by hydrogenation and
hydrogenolysis reaction of intermediates formed by EG conversion, especially by altering the
hydrocarbon selectivity.
To further verify effects of acid sites to platinum metal dispersion and reduction behavior on
the solid acid SA supports, NH
3
ꢀTPD analysis was carried out on the fresh Pt/SA catalysts
are
showed two characteristic peaks at a
and the desorption patterns are displayed in Figure 5 and the amount of desorbed NH
3
summarized in Table 2. The desorption peaks of NH
3
o
maximum desorption temperature of around 200 C (assigned to T for a desorbed amount of
w
o
o
NH
also assigned to weak and strong acidic sites, respectively.
molar ratio on the Pt/SA catalysts, the desorbed amount of NH
was increased and that of strong acidic sites (T ) and total acidic sites (
steadily. In general, the SiꢀOH and Al ions on the mixed metal oxides are known to be
3 S
below 300 C) and 450 °C (assigned to T for that between 300 – 500 C), which can be
5
4-56
With an increase of Si/Al
from weak acidic sites (T
tot) were decreased
3
w
)
S
T
3
+
35-40,54-56
responsible for Brønsted (B) and Lewis acidic sites (L), respectively.
As summarized
in Table 2, weak acid sites was increased and finally approach a constant value from 0.45
mmol/gcat on the Pt/SA(0) to 0.75 mmol/gcat on the Pt/SA(1.0). However, the amount of
strong acid sites was decreased from 5.94 mmol/gcat on the Pt/SA(0) to 3.80 mmol/gcat on the
Pt/SA(1.0) as similar for total acid sites (T ) with an increase of Si/Al ratio on the Pt/SA
tot
catalysts. Therefore, the changes of the molar ratio of Si/Al on the mixed SiO
oxides largely altered the surface acidic properties with various concentrations of Brønsted
and Lewis acid sites. As measured by NH ꢀTPD for total amount and strength of acid sites on
2 2 3
ꢀAl O metal
3
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8

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the Pt/SA catalysts, the types of the acid sites such as Brønsted and Lewis acid sites were
further characterized by fourierꢀtransformed infrared analysis of adsorbed pyridine molecules
(PyꢀIR). To further verify the B/L ratio on the Pt/SA catalysts, the characteristic absorption
ꢀ
bands of pyridine molecules assigned to Bronsted acid sites (B) at a wavenumber of 1550 cm
1
ꢀ1
54,55
,
Lewis acid sites (L) at 1450 cm , and combined Bronsted and Lewis acid sites (B+L)
at
ꢀ1
1
480 cm were integrated and compared of the each pyridine peak. The B/L ratio on the
Pt/SA catalysts as summarized in Table 2 was increased with an increase of Si/Al ratio by
showing the ratio of from 0 to 1.22. This observation strongly suggests that the amounts of
Bronsted acid sites are increased with the increase of Si/Al molar ratio on the Pt/SA catalysts.
These different amounts and types of the acid sites on the Pt/SA catalysts can largely alter the
dispersion of platinum nanoparticles. This variation also change product distribution and EG
conversion to gaseous products during APR and APH reaction by significantly altering the
2
0-23,27-30
activities of CꢀC and CꢀO bond cleavages.
3.3. Roles of acidic sites and metal surface area for hydrocarbon distribution
APR and APH reaction of the biomassꢀderived intermediates have been generally known to
proceed through complicated reaction pathways such as dehydrogenation, the CꢀC and CꢀO
10,14,43,57
cleavages and WGS reaction on the active metals and acid sites as well.
Therefore, a
higher CO selectivity and H production rate can be obtained using hybrid catalysts having
2
2
highly dispersed active metallic sites on the solidꢀacid sites of some mixed metal oxides. In
addition, the solidꢀacid catalysts after properly modifying Bronsted and Lewis acid sites can
1
7,25,38,58
also largely promote a dehydration activity of the biomassꢀderived intermediates.
4
1
From our previous work, conversion of EG to gaseous products for the APR reaction was
mainly depending on the dispersion of platinum crystallites on the mixed metal oxides of
2 2
CeO ꢀZrO and a highly dispersed and larger surface area of metallic platinum crystallites on
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9

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41
ceriaꢀzirconia support showed a higher EG conversion and hydrogen productivity. However,
the catalytic activity on the solidꢀacid hybrid Pt/SA catalysts showed somewhat different
catalytic behaviors by showing the significant effects of the acidic sites on the solidꢀacid
SiO
sites on the solidꢀacid SiO
The observed higher selectivity to CO
2
ꢀAl
2
O
3
, which also modified the interactions of platinum nanoparticles with the acidic
ꢀAl support as well.
2
and H with a higher EG conversion to gaseous
2
2 3
O
2
products on the Pt/SA(0.1) with a lower alkane formation with the values of 43.3% for APR
reaction and 47.9% for APH reaction were mainly attributed to the highly dispersed platinum
nanoparticles with the abundant presence of total acidic sites as summarized in Table 1 and
Table 2. However, the observed lower activity on the Pt/SA(0) was mainly attributed to the
significant coke deposition due to the abundant strong acid sites for strong adsorption of
intermediates. The lower alkane selectivity for APR reaction on the Pt/SA(0.1) seems to be
also attributed to a higher activity for the CꢀO and CꢀC cleavages on the metallic platinum
crystallites as well as on the acidic sites of the SiO
hydrocarbon selectivity especially for CH was increased with an increase of Si/Al ratio and
vice versa for C hydrocarbons. Therefore, to further verify the effects of acid sites for the
2 2 3
ꢀAl O surfaces. Interestingly, the
4
2
hydrocarbon selectivity, supplementary APH reaction was also carried out. The variations of
EG conversion and product distribution were similar with the results of APR reaction except
for the higher hydrocarbon productivity. Hydrocarbon selectivity was well correlated with the
amount of weak Bronsted acid sites, and EG conversion was correlated with the amount of
strong acid sites, which seem to be reasonable by the selective CꢀC and CꢀO cleavages on the
strong acidic sites followed by hydrogenation and WGS activity on the platinum metallic
sites as well as weak acidic sites, except for the Pt/SA(0) due to a fast deactivation by a
3
severe coke deposition as confirmed by NH ꢀTPD, PyꢀIR, and TGA analyses. In addition, the
observed higher CO and H selectivity on the Pt/SA(0.1) during APR and APH reaction
2
2
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seem to be attributed to highly dispersed platinum nanoparticles with a proper interaction
with SiO ꢀAl O surfaces as confirmed by TPR and H chemisorption. We believe that an
2
2
3
2
increased selectivity of CH
4
on the Pt/SA(0.1) can be possibly attributed to a highly dispersed
platinum nanoparticles as well as the abundant weak Bronsted acid sites due to the enhanced
WGS activity on the active metallic sites. The TEM images on the selected Pt/SA catalysts
before and after APR reaction are displayed in Figure 6, and a less aggregation of the wellꢀ
dispersed platinum nanoparticles with a size of below 5 nm was observed on the Pt/SA(0.1)
(Figure 6(B-1) and (B-2)). This revealed a less aggregation of platinum crystallites on the
Pt/SA(0.1) compared with the Pt/SA(0) with a significant aggregation of platinum crystallites
between 5 – 10 nm (Figure 6(A-1) and (A-2)), which was well matched with the results of
XRD analysis as well. In general, the acid site density plays an important role to enhance a
heat of adsorption and interaction between the biomassꢀderived intermediates on the acid
sites, which can largely change the product distribution and conversion of the biomassꢀ
59-61
derived chemicals.
These phenomena were also confirmed by changing the residence
time of reactants and platinum metal loading as shown in Table 1 and the supplementary
Table S2, and a longer residence time and a high loading of platinum metals are responsible
for a high formation rate of CH as well as H and CO through an enhanced hydrogenolysis
4
2
2
and WGS activity. These activity changes can be also attributed to a further dehydration of
the intermediates formed though dehydration and hydrogenation of EG reactant. Therefore,
the hydrocarbon formation during APR reaction seems to follow consecutive reaction
pathways through dehydrogenation over metallic platinum nanoparticles followed by
hydrogenolysis of the dehydrogenated intermediates through CꢀC and CꢀO cleavage mainly
on the acid sites and further WGS reaction on the platinum metallic sites as well. Since C
hydrocarbon can be formed by the selective CꢀC and CꢀO cleavage followed by
hydrogenation on the metallic sites, C selectivity was decreased with an increase of Si/Al
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1

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molar ratio due to a decreased amount of the strong acid sites on the Pt/SA catalysts having a
larger Si/Al molar ratio.
According to the previous study for APR reaction combined with FischerꢀTropsch synthesis
62
reaction in a batch reacting system, the acid component such as sulfuric acid strongly
influences CO production rate and subsequently changes the activity of FischerꢀTropsch
synthesis. The conversion of biomassꢀderived reactants to gaseous products has been known
to be influenced by an initial step activity of dehydrogenation and dehydration, and the
dehydrogenated intermediates can further proceed by dehydrogenation reaction to form
57,58,63
hydrocarbons.
In addition, the solidꢀacid metal oxides after a modification of Bronsted
and Lewis acid sites can largely change the dehydration activity as reported previously by
38,64
many researches.
It has been well known that an increase of Si contents on the solidꢀacid
Al O ꢀSiO catalysts can increase B/L ratio by producing an active SiꢀOH species on the
2
3
2
65
surfaces. In addition, a decrease of surface acidity can be attributed to a lower metalꢀoxygen
bond energy in the order of Al–O > Zr–O > Si–O, which seems to be related with a large
formation of oxygen vacant sites in the mixed metal oxides, which is assigned to Lewis acid
6
6,67
sites.
higher ratio of B/L which also changes hydrocarbon distribution significantly, especially for
CH hydrocarbon during APR and APH reaction. The reducibility of the supported platinum
Therefore, a higher Si/Al ratio on the present Pt/SA catalysts was responsible for a
4
nanoparticles was also influenced by a surface acidity by altering a metal support interaction,
and the strong interaction of the platinum nanoparticles with acid sites can be changed by
shifting a reduction peak to a higher temperature and forming strong metalꢀsupport
43,68-74
interaction on the strong acid sites of the solidꢀacid surfaces.
Based on the present
observation, the surface acidity of the SiO ꢀAl mixed metal oxides largely altered the
2
2 3
O
dispersion of platinum nanoparticles with their interaction on the solid acid surfaces, which
can also significantly altered EG conversion and hydrocarbon selectivity. In addition, the
2
2

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selective coke deposition on the strong acid sites on the Pt/SA(0) also altered catalytic
activity and product distribution, especially for hydrocarbon selectivity.
In summary, EG conversion and hydrocarbon distribution were strongly affected by the
amount and type of acidic sites with the dispersion and reducibility of the supported platinum
2 2 3
nanoparticles, which have a proper interaction with solidꢀacid SiO ꢀAl O surfaces as shown
in Figure 7. The stronger acid sites (or density of total acid sites) on the Pt/SA catalysts are
preferentially responsible for a higher EG conversion through APR and APH reaction, i.e.,
EG conversion was increased with the increase of the strong acid sites through a first step of
hydrogenolysis and dehydration of EG. However, the Pt/SA(0) having a too strong acid sites
is responsible for a significant coke deposition by deactivating the Pt/SA(0) rapidly. In
addition, a larger amount of weak Bronsted acid sites (or higher ratio of Bronsted/Lewis acid
sites (B/L)), which seems to be interacted with the supported metallic platinum nanoparticles
by forming a smaller platinum crystallite size of below 5 nm, is responsible for a higher CH
4
2
hydrocarbon selectivity through a subsequent hydrogenation and WGS activity to form CO
simultaneously during APR and APH reaction. Therefore, the proper controls of the amount
and type of the acid sites by adjusting the metalꢀsupport interaction on the Pt/SA catalysts are
important to enhance catalytic activity for a transformation of biomassꢀderived intermediates
during APR and APH reaction, which can be simply obtained by changing Si/Al molar ratio
on the Pt/SA catalysts.
4. Conclusions
The platinum supported SiO ꢀAl O catalysts were found to be efficient and simple catalytic
2
2
3
system for a chemical transformation of biomassꢀderived intermediates to useful hydrogen
and paraffinic hydrocarbons. A larger metallic surface area of the platinum nanoparticles with
2 2 3
a proper interaction with Bronsted acid sites on the SiO ꢀAl O support was responsible for
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3

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the large hydrocarbon selectivity through a hydrogenation and WGS reaction. In addition, the
stronger Bronsted acid sites play an important role to enhance EG conversion to gaseous
hydrogen product during APR and APH reaction. The APR and APH reaction proceeded
through the consecutive reaction pathways, where the strong acid sites on the Pt/SA catalysts
act as active sites for hydrogenolysis of CꢀC and CꢀO bond cleavages. The weak Bronsted
acid sites are related with the dispersion of the supported platinum nanoparticles, which are
also responsible for a higher reducibility and WGS activity as well. Even though the total
acid sites with theirs types and the reducibility of platinum nanoparticles was well correlated
with the catalytic activity of APR and APH, the catalyst deactivation on the Pt/SA(0) during
APR reaction was strongly affected by the heavy coke deposition on the stronger acid sites.
2 2 3
With an increase of Si/Al on the SiO ꢀAl O mixed metal oxides, EG conversion was
decreased due to the decreased first step activity such as hydrogenolysis and dehydration of
EG originated form the smaller amount of stronger acid sites, and Pt/SA(0.1) was found to be
an optimal catalyst for APR and APH reaction, which can be easily prepared by simply
changing Si/Al molar ratio of the Pt/SA catalysts.
Acknowledgments
The present study was financially supported by the grant from the Industrial Source
Technology Development Programs (2013ꢀ10042712) of the Ministry of Knowledge
Economy (MKE) of Korea. The authors would like to acknowledge the financial support
from the National Research Foundation of Korea (NRF) grant funded by the Korea
government (NRFꢀ2014R1A1A2A16055557 and NRFꢀ2016M3D3A1A01913253). This
work was supported by an institutional program Grant (2E26570ꢀ16ꢀ037) from Korean
Institute of Science and Technology.
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