CHEMCATCHEM
FULL PAPERS
er 2 days at 908C in a closed glass bottle. After cooling, the white
material was filtered, washed thoroughly with distilled water and
dried. The dry sample was calcined at 5508C for 6 h.
catalyst can be explained by considering acid–base bi-
functionality.[39,40]
The synthesis was performed using a molar ratio of Zr4+/Na2B4O7/
CTAB/H2O:1:(0.5–1.5): 0.3: 1000. The amount of borax was varied to
obtain the best catalyst for the solvent-free Knoevenagel reaction.
For the comparison, mesoporous zirconia (BZ-0) was synthesized
using the same protocol in the absence of borax.
Conclusions
Borated zirconia (BZ), with high surface area was synthesized
through a simple, versatile, and economical synthetic protocol
using aqueous zirconium ammonium carbonate complex solu-
tion as a precursor. The characterization results (NH3- and CO2-
TPD) show that the synthesized BZ catalyst contains both
acidic and basic properties. The synthesized BZ catalyst shows
excellent catalytic activity (>90% yield) for Knoevenagel con-
densation reaction between benzaldehyde/substituted benzal-
dehyde and malononitrile/ethyl cyanoacetate at room temper-
ature within 15–30 min of reaction. The high catalytic activity
is explained by considering the acid–base bifunctional proper-
ties of the BZ catalyst and a probable reaction mechanism can
be proposed. No side products through self-condensation, di-
merization or rearrangement were observed. The acid–base bi-
functional nature of the BZ catalyst was further confirmed by
solvent-free Claisen–Schmidt condensation reaction of benzal-
dehyde and acetophenone to chalcone and shows excellent
yields of chalcone in a short period of time. Furthermore, the
catalyst was successfully used for targeted synthesis of cinnam-
yl ethyl ester and coumarin or coumarin ester and results in
a good yield. The catalyst was easily recoverable from the reac-
tion system and reused without a reasonable change in cata-
lytic activity. The developed BZ catalyst can be a potential al-
ternative for other CÀC bond formation reactions.
Catalyst characterization
The nitrogen adsorption–desorption measurements at À1968C
were performed by using a ASAP 2010 Micromeritics, USA, after
the degassing of samples under vacuum (10À2 Torr) at 2508C for
3 h. The surface area was determined by BET equation. Pore size
distributions were determined using the BJH model of cylindrical
pore approximation.
Powder X-ray diffraction patterns were collected in two different
2q ranges of 1–78 and 20–808 by using a Rigaku X-ray powder dif-
fractometer using Ni filtered CuKa (l=1.54178 ꢁ) radiation with
a scan speed of 0.2 sÀ1
.
A scanning electron microscope (Leo series 1430 VP) equipped
with INCA was used to determine the morphology of samples. The
sample powder was supported on aluminum stubs and then
coated with gold by plasma prior to taking the image.
TEM images were collected by using a JEOL JEM 2100 microscope
and samples were prepared by mounting an ethanol dispersed
sample on a lacey carbon coated Cu grid.
Experimental Section
Materials
The FTIR spectroscopic measurements were performed by using
a Perkin-Elmer GX spectrophotometer. The spectra were recorded
in the range 400–4000 cmÀ1 using a KBr technique.
Analytical grade zirconium oxychloride (ZrOCl2·8H2O, 96%), ammo-
nium carbonate (NH4HCO3& NH2CO2NH4, 95.3%) and borax
(Na2B4O7·10H2O) was procured from SDFCL (s.d. fine-chem limited)
India. Benzaldehyde (99.5%), malononitrile (99%), ethyl cyanoace-
tate (98%) and other organic compounds were purchased from
Sigma Aldrich, USA. All the chemicals were used as received with-
out further purification. Water (resistivity, 18 MWcm) was obtained
from a Millipore water purifier.
TPD measurements were conducted by using a Micromeritics Au-
tochem-II Chemisorption analyzer instrument; and for this 100 mg
of calcined sample was placed in a U shaped sample tube. The
sample was flashed with helium for 1 h at 1508C and then cooled
to 508C. NH3 and CO2 were used to study acidic and basic strength
respectively. The corresponding gas was adsorbed on the sample
for 30 min. the loosely adsorbed species was flushed out with
helium for 30 min and the temperature was increased to 8008C
with ramp rate 58C minÀ1. The graph was recorded using a TCD
detector.
Catalyst synthesis
In a typical synthetic procedure, dilute ammonium carbonate solu-
tion was slowly added with to an aqueous solution of 15 g,
ZrOCl2·8H2O as it was stirred. A white precipitate of zirconium car-
bonate formed. After precipitation had completed, it was filtered,
washed with a large amount of distilled water to remove chloride
ions (AgNO3 test). The precipitates of zirconium carbonate were re-
dissolved in an aqueous solution of ammonium carbonate (8 g in
100 mL) by controlled addition with constant stirring and a clear
solution of zirconium carbonate complex was obtained. The
volume of the solution was made up to 150 mL. An aqueous solu-
tion of borax (Na2B4O7, 13.3 g, 268.5 mL) was then added into the
reaction mixture with constant stirring. Then, the clear solution
was added to an aqueous solution of CTAB (5.1 g in 418.5 mL) with
constant stirring, a white precipitate formed. After 12 h stirring, the
mixture was aged at 608C for 2 days, at 758C for 1 day and anoth-
An inductively coupled plasma-optical emission (ICP-OES) spectro-
photometer (Optima 2000 DV, Perkin–Elmer, Eden Prarie, MN) was
used to determine the percentage of the zirconium and boron
(borate ion) present in the synthesized materials. The material was
digested in concentrated HF and diluted with water.
A Bruker Advance II-500 spectrometer equipped with a magic
angle spin probe was used for the solid state 11B NMR study of the
materials at room temperature. The sample may have hydrolyze
partially as it was exposed to the atmosphere after calcination and
prior to analysis. B(OCH3)3 in chloroform (18.1 ppm) was use as the
external reference. The samples were spun at 8 kHz and the spec-
tra were resolved from an average of 4000 scans.
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2013, 5, 331 – 338 337