Effect of precursor acidity on zeolite supported Pd catalyst properties and hydrodeoxygenation activity for the production of biofuel

Article abstract of DOI:10.1016/j.molcata.2015.01.033

In this study, two different zeolite (ZLT) supported palladium catalysts (Pd/Zs) of varying acidity were synthesized, characterized and tested for biofuel production. The first Pd/Z was synthesized via the incorporation of palladium oxalate complex (PdOxC

Full text of DOI:10.1016/j.molcata.2015.01.033

Accepted Manuscript
Title: Effect of precursor acidity on zeolite supported Pd
catalyst properties and hydrodeoxygenation activity for the
production of biofuel
Author: O.B. Ayodele Hamisu U. Farouk Jibril Mohammed
Yoshimitsu Uemura W.M.A.W. Daud
PII:
S1381-1169(15)00048-5
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2015.01.033
MOLCAA 9416
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
26-11-2014
30-1-2015
31-1-2015
Please cite this article as: O.B.Ayodele, Hamisu U.Farouk, Jibril Mohammed,
Yoshimitsu Uemura, W.M.A.W.Daud, Effect of precursor acidity on zeolite
supported Pd catalyst properties and hydrodeoxygenation activity for
the production of biofuel, Journal of Molecular Catalysis A: Chemical
http://dx.doi.org/10.1016/j.molcata.2015.01.033
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Effect of precursor acidity on Zeolite supported Pdcatalyst properties and
hydrodeoxygenation activity for the production of biofuel
1
,2*
1,3
4,
2
O. B. Ayodele , Hamisu U. Farouk , Jibril Mohammed YoshimitsuUemura , W. M. A.
1
,*
W. Daud
1
Department of Chemical Engineering, Faculty of Engineering, University of Malaya, Kuala
Lumpur, Malaysia
2
Centre for Biofuel and Biochemical Research, Department of Chemical Engineering,
UniversitiTeknologi PETRONAS, Tronoh, Perak, Malaysia.
3
Department of Pure and Industrial Chemistry, Faculty of Science, Bayero University Kano,
P.M.B. 3011, Kano state, Nigeria.
4
Department of Chemical Engineering, Abubakar Tafawa Balewa University, P.M.B 0248,
Bauchi, Bauchi State, Nigeria.
Graphical abstract
Effect of Pd precursor acidity on ZeoliteA properties and activity for the
production of biofuel
*
O. B. Ayodele , Wan MohdAshri Wan Daud
Department of Chemical Engineering, University of Malaya, Kuala Lumpur, Malaysia
*
Corresponding author: Tel +60164955453; E-mail address: ayodele_olumide@yahoo.com
Graphical Abstract
1

6
0
5
0
Pd/Z FPd/Z
4
0
3
0
2
0
1
0
0
n-C18H38
iso-C18H38
C17H36
Products
Gases
Unidentified
Highlights




Synthesis of two different palladium precursors of varying acidity.
Incorporation of the two palladium precursors into zeolite support.
Characterization of synthesized zeolite supported palladium catalyst.
Catalytic hydrodeoxygenation of oleic acid with the synthesized catalysts.
Abstract
In this study, two different zeolite supported palladium catalysts (Pd/Zs) of varying
acidity were synthesized, characterized and tested for biofuel production. The first Pd/Z was
synthesized via the incorporation of palladium oxalate complex (PdOxC) prepared from the
functionalization of H
2
PdCl with oxalic acid at pH 5.3 into ZLT. The PdOxC was further
4
modified with drops of HF until pH 3.7 and incorporated into ZLT to synthesize zeolite
supported fluoride ion modified PdOxC catalyst (FPd/Z). Their characterization results
showed that there is considerable crystallinity loss in Pd/Z, while FPd/Z showed drastic
crystallinity loss according to the SEM and XRD results. In addition, the specific surface area
2
3
2
3
and porosity of ZLT increased from 202 m /g and 0.13 cm /g to 371 m /g and 0.23 cm /g in
2
3
Pd/Z, and 427m /g and 0.29 cm /g in FPd/Z catalysts, respectively. Pd/Z catalyst produces
2

5
6% n-C18H38and 11%iso-C18H38, while FPd/Z produces 58% n-C18H38and 28% iso-C18H38in
the hydrodeoxygenation (HDO) and isomerization (ISO) steps, respectively. The
enhancements in the catalysts properties are due to the acidic effect of OxA via the
incorporation of PdOxC, while the additional enhancements in the properties and the ISO
activity of FPd/Z was ascribed to the acidic effect of fluoride ion modification.It is obvious
that OxA functionalization and subsequent fluoride ion modification are highly invaluable
towards biofuel production.
Keywords: Biofuel; Palladium Catalyst; Hydrodeoxygenation; Isomerization; Oleic Acid
1
.
Introduction
Aluminosilicates have been widely applied over the decades in various areas such as
adsorption in water purification and treatments [1-4], catalysis for different operations such
as production of chemicals, pharmaceuticals and fuel, as well as in environmental air
pollution abatement [5,6]. Clays and zeolites are two typical aluminosilicates that have
received tremendous attention. Kaolinites, bentonite and montmorillonite seem to be the most
studied clay minerals for various research and industrial processes [6-9], on the other hand,
there are over 200 known types of zeolites of different categories and classifications such as
the MCM, Y – types, Z – types, Beta zeolites, N – types, etc used for different applications.
Recently, the application of zeolites is gaining more attention that clays minerals in virtually
every field where aluminosilicates are employed, and as such zeolites are presently being
rapidly synthesized from different clay minerals especially kaolinite [1,2,6,7]. Their
selectivity is one of their excellent qualities that made them interesting material for catalyst
support especially in petroleum and petrochemical industries. Naturally occurring zeolites are
usually impure and contaminated at varying degrees by other materials such as metals,
quartz, or other zeolites types. Consequently, naturally occurring zeolites are not good
3

candidates for many important commercial applications especially where uniformity and
purity are essential, and this explains their recent massive synthetic productions[10].
Zeolite A is one of the zeolite types which hitherto has not been frequently used
perhaps due to its susceptibility to dissolution under severe acid attack and because it is rarely
found pure in nature. It has high thermal and structural stabilities, uniform pore
structure,large surface area and possesses excellent adsorption, screening and ion exchange
performance [11,12].Although the synthesis technique of zeolite A is very mature,
theexploration for more economic and effective raw materials is still the focus of attentions
[
12]. Recently, Hui et al. [11] reported a novel and cheap route of zeolite A production with
improved structural stability from coal fly ash (CFA) which hitherto is a waste product of
combustion of coal in coal-fired power stations with about 800 million tons per annum.
Similarly, as an improvement to the existing zeolite A production from kaolinite via the two
steps procedure of thermal treatment to transform kaolinite into metakaolinte and alkali
treatment, Wang et al. [2] reported the hydrothermal synthesis of high purity zeolite A from
natural kaolin without the thermal treatment step to reduce the cost of production. These and
many another studies [1,2,13-15] have made the production and application of zeolite
Aattractive, however, in all these studies,zeolite A was applied mostly for adsorption and
other related environmental problem.Information regarding its application as catalyst support
for biofuel production is rarely found up till now [14,15], unlike other zeolite types such as
HY and HZSM-5 zeolites[16], NaX zeolite[17], Al-MCM-41 [18]that have been extensively
studied and reported for different feed stocks. Therefore in this study, zeolite A is expediently
modified with two different types of metal-organic frameworkcatalyst precursors. Firstly with
palladium oxalate (PdOxC) freshly prepared via the functionalization of palladium salt with
oxalic acid, and the second, with fluoride ion enhanced PdOxC to study the effect of PdOxC
4

acidity on the synthesized catalysts properties and hydrodeoxygenation and isomerization
activity for the production of high grade biofuel from oleic acid.
2
.
EXPERIMENTAL
2
.1
Materials
Analytical grade zeolite A and hydrofluoric acid (68%) were purchased from F.S.
Chemicals, while dihydridopalladium(IV) chlorideand anhydrous oxalic acid are from Sigma-
Aldrich. All materials were used without any pretreatment.
2
.2
Catalyst Development
Two types of catalysts with varying acidity were synthesized. The first was zeolite
supported palladium catalyst (Pd/Z) synthesized via functionalization of 9.44 mmolof
PdCl with equimolaraqueous oxalic acid (OxA) and was aged for 60 min to guarantee the
H
2
4
formation of the polynuclear palladium (II) oxalate complexes (PdOxC) in an aluminum foil
wrapped 500 ml conical flask because of the metal-oxalate complex photo-sensitivity [19].
The PdOxC was subsequently added gradually to 50 g zeolite (ZLT) dispersion under stirring
for 4 h at 50 ºC for the incorporation of PdOxC particles into the ZLT support, the pH was
observed to stabilized at 5.3 ± 0.3 (usingEcoScan SC11-4115, Exatech Enterprise pH meter)
as the stirring progressed. The second catalyst was synthesized following the same protocol
except that the PdOxC was modified with drops of 1.5 M hydrofluoric acid until the pH of
the fluoride ion modified complex (FPdOxC) was stabilized at 3.7 ± 0.2. The Pd/Z and the
obtained fluoride ion modified zeolite supported palladium catalyst (FPd/Z) wasfiltered and
washed to remove the chloride ions followed by drying at 100 ºC for 12 h and calcined at 400
ºC for 3 h based on some few preliminary studies.
5

2
2
.3
Catalyst Characterization
.3.1 Thermal gravimetric analysis (TGA)
TGA was carried out with a SHIMADZU DTG-60/60H instrument to determine the
heat treatment required during calcination. 2 g of each sample was heated in a silica crucible
o
at a constant heating rate of 10 C/min operating in a stream of N
2
atmosphere with a flow
o
rate of 40 mL/min from 30 to 700 C and the weight loss per time, weight loss per temperature
increment and temperature increment versus time were recorded.
2
.3.2 X-ray fluorescence (XRF)
XRF analysis of the samples were done using a µXay µEDX 100 Schmadzu, NY and
X-ray tube of rhodium anode and scintillation detector operating on a 40 mA current and 40
mV voltage to determine the chemical composition of the sample. High-energy X-rays were
used to bombard the samples pressed into circular discs to cause ionization of their
component atoms.. The detected spectra were amplified and recorded using the computer
program installed on the XRF analyzer.
2
.3.3 Energy dispersive X-ray (EDX)
EDX was performed to determine the elemental composition variation in the
synthesized catalysts compared to the ZLT using EDX microanalysis system (Oxford INCA
4
00, Germany) connected to the FESEM machine. The EDX analysis used Mn-Kα as the
o
energy source operated at 15 kV of accelerating voltage, 155 eV resolutions and 22.4 take
off angle.
6

2
.3.4 Scanning electron microscopy (SEM)
SEM was used to study the surface morphology of all the samples. The analysis was
carried out using a scanning electron microscope (Model EMJEOL- JSM6301-F) with an
Oxford INCA/ENERGY-350 microanalysis system. The samples were evenly distributed on
a black double sided carbon tape attached to the aluminum stub and vacuumed for about 10
min prior to analysis.
2
.3.5 Nitrogen adsorption–desorption measurements (BET method)
N
2
adsorption–desorption measurements were performed at liquid N
2
temperature
o
(
−196 C) with an autosorb BET apparatus, Micromeritics ASAP 2020 to determine the
surface area, pore size and structure, and the pore volume. Before each measurement, the
o
samples were first degassed at 350 C for 2 h and thereafter kept at liquid nitrogen
temperature to adsorb nitrogen.
2
.3.6 X-ray diffraction (XRD)
XRD patterns of the samples were measured with Philip PW 1820 diffractometer to
determine the crystal phase and structure of the samples. Diffraction patterns were recorded
o
o
o
in the range of 5-90 (2 theta) with a scanning rate of 2 /min and a step size of 0.01 with Cu
Kα radiation. The X-ray tube was operated at 40 kV and 120 mA.
2
.3.7 Fourier transformed infrared (FTIR) spectroscopy
FTIR analyses were performed on the samples to determine the functional groups
present in order to understand the chemistry of the synthesized catalyst with respect to the
support. The instrument used is Perkin-Elmer Spectrum GX Infrared Spectrometer with
−
1
−1
resolution of 4 cm operating in the range of 4000-400 cm .
2
.3.8 Raman spectroscopy
7

The Raman spectra of all the samples were obtained with a SpexTriplemate
spectrograph coupled to a Tracor Northern 1024 large area intensified diode array detector.
+
The excitation source was a 488-nm line (Lexel Model No. 95 Ar ) laser with a grating
monochromator used to reject any spurious lines and background from the laser before the
-1
radiation entered the spectrometer. The spectra were taken with 1 cm resolution.
2
.4
Oleic acid hydrodeoxygenation experiments
Oleic acid (OA) was hydrodeoxygenated in a 100 mL high pressure semi-batch
reactor. The catalysts activities on the HDO process were tested at the previously [20] best
observed reaction conditions of 360 °C, 20 bar and 100 ml/min for temperature, pressure and
gas flow rate, respectively.The flow of carrier gas and reaction pressure inlet and outlet were
controlled by a flow (Brooks 58505 S) and a pressure controller (Brooks 5866), respectively.
In a typical experiment,40 g (~45 ml) of OA was added to the reactor followed by a known
amount of catalyst (depending on the type of catalysts to be studied) and the catalyst was
reduced in situ under flowing H at 200 °C for 1 h prior to use after which the reactor was
2
purged with He.The operating temperature was established and monitored by a type-K
Omega thermocouple placed inside the reactor. Before the reaction started, 100 ml/min of 90
vol% N
2
and 10 vol% H was passed through the reactor until the desired reaction pressure
2
was reached and the reaction commences by turning on the stirrer at an earlier predetermined
speed of 2000 rpm. Based on preliminary studies, all experiments were performed under 60
min and the reactor set up was cooled by forced air before dismantled for product analysis.
Liquid samples withdrawn from the reactor were dissolved in pyridine and thereafter silylated
with (100 wt% excess of) N,O-bis(trimethyl)-trifluoroacetamide, BSTFA in an oven at 60 °C
for 1 h prior to GC analysis. The internal standard eicosane, C20H42 was added for
quantitative calculations. The withdrawn samples were analyzed with a gas chromatograph
8

(
GC, HP 6890) equipped with DB-5 column (60m x 0.32mm x 0.5 mm) and a flame
ionization detector. 1 μl sample was injected into the GC with split ratio of 50:1 and helium
was used as the carrier gas. The chromatographic program was well-adjusted to achieve
satisfactory separation of the desired product and the product identification was validated
with a gas chromatograph–mass spectrometer (GC–MS). Since there was technical limitation
in online analysis of the evolved gases (Mgas) during the study, they were calculated
according to Eq. 1, and the product distribution was evaluated using Eq. 2.
Mgas = [M
b
+ MH2 – M
a
]
(1)
(2)
ꢂꢃ
ω (%) =ꢁ
∗ 100
ꢀ
ꢄ
∑
ꢂꢃ
ꢃꢅꢆ
Where M
total H gas required during the experiment evaluated from the H
and M is the mass of the reactor with the liquid product and used catalyst after the reaction.
Similarly, ω (%)is the mass fraction of the components in the liquid product.
b
is the mass of reactor with the OA and catalyst before reaction, MH2 is the mass of
2
2
flow rate and its density
a
i
3
3
3
.
RESULTS AND DISCUSSION
.1
Catalyst characterization
.1.1 X-Ray Fluorescence
The XRF spectra of ZLT, Pd/Z and FPd/Z are shown in Fig.1, the spectrum of ZLT
showed its characteristics peaks between 0.51 and 23 keV. The successful intercalation of
PdOxC into the framework of ZLT support is seen in the XRF plot of Pd/Z at Lβ of 3.20keV
1
and another growing peak is observed at 21.2 keV which possibly confirmed successful
dispersion of Pd from PdOxC since Pd(Kα) is only metal that has such peak at 21.2 keV
9

according to the EDXRF-EPSILON 3 XL, PANalytical standard card. However, in contrast
with the two Pd peaks observed in the Pd/Z catalyst, FPd/Z catalyst showed three Pd peaks at
Lα
1
of 2.99 keV, Lβ of 3.20 and 21.2 keV, in addition, the Pd peaks in the FPd/Z catalyst
1
appeared to be comparably more intense than those in the Pd/Z catalyst. These suggest that
the effect of fluoride ion functionalization is effective at guaranteeing higher Pd particle
dispersion and probably minimizes the degree of hydration effect on the active metal during
the catalyst synthesis stage as seen in Table 1.
1
0

Fig.1 XRF spectra of ZLT, Pd/Z and FPd/Z samples
1
1

3
.1.2 Energy Dispersive X-Ray (EDX)
The elemental composition of the ZLT, Pd/Z and FPd/Z samples in Table 1 showed
that silica and alumina are the main components of ZLT with some oxides of calcium and
sodium, its Si/Al ratio was found to be ~1.02 which is typical of zeolite A. After successful
incorporation of acidic PdOxC and FPdOxC catalyst precursors into ZLT and calcination, the
Si/Al ratio increased to 2.2 and 3.45,respectively in Pd/Zand FPd/Z catalysts(Table 1) due to
the reduction in framework and extra-framework aluminum.Typically, reduction/removal of
framework and extra-framework alumina has been ascribed to effect of thermal treatment and
protonation from acid attacks, respectively [19]. However, since both catalysts were
subjected to same thermal treatments, the comparably higher Si/Al ratio of FPd/Z compared
to Pd/Z was ascribed to the effect of fluoride ion functionalization at the synthesis stage.
Table 1 Elemental composition of ZLT, Pd/Z and FPd/Zsamples
Elemental composition (%)
Sample
Si/Al
Si
Al
O
2
Na
Ca
F
Pd
ZLT
16.88 16.48 49.58 12.41 4.65 0.00
0
1.02
2.20
3.45
Pd/Z
FPd/Z
21.11 9.59
22.37 6.44
55.90 8.70
54.81 4.51
2.81 0.00 1.89
1.71 8.30 1.86
Both Pd/Z and FPd/Z catalysts showed increment in the amount of O which can be
2
ascribed to the presence of oxalate functional group of the PdOxC and FPdOxC precursors.
Similarly the incorporation of Pdearlier seen in Fig. 1 and Table 1can be further corroborated
in Fig.2(b,c)between the 2.0 and 3.8 keV in the EDX spectra which also showed the presence
of fluoride ion in the FPd/Z catalyst (Fig.2c). From Table 1, the observed quantity of
Pd(average of three runs) in Pd/Z and FPd/Z catalysts is1.89% and 1.86% which is slightly
1
2

lower than the calculated 2% and this probably could be due to the effect of degree of
hydration at the catalyst synthesis stages [8].
Fig.2 EDXand SEM of ZLT, Pd/Z and FPd/Z samples
1
3

3
.1.3 Scanning Electron Microscopy (SEM)
The SEM morphology of the ZLT, Pd/Z and FPd/Z samples shown inFig.2
(
inset)revealed conspicuous degree of morphological variations in Pd/Zand FPd/Z catalysts
which are expected to have a substantial contributory effect on their catalytic activities.The
morphology of ZLT inFig.2a (inset)depictsagglomerates of sharp micro-sized cubical
symmetry crystal structure [12,20,21] which can be seen to have loss considerable
crystallinity in Pd/Z (Fig.2b (inset))and become apparent amorphous in FPd/Z (Fig.2c (inset))
after the catalyst synthesis. The loss of crystallinity in both catalystscan be seen to have
considerably reduced their particles sizes with attendant increase in surface area compared to
the ZLT supportas shown in Table 2 (BET analysis). As earlier mentioned,
aluminosilicatesusually experience loss of crystallinity under acid influence and thermal
treatment which is usually accompanied by increase in the specific surface area, and such
lossof crystallinity is a function of the acid type and concentration as well as the degree of
thermal treatment [22].The considerable loss of crystallinity in Pd/Z can be ascribed to the
combined effect of OxA functionalization and proper calcination at the Pd/Z synthesis stage
resulting in dealumination from the lattice structure, while the apparent amorphous observed
in FPd/Z can be ascribed to the additionalcrystallinity loss due to intense dealuminationeffect
from fluoride ion. This result further corroborates earlier observation in Table 1.
3
.1.4 Nitrogen Adsorption/Desorption Isotherm
As earlier observed in the catalysts morphology micrographs that the effects of
OxAfunctionalization and thermal treatment resulted into loss of crystallinity which is more
severe in the FPd/Z catalyst due to the fluoride ion modification, the textural properties
results of the samples in Table 2 showed that there is reduction in the average particle sizes
(
APS) of Pd/Z and FPd/Z compared to the ZLT. As expected, the reduction in the APS can be
seen to have increased the specific surface area and porosityof both Pd/Z and FPd/Z, as usual,
1
4

these enhancements are more pronounced in the FPd/Z catalyst due to the additional effect of
fluoride ion modification.From the isotherms of the samples shown in Fig. 3, ZLT sample
exhibited Type II isotherms at lower relative pressures which is a characteristic of the
formation of monolayer followed by multilayer [23]. However, after catalyst synthesis, both
Pd/Z andFPd/Z eventually conformed to Type IV isotherm with the steep uptake of N owing
2
to the development of inter-particle voids formed by agglomeration of the micro- or nano-
sized and plate-like particles containing slit-shaped pores which are typical of H3 hysteresis
loop [3,7,23]. This observation is typical of solids having considerable degree
ofmesopores[19].Theincrease in the amount of N adsorbed in the Pd/Zand FPd/Zcompared
2
to ZLTalso supports the data in Table 2 which is in accordance with previous reports that loss
of crystallinity usually leads to increase in the pore volume and specific surface area [19-23].
As expected, the FPd/Z showed more N
2
uptake and wider hysteresis loop than Pd/Zdue to
the effect of the fluoride ion modification.
Table 2
Textural properties of ZLT,Pd/Z andFPd/Z samples
Sample
Surface area Pore volume Pore diameter Average Particle
2
3
(
m /g)
(cm /g)
(nm)
size (nm)
10404
4655
ZLT
202
371
427
0.13
0.23
0.29
10.41
14.58
20.11
Pd/Z
FPd/Z
2534
1
5

9
8
7
6
5
4
3
2
1
00
00
00
00
00
00
00
00
00
0
ZLT - Adsorption
ZLT - Desorption
Pd/Z - Adsorption
Pd/Z - Desorption
FPd/Z - Adsorption
FPd/Z - Desorption
0
0.2
0.4
0.6
0.8
1
Relative pressure (P/P )
o
Fig. 3 Nitrogen adsorption/desorption isotherm of the ZLT,Pd/Z and FPd/Z samples
3
.1.5 X-Ray Diffraction (XRD)
The XRD pattern for the ZLT support and the synthesizedPd/Z and FPd/Z catalysts
are shown in Fig. 4. According to the JCPDS card 43-0142, the characteristics peaks at 2θ =
.2°, 10.0°, 12.4°, 16.06°, 21.64°, 24.0°, 27.10°, 30.0°, 34.16°, 43.6° and 52.3° in the ZLT
7
support are typical of highly crystalline Zeolite A [11,12]. After the catalyst synthesis, Pd/Z
showed considerable crystallinity loss while FPd/Z reflects almost complete amorphous
structure. These observations corroborate the earlier results seen in the samples SEM
morphology and it was ascribed to the varying intensities of acid attack and also the thermal
treatment that removes extra framework and framework aluminum, respectively leading to
increase in their Si/Al ratios (Table 1).
1
6

1
1
1
1
6000
4000
2000
0000
7
.2
ZLT
Pd/Z
FPd/Z
1
0.1
2.4
8
6
4
2
000
000
000
000
0
2
4
2
9.8
1
27
3
4.1
2
1.6
1
6
38.2 43.6
40
52.3
5
7.9
0
10
20
30
Theta (deg)
50
60
2
Fig. 4 X-ray diffraction of the ZLT, Pd/Z and FPd/Z samples
Typically, loss of crystallinity has been ascribed to proper calcination which in turn
improves the catalytic activity of the synthesized catalysts, in fact Jiaet al.,[24]reported a
linear relationship between excessive thermal treatments and crystallinity (i.e. crystal growth)
but an inverse correlation with catalytic activity. Consequently, the loss of crystallinity in the
Pd/Z and FPd/Z catalysts indicates high Pddispersion in the matrix of ZLT support which is a
pointer to excellent catalytic activity [21]. In addition, the absence of bulk Pd peaks that are
usually seen around 2θ = 18° and 34° [18,25] further confirmed that the Pd particles are
highly disperseddue to increase in thecatalysts acidity at synthesis stage [21,26], i.e. OxA
functionalization in both catalysts and additional fluoride ion modification on
FPd/Z.Furthermore, in view of the minuscule quantity of Pd used during the synthesis (Table
1
) there is speculation that the Pd particles might also have been partly covered by the ZLT
particles. However, the lowering of the diffraction between 2θ of 2.3° and 5.4° in Pd/Z owing
to the expansion of the ZLTlattice structure due to intimate contact of the incorporated
1
7

PdOxC [21], and the presence of the miniature peaks at 38.4°, 44.6° and 58.7° in FPd/Z
further confirmed the successful incorporation of Pd particles into the matrix of the ZLT
support.
3
.1.6 Thermal Gravimetric Analysis (TGA)
The TGA profiles of ZLT, Pd/Z and FPd/Z as well as that of the uncalcinedPd/Z and
FPd/Z are shown in Fig.5a-b.All the samples showedthree characteristics weight loss regions
WLR) typical of the aluminosilicates. Thefirst WLRis due to loosely held moisture and
(
physisorbed water that can be rapidly removed at a temperature around 150 °C[4,9]. The
second WLRwhich is usually observe between 200-500 °Cwas ascribed to the existence of
strongly bonded water molecules that are domiciled in the first coordination sphere and also
probably due to partial occlusion of organic matter [3,19]. The thirdWLR comprises of
thestructural hydroxyl groups that will condense and dehydrateat temperaturesabove 500 °C
[
9,19].A careful study of Fig. 5 shows that the uncalcined catalysts showed increase in weight
loss compared ZLT due to the hydration effect of the catalyst precursors(PdOxC and
FPdOxC)incorporation into ZLTat the catalystssynthesis stages. Although the weight loss is
not very pronounced in the first weight loss region ostensibly due to the effect of drying at
1
00 °C for 12 h, which implied that the drying stage was able to reduce considerable amount
of physissorbed and freely bounded water molecules [19].
1
8

1
00
(a)
ZLT
9
9
8
8
5
0
5
0
Pd/Z (uncalcined)
Pd/Z
0
100 200 300 400 500 600 700
Temperature (ºC)
1
00
(b)
9
5
ZLT
FPd/Z (uncalcined)
FPd/Z
9
8
8
7
0
5
0
5
0
100 200 300 400 500 600 700
Temperature (ºC)
Fig.5 Thermal Gravimetric Analysis of (a) ZLT and Pd/Z, (b) ZLT and FPd/Z.
Furthermore, it can be observed that there is a marginal increase in the weight loss of
the uncalcined Pd/Z, but the weight loss in the uncalcinedFPd/Z is very conspicuous due to
the effect of protonation from the fluoride ion modification at the FPd/Z synthesis stage that
increased the surface area and the amount of amorphous silica (BET, EDX and SEM results),
1
9

thereby increasing the amount of adsorbed and strongly bonded water. This observation is
also consistent with previous study where phosphoric acid was employed [19]. The observed
increase in the weight loss of the uncalcined catalysts even after drying is an indication that
their synthesis protocol was able to guarantee the penetration of aqueous catalyst precursor
into the lattice structure of ZLT. After calcination at 400 °C, both Pd/Z and FPd/Z showed
reduction in weight loss, which suggests that the thermal treatment during the calcination step
was adequate to expel both the physisorbed, strongly bonded water moleculesand any
occluded organic matter thus leaving behind only the PdOxCand FPdOxC particles,
respectively on the ZLT support. Previous works have shown that adequate calcination
around 400 °C increases catalyst surface area and pore volume which in turn increases the
number of active sites thereby guaranteeing a high active metal dispersion [4,21].
3
.1.6 Fourier’s Transform Infrared Spectroscopy (FTIR)
The FTIR spectrums of the ZLT support, Pd/Z and FPd/Zare presented in Fig.6. The
ZLTsample reflects the existence of strongly bondedzeolitic water in the region 3665 –2980
-1
-1
-1
cm with a minimal around 3366 cm and another band at 1655 cm which is attributed to
physisorbed water molecules vibration [3,4]. Previous reports [18,27] have shown that the
presence of these water molecules is detrimental to the activities of HDO catalysts due to
agglomeration of active metal. According to the authors, proper calcination has been highly
invaluable to reduce or completely remove the water molecules thus guarantee proper active
metal dispersion. From Fig. 6, it is obvious that the thermal treatment during the calcination
-1
-1
step is adequate as the water molecule bands at 3665 – 2980 cm and at 1655 cm had
completely disappeared in both Pd/Z and FPd/Z, and this observation corroborates the result
in the samples TGA profile in Fig. 5.
2
0

110
6
75
9
40
1
00
9
8
7
6
0
0
0
0
ZLT
1
655
1
200
Pd/Z
FPd/Z
3
366
3
665
2
980
5
76
4
000
3600
3200
2800
2400
2000
1600
1200
800
400
-1
Wavenumber (cm )
Fig.6 FTIR spectra of ZLT, Pd/Zand FPd/Z samples
According to Li et al.[26], the presence of exchangeable cations and incorporated
-
1
active metals in aluminosilicates are usually seen in the lower wavenumber below 1000 cm
-1
especially in the region 900 - 600 cm . A carefully analysis of the three spectrums (excluding
-
1
the reflections of water molecules) shows that there is a good match until around 1200 cm
-1
and the mismatch became obvious below 1000 cm especially with the relocation of the
-1
-1
strong absorption at 940 cm in ZLT support to 1050 cm in Pd/Z and FPd/Z. Similarly, the
-1
-1
moderate absorption band at 675 cm in the ZLT support also relocated to 753 cm with
reduced intensities in both Pd/Z and FPd/Z, and it almost disappeared in the latter probably to
the fluoride ion modification. These observations are indications of successful formation of
Si-O-Pd bond due to the incorporation of Pd into the ZLT matrix [4]. In addition, the
-1
appearance of a new miniature band at 576 cm can be ascribed to the formation of another
bond between Pd particles and Si–Al structure of the support [25].
2
1

4
.4.1.8 Raman Spectroscopy
The Raman spectrums in Fig.7showed thecharacteristic bands of ZLT, Pd/Zand FPd/Z
samples.Characteristics distinctive peaks of Zeolite A are observed in the spectrum of ZLT at
-1
2
80, 330, 400, 490, 700, 977, 1030, 1150 and 1457 cm . Previous work [28] on Raman
spectroscopy characterization of zeolite A has shown that it possesses 4-, 6- and 8-membered
-1
rings, and smaller rings give bands at higher frequency. Consequently, the band at 280 cm
in the ZLT sample can be assigned to the bending mode ofthe 8 membered rings. Similarly,
-1
the bands at 330 and 410 cm are due to the bending mode of 6-membered Si-O-Al rings
-1
while the strongest band at 490 cm is assigned to the bending mode of 4-membered Si-O-Al
-
1
rings[28]. Typically, Raman bands in the region of 600 – 900cm are assigned to symmetric
-1
T–O stretching modes, on the other hand, the bands at 977, 1030 and 1150 cm are ascribed
-1
to asymmetric T–O stretching motions. A clearly distinctive band at 800 cm which
obviously is not a characteristic of zeolite A can be seen in spectrum of ZLT which possibly
-1
signifies the presence certain impurities since Raman peak at 800 cm is typical of 5-
memebered ring of zeolite ZSM-5.
The effect of the catalysts precursors (i.e. PdOxC and FPdOxC) incorporation into the
ZLTcan be observed to have developed series of multiple stretches of background noise-like
vibrations (BNV) in the Pd/Zand FPd/Z catalysts. These BNV according to Ghule et al., [21]
2
-
reflectsthe presence of carbonate anion (CO
3
) from organics (i.e. oxalate) with D3h
symmetry usually exhibiting four normal vibrational modes which consist of a symmetric
-
1
-1
stretching vibration (ν
1
) around 1063 cm , an out-of-plane bend (ν
2
) around 879 cm , a
) around 1415 cm and lastly doubly degenerate
) around 680 cm [29].The presence of these BNV even after calcination
implied that the Pd particles in the Pd/Zand FPd/Z retained their oxalate ligand structure [21].
-
1
doubly degenerate antisymmetric stretch (ν
3
-1
bending mode (ν
4
-
1
After the catalyst synthesis, earlier bands seen at 490 and 1150 cm in the ZLT were seen to
2
2

-1
have slightly denatured and shifted to 480 and 1120 cm , respectively in both the Pd/Z and
-1
FPd/Z, while the band at 800 cm disappearedcompletely probably due to the acidic effect of
oxalic acid functionalization and calcination that resulted into loss of crystallinity earlier
observed in the SEM and XRD results (Fig. 2(inset) and Fig. 4). The comparably severe loss
of crystallinity in the FPd/Z catalyst compared toPd/Z earlier observed in the SEM and XRD
results which gave rise to its comparably higher Si/Al ratio (Table 1) also explains why
-1
certain peaks such as at 443, 480, 575, 740, 1040 and 1120 cm are less intense in the FPd/Z
-1
-1
catalyst. The new band at 443 cm and the bands at 648, 740 and 928 cm confirmed the
presence of dispersed palladium particles in the Pd/Z and FPd/Z catalyst [18,25,27].
ZLT
Pd/Z
FPd/Z
4
2
0
-
2
2
00
300
400
500
600
700
800-1 900
1000 1100 1200
Wavenumber (cm )
Fig.7 Raman spectra of ZLT, Pd/Zand FPd/Z samples
3
.2
Catalytic activities of Pd/Z and FPd/Z on the hydrodeoxygenation and isomerization
of oleic acid into biofuel
2
3

Recently in attempt to gain thorough insight into the hydrodeoxygenation (HDO)
process of different feed stocks, studies onreaction variablessuch as effects of reaction
pressure and temperature, H gas flow rate, catalyst loading and even types of reactors and
2
mode of operations have been well studied and reported[20,30-34]. However, since existing
hydrotreating units of conventional crude oil refineries can be adapted for the HDO process
of biofuel production, studies on expedient synthesis of suitable catalysts such as types of the
support and metals [34], systematic catalyst preparation procedure [20,26,35]and additives
such as sulfur [36]and phosphorus [31]are currently receiving attention.In this direction, we
recently, functionalized nickel with oxalic acid and supported on alumina for the
hydrodeoxygenation of oleic acid into high grade biofuel [18]. At the best operational
conditions of 20 bar, 360 ºC and 100 ml/min of gas flow, the catalystshowed superior
activities to other alumina supported Ni catalysts in literature. In addition, the catalyst was
able to achieve skeletal isomerization of already hydrodeoxygenated n-paraffin due to the
effect of the oxalic acid functionalization.
As a step further, in this work we modified palladium oxalate catalyst with fluoride
ion and compared its activities with unmodified palladium oxalate catalyst at the earlier best
observed operation condition for the HDO of oleic acid and the result is shown in Fig. 8. It is
very obvious that FPd/Z possesses both higher HDO and isomerization activities compared to
Pd/Z. Even thoughPd/Z and FPd/Z showed almost same n-C18
the latter has superior isomerization ability confirmed that it is more prospective for industrial
application since it is well known that n-C18 38produced in the HDO step is the substrate for
the isomerization step to produce the iso-C18 38. The enhanced HDO activity of FPd/Z
H38quantity, but the fact that
H
H
compared to Pd/Z was ascribed to its increased acidity at the synthesis stages which
improvesthe solubility ofPd in the support and facilitates the formation of Pd (II) polynuclear
complex which in turn guarantees high Pd dispersion as seen in the XRD result (Fig. 4). In
2
4

addition, its increased acidity also modified its morphology from crystalline into amorphous
Fig. 2 (insets)) and enhanced its textural properties (Table 2) which in turn increases the N
adsorption/desorption isotherm hysteresis loop as shown in Fig. 3. This observation is in
agreement with the works of Li et al. [26] on the functionalization of NiMo/γ-Al catalysts
(
2
2
O
3
with varying quantities of urea. They reported that the urea functionalization greatly enhances
the textural propertiesand the solubility of Mo and Ni particles in the support as well as
facilitates the formationof molybdate and polymolybdate species due to increased acidity.
6
0
5
0
Pd/Z FPd/Z
4
0
3
0
2
0
1
0
0
Products
Fig. 8 Product distribution of the HDO of oleic acid at 360 ºC, 20 mg catalyst loading, 20
bar, 10% H gas flow and 60 min.
2
Generally, aluminosilicates gradually transform from crystalline form into amorphous
under acid attacks [19,37] thus leading to increase in Si/Al ratio as seen in Table 1. Such
2
5

transformation is usually accompanied with reduction in particle size which in turn increased
the specific surface area and porosity as observed in Table 2.Such morphological and textural
properties variation has been reported to increase catalyst activities by ensuring well
dispersed activemetal particles[22,26]. Therefore, the enhanced textural properties of FPd/Z
compared to Pd/Z will equally provide additional and sufficient surface area for active metal
incorporation and also guarantee unrestricted access for the reacting molecules owing to
enhanced porosity[19,22]. Furthermore, both catalysts were seen to produce isomerized
products, while FPd/Z produces about 28% iso-C18
H38, Pd/Z produces only 11%. The
presence of the iso-C18 38 was due to FPd/Z increased acidity.Previous studies [32,35]have
H
shown that catalysts with increased acidity are highly favorable forparaffinskeletal
isomerization. Typically, the presence of isomerized product is considered an advantage due
to the ability of iso-paraffin fractions to lower the biofuel freezing point by about 20 ºC since
n-paraffin (C16–C18) has comparable high freezing point (between 18 ºC and 28 ºC) which is
a disadvantage to their cold flow properties such as cold filter plugging point [32,38]. The
increased iso-C18
ion functionalizationwhich further increased the acidity of FPd/Z. The presence of C17
Fig. 8 when using Pd/Z confirmed instances of decarboxylation or decarbonylation, and this
is further corroborated by the increase in the amount of gases (such as CO /CO).
H38content in FPd/Z compared to Pd/Z was unarguably due to the fluoride
H36in
2
Unfortunately, as earlier commented (Section 2.4)the online identification and quantification
of these gases were not technically feasible during this study, hence determination of the gas
species was not possible. The amount of the lumped unidentified products such as unreacted
oleic acid, oligomerized products and other functional group is also higher in Pd/Z showing
that its activity and selectivity is comparably inferior to FPd/Z. It is obvious that effect of
fluoride ion functionalization is highly invaluablesince only the iso-paraffin content of FPd/Z
fall within the range (20 – 40%) reported by Šimácˇek et al. [39] that could significantly
improve the cold flow properties (CFPP, pour point, cloud point, etc.) of biofuel.
2
6

4
.
Conclusion
Two different zeolite supported catalysts were synthesized from palladium
functionalized with oxalic acid, one was further modified with fluoride ion to increse its
acidity. The fluoride ion modified palladium oxalate zeolite supported catalyst (FPd/Z)
showed considerable enhancement in textural properties and loss of crystallinity compared to
the palladium oxalate zeolite supported catalyst (Pd/Z) due to the effect of the fluoride ion. In
addition, the FPd/Z also showed relatively stronger Pd intensity according to the EDX results
as well as higher Pd dispersion. Their catalytic activity tested at 20 bar, 360 ºC, 100 ml/min
of H
similar hydrodeoxygenation activities producing 56% n-C18
respectively, but FPd/Z has superior isomerization ability producing 28% iso-C18
Pd/Z produces 11%iso-C18 38. Finally, the results showed that with expedient synthesis
2
gas flow and 20 mg of each catalyst loading showed that both Pd/Zand FPd/Z shared
H38 and 58% n-C18
38
H ,
H38while
H
protocol, cheap zeolite A can be successfully used as biofuel hydrodeoxygenation and
isomerization catalyst support to cut down production cost and make the process
economically attractive.
Acknowledgment
The authors sincerely acknowledge thefinancial support from Higher Impact Research
–
Minisrty of Higher Education project no D000011-16001 of the Faculty of Engineering,
University of Malaya.
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