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Transesterification of canola oil as biodiesel overNa/Zr-SBA-15 catalysts: Effect of zirconium content

Wen-Kang Chen a, Hui-Hsin Tseng b,c,*, Ming-Chi Wei d, En-Chin Su b,c,I.-Ching Chiu b,c

a National Tainan Institute of Nursing, Tainan City 700, Taiwan, ROCb School of Occupational Safety and Health, Chung Shan Medical University, Taichung 402, Taiwan, ROCc Department of Occupational Medicine, Chung Shan Medical University Hospital, Taichung 402, Taiwan, ROCd Department of Food Science, Central Taiwan University of Sciences and Technology, Taichung 402, Taiwan, ROC

a r t i c l e i n f o

Article history:

Received 31 May 2014

Received in revised form

25 August 2014

Accepted 26 August 2014

Available online 16 October 2014

Keywords:

Biodiesel

Transesterification

Acidic catalyst

Zr-SBA-15

* Corresponding author. Department of OccuTel.: þ886 4 24730022; fax: þ886 4 23248194.

E-mail address: hhtseng@csmu.edu.tw (Hhttp://dx.doi.org/10.1016/j.ijhydene.2014.08.10360-3199/Copyright © 2014, Hydrogen Ener

a b s t r a c t

A series of mesoporous Zr-SBA-15-supported Na catalysts was prepared and applied to the

heterogeneous catalysis of canola oil transesterification. The effects of Si/Zr ratio, reaction

time, and percentage of Na loading on the conversion to fatty acid methyl esters (FAME)

were studied. The dependence of the textural structure and chemical properties of Zr-SBA-

15 supports on Zr content was investigated using small-angle X-ray diffraction, Brunauer

eEmmetteTeller analysis, transmission electron microscopy (TEM), and Fourier transform

infrared (FTIR) spectroscopy. The results obtained from FTIR and TEM indicate that the

incorporation of Zr atoms into the SBA-15 structure facilitated the formation of Br€onsted

acid sites and decreased the particle size of Na species. Catalysts with a higher Zr content

enhanced the FAME yield. The optimum conditions determined were as follows: reaction

temperature of 70 �C, 15 wt.% Na, reaction time of 6 h, and 12% catalyst content (wt.% oil)

with a methanol/oil molar ratio of 6:1. The optimum conditions resulted in a FAME yield of

up to 99%.

Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

Introduction

The continuous consumption of traditional fossil energy re-

sources and increasing environmental concerns have

prompted extensive research on renewable fuels. According

to a recent study from the International Energy Agency, only

energy produced from renewable sources and waste has the

highest potential to replace fossil fuels, especially for trans-

portation. Among such sources, combustible fuels and waste

accounted for 10% of the world's total energy supply from fuel

pational Medicine, Chun

.-H. Tseng).54gy Publications, LLC. Publ

[1]. Hence, renewable energy from combustible energy, such

as biodiesels, is predicted to enter the energy market in the

near future to diversify the global energy source.

Biodiesel, which is an alternative, non-toxic, and eco-

friendly diesel fuel, was developed to ensure energy avail-

ability at an affordable price and to prevent environmental

damage [2e4]. The triglyceride transesterification of edible oils

with methanol to obtain biodiesel in the form of fatty acid

methyl ester (FAME) is a commonly used method. Biodiesel

can be obtained from the transesterification of vegetable oil or

animal fats in the presence of short-chain alcohols and

g Shan Medical University Hospital, Taichung 402, Taiwan, ROC.

ished by Elsevier Ltd. All rights reserved.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 9 ( 2 0 1 4 ) 1 9 5 5 5e1 9 5 6 219556

catalysts. However, vegetable oil and animal fat contain

numerous free fatty acids (FFA) and water, resulting in soap

formation that significantly affects conversion during the

transesterification reaction. The transesterification of edible

oils can be catalyzed by a homogeneous or heterogeneous

base and acid catalysts [4]. Among these catalysts, heteroge-

neous acid catalysts can simultaneously esterify FFA and

transeterify triglycerides, even in the presence of 9% FFA

[5e7]. Therefore, both vegetable and waste oils can be used in

transesterification when acid catalysts are applied to reduce

production costs [8].

Ordered mesoporous zeolites, such as SBA-15, MCM-41,

and hexagonal molecular sieves (HMS), have recently received

considerable attention in industrial applications involving

catalysis and organic transformations because of their large

surface area and controllable pore size [9,10], which enable

reactions to involve larger molecules. Among these zeolites,

silica SBA-15 shows higher thermal and hydrothermal stabil-

ities than MCM-41 or HMS [11]. However, the pure-silica SBA-

15 lacks Br€onsted-acid sites and usually exhibits only mild

Lewis-acid sites and low catalytic activity due to absence of

heteroatom active sites. Thus, the acidity and activity of silica

SBA-15 requires further enhancement andmodification when

applied in catalytic reactions [12,13]. Many studies have been

conducted on improving the surface acidity of silica SBA-15 by

substituting othermetals, such as Al, Ti(IV), Sn(IV), or Zr(IV), in

the silica matrix. This substitution mainly creates Br€onsted

acidic sites [14] or Lewis acidic sites [8], depending on the

synthesis conditions. Generally, the heteroatom can be sub-

stantially incorporated through post-synthesis or direct-

synthesis (also called one-pot synthesis) method. This pro-

cess of incorporation grafts the heteroatom onto a calcined

sample or copolymerizes a metal precursor in the presence of

an organosilane solution [15]. Although the heteroatom-

containing SBA-15 is mainly prepared using the post-

synthesis method to achieve high heteroatom loading, this

method usually destroys the framework of SBA-15, especially

at high heteroatom loadings, because of a complicated syn-

thetic process that uses solvent in a strict condition for

preparation [11,16]. For example, Kao et al. synthesized Al-

SBA-15 using aqueous (NH4)3AlF6 as the aluminum source

and by adjusting the pH of the solution to 9.3 to avoid a con-

dition with strongly acidic reactions [17]. Another disadvan-

tage of these post-synthetic methods is the tendency of metal

oxides to appear in the channel or on the external surface of

the pore wall, which would negatively affect the catalytic ac-

tivity [17,18].

Among these zeolites, mesoporous Zr-SBA-15, which

functions as a beneficial catalyst and a suitable catalytic

support [19], has received considerable attention for its

acidity-generating characteristics. Ijlesias et al. [20] reported

that the synthesis of Zr-SBA-15 materials results in highly

acidic properties and reveals high catalytic activity in trans-

esterification, with the FAME yield reaching over 70%. How-

ever, further incorporation of titanium, molybdenum, and

tungsten as doping metals does not translate into higher

catalytic activity.

Based on this premise, we present the synthesis of Zr-SBA-

15 materials using the direct-synthesis method and the

coating active site using the impregnation method. The use of

Zr-SBA-15 as support resulted in high catalytic activity in the

transesterification reaction compared with previous studies.

The effect of different experimental parameters such as re-

action time, Na catalyst loading weight, and reusability were

also investigated.

Experimental

Catalyst preparation

A series of Zr-SBA-15 supports was synthesized according to a

previously described method [4,21]. In a typical procedure, 5 g

of a pluronic triblock copolymer P123 was dissolved in 2 MHCl

solution at room temperature for 1 h. After the copolymer was

completely dissolved, 11.5 ml of tetraethyl orthosilicate was

added drop wise to the synthesis medium. An appropriate

amount of ZrOCl2$8H2Owas added to achieve the desired Si/Zr

molar ratios: 10, 30, or 50. The suspension was then stirred for

3 h and aged at 110 �C for 24 h. The solid product was collected

through filtration, washed with acetone, and air-dried at

110 �C overnight. Calcination was performed in air at 500 �Cfor 6 h, and the product was denoted as Zr-SBA-15(X), where X

is the Si/Zr molar ratio in the initial gel. For comparison, the

Zr-free SBA-15 sample was synthesized using the same pro-

cedure but without the introduction of ZrOCl2$8H2O and

denoted as SBA-15.

The active site of Na was deposited on the surface of Zr-

SBA-15 support using a conventional impregnation method.

The Zr-SBA-15 support was introduced to various calculated

amounts of NaOH aqueous solution, which were 5, 12, and

15 wt.% of the loading weight in the supported catalyst. After

24 h, the catalyst was dried at 105 �C overnight, followed by

calcination at 400 �C in air for 4 h. The obtained sample was

denoted as YNa/Zr-SBA-15(X), where Y represents loading

weight. The ordered structure of Na-loaded Zr-SBA-15 was

further analyzed with low-angle XRD to confirm that it can

withstand the impregnation solution treatment. For the

sample loaded with Na, a well-resolved XRD pattern with a

prominent peak (100) and two weak peaks (110 and 200) were

observed at around 2q ¼ 1� and 2q ¼ 2�, which is consistent

with the XRD patterns of silica Zr-SBA-15 (Fig. 1).

Characterization

Small angle X-ray diffraction (SAXRD) data were obtained

using a Siemens D5005 (40 kV, 30 mA) with a nickel-filtered

Cu-Ka radiation and a wavelength of 0.15406 nm. The

diffraction patterns were collected under ambient conditions

in the 2q range between 0.2� and 5� at a scanning rate of 1�/min. The a0 unit-cell parameter was estimated from the po-

sition of the (1 0 0) diffraction line (a0 ¼ d100� 2=ffiffiffi3

p) [22].

Inductively coupled plasma with atomic emission spectros-

copy (ICP-AES) technique was used to determine the actual Zr

and Na contents in the catalysts on a Varian Vista-PRO AX

CCD-simultaneous ICP-AES spectrophotometer. Previously,

solid samples were digested with acid solution.

Nitrogen adsorptionedesorption isotherms were obtained

at �196 �C using a surface area analyzer. The surface area

values were calculated using the BrunauereEmmetteTeller

Fig. 1 e Law angle XRD patterns of SBA-15 and Zr-SBA-15

with various Si/Zr ratios.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 9 ( 2 0 1 4 ) 1 9 5 5 5e1 9 5 6 2 19557

(BET) method, and the pore size distributions were deter-

mined using the PMI Automated BET Sorptometer (201AEL).

Transmission electron microscopy (TEM) images were ob-

tained using a Philips CM 200 LaB6 operating at an accelerating

voltage of 200 kV. The solids were ultrasonically dispersed in

ethanol, and the suspension was deposited on a copper grid

with carbon support. Infrared spectra were obtained using a

Shimadzu Fourier Transform Instrument (FTIR-8300) using

KBr pressed powder discs.

Transesterification tests

The transesterification of canola oil with methanol was per-

formed in a three-necked round-bottom flask with a volume

of 150ml. The flask was equippedwith a reflux condenser and

heated in a precisely controlled oil bath at atmospheric pres-

sure. In a typical run, 5.35 g of the catalysts and 9.6 ml

Table 1 e Textural and structural characteristics of SBA-15 and

Material Si/Zr molarratioa

Naa loading(wt%)

Nab/Zrb loadingthe spent catal

Gel Product

SBA-15 ∞ ∞ e e

Zr-SBA-15(50) 50 83.46 e e

Zr-SBA-15(30) 30 62.31 e e

Zr-SBA-15(10) 10 27.60 e e

5Na/SBA-15 e e 4.61 e

5Na/Zr-SBA-15(50) e e 4.73 e

5Na/Zr-SBA-15(30) e e 4.57 e

5Na/Zr-SBA-15(10) e e 4.65 e

15Na/Zr-SBA-15(10) 10 27.60 14.21 27.81/14.06

a Determined by ICP analysis.b The loading weight in the spent catalyst of Zr and Na were representedc a0 ¼ 2d100/√3 is the hexagonal lattice parameter derived from the XRDd Dpore is the mean pore diameter derived from N2 desorption data basede W ¼ a0 e D is the mean pore wall thickness.f S is the specific surface area.g V is the specific pore volume.

methanol were added into the flask and stirred for 30 min at

an ambient temperature. The methanol-to-oil molar ratio

used was 6:1. The temperature was then increased to 70 �C.The reaction was performed for 8 h under magnetic agitation,

after which the reactor was cooled down using an ice-water

bath. During the reaction, a 5 ml aliquot was collected hour-

ly and filtered to remove the catalyst. The residual methanol

was separated from the upper liquid phase (the lower phase is

glycerin). The products were analyzed using gas chromatog-

raphy (Agilent 6890) using a capillary column (DB-Wax) and a

flame ionization detector.

Results and discussion

Physicochemical properties of Zr-SBA-15 supports

Table 1 lists the physicochemical properties of pure SBA-15

and the Zr-incorporated SBA-15 supports with Si/Zr molar

ratios from 50 to 10. Analysis of the metal content obtained

from the final supports indicates the incomplete albeit high

incorporation of Zr species to the silica framework. Increasing

the metal content in the synthesis media leads to lower

incorporation efficiencies, suggesting a possible saturation

effect on the ability of micelles to accommodate the metal

precursor [20].

With regard to the crystal structure obtained from low-

angle XRD patterns (as shown in Fig. 1), all the Zr-

incorporated SBA-15 supports seem to show optimal

ordering of the 2D-hexagonal P6mm structure [23], which

exhibit an intense peak and twoweak peaks. The intense peak

at 2q¼ 0.97� corresponded to the (1 0 0) reflection, whereas the

two other weak peaks between 1.7� and 1.95� respectively

corresponded to the (1 1 0) and (2 0 0) planes in a hexagonal

arrangement. All samples prepared through the direct syn-

thesis method retained their hexagonal structures after the

incorporation of Zr, even at a Si/Zr ratio of 10. Furthermore,

the intensity of all reflections increased with increasing Zr

Zr-SBA-15(X) supports.

inyst

a0c (nm) Dpore

d (nm) We (nm) SBETf

(m�2 g�1)Vtotal

g

(cm3 g�1)

9.82 5.48 4.34 817.89 1.12

9.93 5.98 3.95 723.26 1.08

10.15 7.78 2.37 628.18 1.22

10.39 9.27 1.12 489.26 1.13

e 16.53 e 114.89 0.47

e 10.87 e 283.31 0.77

e 11.19 e 318.35 0.89

e 11.31 e 308.22 0.87

e 10.08 e 298.80 0.79

as molar ration and wt%, respectively.

data.

on the BJH method.

Fig. 2 e DR UVevis spectra of Zr-SBA-15 supports with

various Si/Zr molar ratios.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 9 ( 2 0 1 4 ) 1 9 5 5 5e1 9 5 6 219558

content, suggesting that increasing scatter contrast between

pore walls and pore space was probably caused by the incor-

poration of the metal oxide Zr. As shown in Table 1, an

average unit-cell parameter, a0, indexing to the low angle XRD

diffraction data was increased from 9.82 nm to 10.39 nmwhen

the Si/Zr molar ratio was varied from 50 to 10.

These observations are supported by the N2 adsorp-

tionedesorption isotherms. The textural parameters of the

supports that were deduced from the N2 adsorption isotherms

at �196 �C are also listed in Table 1. The BET surface area

decreases from 817.89 m2/g to 489.26 m2/g when the incor-

porated Zr amount increases, whereas the pore volume and

mean pore size slightly increase. The incorporation of the Zr

Fig. 3 e TEM microphotographs of SBA-15 and Zr-SBA-15 with d

Zr-SBA-15(30), and (d) Zr-SBA-15(10).

species in large content results in an overall reduction of the

surface area, whereas themean pore size and pore volume are

slightly modified. This trend may be a consequence of the

increasing concentration of incorporated Zr species to the

silica intra-framework or to the increasing deposited amount

of ZrO2 on the extra-framework of the micro- or mesopores of

SBA-15 supports. For the previous condition, the diameter of

Zr4þ is significantly greater than that of Si4þ. When Zr4þ is

used to substitute Si4þ in the silicon structure framework, the

bond length of ZreOeSi increases compared with that of

SieOeSi, which deforms the structure and increases the pore

size [20]. For the latter condition, the diffused reflectance (DR)

UVevis spectra were recorded for the various Zr-incorporated

supports that will help us better understand the crystal spe-

cies of zirconium. Iglesias et al. [20] recorded the DR UVevis

spectra of bulk ZrO2 for comparison, and it displayed an

extremely intense and broad coverage from 200 nm to 245 nm.

The intense broadening pattern is attributed to the electron

transition from the valence and to the conduction band of Zr

crystallites [20,24,25], which is a result of the overlap of the

O/Zr(IV) ligand to the metal charge transfer transition. As

shown in Fig. 2, the pure silica SBA-15 support does not show

an absorption peak in the range of 200e600 nm because the

tetrahedral SiO4 in the mesoporous materials does not absorb

light in that range. The Zr-SBA-15 samples display a veryweak

absorption band located at 210 nm that correspond to small

ZrO2 crystallites. That is, a small amount of Zr species is

present in the extra framework of SBA-15.

However, the size of the ZrO2 crystallite should be very

small even when the Zr that loads to the synthesis gel in-

creases Si/Zr from 50 to 10. This size is due to the presence of

ZrO2 that could not be observed in the mesoscopic ordering

channel of SBA-15. The TEM microphotographs in Fig. 3 show

ifferent Si/Zr molar ratios: (a) SBA-15, (b) Zr-SBA-15(50), (c)

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 9 ( 2 0 1 4 ) 1 9 5 5 5e1 9 5 6 2 19559

long-range channel ordering, which suggests that the meso-

structure was preserved for all supports. The above-

mentioned observations demonstrate that Zr atoms have

been incorporated into the SBA-15 framework using the

direct-synthesis method without destroying the original long-

range hexagonal pore structure. Thus, the incorporation of Zr

into the SBA-15 matrix to increase the pore size of the support

would enhance the reactant molecular diffusion in the inter-

nal pores of the catalysts.

Acidic properties of Zr-SBA-15 supports

The surface acidity of Zr-SBA-15(X) supports was studied

using the pyridine adsorption technique. Various bands are

shown in Fig. 4. The bands at 1596 cme1 can be assigned to a

hydrogen-bonded pyridine, bands at 1445 and 1621 cme1 to

strong Lewis-bound pyridine, a band at 1580 cme1 to weak

Lewis-bound pyridine, bands at 1547 and 1639 cme1 to pyr-

idinium ion ring vibration because pyridine binds to Br€onsted

acid sites, and a band at 1490 cme1 to pyridine associated with

both Br€onsted and Lewis sites [26]. The pure SBA-15 exhibited

only Lewis acid site signals because of the pyridine-forming

hydrogen bonds with silanol groups (band at 1596 cme1) and

the pyridine adsorbed on Lewis acid sites (bands at 1445 and

1580 cme1). No Br€onsted acid sites were observed in the

spectrum of the SBA-15 support. Compared with the pure

SBA-15 support, the new adsorption peaks at 1547 and

1639 cme1 can be found in the spectra of Zr-SBA-15 support

after Zr incorporation, suggesting that the intensity of the

Lewis acid site was increased while Br€onsted acid sites were

generated in these supports [27]. As expected, acidity

increased with increasing Zr content. However, the intensity

of the Lewis and Br€onsted acid sites, which is consistent with

the presence of a significant amount of extra-framework Zr in

the SBA-15 structure as mentioned in Sec. Sec. 3.1.

Fig. 4 e Infrared spectra of pyridine adsorbed on SBA-15

and Zr-SBA-15 supports. (B, Br€onsted-bound pyridine; L,

Lewis-bound pyridine.).

Physicochemical properties of Na/Zr-SBA-15 catalysts

Fig. 5 shows the high-angle XRD patterns of Na/Zr-SBA-15

catalysts. No diffraction peaks assigned to crystalline so-

dium species could be detected, suggesting that rational

dispersion of sodium in Zr-SBA-15 was achieved. This case

was similar to that in Zr-SBA-15(10), which possessed the

smallest surface area. Thus, incorporation of Zr atoms in the

SBA-15 support improves the dispersion of Na species. The

textural characteristics of Na catalysts supported on Zr-SBA-

15 mesoporous supports are also shown in Table 1. A signifi-

cant decrease in surface area and pore volume is observed

when Na is supported on Zr-SBA-15(50) supports. This

decrease is more evident for catalysts supported on pure

siliceous SBA-15, where SBET decreased by 86% probably

because of the pore blockage caused by a low dispersion of the

metal phase Na. Zr incorporation into the SBA-15 support re-

sults in a minor change in textural property values. As shown

in Table 1, the loss ratio of SBET decreasedwith Zr loading (61%,

49%, and 37% for Si/Zr ratio of 50, 30, and 10, respectively).

Thus, on the one hand, Zr incorporation in the SBA-15 support

enhances the dispersion of Na oxide species. Therefore, the

surface acidity of the support, rather than the porous struc-

ture (i.e., surface area and pore volume), is the key factor in the

formation of better dispersed Na species on Zr-SBA-15

supports.

Fig. 6 shows the TEM images of the Na/Zr-SBA-15 samples,

where the metallic particles over the mesoporous structure of

SBA-15 supports can be distinguished. The typical meso-

porous structure of Zr-SBA-15 has been well-preserved for

these catalysts, which is consistent with TEM images of Zr-

SBA-15 supports. Moreover, significant differences in the

NaO particle size of these four samples can be observed,

indicating that Na/Zr-SBA-15(10) contains smaller particles

than others, which was consistent with the results of XRD

patterns (Fig. 5).

Fig. 5 e X-ray diffraction patterns of Na catalysts supported

on different Zr-SBA-15 supports: (a) SBA-15, (b) Zr-SBA-

15(50), (c) Zr-SBA-15(30), (d) Zr-SBA-15(10), and (e) spent Na/

Zr-SBA-15(10).

Fig. 6 e TEM images of 5 wt.% Na catalysts supported on supported on different Zr-SBA-15 supports: (a) SBA-15, (b) Zr-SBA-

15(50), (c) Zr-SBA-15(30), and (d) Zr-SBA-15(10).

Fig. 7 e Biodiesel yield as a function of reaction time of

SBA-15 and Zr-SBA-15 supports with different Si/Zr molar

ratios.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 9 ( 2 0 1 4 ) 1 9 5 5 5e1 9 5 6 219560

Transesterification activity

Effect of Zr contentThe effect of Zr content in Zr-SBA-15 supports on catalytic

activity was tested in the transesterification of canola oil. The

catalytic performances of SBA-15 supports were compared.

Their improvement is presented in Fig. 7 in terms of biodiesel

yield toward FAME after 4, 6, and 8 h of reaction time with

different Si/Zr ratios. All Zr-SBA-15(X) supports exhibited

highly catalytic activities without Na catalysts. Biodiesel yield

increased from 16% to 63% as the Si/Zr ratios decreased from

∞ to 10. The use of the Zr-SBA-15(10) support resulted in the

maximal biodiesel yield of 63%, which is almost fourfold that

of pure silica SBA-15 support (16%). Increasing yields of bio-

diesel were obtained as Zr content in the catalyst was

increased, probably because of the higher acidic nature and

larger pore diameter of these supports. Acid catalysts with

Lewis acid sites are extensively used. The carbonyl oxygen

(from triglyceride molecules of vegetable oil) in such sites is

chemisorbed to form the Lewis complex. This carbon is then

attacked by methanol to form a new carbonium ion (CeO

bond) and produce a transesterification reaction that releases

FAME [8,19]. Therefore, the incorporation of Zr into the sili-

ceous SBA-15 framework significantly affects the catalytic

activity in canola oil. Lower Si/Zr molar ratios result in higher

activity because of the strong Lewis and Br€onsted acid sites.

Furthermore, even the Lewis acid sites are accepted as the

major reactive sites for transesterification; the contribution of

Br€onsted acid sites is also important [6]. The Si/Zr ratio of Zr-

SBA-15 also has a slight influence on the FAME yield; when the

Zr content increases Si/Zr from 50 to 10, an enhanced FAME

yield from 54.6% to 60.26% is observed (reaction time ¼ 4 h).

The slightly improved activity is due to the smaller ZrO2

crystallite that formswhen the Zr content increases. Thus, the

acid site of the incorporated Zr-SBA-15(30) and Zr-SBA-15(10)

increases slightly for these materials according to the pyri-

dine adsorption experiments. The performance of the trans-

esterification reaction over this series of Zr-SBA-15(X)

supports is consistent with acidity studies, except in terms of

surface area. This observation reveals that the Zr-SBA-15 can

be employed both as a catalyst and as a support.

The effect of reaction time on the transesterification of

canola oil is also shown in Fig. 7. All the supports exhibit high

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 9 ( 2 0 1 4 ) 1 9 5 5 5e1 9 5 6 2 19561

activities after 4 h. The catalytic activity of all supports slightly

increases with prolonged reaction time. A 60.26% biodiesel

yield is achieved with the Zr-SBA-15(10) support after 6 h.

Further increase in the reaction time increases energy con-

sumption. Therefore, based on this data, the reaction time for

the experiments was set to 6 h.

Effect of Na loadingNa metals were further deposited through the impregnation

method to promote the catalytic activity of Zr-SBA-15 mate-

rials in the transesterification. Fig. 8 shows the catalytic ac-

tivity obtained from 5 wt.% Na loaded on pristine SBA-15 and

Zr-SBA-15 supports with different Si/Zr ratio. Notably,

enhanced catalytic activity from SBA-15materials is exhibited

without the need to promote acid strength by incorporating

Zr. Thus, catalyst 5Na/SBA-15 provided FAME yields of

approximately 48%, which is thrice that recorded in the

presence of the pristine SBA-15 support (16%). The observed

FAME yield in this blank reaction is not attributed to the

enhancement of acidity of pristine SBA-15 support but is

contributed by the presence of solid base catalyst, Na, which

catalyzes transesterification reactions.

However, the impregnation of 5 wt.% Na metals on the

surface of a series of Zr-SBA-15(X) supports (Fig. 8) does not

provide the expected increase in catalytic activity, even with

the enhancement produced in the Na dispersion and surface

area when using Zr-SBA-15(X) as supports. All 5 wt.% Na/Zr-

SBA-15(X) displayed a slightly lower catalytic activity than

the Zr-SBA-15(10) support. Consequently, although the acidity

of SBA-15 support is enhanced by Zr, this enhancement isin-

sufficient for the improvement of the catalytic activity of 5Na/

SBA-15 catalysts for FAME production via the trans-

esterification of canola oil. The explanation for this behavior

could be related to the mechanism behind the trans-

esterification of triglycrides. The mechanism of heteroge-

neous base catalyst in transesterification first involves the

abstraction of proton frommethanol by the basic sites to form

methoxide anion [1]. Compared with the mechanism of het-

erogeneous acid catalsyt Zr-SBA-15, the competition of

methanol occured andhindered the basic transesterification

Fig. 8 e Biodiesel yield as a function of Na loading weigh of

Na/Zr-SBA-15 catalysts with different Si/Zr molar ratios.

of canola oil. Thus, deposition of 5 wt.% Na metal on the

surface of Zr-SBA-15(X) supports appear to be negative for

catalytic function.

The loading weight of Na active phase was increased from

5 to 12 and 15 wt.% of Na with respect to the weight of the Zr-

SBA-15 support to shift the transesterification mechanism to

basic catalysis. As shown in Fig. 8, the biodiesel formation

increased with the amount of Na loading weight, almost

reaching 98% at 15 wt.% loadingof Na/Zr-SBA-15(10) catalysts,

which could be attributed to a more suitable dispersion of Na

active sites on the surface of the mesoporous support. The

heteroatom Zr incorporation in the SBA-15 framework can

induce acid sites and improve the interaction between Na and

support.

Recyclability of Na/Zr-SBA-15

Finally, the reusability of the catalysts under optimum con-

ditions (at 70 �C, 6 h, 15 wt.% of Na loading, and a catalyst

amount of 12 wt.% based on canola oil weight) was studied

through processes of filtration from oil, washing with ben-

zene, and drying in an oven to remove any oil residue that

adhered to the surface of the catalysts. The percentage of

FAME yield, which ranged from 85% to 88%, decreased for the

three cycles of transesterifications of canola oil when the re-

generated catalysts were used. The results show that this

catalyst can be reused for at least three cycles without sig-

nificant loss of catalytic activity because FAME formation de-

creases by 12%e15% after the first run, after which the

conversion into FAME is maintained. However, the washing

procedure is not completely efficient because of a slight loss of

activity, such that regeneration of the initial catalytic activity

is not complete.

The stability of the spent catalysts was checked by

analyzing their Na and Zr contents. As shown in Table 1, the

molar ratio and loadingweight of Si/Zr with Nawere 27.81 and

14.06 wt%, respectively, which are very close to the values of a

fresh catalyst. Obviously, no significantly leaching of Zn or Na

was observed during the conversion process. Furthermore,

the crystal phase of the Na-active site was analyzedwith an X-

ray diffractometer. The XRD patterns of samples after the

reaction tests are shown in Fig. 5, which exhibits the high-

angle XRD patterns of Na/Zr-SBA-15(10) catalysts. Three

intense diffraction peaks at 2q ¼ 29.1�, 33.9�, and 39.8� for thespent sample correspond to the planes of cubic NaO. Thus, the

aggregation of Na-active sites occurs after the trans-

esterification reaction. In addition, following a calcination

procedure for catalyst regeneration requires another method

to fully recover to the initial activity. Further investigations

are in progress to understand this phenomenon.

Conclusion

The one-pot synthesis of Zr into the SBA-15 matrix provides

an easy and low-cost method for the preparation of meso-

porous acidic solids using different Si/Zr molar ratios. Inter-

esting acidic properties were observed because of the

incorporation of Zr ions into the silica framework, wherein

SieOeZr bonds are formed. The total acidity of these supports

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 9 ( 2 0 1 4 ) 1 9 5 5 5e1 9 5 6 219562

depends on Zr concentration, which enables the trans-

esterification of canola oil with methanol at 70 �C to achieve a

99% yield. The catalytic performance in the transesterification

reaction of the series of Na/Zr-SBA-15 catalysts is effective if

we consider the reaction temperature (70 �C), which is

significantly lower than that used by Furuta et al. [28,29] and

Jacobson et al. [30] for the transesterification of soybean and

waste cooking oil with methanol at 200 �Ce300 �C.

Acknowledgment

The authorswould like to gratefully acknowledge the financial

support provided by the National Science Council Taiwan

program (NSC 101-2815-C-040-002-E).

r e f e r e n c e s

[1] Lam MK, Lee KT, Mohamed AR. Homogeneous,heterogeneous and enzymatic catalysis fortransesterification of high free fatty acid oil (waste cookingoil) to biodiesel: a review. Biotechnol Adv 2010;28:500e18.

[2] Abdullah AZ, Razali N, Lee KT. Optimization of mesoporousK/SBA-15 catalyzed transesterification of palm oil usingresponse surface methology. Fuel Process Technol2009;90:958e64.

[3] Samart C, Sreetongkittikul P, Sookman C. Heterogeneouscatalysis of transesterification of soybean oil using KI/mesoporous silica. Fuel Process Technol 2009;90:922e5.

[4] Sun H, Han J, Ding Y, Li W, Duan J, Chen P, et al. One-potsynthesized mesoporous Ca/SBA-15 solid base fortransesterification of sunflower oil with methanol. ApplCatal A 2010;390:26e34.

[5] Liu X, He H, Wang Y, Zhu S, Piao X. Transesterification ofsoybean oil to biodiesel using CaO as a solid base catalyst.Fuel 2008;87:216e21.

[6] Jim�enez-Morales I, Santamarı́a-Gonz�alez J, Maireles-Torres P, Jim�enez-L�opez A. Methanolysis of sunflower oilcatalyzed by acidic Ta2O5 supported on SBA-15. Appl Catal A2011;405:93e100.

[7] Jim�enez-L�opez A, Jim�enez-Morlaes I, Santamaı́a-Gonz�alez J,Maireles-Torres P. Biodiesel production from sunflower oil bytungsten oxide supported on zirconium doped MCM-41silica. J Mol Catal A 2011;335:205e9.

[8] Jim�enez-Morlaes I, Santamaı́a-Gonz�alez J, Maireles-Torres P,Jim�enez-L�opez A. Aluminum doped SBA-15 silica as acidcatalyst for the methanolysis of sunflower oil. Appl Catal B2011;105:199e205.

[9] Sujandi SS, Han DS, Koo JB, Park SE. Transesterificationreactions over morphology controlled amino-functionalizedSBA-15 catalysts. Catal Commun 2008;9:158e63.

[10] Chen LF, Noreena LE, Navarrete J, Wang JA. Improvement ofsurface acidity and structural regularity of Zr-modifiedmesoporous MCM-41. Mater Chem Phys 2006;97:236e42.

[11] Dai Q, Wang X, Chen G, Zheng Y, Lu G. Direct synthesis ofCerium(III)-incorporated SBA-15 mesoporous molecularsieves by two-step synthesis method. Micro Meso Mater2007;100:268e75.

[12] Ungureanu A, Dragoi B, Hulea V, Cacciaguerra T, Meloni D,Solinas V, et al. Effect of aluminium incorporation by the“pH-adjusting” method on the structural, acidic and catalyticproperties of mesoporous SBA-15. Micro Meso Mater2012;163:51e64.

[13] Liang C, Wei MC, Tseng HH, Shu EC. Synthesis andcharacterization of the acidic properties and pore texture ofAl-SBA-15 supports for the canola oil transesterification.Chem Eng J 2013;223:785e94.

[14] Kim HJ, Kang BS, Kim MJ, Park YM, Kim DK, Lee JS, et al.Transesterification of vegetable oil to biodiesel usingheterogeneous base catalyst. Catal Today2004;93e95:315e20.

[15] Nguyen TPB, Lee JW, Shim WG, Moon H. Synthesis offunctionalized SBA-15 with ordered large pore size and itsadsorption properties of BSA. Micro Meso Mater2008;110:560e9.

[16 ] Han Y, Meng X, Guan H, Yu Y, Zhao L, Xu X, et al. Stable iron-incorporated mesoporous silica materials (MFS-9) preparedin strong acidic media. Micro Meso Mater 2003;57:191e8.

[17] Kao HM, Ting CC, Chao SW. Post-synthesis alumination ofmesoporous silica SBA-15 with high framework aluminumcontent using ammonium hexafluoroaluminate. J Mol CatalA-Chem 2005;235:200e8.

[18] G�omez-Cazalilla M, M�erida-Robles JM, Gurbani A, Rodrı́guez-Castell�on E, Jim�enez-L�opez A. Characterization and acidicproperties of Al-SBA-15 materials prepared by post-synthesisalumination of a low-cost ordered mesoporous. J Solid StateChem 2007;180:1130e40.

[19] Kumaran GM, Garg S, Soni K, Kumar M, Gupta JK, Sharma LD,et al. Synthesis and characterization of acidic properties ofAl-SBA-15 materials with varying Si/Al ratios. Micro MesoMater 2008;114:103e9.

[20] Iglesias J, Melero JA, Bautista LF, Morales G, S�anchez-V�azquez R, Andreola MT, et al. Zr-SBA-15 as an efficient acidcatalyst for FAME production from crude palm oil. CatalToday 2011;167:46e55.

[21] Du Y, Liu S, Zhang Y, Nawaz F, Ji Y, Xiao FS. Urea-assistedsynthesis of hydrothermally stable Zr-SBA-15 and catalyticproperties over their sulfated samples. Micro Meso Mater2009;121:185e93.

[22] Klimova T, Esquivel A, Reyes J, Rubio M, Bokhimi X, Aracil J.Factorial design for the evaluation of the influence ofsynthesis parameters upon the textural and structuralproperties of SBA-15 ordered materials. Micro Meso Mater2006;93:331e43.

[23] Lindo M, Vizcaı́no AJ, Calles JA, Carrero A. Ethanol steamreforming on Ni/Al-SBA-15 catalysts: effect of the aluminiumcontent. Int J Hydrogen Energy 2010;35:5895e901.

[24] Krishnan CK, Hayashi T, Ogura M. A new method for post-synthesis coating of zirconia on the mesopore walls of SBA-15 without pore blocking. Adv Mater 2008;20:2131e6.

[25] Chen SY, Lee JF, Cheng S. Pinacol-type rearrangementcatalyzed by Zr-incorporated SBA-15. J Catal2010;270:196e205.

[26] Klimova T, Reyes J, Guti�errez O, Lizama L. Novel bifunctionalNiMo/Al-SBA-15 catalysts for deep hydrodesulfurization:effect of support Si/Al ratio. Appl Catal A 2008;335:159e71.

[27] Faria EA, Marques JS, Dias IM, Andrade RDA, Suarez PAZ,Prado AGS. Nanosized and reusable SiO2/ZrO2 catalyst forhighly efficient biodiesel production by soybeantransesterification. J Braz Chem Soc 2009;20:1732e7.

[28] Furuta S, Matsuhashi H, Arata K. Biodiesel fuel productionwith solid superacid catalysis in fixed bed reactor underatmospheric pressure. Catal Commun 2004;5:721e3.

[29] Furuta S, Matsuhashi H, Arata K. Catalytic action of sulfatedtin oxide for etherification and esterification in comparisonwith sulfated zirconia. Appl Catal A 2004;269:187e91.

[30] Jacobson K, Gopinath R, Meher LC, Dalai AK. Solid acidcatalyzed biodiesel production from waste cooking oil. ApplCatal B 2008;85:86e91.