T. Parangi et al. / Applied Catalysis A: General 467 (2013) 430–438
431
stability of the materials in various acids, bases and organic solvent
media has been studied and their potential use as solid acid cata-
lysts has been explored and compared by studying esterification as
a model reaction wherein mono esters such as ethyl acetate (EA),
propyl acetate (PA), butyl acetate (BA), benzyl acetate (BzAc) and
diesters such as diethyl malonate (DEM), diethyl succinate (DES),
dibutyl phthalate (DBP), dioctyl phthalate (DOP) have been synthe-
sized optimizing several parameters such as reaction time, catalyst
amount and mole ratio of reagents.
– Table 3), then filtered, washed with double distilled water to
remove adhering ions and dried at room temperature (Step-II).
2.2.4. Acid treatment
The above dried materials obtained in step-II were broken down
to the desired particle size [30–60 mesh (ASTM)] by grinding and
sieving. 5 g of this material was treated with 50 mL of 1 M HNO3
for 30 min with occasional shaking. The material was then sepa-
rated from acid by decantation and treated with double distilled
water to remove adhering acid. This process (acid treatment) was
repeated at least 5 times for both the materials. After final washing,
the material was dried at room temperature.
2
. Experimental
2.1. Chemicals
Thorium
nitrate
and
2
(Th(NO ) ·5H O),
ceric
dihydrogen
sulphate
phosphate
3
4
2
2
2
.3. Characterization
(
(
Ce(SO ) ·4H O)
sodium
4
2
NaH PO ·2H O) were procured from Loba Chemicals, Mum-
2
4
2
.3.1. Chemical stability
The chemical stability of the catalysts in various acids (HCl,
bai, while ethanol, 1-propanaol, 1-butanol, benzyl alcohol, octanol
2-ethyl 1-hexanol), acetic acid, phthalic anhydride, malonic acid,
(
H SO , HNO ), bases (NaOH and KOH) and organic solvent media
2
4
3
succinic acid, cyclohexane, xylene and toluene were obtained
from Across Organics. Double-distilled water was used for all the
studies.
(ethanol, propanol, butanol, benzyl alcohol, cyclohexane, toluene,
xylene and acetic acid) was examined by taking 500 mg of each
of the synthesized catalyst in 50 mL of the particular medium and
allowed to stand for 24 h. The change in colour, weight and nature
was observed.
2
.2. Catalyst synthesis
CP and TP were synthesized by sol–gel method varying several
parameters such as mole ratio of reactants, mode of mixing (metal
salt solution to anion salt solution or vice versa), temperature, pH
and rate of mixing. The main objective was to obtain a material with
high cation exchange capacity (CEC) values which reflect on the
protonating ability and thus the acidity in the materials. The term
CEC is intended to describe the total available exchange capacity of
an ion exchanger, as described by the number of functional groups
on it. This value is constant for a given ion exchange material and
is expressed in milli equivalents per gram, based on dry weight of
2.3.2. Instrumentation
All synthesized materials were subjected to instrumental meth-
ods of analysis/characterization. CP and TP were analyzed for
cerium, thorium and phosphorus by ICP-AES. FTIR spectra were
recorded using KBr pellet on Shimadzu (Model 8400S). Thermal
analysis (TGA) was carried out on a Shimadzu (Model TGA 50)
◦
−1
thermal analyzer at a heating rate of 10 C min . X-ray diffrac-
◦
◦
◦
togram (2ꢀ angles = 10 –90 , scanning time = 2 /min and sample
run time = 8 min) was obtained on X-ray diffractometer (Brucker
AXS D8) with Cu K␣ radiation with nickel filter. SEM and EDX
of the sample were scanned on Jeol JSM-5610-SLV scanning elec-
tron microscope. Surface area was determined by BET multipoint
method using a Micromeretics Gemini 2220 series surface area
analyzer. Surface acidity was determined on Chemisorb 2720, by a
temperature programmed desorption (TPD) of ammonia. All mate-
+
+
material in given form (such as H ). The Na ion exchange capacity
CEC) of materials was determined by the column method [29] by
(
optimizing volume and concentration of sodium acetate solution.
Several sets of materials were prepared varying conditions in
each case using CEC as the indicative tool. (ESM – Tables 1 and 2
describe optimization of reaction parameters for synthesis of CP
and TP respectively)
◦
◦
◦
◦
rials were preheated at 150 C, 200 C and 700 C temperatures and
thereafter ammonia was chemisorbed at 120 C and then desorp-
tion was carried out upto 700 C at a heating rate of 10 C min
◦
◦
−1
2.2.1. Synthesis of CP at optimized condition
A solution containing Ce(SO ) ·4H O [0.1 M, 50 mL in 10% (w/v)
in all cases. The products were analyzed by Ceres 800 Plus gas
chromatograph (GC) using flame ionization detector.
4
2
2
H SO ] was prepared, to which NaH PO ·2H O [0.3 M, 50 mL] was
2
4
2
4
2
−
1
added dropwise (flow rate 1 mL min ) with continuous stirring for
an hour at room temperature, when gelatinous precipitates were
obtained (Step-I). The resulting gelatinous precipitate was allowed
to stand for 3 h at room temperature, then filtered, washed with
conductivity water to remove adhering ions and dried at room
temperature (Step-II).
2
2
.4. Synthesis of esters
.4.1. Synthesis of monoesters (EA, PA, BA and BzAc)
In a typical reaction, a 100 mL round bottomed flask equipped
with a Dean and Stark apparatus, attached to a reflux condenser
was used and charged with acetic acid (0.05–0.10 M), alcohol
2
.2.2. Synthesis of TP at optimized condition
(0.05–0.10 M), catalyst (0.10–0.20 g) and a suitable solvent (15 mL).
An aqueous solution of Th(NO ) ·5H O[0.1 M, 50 mL] was added
3
4
2
−
1
The reactions were carried out varying several parameters such as
reaction time, catalyst amount, mole ratio of reactants and these
parameters optimized. The temperature parameter has not been
varied as the reaction temperature is sensitive to boiling points of
drop wise (flow rate 1 mL min ) to an aqueous solution of
NaH PO ·2H O [0.2 M, 100 mL] with continuous stirring for an hour
2
4
2
at room temperature, when gelatinous precipitates were obtained
(
Step-I). The resulting gelatinous precipitate was allowed to stand
for 5 h at room temperature, then filtered, washed with double dis-
tilled water to remove adhering ions and dried at room temperature
◦
◦
◦
reactants [ethanol (78 C), 1-propanol (97 C), 1-butanol (118 C)
◦
and benzyl alcohol (205 C)] as well as solvents used as azeotrope.
Cyclohexane (80 C) was used as a solvent for the synthesis of ethyl
acetate and toluene (110 C) for propyl acetate, butyl acetate and
◦
(
Step-II).
◦
benzyl acetate. After completion of reaction, catalyst was separated
by decantation and reaction mixture was distilled to obtain the
product.
2
.2.3. Synthesis of CP and TP under microwave irradiation
Gelatinous precipitate obtained in step-I was subjected to
microwave irradiation for optimum time and temperature (ESM