chapter i - inflibnetshodhganga.inflibnet.ac.in/bitstream/10603/8415/5/05_chapter 1.pdf · with the...

LDH

Catalyst

AdsorbentSupport

Chapter IChapter IChapter IChapter I

CompositeElectrodes

Medical

Introduction

1. Layered double hydroxide (LDH)

1.1 Historical background

1.2 Structural features

1.3 General formula

1.4 Catalysis

1.4.1 Base catalysis

1.4.2 Redox catalysis

2. Synthesis of LDH

2.1 Co-precipitation method

2.2 Urea & hexamine hydrolysis methods

2.3 Sol-gel method

2.4 Miscellaneous methods

3. LDH derived materials

3.1 Mixed metal oxides

3.2 Rehydrated LDH

3.3 LDH composite materials

4. Physico-chemical characterization

4.1 Powder X-ray diffraction (PXRD) studies

4.2 Fourier transformed infrared (FT-IR) spectroscopy

4.3 Thermogravimetric analysis (TGA)

4.4 Elemental analysis

4.5 Adsorption measurements (surface area and pore size distribution)

4.6 Scanning electron microscopy (SEM)

4.7 Transmission electron microscopy (TEM)

4.8 X-ray photoelectron spectroscopy (XPS)

4.9 Temperature programmed reduction (TPR)

4.10 Nuclear magnetic resonance (NMR) & Mass spectrometry (MS)

5. Scope and objectives of the work

6. References

Introduction Chapter-I

1

1. Layered double hydroxide (LDH)

1.1 Historical background

Clays are naturally occurring materials composed primarily of fine-grained

minerals. Clay has been defined as an earthy material that forms a coherent, sticky mass

when mixed with water and when wet this mass can be readily moldable. The two main

features that evoke the interest on clays are their common availability and their extra

ordinary properties [1]. Clays find their potential application in ceramics, building

materials, adsorbents, ion–exchangers, sensors, decolorizing agents and catalysis [2].

The adsorptive power and high water retention capacity of clays are responsible for

their wide applications. The first and most widely known application of clay on

catalysis is French Houdry cracking process developed in 1930 [3]. Clays, forms a

subset of large discipline of catalysts in particular as heterogeneous catalysts. This

shows the importance of working on clays and clay based compounds.

Clays are classified into two categories:

1. Cationic or smectite type of clays having layered lattice structure in which two

dimensional oxy-anions are separated by layers of hydrated cations.

2. Anionic or brucite type of clays in which the charge on the layer and the gallery

anion is reversed, complementary to smectic-type clays [4].

Anionic clay, synthetic and natural layered mixed hydroxides containing

exchangeable anions are less well known and diffuse in nature than cationic clays.

Hydrotalcite (HT) belongs to the large class of anionic clays, and will be taken as a

reference name for many other isomorphous and polytype compounds. It is also

evidenced from the literature that the layered perovskites (LP), pillared clays (PILC)

materials are still mainly at the lab-scale development stage, while HT and especially

clays find a broad range of application [5].

Hydrotalcites (HTs) or Hydrotalcite-like (HT-like) materials also called as layered

double hydroxides (LDHs) are naturally available anionic clays, discovered in Sweden

at 1842. It can be easily crushed into a white powder similar to talc [6]. LDH belongs to

a large class of minerals with closely related structures is usually known to

mineralogists as the sjogrenite-hydrotalcite group [7]. The stoichiometry of


2

hydrotalcite, [Mg6Al2(OH)2]CO3.4H2O, was first correctly determined by Manasse [8]

in 1915. Aminoff and Broome [9] first recognized the existence of two polytypes of

hydrotalcites with rhombohedral and hexagonal symmetry from X-ray investigation.

Pioneering single crystal X-ray diffraction (XRD) studies on the mineral samples were

carried out by Allmann [10] and Taylor [11, 12] in the 1960s and main structural

features of LDHs were understood. However for many years the fine details of the

structure such as the range of possible compositions and stoichiometry, the extent of

ordering of metal cations within the layers, the stacking arrangements of the layers and

the arrangement of the anions and water molecules in the interlayer galleries are not

fully understood. ISI Web of knowledge [v. 4.10] database search on these materials

with the topic search keyword of “Hydrotalcite* OR Layered double hydroxide*”

showed 8448 records over these materials on Feb-2011 (Fig. 1.1).

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

0

100

200

300

400

500

600

700

800

900

Art

icle

s &

Pa

ten

ts p

ub

lis

he

d

Year

Fig. 1.1 Number of articles and patents published in LDHs

Number of articles published in 2001 on LDHs is 310 and it increased to 883 in

2010; this shows the importance of working on these materials [13].

1.2 Structural features

The basic layer structure of LDH is based on that of brucite [Mg(OH)2] structure

and it consists of magnesium ions surrounded approximately octahedrally by hydroxide

ions. These octahedral units form infinite layers by edge-sharing, with the hydroxide ions

sitting perpendicular to the plane. The layers then stack on top of one another to form the

three dimensional structure. The metal cations occupy the octahedral holes between


3

alternative pairs of OH planes and thus occupy a triangular lattice identical to that

occupied by the OH- ions.

Fig. 1.2 Structure of LDH

If some Mg2+

ions are replaced by a higher valent ion having similar radius (such

as Fe3+

in pyroaurite, Cr3+

in stichtite and Al3+

in hydrotalcite) [14], the brucite-type layer

becomes positively charged. To maintain electrostatic neutrality, this excess positive

charge is balanced by anions located in the interlayer region between brucite-layers. The

schematic representation of the hydrotalcite structure is shown in Fig. 1.2. X-ray unit cell

determination, based on early crystallographic work, confirmed that brucite-like sheets

can stack one on the other with two different symmetries, differing only in their interlayer

stacking sequences viz., rhombohedral and hexagonal [9]. The brucite-like layers in

LDHs may be stacked in different ways, which gives raise to variety of possible polytype

structures. LDHs usually crystallize in two different polytypes, one with two-layer

hexagonal stacking sequence (polytype 2H) and another with a three-layer rhombohedral

sequence (polytype 3R). All sites in the (110) plane of the close packed hydroxide layers

may be represented as A, B or C related by lattice translations of (1/3, 2/3, 0) or (2/3, 1/3,

0) and the locations of octahedral holes occupied by metal cations can be described

analogously as a, b or c. Thus single brucite layer can be represented as AbC (since, if

close packed hydroxyl groups occupy A and C sites, the cations must, of necessity,

occupy b sites). AbC layers may be stacked in various ways giving rise to a large number

of possible polytypes. These polytypes may be classified in terms of the number of sheets


4

stacked along the c axis of the unit cell. If the opposing OH groups of adjacent layers lie

vertically above one another (say both in C sites), a trigonal prismatic arrangement

(denoted by =) results; if the hydroxyls are offset (say one layer in C sites and those of an

adjacent layer in either A or B sites) then six OH groups form an octahedral arrangement

(denoted by ~). Thus brucite itself can be denoted as …AbC~AbC~… or 1H, where “1”

denotes a one layer polytype and the “H” denotes a stacking sequence with hexagonal

symmetry. Bookin and Dirts [15, 16] have systematically derived all of the possible

polytypes for other stacking sequences. There are three possible two layer polytypes,

each of which has hexagonal stacking of layers, which can be denoted as,

….AbC=CbA=AbC…. 2H1

….AbC~AcB~AbC…. 2H2

….AbC~BcA=AbC…. 2H3

The interlayers in the 2H1 polytype are all prismatic and those in the 2H2 polytype are

all octahedral, whilst in the 2H3 polytype both types of interlayers are present. There are

nine possible three-layer polytypes. Two of these have rhombohedral symmetry (3R):

….AbC=CaB=BcA=AbC…. 3R1

….AbC~BcA~CaB~AbC…. 3R2

the remaining seven have hexagonal symmetry:

….AbC~AcB~AcB~AbC…. 3H1

….AbC~AcB~CaB~AbC…. 3H2

….AbC~AcB=BcA~AbC…. 3H3

….AbC~AbC=CbA=AbC…. 3H4

….AbC~AcB=BaC~AbC…. 3H5

….AbC~AcB~CbA=AbC…. 3H6

….AbC~AbA~BcA=AbC…. 3H7


5

For the 3R1 polytype, the interlayers are all prismatic and in the case of 3R2, 3H1 and

3H2 they are all octahedral; other polytypes involve both types of interlayers. Bookin

and Drits have also described the large number of possible six-layer polytypes, some of

which have rhombohedral symmetry (6R) and the remaining hexagonal symmetry (6H)

1.3 General formula

The chemical composition of LDH phase is generally described by;

[M(II)1- x M(III)x(OH)2]x+

[An-

x/n]x-

.mH2O

where M(II) and M(III), represent divalent and trivalent metal ion respectively, A is the

interlayer anion with charge n, x{M(II)/M(III)} is the fraction of the trivalent cations and

m is the water of crystallization. The value of x can be in the range 0.2 - 0.35. For values

outside this range pure hydroxides or other compounds with different structure are

obtained (with some exceptions) [17, 18]. The main criteria for elements to crystallize in

this network are their ionic radius. M(II) and M(III) having an ionic radius not too

different from that of Mg2+

may be accommodated in the octahedral sites of the close-

packed configuration of the OH- ions in the brucite-like layers to form HT-like

compounds. The ionic radii of M(II) cation between 0.65 to 0.80 Å and M(III) cation of

0.62 to 0.69 Å (with the main exception of Al 0.5 Å) can form LDHs [19].

Higher ionic radii (Cd and Sc) seem to be incompatible with the formation of true

brucite-like layers. LDHs can also be obtained with a Li-Al monovalent-trivalent and Co-

Ti divalent-tetravalent associations. The single phase formation of hydrotalcite occurs,

after proper selection of M(II) and M(III) ions. A wide variety of anions like inorganic

anions (CO32-

, SO42-

, NO3-, OH

-, CrO4

2-, WO4

2-, S2O3

2- etc.), isopoly anions (V10O28

2-,

Mo7O242-

etc.), heteropoly anions (PMo12O403-

, PW12O403-

etc.), complex anions

(Fe(CN)63-

, Fe(CN)64-

, IrCl62-

etc.) and organic anions (carboxylates, porphyrins,

pharmaceutically active functional anions and alkyl sulfates etc.) can be intercalated in

the LDH layers.


6

1.4 Catalysis

Catalysis is one of the most important fields in chemistry, which has very good

application in industrial research [20]. Catalyst can be defined as “a substance that alters

the rate of attainment of chemical equilibrium without itself undergoing chemical

change” and catalyst did not influence the position of equilibrium. If the rate of a forward

reaction is speeded up in presence of a particular catalyst, the reverse reaction will

likewise be facilitated to the same degree. A catalyst can also be defined as an entity that

makes it possible for the reaction to proceed at rates high enough to permit their

commercial exploitation on a large scale, resulting in economic benefits. In 1814,

Kirchoff noticed that acid catalyzed hydrolysis occurring in starch – a classic example of

homogeneous catalysis. The first application of catalysis was done in 1820s by

Dobereiner, who introduced “tinderbox” which was commercially used for the purpose of

lightning fires and smoking pipes. A jet of hydrogen produced by zinc and sulphuric acid

was directed on to the supported platinum where it catalytically combined with oxygen to

yield gentle flame (Million tinder boxes sold in 1820). In 1836, Berzelius first introduced

the term catalysis (comes from Greek word katalysis; meaning breaking down or

loosening) endowed catalysts with mysterious quality. Followed by them several

important industrial applications on catalysis found such as

Industrial oxidation of HCl to Cl2 using clay brick impregnated with cupric salt as

catalyst (Deacon process 1871).

Karlsruhe Fritz Haber prepared copious quantities of ammonia from nitrogen and

hydrogen in presence of a reduced magnetite (Fe3O4) catalyst using high pressure

apparatus (1909).

Industrial synthetic production of methanol using zinc oxide – chromium oxide

catalyst at 400 oC and 200 bar pressure (1923).

Synthetic zeolites were first reported for the selective isomerization of

hydrocarbons in 1960.

Over a billion (109) kilograms of fructose were produced in USA for soft drink

from corn syrup using immobilized glucose isomerase as catalyst (1980).


7

Now more than 90% of chemical manufacturing processes in use throughout the world

utilize catalysts in one form or another. Much of the food we eat and medicines we take,

many of the fabrics and building materials that keep up warm and almost all the fuels that

transport us by road, sea or air are being produced by heterogeneously catalyzed

reactions.

A literature survey of layered materials, over the period of 2000–2006 (limiting to

English as language), revealed that nearly 20,000 papers have been published on clays

which includes layered perovskites (LP), pillared clays (PILC) and LDH materials, of

which about 85% were dealing on catalysis. Among the publications dealing on catalysis,

the percentage of patents was about 2% for LP, 26% for LDH and 6% for PILC. This

evidences that the LP and PILC materials are still mainly at the lab-scale development

stage, while LDH and especially clays find a broad range of application [4]. The presence

of both Lewis and Bornsted type basic sites in LDHs and ability to host different metal

ions extended its applications in both base catalyzed reactions and oxidation reactions

[21].

1.4.1 Base catalysis

Base catalysts play a decisive role in a number of reactions essential for fine-

chemical synthesis as compared to acid catalyst which finds applications in petroleum

refining. Heterogeneous base catalysts are widely used in industrial research, due to easy

recovery, recycling, atom utility and enhanced stability. Solid-base catalysts find

application in reactions including isomerization, aldol condensation, Knoevenagel

condensation, Michael condensation, oxidation and Si–C bond formation [22]. Base

catalyzed condensation is one of the well known methods for C-C bond formation. Busca

recently reviewed the basic properties of different solids which found application in

industrial catalysis [23] and one among them is LDHs. Compared to other basic materials

like sepiolite, zeolites and organic resins, LDH derived materials show improved thermal

stability and diffusion resistance [24]. These materials on calcination (weight loss of up

to 40 %) leads to formation of highly dispersed, large surface area and porous nano

dimensional mixed metal oxides, which can be potentially used for many base catalyzed

reactions [25].


8

The basic property of these materials was initially envisaged by Nakatsuka et al.

[26], Reichle [27] and Laylock et al. [28], for catalytic polymerization and aldol

condensation reactions. The basicity of LDH is affected by the calcination procedure,

typically at 673–773 K and by structural and compositional parameters [28, 29]. Cations

like Zn or Ni give less basicity than Mg; less basic catalysts are also obtained from Cl- or

SO42-

precursors than from CO32-

or OH-containing materials [27] and the basicity also

depends on the Mg/Al ratio [30, 31].

Corma et al. studied the basic property of the materials by carrying out the

condensation of benzaldehyde with activated methylenic groups with different pKa

values, in the presence of a Mg-Al LDH catalyst. They found that this material shows

basic sites with pKa values up to 16.5, which normally uncommon among the other

commercial basic zeolite material. In the use of zeolites as catalyst, the only reaction

observed was Knoevenagel condensation, while on calcined LDHs showed other

reactions like Michael-type addition and Claisen condensation, which requires stronger

basic sites. The total amount of basic sites and their strength distribution in the material

were determined by carrying out the Knoevenagel condensation reaction with methylenic

groups of different pKa values in presence of increasing amount of benzoic acid. By

increasing the Mg/Al ratio in the LDH, the number of basic sites with 9.0 ≤ pKa ≤ 13.3

increases, whereas the amount of basic sites within 13.3 ≤ pKa ≤ 16.5 decreases [32]. The

correlation of the LDH basic properties with the Mg/Al ratio, however, is not always

straightforward [27].

Yamaguchi et al. used MgAl mixed oxides derived from LDHs as catalyst for the

synthesis of cyclic carbonates from epoxide and carbondioxide (Fig 1.3). Mg-Al mixed

oxides obtained by the calcination of hydrotalcites acted as efficient catalysts for the

addition of CO2 with various epoxides under mild reaction conditions [33] and mixed

oxide with the Mg/Al ratio of 5 calcined at 400 °C showed the highest catalytic activity.

Cooperative action of acid-base sites derived from the formation of Mg-O-Al bonds leads

to higher activity.


9

Fig. 1.3 Mechanism of cyclic carbonate formation over MgAl(O) (reproduced from ref.

33)

CO2 and NH3 TPD experiments and FT-IR spectroscopy, using CO2 and NH3 as probe

molecules on calcined LDHs showed the presence of strong O2-

Lewis basic sites, Mn+

Lewis acid sites, Mn+

-O2-

pairs and OH- Bronsted sites [34]. Sol-gel derived materials

showed higher basic character than the co-precipitated materials. Different other

synthetic procedures like microwave and sonication leads to materials with different

basic characters. Homogenous particles of ~80nm average particle size and with higher

defects was produced using sonication showed high basicity [35].

Kustrowski et al. studied the acidic and basic properties of the MgAl mixed

oxides derived from LDHs with different interlayer anions using both NH3 and CO2 TPD

[36]. These results showed that concentration of basic sites are in the order of CO32-

> Cl-

> HPO42-

> Terephthalate > SO42-

and the acidic sites are in the order of CO32-

>

Terephthalate > Cl- > HPO4

2- > SO4

2-. Both CO3

2- and Cl

- showed higher basic sites

whereas HPO42-

, SO42-

and terephthalate showed weak basic sites.

Kustrowski et al. also studied the variation of Mg/Al ratio over the acidic and

basic property of the LDH using NH3 and CO2 TPD [37]. Materials calcined at different

temperatures showed different acid base behaviours. For materials calcined at 550 oC the

concentration of acidic sites are in the order of 3.5:1 > 3:1 > 4:1 > 2:1 Mg:Al ratios,

whereas concentration of basic sites are in the order of 2:1 > 3:1 > 3.5 :1 > 4:1.


10

Ebitani et al. showed that reconstructed LDH found to be active for the aldol

reactions to produce α-hydroxy carbonyl derivatives in the presence of water and also can

promote the aqueous Knoevenagel and Michael reactions using nitriles. The mechanism

of the above unique catalysis of the reconstructed HT is discussed on the basis of the

nature, strength, and amount of surface acid-base sites [38] given in Fig 1.4.

Fig. 1.4 Mechanism on LDH surface (reproduced from ref. 38)

Followed by them Chimentao et al. studied the effect of using mechanical

stirring or ultrasound during reconstruction of the mixed oxides and showed that this

leads to an enhancement in the catalytic activity. Modifications in the structure and

basicity of the resulting materials, together with an increased surface area and improved

accessibility to the active sites lead to high activity. Increasing the rehydration time

during stirring or sonication also strongly affects the final catalyst and the performance of

these materials has been disclosed for the epoxidation of styrene [39].

Onda et al. used activated hydrotalcites for the lactic acid production from D-

glucose in flow reactors at 323 K under water media. The number of accessible Brønsted-

base sites determined by the ion-exchange method with sodium salts, based on the OH/Al


11

ratio. The catalytic activity for the lactic acid production showed a linear increase with

the number of the Bronsted-basic sites [40].

Zeng et al. showed that calcined LDH with Mg/Al molar ratio of 4.0 exhibited the

highest catalytic activity in the synthesis of propylene glycol methyl ether from

etherification of propylene oxide with methanol. The catalytic activity of the material was

correlated with the amount of the basic sites determined by Hammett indicators [41].

Recently LDHs have been exploited for various base catalyzed transformations

such as condensation [27, 42], double bond isomerization of allylic substrates such as

eugenol and safrole [43-45] and dehydrogenation of 2-propanol [46].

1.4.2 Redox catalysis

The ability of different transition metal ions (Co2+

, Ni2+

, Cu2+

, Mn2+

, Fe2+

, Fe3+

and Cr3+

etc.) to be crystallized in LDH and potential surface for adsorption of different

metals extended its application in redox catalysis. Functionalized anions can be

intercalated into the interlayers which are otherwise difficult to incorporate in the two-

dimensional sheets thereby creating new active centers for redox catalysis is another

approach in this direction.

Ruthenium incorporated LDHs showed excellent activity for oxidation of allylic

alcohol to aldehydes and ketones using molecular oxygen [47]. Alcohol reacts with Ru

hydroxide of LDH to form alkoxide species and which undergoes β elimination to form a

aldol product. Molecular oxygen reacts with remaining Ru-hydride species to generate

the Ru-hydroxyl species on the hydrotalcite. In another application ruthenium grafted

LDHs showed multifunctional catalytic activity in the one-pot synthesis of quinolines

from 2-aminobenzyl alcohol and various carbonyl compounds via aerobic oxidation and

aldol reaction [48] and also in the α-alkylation of nitriles with primary alcohols [49].

Kishore et al. reported the catalytic oxidation of isophorone to ketoisophorone over

ruthenium supported MgAl-LDH [50].

Velu et al. synthesized the manganese incorporated LDH using co-precipitaion

method and tested the liquid phase oxidation of toluene using tert-butyl hydroperoxide as

oxidant [51]. Maximum conversion of 14.3% with 75% benzoic acid selectivity was


12

obtained. Choudhary et al. synthesized MnO4- exchanged LDH through reconstruction

method and studied the molecular oxygen catalyzed oxidation of ethylbenzene to

acetophenone and diphenylmethane to benzophenone [52].

Fe containing LDHs showed excellent catalytic activity for the reduction of 4-

nitrotoluene to 4-aminotoluene using phenyl hydrazine or hydrazine as reducing agent

[53]. Coq et al. showed catalytic reduction of nitriles over Co/Ni/Mg/Al LDH derived

mixed oxides [54]. High activity of this catalyst is due to the bifunctional mechanism

over the metal sites. Mg-Fe LDH showed excellent activity for the catalytic reduction of

aromatic nitro compounds with hydrazine hydrate [55]. Recently iron (III) porphyrins

immobilized on Mg–Al LDH modified with triethanolamine showed cyclohexane

oxidation using iodosylbenzene as oxidant [56] and Fe (III)-Schiff base complex in a Zn-

Al LDH was found to be an effective catalyst for the catalytic oxidation of cyclohexane

using H2O2 as oxidant [57].

In LDH catalyzed oxidation, the basic property of the material activate either the

substrate or oxidant giving rise to electrophilic attack on carbanions or nucleophilic

attack with peroxoanions [58, 59]. Multi-metallic LDHs have been found to show high

catalytic activity for the heterogeneous Baeyer–Villiger oxidation of various carbonyl

compounds using a combination system of molecular oxygen and benzaldehyde [60].

LDHs with high basic character showed high activity for Baeyer–Villiger oxidation. Sn

exchanged LDHs showed selective Baeyer–Villiger oxidation of ketones using hydrogen

peroxide as oxidant [61].

Ni/Mg/Al LDH with high dispersion of nickel found to be the active catalyst for

the partial oxidation of propane [62]. Choudhary et al. claimed that molecular oxygen

was activated over NiAl-LDH and gave excellent catalytic activity for alcohol oxidation

[63]. Followed by them Kawabata et al. showed that alcohol oxidation was accelerated

by the presence both Mg and Ni sites together and proposed that the Ni(II) sites work as

the active sites by activating molecular oxygen assisted by the Mg(II) sites as a base and

simultaneously alcohol was activated by the Al(III) sites as an acid, resulting in an

enhancement of the activity of the Mg2.5(Ni0.5)–Al LDH heterogeneous catalyst for

alcohol oxidation [64]. NiAl-LDH also showed excellent activity for the solvent-free

liquid-phase selective oxidation of ethylbenzene to acetophenone with 1 atm of molecular


13

oxygen [65]. Li et al. recently showed the Ni/Mg/Al catalyzed hydrogen production from

ethanol steam reforming, the NiMgO solid solution phase exhibited high activity and

stability for ethanol steam reforming [66]. Supported Ni nanoparticles via self-reduction

of hybrid NiAl-LDH/C composites, exhibited excellent activity for catalytic growth of

CNTs, which could be delicately tuned by varying the compositions of hybrid composites

[67]. In another investigation CuMgAl-LDH showed high activity for the total oxidation

of phenol [68].

Mastalir et al. synthesized the hydrophobic Pd nano particles incorporated LDH

using ion exchange of nitrate containing LDH with Pd hydrosol stabilized by the anionic

surfactant sodium dodecyl sulfate [69]. These materials showed excellent activity for

selective semihydrogenation of alkynes. Albertazzi et al. used Pd/Pt supported on MgAl

mixed oxides derived from LDH as catalyst for the hydrogenation and hydrogenolysis of

naphthalene [70].

Hydrogen peroxide in presence of LDH leads to the formation of active hydrogen

peroxide ion (HOO-), which gives nucleophilic epoxidation of electron deficient olefins

[71]. Synergism between the interaction of Co and Ru cations gave high activity of

CoAlRu-LDH over molecular oxygen catalyzed oxidation of various alcohol (aromatic

allylic, benzylic, secondary saturated alcohols) to the corresponding carbonyl compounds

in high yields [72]. Several works are being published on hydroxylation of phenol using

various transition metals containing multi-metallic hydrotalcites [73-76].

Zavoianu et al. synthesized molybdenum containing LDHs through ion exchange

method and studied cyclohexene oxidation using H2O2 [77]. The catalysts containing

Mo7O245-

species was more active for epoxidation and low Mo content (about 2.5–2.8%)

in the form of MoO42-

was more active for hydroperoxidation.

Recently Kaneda et al. used silver and copper nano particles supported on LDH

for oxidant free alcohol dehydrogenation [78, 79]. It was also observed that Ag/LDH

showed the highest chemoselectivity for the dehydrogenation of cinnamyl alcohol to

cinnamaldehyde without hydrogen transfer or isomerization. Silver nanoparticles

supported on LDH efficiently catalyzed the deoxygenation of styrene oxide derivatives

into the corresponding alkenes using CO/H2O as a reductant [80]. LDH supported gold

nanoparticles acted as a reusable catalyst for synthesis of lactones from diols using


14

molecular oxygen as an oxidant under mild conditions [81] and lactonization of 1,4-

butanediol gave γ-butyrolactone with an excellent turnover number of 1400. Au

nanoparticles supported on Mg-Al-layered double hydroxide (Au/LDH) synthesized by

ion-exchange and reduction showed excellent catalytic activity for alcohol oxidation [82].

Vasile et al. synthesized W containing LDHs through ion exchange method and studied

the catalytic oxidation of thiophenes and thioethers using H2O2 as oxidant [83]. The

catalytic activity depends on the nature of the W-containing anions present.

This shows the importance of working with LDH and LDH derived materials and

superior properties of the materials can be obtained through deeper understanding of the

synthesis methodology and post synthetic treatments.

2. Synthesis of LDH

2.1 Co-precipitation method

Mg–Al hydrotalcites are conventionally

synthesized by co-precipitation of aqueous alkaline

solutions of Mg and Al salts (nitrates or chlorides) at fixed

pH under stirring and inert atmosphere (Fig. 1.5).

Classically, an aqueous NaOH or KOH solution is used to

adjust the pH and an aqueous Na2CO3 or K2CO3 solution

is added as the carbonate source [84]. After ageing of the

slurry, the resulting material is filtered and washed with

deionised water and dried (~373 K). The ageing step may

itself be used as a tool to change the properties of the final

material. For example, microwave irradiations may be

used during aging in order to provoke a reduction of the size of the particles, an increase

in the specific surface areas and an increase in the basicity [85]. Hydrotalcites based on

other metals (Co, Ni, Cu, etc.) can be synthesized in the same way by introducing the

proper nitrate salt, [86, 87] however it is necessary to precipitate at a pH higher than that

of pH of precipitation of metal hydroxides. Materials synthesized by this method has

several advantages like high surface area, multiple metal ions containing LDHs can be

synthesized simply by taking different metal nitrate precursors, highly dispersed metal

Fig. 1.5 Synthesis scheme

of co-precipitation


15

ions containing LDHs and crystallinity of the material can be tuned by varying the ageing

time and temperature. Several tetravalent metal cations containing LDHs were also

synthesized successfully using this method [88, 89].

2.2 Urea & hexamine hydrolysis methods

Urea on hydrolysis at high temperature releases ammonia which precipitates the

metal cations in the synthesis of LDH.

Fig. 1.6 SEM and particle size distribution of hydrotalcites synthesized at (a)100 oC, (b)

120 oC (c) 150

oC (reproduced from ref. 93)


16

The urea method was developed by Costantino and co-workers [90] has become

very popular and has undergone several modifications. A typical synthetic procedure is as

follows: An aqueous stock solution of urea (1.0 M), magnesium chloride (0.1 M) and

aluminium chloride (0.1 M) are mixed together at the molar Mg/Al/urea ratio of 4:1:10

with magnetic stirring at room temperature. The concentrations of the components in the

starting solutions are 4 x 10-3

, 1 x 10-3

, and 1 x 10-2

M for MgCl2, AlCl3 and urea

respectively.

Then the homogeneous solution is transferred into a Teflon-lined autoclave and

heated ranging from 100 to 180 oC for different time intervals. After cooling to room

temperature, the solid precipitate is collected by centrifugation and washed with

deionized water subsequently.

In aqueous solutions, urea decomposes on heating to give ammonia and HNCO:

In acidic or neutral media, HNCO is converted into CO2, and ammonia takes up a proton

to give NH4+

Both reactions lead to consumption of H+ and hence increase the pH of the medium [91,

92] Urea hydrolysis is found to be one of the best method to produce the highly

crystalline LDHs [93]. Size and morphology controlled LDHs (Fig. 1.6) obtained through

this method [94] prompted us to synthesize various materials using this synthesis

methodology.

Hexamethylenetetramine (HMT) also called as hexamine, found to hydrolyze at

higher temperature in aqueous solution releasing ammonia, which makes the solution

alkaline. In a typical procedure metal nitrates or chlorides with hexamine in molar ratio

of (M2+

+ M3+

) : HMT with 0.15 M : 0.45 M were taken in a Teflon inner vessel with a

stainless steel outer vessel and allowed to react at 140 oC for 24 h. Pioneer synthesis of

LDH using hexamine was done by Iyi et al. [95] and they have achieved hexagonal

crystalline MgAl-LDH. Hexamine on hydrolysis gives ammonia and formaldehyde, this


17

formaldehyde on reductive amination with ammonia (Leuckart reaction) gives formic

acid and which leads to carbonate containing LDH. It was also proposed that slow release

of ammonia leads to highly crystalline hexagonal shape LDH. Followed by Iyi several

works were reported on the synthesis of LDH as well as brucite-like mixed hydroxides

using HMT hydrolysis [96-98].

2.3 Sol-gel method

The sol–gel synthesis of materials based on the hydrolysis and condensation of

molecular precursors is used to prepare a wide range of inorganic materials. This

procedure gives sols and these sol colloidal particles suspended in a liquid, progress

through a gelation process to form two interpenetrating networks between the solid phase

and the solvent phase. Although the roots of sol–gel chemistry can be traced to the 19th

century, only during the past 30 years this field witnessed remarkable growth in its

sophistication and applications.

Fig. 1.7 TEM images of sol-gel LDHs: (a) MgAl, (b) NiAl-A, (c) NiCoAl, (d) NiAl-N

(reproduced from ref. 104)

This technique limits the amount of alkaline required and thus sometimes

preferred for industrial synthesis processes [99, 100]. The synthesis procedure is as


18

follows: Magnesium ethoxide was dissolved by acid hydrolysis with HCl (35% in water)

or with HNO3 (65%) into 120 ml of ethanol; the dissolution was refluxed at 353 K, under

constant stirring. A second solution, containing a suitable amount of aluminium

acetylacetonate in 80 ml of a mixture acetone/ethanol 1:1 was added, in order to obtain

Mg2+

/Al3+

ratios in the range 3±6, was then slowly added, and the pH was adjusted to

about 10 with NH4OH. The solution was refluxed at 353 K up to 17 h, until the gel was

formed.

Gel was then repeatedly washed with ethanol and dried overnight at 353 K and

gel can also be exchanged with Na2CO3 aqueous solution to get carbonate in the

interlayers of LDH [101]. Sol-gel synthesis of ZnAl-LDH without impurity phase was

prepared [102] which was not possible previously. Recently, Valente et al. synthesized

the novel multi-metallic LDHs with nanocapsular morphology (Fig. 1.7) using sol-gel

method [103, 104] and one of the advantage here is that these material shows high

surface area than both co-precipitation and urea/hexamine hydrolysis materials.

2.4 Miscellaneous methods

Apart from these three important largely attempted methods, several other

methods are also available. Duan et al. synthesized LDH nanomaterials with uniform

crystallite size using separate nucleation and aging steps [105] and explored these

materials for various applications. NiAl-LDH was synthesized by Mizuhata et al. using

liquid phased deposition (LPD) using aluminium metal [106], highly stable LDH

obtained through this method can be applied in nickel–metal hydride batteries. Davila et

al. synthesized MgAl-mixed oxides using combustion method using sugar as fuel [107]

and which was further converted to LDH using memory effect. Recently O‟Hare

synthesized LDHs with unique morphologies using reverse microemulsion method [108],

the surfactant/water ratio enables them obtain nanometer sized LDH platelets typically

with a 40-50 nm diameter and 10 nm thickness. MgAl and ZnAl-LDH were synthesized

using lazer ablation in water [109] and they can also be synthesized through

electrochemical methods [110].


19

3. LDH derived materials

3.1 Mixed metal oxides

Thermal calcinations of LDHs materials results in 30-45% weight loss leads to the

formation of non-stoichiometric mixed metal oxides with characteristic properties, which

are exploited as active catalysts for many important catalytic transformations.

Thermogravimetric analyses (TGA) of LDHs reveal successive steps of weight loss

during temperature rise. In the range of 343–553 K first step is attributed to the loss of

adsorbed and interlayer water. The second step in the 553–1073 K range accounts for the

loss of hydroxyl groups from the brucite-like structure. Multi weight-loss steps can be

detected for hydrotalcites that contain carbonate and nitrate counter ions attributed to the

evolution of the corresponding CO2 and NOx molecules [111]. Fresh HTs exhibit poor

basic properties, because adsorbed water hinders the access to basic sites on the surface

[112]. The nature of the surface basic sites varies with severity of pre-treatment

conditions. Besides removal of water and carbon dioxide, rearrangement of surface and

bulk atoms occurs during pre-treatment, which changes the number and nature of the

basic sites with increasing pre-treatment temperature. Therefore, the optimum pre-

treatment temperature varies with the type of reaction [113]. Highly dispersed mixed

metal oxides obtained through LDHs showed superior properties as compared to other

processes. Cu/ZnAlO obtained through LDH showed excellent catalytic property towards

oxidative methanol reforming [114]. CuMgAlO obtained through CuMgAl-LDH showed

high activity for aqueous phase ozonation of phenol and oxalic acid [68]. Recently Duan

et al. showed that ZnO based mixed metal oxides obtained through the calcinations of

ZnAl-LDH showed superior UV-blocking properties to both commercial ZnO and a

physical mixture of ZnO and ZnAl2O4 [115].

3.2 Rehydrated LDH

Calcined LDHs can be reconstructed back to a layered structure if put in contact

with water and appropriate anions [21]. This property is called retro-topotactical

transformation and is also known as the “memory effect” [116-118]. Reconstruction

process of the LDH (Fig. 1.8) can also be followed by XRD (Fig. 1.9): by the appearance

of diffraction lines characteristic of the hydrotalcite.


20

Fig. 1.8 Schematic representation of rehydration

The memory effect depends on the calcination temperature of the parent LDH;

high calcination temperature leads to reduced memory effect [119] and the calcination

temperature has to be lower than that which leads to phase segregation (spinel).

Rehydration results in an decrease of the specific surface area with respect to the

corresponding calcined LDH [120].

Fig. 1.9 XRD patterns of a Mg–Al hydrotalcite freshly synthesized (HT-as), calcined

under air at 723 K for 15 h (HT-c), rehydrated in a water saturated gas flow (HT-rg) or

rehydrated in the liquid phase (HT-rl) (reproduced from ref. 120)

Nature of divalent cation also has considerable influence on the reconstruction of

LDH [121]. Reconstruction of decomposed hydrotalcites is reported to enhance the

catalytic activity in several base-catalyzed reactions, for which OH- acts as active

Brønsted basic site. Reconstructed MgAl-LDH showed higher catalytic activity for aldol

condensation between benzaldehyde and acetone compared to as-synthesized and

calcined LDHs [122]. Recently Gunawan and Xu synthesized spherical hollow nano

spheres of LDH using reconstruction behavior [123] and Duan et al. have done erasable

nanoporous antireflection coatings based on the reconstruction effect of layered double

hydroxides [124].


21

3.3 LDH composite materials

Recently, polymer/layered double hydroxide (LDH) nanocomposites have

attracted great interest in the field of materials chemistry because of their novel

mechanical, optical, fire retardant and thermal properties. Generally, the performance of

these unique properties mainly depends on the dispersion degree of LDH layers in the

polymer matrix [125, 126]. Thus, it is required that the LDH layers should have

hydrophobic surfaces and completely exfoliated structures to reach a stable homogeneous

dispersion in the polymer matrix. However, because of their strong interlayer electrostatic

interactions and significantly hydrophilicity, LDHs have very tight layer stacking and it is

very difficult to exfoliate these layers. There are three principal options to obtain a

polymer intercalated LDHs,

Direct intercalation of extended polymer chains in the LDH lattice.

Transformation of the host material into a colloidal system and precipitation in the

presence of polymer.

Intercalation of the monomer molecules and subsequent in situ polymerization.

Recently, several efforts have been made to synthesize polymer intercalated LDH, in

which the most common strategy is the pre-intercalation of pristine LDHs by organic

materials, such as sodium dodecyl sulfate (SDS) [127, 128]. Through this method, the

organo-modified LDHs are endowed with hydrophobic characteristics ready to be

intercalated into polymer chains. However, the introduction of these organic materials

with small molecules will deteriorate some properties of the nanocomposites especially

when the LDH content is high. Thermal properties of the polymer/LDH nanocomposites

were sharply decreased when the LDH loadings were increased from 2–5 wt% to 10–20

wt%. This is because that the charged layers are no longer stable enough during the

thermal degradation when a relatively large content of polymer is introduced along with

the LDH layers [129-131]. On the other hand, most recently, living radical

polymerization (LRP) has been proved an efficient strategy for preparing well-dispersed

and high quality polymer/layered inorganic nanocomposites, such as atom transfer radical

polymerization (ATRP) and reversible addition–fragmentation chain transfer (RAFT)

polymerization [132, 133]. Qu et al. synthesized polystyrene (PS)/layered double


22

hydroxide (LDH) nanocomposites by in situ reversible addition–fragmentation chain

transfer (RAFT) polymerization using the multifunctional RAFT agent SBC, sodium 4-

(benzodithioyl)-4-cyanopentanoic salt with enhanced thermal properties [134].

4. Physico-chemical characterization

4.1 Powder X-ray diffraction (PXRD) studies

The powder X-ray diffraction (PXRD) is a diagnostic tool for the phase

identification of these compounds. The PXRD patterns of all clay minerals possesses

layered structure generally with sharp, symmetric peaks at lower angels (2θ) and broad,

asymmetric peaks at higher diffraction angles. The thickness of the brucite-like layers

(4.8 Å) [135], and the interlayer space varied depending on the size and orientation of

anion (2.8 Å shows presence of carbonate anion with its molecular plane parallel to the

brucite-like layers). Lattice parameter „a‟ is the distance between the neighboring cations

in the brucite-like layers, which can be estimated from the ionic radii of the cations in the

brucite-like lattice [86] and their molar fractions in the samples while the parameter „c‟ is

three times the distance between the adjacent brucite-type layer, controlled mostly by the

size (and orientation) of the interlayer anion and the electrostatic forces operating

between the interlayer anion and the layers. PXRD was carried out in a Philips X‟Pert

MPD system using Cu K radiation ( = 1.5406 Å). The operating voltage and current

were 40 kV and 30 mA, respectively. A step size of 0.04˚ with a step time of 2 seconds

was used for data collection. The data were processed using the Philips X‟Pert (version

2.2e) software. Identification of the crystalline phases was made by comparison with the

JCPDS files [136].

4.2 Fourier transformed infrared (FT-IR) spectroscopy

Although infrared (IR) analysis is not a primary tool for the characterization of

LDHs, yet it has been routinely used especially for the identification of the foreign anions

in the interlayer space and its interaction with the brucite-like sheets. Besides that,

information about the type of bonds formed by the anions and about their orientation can

also be discerned.


23

FT-IR absorption spectra of the samples were recorded in a Perkin-Elmer FT-IR

spectrometer (Model-FT-1730). The powdered samples were ground with KBr in 1:20

ratio and pressed into pellets for recording the spectra. 64 spectra (recorded with a

nominal resolution of 4 cm-1

) were accumulated and averaged to improve the signal-to-

noise ratio.

4.3 Thermogravimetric analysis (TGA)

The thermal behavior of LDHs is generally characterized by two transitions: The

first one being reversible, endothermic, at low temperature corresponds to the loss of

interlayer water, without collapsing the structure and the second one endothermic, at

higher temperature is due to the loss of hydroxyl group from the brucite-like layer as well

as of the anions. The nature of these two transitions depends on many factors such as:

M(II)/M(III) ratio, type of anions, low temperature treatment (hydration, drying etc.) heat

treatment (in case of oxidizable element such as Cr(III)).

Thermogravimetric analysis (TGA) was carried out in Mettler TGA/SDTA 851e

and the data were processed using Stare software, in flowing nitrogen in a flow rate of 60

ml/min and at a heating rate of 10 oC/min.

4.4 Elemental analysis

Elemental chemical analyses of the samples were determined using inductively

coupled plasma emission spectrometry (ICPES; Perkin Elmer, OES, Optical 2000 DV).

The samples were digested in minimum amount of concentrated HNO3 and diluted using

milli Q water <10 ppm and analyzed.

4.5 Adsorption measurements (surface area and pore volume)

Specific surface area and pore size analysis of the samples were measured by

nitrogen adsorption at -196 oC using a sorptometer (ASAP-2010, Micromeritics). The

samples were degassed under vacuum at 120 oC for 4 h prior to measurements in order to

expel the interlayer water molecules. The BET specific surface area (SA) was calculated

by using the standard Brunauer, Emmett and Teller method [137] on the basis of

adsorption data. Pore volume (PV), micropore area and mesopore area were determined


24

by using the t-plot method of De Boer [138]. Average pore size distributions (APD) were

calculated from the desorption branch of the isotherms using the Barret, Joyner and

Halenda (BJH) method [139].

4.6 Scanning electron microscopy (SEM)

The electron microscopic study has been done with scanning electron microscope

(Leo series VP1430) equipped with Oxford instruments EDX facility, having silicon

detector. The samples were coated with gold using sputter coating before analysis to

avoid charging effects during recording. Analyses were carried out with an accelerating

voltage of 20 kV and a working distance of 17 mm, with magnification values up to

100,000x.

4.7 Transmission electron microscopy (TEM)

Transmission electron microscope (TEM) images were obtained with a JEOL

JEM-2100 microscope with acceleration voltage of 200 kV using carbon coated 200

mesh copper/gold grids. The samples were ultrasonically dispersed in ethanol for 5 min

and deposited onto carbon film using capillary and dried in air for 30 min. Elemental

mapping and analysis were done using STEM mode of HRTEM using an energy

dispersive X-ray (EDX) detector (Oxford EDX detector: Model INCAx-Sight).

4.8 X-ray photoelectron spectroscopy (XPS)

X-ray photoelectron spectra were acquired on a VG Microtech Multilab ESCA

3000 spectrometer using a non-monochromatized Mg Kα, X-ray source (1253.6 eV) on in

situ scraped fresh catalyst pellets and powder samples of spent catalysts. Base pressure in

the analysis chamber was maintained in the range of 3–6×10−10

Torr. The error in the

reported BE values is ±0.1 eV [140].

4.9 Temperature programmed reduction (TPR)

Temperature programmed reduction (TPR) measurements were done using

Autochem-2920 series. Prior to TPR analysis, the samples were heated at 200 oC under

nitrogen flow and cooled to room temperature. TPR studies were carried out by passing


25

10% H2 in argon. Flow rate of the gas and amount of the catalyst were calculated as

reported by fixing the characteristic number K = 100 [141]. The temperature of the

catalyst was increased at a heating rate of 10 oC/min from 50 to 800

oC.

4.10 Nuclear magnetic resonance (NMR) & Mass spectrometry (MS)

FT-NMR data were recorded using a BRUKER DPX-200 NMR spectrometer at

200 MHz using TMS as standard and CDCl3 as solvent. High-resolution mass

spectrometry (HRMS) analyses were performed using electrospray ionization (ESI+)

technique on a Waters Q-TOF micromass spectrometer.


26

5. Scope and objectives of the work

The potential application of LDHs and their derived materials for functional

nanocomposites or nano structures, sensors, fire retardants, films and materials having

electrochemical response attracted our research on LDHs. High surface area, acid-base

property, ability to accommodate different metal cations homogeneously in the layer and

improved basic property through memory effect promises these materials for catalysis.

Synthesis methodology has profound influence on the final properties of LDHs; hence

there is great scope to synthesize LDHs using different/novel synthetic procedures and

study their properties. In this thesis, chapters II & III discuss about the synthesize of

cobalt containing LDHs, owing to their good electrochemical behavior and application in

catalysis, using different ammonia releasing agents like urea and hexamine at different

hydrolysis temperature and hydrothermal conditions. It also covers the synthesis of

delaminated LDH and morphologically different cobalt carbonate materials using novel

synthetic route. Recently copper containing LDHs showed potential application in

oxidation reaction; however interaction of copper with other divalent metal ion and

mechanism of the oxidation was not studied in detail. Chapters IV &V discuss the

oxidation behavior of copper containing LDHs. Homogeneously dispersed copper

containing LDHs with different co-bivalent ions are synthesized by co-precipitation

method and their hydroxylation behavior is studied for benzene and phenol to delineate

the interaction of different co-bivalent ions on the catalytic activity. Sequential or

concomitant reactions find application in the greener production of industrially important

chemicals. Due to the tunable basic and redox properties, LDHs can potentially be

applied for green catalytic processes. Chapters VI & VII discuss the multifunctional

property of LDHs. LDHs are explored for the multi-component synthesis of precursors

for liquid alkanes and Hantzsch pyridines. Further, wherever possible structure property

relationship is deduced.

The objectives of the present thesis contain the following:

Synthesis of delaminated LDH: A facile two step approach.

Synthesis of CoCO3 and Co3O4: Soft chemical approach using LDH as precursor.


27

Hydroxylation of benzene to phenol over copper containing LDHs.

Hydroxylation of phenol to catechol and hydroquinone over copper containing

LDHs.

Liquid fuels from renewable using LDHs derived materials as multifunctional

catalyst in water.

Hantzsch pyridine synthesis of dihydropyridines using LDHs as solid base.


28

6. References

1 F. Bergaya, B. K. G. Theng, G. Lagaly in Handbook of clay science, Elsevier,

Oxford, UK.

2 E. C. Kruissink, L. L. van Reijden, J. R. H. Ross, J. Chem. Soc. Faraday Trans. (I),

77 (1981) 649.

3 E. Houdry, W. F. Burt, A. E. Pew, W. A. Peters in Catalytic processing by the

houdry process, National petroleum news, R570-R580, 1983

4 T. J. Pinnavaia, Science, 220 (1983) 365.

5 G. Centi, S. Perathoner, Microporous Mesoporous Mater., 107 (2008) 3.

6 F. Cavani, F. Trifirò, A. Vaccari, Catal. Today, 11 (1991) 173.

7 R. V. Gaines, H. C. W. Skinner, E. E. Foord, B. Mason, A. Rosenzweig, (1997)

Dana‟s New Mineralogy, 8th edn. New York.

8 E. Manasse, Atti. Soc. Toscana Sci. Nat. Proc. Verb., 24 (1915) 92.

9 G. Aminoff, B. Broome, Kungl. Sven. Vet. Akademiens Handlingar., 9 (1930) 23.

10 R. Allmann, Acta Crystallogr., Sect. B: Struct. Sci., 24 (1968) 972.

11 H. F. W. Taylor, Miner Mag., 37 (1969) 338.

12 H. F. W. Taylor, Miner Mag., 39 (1973) 377.

13 ISI Web of knowledge, Thomson Reuters, www.isiknowledge.com.

14 R. D. Shannon, Acta Crystallogr., Sect. A: Found. Crystallogr., 32 (1976) 751.

15 A. S. Bookin, V. A. Drits, clays clay Miner., 41 (1993) 551.

16 A. S. Bookin, V. I. Cherkasin, V. A. Drits, Clays Clay Miner., 41 (1993) 558.

17 M. C. Gastuche, G. Brown, M. Mortlans, Clay Miner., 7 (1967) 177.

18 G. Mascolo, O. Marino, Miner. Mag., 48 (1980) 619.

19 Rives V. (ed.), Layered Double Hydroxides: Present and Future, Nova Sci. Publ.,

New York, USA, 2001.

20 J. M. Thomas, W. J. Thomas in Introduction to the Principles of Heterogeneous

Catalysis, Acadamic Press, London (1967).

21 D. Tichit, B. Coq, CATTECH, 7 (2003) 206.

22 Y. Ono, J. Catal., 216 (2003) 406.

23 G. Busca, Ind. Eng. Chem. Res., 48 (2009) 6486.


29

24 Y. Liu, E. Lotero, J. G. Goodwin, X. Mo, Appl. Catal. A Gen., 331 (2007) 138.

25 S. Kannan, Catal. Surv. Asia, 10 (2006) 117.

26 T. Nakatsuka, H. Kawasaki, S. Yamashita, S. Kohijiya, Bull. Chem. Soc. Jpn., 52

(1979) 2449.

27 W. T. Reichle, J. Catal., 94 (1985) 547.

28 D. E. Laylock, R. J. Collacott, D. A. Skelton, M. F. Tchir, J. Catal., 130 (1991)

354.

29 M. Bellotto, B. Rebours, O. Clause, J. Lynch, D. Bazin, E. Elkaiim J. Phys. Chem.,

100 (1996) 8535.

30 D. Tichit, M. Lhouty, A. Guida, B. Chiche, F. Figueras, A. Auroux, D. Bartalini, E.

Garrone, J. Catal., 151 (1995) 50.

31 H. Schaper, J. J. Berg- Slot, W. H Stork, J. Appl. Catal., 54 (1989) 79.

32 A. Corma, V. Fornes, R. M. Martin-Aranda, F. Rey, J. Catal., 134 (1992) 58.

33 K. Yamaguchi, K. Ebitani, T. Yoshida, H. Yoshida, K. Kaneda, J. Am. Chem. Soc.,

121 (1999) 4526.

34 F. Prinetto, G. Ghiotti, R. Durand, D. Tichit, J. Phys. Chem. B, 104 (2000) 11117.

35 M. J. Climent, A. Corma, S. Iborra, K. Epping, A. Velty, J. Catal., 225 (2004) 316.

36 P. Kustrowskia, L. Chmielarz, E. Bozek, M. Sawalha, F. Roessner, Mater. Res.

Bulletin, 39 (2004) 263.

37 P. Kustrowski, D. Sulkowska, L. Chmielarz, A. Rafalska-Lasocha, B. Dudek, R.

Dziembaj, Microporous Mesoporous Mater., 78 (2005) 11.

38 K. Ebitani, K. Motokura, K. Mori, T. Mizugaki, K. Kaneda, J. Org. Chem., 71

(2006) 5440.

39 R. J. Chimentao, S. Abelloa, F. Medina, J. Llorca, J. E. Sueiras, Y. Cesteros, P.

Salagre, J. Catal., 252 (2007) 249.

40 A. Onda, T. Ochi, K. Kajiyoshi, K. Yanagisawa, Catal. Commun., 9 (2008) 1050.

41 H. Zeng, Y. Wang, Z. Feng, K. You, C. Zhao, J. Sun, P. Liu, Catal. Lett., 137

(2010) 94.

42 B. M. Choudary, M. L. Kantam, V. Neeraja, K. K. Rao, F. Figueras, L. Delmotte,

Green Chem., 3 (2001) 257.

43 D. Kishore, S. Kannan, Green Chem., 4 (2002) 607.


30

44 D. Kishore, S. Kannan, J. Mol. Catal. A Chem., 223 (2004) 225.

45 D. Kishore, S. Kannan, Appl. Catal. A Gen., 270 (2004) 227.

46 J. I. Di Cosimo, V. K. Diez, M. Zu, E. Iglesia, C. R. Apesteguia, J. Catal., 178

(1998) 499.

47 K. Kaneda, T. Yamashita, T. Matsushita, K. Ebitani, J. Org. Chem., 63 (1998)

1750.

48 K. Motokura, T. Mizugaki, K. Ebitani K. Kaneda, Tetrahedron Lett., 45 (2004)

6029.

49 K. Motokura, D. Nishimura, K. Mori, T. Mizugaki, K. Ebitani, K. Kaneda, J. Am.

Chem. Soc., 126 (2004) 5662.

50 D. Kishore, A. E. Rodrigues, Catal. Commun., 8 (2007) 1156.

51 S. Velu, N. Shah, T. M. Jyothi, S. Sivasanker, Microporous Mesoporous Mater., 33

(1999) 61.

52 V. R. Choudhary, J. R. Indurkar, V. S. Narkhede, R. Jha, J. Catal., 227 (2004) 257.

53 S. M. Auer, J. D. Grunwaldt, R. A. Koppel, A. Baiker, J. Mol. Catal. A Chem., 139

(1999) 305.

54 B. Coq, D. Tichit, S. Ribet, J. Catal., 189 (2000) 117.

55 P. S. Kumbhar, J. Sanchez-Valente, J. M. M. Millet, F. Figueras, J. Catal. 191

(2000) 467.

56 K. A. D. F. Castro, A. Bail, P. B. Groszewicz, G. S. Machado, W. H. Schreiner, F.

Wypych, S. Nakagaki, Appl. Catal. A Gen., 386 (2010) 51.

57 K. M. Parida, M. Sahoo, S. Singha, J. Mol. Catal. A Chem., 329 (2010) 7.

58 K. Yamaguchi, K. Mori, T. Mizugaki, K. Ebitani, K. Kaneda, J. Org. Chem., 65

(2000) 6897.

59 K. Kaneda, K. Ebitani, T. Mizugaki, K. Mori, Bull. Chem. Soc. Jpn., 79 (2006)

981.

60 K. Kaneda, S. Ueno, T. Imanaka, J. Chem. Soc. Chem. Commun., (1994) 797.

61 U. R. Pillai, E. Sahle-Demessie, J. Mol. Catal. A Chem., 191 (2003) 93.

62 K. Schulze, W Makowski, R. Chyzy, R. Dziembaj, G. Geismar, Appl. Clay Sci., 18

(2001) 59.

63 B. M. Choudhary, M. L. Kantam, A. Rahman, C. V. Reddy K. K. Rao, Angew.


31

Chem. Int. Ed., 40 (2001) 763.

64 T. Kawabata, Y. Shinozuka, Y. Ohishi, T. Shishido, K. Takaki, K. Takehira, J.

Mol. Catal. A Chem., 236 (2005) 206.

65 S. K. Jana, P. Wu, T. Tatsumi, J. Catal., 240 (2006) 268.

66 M. Li, X. Wang, S. Li, S. Wang, X. Ma, Int. J. Hydrogen Energy, 35 (2010) 6699.

67 X. Xiang, L. Bai, F. Li, AIChE J., 56 (2010) 2934.

68 M. Shiraga, T. Kawabata, D. Li, T. Shishido, K. Komaguchi, T. Sano, K. Takehira,

Appl. Clay. Sci., 33 (2006) 247.

69 A. Mastalir, Z. Kiraly, J. Catal., 220 (2003) 372.

70 S. Albertazzi, G. Busca, E. Finocchio, R. Glockler, A. Vaccari, J. Catal., 223

(2004) 372.

71 T. Honma, M. Nakajo, T. Mizugaki, K. Ebitani K. Kaneda, Tetrahedron Lett., 43

(2002) 6229.

72 T. Matsushita, K. Ebitani, K. Kaneda, Chem. Commun., (1999) 265.

73 S. Kannan, A. Dubey, H. Knozinger, J. Catal., 231 (2005) 381.

74 A. Dubey, S. Kannan, S. Velu, K. Suzuki, Appl. Catal. A Gen., 238 (2003)319.

75 V. Rives, O. Prieto, A. Dubey, S. Kannan, J. Catal., 220 (2003) 161.

76 S. Kannan in Bevy L. P. (ed.) Trends in Catalysis Research, Nova Sci. Publ., New

York, USA, 2006.

77 R. Zavoianu R. Birjega, O. D. Pavel, A. Cruceanu, M. Alifanti, Appl. Catal. A

Gen., 286 (2005) 211.

78 T. Mitsudome, Y. Mikami, H. Funai, T. Mizugaki, K. Jitsukawa, K. Kaneda,

Angew. Chem. Int. Ed., 47 (2008) 138.

79 T. Mitsudome, Y. Mikami, K. Ebata, T. Mizugaki, K. Jitsukawa, K. Kaneda, Chem.

Commun., (2008) 4804.

80 Y. Mikami, A. Noujima, T. Mitsudome, T. Mizugaki, K. Jitsukawa, K. Kaneda,

Tetrahedron Lett., 51 (2010) 5466.

81 T. Mitsudome, A. Noujima, T. Mizugaki, K. Jitsukawaa, K. Kaneda, Green Chem.,

11 (2009) 793.

82 W. Liang, M. Xiangju, X. Fengshou, Chin. J. Catal., 31 (2010) 943.

83 V. Hulea, A. Maciuca, F. Fajula, E. Dumitriu, Appl. Catal. A Gen., 313 (2006) 200.


32

84 S. Kannan, D. Kishore, K. Hadjiivanov, H. Knozinger, Langmuir, 19 (2003) 5742.

85 S. Kannan, R. V. Jasra, J. Mater. Chem., 10 (2000) 2311.

86 V. Rives, S. Kannan, J. Mater. Chem., 10 (2000) 489.

87 S. Kannan, V. Rives, H. Knozinger, J. Solid State Chem., 177 (2004) 319.

88 P. Koilraj, S. Kannan, J. Colloid Interface Sci., 341 (2010) 289.

89 S. Velu, K. Suzuki, M. P. Kapoor, S. Tomura, F. Ohashi, T. Osaki, Chem. Mater.,

12 (2000) 719.

90 U. Costantino, F. Marmottini, M. Nocchetti, R. Vivani, Eur. J. Inorg. Chem.,

(1998) 1439.

91 M. Rajamathi, P. V. Kamath, Int. J. Inorg. Mater., 3 (2001) 901.

92 L. Perioli, M. Nocchetti, V. Ambrogi, L. Latterini, C. Rossi, U. Costantino,

Microporous Mesoporous Mater., 107 (2008) 180.

93 M. Ogawa, H. Kaiho, Langmuir, 18 (2002) 4240.

94 M. Adachi-Pagano, C. Forano, J. P. Besse, J. Mater. Chem., 13 (2003) 1988.

95 N. Iyi, T. Matsumoto, Y. Kaneko, K. Kitamura, Chem. Lett., 33 (2004) 1122.

96 L. Li, R. Ma, Y. Ebina, N. Iyi, T. Sasaki, Chem. Mater., 17 (2005) 4386.

97 R. Ma, Z. Liu, K. Takada, N. Iyi, Y. Bando, T. Sasaki, J. Am. Chem. Soc., 129

(2007) 5257.

98 N. Iyi, Y. Ebina, T. Sasaki, Langmuir, 24 (2008) 5591.

99 K. Diblitz, K. Noweck, WO9623727 (1996).

100 K. Noweck, K. Diblitz, US6517795 (2003).

101 F. Prinetto, G. Ghiotti, P. Graffin, D. Tichit, Microporous Mesoporous Mater., 39

(2000) 229.

102 D. Tichit, O. Lorret, B. Coq, F. Prinetto, G. Ghiotti, Microporous Mesoporous

Mater., 80 (2005) 213.

103 J. S. Valente, M. S. Cantu, J. G. H. Cortez, R. Montiel, X. Bokhimi, E. Lopez-

Salinas, J. Phys. Chem. C, 111 (2007) 642.

104 J. Prince, A. Montoya, G. Ferrat, J. S. Valente, Chem. Mater., 21 (2009) 5826.

105 Y. Zhao, F. Li, R. Zhang, D. G. Evans, X. Duan, Chem. Mater., 14 (2002) 4286.

106 M. Mizuhata, A. Hosokawa, A. B. Beleke, S. Dekiy, Chem. Lett., 38 (2009) 972.

107 V. Davila, E. Lima, S. Bulbulian, P. Bosch, Microporous Mesoporous Mater., 107


33

(2008) 240.

108 G. Hu, D. O‟Hare, J. Am. Chem. Soc., 127 (2005) 17808.

109 T. B. Hur, T. X. Phuoc, M. K.Chyu, Opt. Laser Eng., 47 (2009) 695.

110 M. S. Yarger, E. M. P. Steinmiller, K. S. Choi, Inorg. Chem., 47 (2008) 5859.

111 F. Medina, R. Dutartre, D. Tichit, B. Coq, N. T. Dung, P. Salagre, J. E. Sueiras, J.

Mol. Catal. A Chem., 119 (1997) 201.

112 M. Turco, G. Bagnasco, U. Costantino, F. Marmottini, T. Montanari, G. Ramis, G.

Busca, J. Catal., 228 (2004) 43.

113 H. Hattori, Appl. Catal. A Gen., 222 (2001) 247.

114 S. Murcia-Mascaro, R. M. Navarro, L. Gomez-Sainero, U. Costantino, M.

Nocchetti, J. L. G. Fierro, J. Catal., 198 (2001) 338.

115 X. Zhao, F. Zhang, S. Xu, D. G. Evans, X. Duan, Chem. Mater., 22 (2010) 3933.

116 S. Abell, F. Medina, D. Tichit, J. Perez-Ramirez, J. C. Groen, J. E. Sueiras, P.

Salagre, Y. Cesteros, Chem. Eur. J., 11 (2005) 728.

117 F. Kooli, V. Rives, M. A. Ulibarri, Inorg. Chem., 34 (1995) 5114.

118 J. A. van Bokhoven, J. Roelofs, K. P. de Jong, D. C. Koningsberger, Chem. Eur. J.,

7 (2001) 1258.

119 A. J. Marchi, C. R. Apesteguia, Appl. Clay Sci., 13 (1998) 35.

120 J. Perez-Ramirez, S. Abello, N. M. van der Pers, Chem. Eur. J., 13 (2007) 870.

121 J. Perez-Ramırez, S. Abello, N. M. van der Pers, J. Phys. Chem. C, 111 (2007)

3642.

122 K. K. Rao, M. Gravelle, J. S. Valente, F. Figueras, J. Catal., 173 (1998) 115.

123 P. Gunawan, R. Xu, Chem. Mater., 21 (2009) 781.

124 J. Han, Y. Dou, M. Wei, D. G. Evans, X. Duan, Angew. Chem. Int. Ed., 49 (2010)

2171.

125 F. Leroux, J. P. Besse, Chem. Mater., 13 (2001) 3507.

126 F. Leroux, J. Nanosci. Nanotechnol., 6 (2006), 303.

127 F. Leroux, C. Taviot-Gueho, J. Mater. Chem., 15 (2005) 3628.

128 D. G. Evans, D. A. Xue, Chem. Commun., (2006) 485.

129 W. Chen, L. Feng, B. J. Qu, Chem. Mater., 16 (2004) 368.

130 P. Ding, B. J. Qu, J. Appl. Polym. Sci., 101 (2006) 3758.


34

131 P. Ding, B. J. Qu, J. Colloid Interface Sci., 291 (2005) 13.

132 B. Q. Zhang, C. Y. Pan, C. Y. Hong, B. Luan, P. J. Shi, Macromol. Rapid

Commun., 27 (2006) 97.

133 N. Salem, D. A. Shipp, Polymer, 46 (2005) 8573.

134 P. Ding, M. Zhang, J. Gai B. Qu, J. Mater. Chem., 17 (2007) 1117.

135 M. A. Drezdzon, Inorg. Chem., 27 (1988) 4628.

136 Joint Committee on Powder Diffaraction Standards, International Centre for

Diffraction Data, Pennsylvania, 1996 (Set No. 46).

137 S. Brunauer, P. H. Emmett, E. Teller, J. Am. Chem. Soc., 60 (1938) 309.

138 S. J. Gregg, K. S. W Sing in Adsorption Surface Area and porosity, Second ed.,

Academic Press, London, 1982.

139 E. P. Barrett, L. G. joyner, P.P Halenda, J. Am. Chem. Soc., 73 (1951) 373.

140 M. Vijayaraj, C. S. Gopinath, J. Catal., 241 (2006) 83.

141 D. A. M. Monti, A. Baiker, J. Catal., 83 (1983) 323.

chapter i - inflibnetshodhganga.inflibnet.ac.in/bitstream/10603/8415/5/05_chapter 1.pdf · with the...

Documents