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Applied Catalysis A: General 487 (2014) 158–164

Contents lists available at ScienceDirect

Applied Catalysis A: General

jou rn al hom epage: www.elsev ier .com/ locate /apcata

elective and efficient hydrogenation of halonitrobenzene catalyzedy clay supported Nio-nanoparticles

ipanka Dutta, Dipak Kumar Dutta ∗

aterials Science Division, CSIR-North East Institute of Science and Technology, Jorhat 785006, Assam, India

r t i c l e i n f o

rticle history:eceived 13 May 2014eceived in revised form 9 August 2014ccepted 7 September 2014vailable online 16 September 2014

eywords:

a b s t r a c t

Nio-nanoparticles of approximately 5 nm were generated by incipient wetness impregnation ofNiCl2·6H2O into the nanopores of the acid activated montmorillonite (AT-Mont) followed by reductionwith hydrazine hydrate. The modification of montmorillonite was carried out by activating with H2SO4

under controlled conditions for generating nanopores up to about 10 nm size on the surface, which act asa “Host” for Nio-nanoparticles. Powder-XRD, SEM-EDX, HR-TEM, N2 adsorption, XPS, etc. analyses werecarried out to characterize the stabilized nanoparticles as well as the supports. TEM study reveals that

o

io-nanoparticlesontmorilloniteanoporesace centred cubic latticeydrogenation of halonitrobenzene

Ni -nanoparticles of size below 5 nm were evenly distributed over the support and exhibit face centredcubic (fcc) lattice. The supported Nio-nanoparticles serve as efficient and selective heterogeneous cata-lyst for hydrogenation of halonitrobenzene (HNB) to corresponding haloaniline (HAN) with conversion78–100% and selectivity 96–99.4%. The metal nanocatalysts could be recycled and reused several timeswithout significant loss of their catalytic activities.

. Introduction

Nickel nanoparticles attract significant attention in many fieldsncluding catalysis, permanent magnets, magnetic fluids, magneticecording media, solar energy absorption, fuel cell electrodes, drugelivery, etc. owing to their unique size and shape dependent struc-ure and properties [1,2]. Recently, attempts were made to stabilizeio-nanoparticles into 1D or 2D supporting materials such as car-on nanotube, carbon nanofibres, graphene, silica, TiO2, indiumin oxide and inorganic clay in order to construct new compos-te materials [3–6]. Although fabrication of these nanocomposites

as successful, most of it involves complicated modifications usingrganic surfactants [7], organic ligands [8,9], alkylammonium salts10], polymer or ionic liquid stabilizers [11,12] with negative con-equences such as reduced activity or unwanted organic residuesuring various applications. On the other hand, clay is low cost inor-anic mineral with layered structure which finds enormous interests functional materials due to their incredible properties such asppreciable surface area, ordered structure, intercalation abilities

nd high exchange capacities. Datta et al. used organically modifiedminoclay [i.e. CH2CH2NH2Si8Mg6O16(OH)] to prepare compos-tes with various nanoparticles [13]. Zhang et al. synthesized

∗ Corresponding author. Tel.: +91 376 2370 081; fax: +91 376 2370 011.E-mail addresses: dipakkrdutta@yahoo.com,

utta dk@rrljorhat.res.in (D.K. Dutta).

ttp://dx.doi.org/10.1016/j.apcata.2014.09.004926-860X/© 2014 Elsevier B.V. All rights reserved.

© 2014 Elsevier B.V. All rights reserved.

clay-3-aminopropyltriethoxyilane (APTES)-gold nanocompositesin which the APTES act as a linkage [14]. Platinum and goldnanoparticles embedded in clay or layered double hydroxides havebeen used for catalytic applications [15–17]. The majority of theseprotocols involve intricate multistep synthesis, elevated temper-ature or stabilizer such as polymer or organic ligands to inhibitagglomeration of particles. Therefore, with growing environmentalregulations, chemical industry needs the development of eco-friendly and sustainable synthetic methods without any organicmodification. Keeping in view of the above, we used environmen-tally benign, cheap, easily available and robust montmorillonite forgeneration of Nio-nanoparticles. Herein, we report a procedure forthe in situ synthesizing Nio-nanoparticles using environmentallybenign montmorillonite as a support. The virgin montmorillonitewas purified and activated with mineral acid by controlling theacid concentration, activation time or temperature to generate amatrix having high surface area and contain micro- and mesoporeswith diameter in the range 0–10 nm on the surface [18–24]. Thesenanopores act as a host for generation of Nio-nanoparticles andlimit the growth of the particles up to the desired range [25–29].Furthermore, the potential applications of these Nio-nanoparticleswere confirmed by investigating their catalytic activity.

Aromatic haloamines are important class of industrial inter-

mediate for the synthesis of organic fine chemicals, such as dyes,analgesic, herbicides, pesticides and antipyretic drugs [30–33]. Themain routes of synthesis of the haloamines involved reductionof corresponding nitrocompounds catalyzed by either metal–acid

talysis A: General 487 (2014) 158–164 159

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2

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D. Dutta, D.K. Dutta / Applied Ca

ystems or with noble metal. Processes involving later route areavoured now a days due to environmental issues associated withhe use of hydrochloric acid in the former route. Control of selec-ivity is the critical problem while carrying out hydrogenation ofalonitroaromatics with noble metal. For this type of hydrogena-ion reaction, various precious catalysts (Pt, Pd, Ru and Rh) haveeen well-studied [30–36]. However, it has been found that theydrogenation process is accompanied by hydrogenolysis of thearbon–halogen bond over most of catalysts and that hydrogenalide (e.g. hydrogen chloride) produced from this process is cor-osive to the reactor in addition to their higher cost. Therefore,uch effort have been made to overcome this problem over the

ast decades, including introducing special additives (promotersnd inhibitors), modifying the active metal with a second metalomponent and tuning the particle sizes of the catalysts.

There are several reports that dechlorination can be suppresseduring hydrogenation of chloronitrobenzene (CNB) by using nobleetal catalyst such as Ag/SiO2 [37], Au/SiO2 [38], Au/ZrO2 [39],uPd/Al2O3 [40], Au/Fe(OH)x [41], Pt/γ-Fe2O3 [42,43], Pt/γ-ZrP

44], decorated Pt/TiO2 [45,46], and Ru/SnO2 [33]. The hydrogena-ion of CNB was usually carried out at 90–150 ◦C with Au and Aganoparticles and at 30–60 ◦C with Pt catalysts and the selectivityo the undesired aniline was less than 1% [47]. However, the use ofhese noble and platinum metal catalysts (Au, Ag, Pd, Ru and Pt) inarge scale production should be expensive. Therefore, from bothconomic and environmental point of view, there has recently beenncreasing interest in hydrogenation of chloronitrobenzene withifferent chlorine substituent sites (o-, m-, or p-CNB) to correspond-

ng chloroaniline (CAN) catalyzed by less costly metal like nickel.ahata et al. reported that when the hydrogenation of CNB was

erformed at 120 ◦C over filamentous carbon-stabilized Ni cata-yst in methanol, the specific activity was ∼50 mmol h−1 g−1 Ni andhere was no intermediate detected at any level of CNB conversion48]. The catalyst was prepared by methane decomposition overaney Ni, which is expensive for industrial catalyst preparation.ence, none of these methods have been completely satisfactorynd is still a lot of scope to enhance the catalytic performance bymproving the reaction time, catalyst quantity, selectivity keepingn mind both the economic and environmental issues. Herein, weeport a procedure for synthesizing Nio-nanoparticles using envi-onmentally benign modified montmorillonite as a support andheir catalytic performance in hydrogenation of halonitrobenzene.

. Results and discussion

.1. Characterization of Support

The characterization of modified montmorillonite was carriedut thoroughly with the help of different analytical instrumentsike Powder-XRD, 29Si and 27Al MAS-NMR, FTIR, SEM studies, N2dsorption–desorption and are well documented in our earliereports [25–29]. The powder XRD of the parent montmorillonitehows an intense band at 2� = 7.06 corresponding to basal spacingd001) of 12.5 A while in acid activated montmorillonite (AT-Mont-

and AT-Mont-II), the band almost disappear indicating depletionf the lamellar structure [18,19] (supporting information, Fig. S1).he CEC of the modified montmorillonite decreased from 126 to0.8 and 21.0 meq/100 g of clay upon acid activation for 1 and

h, respectively. The parent montmorillonite showed an intensei peak at about −93 ppm [Q3(OAl)], attributed to tetrahedral (3Si,l) units (supporting information, Fig. S2). With increasing acid

ctivation time, the intensity of the peak at −93 ppm decreasesnd a new peak appeared at −111 ppm due to Q4 Si after 2 h acidctivation [20]. The 27Al MAS-NMR spectra of parent montmoril-onite exhibited an intense peak at 3.48 ppm and a weak peak at

Fig. 1. Solid state UV of Nio-AT-Mont.

67.39 ppm for octahedral and tetrahedral Al, respectively (suppor-ting information, Fig. S2). During acid activation, the intensity ofthe octahedral Al peak decreased and shifted to 2.03 ppm after 2 h,while the tetrahedral Al peak remained unchanged. IR study revealsthat the parent montmorillonite exhibits an intense absorptionband at ∼1034 cm−1 for Si–O stretching vibrations of tetrahedralsheet and also shows broad absorption band at 3633 cm−1 due tostretching vibrations of –OH groups of Al–OH (supporting infor-mation, Fig. S3). The bands at 522 and 460 cm−1 were due toSi–O–Al and Si–O–Si bending vibrations, respectively. Acid acti-vation shifted the band from ∼1034 to ∼1083 cm−1 indicatingthe change in bonding environment surrounding the tetrahedralsheet [21,22]. Upon acid activation, the surface area 417 m2 g−1

(AT-Mont-I) and 362 m2 g−1 (AT-Mont-II) and the pore volume∼0.57 cm3 g−1 (AT-Mont-I) and ∼0.70 cm3 g−1 (AT-Mont-II) wereobserved for 1 and 2 h acid treatment, respectively. Acid activationleads to modification of layered structure of montmorillonite byleaching out Al from their tetrahedral and octahedral sites, whichalso introduced permanent porosity on the clay surface. The claymatrix contained micro- (<2 nm) and mesopores (2–50 nm) withaverage pore diameters ∼4.45 nm (AT-Mont-I) and ∼6.70 nm (AT-Mont-II), respectively. The plot of differential volumes against porediameter, i.e. BJH plot indicated relatively narrow pore size distri-butions for AT-Mont-I than AT-Mont-II (supporting information,Fig. S4). The initial increase in surface area for AT-Mont-I may bedue to the formation of micro- and mesopores by leaching out alu-minium from octahedral sites but it decreases on prolonging acidactivation time (2 h) because of destruction of the pore walls, thereby forming bigger pores resulting in wider pore size distribution.The shape of N2 adsorption–desorption isotherm (supporting infor-mation, Fig. S4) was of the type-IV with an H3 hysteresis loop atP/P0 ∼ 0.4–0.8, indicating mesoporous solids [23,24]. Consideringhigher surface area and narrow pore size distribution, AT-Mont-I isadvantageously utilized for generation of Nio-nanoparticles.

2.2. Characterization of supported Nio-AT-Mont

The preliminary investigation on the formation of Nio-nanoparticles into the pores of modified montmorillonite wascarried out by UV–Visible spectroscopy (Fig. 1). The surfaceplasmon resonance band at 412 nm indicates the formation of Nio-nanoparticles [6]. The crystalline natures of the Nio-nanoparticles

were confirmed by their corresponding powder XRD pattern(Fig. 2). The three characteristic peaks at 2� values 44.5, 51.8 and76.4 degrees can be assigned to the corresponding (111), (200)and (222) indices of fcc Ni, which are in good agreement with

160 D. Dutta, D.K. Dutta / Applied Catalysis

vIpctscwDtpTwcN

Fig. 2. The powder XRD pattern of Nio-AT-Mont.

alues of Ni (JCPDS 04-0850) [49]. The FE-SEM images of AT-Mont- (Fig. 3A) and Nio-nanoparticles (Fig. 3C) and corresponding EDXatterns (Fig. 3B and D) indicate the presence of Ni metal on thelay surface with spherical morphology and evenly distributedhroughout the support. TEM images of Nio-nanoparticles (Fig. 4A)how the average size of the particles below 5 nm. The micrographslearly indicate that the particles have a spherical morphology andell dispersed on the support. The HR-TEM image (Fig. 4C and) depicts clearly the visible lattice fringes inside the nanopar-

icles and these fringes are continuously extended to the wholearticles indicating the formation of crystalline Nio-nanoparticles.

he measured inter-planer lattice fringe spacing is about 0.203 nm,hich coincides with the (111) d-spacing of fcc Nio crystals. The

orresponding selected area electron diffraction (SEAD) pattern ofio-nanoparticles obtained by focussing the electron beam on the

Fig. 3. (A) FE-SEM image of AT-Mont-I; (B) EDX analysis of AT-Mont-I; (C

A: General 487 (2014) 158–164

nanoparticles lying on the TEM grid is shown in Fig. 4B. The SAEDpattern, exhibited three diffused rings, which could be assignedto (111), (200) and (222) reflections, respectively of the fcc latticeof Ni indicating that the Nio-nanoparticles are of polycrystallinein structure. In order to ascertain the oxidation state, the Nio-nanoparticles is characterized by XPS analysis (Fig. 5) wherein, Ni2p3/2 photoelectron peak at 852.4 eV with typical doublet sepa-rated by approximately 17.2 eV was observed. The binding energyvalues of Ni 2p3/2 level in Nio-nanoparticles supported on modifiedmontmorillonite is lower by 0.4 eV than that of the free metal-lic Ni [50,51], suggesting that the electron transfer occurred fromthe support to the Ni particles, due to which Ni becomes slightlyelectron-rich. However, the other peaks appearing at the higherbinding energy may be due to the presence of oxidized Ni (Fig. 5).The specific surface area of Nio-nanoparticles supported on AT-Mont-I (N2-adsorption) decreases remarkably to 292 m2 g−1 fromthe parent value 417 m2 g−1, which indicates the generation of Nio-nanoparticles insides the pores on the clay matrix. The BJH pore sizedistribution reveals that the dominant pore size was approximatelybelow 5 nm. The amount of Ni content in the catalyst were deter-mined by AAS and found to be 1.05 wt %. Hence, the combinationof high surface area and nanoarchitecture should be advantageousfor efficient catalytic applications.

2.3. Catalytic properties of Nio-nanoparticles in selectivehydrogenation of halonitrobenzene

The catalytic performance of Nio-nanoparticles stabilized onmodified clay (Nio-AT-Mont) was evaluated as a heterogeneouscatalyst in hydrogenation of halonitrobenzene (Scheme 1) and

the results are presented in Table 1. The conversion of p-CNBto p-CAN at 5 bar H2 pressure showed a value of 43.0% whichenhanced to 97.0% on increasing the hydrogen pressure to 10 bar,however, the selectivity showed a reverse trend, i.e. it decreased

) FE-SEM image of Nio-AT-Mont; (D) EDX analysis of Nio-AT-Mont.

D. Dutta, D.K. Dutta / Applied Catalysis A: General 487 (2014) 158–164 161

F D) paH

ftwitoiophAtwrrcvM

S

tribution. Different solvents like methanol, ethanol, isopropanoland ethyl acetate were tried for hydrogenation of p-CNB (Table 2)and the most appropriate solvent in which the catalyst proceeds

ig. 4. (A) TEM images of Nio-AT-Mont; (B) selected area electron diffraction (SEAR-TEM with fringe spacing.

rom 99.4 to 99.1%. On further increasing the hydrogen pressureo 15 bar (entry 5) 100.0% conversion within 0.8 h reaction timeas observed but with further lowering of selectivity to 96.0%. This

ndicates that higher pressure has a negative effect on the selec-ivity of the products. In case of o- and m-CNB, the conversionf 96.5 and 98.2% was observed with almost the same selectiv-ty, i.e. 98.3 and 98.2%, respectively. It is known that [52] in casef other halogen derivatives like p-bromonitrobenzene (p-BNB),-iodonitrobenzene (p-INB) and p-fluronitrobenzene (p-FNB), theydrogenation by conventional catalysts are difficult, but the Nio-T-Mont catalyst showed efficient conversions 92.3 and 92.0% in

he former two cases, respectively, while in the later, i.e. p-FNB, itas only 78.0% (Table 1, entry 10). The selectivity in all the cases

emains almost the same, i.e. about 97%. The recyclability tests, car-ied out only with the p-CNB, showed that up to the 3rd run, the

onversion decreased from 97 to 88.4% and the selectivity decreaseery marginally from 99.1 to 97.9%. A control reaction with AT-ont-I without the presence of the catalyst, however, did not form

NO2

X Nio-nanoparticl es, AcOEt

H2 (10 ba r), 45 oCNH2

X

Wher e X = F, Cl. Br and I

cheme 1. Hydrogenation of halonitrobenzenes catalyzed by Nio-nanoparticles.

ttern of Nio-AT-Mont; (C) HR-TEM images of Nio-AT-Mont; (D) enlarge image of

any product, which indicates that acid activated clay has no cat-alytic effect.

Solvents always play an important role in chemical reaction andhave a significant effect on the reaction rate and products dis-

Fig. 5. XPS pattern of Nio-AT-Mont.

162 D. Dutta, D.K. Dutta / Applied Catalysis A: General 487 (2014) 158–164

Table 1Results of hydrogenation of halonitrobenzene over Nio-AT-Mont.

Entry Substrate H2 pressure (bar) Reaction time (h) Conversion (%) Selectivity (%)

HAN AN Others

1 p-CNB 5 1.0 43.0 99.4 0.6 –2 p-CNB 10 1.0 97.0 99.1 0.3 0.63 p-CNB (2nd run) 10 1.0 92.0 98.6 0.6 0.84 p-CNB (3rd run) 10 1.0 88.4 97.9 0.8 1.35 p-CNB 15 0.8 100.0 96.0 1.6 2.46 o-CNB 10 1.0 96.5 98.3 0.7 1.07 m-CNB 10 1.0 98.2 98.2 0.6 1.28 p-BNB 10 1.0 92.3 97.9 2.0 0.19 p-INB 10 1.0 92.0 97.8 1.7 0.510 p-FNB 10 1.0 78.0 97.1 1.2 1.7

Table 2Results of hydrogenation of p-CNB over Nio-AT-Mont in different solvents.

Entry Solvent Reaction time (h) Conversion (%) Selectivity (%)

p-CAN AN Others

1 Methanol 1.0 69.2 93.1 1.4 5.52 Ethanol 1.0 52.0 90.2 1.8 8.0

39

e>ofhaNtamaetemOmash

aTt1papormiobTtctwac

by N2 adsorption was 101 m2 g−1. The oxide compositions of theclay determined by wet chemical and flame photometric meth-ods were SiO2: 49.42%; Al2O3: 20.02%; Fe2O3: 7.49%; MgO: 2.82%;

3 Isopropanol 1.04 Ethyl acetate 1.0

fficiently is ethyl acetate wherein maximum 97% conversion and99% selectivity were observed. It is well known that adsorptionf substrate molecules to the surface of the catalyst is the mainactor determining catalytic activity [44,53]. The nitro group ofalonitrobenzene, being a strong electron-withdrawing character,dsorb on the electron enriched Nio-nanoparticles. Therefore, the

O bond of halonitrobenzene is activated by electronic interac-ion between the nitrogen atom of the nitro group and Ni atomsnd becomes more susceptible to hydrogen attack, thereby pro-oting the hydrogenation of halonitrobenzene. Furthermore, the

mino group of the produced haloaniline molecules acts as anlectron-donating substituent in the aromatic ring which favourhe hydrogenolysis of the C X bond in aromatic haloamines bylectrophilic attack of cleaved hydrogen on the absorbed aro-atic halides [44,54]. Due to acid–base interaction between theH groups of clay and NH2 groups of the produced haloanilineolecules decreases the electron-donating ability of NH2 groups

nd therefore the hydrogenolysis of the C X bond of haloaniline isuppressed considerably and thus resulting in higher selectivity ofaloaniline.

The recovered catalyst was further investigated through N2-dsorption–desortion analysis, TEM and powder XRD studies.he specific surface area of the recovered catalysts decreaseo 248 m2 g−1 (after 1st run), 195 m2 g−1 (after 2nd run) and68 m2 g−1 (after 3rd run) compared to 292 m2 g−1 of freshly pre-ared catalyst. The decrease of the surface area of the catalystfter reaction may be due to the partial destruction of the sup-ort at higher pressure used in the reaction. The identical shapef the isotherms reveals that the mesoporosity of the catalysts areetained even after successive catalytic reactions (supporting infor-ation, Fig. S5). The BJH pore size distribution curve (supporting

nformation, Fig. S6) of the recovered catalyst shows broadeningf the distribution pattern compared to fresh catalyst indicatingreakdown of the pore walls forming larger pores at high pressure.he recovered catalyst showed almost the same powder XRD pat-ern (Fig. 6) like the fresh catalyst. This indicates that no crystallinityhange occurred to the catalyst during reaction. The TEM images of

he recovered catalyst (Fig. 7) showed that the Nio-nanoparticlesere still inside the clay matrix but small fractions of the particles

gglomerated to form bigger size. The Ni content in the recoveredatalyst after third run was estimated using AAS, which show the

6.4 96.0 0.8 3.27.0 99.1 0.3 0.6

presence of 0.98 wt% Ni per 100 g of the catalyst. This indicates thatonly very small amount of Nio-nanoparticles is leached out. There-fore, the catalyst remained active for several catalytic runs withoutsignificant loss of its efficiency. A comparison of the efficiency ofcatalytic activity of the modified montmorillonite supported Nio-nanoparticles with several previously reported ones are presentedin Table 3, which shows that the present catalyst system is betterthan the others in terms of yield, reaction conditions and time.

3. Experimental

3.1. Materials and methods

Bentonite (Procured from Gujarat, India) contains impuritieslike silica sand, iron oxide, etc. and were purified by dispersioncum sedimentation technique to collect the <2 �m fraction. Airdried samples were characterized by XRD and basal spacing (d001)value was found to be 12.5 A. Specific surface area determined

Fig. 6. The powder XRD pattern of recovered catalyst (Nio-nanoparticles supportedon AT-Mont).

D. Dutta, D.K. Dutta / Applied Catalysis A: General 487 (2014) 158–164 163

run an

Cmfdairc

SstDtaus7tsvFaoCai

TC

Fig. 7. HR-TEM image of recovered catalyst after (A) 2nd

aO: 0.69%; LOI: 17.51%; others (Na2O, K2O and TiO2): 2.05%. Theontmorillonite was converted to the homoionic Na+-exchanged

orm by stirring in 2 M NaCl solution for about 78 h, washed andialysed against distilled water until the conductivity of the waterpproached that of distilled water. The cation exchange capac-ty (CEC) was 126 meq/100 g of clay (sample dried at 120 ◦C). Theeagents were purchased from Sigma Aldrich, USA and used as pur-hased from the supplier without further purification.

IR spectra (4000–400 cm−1) were recorded on KBr discs in ahimadzu IR Affinity-1 spectrophotometer. Solid state UV–Visiblepectra were obtained at room temperature by the UV–Visible spec-rophotometer model Lambada 35, Perkin Elmer. Powder X-rayiffraction were acquired on a Rigaku Ultima IV X -ray diffractome-

er from 2–80o 2� using Cu K� source (� = 1.54 A). Specific surfacerea, pore volume and average pore diameter were measured bysing Autosorb-1 (Quantachrome, USA). Specific surface areas ofolids samples were measured by adsorption of nitrogen gas at7 K and applying Brunauer–Emmett–Teller (BET) isotherm. Prioro adsorption, the samples were degassed at 250 ◦C for 3 h. Poreize distributions were derived from desorption isotherms at P/P0alue of >0.35 and using Barrett–Joyner–Halenda (BJH) method.ield emission scanning electron microscopy (FE-SEM) imagesnd energy dispersive X-ray spectroscopy (EDX) patterns were

btained by Field Emission Scanning Electron Microscope fromarl Zeiss (�igma VP). Transmission electron microscopy (TEM)nd high resolution transmission electron microscopy (HR-TEM)mages were recorded on a JEOL JEM-2011 electron microscope and

able 3omparison of results of p-CNB hydrogenation over Nio-AT-Mont with earlier reported ca

Entry Catalyst/solvent H2 pressure (Bar) Reaction temperature(◦C)

1 Ni7S6, ethanol 40 150

2 W-modified NiCoB,methanol

12 80

3 Ni/TiO2, scCO2 40 35

4 Pt/polysiloxane gel,ethyl acetate

10 25

5 Raney Ni, ethanol <100 100

6 Ni-B/boehmite,ethanol

15 100

7 Ni-P-B, ethanol 10 80

8 Ni/CNFs-EG-80,ethanol

20 140

9 Ni-clay, ethylacetate

10 45

d (B) 3rd run (Nio-nanoparticles supported on AT-Mont).

specimens were prepared by dispersing powdered samples in iso-propanol, placing them on a carbon coated copper grid and allowingthem to dry. XPS experiments were performed on a Kratos ESCAmodel Axis 165 spectrophotometer with a position sensitive detec-tor and hemispherical energy analyser in an ion pumped chamber.The amount of Ni content was determined by atomic absorptionspectrophotometer (Model: A Analyst, −700).

3.2. Preparation of support

Purified air dry montmorillonite (10 g) was taken into 250 mlthree necked round bottom flask in which 200 ml of 4 M sul-phuric acid was added to it. The resulting dispersion was refluxedfor 1 and 2 h, respectively. After cooling, the supernatant liquidwas discarded and the acid activated montmorillonite was repeat-edly redispersed in deionised water until no SO4

2− ions could bedetected by BaCl2 test. The modified montmorillonite was recov-ered and dried in an air oven at 50 ± 5 ◦C overnight to obtain thesolid product. The acid activated montmorillonite were designatedas AT-Mont-I and AT-Mont-II corresponding to activation time for1 and 2 h, respectively.

3.3. Preparation of supported Nio-nanoparticles (Nio-AT-Mont)

0.5 g of AT-Mont-I was taken into 250 ml beakers and 100 ml(1 mM) aqueous solution of NiCl2·6H2O was added to it slowlyunder vigorous stirring condition. The stirring was continued for

talysts.

Reaction time(h)

Yield/conversion(%) of CAN

Yield/conversion(%) of AN

Ref.

24.0 74.0 – 551.7 97.2 2.8 56

1.5 >97.0 <0.5 524.0 >99.0 – 57

0.38 97.0 – 342.0 98.0 – 58

1.5 93.2 – 590.5 98.0 – 60

1.0 99.1 0.3 Present work

1 talysis

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64 D. Dutta, D.K. Dutta / Applied Ca

nother 6 h followed by evaporation to dryness in rotary evap-rator. 0.3 g of dry clay–NiCl2 composite was dispersed in 50 mlthylene glycol in a 100 ml double-necked round bottom flasks andhen 10 ml of hydrazine hydrate (0.05 M) and of 1 M NaOH solutionere added in sequence at a temperature of 60 ◦C under constant

tirring conditions. The reaction started immediately and colourhanged from blue to black within 1 h, due to conversion of Ni(II)o Ni(0). The black Nio-nanoparticles was recovered, washed with

ethanol until it was free from ethylene glycol and then dried in aesiccator for 12 h. The samples thus prepared were designated asio-AT-Mont.

.4. Catalytic hydrogenation of halonitrobenzene

1 mmol of halonitrobenzene was dissolved in ethyl acetate5 ml) and 16 mg of Nio-AT-Mont supported on modified mont-

orillonite clay was added in a 50 cm3 capacity of a high pressureeactor (Parr-4592, USA) fitted with a pressure control. The reactionessel was purged with H2 gas for about 5 min and then pressur-zed with H2 gas up to 10 ± 1 bar at room temperature (25 ◦C). Theeaction was carried out at temperature 45 ± 5 ◦C for a period of 1 ht 500 rpm. To investigate the recyclability, the used catalyst wasltered after the reaction and washed with methanol followed byater and finally vacuum dried at 40 ◦C before the next reaction

un. The yields of the products were analyzed by gas chromatog-aphy (Chemito 8510) using BP-20 Wide bore capillary column,0 m × 0.53 mm id × 1.0 �m film thickness and hydrogen as carrieras.

. Conclusion

Nio-nanoparticles below 5 nm size were generated into theicro- and mesopores of acid activated montmorillonite by incip-

ent wetness impregnation of NiCl2·6H2O, followed by reductionith hydrazine. Nanopores in the modified montmorillonite were

reated by acid activation under controlled condition. Electronicroscopy as well as other analytical techniques confirm the for-ation of Nio-nanoparticles. The synthesized Nio-nanoparticles

how high activity and selectivity for hydrogenation of haloni-robenzene to the corresponding haloaniline. The catalyst is alsoound to remain active for several runs without significant loss inctivity.

cknowledgements

The authors are grateful to Dr. D. Ramaiah, Director, CSIR-North-ast Institute of Science and Technology, Jorhat, Assam, India, foris kind permission to publish the work. Thanks are also given toSIR, New Delhi for a financial support (Network projects: BSC-12, CSC-0125, 0135 and MLP-6001). The authors also acknowledgeAIF, NEHU, Shillong for TEM and HRTEM images and Dr. K. R. Patil,cientist, NCL, Pune for XPS analysis. A special thank is due to Mr.. G. Pathak, Technical Officer, for his strong analytical support.

ppendix A. Supplementary data

Supplementary data associated with this article can beound, in the online version, at http://dx.doi.org/10.1016/j.apcata.014.09.004.

eferences

[1] C.N.R. Rao, G.U. Kulkarni, P.J. Thomas, P.P. Edwards, Chem. Soc. Rev. 29 (2000)27–35.

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