C5-C7 linear alkane hydroisomerization over MoO 3-ZrO2 and Pt/MoO3-ZrO2 catalysts

Article abstract of DOI:10.1016/j.jcat.2013.03.016

The catalytic activity of MoO₃-ZrO₂ and Pt/MoO ₃-ZrO₂ has been assessed based on the C₅-C ₇ linear alkane hydroisomerization in a microcatalytic pulse reactor at 323-623 K. The introduction of Pt altered the crystallinity and acidity of MoO₃-ZrO_2. The catalytic activity of Pt/MoO ₃-ZrO₂ was inferior than that of MoO₃-ZrO ₂, although the Pt/MoO₃-ZrO₂ performed higher hydrogen uptake capacity. IR and ESR studies confirmed the heating of MoO ₃-ZrO₂ in the presence of hydrogen formed active protonic acid sites and electrons which led to change in the Mo oxidation state. Similar phenomenon was observed for Pt/MoO₃-ZrO₂ at ≤323 K. Contrarily, heating of Pt/MoO₃-ZrO₂ in the presence of hydrogen at higher temperature did not form protonic acid sites but intensified Lewis acidic sites. It is suggested that Pt facilitates in the interaction of spiltover hydrogen atom and MoO₃ to form MoO₂ or Mo ₂O₅ over ZrO₂ support which may be intensified the Lewis acidic sites.

Full text of DOI:10.1016/j.jcat.2013.03.016

Journal of Catalysis 303 (2013) 50–59
Contents lists available at SciVerse ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
C5–C7 linear alkane hydroisomerization over MoO3–ZrO2 and Pt/MoO3–ZrO2
catalysts
c
a
c
c
S. Triwahyono a,b, , A.A. Jalil , N.N. Ruslan , H.D. Setiabudi , N.H.N. Kamarudin
⇑
a Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Malaysia
b Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Malaysia
c Institute of Hydrogen Economy, Faculty of Chemical Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history:
The catalytic activity of MoO3–ZrO2 and Pt/MoO3–ZrO2 has been assessed based on the C5–C7 linear
alkane hydroisomerization in a microcatalytic pulse reactor at 323–623 K. The introduction of Pt altered
the crystallinity and acidity of MoO3–ZrO2. The catalytic activity of Pt/MoO3–ZrO2 was inferior than that
of MoO3–ZrO2, although the Pt/MoO3–ZrO2 performed higher hydrogen uptake capacity. IR and ESR stud-
ies confirmed the heating of MoO3–ZrO2 in the presence of hydrogen formed active protonic acid sites
and electrons which led to change in the Mo oxidation state. Similar phenomenon was observed for
Pt/MoO3–ZrO2 at 6323 K. Contrarily, heating of Pt/MoO3–ZrO2 in the presence of hydrogen at higher tem-
perature did not form protonic acid sites but intensified Lewis acidic sites. It is suggested that Pt facili-
tates in the interaction of spiltover hydrogen atom and MoO3 to form MoO2 or Mo2O5 over ZrO2
support which may be intensified the Lewis acidic sites.
Received 7 February 2013
Revised 19 March 2013
Accepted 21 March 2013
Keywords:
MoO3–ZrO2
Pt/MoO3–ZrO2
Protonic acid sites
Lewis acid sites
C5–C7 alkane isomerization
Ó 2013 Elsevier Inc. All rights reserved.
1. Introduction
Recently, a special interest was devoted to molybdenum oxide
promoted zirconia (MoO3–ZrO2) in the catalysis. Afanasiev studied
The isomerization of linear alkanes over solid acid catalysts has
received great attention as an environmentally safety way to im-
prove the octane number of gasoline in recent year [1–5]. Zeolite
and chlorided alumina-based catalysts have been studied exten-
sively in the linear alkane isomerization for industrial purposes;
however, they have some disadvantages such as relatively low
activity and tolerance to the impurities which lead to decrease
the yield of isomer products [6]. Recently, the use of transition me-
tal-loaded catalysts has drawn much attention due to their ability
to isomerize C4–C7 linear alkane effectively. In addition, the pres-
ence of noble metals such as Pt or Pd in zeolitic materials, chlorid-
ed alumina, and zirconia-based catalysts is widely reported to
improve the stability and activity of the catalysts [7–15]. The Pt
has a role in the formation of active protonic acid sites and/or
assisting in the removal of coke deposits through hydrogenation
processes. Iglesia and co-workers reported the roles of Pt and
hydrogen on WO3–ZrO2 catalyst in the n-heptane isomerization
in which they concluded that Pt/WO3–ZrO2 showed a higher activ-
ity than that of Pt/SO24ꢀ–ZrO2 due to the availability of hydrogen on
the surface of WO3–ZrO2 to suppress cracking process [16,17].
the preparation of MoO3/ZrO2 in which the metastable monolayer
coverage of zirconia surface can be obtained by solid–solid wetting
preparation method with the Mo/Zr ratio of 0.13–0.15 [18]. While,
Calafat et al. reported the effect of Mo/Zr ratio and digestion time
in the physical properties of MoO3/ZrO2 [19]. The surface area of
MoO3/ZrO2 was increased with the increasing Mo/Zr ratio and de-
creased with the increasing the digestion time. In addition, they
also have suggested that the addition of (NH4)6Mo7O24 after forma-
tion of the Zr(OH)4 gel results in an increase in surface area than
those obtained by co-precipitation. Xie et al. studied the crystalline
structure in MoOx/ZrO2 evidenced by X-ray absorption and Raman
spectroscopy in which the isolated tetrahedral MoOx species was
observed at low surface density (<5 Mo/nm2) of sample treated
at 873 K and below [20]. For MoOx/ZrO2 samples with higher
surface density (>5 Mo/nm2), treatment in air at 723 K led to the
predominant formation of MoO3, while higher treatment tempera-
tures led to a solid-state reaction between MoO3 and ZrO2 to form
Zr(MoO4)2. Meanwhile, the effect of Mo loading on ZrO2 in respect
to the catalytic activities was reported by Chary et al. [21] and Ken-
ney et al. [22]. Chary et al. demonstrated the catalytic ammoxida-
tion of toluene to benzonitrile over MoO3–ZrO2 increased with
loading up to 6.6 wt.% MoO3. They have also claimed that the the-
oretical monolayer loading of MoO3 on the ZrO2 was obtained at
6.6 wt.% MoO3 loading in which this monolayer MoO3 on ZrO2 re-
sulted to the strongest acidity and highest reducibility of the
⇑
Corresponding author at: Ibnu Sina Institute for Fundamental Science Studies,
Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Malaysia. Fax: +60 7
5536080.
E-mail address: sugeng@utm.my (S. Triwahyono).
0021-9517/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.jcat.2013.03.016

S. Triwahyono et al. / Journal of Catalysis 303 (2013) 50–59
51
MoO3/ZrO2 catalyst, whereas Kenney et al. reported the influence
of Mo loading on ZrO2 in the methylcyclopentane conversion. They
have concluded that the most active catalyst for methylcyclopen-
tane conversion corresponds to a molybdenum loading of 3.2 at.%
Mo, which has the highest acidity per surface area of the ZrO2–
MoO3 catalysts studied. In addition, the surface area of ZrO2–
MoO3 reached a maximum value of 124 m2/g at a loading of
15.8 at.% Mo, while the isothermal CO2 adsorption and ammonia
TPD results indicated the strength of basic sites and specific NH3
desorption decreased with increasing molybdenum content.
We have previously reported the acidic properties of MoO3–ZrO2,
in relation to the active sites which participate in the formation of
active protonic acid sites from molecular hydrogen that favor in n-
heptane isomerization [23,24]. Although it has also been reported
widely that the introduction of Pt site is able to improve the activity
The nitrogen adsorption–desorption isotherms was determined
with a Quantachrome Autosorb-1 at 77 K. Prior to measurement,
the samples were outgassed at 573 K for 3 h. The specific surface
areas of the samples were determined from the linear portion of
the BET plots. Pore size distribution was calculated from the
desorption branch of N2 adsorption–desorption isotherm using
the conventional Barret–Joyner–Halenda (BJH) method, while the
metal content on the catalyst was measured with Agilent 4100
Microwave Plasma – Atomic Emission Spectrometer.
In the measurement of IR spectra, a self-supported wafer was
placed in an in situ stainless steel IR cell with CaF2 windows and
outgassed at 623 K for 3 h. For pyridine adsorption measurement,
2 Torr of pyridine was adsorbed on activated samples at 423 K
for 30 min followed by outgassing at 573 K for 30 min [11]. In
the H2-exposure experiments, the sample was exposed to 6.7 kPa
of hydrogen at room temperature to 473 K in 50 K increments.
All spectra were recorded on an Agilent Cary 640 FTIR Spectrome-
ter at room temperature. The intensity of acidic sites was deter-
mined by Gaussian curve fitting method.
The ESR measurement was carried out in a JEOL JES-FA100 ESR
spectrometer, to observe the formation of unpaired electrons in va-
cuo heating and to observe the interaction of the unpaired elec-
trons with electrons formed from molecular hydrogen at room
temperature to 473 K [27]. The catalyst was outgassed at 623 K
for 3 h followed by the introduction of 6.7 kPa of hydrogen gas at
room temperature. Then, the catalyst was held at room tempera-
ture and heated at 323, 373, 423, and 473 K in the presence of
hydrogen gas. All signals were recorded at room temperature.
The hydrogen uptake capacity of catalysts was measured using
the automatic gas adsorption apparatus Belsorp-28SA. A catalyst
sample was placed in an adsorption vessel and activated in a
hydrogen flow at 623 K for 3 h followed by evacuation at 623 K
for 3 h. The sample was subsequently cooled to an adsorption tem-
perature and held for 3 h in order to stabilize the temperature [28].
The adsorption temperature was verified from 323 to 573 K.
6.7 kPa of hydrogen gas was then introduced into the adsorption
system, and the pressure change was monitored to calculate the
hydrogen uptake.
and stability of zeolites, alumina, WO3–ZrO2, and SO2ꢀ–ZrO2, there is
4
almost no report related to the study of Pt loaded on MoO3–ZrO2 for
hydroisomerization of alkanes in the literature. In this study, we ex-
plored the effects of Pt in the properties and activity of MoO3–ZrO2.
The MoO3–ZrO2 with and without Pt were examined in the hydro-
isomerization of n-pentane, n-hexane, and n-heptane, whereas the
interaction of molecular hydrogen and surface catalyst was ob-
served by quantitative hydrogen adsorption measurement, IR and
ESR spectroscopy. We found that the presence of Pt did not enhance
the activity of MoO3–ZrO2 in the hydroisomerization of n-alkanes,
although the Pt enhanced the hydrogen uptake capacity of MoO3–
ZrO2. IR and ESR studies revealed that the presence of Pt did not pro-
mote the formation of protonic acid sites from molecular hydrogen.
In contrast, the presence of Pt intensified the Lewis acid sites in
which this may correspond to presence of MoO2 or Mo2O5 species
on the surface of ZrO2.
2. Experimental
2.1. Catalyst preparation
Zirconium hydroxide (Zr(OH)4) was prepared from aqueous
solution of ZrOCl2ꢁ8H2O (Wako Pure Chemical) by hydrolysis with
2.5% NH4OH (Merck) aqueous solution [25]. The final pH of solu-
tion was 9.0. The product was decanted and filtered, followed by
drying at 383 K overnight to form zirconium hydroxide. The
MoO3–ZrO2 sample was prepared by impregnation of zirconium
hydroxide with aqueous solution of ammonium heptamolybdate
([NH4]6Mo7O24ꢁ4H2O, Merck), followed by drying at 383 K and cal-
cination at 1093 K in air. The surface area of MoO3–ZrO2 was
56 m2/g, and the content of Mo was 5 wt.%. The Pt/MoO3–ZrO2
sample was prepared by impregnation of the MoO3–ZrO2 with an
aqueous solution of hexachloroplatinic acid (H2PtCl6ꢁH2O, Wako
Pure Chemical) followed by calcination at 823 K in air. The surface
area was 54 m2/g, and the content of Pt and Mo was 0.5 and
4.7 wt.%, respectively.
2.3. Hydroisomerization of n-alkane
The hydroisomerization of n-pentane, n-hexane, and n-heptane
was performed under hydrogen atmosphere in a microcatalytic
pulse reactor at temperature range of 423–623 K. Prior to the reac-
tion, the catalyst was activated in an oxygen stream (FOxygen = 100 -
mL/min) at 623 K for 1 h, followed by heated in a hydrogen stream
(FHydrogen = 100 mL/min) at 623 K for 3 h, and then cooled to a reac-
tion temperature in a hydrogen stream. A dose of n-alkane (n-pen-
tane = 43 lmol, n-hexane = 38 lmol, n-heptane = 34 lmol) was
passed over the 0.4 g of activated catalyst in a hydrogen stream
(FHydrogen = 100 mL/min), and the products were trapped at 77 K
before being flash-evaporated into an online 6090 N Agilent gas
chromatograph equipped with a VZ-7 packed column and an FID
detector. Since all catalysts reached steady-state condition within
seven pulses (280 min), results at seven pulses were used.
The specific rate of reactant conversion (r) from the differential
conversion data was determined by the following equation:
P
2.2. Characterization of catalyst
The crystalline structure of catalysts was determined with X-
ray diffraction (XRD) recorded on a Bruker AXS D8 Automatic Pow-
der Diffractometer using Cu Ka radiation with k = 1.5418 Å at
40 kV and 40 mA over a range of 2h = 20–80°. The fraction of the
tetragonal phase of zirconia in the sample was determined based
on the formula proposed by Toraya et al. [26]. The XRD measure-
ment of H2-reduced sample was determined as follows: Sample
was reduced with H2 at 673 K for 3, 6, and 12 h. After cooling to
room temperature under H2 atmosphere, the reduced sample
was transferred to a glove box without exposure to air then dis-
persed in a solution of heptane to avoid any bulk oxidation.
½Cꢂi ꢀ ½Cꢂresidual
reactant
P
rð
l
mol=ðs m2catÞÞ ¼ k
ð1Þ
½Cꢂi
where [C]i and [C]residual_reactant are mol number for particular prod-
uct and for residual reactant, which was calculated based on the
Scott hydrocarbon calibration standard gas (Air Liquide America
Specialty Gases LLC). The rate constant (k) was determined by the
molar concentration of the reactant divided by the surface area of

52
S. Triwahyono et al. / Journal of Catalysis 303 (2013) 50–59
catalyst per unit time, with the assumption that the retention time
for reactant in the catalyst bed was negligibly small. The calculated
k values of n-pentane, n-hexane, and n-heptane for MoO3–ZrO2
Mo loading was 5 and 4.7 wt.% for MoO3–ZrO2 with and without
Pt. In addition, the specific surface area altered slightly from 56
to 54 m2/g. Fig. 1B shows the XRD patterns of Pt/MoO3–ZrO2 re-
duced with H2 at 673 K for 3, 6, and 12 h. There were no significant
changes on the H2-reduced Pt/MoO3–ZrO2. This may be due to the
amount of Mo loading was very small compared to the ZrO2
support.
were 1.94, 1.70, and 1.51
calculated k values of n-pentane, n-hexane, and n-heptane for Pt/
MoO3–ZrO2 were 2.01, 1.76, and 1.57
mol/(s m2cat), respectively.
l
mol/(s m2cat), respectively, while the
l
The selectivity (Si) and yield (Yi) to particular product was calcu-
lated according to following equations:
The N2 adsorption–desorption isotherms and pore size distribu-
tion for MoO3–ZrO2 and Pt/MoO3–ZrO2 are plotted in Fig. 2A and B,
respectively. The introduction of Pt did not much alter the N2 phys-
isorption results. The N2 adsorption–desorption isotherms can be
classified as a type IV isotherm for both catalysts, with the pore fill-
ing restricted to a range of P/Po = 0.55–0.8, typical of mesoporous
materials. According to IUPAC classification, the hysteresis loop is
type H2 indicating a complex mesoporous structure. This type of
hysteresis is characteristic of solids consisting of particles crossed
by nearly cylindrical channel. The pore size distribution of samples
was derived from the desorption branch of the N2 adsorption–
desorption isotherm, shown in Fig. 2B. Both samples exhibited nar-
row pore size distribution and sharp pore distribution peak with
pore diameter of 5 nm. The peak at 5 nm decreased slightly after
the introduction of Pt on MoO3–ZrO2, indicating some Pt particles
plugged into the pore of MoO3–ZrO2 which led to decrease the spe-
cific surface area of ZrO2.
½Cꢂi
P
Sið%Þ ¼
ꢃ 100
ð2Þ
ð3Þ
½Cꢂi ꢀ ½Cꢂreactant
r
Yið%Þ ¼ S
i k
3. Results and discussion
3.1. Properties of Pt/MoO3–ZrO2
Fig. 1A shows the XRD pattern of MoO3–ZrO2 and Pt/MoO3–
ZrO2, respectively. MoO3–ZrO2 exhibited three well-established
polymorphs: the monoclinic, tetragonal, and cubic phase of ZrO2.
The sharp diffraction lines at 2h = 17.3°, 28.2°, 31.5°, 33.9°, 38.4°,
40.6°, 44.5°, 50.1°, and 55.3° correspond to the monoclinic phase
of ZrO2, peaks at 2h = 30.2°, 34.3°, 49.1°, 59.7°, and 62.6° corre-
spond to the tetragonal phase of ZrO2, while the peaks at
2h = 32.9° and 70.4° correspond to cubic phase of ZrO2. A small
peak was observed at 2h = 23.9° which may be related to the pres-
ence of Zr(MoO4)2 hexagonal phase [23,29]. No intensity corre-
sponds to the reflections of Pt (111), which should appear at
2h = 40°, was observed in the XRD pattern of Pt/MoO3–ZrO2. This
suggested that the quantity of Pt loading was small and therefore
finely dispersed on the surface or below the XRD detection limit.
The introduction of Pt changed slightly the crystallinity of ZrO2.
The fraction of tetragonal phase of ZrO2 decreased from 0.51 to
0.44 which may be due to the collapsing of crystalline phase during
calcination. The decrease in the crystallinity may not be due to the
altering of Mo loading. In fact, MP-AES results indicated that the
3.2. Intrinsic acidity
The type of acid sites for MoO3–ZrO2 and Pt/MoO3–ZrO2 was
qualitatively probed by pyridine adsorption using IR spectroscopy
[30]. Fig. 3A shows the IR spectra of pyridine adsorbed on MoO3–
ZrO2 and Pt/MoO3–ZrO2 activated at different temperatures. The
catalysts were activated at 573, 623, and 673 K for 3 h, the spectra
were recorded after the adsorption of pyridine on samples reach
equilibrium at 423 K, and the physisorbed state was subsequently
removed by heating at 573 K under vacuum. Thus, the resulting
absorbance bands indicated only strong adsorptions between the
pyridine molecules and acidic sites. Typical Brønsted acid sites
Fig. 1. (A) X-ray diffraction patterns of MoO3–ZrO2 and Pt/MoO3–ZrO2. (d) Monoclinic phase of ZrO2; (⁄) tetragonal phase of ZrO2; (N) cubic phase of ZrO2; (j) Zr(MoO4)2
phase. (B) X-ray diffraction patterns of Pt/MoO3–ZrO2 reduced with H2 at 673 K for 3, 6 and 12 h.

S. Triwahyono et al. / Journal of Catalysis 303 (2013) 50–59
53
(B)
(A)
Fig. 2. (A) Adsorption–desorption isotherms of N2 on MoO3–ZrO2 and Pt/MoO3–ZrO2. Open and solid symbols represent adsorption and desorption isotherms, respectively.
(B) Pore size distribution of MoO3–ZrO2 and Pt/MoO3–ZrO2.
5.5
5.5
(B)
573 K
(A)
673 K
5
5
4.5
4.5
473 K
623 K
4
4
423 K
573 K
3.5
3.5
MoO -ZrO2
MoO -ZrO2
3
3
0.2
0.2
Pt/MoO -ZrO2
Pt/MoO -ZrO2
3
3
3
3
1600
1550
1500
1450
1400
1600
1550
1500
1450
1400
Wavenumber [cm-1]
Wavenumber [cm-1]
Fig. 3. (A) IR spectra of pyridine adsorbed on MoO3–ZrO2 and Pt/MoO3–ZrO2 samples activated at different temperatures. Pyridine was adsorbed at 423 K and outgassed at
573 K. (B) IR spectra of pyridine adsorbed on MoO3–ZrO2 and Pt/MoO3–ZrO2 at 423 K and outgassed at different temperatures. Samples were activated at 573 K.
were observed in the samples, suggesting that pyridine was ad-
sorbed in the form of a pyridinium ion at the IR frequency of
1540 cmꢀ1, whereas strong Lewis electron pair acceptors were ob-
served at 1450 cmꢀ1 in the samples. The absorbance band at
1490 cmꢀ1 corresponds to the mixture of Brønsted and Lewis acid
sites. For MoO3–ZrO2 sample, as the activation temperature in-
creased, the absorbance band at 1540 cmꢀ1 decreased and the
other absorbance band at 1450 cmꢀ1 increased markedly due to
the dehydration and/or dehydroxylation which eliminated acidic
OH groups, leaving Lewis acid sites. This is commonly observed
for zeolites, mesoporous materials, and other mixed metal oxide
such as silica–alumina and tungsten oxide–zirconium oxide.
Meanwhile, different phenomenon was observed for Pt/MoO3–
ZrO2. In general, the intensity of the absorbance bands attributed
to both Brønsted and Lewis acid sites for Pt/MoO3–ZrO2 is lower
than that of MoO3–ZrO2. The difference is not due to the amount
of Mo, as both catalysts have almost similar Mo loading. However,
this may be due to the small altering of the crystallinity of ZrO2
during the calcination in which the tetragonal phase of zirconia de-
creased with Pt-addition. Increase in the activation temperature of

54
S. Triwahyono et al. / Journal of Catalysis 303 (2013) 50–59
Pt/MoO3–ZrO2 decreased moderately the Brønsted acid sites,
whereas the band ascribed to the Lewis acid sites did not change
much significantly. These results indicated that MoO3–ZrO2 pos-
sessed several acidic OH groups with different strength in which
the acidic OH groups were extensively eliminated at higher activa-
tion temperature leaving Lewis acid sites. Meanwhile, most of the
acidic OH groups and Lewis acid sites were strong for Pt/MoO3–
ZrO2. The weak to moderate strength of acidic OH groups was elim-
inated at relatively low activation temperature. Therefore, the
change was not observed for both acidic sites on Pt/MoO3–ZrO2
with increasing the activation temperature. Fig. 3B shows the vari-
ations of the IR spectra as a function of outgassing temperature
after pyridine adsorption for the sample activated at 573 K. If the
outgassing temperature is raised, pyridine molecules adsorbed on
weak acid sites should be desorbed at lower temperatures, and
those adsorbed on strong acid sites should be desorbed at higher
temperatures. For MoO3–ZrO2, both Brønsted and Lewis acid sites
decreased significantly with outgassing temperature indicating
the wide distribution of both acidic sites on the MoO3–ZrO2 sample
[23]. It should be noted that the decrease was extensively observed
for Lewis acid sites than that of Brønsted acid sites. This showed
that most of the Brønsted acid sites on the MoO3–ZrO2 were strong.
In addition to the strong Lewis acid sites, there existed weak acid
sites for which the pyridine was desorbed at 423 K and above,
whereas small decreased was observed for both acidic sites on
Pt/MoO3–ZrO2, indicating the sample possesses small distribution
of both acidic sites.
The properties of acidic sites on MoO3–ZrO2 types are essen-
tially similar with WO3–ZrO2 types [31]. For both catalysts,
Brønsted and Lewis acid sites were strong in which the pyridine
molecules remain on both acid sites after outgassing at 573 K. In
addition to strong Lewis acid sites, there existed a number of weak
Lewis acid sites from which pyridine molecules were desorbed by
outgassing at elevated temperature. While the Lewis acid sites
were predominantly for WO3–ZrO2 types, the Brønsted acid sites
were the most part for MoO3–ZrO2. The other difference between
MoO3–ZrO2 and WO3–ZrO2 types was observed on the acidity of
catalysts after the introduction of Pt. The presence of Pt did not
change much the acidity for WO3–ZrO2 types, while the concentra-
tion of acidic sites was significantly reduced by the presence of Pt
for MoO3–ZrO2 types. The intensity of Brønsted and Lewis acid
sites for Pt/MoO3–ZrO2 did not change much by activation, and
outgassing of pyridine indicating all the weak acid sites were elim-
inated by the presence of Pt. The other difference between MoO3–
ZrO2 and WO3–ZrO2 types was observed in the distribution of
Brønsted acid site. In addition to the strong Brønsted acid sites,
MoO3–ZrO2 possesses significant number of weak Brønsted acid
sites, whereas only strong Brønsted acid sites were observed on
WO3–ZrO2 types.
3.3. Hydrogen interaction
The interaction of molecular hydrogen and surface MoO3–ZrO2
types was studied by hydrogen uptake measurement, pyridine
pre-adsorbed IR and ESR spectroscopy in order to reveal the acidity
induced by molecular hydrogen and the role of hydrogen in the
activity of catalysts. Several research groups have reported the role
of Pt metal and molecular hydrogen in the solid acid materials in
which the presence of metal has affected positively in the acid-cat-
alytic reaction under hydrogen stream. While the presence of Pt
and molecular hydrogen has been reported to increase the stability
and activity of catalysts due to the assisting of Pt to remove coke
deposits on the surface catalyst by hydrogenation process [32–
34], our research group has suggested that the presence of Pt facil-
itates the formation of active protonic acid sites for maintaining
the activity and stability through hydrogen spillover phenomenon
[35,36]. We have reported the formation of protonic acid sites
through hydrogen spillover phenomenon evidenced by ESR and
IR studies on the zeolitic-based and zirconia-based catalysts
[31,36,37]. In addition, the presence of Pt enhanced the hydrogen
uptake capacity of WO3–ZrO2 [35,38], SO24ꢀ–ZrO2 [39] and also
MoO3 [28] catalysts.
Fig. 4 shows the isothermal hydrogen adsorption for MoO3–
ZrO2 type catalysts and effect of adsorption temperature in the
hydrogen uptake capacity. The general features of hydrogen uptake
for MoO3–ZrO2, SO2ꢀ–ZrO2, and WO3–ZrO2 types were essentially
4
0.1
0.2
(B)
(A)
MoO -ZrO
3
2
Pt/MoO -ZrO2
3
0.16
0.12
0.08
0.04
0
0.08
Pt/MoO -ZrO2
3
0.06
0.04
0.02
0
MoO -ZrO2
3
0
5
10
323
373
423
473
573
Time [h]
Adsorption Temperature [K]
Fig. 4. (A) Hydrogen uptake on MoO3–ZrO2 and Pt/MoO3–ZrO2 as a function of time at 373 K. (B) Hydrogen uptake capacity of MoO3–ZrO2 and Pt/MoO3–ZrO2 at different
adsorption temperatures after 10 h adsorption.

S. Triwahyono et al. / Journal of Catalysis 303 (2013) 50–59
55
MoO3-ZrO2
Pt/MoO3-ZrO2
(B)
(A)
f
f
e
e
d
c
d
c
b
a
b
a
0.2
0.2
1600
1550
1500
1450
1400
1600
1550
1500
1450
1400
Wavenumber [cm-1]
Wavenumber [cm-1]
Fig. 5. IR spectra change of (A) MoO3–ZrO2 and (B) Pt/MoO3–ZrO2 when pyridine pre-adsorbed sample was heated in hydrogen at (b) room temperature, (c) 323 K, (d) 373 K,
(e) 423 K and (f) 473 K. (a) Before exposure to hydrogen.
1
the same in which the presence of Pt enhanced the hydrogen up-
take markedly [38,39]. For all adsorption temperatures, Pt loaded
on SO24ꢀ–ZrO2 and WO3–ZrO2 performed fast adsorptions in the
first few minutes followed by slower adsorption until equilibrium
0.8
was reached. The decrease in the rate of hydrogen uptake with the
time for both catalysts may be due to the decreasing of free Lewis
acid sites for stabilizing of adsorbed hydrogen atoms by trapping of
electrons. In the case of Pt/MoO3–ZrO2 catalyst, the presence of Pt
continued the hydrogen uptake with time, and the adsorption did
0.6
not reach equilibrium even after 10 h at 373 K. Different behaviors
were observed for Pt-free MoO3–ZrO2 in which the hydrogen up-
take increased to lesser extent with time and almost reached equi-
0.4
librium within 3 h. For 10 h adsorption, the hydrogen uptake
reached 8.13 ꢃ 1018 and 1.80 ꢃ 1018 H-atom/g cat for MoO3–ZrO2
with and without Pt at 373 K, respectively. This difference clearly
verified that the presence of Pt facilitates the adsorption of hydro-
gen on MoO3–ZrO2 catalyst for all adsorption temperatures as
illustrated in Fig. 4B. In particular, the effect of Pt was obviously
observed at 373 K and below due to the ability of Pt to interact
with molecular hydrogen at relatively low temperature, while
MoO3–ZrO2 began to interact with molecular hydrogen extensively
at 423 K and above. This may indicate that Pt-free MoO3–ZrO2 pos-
sess a higher energy barrier to be crossed over for hydrogen uptake
than that of Pt/MoO3–ZrO2.
0.2
0
250
350
450
Temperature [K]
Fig. 6. Plot of (N,D) MoO3–ZrO2 and (d,s) Pt/MoO3–ZrO2 pre-adsorbed pyridine
followed by heating in the presence of hydrogen. Solid symbol: Brønsted acid sites;
open symbol: Lewis acid sites.
The interaction of hydrogen with the MoO3–ZrO2 type catalysts
then was observed by IR and ESR spectroscopy (Figs. 5–7). We have
previously reported the hydrogen spillover phenomenon over zirco-
nia- and zeolite-based catalysts in which the molecular hydrogen
dissociatively adsorbed on a specific site to form hydrogen atoms
that undergo spillover onto the surface, followed by surface diffu-
sion. Each spiltover hydrogen atom reaches a Lewis acid site and do-
nates an electron to form an H+. The H+ is stabilized on an O atom
near the Lewis acid site. The Lewis acid site trapping an electron re-
acts with a second spiltover hydrogen to form an Hꢀ bound to a
Lewis acid site [5,11]. The formation of protonic acid sites was mon-
itored by IR spectroscopy, while the formation of electron was mon-
itored by ESR spectroscopy [24,27]. Similar phenomenon was
observed for MoO3–ZrO2 in which the interaction of hydrogen with
the surface catalyst formed protonic acid sites and electrons which
led to change in the Mo oxidation state. Heating in the presence of
hydrogen, the absorbance band of acidic OH group at 1545 cmꢀ1
was intensified indicating the formation of OH groups (Fig 5A), while
the ESR signal at g = 1.93 corresponds to hexa-coordinated Mo5+
species decreased due to the increase in the interaction of electrons
and electron-deficient Mo5+ cations (Fig. 7A inset) [24,40]. The
changes were clearly seen in the Figs. 6 and 7B. The fraction of pro-
tonic acid sites increased with increasing temperature and simulta-
neously decreased in the fraction of Lewis acid sites, while the ESR
signal at g = 1.93 decreased continuously with increasing the heat-
ing temperature. These results strongly evidenced that the forma-
tion of proton and electron from hydrogen atom increased
extensively with increasing the temperature.

56
S. Triwahyono et al. / Journal of Catalysis 303 (2013) 50–59
Fig. 7. (A) ESR spectra of Pt/MoO3–ZrO2 when 100 Torr of hydrogen was adsorbed at (a) room temperature, (b) 323 K, (c) 373 K, (d) 423 K and (e) 473 K. The sample was
outgassed at 673 K (bold line) prior the hydrogen adsorption. Inset shows ESR spectra of MoO3–ZrO2. (B) Relative intensity of ESR spectra change for MoO3–ZrO2 and Pt/
MoO3–ZrO2 upon hydrogen adsorption.
Similar to SO24ꢀ–ZrO2 and WO3–ZrO2 type catalysts, the interac-
tion of hydrogen with surface MoO3–ZrO2 is a reversible process in
which the IR results indicated that the heating of the MoO3–ZrO2 in
the presence of hydrogen gas altered the intensity of both Lewis
and protonic acid sites (Fig. 6). while heating of the hydrogen ad-
sorbed MoO3–ZrO2 in vacuum restored both Lewis and protonic
acid sites to their original intensities (figure not shown). Differ-
ently, heating of the hydrogen adsorbed Pt/MoO3–ZrO2 in vacuum
restored partially the intensity of both Lewis and protonic acid
sites (figure not shown). The results also indicated that higher tem-
perature is required to desorb the hydrogen uptake from the sur-
face of Pt/MoO3–ZrO2.
In general, the presence of specific site likes Pt on solid acid cat-
alyst is reported to increase the interaction of hydrogen and acidic
surface which led to enhance the activity of catalyst in the acid-
catalytic reaction. In this study, we are also reporting the hydrogen
adsorption on MoO3–ZrO2 in which the presence of Pt increased
the rate of hydrogen adsorption and hydrogen uptake capacity of
MoO3–ZrO2. However, the hydrogen adsorbed IR and ESR studies
on MoO3–ZrO2, indicating that the presence of Pt did not promote
the formation of electron and active protonic acid sites such as
MoO2ꢀx(OH)y phase or MoO2–OH species at 373 K and above. In
general, heating of Pt/MoO3–ZrO2 in the presence of hydrogen
slightly decreased the Brønsted acid sites at 1545 cmꢀ1 and in-
creased gradually the Lewis acid sites at 1450 cmꢀ1 (Fig. 5B). The
changes of both Lewis and Brønsted acid sites caused by heating
in the presence of hydrogen can be clearly seen when the fraction
of absorbance bands at 1450 and 1545 cmꢀ1 is plotted against the
heating temperature (Fig. 6). Heating at 323 K and below, the
Brønsted acid sites increased slightly with simultaneous decrease
in the Lewis acid sites, indicating the formation of protonic acid
sites from hydrogen atom. The further heating of Pt/MoO3–ZrO2
at 373 K, the Brønsted acid sites began to decrease and the de-
crease continued up to 473 K. In tandem, the intensity of Lewis
acid sites increased at temperature range of 373–473 K. Similarly,
the hydrogen adsorbed ESR spectroscopy showed that the signal
at g = 1.93 decreased when the Pt/MoO3–ZrO2 was heating at
323 K and below (Fig. 7). This may be due to the interaction of
electron with electron-deficient Mo5+ cation. However, the heating
at 373 K and above, ESR signal at g = 1.93 increased significantly
indicating the increase in the number of electron-deficient Mo5+
cation and/or oxygen radical in the catalyst. The electron formed
from hydrogen atom which subsequently pairing with electron-
deficient Mo5+ cation and/or oxygen radical was not observed at
373 K and above. This result obviously indicated that Pt plays a dif-
ferent role on MoO3–ZrO2. The presence of Pt enhanced the inter-
action of hydrogen with the surface MoO3–ZrO2; however, the
interacted-hydrogen did not successively form protonic acid sites
but intensified the Lewis acid sites at >323 K.
Previously, Al-Kandari and co-workers have studied the interac-
tion of hydrogen with MoO3/TiO2 catalysts [41–46]. They found
that Mo2O5 species was most likely formed as an intermediate sur-
face species in the reduction course of MoO3 to MoO2. All the
molybdena species formed the surface Lewis acidity via exposed
Mo6+ sites. Further exposure of the sample to hydrogen at 673 K
for 12 h resulted in the formation of Brønsted (Mo–OH) acidic
function on the surface of the MoO2 structure, thereby producing
a metal–acid (bifunctional) MoO2ꢀx(OH)y phase. Their results are
quite similar to the results in this report on MoO3–ZrO2 type cata-
lysts, although the formation of MoO2ꢀx(OH) on both MoO3–ZrO2
and Pt/MoO3–ZrO2 was not observed by XRD results. However,
the IR results suggested that the formation of protonic acid sites
on MoO3–ZrO2 may be due to the presence of Mo–OH phase, while
the formation of Lewis acid sites on Pt/MoO3–ZrO2 may be due to
the presence of MoO2 or Mo2O5 [41].
3.4. Hydroisomerization of n-pentane, n-hexane and n-heptane
Fig. 8 demonstrates the rate of conversion of MoO3–ZrO2 and Pt/
MoO3–ZrO2 in the C5–C7 linear alkane hydroisomerization at differ-
ent temperatures. The results indicated that both catalysts were
not active for n-pentane hydroisomerization at 323–573 K, in spite
of trace amount of C1–C2 and C3–C4 cracking products was ob-
served at 573 K and above. Meanwhile, both catalysts were active
in n-hexane and n-heptane hydroisomerization. This result may be
due to the dehydroisomerization and hydrocracking of n-pentane

S. Triwahyono et al. / Journal of Catalysis 303 (2013) 50–59
57
1.2
1.2
1
MoO -ZrO
Pt/MoO -ZrO
3
2
3
2
(A)
(B)
1
0.8
0.6
0.4
0.2
0
0.8
0.6
0.4
0.2
0
300
400
500
600
700
300
400
500
600
700
Temperature [K]
Temperature [K]
Fig. 8. Rate conversion for hydroisomerization of n-pentane, n-hexane and n-heptane at different reaction temperatures over (A) MoO3–ZrO2 and (B) Pt/MoO3–ZrO2.
Table 1
Product distribution of n-pentane, n-hexane and n-heptane isomerizations over MoO3–ZrO2 and Pt/MoO3–ZrO2 in the presence of hydrogen.
MoO3–ZrO2 Pt/MoO3–ZrO2
React. temp. (K)
323
373
423
473
523
573
623
323
373
423
473
523
573
623
n-pentane
Rate of conversion (
Selectivity (%)
C1–C2
l
mol/(s m2cat))
0
<0.04
<0.04
<0.04
<0.04
0.08
0.52
0
<0.04
<0.04
<0.04
<0.04
0.09
0.15
0
0
0
0
100
0
0
100
0
0
100
0
0
100
0
0
95.8
4.2
0
87.5
12.5
0
0
0
0
0
100
0
0
100
0
0
100
0
0
100
0
0
100
0
0
100
0
0
C3–C4
2-Methylbutane
Yield of i-C5 (%)
0
0
0
0
0
0
0
0
0
0
0
0
n-hexane
Rate of conversion (
Selectivity (%)
C1–C2
l
mol/(s m2cat))
0
0.16
0.26
0.35
0.48
0.62
1.00
0
<0.04
<0.04
0.36
0.41
0.54
0.79
0
0
0
0
0
0
6.2
6.5
6.0
11.4
5.6
28.0
35.5
19.5
15.4
11.0
7.0
25.0
38.3
18.7
20.5
10.0
6.0
23.0
45.7
15.3
35.9
0
0
0
0
0
0
100
0
0
0
0
81.0
19.0
0
0
0
45.0
18.2
21.3
12.5
3.0
38.0
10.0
11.0
25.0
16.0
7.2
35.0
12.0
11.0
25.2
16.8
12.8
29.5
15.0
2.5
38.4
14.6
23.9
C3–C4
C5
3-Methylpentane
2-Methylpentane
Yield of i-C6 (%)
40.6
18.0
24.3
10.9
3.4
35.0
20.5
25.0
13.0
5.7
18.8
30.2
25.0
20.0
9.0
0
0
3.1
n-heptane
Rate of conversion (
Selectivity (%)
C1–C2
l
mol/(s m2cat))
0
<0.03
0.05
0.13
0.23
0.47
0.63
0
<0.03
<0.03
<0.03
0.11
0.39
0.67
0
0
0
0
0
0
0
100
0
0
0
0
96.0
4.0
0
0
0
28.0
26.0
32.8
5.0
8.0
0.2
13.6
13.5
45.2
10.0
17.0
0.7
13.3
15.0
27.0
21.0
22.0
1.7
16.2
15.0
36.0
23.0
23.8
1.2
0
0
0
0
0
0
0
100
0
0
0
0
100
0
0
0
0
100
0
0
0
0
100
0
0
0
0
83.0
17.0
0
0
0
55.0
24.0
12.0
3.5
5.5
0
C3–C4
C5–C6
2-Methylhexane
3-Methylhexane
3-Ethylpentane
Yield of i-C7 (%)
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1.1
4.2
13.8
19.7
3.8
are more difficult catalytic processes as compared to n-hexane and
n-heptane [44]. Although the n-pentane hydroisomerization has
been observed for MoO3/TiO2 catalyst [41–46], the presence of
metallic function in balance with the acid function for MoO3–
ZrO2 and Pt/MoO3–ZrO2 seems to be not in an optimized condition
for the reaction to occur. High activity in n-hexane and n-heptane
hydroisomerization was observed on MoO3–ZrO2 at 323–623 K
and the yield increased continuously with reaction temperature.
In contrast, Pt/MoO3–ZrO2 was active only in the n-hexane hydro-
isomerization, though trace amount of several cracking products
was observed in the hydroisomerization of n-heptane over Pt/
MoO3–ZrO2 at 573 K and above. The detail results were listed in
Table 1.
Fig. 9 shows yield of isomer products for C5–C7 alkane hydroiso-
merization over MoO3–ZrO2 and Pt/MoO3–ZrO2. The yield of
isopentane was nil for all reaction temperature over MoO3–ZrO2
and Pt/MoO3–ZrO2 catalysts, whereas the yield of isohexane and
isoheptane varied with reaction temperature for both catalysts.
Overall, the yield of isoproducts was higher for MoO3–ZrO2 than
that of Pt/MoO3–ZrO2. In addition, the Pt/MoO3–ZrO2 was not

58
S. Triwahyono et al. / Journal of Catalysis 303 (2013) 50–59
40
35
30
25
20
15
10
5
40
MoO -ZrO2
Pt/MoO -ZrO2
3
3
(A)
(B)
35
30
25
20
15
10
5
0
300
0
300
400
500
600
700
400
500
600
700
Temperature [K]
Temperature [K]
Fig. 9. Yield of isomer products for hydroisomerization of n-pentane, n-hexane and n-heptane at different reaction temperatures over (A) MoO3–ZrO2 and (B) Pt/MoO3–ZrO2.
active at low temperature. In fact, the yield for n-hexane and n-
heptane hydroisomerization over Pt/MoO3–ZrO2 was observed
only at >473 and >623 K, respectively. These results showed that
the presence of Pt did not enhance the activity of MoO3–ZrO2 in
n-pentane, n-hexane, and n-heptane hydroisomerization. In con-
trast, the presence of Pt has suppressed the selectivity of isoprod-
ucts and conversion of reactants. For instant, at 523 K, the yield of
isohexane and isoheptane decreased by about 7% and 4%, respec-
tively, whereas the rate of conversion of n-hexane and n-heptane
hydrogen. The Pt on MoO3–ZrO2 may facilitate in the hydrogen up-
take in which the hydrogen then interact with MoO3 to form Mo
with different oxidation state such as MoO2 or Mo2O5 [41]. In fact,
heating of Pt/MoO3–ZrO2 in the presence of hydrogen intensified
the Lewis acid sites at 1450 cmꢀ1 in which the peak may
correspond to the presence of Mo with different oxidation state
on the surface of catalyst (Fig. 5). These results also confirmed that
the activity of Pt/MoO3–ZrO2 could not be correlated directly to the
hydrogen uptake capacity of the catalyst. The low activity of
Pt/MoO3–ZrO2 was also observed on the isomerization of alkanes
in the absence of hydrogen in which this suggested that the activ-
ity of Pt/MoO3–ZrO2 strongly depends on the active protonic acid
sites originated from molecular hydrogen. Moreover, the low
activity of Pt/MoO3–ZrO2 was not due to the low Mo loading or
low concentration of permanent Brønsted acid sites.
were decreased by about 0.07 and 0.12 l
mol/(s m2cat), respec-
tively. Although it is not certain at present, the low activity of Pt/
MoO3–ZrO2 may be caused by the Pt plays different role over
MoO3–ZrO2 than those on the common catalysts such as WO3–
ZrO2, SO2ꢀ–ZrO2 or zeolite type catalysts. In the common solid acid
4
catalysts, the presence of Pt facilitated the formation of active pro-
tonic acid sites from molecular hydrogen which finally enhanced
the isomerization. However, IR and ESR results on Pt/MoO3–ZrO2
showed that the presence of Pt did not assist or enhance in the for-
mation of protonic acid sites and electrons from molecular
Several research groups have reported the enhancement in the
catalytic activity for platinum loaded on MoO3-based catalysts.
Al-Kandari and co-workers have studied the effects of Pt on the
isomerization properties of MoO3/TiO2 catalyst [44–45]. They
0.6
Reactivation
Reactivation
0.5
0.4
0.3
0.2
0.1
0
MoO3-ZrO2
Pt/MoO3-ZrO2
0
3
6
9
12
15
18
21
24
27
30
33
36
Time [h]
Fig. 10. Stability of MoO3–ZrO2 and Pt/MoO3–ZrO2 in the n-heptane hydroisomerization at 573 K. The reactivation was done under hydrogen stream at 623 K for 3 h. The
intervals between each dose were kept constant at 40 min for more than 30 h.

S. Triwahyono et al. / Journal of Catalysis 303 (2013) 50–59
59
found that the addition Pt on MoO3/TiO2 catalyst resulted in an in-
crease in the catalytic activity of the system in favor of hydrocrack-
ing products at high reaction temperatures due to the
enhancement in the metallic character of the system by metallic
Pt(0), whereas Matsuda and co-workers have reported the effects
of Pt on the catalytic activity of H2-reduced MoO3-based catalysts
[47,48]. They found that H2-reduced MoO3 was almost inactive
for heptane isomerization, while higher activity was obtained on
H2-reduced Pt/MoO3. They suggested that the enhancement in
the activity of H2-reduced Pt/MoO3 corresponds to the conversion
of hydrogen molybdenum bronze, HxMoO3, to acidic molybdenum
oxyhydride, MoOxHy. The MoOxHy species plays an important role
in the generation of acid sites and led to the enhancement in the
catalytic activities for heptane isomerization.
gratitude also goes the Hitachi Scholarship Foundation for the
Gas Chromatograph Instruments Grant.
References
[1] J.G. Santiesteban, D.C. Calabro, C.D. Chang, J.C. Vartulli, T.J. Fiebig, R.D. Bastian,
J. Catal. 202 (2001) 25.
[2] M. Busto, V.M. Benitez, C.R. Vera, J.M. Grau, J.C. Yori, Appl. Catal. A: Gen. 347
(2008) 117.
[3] K. Kim, R. Ryoo, H. Jang, M. Choi, J. Catal. 288 (2012) 115.
[4] I.R. Choudhury, K. Hayasaka, J.W. Thybaut, C.S.L. Narasimhan, J.F. Denayer, J.A.
Martens, G.B. Marin, J. Catal. 290 (2012) 165.
[5] H.D. Setiabudi, A.A. Jalil, S. Triwahyono, J. Catal. 294 (2012) 128.
[6] Y. Ono, Catal. Today 81 (2003) 3.
[7] A.H. Karim, S. Triwahyono, A.A. Jalil, H. Hattori, Appl. Catal. A: Gen. 433–434
(2012) 49.
[8] D. Fraenkel, N.R. Jentzsch, C.A. Starr, P.V. Nikrad, J. Catal. 274 (2010) 29.
[9] X. Zhu, L.L. Lobban, R.G. Mallinson, D.E. Resasco, J. Catal. 281 (2011) 21.
[10] N.H. N Kamarudin, A.A. Jalil, S. Triwahyono, R.R. Mukti, M.A.A. Aziz, H.D.
Setiabudi, M.N.M. Muhid, H. Hamdan, Appl. Catal. A: Gen. 104 (2012) 431–432.
[11] S. Triwahyono, T. Yamada, H. Hattori, Catal. Lett. 85 (2003) 109.
[12] T.N. Vu, J. van Gestel, J.P. Gilson, C. Collet, J.P. Dath, J.C. Duchet, J. Catal. 231
(2005) 468.
[13] M. Occhiuzzi, D. Cordischi, S. De Rossi, G. Ferraris, D. Gazzoli, M. Valigi, Appl.
Catal. A: Gen. 351 (2008) 29.
[14] S. Kuba, P. Lukinskas, R. Ahmad, F.C. Jentoft, R.K. Grasselli, B.C. Gates, H.
Knözinger, J. Catal. 219 (2003) 376.
[15] X. Wang, H. Wang, Y. Liu, F. Liu, Y. Yu, H. He, J. Catal. 279 (2011) 301.
[16] D.G. Barton, S.L. Soled, G.D. Meitzner, G.A. Fuentes, E. Iglesia, J. Catal. 181
(1999) 57.
[17] E. Iglesia, D.C. Barton, S.L. Soled, S. Miseo, J.E. Baumgartner, W.E. Gates, G.A.
Fuentes, G.D. Meitzner, Stud. Surf. Sci. Catal. 101 (1996) 533.
[18] P. Afanasiev, Mat. Chem. Phys. 47 (1997) 231.
Fig. 10 shows the stability of MoO3–ZrO2 and Pt/MoO3–ZrO2 in
the n-heptane hydroisomerization at 573 K. The reaction was done
for more than 30 h with the intervals between each dose were kept
constant at 40 min. The activity of the MoO3–ZrO2 and Pt/MoO3–
ZrO2 reaches
a steady-state condition within seven pulses
(280 min) and decreased slightly after 12 pulses (480 min). How-
ever, the activity of the catalysts recovered after the activation in a
hydrogen stream at 623 K for 3 h. It is noteworthy that the high
activity of the MoO3–ZrO2 and Pt/MoO3–ZrO2 in the alkane hydro-
isomerization still has been observed after 30 h.
4. Conclusion
[19] A. Calafat, L. Avilán, J. Aldana, Appl. Catal. A: Gen. 201 (2000) 215.
[20] S. Xie, K. Chen, A.T. Bell, E. Iglesia, J. Phys. Chem. B 104 (2000) 10059.
[21] K.V.R. Chary, K.R. Reddy, G. Kishan, J.W. Niemantsverdriet, G. Mestl, J. Catal.
226 (2004) 283.
[22] C. Kenney, Y. Maham, A.E. Nelson, Thermochim. Acta 434 (2005) 55.
[23] N.N. Ruslan, N.A. Fadzlillah, A.H. Karim, A.A. Jalil, S. Triwahyono, Appl. Catal. A:
Gen. 406 (2011) 102.
[24] N.N. Ruslan, S. Triwahyono, A.A. Jalil, S.N. Timmiati, N.H.R. Annuar, Appl. Catal.
A: Gen. 413–414 (2012) 176.
[25] S. Triwahyono, Z. Abdullah, A.A. Jalil, J. Nat. Gas. Chem. 15 (2006) 247.
[26] H. Toraya, S. Yoshimura, S. Somiya, J. Am. Ceram. Soc. 67 (1984) 119.
[27] M.A.A. Aziz, N.H.N. Kamarudin, H.D. Setiabudi, H. Hamdan, A.A. Jalil, S.
Triwahyono, J. Nat. Gas Chem. 21 (2012) 29.
The introduction of Pt on MoO3–ZrO2 did not change much the
crystallinity and BET specific surface area of MoO3–ZrO2 but al-
tered significantly the concentration of acid sites of MoO3–ZrO2.
Particularly, the presence of Pt partially eliminated strong perma-
nent Brønsted and Lewis acid sites on MoO3–ZrO2. The alteration of
the acidity is not due to the Mo loading, as both MoO3–ZrO2 and Pt/
MoO3–ZrO2 have almost similar Mo loading. This alteration may be
due to the small decrease in the crystallinity of ZrO2 during the
treatment. Interaction of molecular hydrogen with MoO3–ZrO2
showed the formation of protonic acid sites with simultaneous de-
crease in the Lewis acid sites through hydrogen spillover phenom-
enon in which the protonic acid sites act as active sites in n-hexane
and n-heptane hydroisomerization. Contrarily, the presence of Pt
on MoO3–ZrO2 lowered the catalytic activity of MoO3–ZrO2. Quan-
titative hydrogen adsorption, ESR and IR spectroscopy revealed
that the presence of Pt enhanced the hydrogen adsorption rate
and capacity of MoO3–ZrO2; however, the interacted-hydrogen
did not successively form active protonic acid sites but intensified
the Lewis acid sites. Therefore, the activity of Pt/MoO3–ZrO2 in the
linear alkane isomerization is lower than that of MoO3–ZrO2 due to
the inability of Pt to promote the formation of active protonic acid
sites from molecular hydrogen on the surface of catalyst. In addi-
tion, the low activity of Pt/MoO3–ZrO2 was not due to the low
Mo loading, as the Mo loading is almost similar for MoO3–ZrO2
with and without Pt. The low activity was also not due to the
low concentration of permanent Brønsted acid sites in which the
permanent Brønsted acid sites have no role in the isomerization.
[28] S. Triwahyono, A.A. Jalil, S.N. Timmiati, N.N. Ruslan, H. Hattori, Appl. Catal. A:
Gen. 372 (2010) 103.
[29] K. Chen, S. Xie, E. Iglesia, A.T. Bell, J. Catal. 189 (2000) 421.
[30] M. Tamura, K. Shimizu, A. Satsuma, Appl. Catal. A: Gen. 433–434 (2012) 135.
[31] S. Triwahyono, T. Yamada, H. Hattori, Appl. Catal. A: Gen. 242 (2003) 101.
[32] M.A. Alotaibi, E.F. Kozhevnikova, I.V. Kozhevnikov, J. Catal. 293 (2012) 141.
[33] M. Busto, C.R. Vera, J.M. Grau, Fuel Process. Technol. 92 (2011) 1675.
[34] P. Sun, G. Siddiqi, W.C. Vining, M. Chi, A.T. Bell, J. Catal. 282 (2012) 165.
[35] S. Triwahyono, A.A. Jalil, H. Hattori, J. Nat. Gas Chem. 16 (2007) 252.
[36] S. Triwahyono, A.A. Jalil, R.R. Mukti, M. Musthofa, N.A.M. Razali, M.A.A. Aziz,
Appl. Catal. A: Gen. 407 (2011) 91.
[37] H.D. Setiabudi, S. Triwahyono, A.A. Jalil, N.H.N. Kamarudin, M.A.A. Aziz, J. Nat.
Gas Chem. 20 (2011) 477.
[38] S. Triwahyono, T. Yamada, H. Hattori, Appl. Catal. A: Gen. 250 (2003) 65.
[39] N. Satoh, J.-i. Hayashi, H. Hattori, Appl. Catal. A: Gen. 202 (2000) 207.
[40] M. Occhiuzzi, D. Cordishi, R. Dragone, J. Phys. Chem. B 106 (2002) 12464.
[41] S. Al-Kandari, H. Al-Kandari, F. Al-Kharafi, A. Katrib, Appl. Catal. A: Gen. 341
(2008) 160.
[42] H. Al-Kandari, F. Al-Kharafi, A. Katrib, Appl. Catal. A: Gen. 361 (2009) 81.
[43] H. Al-Kandari, F. Al-Kharafi, A. Katrib, Appl. Catal. A: Gen. 383 (2010) 141.
[44] H. Al-Kandari, A.M. Mohamed, F. Al-Kharafi, A. Katrib, Catal. Commun. 12
(2011) 1188.
[45] H. Al-Kandari, A.M. Mohamed, F. Al-Kharafi, M.I. Zaki, A. Katrib, Appl. Catal. A:
Gen. 417–418 (2012) 298.
[46] H. Al-Kandari, A.M. Mohamed, S. Al-Kandari, F. Al-Kharafi, G.A. Mekhemer, M.I.
Zaki, A. Katrib, J. Mol. Catal. A: Chem. 368–369 (2013) 1.
[47] T. Matsuda, T. Ohno, Y. Hiramatsu, Z. Li, H. Sakagami, N. Takahashi, Appl. Catal.
A: Gen. 362 (2009) 40.
[48] T. Ohno, Z. Li, N. Sakai, H. Sakagami, N. Takahashi, T. Matsuda, Appl. Catal. A:
Gen. 389 (2010) 52.
Acknowledgments
This work was supported by the Universiti Teknologi Malaysia
(Malaysia) through Research University Grant No. 04H26. Our