Fuel Processing Technology 95 (2012) 119–126

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Fuel Processing Technology

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Synthesis and characterization of novel aminopropylated fly ash catalyst and itsbeneficial application in base catalyzed Knoevenagel condensation reaction

Deepti Jain a, Manish Mishra b, Ashu Rani a,⁎a Department of Pure and Applied Chemistry, University of Kota-324005, Rajasthan, Indiab Department of Chemical Engineering, Dharmsinh Desai University, Nadiad-387001, Gujarat, India

⁎ Corresponding author at: 2-m-1, Rangbari scheme,Tel.: +91 9352619059.

E-mail addresses: deepti_skjain@yahoo.com (D. Jain(M. Mishra), ashu.uok@gmail.com (A. Rani).

0378-3820/$ – see front matter © 2011 Elsevier B.V. Alldoi:10.1016/j.fuproc.2011.12.005

a b s t r a c t

a r t i c l e i n f o

Article history:Received 19 May 2010Received in revised form 8 June 2011Accepted 2 December 2011Available online 29 December 2011

Keywords:Fly ashSolid base catalystKnoevenagel condensationThermo-chemical activation

A series of solid base catalysts were synthesized by functionalization of different weight fractions (5, 10, and15 wt.%) of 3-aminopropyltrimethoxysilane (APTMS) on thermally activated F- type fly ash (SiO2 andAl2O3>70%). Catalyst characterization was undertaken using different analytical techniques such as FTIR,XRD, SEM–EDX, TEM, N2

− adsorption desorption, BET surface area analysis, TGA and AAS. The results showedthat appropriate amount (10 wt.%) of aminopropyl groups results in excellent catalytic performance testedfor condensation of ethyl cyanoacetate and cyclohexanone at 120 °C to produce Ethyl (cyclohexylidene) cya-noacetate (92% yield), an important intermediate of gabapentin (Neurontin), widely used in the treatment ofepilepsy to relieve neuropathic pain, under solvent free conditions and in low cost route. The catalyst NH2FA-10 was reusable up to three reaction cycles. The work reports an innovative use of solid waste fly ash as aneffective solid base catalyst.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Amines are well known basic functions and have been used as theactive basic sites in several support based catalysts for wide variety oforganic transformations [1]. Immobilization of other catalytically ac-tive species viz. amino acids, immines and imidazonium on inorganicsolid supports enables generation of recyclable catalyst for higher cat-alytic activities compared with their homogeneous analogues whichmay be due to the enhancement of substrate density around activesites [2]. Various inorganic support materials, have received much at-tention over the past years for functionalization of another bases onits surface. Amine functionalized-SBA-15 material has been widelyused as heterogeneous base catalyst in various organic transforma-tions such as Knoevenagel condensation, Claisen–Schmidt condensa-tion and Henry reaction [3]. Aminopropylated mesoporous silicaprepared by sol–gel process with tetra ethyl ortho silicate (TEOS)and Aminopropyltriethoxysilane (APTES) under strong acidic condi-tions has been used as heterogeneous catalyst for synthesis of flava-nones [4]. Some other materials like silica supported N,N′-dimethyldecylamine [5], silica supported immines [6], silica–aluminasupported tertiary amine [7], heterogenised chiral amine loaded onsilica, MCM-41 and delaminated zeolite ITQ-2 [8] have also been

Kota-324005, Rajasthan, India.

), manishkm2@rediffmail.com

rights reserved.

used as solid base catalysts for Knoevenagel condensation, Claisen–Schmidt condensation and Michael addition reactions. Most of theaforesaid synthetic processes require either complicated preparationof the catalyst or the use of expensive toxic solvents to facilitateheat and mass transfer in liquid phase reaction system.

Coal generated F-type fly ash, a mixture of various inorganic ox-ides viz. silica, alumina, ferric oxide, calcium oxide and other metaloxides (Mn2O3 and TiO2) along with mullite, quartz and magnetite[9,10] has been used as a solid catalytic material after activation. Pre-viously, fly ash supported catalysts have been used in catalytic de-composition of ammonia [11,12], in synthesis of aspirin [13] and oilof wintergreen [14] by esterification of salicylic acid with acetic anhy-dride and methanol respectively and in benzylation of benzene andtoluene [15]. Recently, we have also reported few fly ash supportedsolid base catalysts suitable for Knoevenagel condensation [16] andClaisen–Schmidt condensation [17] reactions. In the present work, aseries of solid base catalysts have been reported using thermally acti-vated F-type fly ash as a solid support material for functionalization ofdifferent weight fractions (5, 10 and 15) of aminopropyltrimethoxysi-lane. The use of solid waste fly ash as a support material reduced thecost of the catalyst without altering the basicity and catalytic activityof the catalyst suggesting fly ash as a replacement of other costly silicasupports. The NH2FA-10 catalyst prepared by functionalizing 10 wt.%of APTMS on thermally activated fly ash, was found effectively recy-clable up to three cycles of synthesis, indicating that the active sitesare not lixiviated in the reaction mixture. The synthesized NH2-FAcatalysts give a solution to overcome the use of harmful liquid basesand other costly commercial heterogeneous catalysts for industriallyimportant condensation reactions.

120 D. Jain et al. / Fuel Processing Technology 95 (2012) 119–126

2. Experimental

Fly ash having SiO2 (54%), Al2O3 (21%), Fe2O3 (9%), CaO (1.6%),MgO (0.8%), TiO2 (1.3%), Na2O (4.8%), K2O (3.2%) and trace elements(4.0%), analyzed by Flame Atomic Absorption Spectrophotometer(AA-6300, Shimadzu), was collected from Kota Thermal Power Plant(Rajasthan, India). The L.O.I. (loss on ignition) was 3 wt.% at 900 °Cfor 4 h. Ethyl cyanoacetate (99%) and cyclohexanone (98.5%) werepurchased from S. D. Fine Chem. Ltd., India and Aminopropyltri-methoxysilane (95%) was procured from Sigma Aldrich.

2.1. Catalyst preparation

The amino-functionalized fly ash catalysts (NH2FA-5, NH2FA-10and NH2FA-15) were synthesized by functionalization of APTMS 5,10 and 15 wt.% on thermally activated fly ash by following proce-dure: — 10 g fly ash was preheated for 4 h at 900 °C at the rate18 °C/min to remove C, S and other impurities [18], cooled downto room temperature and then transferred into a 250 ml round bot-tom flask. After mixing with 20 ml methanol and Aminopropyltri-methoxysilane (0.5 g for 5 wt.%, 1.0 g for 10 wt.% and 1.5 g for15 wt.%), the mixture in conical flask was put into a stirred reactorand refluxed at 110 °C for 24 h under constant stirring. The solidwas separated by filtration, washed several times with dichloro-methane and finally dried at 110 °C for 24 h, followed by calcina-tion at 250 °C for 4 h.

2.2. Catalyst characterization

The samples were characterized by Fourier transform infraredspectroscopy (FTIR), powder X-ray diffraction study (XRD), thermogravimetric analysis (TGA), BET surface area analysis, scanning elec-tron microscopy (SEM) and transmission electron microscopy(TEM). The functionalization of the fly ash with aminopropyl groupswas confirmed by FTIR study using FTIR spectrophotometer (IRPres-tige-21, Shimadzu) having a Diffuse Reflectance Scanning techniqueby mixing the sample with dried KBr (in 1/20 wt. ratio) in the rangeof 400–4000 cm−1 with a resolution of 4 cm−1. X-ray diffractionstudies were carried out by using X-ray diffractometer (PhilipsX'pert) with monochromatic CuKα radiation (λ=1.54056 Å) in a 2θrange of 5 to 65°. The thermogravimetric analysis (TGA) of the sam-ples was carried out using Mettler Toledo thermal analyzer (TGA/DSC1 SF/752), by heating the sample in the range of 25–800 °C witha heating rate of 10 °C/min under nitrogen flow (50 cm3/min). TheBET surface area of the samples was measured by N2 adsorption–de-sorption isotherm study at liquid nitrogen temperature (77 K) usingQuantachrome NOVA 1000e surface area analyzer. The sample wasdegassed under vacuum at 120 °C for 2 h, prior to adsorption mea-surement in order to evacuate the physisorbed moisture. The detailedimaging information about the morphology and surface texture of thesample was provided by SEM–EDX (Philips XL30 ESEM TMP). Thefunctionalization of APTMS on fly ash particles was confirmed byTEM analysis (Tecnai 20 G2 (FEI make), Resolution: Line-1.4 A, Point2.04 A).

Scheme 1. Knoevenagel condensation of cyclohexano

2.3. Catalytic activity

2.3.1. Reaction procedure for Knoevenagel condensation of cyclohexa-none with ethyl cyanoacetate

The catalytic activity of the synthesized NH2FA catalysts was test-ed by Knoevenagel condensation of cyclohexanone and ethyl cyanoa-cetate (Scheme 1) in liquid phase under solvent free condition.

The condensation was performed in liquid phase batch reactorconsisting of 25 ml round bottom flask with condenser in a constanttemperature oil bath with magnetic stirring. A mixture of cyclohexa-none (5 mmol) and ethylcyanoacetate (5 mmol) was taken in roundbottom flask. The catalysts (substrate to catalyst ratio=10), activatedat 250 °C for 2 h were added in the reaction mixture. The reactionmixture was kept on hot oil at different temperatures ranging from30 to 150 °C and time from 30 min to 6 h. The kinetics of condensa-tion reaction was studied using NH2FA-10 as it showed highest cata-lytic activity. After the completion of the reaction, air cooled reactionmixture was filtered to separate the catalyst. The product was ana-lyzed by gas chromatography (Dani Master GC) having a flame ioni-zation detector and HP-5 capillary column of 30 m length and0.25 mm diameter, programmed oven temperature of 50–280 °Cand N2 (1.5 ml/min) as a carrier gas. The conversion and yield wascalculated as follows:

Conversion (wt.%)=100×[Initial wt.%−Final wt.%]/ Initial wt.%

Yield%of Ethyl cyclohexylideneð Þ cyanoacetate ¼ 100

� Gramsof Ethyl cyclohexylideneð Þcyanoacetateobtainedð ÞGramsof Ethyl cyclohexylideneð Þcyanoacetateobtainedtheoriticallyð Þ

2.4. Catalyst regeneration

The spent NH2FA-10 catalyst was washed with acetone and driedin oven at 110 °C for 12 h followed by activation at 250 °C for 2 h andreused in next reaction cycle under similar reaction conditions asearlier.

3. Results and discussion

3.1. Characterization of synthesized catalysts

The FT-IR spectrum of fly ash (Fig. 1) shows the characteristicpeaks of silica at 1085, 815 and 459 cm−1. The intense peak at1085 cm−1 is attributed to the stretching of Si–O–Si bond and thepeaks at 815 and 459 cm−1 represent the stretching frequencies ofSi–O bond of the ring structure of silica. The broad band between3600 and 3000 cm−1 is assigned to stretching mode of hydroxylgroups of silanols (≡Si–OH) and adsorbed water molecules on thesurface. The broadness of the band indicates the strong hydrogenbonding between the hydroxyl groups of silanols and adsorbedwater molecules. A peak at 1650 cm−1 is attributed to bendingmode (δO–H) of adsorbed water molecules. In the FTIR spectra(Fig. 1) of amino functionalized fly ash catalysts (NH2FA-5, NH2FA-10 and NH2FA-15), the bands at 2922 and 2857 cm−1 are asymmetricand symmetric stretching frequencies of –CH2

− groups and the peakat 1468 cm−1 is assigned for bending mode of frequencies of –CH2

−

ne with ethyl cyanoacetate over NH2FA catalyst.

4000 3500 3000 2500 2000 1500 1000 500

Tra

nsm

itan

ce (

a.u

.)

cm-1

(i)

(ii)

(iii)

(iv)

3404

29222857

1633

1468

1085815

459

569

Fig. 1. FTIR spectra of (i) thermally activated fly ash, (ii) NH2FA-5, (iii) NH2FA-10 and(iv) NH2FA-15 samples.

121D. Jain et al. / Fuel Processing Technology 95 (2012) 119–126

groups [19]. The presence of these bands indicates the presence ofaminopropyl groups on the fly ash surface [20]. The stretching bandfor –NH2 groups, which is usually found in the range of 3600 to3000 cm−1, could not be observed in the spectra because of the

Fig. 2. X-ray diffraction patterns of (a) Ra

Fig. 3. TGA profiles of (i) raw fly ash, (ii) NH2FA-5

overlapping of the band with that of –OH vibration groups [21]. Thesurface –OH groups in the fly ash sample were in association by hy-drogen bonding showing broad band in hydroxyl region of spectra.The broadness of this band was observed to be decreased after thefunctionalization of the fly ash with aminopropyl groups due to thesurface reaction of aminopropyltrimethoxysilane with surface –OHgroups of silanols breaking the hydrogen linkages. Thus FTIR studyclearly indicates the presence of grafted aminopropyl species on thefly ash surface.

Powder X-ray diffraction (XRD) analysis was carried out to studythe effect of functionalization of fly ash with aminopropyl groups onthe crystalline nature of the fly ash. The XRD pattern of fly ash andNH2FA-10 (Fig. 2) shows that hexagonal quartz (SiO2) and ortho-rhombic mullite (3Al2O3•2SiO2) are the main crystallite phases bothin pure fly ash as well as in the amino functionalized fly ash catalysts.In addition, small amount of hematite (Fe2O3) and magnetite (Fe3O4)remain in the catalyst even after the functionalization of amine on flyash, thus no apparent change in mineral phases is being observed as aconsequence of functionalization of amine [22]. Fly ash after functio-nalization of amine is observed to be less crystalline due to formationof silanated silica [23], which is evident from the decrease in relativepeak intensities after surface modification.

TGA profiles of pure fly ash and NH2FA catalysts are given in Fig. 3.The total weight loss of pure fly ash in the temperature range of 25 to

w fly ash and (b) NH2FA-10 catalyst.

(iii) NH2FA-10 and (iv) NH2FA-15 catalysts.

Fig. 4. SEMmicrographs of a) raw fly ash, b) NH2FA-10 catalyst and c) magnified imageof NH2FA-10 catalyst.

Fig. 5. EDX of NH2F

122 D. Jain et al. / Fuel Processing Technology 95 (2012) 119–126

800 °C was 1.5 wt.%, whereas the weight loss of NH2FA catalysts inthe same temperature range was significantly higher (2.5–4.0 wt.%).The total weight loss of NH2FA-10 was found to be higher thanNH2FA-5 and NH2FA-15 indicating more grafting or functionalizationof fly ash with aminopropyl species in NH2FA-10 sample. The higherfunctionalization of aminopropyl groups in NH2FA-10 as comparedto NH2FA-5 is attributed to higher concentration of APTMS solution(10 wt.% in methanol) during the synthesis, which facilitates themore surface reaction of APTMS with silanols. The lesser aminopropylfunctionalization in NH2FA-15 in comparison of NH2FA-10 indicatesthat the further increase in APTMS concentration (15 wt.%) may bereducing the probability of surface reaction, which may be due toself condensation of APTMS. Our results are consistent with some pre-vious reports stating that higher wt.% of loading results in lower func-tionalization of aminopropylated groups on silica surface thusinfluencing the performance of the catalyst [4].

The weight loss of prepared catalysts (NH2FA-5, NH2FA-10 andNH2FA-15), containing 5%, 10% and 15% APTMS is illustrated inFig.3. The weight loss occurred in the range of 25 to 150 °C corre-sponds to the removal of adsorbed water in the samples. The weightloss in 200 to 300 °C temperature range may be due to the re-arrangement of grafted silanols groups, as well as release of stronglybound water on the surface. The weight loss observed above 450 °Cis attributed to the complete decomposition of aminopropyl speciesfunctionalized on the fly ash. The higher weight loss in NH2FA-10sample at 450 °C temperature (0.6 wt.%) as compared to NH2FA-5and NH2FA-15 samples (0.5 and 0.4 wt.% respectively) indicates thesignificantly higher functionalization of APTMS on fly ash in NH2FA-10 sample. The amount of aminopropyl groups present in the threesamples, NH2FA-5 NH2FA-10 and NH2FA-15 was calculated as fol-lows:

W ¼ WNH2−FA–WFAð Þ=FWAP

where, WNH2-FA=weight loss (mg/g) of NH2FA catalyst from 25 °C to800 °C, WFA=weight loss (mg/g) of pure fly ash from 25 °C to 800 °Cand FWAP=molecular weight of aminopropyl siloxane species (≡Si–CH2–CH2–CH2–NH2).

The aminopropyl content in the samples NH2FA-5, NH2FA-10 andNH2FA-15 measured from TGA data, was found to be 0.1627 mmol/g,0.2906 mmol/g and 0.1976 mmol/g respectively. The thermo gravi-metric analysis clearly shows the presence of significant amount ofaminopropyl groups grafted on the fly ash surface.

The BET surface area of pure fly ash, calculated from N2 adsorptiondesorption isotherm data, was 7.0 m2/g, which was observed to bedecreased to ~0.1 m2/g for all three NH2-FA catalysts. It reveals thatthe functionalization of fly ash with aminopropyl species significantly

A-10 catalyst.

Fig. 6. TEM micrographs of a) raw fly ash and b) NH2FA-10 catalyst.

Fig. 8. Variation of conversion (%) of cyclohexanone over NH2FA-10 catalyst with tem-perature in 2 h with molar ratio 1:1.

123D. Jain et al. / Fuel Processing Technology 95 (2012) 119–126

reduces the surface area of the fly ash catalysts indicating the pres-ence of considerable amount of aminopropyl groups on the surface.The decrease in surface area of silica material after loading of APTESis well precedented in literature [24]. The SEM micrograph of purefly ash (Fig. 4a) demonstrates particles of different shapes and sizes,hollow cenospheres, irregularly shaped unburned carbon particles,mineral aggregates and agglomerated particles, whereas the typicalSEM images of the NH2FA-10 catalyst (Fig. 4b and c) show agglomer-ated particles with loaded aminopropyl species on fly ash surface[25].

Typical EDX spectra showing the microchemistry of the catalystare given in Fig. 5. The elements detected are Si — 8.44%, Al —

4.62%, O — 57.12%, K — 0.20%, Fe — 0.47%, and Ti — 0.21%). The pres-ence of nitrogen and carbon (N — 10.16% and C —18.57%) in the cat-alyst also confirms the functionalization of aminopropyl groups onthe fly ash surface [20].

TEM images of raw fly ash and NH2FA-10 catalyst are given inFig. 6a and b respectively. TEM image of pure fly ash shows smooth

Table 1Catalytic activity of fly ash (FA), thermally activated fly ash (TFA) and amino functiona-lized fly ash (NH2FA) catalysts for condensation of cyclohexanone and ethylcyanoacetate.

Catalyst Conversion (%) Yield (%)

FA NIL NILTFA NIL NILNH2FA-5 69 54NH2FA-10 87 92NH2FA-15 71 57

Time=2 h; Temperature=70 °C; molar ratio (cyclohexanone/ethylcyanoacetate=1:1);substrate/catalyst ratio=10; activation of NH2FA catalyst=250 °C for 2 h.

Fig. 7. Variation of conversion (%) of cyclohexanone over NH2FA-10 catalyst with timeat 70 °C with molar ratio 1:1.

Scheme 2. The schematic presentation of the functionalization of the fly ash withAPTMS and proposed structure of NH2FA catalyst.

124 D. Jain et al. / Fuel Processing Technology 95 (2012) 119–126

spherical particles, while TEM image of NH2FA-10 catalyst clearlyshows deposited amine on fly ash surface.

The characterization results confirm the functionalization of flyash surface with significant amount of aminopropyl groups by surfacereaction of APTMS with surface silanols of the fly ash. The surfaceamino groups generate the significant basicity in the NH2FA catalystsfor base catalyzed condensation reactions.

3.2. Catalytic activity of NH2FA catalysts for Knoevenagel condensation ofethyl cyanoacetate and cyclohexanone

The catalytic activities of NH2FA catalysts were investigated forKnoevenagel condensation of ethyl cyanoacetate and cyclohexanone.Results given in Table 1 show that both fly ash (FA) and thermally ac-tivated fly ash (TFA) do not possess any catalytic activity for studiedreaction. NH2FA-10 catalyst under optimized reaction conditions, insolvent free system showed maximum activity.

The reaction temperature and time were optimized to study theeffect of reaction conditions and to achieve maximum conversion/yield using NH2FA-10 catalyst.

3.2.1. Time dependenceIn order to find the reaction duration to get highest conversion

with NH2FA-10 catalyst, the reaction was carried out at 70 °C for

Scheme 3. Mechanistic pathway of Knoevenagel condensation o

different reaction times ranging from 30 min to 6 h as shown inFig. 7. It was found that in the first 2 h of the reaction period the con-version increases linearly up to 87%, which remained constant till 6 h.The optimized reaction time was found to be 2 h, in which NH2FA-10catalyst gave highest conversion (87%) of cyclohexanone to Ethyl(cyclohexylidene) cyanoacetate with 92% yield.

3.2.2. Temperature dependenceTo optimize the reaction temperature giving maximum yield of

Ethyl (cyclohexylidene) cyanoacetate, reaction of cyclohexanoneand ethyl cyanoacetate was carried out at different temperaturesranging from 30 °C to 150 °C for 2 h. The results showed that theyield of Ethyl (cyclohexylidene) cyanoacetate was gradually in-creased with increase in temperature from 30 °C to 70 °C as inferredfrom Fig. 8. The maximum yield (92%) of Ethyl (cyclohexylidene) cya-noacetate was obtained at 70 °C within 2 h, which remained constanttill 150 °C.

3.3. Proposed mechanism

The plausible structure for active basic sites of the NH2FA-10 cata-lyst is shown in Scheme 2. The reaction mechanism over NH2FA-10catalyst shows (Scheme 3) that the surface basic sites of the NH2FA-10 catalyst initiate the reaction by abstracting proton from ethyl

f cyclohexanone and ethylcyanoacetate over NH2FA catalyst.

Table 2Condensation of cyclohexanone with ethyl cyanoacetate over fresh and regeneratedNH2FA-10 catalyst.

Reaction cycle Conversion (%) Yield%

Ist 87 92IInd 86 91IIIrd 86 91IVth 79 87

Reaction conditions: substrate/catalyst=10; temperature=70 °C; time=2 h; molarratio=1:1; catalyst activation=250 °C for 2 h.

125D. Jain et al. / Fuel Processing Technology 95 (2012) 119–126

cyanoacetate, resulting in the formation of carbanion, which then at-tack on the electron deficient carbon of carbonyl group of cyclohexa-none attached to adjacent basic site to form Ethyl (cyclohexylidene)cyanoacetate with loss of water [4]. A detailed schematic representa-tion of proposed mechanism is given as Scheme 3.

3.4. Catalyst regeneration

The spent NH2FA-10 catalyst was filtered from the reaction mix-ture, washed with acetone and regenerated at 250 °C for use in thenext reaction cycles. The catalyst was found to be equally efficientup to three reaction cycles giving approximately similar yield ofEthyl (cyclohexylidene) cyanoacetate in the range of 92–87% andconversion of cyclohexanone in the range of 87–79% (Table 2). Theregeneration study shows that the catalyst is reusable and there isno considerable change in the catalytic activity of the catalyst evenafter third reaction cycle. The FTIR spectrum (Fig. 9) of regeneratedcatalyst resembles that of fresh NH2FA-10 catalyst indicating the sta-bility of grafted aminopropyl groups on fly ash.

4. Conclusion

In the present study, an efficient solid base catalyst was synthe-sized by functionalization of thermally activated fly ash with 3-aminopropyltrimethoxysilane. The thermal activation of fly ashremoves C, S and other impurities, thus increases silica percentage.The characterization of the catalysts confirmed the functionalizationof fly ash surface with significant amount of aminopropyl groups bysurface reaction of APTMS with surface silanols of the fly ash. The pre-pared NH2-FA catalyst was found to possess significant basicity due toattachment of aminopropyl group on fly ash surface, which catalyzethe Knoevenagel condensation of cyclohexanone with ethyl cyanoa-cetate giving high yield (92%) of the desired product in solvent free

4000 3500 3000 2500 2000 1500 1000 500

459

569

8151085

16331468

285729223404

Tra

nsm

itan

ce (

a.u

.)

cm-1

(i)

(ii)

Fig. 9. FTIR spectra of (i) NH2FA-10 and (ii) regenerated NH2FA-10 catalyst.

condition. The present work provides a pathway for utilization ofabundantly available solid waste fly ash, as a support material for syn-thesis of solid base catalysts. This fly ash supported catalyst is a prac-tical alternative to soluble analogues in the view of high stability ofreactive sites, high activity under solvent free conditions, easy separa-tion of catalyst by simple filtration and reuse after activation withoutloss of activity. This study suggests that fly ash could be an economi-cal source of silica and alumina for synthesizing novel solid base cat-alysts for catalyzing industrially important reactions in cost effectivemanner.

Acknowledgement

The authors are thankful to Dr. N.P. Lalla for TEM and Dr. D.D.Phase and Er. V.K. Ahire for SEM–EDX analysis, conducted at UGCDAE-CSR Lab Indore. TGA and surface area analysis were conductedat D.D. University, Nadiad, Gujarat. The financial support was provid-ed by Fly Ash Unit, Department of Science and Technology, NewDelhi, India, vide project sanction no. FAU/DST/600(23)/2009-10.

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