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00
S.Z. Mohamed Shamshuddin et al. / C. R. Chimie 15 (2012) 799–807
industrially important organic transformations. Much
work has been done on sulfated zirconia as a solid acid in
the field of fine chemical synthesis [13,14]. Due to a
major disadvantage associated with sulfated zirconia,
many efforts have been made to synthesize sulfate free-
zirconia based solid acids. Sulfate free-zirconia based
by impregnation method. The honeycomb was wash coated
with zirconia before coating the active catalysts. Wash
coating is done to increase the surface area and to have a
support material which has a better interaction with the
active catalyst [21]. For wash coating, a dilute solution of
zirconyl nitrate in presence of a binder (cellulose) was
prepared which was then coated on a bare honeycomb
monolith by dipping and drying in a furnace maintained at
400 8C.
x 2 x 2
solid acids such as MoO /ZrO and WO /ZrO have been
synthesized and used as solid acid catalysts in a few
liquid and vapor phase reactions [15–17]. It is reported
that modification of ZrO
2
with Mo or W ions can
Typically, for coating 5%Mo/ZrO
dilute solution containing 0.96 g of zirconyl nitrate
[ZrO(NO . 8H O] and 0.25 g of ammonium molybdate
[(NH Mo 24. 4H O] with 50 mL of deionised water, was
prepared. The resulting solution was coated on a wash-
coated monolith by dipping and drying in a furnace pre-
heated at 400 8C. The dipping and drying steps were
repeated for 12 to 15 times until ꢀ0.2 g of the catalyst is
coated on the monolith. The honeycomb coated with
2
on a honeycomb,
generate strong acid sites including super acid sites [18].
Though these sulfate free-zirconias are superior solid
acid catalysts and free form deactivation, unlike sulfated
zirconia, they are less explored for organic synthesis
3
)
3
2
4
)
6
7
O
2
[
19].
Salicylates are an important group of esters used in the
synthesis of drugs, food preservatives, plasticizers,
pharmaceuticals, polyesters, solvents, perfumes and
cosmetics [20]. Especially, phenyl salicylate (salol) is an
ester, which has a pleasant taste and odor, is more useful
in sun-tan lotions, as an antiseptic, anodyne and pain-
relieving agent. It can be prepared by simple esterification
of salicylic acid with phenol in presence of a liquid/solid
acid catalyst. But an anhydrous condition prevalent in
transesterification is advantageous in increasing the yield
of the desired ester and also in increasing the lifetime of
the catalyst system.
5%Mo/ZrO
furnace before its use as a catalyst. Similarly, 10% and
15%Mo/ZrO were synthesized by using the above-
2
was calcined at 550 8C for 5 h in a muffle
2
described procedure.
2
Five percent, 10% and 15%W/ZrO were coated on a
honeycomb by adopting the procedure described in the
above paragraph using known amounts of zirconyl nitrate
and ammonium tungstate salts.
In this article, the work done on the synthesis of
2.1.2. Synthesis of catalytic material in powder form
cordierite honeycomb coated with solid acids such as ZrO
2
,
2 2 2
ZrO , Mo/ZrO and W/ZrO were also prepared in
Mo/ZrO and W/ZrO , determination of their physico-
2
2
powder forms by impregnation method using salts such as
zirconyl nitrate with/without ammonium molybdate or
ammonium tungstate. Known amounts of the required
salts were taken in a china dish and a paste is made by
using small amount of water. The paste was then dried in
an air oven at 120 8C for 12 h and calcined at 550 8C for 5 h
in a muffle furnace.
chemical properties and catalytic properties in liquid
phase synthesis of phenyl salicylate and other salicylate
esters via transesterification is reported. The effect of
2
concentration of Mo or W ions on ZrO , nature of the
catalyst (whether honeycomb coated or powder form),
reaction temperature, reaction time and reusability of the
catalytic material in transesterification is studied to obtain
highest possible yield of salol with good selectivity. The
use of honeycomb monoliths as catalyst carriers especially
2.2. Physicochemical characterization of catalytic materials
for solid acids such as ZrO
2
and its modified forms would
The catalytic material (both honeycomb coated and
be a very cost effective and ecofriendly process and also
will be very interesting initiative step in the field of organic
synthesis.
powder forms of ZrO
characterized by BET, NH
tion, powder XRD and SEM techniques for their specific
surface area, surface acidity, crystallinity and morphology,
respectively.
2
, Mo/ZrO
2 2
and W/ZrO ) were
3
-TPD/n-butylamine back titra-
2
. Experimental
The specific surface area of the catalytic material was
evaluated by a NOVA 1000 Quanta chrome high-speed gas
sorption analyzer instrument. In this analysis, the catalytic
material was degassed at 523 K for 5 h before measure-
ments. Specific surface area was calculated using the BET
2.1. Preparation of the catalytic material
Cordierite honeycomb monoliths (height = 1.20 cm,
diameter = 2.50 cm and hole size = 0.2 cm) were used for
the present work and they were supplied by Shrey
Ceramics, Baroda, India.
Zirconyl nitrate, ammonium molybdate and ammoni-
um tungstate were supplied by M/S LOBA Chemie India
Ltd., India.
3
equation. The total surface acidity was measured by NH -
TPD method by using Puls Chemi-sorb 2705 from
Micromeritics. Here, the catalytic material was degassed
under a helium stream for 1 h, ammonia (99.99%) gas was
injected into the stream until saturation was reached,
cooled to 323 K. The system was maintained at 323 K for
3
0 min. After purging, the system with flowing helium for
ꢁ
1
2
.1.1. Synthesis of catalytic material in honeycomb coated
form
Solid acids such as ZrO
W/ZrO (%W = 5, 10, 15) were coated on different monoliths
2 h at 323 K, the sample was heated at the rate of 5 K min
in helium to 973 K. The change in concentration of the
desorbed NH was monitored using an online thermal
conductivity detector. The total surface acidity was also
2
, Mo/ZrO
2
(%Mo = 5, 10, 15) and
3
2