Zirconium Dioxide Dispersed in SiO -Montmorillonite: Heterogeneous Catalyst For

Journal of A pplied Sciences Res earch, 5(10): 1277-1284, 2009
© 2009, INSInet Publication
Zirconium Dioxide Dispersed in SiO2 -Montmorillonite: Heterogeneous Catalyst For
Citronellal Conversion To Isopulegol
Is Fatimah
Chemistry Dept., Islamic University of Indonesia Kampus Terpadu UII, Jl. Kaliurang Km.14, Besi,
Yogyakarta, Indonesia 55581
Abs tract: Study on preparation of ZrO2 dis p e rs e d in S iO2 - pillared montmorillonite (ZrO2 /SiO2 M ontmorillonite) and its application as heterogeneous catalys t for citronellal convers ion to is opulegol has
been inves tigated. The catalys t preparation involving zirconia dis pers ion by impregnating ZrOCl2 precurs or
to s ilica pillared montmorillonite was evaluated by s everal technique in phys icochemical character
meas urements s uch as XRD, s pecific s urface area, F T IR a n d SEM micrograph. Bas ed on the
phys icochemical data, the improved catalys t character was correlate with its activity in citro n ellal
convers ion to is o p u legol. In general, it was s howed that dis pers ion produce in s urface acidity and
s pecific s urface area as well as the catalys t activity in producing is opulegol. It was found t h a t the us e of
ZrO2 / S iO 2 -M o n t mo rillonite increas e the kinetic cons tant rate in the ratio of 1.97. Prepared material give
94.640 % s electivity in producing is opulegol and it is much higher than the s electivity gained by us ing
montmorillonite and SiO2 -M ontmorillonite with the values of 0.003% and 14.496 % res pectively.
Key words : pillarization, impregnation, citronellal convers ion
INTRODUCTION
Is opulegol is important chemical intermediate in
the manufacture of menthols (C1 0 H2 0 O) and o t h e r
compound in pharmac e u t ical indus try. The s imples t
way to s ynthes is is opulegol is the cyclis ation of
citronellal, which is a ls o a main component in lemon
gras s oil [2 ,1 0 ]. The reaction of citronela l c onvers ion
(Fig. 2:) s h o w that acid catalys t needed for the
convers ion. In the Takas ago proces s aqueous ZnBr2 is
us ed t o perform the ene-cyclis ation in very good yield
and excellent s electivity. Other c a t a lys t as a recent
p a t e n t o f t h is c o mp a n y
is
t r i s (2,6triarylphenoxy )a lu min iu m, w h ic h g iv e s a lmo s t
e xclus ively (2)-is opulegol, 99.3%, with only traces o f
the other is omers [1 0 ].
Lewis acidit y p lay important role in the
mechanis m. However, the us e of homogeneous catalys t
in indus try make new problem in e n v ironment due to
its difficulties in catalys t recyc ling and the product
s eparation. T he us e of heterogeneous catalys ts can be
indus trially a more attractiv e a lternative for the
production of fine chemicals due to the eas y s eparation
and re u s e of thes e catalys ts . A dditionally the us e of
hetero geneous catalys ts allows more environmentally
friendly proces s es than homogeneous catalys ts . This
advantageous make the proces s more e c o nomic [1 , 6 ].
For this purpos e, s everal inorga n ic material us ed as
Corresponding Author:
s olid s upport o f lewis acid s ite needed in the
mechanis m [3]. Zeolite, s ilic a a n d M CM -41 are reported
by s everal author. The s ign ificant point of the res ults
is the domination of s urfa ce acidity and reactant
acces s to the catalys t pore or s urface to the convers ion
p e rc e ntage and product s electivity. Zirconium in the
ionic and oxide form are the exclus ive active s ite for
this s urface reaction [4 ,1 4 ,1 5 ].
A iming to improve the activity and s electivity to
(-)-is opulego l, c o mb ining zirconium with s everal
inorganic matrices s uch a s s ilica alumina and zeolite
minerals was s tudied [1 2 ,1 6 ]. In other s id e , pillared clays
are new clas s of inorganic matrix h ave received
wides pre a d interes t as a novel clas s of microporous
s olid acids . The bas ic principle of its s ynthes is cons is t
of metal oxide ins ertion in interlayer s ilica s pace make
t h e s tructure of pillared clay in the zeolite-like mate ria l
clas s ification. Bes ide of its us e as catalys t, available
s pace in pore s tructure and thermal s tability lead the
potential application as catalys t s upport [5].
This res earch inves tigate the s ynthes is of ZrO2
dis pers ed into s ilica-pillared montmorillon ite s upport.
Natural montmorillonite called as bentonite was us ed as
raw clay con s idering that this s tructure is s mectitic
c lay. Simple preparation method of s ilica pillare d
montmorillonite and many reports regarding to the high
a c t iv it y o f ZrO2 combined with SiO2 in org a n ic
s ynthes is are the promis ing idea for this s ynt hes is .
Is Fatimah, Chemistry Dept., Islamic University of Indonesia Kampus Terpadu UII, Jl. Kaliurang
Km.14, Besi, Yogyakarta, Indonesia 55581
Tel: +62818 273 001
E-mail: [email protected]
1277
J. App. Sci. Res., 5(10): 1277-1284, 2009
Some res earch reported the important increa s e in
phys icochemical character of s pecific s urface area and
homogeneous pore dis tribution in the mes oporous range
as a new challenge in its u t ilization for ZrO 2 hos t
matrix [7 ,8 ,9 ,1 1 ]. Homo geneous dis pers ion in the matrix
hope This paper dis cus s es the relations hip of the
phys icochemical character of prepared material with the
catalys t activity and s electivity in producing is opulegol.
MATERIAL AND METHOD
Raw Mate r ial and S ilica Pillarization Proces s : The
natural clay mineral us ed in this work was bentonite
from PT. Tunas Inti M akmur, Semarang, Indones ia.
The fraction with particle s ize s maller than 200 mes h
was obt ained after was hing and careful aqueous
d e cantation of the natural clay, and was then us ed fo r
intercalation e xperiments . Its chemical compos ition is
given in Table 1.
Silica pillarization was condu c ted by us ing s ilica
precurs or of tetraethyl ortho s ilicate (TEOS) followed
the modified method pres ented b y M ao et al.[1 1 ] with
chloride acid in the hydrolys is s ys te m. T h e SiO2 pillare d mo n t morillonite was
prepared by the
dis pers ing s olution
of TEOS in eth a n ol into
montmorillonite s us pended in low concentration of HCl
s olution under vigorous ly s tirring. The s us pens ion was
kept for 48 h at room temperature, was hed with
aquades t until abs ence of chloride (A g + tes t) and dried
at 70 NC for 16 h. The s olid from this s tep was called
as Si-intercalated montmo rillonite. The intercalated
s olid was calc in e d with a heating rate of 1 NC/min and
main tained at the final calcination temperature of 400o C
for 4 h under N2 ga s flowing. Solid produced by this
proces s was called as SiO2 -montmorillonite.
Zirconia D i s pers ion: Zirconium oxide chloride was
us ed as zirconia precurs o r in the catalys t preparation.
Impregna t io n proces s was performed by mixing the
precurs or s olution with SiO 2 -montmorillonite, s tirring at
60o C fo r 4 h a nd evaporating s olvent. Solid gained by
this s tep was calcined at 400o C for 4 h u n d e r N2 gas
flowing. The s olids pro d u c e d is labeled as ZrO2 /SiO2 montmorillonite.
S olid Characterization:
X-ray Diffraction: XRD analys es were c a rried out
with a Shimadzu X6000 diffractome t e r us ing a CuKá
radiation s o urce. The analys is was performed from 3
to 65o .
Area and Pore S ize D i s tribution: The s pecific s urface
area and the pore s ize dis tribution were determined by
nitrogen ads orption is o t h e rms at 77 K by us ing
1278
NOVA 1000 gas s orpt ion analyzer. BET-is otherm
eq u a t ions were applied to determine s pecific s urface
area and pore s ize dis tribution res pectively.
S canning Electron Mi c r os copy (S EM): SEM was
performed us ing JSM -5310 LV micros cope.
Catalytic Activity Tes t: Ca t a ly t ic a c t iv it y o f
ZrO2 /SiO2 -M ontmorillonite for the citronellal convers ion
reaction was carried out at reflux s ys tem. A nalys is of
t h e reaction res ult compos ition in the certain interva l
t ime was meas ured by GC and the data pres en t e d in
kinetic s tudy. Effect of catalys t to reactant ma s s ratio
(c/r) to the catalys t activity and s electivity in is opulegol
production was s tudied.
S u r fac e A c i di ty Me as u r e ment by P yr i di n e
A ds or pti on-FTIR Analys is : Surfa c e a c id it y o f
materials are evaluated by ads orption proces s of
pyridine vapor by materials followed by FTIR analys is .
M aterials are h e a t e d in 103o C
for 4 h before
evacuated in low pres s ure ( ~ 300 mmH g ) fo r 1 h in
a chamber. Pyridine vapor was flo wed to the chamber
and le ft for 24 h. Solids were evacuated in low
pres s ure ( ~ 300 mmHg) for 1 h in orde r t o o u s t
u n a d s o rb e d pyridine before analyzed by FTIR
s pectrophotometry.
RES ULT AND DIS CUS S ION
Material Char acterization: Table 2 pres ent the
chemical compos ition, s urface analys is data and the
value of d 0 0 1 bas al s pacin g meas ured by XRD. From
the data, it is found t h a t SiO2 and A l2 O3 are main
component repres enting the s ilica alumina framework.
T h e higher content in Na than to Ca in the ra w
montmorillonite s how the typical cha ra c t e ris tics of a
Na-s mectite with the s w eallable properties . Res ult of
d 0 0 1 bas al s pacing meas u re ment due to the XRD
reflection indicating the d 0 0 1 bas al reflect ion equal to
14.39 Å . A s s uming that the thicknes s of s ilica layer c.a
9.6Å , the interlayer dis tance between two s ilica layer
is equal to 4.79Å . The evolution on phys icochemical
charact e r
of material after s ilica pillarization and
zirconia dis pers ion. s h o w n b y the alteration in d 0 0 1
bas al s pacing value, s pecific s urfa ce area and pore
volume.
Fig. 2: s how t h e re flection of X-ray diffraction
analys is . The patterns indica t e that the ZrO2 /SiO2 M ontmorillonite was s ucces s fully s ynthes ized.
Reflections of natural montmorillonite (NM ) s how
t h e s ignificant characteris tic peaks at 2è = 6.30o (d=
14.47Å ) and 2è = 19.91o (d= 4.45Å ) with the valuable
intens ity and other reflections at 2q = 20.18o , 23.57o and
J. App. Sci. Res., 5(10): 1277-1284, 2009
Table 1: Elemental analysis result of montmorillonite and saponite
Mineral/element
Composition (% wt.)
SiO 2
59.80±0.67
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Al 2 O 3
22.19±0.65
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------MgO
2.82±0.27
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------CaO
0.77±0.27
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Na
5.25
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Cation Exchange capacity (meq/100gram)
68,00-69,72
Table 2: Specific Surface Area and Pore Volume data of Materials
Sampel
Specific Surface area (m 2 /g)
Pore Volume (cc/g)
Natural Montmorillonite
45.82
54.88
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------SiO 2 -Montmorillonite
165.32
171.64
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ZrO2 / SiO 2-Montmorillonite
79.05
67.98
Fig. 1: Convers ion of citronellal to is opulegol is omers
Fig. 2: XRD pattern of (a) M ontmorillonite (b) SiO2 -M ontmorillonite (c) ZrO2 /SiO2 -M ontmorillonite
1279
d 001 (D)
14.47
15.85
15.84
J. App. Sci. Res., 5(10): 1277-1284, 2009
Fig. 3:
FTIR Spectra of (a) montmorillonite (b) SiO2 -M ontmorillonite (d) ZrO 2 /SiO 2 -M on t mo rillo nite after
ads orbed pyridine
26.57 o . T h e reflection at 2è = 5.92o is correlated to the
d 0 0 1 bas al s pacing of s mect itic clay s tructure. Other
reflections corres ponding to the impurities minerals of
quartz and crys toballite are als o identified. Specific
a lteration to the montmorillonite reflectio n w a s
obs erved, which s hows a s hift of d 0 0 1 to the lower
angle after pillarization and zirconia dis pers ion. The
d 0 0 1 reflection of SiO2 -M ontmorillonite is a t 5.75o
implying a larg e r d 0 0 1 value of arrond 15.85D res ulted
from s ilica pillarization. ZrO2 dis pers ion into SiO2 montmorillonite do not s how any differences in
reflection pattern. Compared to SiO2 -M ontmorillonite,
the d 0 0 1 peak of s lightly decreas ed, which refle c t ed the
lower crys tallinity in the clay layer, b u t t h ere is no
s hift of d 0 0 1 is reflection after zirconia pillarization.. It
is predicted that the dis pers ion fo rm metal oxide was
s lightly affect to th e p illared montmorillonite s tructure.
The acid environment of zirconia precurs or a nd
calcinations proces s during th e d is pers ion may the
pos s ible affecting s tep. However, the relative low in
decreas ing intens ity of d 0 0 1 reflection s u gges t that the
SiO2 -M ontmorillonite is s table enough a s hos t matrix
of zirco n ia loading. Furthermore, there were no
characteris tic reflections res p o ns ible to the zirconia
1280
phas e identified in ZrO2 / SiO2 -M ontmorillonite. The
res epons ible reas on for this ind ication is that there is
no zirconia aggregatio n found in s urface or the
dis pers ion occurs homogeneous ly.
In agre e ment with XRD data, s urface area s how
the increase of phys ic o c h e mical character after
pilla rization proces s . However, and pore dis tribution
analys is of material indicatin g t h e mes oporous
formation that can be produced either by hous e of
cards formation or s urfa c e from the pillar gallery in the
pillared s tructure. The s pecific s urface area and pore
v o lume from the N2 ads orption data are giv e n in
Table 2. During pillaring, the expans ion in the clay
s tructure largely contributed to the enhancement of the
s urface area of th e c lay. The s urface area analys is
indicated that pillaring with SiO2 s ignificantly increas ed
t h e s u rfa c e a re a , fro m 45.82 m2 /g o f t h e
mo ntmorillonite to a value of 165.32 m2 /g, and
increas e d the pore volume by a factor of at leas t 3.12
(from 54.88 cc/g to 171.64 c c/g). ZrO2 dis pers ion into
SiO2 -montmorillonite producing the s pecific s urface
area of 79.05 m2 /g as being c aus ed by metal oxide
aggregation of me tal oxide particles as refer to the
XRD interpretation.
J. App. Sci. Res., 5(10): 1277-1284, 2009
FTIR s pectum of
materials after pyridine
ads orption are s hown in Fig. 3:
Pyridine s pecies that are forme d b y interaction
between catalys t are pres e n t e d in Fig. 4. Species A
(Lpy) is formed by co ordination bond of paired
e lectron of the nitrogen atom with Lewis acid s it e o f
the s urfac e , i.e from A l or Zr in s urface. Species II
(Bpy) is pyridinium ion t h a t is formed by H+ trans fer
from Brøn s ted acid–OH2 + of the clay s tructure with
pyridine. Species III (Hpy) is formed by hydrogen
bonding between N atom with –OH functional group of
clay s tructure. The vibrations s howing the pyrid in e
fundtio n al group are depicted in the region of
1400–1700 cm-1 . Vibration s pectrum in t h e range of
1640 cm-1 is correla ted to the Bpy acid s ite and
vibrations in the range of 1450–1455 cm-1 are
characteris tics for Lpy s ite [1 3 ].
FTIR s pectra of the ZrO2 /SiO2 -montmorillonite
s how t h e more intes ive abs orption at around 1430.83
cm-1 than in natural montmorilonite a n d S iO 2 mo ntmorillonite i.e are s hown at 1435.07 cm- 1 a n d
1434.39 cm-1 res pectively. The s hift of the s pectrum
to the lower w a v e number was predicted to be in
correlation with pyrid ine-Lewis acid s ite of ZrO2 in
s olid. T h is s hifting band at lower wave number was
probably caus ed by ZrO2 dis pers ion. However, the
s imilar in d ic a t io n is n ot found in ZrO2 /SiO2 M ontmorillonite.
From the SEM profile (Fig. 5 ), it was es tablis hed
that there w a s an improvement in porous s tructure by
pillarization in that tightly packaged s t ru cture of the
o rig inal clay s ample w e re o p e n e d in S iO 2 mon tmorillonite. The exis tence of ZrO 2 nanoparticles
attached on the s urface as s hown by clearer p a rt ic les ,
however it is very difficult to dis tinguis h th e ir s ize
and s hape are in irregular formation.
the react io n rate of citronellal convers ion increas e by
us in g catalys t in this order : raw-montmorillonite <
SiO2 -M ontmorillo n t e < Z rO 2 / SiO2 -M ontmorillonite.
This indica tion is appeared from the lower citronellal
concentration in the product as a function of the
reaction time. Quantitat iv e meas urement of kinetics
data was evaluat e d by kinetics s imulation bas ed on eq
(1).
Data in Table 3 s how that the rea ctions are fit to
the firs t orde r as the higher correlation coefficient for
firs t order reaction than for the s econd o rd e r reaction.
T h e reaction cons tant s how that ZrO2 dis pers ion into
SiO 2 -M ontmorillonite make up the catalys t activity in
the ratio of 1.88 to 1.97. T h is ratio is not much
s ignificant in the role of improving catalys t efficiency.
However, t he s electivity of reaction in producing
is opulegol is the important goal as well. Selectiv it y
value is d e t ermined as the percentage of is opulegol
concentration in the product compared to the other
comp o nent in the product. The values meas ured from
9 hours reaction are pres ented in Table 4.
The s ignificant improvement of the s electivity is
determined by higher value of s elect iv it y in producing
is opulegol by us ing ZrO2 / SiO2 -M ontmorillonite in th a t
this value is als o needed in fin e chemicals indus try.
Study on the correlation between ph ys icochemical
character of materials with t h e catalytic activity tes t
s how that there are s imilar pattern of phys icochemical
chara c t e r produced by both metal oxide dis pers ion in
that s pecific s urface area decreas e as well as
crys tallinity of the materials . A lthough the s pecific
s urface area d a t a for both metal oxide s upported SiO2 M ontmorillonite are s imilar, there is a s ignificant
difference in the catalys is tes t res ult. It is mean that
Z rO 2 play an active mechanis m in pro d u c in g
is opulegol.
C atal ys t Activity: The kine t ic s o f c it ro n e lla l
convers ion was s tudied ba s e d on the citronellal
concentration in the product. T h e activity values were
meas ured by the percentage value of citronellal peak in
the product. Reaction rate of the reac t io n can be
expres s ed as :
Effect of Catalys t to Citronellal Ratio: The effect o f
catalys t to citronellal mas s ration was s tudied at the
1:1, 1:5 and 1: 10. The reaction was conducted for 6
hours before analyzed by GC-M S . The chromatogram
of products as the res ult of varied ratio is pres ented in
Fig. 7
A s s hown in Fig. 7, is opu legol, neois o-is opulegol
a n d neois opulegol are the identified products . Effect
of cata lys t to citronellal mas s ratio to the total
convers ion, catalys t activity and als o s electivity in
producing is opulegol is tabulated in Table 5.
W hat can be concluded by the variation of catalys t
to citro n e llal mas s ratio as pres ented in Table 5 is that
the varied ratio is not give s ignific a nt effect on
s electivity to produce is opulegol, citronellal convers ion
and als o percent a ge of total product A lthough more
area is available and pronounced s urface area to
(1)
W ith :
[citronellal]= citronellal convers ion
n
= order of reaction
k
= rate cons tant
t
= reaction time
From the curve in Fig. 6, it can be c o ncluded that
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J. App. Sci. Res., 5(10): 1277-1284, 2009
Table 3: Simulation data for kinetics reaction of citronellal conversion
Catalyst
Simulation
----------------------------------------------------------------------------------------------------------------------------------Order 1
Order 2
---------------------------------------------------------------------------------------------------------------------Correlation Coef.
k
Correlation Coef.
k
Raw- Montmorillonite
-0.9616
0.2376
0.9577
-0.0007
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------SiO 2 -Montmorillonite
-0.9563
0.2486
0.9538
-0.0009
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ZrO2 / SiO 2-Montmorillonite
-0.9678
0.4692
0.8788
-0.00072
Table 4: Selectivity value to isopulegol product
Catalyst
Selectivity to isopulegol (%)
Natural Montmorillonite
0.003
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------SiO 2 -Montmorillonite
14.496
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ZrO2 / SiO 2-Montmorillonite
94.640
Table 5: Reaction Parameters at varied catalyst to citronellal mass ratio
Catalyst to Feed mass ratio
Reaction Parameter
--------------------------------------------------------------------------------------------------------------------------------Selectivity to Produce Isopulegol (%)
Citronellal Conversion(%)
T otal Product (%)
1 : 5
95.10
62.26
81.92
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------1 : 10
94.64
76.21
81.92
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------1 : 15
96.19
59.22
76.77
Fig. 4: Pyridine s pecies s on the s urface
Fig. 5: SEM micrograph profile of (a) M ontmorillonite (b) SiO2 -montmorillonite (c ) Z rO 2 / SiO2 -montmorillonite
(magnification : 5000 x)
1282
J. App. Sci. Res., 5(10): 1277-1284, 2009
Fig. 6: Citronellal concentration in product as function of reaction time
Fig. 7:
Chromatogram of reaction product as fu n c t io n o f catalys t to reactant mas s ratio ( A : is opulegol, B:
citronellal, C : neois o-is opulegol, D: neois opulegol.
1283
J. App. Sci. Res., 5(10): 1277-1284, 2009
increas e the s urface mechanis m, the additional catalys t
does not particip a te in the reaction and the reaction
rate d o es not increas e with growing catalys t load
beyond a certain level. It indicates that th e c a talys t
p ro file is more determined by the zirconia loading than
the s urface a re a of s olids . It is als o imply that at the
conditions , the reaction pos es at ps eudo firs t order
reaction in that the amount of catalys t give no effect to
the reaction rate and other reaction parameters .
Conclus s ion: SiO2 -montmorillonite is promis ing hos t
matrix for Z rO2 and play role as acid catalys t toward
c it ronellal convers ion to is opulegol. Its increas ed
phys icochemical character of acidit y a nd s pecific
s u rface area is reas onable as pect for the rate of
conves ion and in creas e in is opulegol s electivity in the
product.
7.
8.
9.
10.
Ack nowledgement
11.
A uthors wis h to thank DP2M -DIKTI for financial
s upport through Hibah Bers aing 2007-2008 and Bayu
W iyantoko, S.Si, M us tofa A hda, S.Si and Iin Setyowati
for their lab.work as is tance.
12.
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