Characterization of AlFe-pillared Unye bentonite: A study of the surface acidity and catalytic property

Article abstract of DOI:10.1016/j.molstruc.2015.02.034

Aluminium-iron-pillared bentonite has been prepared by incorporation of the iron mixed aluminium-polyoxocation into bentonite layers and characterized by the powder X-ray diffraction, Fourier transform infrared, thermal analysis and surface area measurement techniques. The characteristic d₀₀₁ basal spacing of raw bentonite increased with the pillaring process and reached to 18.05 ?. The siloxane layers of bentonite were perturbed and the positions of Si-O stretching vibrations were altered by pillaring process. However, these pillars in the interlayer gallery spacing enhanced the thermal stability of bentonite. The new micropores were formed by the pillaring process and the specific surface area of raw bentonite increased by ca. 2-fold for aluminium-iron-pillared bentonite. FTIR spectra and thermal analysis curves of pyridine adsorbed samples clearly show that the surface Lewis acidity of aluminium-iron-pillared bentonite is greater than that of raw bentonite. Raw and aluminium-iron-pillared bentonites have been utilized as solid catalysts for benzoylation of benzene with benzoyl chloride. The aluminium-iron-pillared bentonite catalyst showed promising catalytic activity whereas raw bentonite showed no catalytic activity in benzoylation of benzene with benzoyl chloride.

Full text of DOI:10.1016/j.molstruc.2015.02.034

Accepted Manuscript
Characterization of AlFe-Pillared Unye bentonite: A Study of the surface acidity
and catalytic property
Bulent Caglar, Osman Cubuk, Ersin Demir, Fatih Coldur, Mustafa Catir, Cihan
Topcu, Ahmet Tabak
PII:
S0022-2860(15)00119-2
DOI:
http://dx.doi.org/10.1016/j.molstruc.2015.02.034
MOLSTR 21332
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Revised Date:
Accepted Date:
28 November 2014
9 February 2015
9 February 2015
Please cite this article as: B. Caglar, O. Cubuk, E. Demir, F. Coldur, M. Catir, C. Topcu, A. Tabak, Characterization
of AlFe-Pillared Unye bentonite: A Study of the surface acidity and catalytic property, Journal of Molecular
Structure (2015), doi: http://dx.doi.org/10.1016/j.molstruc.2015.02.034
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Characterization of AlFe-Pillared Unye bentonite: A Study of the surface
acidity and catalytic property
1
1*
2
1
1
Bulent Caglar , Osman Cubuk , Ersin Demir , Fatih Coldur , Mustafa Catir ,
1
3
Cihan Topcu , Ahmet Tabak ,
1
Department of Chemistry, Faculty of Arts and Sciences, Erzincan University, 24100
Erzincan, Turkey
2
Vocational School of Health Services, Perfusion Techniques, Okan University, 34959,
İstanbul, Turkey
3
Department of Chemistry, Faculty of Arts and Sciences, Recep Tayyip Erdoğan University,
5
3100 Rize, Turkey
Corresponding Author: Department of Chemistry, Faculty of Arts and Sciences, Erzincan
University, 24100 Erzincan, Turkey, e-mail: ocubuk@erzincan.edu.tr, Tel: +904462243097-
4
0010, Fax: +904462243016

Abstract
Aluminium-iron-pillared bentonite has been prepared by incorporation of the iron
mixed aluminium-polyoxocation into bentonite layers and characterized by the powder X-Ray
diffraction, Fourier transform infrared, thermal analysis and surface area measurement
techniques. The characteristic d001 basal spacing of raw bentonite increased with the pillaring
process and reached to 18.05 Å. The siloxane layers of bentonite were perturbed and the
positions of Si-O stretching vibrations were altered by pillaring process. However, these
pillars in the interlayer gallery spacing enhanced the thermal stability of bentonite. The new
micropores were formed by the pillaring process and the specific surface area of raw
bentonite increased by ca. 2-fold for aluminium-iron-pillared bentonite. FTIR spectra and
thermal analysis curves of pyridine adsorbed samples clearly show that the surface Lewis
acidity of aluminium-iron-pillared bentonite is greater than that of raw bentonite. Raw and
aluminium-iron-pillared bentonites have been utilized as solid catalysts for benzoylation of
benzene with benzoyl chloride. The aluminium-iron-pillared bentonite catalyst showed
promising catalytic activity whereas raw bentonite showed no catalytic activity in
benzoylation of benzene with benzoyl chloride.
Keywords: Pillared bentonite, Friedel-Crafts acylation, Surface acidity, Micropores

Characterization of AlFe-Pillared Unye bentonite: A Study of the surface
acidity and catalytic property
1
1*
2
1
1
Bulent Caglar , Osman Cubuk , Ersin Demir , Fatih Coldur , Mustafa Catir ,
1
3
Cihan Topcu , Ahmet Tabak ,
1
Department of Chemistry, Faculty of Arts and Sciences, Erzincan University, 24100
Erzincan, Turkey
2
Vocational School of Health Services, Perfusion Techniques, Okan University, 34959,
İstanbul, Turkey
3
Department of Chemistry, Faculty of Arts and Sciences, Recep Tayyip Erdoğan University,
5
3100 Rize, Turkey
Corresponding Author: Department of Chemistry, Faculty of Arts and Sciences, Erzincan
University, 24100 Erzincan, Turkey, e-mail: ocubuk@erzincan.edu.tr, Tel: +904462243097-
4
0010, Fax: +904462243016

Abstract
Aluminium-iron-pillared bentonite has been prepared by incorporation of the iron
mixed aluminium-polyoxocation into bentonite layers and characterized by the powder X-Ray
diffraction, Fourier transform infrared, thermal analysis and surface area measurement
techniques. The characteristic d001 basal spacing of raw bentonite increased with the pillaring
process and reached to 18.05 Å. The siloxane layers of bentonite were perturbed and the
positions of Si-O stretching vibrations were altered by pillaring process. However, these
pillars in the interlayer gallery spacing enhanced the thermal stability of bentonite. The new
micropores were formed by the pillaring process and the specific surface area of raw
bentonite increased by ca. 2-fold for aluminium-iron-pillared bentonite. FTIR spectra and
thermal analysis curves of pyridine adsorbed samples clearly show that the surface Lewis
acidity of aluminium-iron-pillared bentonite is greater than that of raw bentonite. Raw and
aluminium-iron-pillared bentonites have been utilized as solid catalysts for benzoylation of
benzene with benzoyl chloride. The aluminium-iron-pillared bentonite catalyst showed
promising catalytic activity whereas raw bentonite showed no catalytic activity in
benzoylation of benzene with benzoyl chloride.
Keywords: Pillared bentonite, Friedel-Crafts acylation, Surface acidity, Micropores

1
. Introduction
Clays have been used as adsorbents, ion exchangers and catalysts in many fields of
industry because of their environmental compatibility, lower cost, operation simplicity, easy
availability and reusability [1-6]. However, the weak porosities, low acidities and thermal
stabilities of raw clays limit their further potential applications in various industries.
Therefore, the pillaring process, which leads to the formation of a new class of material
known as pillared clays, is a commonly used process for modifying the structural, thermal and
surface properties of layered clays such as smectites [7-10]. Pillared clays are prepared by the
insertion of various polyoxocations into clay layers with the replacement of exchangeable
cations, followed by calcinations. The calcinations induce the dehydration and
dehydroxylation of polyoxocations and thus yield thermally stable oxides, known as pillars,
which act as pillar to prop up the opened clay layers and prevent their collapse [11-13].
Changing the type of pillars influences the textural, structural, catalytic and adsorptive
properties of pillared clays directly and for this reason, many different pillared clays are
prepared by forming metal oxides and, mixed metal oxides into the clay layers such as Al
ZrO , TiO , Cr , Fe , Al -ZrO , Al -SiO , Al -Fe , Al -MoO , Al
La , Al -V etc [14-24]. Pillared clays which have good thermal stability, high surface
2
3
O ,
2
2
2
O
3
2
O
3
2
O
3
2
2
O
3
2
2
O
3
2
O
3
2
O
3
3
2
3
O -
2
O
3
2
O
3
2
O
3
area, suitable porosity, shape selectivity and enhanced acidities (both Brønsted and Lewis
acidic sites) are potential heterogeneous catalyst for organic reaction such as cracking,
oligomerization, oxidation, acetalization, isomerisation, alkylation of aromatic hydrocarbons,
methanol conversion, decomposition of organic pollutants etc [25-32]. The conversion and the
selectivity of these reactions depend on the concentration, type and strength of the acid sites
[
33]. Hammet indicator method, n-butylamine back titration, FTIR analysis of the adsorbed
probe molecules and thermal decomposition of probe base molecules from catalyst surface are used
for rapid determination of the type and amount of acid sites in solid catalyst [34-36].
Furthermore, Friedel-Crafts alkylations and acylations are most common test reactions
used for examining the acidic properties of catalysts [37-42]. These reactions are executed by
utilizing various homogeneous Lewis acid catalysts such as AlCl
3
, HF, ZnCl
2
, FeCl
3
or BF
3
but these homogeneous catalysts originate some problems, including corrosion, toxicity,
separation difficulties, recovery from the reaction product, disposal of wastes and catalysts
[
43-44]. Clays and modified clays are particularly promising candidates to replace liquid
acids in Friedel Crafts reactions and other chemical reactions due to their superior properties

such as eco-friendly nature, non-toxicity, simple filtration, non corrosive form and reusability
15,37-42].
[
In the present study, the structural and thermal properties of raw Unye bentonite and
Fe-Al-pillared bentonite was examined by using the powder X-Ray diffraction (PXRD),
Fourier transform infrared (FTIR), thermal analysis (TG-DTG) and surface area measurement
techniques. The surface acidity and type of acidic sites in bentonites were determined by
FTIR and thermal decomposition measurements with the use of pyridine as a probe molecule.
The benzoylation of benzene with benzoyl chloride was utilized as a model reaction to
investigate acidic manner and catalytic activities of raw and pillared bentonites.
2
. Experimental
.1. Materials
The clay used as the starting material in the preparation of AlFe-PILC sample was
2
Unye bentonite from Turkey. The raw bentonite (RB) dried at 105 ºC was mixed with 100 ml
of 0.1 M NaCl solution at room temperature for 1 day. The products (Na-B) were washed
with deionized water thoroughly and AgNO
3
test was applied to the filtrate. The solid
products which were dried at 105 ºC were ground to 200 μm.
2
.2. The preparation of the materials
The pillaring reagent was prepared by slow addition of 0.2M NaOH solution to 0.2M a
mixture of Al(NO and Fe(NO (Al/Fe= 9/1) solution to reach an OH/(Al+Fe) molar ratio
3
)
3
)
3 3
of 2.2. The pillaring solution was aged for 12 days at room temperature under constant stirring
to allow the formation of the iron mixed aluminium polyoxycation. The pillaring solution is
added drop wise to a 2% suspension of the Na-B in the ratio of 10 mmol of metals (Al+Fe)
per gram of clay. The suspension was aged for 7 days at 40 ºC, then it was filtered off and the
supernatants were washed with deionized water until the conductivity was reduced to below
1
0 μS. Finally, the solid products were calcined at 400 ºC for 4h and AlFe-PILC-B sample
was obtained.
The bentonite samples were dried in hot air oven for 24 h at 120 C before pyridine
treatment. Exposure of RB and AlFe-PILC-B surfaces to pyridine (Py) were carried out by
heating 0.01g samples with 1ml pyridine (bp=115C) in sample cup at 120C for 1h in the oven [36].

After cooling down to room temperature and adsorption of pyridine, the sample adsorbed
pyridine was evacuated for 20 min at several temperatures (120-320 C). The chemisorped
pyridine onto RB and AlFe-PILC-B samples were labelled as RB-Py and AlFe-PILC-B-Py,
respectively.
2
.3. Catalytic experiment
The benzoylation of benzene with benzoyl chloride has been selected as the test
reaction to investigate surface acidity and catalytic properties of raw and AlFe-PIL-B. To a
mixture of benzoyl chloride (1 mmol, 116 µL) and benzene (4 mL) was added 400 mg of
o
catalyst. The reaction mixture was then heated to 80 C and stirred for 24 h [40,41]. After
o
evaporation of benzene under reduced pressure (10 mbar, 25 C) the residue was diluted with
saturated NaHCO (10 mL) and extracted with dichloromethane (3x15 mL). The solvent was
3
evaporated and the product was purified by silica gel column by eluting with EtOAc-hexane
1
(
02:98) to give benzophenone as the white powder (65 mg, 46%). H-NMR (200 MHz,
1
3
CDCl
3
, ppm)  7.83-7.78 (m, 4H), 7.62-7.43 (m, 6H); C-NMR (50 MHz, CDCl
3
, ppm) 
98.6, 139.6, 134.3, 132.0, 130.2; IR (KBr, cm ) 3059, 1658, 1598, 1577, 1446, 1317, 1277,
176, 1149, 941, 919.
The XRPD patterns were obtained at ambient temperatures on a Rigaku 2000
automated diffractometer by using Ni filtered CuK radiation (=1.54050 Å; 40kV and
0mA). Bragg’s law, defined as n=2dSin, was used to compute the crystallographic
-1
1
1

4
spacing (d) for the examined bentonite samples. The FTIR spectra of the bentonite samples
were recorded on a Bruker Vertex 80V-spectrometer equipped with a MCT/A detector in the
-1
-1
region 4000-400 cm at a resolution of 4 cm , using KBr pellet technique. Specimens for
measurement were prepared by mixing 0.9 mg of the sample powder with 70 mg of KBr and
pressing the mixture into a pellet. The TG and DTA curves were scanned by using a PYRIS
o
-1
Diamond TG/DTG apparatus in a dynamic air atmosphere (heating rate: 10 C min , platinum
o
crucibles, mass 10 mg and temperature range 30-1000 C). Nitrogen adsorption/desorption
o
isotherms were measured at 77K (-196 C) with a Quantachrome Autosorb-İQ analyzer. The
o
samples were degassed in vacuum at 275 C for 6h prior to the textural measurements at 77K
o
(
(
-196 C). Specific surface areas were calculated according to the Brunauer-Emmett-Teller
BET) method adsorption data in the relative pressure (P/Po) range 0.02-1.00. The micropore
surface area and micropore volume were calculated by t-plot analysis. The pore size
distributions were derived from adsorption branches of isotherms applying the non-local
density functional theory (NLDFT) method for cylindrical pores.

3
. Results and discussion
3
.1. PXRD data of samples
Fig. 1. shows the PXRD patterns of the RB and AlFe-PILC-B samples. The d001, d020-
1
00, d130-200 and d060 reflections of the main montmorillonite component were observed at 5.59,
9.75, 35.05 and 61.83(2) with the corresponding distance of 15.80, 4.49, 2.56 and 1.50 Å,
respectively (Fig. 1a). The high CaO content (1.25%) and the basal spacing of RB (d001
5.80 Å) indicate that bentonite contains a calcium-montmorillonite as a dominant clay
1
=
1
mineral [45,46]. In addition, the d060 peak value of 1.50 Å indicates the presence of an Al-rich
dioctahedral montmorilonite. The bands originating from external clay component cristobalite
are observed at 21.65, 28.11 and 49.01(2) with the distance of 4.10, 3.17 and 1.86 Å,
respectively. It may be concluded from the comparison of the intensities of the d001 peak of
RB and the diffraction of the nonclay component that the main component of bentonite is
montmorillonite. When the RB interacts with pillaring solutions, an expansion is observed
along the c-axis. The characteristic d001 spacing of raw bentonite increased from 15.80 to
1
8.05 Å for AlFe-PILC-B which denote the formation of the (FeAl)
interlayer space of bentonite after calcinations. This result is in agreement with the previous
literature [8,10,19,21] (Fig. 1b). Furthermore, the diffraction peaks belonging to the d020-100
130-200 and d060 planes of bentonite are observed at 19.93, 35.25 and 61.77(2) with the
2
O pillars species into the
3
,
d
distances of 4.45, 2.54 and 1.50 Å, respectively. The RB has a well-defined d001 pattern while
the d001 peaks of AlFe-PILC-B is broad and its intensity lower than RB, which means that
AlFe-PILC-B is semi crystalline in nature (since the heterogeneity in the size of the pillars).
Also, the presence of a wide signal regarding d001 is related to the long range face to face layer
aggregation which arisen from the inadequate entrance of ion in the interlayer space [21-23].
An interlayer opening caused by pillaring process were calculated as 8.45 Å for AlFe-PILC-B
by subtracting the thickness of SiO
2
-Al
2
O
3
-SiO sheet (9.6 Å) from the d(001) value of
2
pillared clay [7]. The amount of the interlayer expansion for the Fe containing pillared
3
+
samples slightly larger than the Al pillared samples might be due to the substitution of Al by
3
+
the somewhat larger Fe ions in the original Al13-pillars [19].

3
.2. FTIR data of samples
The FTIR spectra of the RB and AlFe-PILC-B samples are shown in Fig. 2. The
comparative infrared spectra of raw and pillared bentonite are extensively utilized for
investigation of the structural changes in clay framework. There are significant differences
between the spectra of RB (Fig. 2a) and pillared bentonite (Fig. 2b). The peaks at 3627 and
-1
9
18 cm are ascribed to the OH stretching of structural hydroxyls and deformation of
-
1
AlAlOH in the octahedral layers of RB whereas the peaks at 3456 and 1641 cm correspond
to the OH stretching and OH deformation of water of RB, respectively. After pillaring, the
intensities of these peaks decrease since the removal of the hydroxyl groups and the adsorbed
-1
water [8]. The features at 1041 and 1090 cm correspond to the Si-O stretching vibration and
the Si-O stretching band (longitudal mode) of tetrahedral sheet. As in the previously reported
studies, the original positions and intensities of these peaks were altered by the pillaring of the
RB which may be due to the siloxane layers perturbed by pillars. In addition, the vanish of the
-
1
peaks at 627 and 523 cm belong to coupled Al-O, Si-O (out of plane) and Al-O-Si
deformation of bentonite show that the clay layer structure was affected by pillaring process.
However, absence of additional peaks suggests that no bond formation occurs between
-1
bentonite and pillars [47]. In addition the band at 793cm may reflect the presence and
survival of cristobalite after the pillaring process. This state was also supported by PXRD
measurements.
3
.3 Thermal analysis of samples
The thermal analysis (TG-DTG and DTA) profiles of the samples are shown in Fig. 3.
On the curve of RB, two dehydration stages with a total mass loss of 12.26 % in the
o
temperature range of 31-212 C are noticeable. The removal of adsorbed water with a mass
o
loss of l0.73 % in the first stage 31-142 C gives rise to an endothermic DTA peak centred at
o
o
o
9
0 C and the endothermic feature at 163 C in the range of 142-212 C which is accompanied
by a mass loss of 1.53 corresponds to the elimination of the water species coordinated to the
interlayer cations. Noticeable differences between the thermal curves of RB and AlFe-PILC-B
were observed. The total amount of waters removed from pillared bentonite (9.2%) are less
than that of RB and the elimination of the adsorbed water from pillared bentonite occurred at
lower temperature. The dehydration of adsorbed water from AlFe-PILC-B with a mass loss of
o
o
9
.2 % in the temperature interval of 31-148 C, give rise to DTA peaks at 77 C. Moreover the

removal of cation-coordinated water species is not observed in the pillared clay. It could be
concluded that the interlayer cations are completely exchanged with keggion ions and the
pillared clay obtained after the calcination has low amount of adsorbed waters. However,
dehydroxylation processes of AlFe-PILC-B resulted in a mass loss of 2.6% in the range of
o
o
3
37-731 C (DTGmax=655 C) The dehydroxylation maxima of pillared bentonite shifts to
o
higher temperature compared to the RB (DTGmax=625 C). The position of this peak is very
important in estimating thermal stability of the pillar bentonites [7,13]. It is clearly seen that
the thermal stability of clay enhanced by the pillars present in the interlayer gallery spacing.
3
.4. Textural characterization of samples
The surface areas of clay minerals are related to the numbers and sizes of internal and
external pores they contain. The total number of micropores (pore width≤ 2 nm) and
mesopores (pore width, 2-50 nm) has primary importance on the surface areas of clays but the
contribution of macropores (pore width≥50 nm) to these characteristics is at negligible level
[
48]. Nitrogen adsorption-desorption isotherms of samples are illustrated in Fig. 4a and
Fig.4b. These isotherms of bentonite samples were similar to those reported by the other
authors [30,31,49]. According to the IUPAC classification or or BDDT (Brunauer, Deming,
Deming and Teller) classification, the nitrogen adsorption/desorption isotherms of bentonite
samples demonstrate Type IV behaviour which is characteristic of mesoporous solids [50].
The most important differences between the nitrogen adsorption isotherms of the RB and
AlFe-PILC-B can be seen at relative pressures lower than 0.10. For AlFe-PILC-B, the
significant increase in adsorbed volume at low relative pressure (P/P <0.01) indicated the
0
presence of micropores [30,31,49]. On the other hand, the isotherms of two samples were
similar at relative pressure range of 0.40 to 0.99 and showed H4 type hysteresis loops
representing the slit shaped pores and plate-like particles with spaces between the parallel
plates, which all closed at a relative pressure of about 0.40 [17]. The mesoporosity in the
samples is evident from the presence of hysteresis in the isotherms of adsorption/desorption,
which are clearly seen in two samples [51]. The AlFe-PILC-B isotherm is in the narrow shape
which depends on the pore size distribution, pore geometry, cristallinity and connectivity of a
mesoporous adsorbent. Besides, adsorption jumps in the above isotherms appeared due to the
capillary condensation in the mesopore between the relative pressures range of 0.2-0.4 (P/Po)
[
20,52].

The textural parameters of RB and AlFe-PILC-B samples are shown in Table 1. The
2
specific BET surface area of RB (121.32 m /g), which contains the micropore and mesopore
2
2
surface area of 6.07 m /g and 115.25 m /g, respectively, increased by ca. 2-fold for AlFe-
2
2
PILC-B (234.49 m /g) which arise from the micropore surface area of 67.96 m /g and
2
mesopore surface area of 166.53 m /g). This increase was expected because the pillaring
process mainly creates microporosity. A more detailed description of the microporous and
mesoporous regions of the bentonite samples was obtained from the pore size distributions.
Typical micropore and the mesopore size distribution curves (calculated by DFT) of RB and
AlFe-PILC-B are presented in Fig. 4c and Fig. 4d, respectively. As shown in the figures, the
RB possess a unimodal and a fairly broad pore size distribution around pore width of 68 Å
(
mesopores), whereas AlFe-PILC-B posses trimodal and more sharp pore size distribution
around pore width of 10 Å (micropore), 26 Å (mesopore) and 66 Å (mesopore). This situation
shows that the mesoporous structure was slightly influenced but micropore structure was
significantly influenced and new additional micropores formed by the pillaring process. The
similarity of the mesopore size distributions indicates that the size of the mesopore may
depend more on the stacking of the silicate leaves rather than on the interlayer distance [17].
Although, the pillaring process produced a remarkable increase in the micropore volume from
0
.001 cc/g to 0.027 cc/g for AlFe-PILC-B, but the total pore volume did not significantly
change. In addition, RB has the average pore width of 67.94 Å whereas the value of this
parameter decreases to 8.63 Å for AlFe-PILC-B. These results were in great agreement with
the nitrogen adsorption/desorption isotherms. The increasement of the surface areas of
pillared bentonite may be ascribed to the increasing effect of the formation of the micropores
and enlarged cumulative pore volume of micropores.
3
.5. Surface acidities of samples
Pyridine has been utilized as a probe molecule for the determination of the chemical
nature of acidic sites in the raw and pillared bentonites [15,36,53] The specific IR absorption
-1
peaks of adsorbed pyridine in the region of 1700-1350 cm have been used to differentiate
between the Brønsted and Lewis sites of RB and AlFe-PILC-B samples (Fig. 5). Following
-
1
the pyridine adsorption on RB, the peaks at 1635, 1595, 1541, 1492 and 1441 cm were
-
1
observed. The peaks at 1595 and 1441 cm originated from H-bonded pyridines species
-1
whereas the peaks at 1635 and 1541 cm represent the pyridine molecules interacted with the

-1
Brønsted acidic sites. In addition, the prominent peak at 1492 cm mainly originated from the
pyridine species held by both the Brønsted and Lewis centres [15,36,53]. The corresponding
peak intensities of adsorbed pyridine indicated that Brønsted acidity was predominant in the
raw bentonite and these observations are in accordance with the thermal analysis results of
pyridine adsorbed onto RB. The unsaturated metal atoms located at the edges of the siloxane
layer are the major sources of Lewis acidity for RB while the interlamellar water coordinated
to exchangeable cations and the terminal silanols of the clay contribute to the Brønsted acidy.
o
The spectrum of AlFe-PILC-B-Py recorded at 100 C shows the presence of both Lewis and
-1
Brønsted acid sites (Fig. 5b). The most prominent peaks at 1610 and 1451 cm come from the
pyridine species coordinated to Lewis acid centres were observed as significantly
strengthened whereas the peaks related to the pyridine species protonated at Brønsted acidic
-1
centres at 1638 and 1542 cm were observed as slightly increased for AlFe-PILC-B. The
formation of AlFe-pillars between the bentonite layers strongly increases the Lewis acidity
but do not have further special improvement over the Brønsted acidity. Because the Brønsted
acidity come from the clay structure as mentioned above, pillars have a little contribution. IR
spectrums of samples clearly show that the surface Lewis acidity of AlFe-PILC-B is greater
than that of RB.
Additionally, thermal desorption of pyridine onto bentonite samples was also followed
by thermal analyses techniques (TG/DTG) to calculate the acidity of samples and estimate the
acidic strength of both Brønsted and Lewis acid centres (Table 2). The desorption of the
pyridine species on the bentonite composites in the temperature range of 30-500 C give rise
to three different mass losses depending on the surface acidity of bentonites. The first mass
loss in the temperature range of 30-95 C usually corresponds to the removal of moisture or
desorption of physisorbed pyridine on weak acid sites. However, the IR spectra of pyridine
-1
adsorbed on bentonite samples did not show any band at 1575cm which is diagnostic of
physisorbed pyridine. Thus, this mass loss at near 63C must be related to desorption of
moisture and/or H-bonded pyridine attached to external surface sites. The second and third
mass losses in the temperature interval of 100-235C and 243-357C are attributed to
desorption of pyridine species onto Brønsted and Lewis acid sites, respectively [54,55]. The
acidity (A) of the two composites was calculated as mmol pyridine/gram catalyst based on the
thermal analysis data. The RB-Py species presents three DTG peaks corresponding to
desorption of pyridine at 63, 169 and 280 C in the temperature ranges of 30-95 C, 100-235

C and 243-357 C with the mass losses of 3.90, 7.81 (together 1.53% mass loss of removal

of water coordinated to the interlayer cation) and 1.33%, respectively. These mass losses are
related to the elimination of moisture, removal of protonated pyridine species on Brønsted
acid sites and desorption of pyridine from Lewis acid sites (A=0.158), respectively, while the
classic DTG peak at 621 C corresponds to dehydroxylation process. RB has more Brønsted
acid sites (A=0.77) than Lewis acid sites (A=0.158). For AlFe-PILC-B, in the temperature
interval of 100-235 C, the removal of pyridine species from Brønsted acid sites (A= 0.827)
with a mass loss of 6.54% gives rise to a DTG peak at 174 C. In addition, the DTG peak at
3
52 C with a mass loss of 6.80% corresponds to desorption of pyridine from Lewis acid sites
(
A=0,872). It is clearly seen that the Lewis acidity of the RB (A=0.158) is enhanced by ca 6-
fold for AlFe-PILC (A=0,872) whereas the Brønsted acidity of RB is slightly increased by
pillaring process. The increase of Lewis acidity is due to the formation of pillar oxides in the
interlayer region as interpreted in FTIR results. Furthermore, the pyridine species coordinated
to the Lewis centres gets extra thermal stability of about 72C for AlFe-PILC-B compared to
RB. In addition, the total acidity value of RB (0.928) remarkably increased to 1.699 for AlFe-
PILC-B with the pillaring process.
3
.6. Friedel–Crafts acylation
Friedel–Crafts type acylation of aromatic compounds to aromatic ketones is one of the most
important synthesis methods used in organic chemistry [37-42]. As an example, this reaction
is widely used to test the acidic properties of catalyst [42]. To test the catalytic activity of our
samples, we studied the Fridel-Crafts benzoylation of benzene with benzoyl chloride in the
presence of raw and pillared bentonites (Fig. 6). Benzene and benzoyl chloride were
o
separately treated with raw and AlFe-PILC-B bentonites as the catalysts at 80 C for 24 h. No
1
benzophenone formation was observed by H-NMR spectroscopy when raw bentonite was
used as catalyst, whereas benzophenone was obtained with the yield of 46% in the case of
AlFe-PILC-B utilization. Benzophenone was purified by means of column chromatography
1
13
and characterized by its H and C NMR spectra, shown to be identical with an authentic
sample. The amount of benzophenone yield significantly depends on the concentration and
strength of the Lewis acidic sides of bentonite samples.

4
. Conclusion
The XRPD pattern showed that the pillaring of bentonite caused an expansion of basal
spacing from 15.80 to 18.05 Å. The original positions and intensities of peaks at 1041 and
-1
1
090 cm correspond to the Si-O stretching vibration and the Si-O stretching band of
tetrahedral sheet were altered by the pillaring of the RB. The pillars in the interlayer gallery
spacing enhanced the thermal stability of raw bentonite. Nitrogen adsorption-desorption
isotherms of samples showed that the mesoporous structure was not significantly influenced
but a new micropores were formed by pillaring process. The formation of FeAl-pillars into the
bentonite layers on AlFe-PILC strongly increased especially the Lewis acidity but do not have
further special advantage over the Brønsted acidity. The present data shows that the AlFe-
pillared bentonite material can be used as a solid catalyst for Friedel Crafts acylation of
aromatic hydrocarbons. Also, the data obtained in this study may provide further insight into
heterogenous catalysis studies and may be utilized for developing new eco-friendly solid
catalysts.
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Figure Legends:
Fig. 1. PXRD patterns of the bentonite samples (a) RB, (b) AlFe-PILC-B
Fig. 2. FTIR spectra of the bentonite samples (a) RB, (b) AlFe-PILC-B
Fig. 3. DTA, DTG and TG curves of bentonite samples (a) RB, (b) AlFe-PILC-B
Fig. 4. Nitrogen adsorption-desorption isotherms of samples (a) RB, (b) AlFe-PILC-B and typical
micropore and the mesopore size distribution curves of samples (c) RB, (d) AlFe-PILC-B
Fig. 5. FTIR spectra of the pyridine adsorbed bentonite samples (a) RB-Py, (b) AlFe-PILC-B-Py
Fig. 6. Benzoylation of benzene with benzoyl chloride over the AlFe-PILC-B catalyst

Table Captions
Table 1. Textural parameters of bentonite samples
Table 2. Thermal analysis data of the pyridine adsorbed bentonite samples
Table 1. Textural parameters of bentonite samples
BET
p
mp
p
mp
3 -
S
tS
BJH
S
tV
BJHV (cm g
1
)
2
-1
2
-1
2
-1
3 -1
Sample
RB
(m g )
121.32
234.49
(m g )
(m g )
115.25
166.53
(cm g )
0.002
6.07
0.249
0.244
AlFe-PILC-B
67.96
0.027

Table 2. Thermal analysis data of the pyridine adsorbed bentonite samples
Sample
RB-Py
Temp. range
ºC)
30-95
Mass loss (%)
DTGmax.
Acidity (A)
Thermal process
(
(mmol/gcat)
3.90
63
-Removal of moisture and H-bonded pyridine
-Desorption of Py from Brønsted sites and
removal of coordinated water (1.53%)
100-235
7.81
169
0.770
-
-
Desorption of Py from Lewis sites
Dehydroxylation
2
43-357
60-691
1
.33
.30
280
621
0.158
3
5
AlFe-PILC-B-Py
32-91
0.92
60
-Removal of moisture and H-bonded pyridine
1
0-235
40-400
68-705
6.54
174
-Desorption of Py from Brønsted sites
0
.827
.872
2
4
6.80
1.82
352
650
-Desorption of Py from Lewis sites
0
-
Dehydroxylation

Highlights



The AlFe-pillared bentonite catalyst was characterized by various techniques.
The new micropores and Lewis acidic sites were formed by pillaring process.
The AlFe-pillared bentonite as catalyst was used in the benzoylation of benzene with
benzoyl chloride.

The AlFe-pillared bentonite is a promising eco-friendly catalyst in organic reactions