stpauls.ac.instpauls.ac.in/.../201612090401586619-20.docx · Web viewThis work concerns with the laboratory production of an industrially important catalyst material namely: ZSM 5

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Final Report of the Minor Research Project

Preparation,Characterisation and acidity studies of ZSM-5

modified by transition metals and non metal oxides

MRP(S)-0773/13-14/KLMG015/UGC-SWRO dated 28-03-14

Submitted to

UNIVERSITY GRANTS COMMISSION

South Western Regional Office

Bangalore-560 009

By

Texin Joseph B J

Assistant Professor

Department of chemistry

St.Pauls college,Kalamassery

(Affiliated to Mahatma Gandhi University, Kottayam, Kerala)

MARCH 2016

MRP Report On Preparation,Characterisation and acidity studies of ZSM-5 modified by transition metals and non metal oxides

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CERTIFICATE

I hereby declare that, the Minor Research Project entitled

“Preparation,Characterisation and acidity studies of ZSM-5 modified by

transition metals and non metal oxides” (MRP (S)/13-14/KLMG/UGC-SWRO

dated 28-03-14) is a bonafide work carried out by Texin Joseph B J, Assistant

Professor, Department of Chemistry, St.Pauls College, Kalamassery. Further

certify that the work presented in the report is original and carried out according

to the plan in the proposal and guidelines of the XII Plan of University Grants

Commission.

Principal

St.Pauls College,

Kalamassery


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DECLARATION

I, Texin Joseph B J hereby declare that the project work entitled

“Preparation,Characterisation and acidity studies of ZSM-5 modified by

transition metals and non metal oxides” has been prepared by me and also

declare that this is a bonafide record of research work done by me during the

course of minor research project allotted to me by the University Grant

Commission, New Delhi and no part of this study has been submitted earlier or

elsewhere for any similar purpose.

Kalamassery Texin Joseph B J

Date:29.09.16 (Principal Investigator)


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ACKNOWLEDGEMENT

I thank the Almighty, the father of all, whose blessings have enabled me

to complete my project work successfully. I take this opportunity to express my

gratitude to University Grants Commission, for providing me financial

assistance, in the form of Minor Research Project to complete the present work

successfully.

I am grateful to Dr. Edwin Xavier (Former Principal) and Dr. V J Peter,

Principal, St. Pauls College,Kalamassery, Dr. Raju P( Former HOD, Dept. of

Chemistry),Dr.Rose Philo K J(HOD) and my colleagues for their

encouragement and help for completing my work.

I express my heartfelt gratitude to the Management for providing the

necessary facilities to carry out this project. I am also grateful to non-teaching

staff of Chemistry department for their help and support.

I express my sincere gratitude to the staff School of Chemical Science,

Mahatma Gandhi University and STIC, CUSAT for helping me with the

analytical part.

I express my sincere thanks to my M.Sc students for assisting and helping

me to complete this work.

Texin Joseph


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INDEX Page No

Abstract 6

Objectives 7

Relevance 7

Chapter 1 : Introduction 9

Chapter 2 :Review of literature 19

Chapter 3 : Materials and methods 29

Chapter 4 :Results and discussions 44

Chapter 5 : Summary of Findings 59

References 62


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ABSTRACT

Catalysis posses a great influence in today’s advancement in the field

of chemistry and material science. The sect of compounds termed as Zeolites

are inevitable when we consider the modern catalysis and the attempts to

improve the qualities of these are much anticipated by the field of research. This

work is such an attempt to prepare one of the well known Zeolites, namely the

ZSM 5(Zeolite Socony Mobil-5), compare with a commercial sample and

perform successful doping in it with different transition metals. The analysis of

homogeneity and crystalline nature of post doping samples are also an aim of

the work. Considering the importance of ZSM 5 as an efficient adsorption

catalyst, and potential solution for the harmful solvent crisis , the green

chemical aspect of this work is also much important. The preparation of Zeolite

is done by seeding gel technique in laboratory using an autoclave in the sodium

form. Various methods such as, TGA(thermo gravimetric analysis),

SEM(scanning electron microscopy),FTIR(Fourier transform infra red

spectroscopy) and XRD( X-Ray diffraction) were employed in the course of

work to obtain results regarding the thermal stability, crystalline nature,

homogeneity and quality of doping. The preparation of ZSM 5 in the seeding

gel method using sodium hydroxide and sodium aluminate in silica is found to

be producing product that could be compared with the commercial sample. The

simple laboratory doping technique is found to be producing good quality doped

ZSM 5 which retains the crystalline nature, homogeneity and thermal stability

of the pure ZSM 5 and possessing better catalytic property by the combined

effect of adsorption inherent in ZSM 5 and the catalytic effect of transition

metals present.


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OBJECTIVES AND RELEVANCE OF THE WORK

Objectives

To prepare the Zeolite ZSM -5 (Zeolite socony Mobil -5) under

laboratory conditions .

To compare the product with industrial ZSM -5, in physical and

crystalline properties.

To dope the samples of ZSM 5 with various transition metals.

To study the change in properties of ZSM-5 Zeolite by the doping using

different transition metals, by means of X ray diffraction and Scanning

Electron Microscope.

To conduct acidity studies

Relevance

The title of the pursuing minor project is “Preparation, Characterisation

and Acidity Studies of ZSM-5, Modifies by Transition Metal Oxides”. This

work concerns with the laboratory production of an industrially important

catalyst material namely: ZSM 5 and the modifications of the same using the

doping techniques by the various transition metals which are theoretically

expected to improve the qualities of the zeolite in the industrial world. The

work obviously has a major effect on the fields of advanced chemical research

and the chemical industry, which are in a desperate quest for reaction pathways

with lower energy requirements, high yields and most importantly, a greener

approach.

The responsible scientific and industrial world has been realizing that the

green chemistry is an inevitable concept now. This work which deals with the

quest for a more energy effective catalysis compared to usual Zeolite catalysis

by means of incorporating the adsorption properties of Zeolite along with the


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effective metallic catalysis and the click concept and tries to find a path to

progress utilizing the energy resources more effectively. Also, the study

considers the fact that one of the most dangerous sect of pollutants emitted by

the industrial world is used organic solvents which creates myriad of

environmental and health hazards within shorter periods of time. The organic

synthesis and different cracking reactions, which are industrially quite

important, are usually done in the organic solvents. This project attempts to

consider the adsorption and molecular sieving properties of the zeolites and

modified zeolite structures as better and greener substitutes for the polluting

solvents. In that way this work considers the threat on the environment and

biosphere.


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CHAPTER 1

INTRODUCTION

The entire world is an application of chemistry. Every day of a human

being is beginning with chemical reactions. On that sense chemistry plays a

very important role in the society and to the world also. Every chemical reaction

is not taking place at the same speed. Catalyst is the substance that is used to

regulate the speed of a chemical reaction.Catalyst has now become an

indispensable component in majority of chemical reactions. In every field of

human activity catalyst plays a vital role leading to the production of industrial

chemicals, fuels, pharmaceuticals as well as environmental pollutant

destruction.Catalysis is a complex surface phenomenon occurring on the surface

of a catalyst.The study of catalytic reactions begins with the dehydrogenation

studies of alcohol using metals by Von Marum (1776). John Jacob Berzelius

formulated the term ‘catalysis’ in the year 1835. The term catalysis as defined

by Ostwald in 1894 “the phenomenon in which a small quantity of the

substance that increases the rate of chemical reaction without being consumed”

is a kinetic phenomenon. Catalysis has wide ranging applications in chemical

industry and has a major impact on the quality of human life as well as

economic development. In recent years catalysis is also looked up as a solution

to eliminate or replace polluting processes due to inherent characteristics of

most catalytic processes as clean technologies. A typical industrial catalyst

should be regenerable, reproducible, mechanically and thermally stable, and

economical and should possess suitable morphological characteristics apart

from its activity, selectivity, and stability.The adsorption of the reactant

molecules and their interaction to give product on the active phase of the

catalyst depend not only on the reaction variables, but also on the nature of sites

on the catalyst surface, which in turn determines the quality of the catalyst


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Catalysis is classified in to two broad areas according to the phase of

reactant and catalyst. They are homogeneous and heterogeneous catalysis. Both

the categories have their advantages and disadvantages, though heterogeneous

catalysis has been more widely used, as it is more environmentally benign.

1.1. Homogeneous Catalysis

Homogeneous catalysis is a sequence of reactions that involve a catalyst

in the same phase as the reactants. Phase here refers to solid, liquid and gas.

Most commonly, a homogeneous catalyst is codissolved in a solvent with the

reactants.There are several example of homogeneous catalysis. Among these the

acid –base catalysis and enzyme catalysis are important.Acid-base catalysis

includes reaction in solution which is catalyzed by acid or base. A reaction

which is catalysed by H+ ion but not by other Brönsted acids is said to be

specifically proton-catalysed reactions.Examples are solvolysis of water,

inversion of cane sugar.On the other hand,a reaction that is catalysed by any

Brönstedacidis an example of general acid catalysis.Similarly,a reaction

catalysed only by OH- ions is said to be specifically base-catalyzed reaction

while that cataysed by any Brönstedbase is an example of general base

catalysis.

Another very important type of homogenous catalysis includes reactions

catalysed by certain complex organic substances known as enzymes.Enzymes

are proteins with high relative molar mass of the order of 10,000 or even more

and are derived from living organisms.Each enzyme can catalyze a specific

reaction.For instance,the enzyme diastase produce in germinated barley seeds

coverts starch in to maltose sugar.


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1.2. Heterogeneous catalysis

Heterogeneous catalysts act in a different phase than that of the reactants.

Most heterogeneous catalysts are solids that act on substrates in a liquid or

gaseous reaction mixture. Diverse mechanisms for reactions on surfaces are

known, depending on how the adsorption takes place. The total surface area of

solid has an important effect on the reaction rate. The smaller the catalyst

particle size, the larger will be the surface area for a given mass of particles.For

example, in the Haber process, finely divided iron serves as a catalyst for the

synthesis of ammonia from nitrogen and hydrogen. The reacting gasesadsorb

onto "active sites" on the iron particles. Once adsorbed, the bonds within the

reacting molecules are weakened, and new bonds between the resulting

fragments form in part due to their close proximity. In this way the particularly

strong triple bond in nitrogen is weakened and the hydrogen and nitrogen atoms

combine faster than would be the case in the gas phase, so the rate of reaction

increases. Heterogeneous catalysts are typically "supported," which means that

the catalyst is dispersed on a second material that enhances the effectiveness or

minimises their cost. Supports prevent or reduce agglomeration and sintering of

the small catalyst particles, exposing more surface area, thus catalysts have a

higher specific activity (per gram) on a support. Sometimes the support is

merely a surface on which the catalyst is spread to increase the surface area.

More often, the support and the catalyst interact, affecting the catalytic reaction.

Supports are porous materials with a high surface area, most commonly

alumina, zeolites or various kinds of activated carbon. Specialized supports

include silicon dioxide, titanium dioxide, calcium carbonate, and barium sulfate

etc.Using solid acid catalysts, product isolation is easy and reactions often run

under milder conditions and give higher selectivity. The atom efficiency of the

reaction is improved, the process is simplified, precious raw materials used in


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the manufacture of the catalysts are given increased lifetime (through reuse),

and the volume of waste is significantly reduced.

1.3. Solid acid catalyst

Solid acid catalysis is one of the most important areas of research and has

assumed great relevance as an economic alternative to many homogenously

catalysed, industrially important reactions. Solid acid catalysts play a crucial

role in the petrochemical industry, where they have largely replaced traditional

acids active in the liquid phase for hydrocarbon transformations. The solid acid

catalysts have many advantages over liquid Brönsted and Lewis acid catalysts

[1]. They are non-corrosive, environmentally benign and easily separable from

the reaction mixture and pose few problems of disposal. The solid acid catalysts

can also be designed to give higher activity, selectivity, regenerability and

longer catalyst life. In the last two decades substantial progress has been made

and several industrial processes that use solid acid catalyst have been introduced

successfully. As well as, being convenient to handle, solids can be used at high

temperatures and give enhanced product selectivity. They are also finding

increasing use in the production of feedstock organic chemicals and the

synthesis of fine chemicals.

Many features of acid sites in solids are closely parallel to those in

solution. Materials that are Brönsted acids (proton donors) and Lewis acids

(electron acceptors) are known, with the action of Brönsted sites in zeolites

being particularly well understood. Solid acids can be described in terms of

their Brönsted / Lewis acidity, the strength and number of these sites, and the

morphology of the support (typically in terms of surface area and porosity).

Typically, Brönsted acid sites in mixed metal oxides occur where the oxygen

atoms of a hydroxyl group attached to a metal atom of one kind are coordinating

(acting as a Lewis base) to atoms of a different kind, resulting in more acidic


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centres. Lewis acid sites are usually associated with incompletely coordinated

cations that accept electrons. In some cases, “super acid'' sites (with stronger

acidity than concentrated sulfuric acid) are also observed. High product

selectivity can depend on the fine-tuning of these properties. For instance, some

rearrangement reactions require pure Lewis acidity, Friedel-Crafts reactions

require Lewis acidity (e.g., for alkylations using alkyl halides) or Brönsted

acidity (e.g., for alkylation using alcohol), or indeed, a combination of both

(e.g., for Friedel-Crafts acylations using acid chlorides. At a more fundamental

level, the use of mesoporous supports have enabled supported reagents and

catalysts to be used in reactions of much bulkier substrates than could be

considered for micro porous (zeolite) materials [2]. The synthesis of pure

Lewis or Brönsted solid acids is a particularly important challenge where some

progress has been made. Chemically modified micelle-templated silica (MTS)

materials as analogues for sulfonic acids have recently been reported and show

great promise as solid Brönsted acids [3]. Pure Lewis acids are more difficult to

achieve, because Brönsted acidity often arises from Lewis acid-

basecomplexation. To obtain high selectivity toward the desired products in

synthetic reaction all these properties must be considered. In addition, steric

constraints imposed by the pore structure of the solid acid can influence the

reaction pathway resulting in “shape-selective catalysis”. Recent development

in the preparation of mesoporous materials has allowed liquid-phase reactions

with bulky substrates.

The catalytic action consists in accelerating a useful reaction at the

expense of other thermodynamically possible transformations. For saving

energy and raw materials, catalysts must be extremely selective. This requires

that surface composition be very precisely adjusted at the scale of the

elementary catalytic process that is at the scale of molecules. This is necessary

for the different surface atoms to work in co-operation with each other.


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Consequently, one of the major challenges in catalyst preparation is to

synthesize highly dispersed solids (high surface area per unit mass of material)

with a composition uniform at the atomic scale.

1.4. Zeolites

Over last several decades, the chemical engineering and the involvement of

the new chemical techniques in industries have flourished in a very high rate.

The rapidly developing industries demanded much more efficiency in all means.

In the field of energy efficient and highly productive chemistry, Zeolite

Catalysis is very much popular and quite substantial.

The Zeolite, a term which was coined by Swedish mineralogist, Axel Fredrik

Cronstedt, which literally means “boiling stone”. The term we use makes an

indirect notion of the special property of the class of compounds we refer. The

rock which was found in nature by Cronstedt has become something inevitable

in the field of catalysis. Basically, Zeolites fall in the section of minerals. They

are Aluminosilicate minerals, occurring in nature in different structures and also

synthesized chemically. These minerals has the general formula :

Mn+x/n [(AlO2 )x(SiO2)y].n H2O.

Where M is a cation with charge n+ . An important quantity here is the

ratio y/x, ie the silicon-aluminium ratio. This is usually larger than one and can

be infinity in some versions of Zeolites like silicalites. The primary building

blocks of Zeolites are formed as open anion framework consisting of oxygen-

sharing TO4 tetrahedra, where T is Si or Al. Their framework structure contains

interconnected voids that are filled with adsorbed molecules or cations. Zeolite

micropore channels have very well-defined diameters so that bulky molecules

will be excluded from the internal surface. The channels and cavities are the

natural possessions of Zeolites which makes them able to act as catalysts. The

micro porous nature of a Zeolite is the basic quality of it for being effective. The


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large majority of zeolite structures are constructed by repeating so-called

secondary building units (SBUs). There are presently 19 SBUs. Another way to

classify zeolites is to take into account their pore openings and the

dimensionality of their channels. Thus, one distinguishes small pore zeolites

(eight-membered-ring pores), medium pore zeolites formed by ten-membered

rings and large pore zeolites with twelve-membered-ring pores. Recently an

extra-large pore zeolite category has been added. This classification simplifies

comparisons in terms of adsorptive, molecular sieving and catalytic properties.

There are more factors that determine the quality of a zeolite as catalyst, like:

the Si/Al ratio, Crystallinity ,presence of transition metals, and the morphology.

ZSM 5, Zeolite Socony Mobil -5 is much utilized in the field of chemical

industry and research. The product left the mark of synthetic zeolites in research

and catalysis. Barrer and Daney, were the first to report the synthesis of a

number of high silica or silicaceous zeolites,and introduced the concept of

scientist’s control on the pore size and acidity of zeolite by variation of Al

content. The ZSM % was synthesized by Argauer and Landolt of the Mobil Oil

Corporation in 1972. They designed ZSM 5 as a product with medium size,

interconnecting channels and a possible ratio of Si:Al as 5:infinity. The ZSM 5

is a silicaceous material. The introduction of this brought the catalysis a boost.

An additional +ve charge is required when Si4+ is replaced by an Al3+ and

this is effectively fulfilled by an H+ ion . This structural specialty makes the

material strongly acidic due to the readily discharged protons. This property

makes the ZSM 5 much essential in the industrial articulations of acid

catalyzed reactions like Hydrocarbon isomerization and alkylation. The size

selectivity of the ZSM5 enables it to carry out these. Shape selectivity was first

observed by Weisz and Frilette in 1960. Reactions within zeolites can be

inhibited if there is no matching between certain molecules and a sterically


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confined environment allowing conversion of reactants. The unique one, two or

three-dimensional pore system of zeolites enables shape selective catalysis.

Reactant selectivity: This occurs when some molecules preferentially enter the

zeolite pore mouth whereas others are rejected because they are too large with

respect to the pore openings. Once a reactant has adsorbed in the zeolite

channels, it must diffuse towards active sites where reactions can occur. This is

where the two following selectivity phenomena can occur.

Transition state selectivity

The distinction between transition state selectivity and product

selectivity is not always obvious. It takes place when the transition state cannot

be accommodated in the space available in the intra crystalline volume. A way

to differentiate product and transition state selectivity is to vary the crystal size

because only product selectivity depends on crystal size, whereas transition

state shape selectivity does not.

Product selectivity

This occurs when some reaction products or intermediates formed within

the pores are too bulky to diffuse out. They are either converted to smaller

molecules or deactivate the catalyst by blocking of the pores. After reaction has

occurred, products must diffuse away from the micropores which results in a

kind of molecular traffic control.

ZSM 5 has its general formuls as , Nan AlnSi96-nO192 . 16H2O.

(0<n<27). The ZSM 5 falls in the pentasil family of of zeolites.The preparation

of it was designed by the use of organic Amines as the templating agents.These

molecules gives the structural features we require for the synthesized zeolite.

Compounds like tetrapropylammonium were used for this purpose. In the


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synthesis, along with this, a source solution of Silica,source solution of Na+

ions ,Alumina , and Hydroxyl ions are used.

The molecular interactions occurring in the zeolites, particularly ZSM 5

here, is quite based on the structure of it. The concept of transition metal

impregnated ZSM 5 was much fascinating and extremely effective in the angle

of catalysis.

The concept has a greater importance as the world of chemistry needs to

be greener and less harmful to the biosphere. The industries Although the most

creative, the pharmaceutical industry cause major environmental impacts. In

contrast, petrochemical and bulk industries have a minor impact due to

extensive use of heterogeneous catalysts, thereby improving selectivity and

facilitating product and catalyst recovery, and thus minimizing energy and

waste.

The increased use of the heterogeneous catalysis tends to reduce the

usage of organic solvents which turns out to be one of the major contributors to

the environmental pollution from industries related to chemistry. The specialty

in structure of ZSM 5 and the other Zeolites is well utilized by the industries in

catalysis, but the concept of “doping” of aluminosilicate structures with metals

especially transition metals is the result of an extensive and ongoing research

interest of increasing the efficiency of catalysis.

Since numerous organic transformations are now often based on metal-

catalyzed processes, usually under homogeneous conditions, it would be

interesting to combine such metal-ion catalysis with the typical properties of

Zeolite.

A homogeneous process could thus become heterogeneous by

immobilizing the metal catalyst in Zeolites, taking furthermore advantage of

their size and shape selectivity.


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Moreover, the Zeolite framework can act as a polydentate ligand toward

the metal ion .Distortion in coordination may occur, leading to a modification of

the catalytic behavior. Therefore, new conditions and reactions could be

achieved with such modified Zeolites. With the “greening” of organic synthesis

as a goal.

The transition metal catalysis is much improved with the advantage of the

shape and size selectivity. ZSM 5 was selected for the study on the alterations

brought about by the Impregnation with various transition metals like: Cobalt,

Chromium, Manganese and Iron. The ZSM 5 is a very widely used Zeolite

structure and the modifications has important implications. It was expected on

the theoretical basis, the structural properties as well as the performance as a

catalyst gets modified positively. A certain amount of the ZSM 5 is used in each

experimental doping with the nitrates of the metals. The amounts of nitrates

were calculated according to the weight percentage in the whole mixture. The

continuous stirring on a magnetic stirrer in slightly warm temperature is

employed as the process for impregnating the samples. The resultant samples

are made fine powder and the color, weight are analysed. The samples are

analysed with X Ray Diffraction and SEM analysis.The comparison of the

results with those of pure zeolite is done.


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CAPTER 2

REVIEW OF LITERATURE

Zeolites are crystalline, microporous, hydrated aluminosilicates of

alkaline or alkaline earth metals. The frameworks are composed of [Si04]4- and

[A104]5- tetrahedra, which corner-share to form different open structures. The

tetrahedra are linked together to form cages connected by pore openings of

defined size; depending on the structural type, the pore sizes range from

approximately 0.3-1 nm [1]. The negative charge on the lattice is neutralized by

the positive charge of cations located within the material's pores. In the basic

zeolites, these are usually univalent and bivalent metals or a combination. The

metal cations may be replaced by acidic protons via ion-exchange to ammonium

and subsequent calcination. By reason of electrostatic forces it is not possible to

make an Al-O-Al bond. They are made up of "Т-atoms" which are tetrahedrally

bonded to each other with oxygen bridges. Other "Т-atoms" such as P, Ga, Се,

В and Be can also exist in the framework. Due to their exceptional properties,

zeolites have been widely used in numerous technical applications as catalysts,

adsorbents and ion exchangers [2,3].

The structure formula of zeolite is based on the crystallographic unit cell :

Mx/n [(AlO2)x(SiO2)y] wH2O, where (M) is an alkali or alkaline earth

cation, (n) is the valence of the cation, (w) is the number of water molecules per

unit cell, x and y are the total number of tetrahedra per unit cell, and the ratio

y/x usually has values of 1 to 5, though for the silica zeolite, y/x can be raging

from 10 to 100.

Zeolites have been well studied in terms of the relations among structure,

properties and synthesis. Nowadays 180 synthetic zeolites are known. Some of


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the earlier synthetic zeolites include zeolites A, X, Y, L, ZSM-5 and omega.

The Atlas of Zeolite Structure Types [4] , published and frequently updated by

the IZA Structure Commission, assigns a three - letter code to be used for a

known framework topology irrespective of composition. Illustrative codes are

LTA for Linde zeolite A, FAU for molecular sieves with a faujasite topology

(e.g., zeolites X, Y), MOR for the mordenite topology, MFI for the ZSM - 5 and

silicalite topologies and AFI for the aluminophosphate AlPO4-5 topology. The

acceptance of a newly determined structure of a zeolite or molecular sieve for

inclusion in the offi cial Atlas is reviewed and must be approved by the IZA

Structure Commission. The IZA Structure Commission was given authority at

the Seventh International Zeolite Conference (Tokyo, 1986) to approve and/or

assign the three - letter structure code for new framework topologies [4].

A typical crystal chemical formula for zeolite A (LTA) [5] would be:

| Na12 (H2O)27 | [ Al12 Si12 O48 ] (1)

Here, the fact that the host is 3-dimensional and can be constructed by

linking double 4-rings as composite building units is highlighted. The

description of the pores indicates that there are sodalite cages and a 3-

dimensional channel system which contains α-cavities. The channels run

parallel to <100> (i.e.,parallel to [100], [010], and [001]), and have an effective

channel width of 0.41 nm (Fig.1) [5].

In most zeolite structures the primary structural units, the AlO 4 or SiO 4

tetrahedra, are assembled into secondary building units which may be simple

polyhedra, such as cubes, hexagonal prisms or cubo - octahedra. The fi nal

framework structure consists of assemblages of the secondary units. More than

70 novel, distinct framework structures of zeolites are known. They exhibit pore

sizes from 0.3 to 1.0 nm and pore volumes from about 0.10 to 0.35 cm3/g.


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Typical zeolite pore sizes include: (i) small pore zeolites with eight - ring pores,

free diameters of 0.30 – 0.45 nm (e.g., zeolite A), (ii) medium pore zeolites with

10 – ring pores, 0.45 – 0.60 nm in free diameter (ZSM - 5), (iii) large pore

zeolites with 12 – ring pores of 0.6 – 0.8 nm (e.g., zeolites X, Y) and (iv) extra -

large pore zeolites with 14 -ring pores (e.g., UTD - 1) [4, 5].

The zeolite framework should be viewed as somewhat fl exible, with the

size and shape of the framework and pore responding to changes in temperature

and guest species. For example, ZSM - 5 with sorbed neopentane has a near -

circular pore of 0.62 nm, but with substituted aromatics as the guest species the

pore assumes an elliptical shape, 0.45 to 0.70 nm in diameter. Some of the more

important zeolite types, most of which have been used in commercial

applications, include the zeolite minerals mordenite, chabazite, erionite and

clinoptilolite, the synthetic zeolite types A, X, Y, L, “ Zeolon ” mordenite, ZSM

- 5, beta and MCM - 22 and the zeolites F and W [5].

R. M. Barrer [1] began his pioneering work in zeolite adsorption and

synthesis in the mid - 1930s to 1940s. He presented the fi rst classifi cation of

the then - known zeolites based on molecular size considerations in 1945 and in

1948 reported the fi rst defi nitive synthesis of zeolites, including the synthetic

analog of the zeolite mineral mordenite and a novel synthetic zeolite much later

identifi ed as the KFI framework. Barrer ’ s work in the mid - to late 1940s

inspired R. M. Milton of the Linde Division of Union Carbide Corporation to

initiate studies in zeolite synthesis in search of new approaches for separation

and purifi cation of air. Between 1949 and 1954 Milton and coworker D. W.

Breck discovered a number of commercially signifi cant zeolites, types A, X

and Y. In 1954 Union Carbide commercialized synthetic zeolites as a new class

of industrial materials for separation and purifi cation. The earliest applications


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were the drying of refrigerant gas and natural gas. In 1955 T.B. Reed and D.W.

Breck reported the structure of the synthetic zeolite A . In 1959 Union Carbide

marketed the “ISOSIV” process for normal – isoparaffi n separation,

representing the fi rst major bulk separation process using true molecular

sieving selectivity. Also in 1959 a zeolite Y - based catalyst was marketed by

Carbide as an isomerization catalyst [1-3] .

In 1962 Mobil Oil introduced the use of synthetic zeolite X as a

hydrocarbon cracking catalyst. In 1969 Grace described the fi rst modifi cation

chemistry based on steaming zeolite Y to form an “ ultrastable ” Y. In 1967 –

1969 Mobil Oil reported the synthesis of the high silica zeolites beta and ZSM -

5. In 1974 Henkel introduced zeolite A in detergents as a replacement for the

environmentally suspect phosphates. By 2008 industry - wide approximately

367 000 t of zeolite Y were in use in catalytic cracking . In 1977 Union Carbide

introduced zeolites for ion – exchange separations [3].

ZEOLITE SYNTHESIS

The synthetic zeolites are used commercially more often than natural

zeolites due to the purity of crystalline products and the uniformity of particle

sizes. The sources for early synthesized zeolites were standard chemical

reagents. Much of the study of basic zeolite science was done on natural

zeolites. The main advantages of synthetic zeolites in comparison to naturally-

occurring zeolites are that they can be engineered with a wide variety of

chemical properties and pore sizes and that they have greater thermal stability.

The zeolite synthesis involves the hydrothermal crystallization of

aluminosilicate gels (formed upon mixing an aluminate and silica solution in the

presence of alkali hydroxides and/or organic bases), or solutions in a basic


23 | P a g e

environment. The crystallization is in a closed hydrothermal system at

increasing temperature, autogenous pressure and varying time (few hours to

several days). The type of the zeolite is affected by the following factors [9-11]:

- Composition of the reaction mixture (silica to alumina ratio; OH-;

inorganic cations). Increasing the Si/Al ratio strongly affects physical properties

of the zeolites. OH- modifies the nucleation time by influencing transport of

silicates from the solid phase to solution. Inorganic cations act as structure

directing agents and balance the framework charge. They affect the crystal

purity and product yield.

- Nature of reactants and their pretreatments. The zeolite synthesis is

carried out with inorganic as well as organic precursors. The inorganic

precursors yielded more hydroxylated surfaces whereas the organic precursors

easily incorporated the metals into the network.

- Temperature of the process. The rate of crystallization is directly

proportional to temperature while the rate of nucleation is inversely proportional

to temperature).

- Reaction time. Crystallization parameter must be adjusted to minimize

the production of the other phases while also minimizing the time needed to

obtain the desired crystalline phase.

- pH of the reaction mixture. The process of zeolitezation is carried out in

alkaline medium (pH>10).


24 | P a g e

- Other factors. The synthesis can be carried out on a continuous or semi

continuous mode, which enhances the capacity, making it compatible for

industrial applications.

The main problem in zeolite researchs is the availability and cost of raw

material specifically the silica source. On the other hand, commercial silica

(made of sand) which is available in gel, sol, fumed or amorphous solid is found

to be variable in reactivity and selectivity. The preparation of synthetic zeolites

from silica and alumina chemical sources is expensive. Yet, cheaper raw

materials, such as clay minerals, natural zeolites, coal ashes, municipal solid

waste incineration ashes and industrial slags, are utilized as starting materials

for zeolite synthesis. The use of waste materials in zeolite synthesis contributes

to the mitigation of environmental problems, generally in the field of water

purification, removing heavy metals or ammonium, and turns them into

attractive and useful products.

Kaolin based zeolites. Kaolin is clay mineral which structure represent

SiO4 tetrahedral sheets joined to Al(O,OH)6 octahedral sheets through shared

oxygens. Zeolites prepared from natural kaolin are always contaminated with

trace amount of iron, titanium, calcium, magnesium, etc. which are originally

present in the natural kaolin. These elements may have some influence on the

zeolite properties such as brightness, hardness, catalytic activity, electrical

properties, etc. Presently, many researchers are working actively in various

aspects on the synthesis of zeolite from kaolin. Clay minerals such as kaolin ,

illite, smectite, interstratified illite-smectite, montmorillonite and bentonite are

widely used for synthesis of zeolites. The benefits of using kaolin as an

aluminosilicate source in zeolite synthesis widely known. These authors have

already studied the preparation of various zeolites from kaolin or other ashes


25 | P a g e

and have made great progress in synthesis of 4A, mordenite, X, Y zeolites, etc.

Kaolin is usually used after calcination at temperatures between 550-950°C to

obtain a more reactive phase metakaolin under chemical treatments, with the

loss of structural water. Only a small part of AlO6 octahedra is maintained,

while the rest are transformed into much more reactive tetra- and penta-

coordinated units . The conditions of the kaolin calcination strongly influence

the reactivity of the obtained solids. The best conditions for obtaining a very

reactive metakaolin have been discussed by several authors who reported values

between 600-800 °C [6-8].

Environmental impact. Globally, millions of tones of miscellaneous solid,

liquid and gaseous waste materials, such as household, commercial, industrial,

agricultural, radioactive and clinical wastes, are generated annually. It follows

that for efficient use of the world’s resources recycling and reuse of waste is

necessary. On the other hand, large daily output and the limited landfill capacity

have resulted in social and environmental problems. Furthermore, the amount of

these material is expected to increase dramatically in the near future and may

cause major challenges and serious environmental problems.

Fly ash based zeolites. Various processes have been developed for

synthesis of zeolite from fly ash, which have been reported by several patents

and research articles. The processes developed include five different

methodologies with variations in pretreatment steps, sodium aluminate addition,

etc. as a function of structure development and exchange capacity. Fly ash is an

inorganic residue resulting from the combustion of coal in electricity generating

plants, consisting mostly of SiO2, Al2O3 and Fe2O3. As an industrial by-

product fly ash is in the process of being beneficially used in several

applications. Although the Si and Al concentrations are determined by the


26 | P a g e

starting fly ash composition, the type and yield of synthesized zeolite strongly

depended on alkaline condition and SiO2/Al2O3 ratio of the starting fly ash.

This ratio is important to predict whether the fly ash could successfully be

converted into a specific zeolitic material by the adopted synthesis procedures.

On the other hand, it is necessary to clarify the influence of the silica–alumina

composition for the zeolite formation because the fly ash composition seriously

changes depending on the origin of coal sources, in order to synthesize a

specific zeolite from any fly ash source [8].

Classical hydrothermal synthesis of zeolites from kaolin include: (i)

thermally activated of kaolinite in order to get metakaolinite; (ii) hydrothermal

reaction of metakaolinite with various aqueous alkali media;(iii) purification

and activation of the resulting zeolite. Numerous papers have appeared on the

subject of synthesized zeolites.

The synthesis of zeolite Type NaA from Bulgaria kaolinite by

conventional alkaline activation was investigated in [9-12]. The recommended

molar composition for NaA zeolite synthesis was Na20/AI203 ratio of 1-2 and

Si02/AI203 ratio of 1-2. In this research, NaA zeolite was synthesized via

hydrothermal method. Also, the effects of reaction time and temperature on

morphology and crystalline of the synthesized zeolites were investigated. The

final products were characterized by X-ray diffraction and scanning electron

microscopy (SEM). It is found that the reaction time has a great effect on the

crystalline of the synthesized zeolites. The low grade Kalabsha kaolin

coexisting with quartz, anatase was thermally activated between 600 and 1000

°C and treated hydrothermally with 2–8 M NaOH solution with or without

added water glass, using water bath or autoclave. Zeolite 4A, zeolite P, analcim

and hydroxy sodalite were identified by [13]. In [14] produced zeolite NaA


27 | P a g e

from the synthesis mixture which has a composition of

1SiO2:1Al2O3:1.5Na2O:6.5H2O molar ratios by using a microwave oven.

They characterized the products by XRD and SEM techniques. In [15]

synthesized laumontite in a wide temperature range (between 30 °C and 450 °C)

by hydrothermal treatment of artificial glasses of composition 1CaO– 1Al2O3–

4SiO2 at 1 kbar water pressure. Chandrasekhar et al. [13] synthesized zeolite

NaX from locally available natural kaolinite. First, they obtained the

metakaolinite at 900 °C. Then, the metakaolinites were separately mixed with

the calculated amount of NaOH solution and sodium silicate to get molar ratio

(SiO2/Al2O3) = 3; (Na2O/SiO2) = 1.1 and (H2O/Na2O) = 40 for the reaction

mixture. This was aged for 24 h at room temperature and heated in air oven at

87 ± 2 °C. In [15] synthesized zeolite A and X from kaolin activated by

mechanochemical treatment. They used kaolinite with a mean particle size of

1.7 μm. The process consists of grinding of kaolinite and subsequent reaction

with NaOH solution at 60 °C. In [16] have achieved zeolite synthesis by

hydrothermal treatment of the waste solution from selective leaching by 2 M

NaOH solution of kaolinite calcined at 1000 °C for the preparation of

mesoporous γ-Al2O3. The spent leaching solution was hydrothermally treated

at 100 °C and 150 °C for 12–72 h. The initial product, hydroxy sodalite, was

converted to zeolite P, after a reaction time of 72 h [17,18].

The possibility to prepare synthetic zeolites A, X from Bulgarian kaolin

as the basic raw material was studied in [19-21]. The synthesis of zeolites A, X

involves preliminary formation of granules granules by the method of “fluidized

bed”, followed by crystallization (zeolitization). Thus, the following

experimental results were obtained: using the method of “fluidized bed”, the

conditions for preparation of suitable granules (“Blackberry” type) with

preferred size (1-3 mm) were studied with five amorphous ceramic blends


28 | P a g e

containing kaolin, amorphous SiO2, sodium silicate and sodium aluminate at

proper quantitative ratios; five crystallizing reactive solutions containing

sodium hydroxide and lithium hydroxide as additive were developed, hhe role

of the additive in the crystallization process optimization and in the

achievement of high phase purity of the zeolite synthesized was established; the

conditions for hydrothermal crystallization (zeolitization) of granules were

found to be: 36 h at temperature of 95oC. The structure of the synthetic product

Zeolites A,X , was studied by the methods of XRD, DTA/TGA, SEM and IR

spectroscopy.

In recent years there has been considerable progress made in the field of

accelerating the kinetics of low-temperature inorganic synthesis. Several

techniques, like sonochemical (acoustic wave stimulation), ionizing and

nonionizing radiation, microwave hydrothermal, hydrothermal process with

superimposed electric fields, hydrothermal process with mechanical forces, and

mechanochemical, including very high uniaxial pressure


29 | P a g e

CHAPTER 3

MATERIALS AND METHODS

3.1.The preparation of the Zeollite ZSM 5

Chemicals

1. Sodium hydroxide

2. Tetrapropylammonium bromide

3. Sodium aluminate

4. Colloidal silica

Equipments

1. Autoclave

2. Muffle furnace

3. Magnetic stirrer-heater

Procedure

Step 1: Preparation of seeding gel

0.2018 g of NaOH was dissolved in 36 ml of distilled water. 3.771 g of

TPABr was added to the NaOH solution with continuous stirring. The mixture

is then stirred for another 30 minutes. After that 3.889 g of colloidal silica is

added to the mixture with continuous stirring. Total mixture is stirred for

another one hour.

Step 2: Preparation of the second gel

In this step, 1.099 g of NaOH is dissolved in 26 ml of distilled water.

0.410 g NaAlO2 and 72 ml distilled water as solvent were added and mixture

was stirred for 30 min. 11.1308 g of colloidal silica is added to mixture with

continuous stirring and then the mixture is stirred for one hour. Finally the


30 | P a g e

seeding gel prepared in first step was added slowly and with continuous stirring

in the second gel, and the mixture is stirred for 1 hour to get a homogeneous

mixture . the ph of the final gel is found. The gel was transferred into an

autoclave and heated at 200 oC for 16 hours. The solid product obtained is

filtered, washed with distilled water and dried at room temperature overnight

and then at 1100C for 6 hours. The sample was calcined at 480oC in a muffle

furnace for 6 hours. The synthesized product will be in the sodium form of ZSM

5.

3.2 CHARECTERISATION TECHNIQUES

The prepared sample, commercial sample and the doped samples were

analyzed using the mentioned techniques and the results are included.

Methods for characterisation

A brief discussion of each method of characterization adopted along with

its experimental aspects is presented in the following sections. Before each

characterization, the samples were activated at 350 oC for 1 hour.

3.2.1. X- ray diffraction studies (XRD)

X-ray diffraction is one of the most important tools in solid state

chemistry since it is a powerful and readily available method for the

identification and characterization of crystalline solid phases in heterogeneous

catalysis. It can provide information about specific component in a system,

purity of substance, transition to different phases etc.

The principle of XRD is based on the interaction of X-rays with the

periodic structure of a polycrystalline material, which acts as a diffraction

grating. A fixed wavelength is chosen for the incident radiation and the


31 | P a g e

diffraction patterns obtained by observing the intensity of the scattered radiation

as a function of scattering angle 2.

The relationship among the wavelength of X-ray beam, the angle of diffraction

and the inter planar distance or d-spacing d, is given by Bragg’s equation [5],

n w = 2d sinq

Where,

n - Order of diffraction

q - Bragg angle

d - Inter planar spacing

w - Wavelength of x-rays

This relation demonstrates that interference effects are observable only

when radiation interacts with physical dimensions that are approximately the

same size as the wavelength of the radiation. Since thedistances between atoms

or ions are of the order of 1Å, diffraction methods require radiation in the X-ray

region of the electromagnetic spectrum, or beams of electrons or neutrons with

similar wavelength. So, through X-ray spectra one can identify and analyse any

crystalline matter. The degree of crystallinity or order will decide the quality of

the obtained result. In order to do this, a diffractometer is needed. Basically, an

X-ray diffractometer consists of X-ray generator, sample holder and an X-ray

detector, such as photographic film or a movable proportional counter. The

most usually employed instrument to generate X-rays is X-ray tubes, which

generate X-rays by bombarding a metal target with high energy (10-100 keV)

electrons which knock out core electrons. Thus, an electron in an outer shell

fills the hole in the inner shell and emits an X-ray photon. Two common

targets are Mo and Cu, which have strong Kα X-ray emissions at 0.71073 and

1.5418 Å, respectively. Apart from the main line, other accompanying lines


32 | P a g e

appear which have to be eliminated in order to facilitate the interpretation of the

spectra. These are partially suppressed by using crystal monochromator.

Perhaps the most routine use of diffraction data is for phase identification [6].

Each crystalline powder gives a unique diffraction diagram, which is the basis

for a qualitative analysis by X-ray diffraction.

The X-ray diffraction pattern of a crystalline phase is a characteristic

fingerprint, which enables the determination of phase purity and of the degree

of crystallinity. Identification is practically always accompanied by the

systematic comparison of the obtained spectrum with a standard one (a

pattern), taken from any X-ray powder data file catalogues, published by the

American Society for Testing Materials (JCPDS). Structural details of porous

materials on a scale covering from approximately 1 to 100 nm maybe

determined from measurements of the small angle scattering (SAS) of both X-

rays (SAXS) and neutrons (SANS). For mesoporous materials reflexes are

observed in X-ray powder patterns at low 2θ angles (0.5 < 2 θ < 10º). These

reflexes are due to the long-range order induced by the very regular

arrangement of the pores. Because d-spacings are rather big for the mesopores,

the reflexes appear at low angles.Unit cell parameter (ao) of cubic lattice can be

calculated from,

a0 = d (h2+ k2+l2)1/2.

The unit cell dimension determined by XRD is also used to calculate the

frame wall thickness (FWT) of the channels of the mesoporous materials.

A rough estimate of crystallite size can be obtained from the line broadening

using the Scherrer’s equation [7]

d = 0.9l /bcos

Where

b : Full Width half maximum (FWHM) of the strongest peak

d : Inter planar spacing


33 | P a g e

2q : Scattering angle

Powder XRD of the prepared samples were taken on a RigakuXpert PRO

MPD model with Ni filtered Cu Kα radiation (λ-1.5406 Å) within the 2θ range

0-10º at a speed of 1º/min. The crystalline phases were identified by comparison

with standard JCPDS (Joint Committee on Powder Diffraction Standards) data

file[7]

.

3.2.2. BET Surface area and pore volume measurements

Surface area determination is an important factor in predicting the

catalyst performance. Of the several techniques to estimate the surface area and

pore volume of the porous materials, BET method is the widely adopted

procedure and this method is based on the extension of the Langmuir theory to

multilayer adsorption. This method was established by Brunauer, Emmet and

Teller [8]. The model, on which it is based, assumes that the heat of adsorption

on the bare surface is different from the heats of adsorption of all successive

layers.The BET equation extends the Langmuir isotherm to multilayer

adsorption,

The general form of BET equation can be written as

P/ V (P0-P) = 1/CVmono + C-1/CVmono (P/P0) (2.1)

Where

P : Adsorption equilibrium pressure

P0 Saturated vapor pressure of the adsorbate

V Volume occupied by the molecules adsorbed at equilibrium pressure

Vm: Volume of the adsorbate required for monolayer coverage

C Constant related to the heat of adsorption

The BET plot is linear as long as only multilayer adsorption occurs. Plot

of P/V (P0-P) against P/P0 is a straight line with slope C-1/CVm and intercept


34 | P a g e

1/CVm. From the slope and intercept Vm can be calculated and the specific

surface area of the sample can be calculated using the relation,

A = Vm No Am / W x 22.414 (2.2)

Where

No : Avogadro number

Am : Molecular cross sectional area of the adsorbate (0.162nm2 for N2)

W : Weight of the catalyst sample

In BET method, adsorption of nitrogen is carried out at liquid nitrogen

temperature. Previously activated samples were degassed at 200°C under N2 for

2hrs and then brought to –196°C using liquid N2 for adsorbing N2 gas at

various pressures. The pore volume is measured by the uptake of nitrogen at a

relative pressure of 0.9. When data points in the pressure range of capillary

condensation are included in the BET analysis, the plot is not linear. The

obtained specific surface areas are too large. To avoid that, data points in the

relative pressure range of 0.02 < p/p0< 0.2 were used in this work.

In the t-plot method the measured adsorbed volumes are plotted against the

statistical layer thickness‘t’ [9]. The t-plot allows the examination of three

properties of an adsorbent (a) to detect the onset of capillary

condensation,denoted by deviation from linearity in the higher regions of the

plot; (b) to detect the micro porosity from an estimate of the amount of micro

pores, from the intercept of the extrapolated plot on the ordinate, (c) to compute

the Vm from the multi-layer region of the isotherm. This method of isotherm

data analysis was introduced by de Boer. The statistical thickness is specific for

the combination of an adsorptive capacity, the temperature, and the surface of a

solid material. The specific pore volume is calculated from the intercept of the

straight line that is drawn through the second linearregion in the t plot. From the

slope of this line a value for the external surface area could be calculated.


35 | P a g e

Pore diameter distributions were calculated by the BJH method developed by

Barret, Joyner and Halenda [9]. In this approach the filled pores are taken as a

starting point. The emptying of the filled pores with decreasing relative pressure

is incrementally evaluated to obtain a pore diameter distribution. For each

increment the pore diameter of pores emptied is calculated according to the

Kelvin equation (equation 2.3).

P/P0 =exp(- 2ƴv1/ rkRT) (2.3)

In Kelvin equation, ( P/P0) is the relative vapour pressure over a curved

surface, γ is the surface tension, Vl is the molar volume of the liquid, and rkis

the radius of curvature expresses mathematically that adsorption on a curved

surface is more favourable than on a flat surface. According to equation (2.3),

the vapour pressure over a concave surface is lower than over a flat surface.This

causes the filling of the mesopores at relative pressures, which are characteristic

for the pore diameter. This process is often called capillary condensation

because the environment of the adsorbate in filled mesopores is comparable to a

liquid state environment. Since the assumptions of Kelvin equation (2.3) are not

completely fulfilled in small mesopores, the real pore diameter may vary a little

from the calculated value. But in a relative sense the BJH distributions are

correct.

Nitrogen adsorption measurements were performed at liquid nitrogen

temperature with a MicromeriticsTristar 3000 surface area and porosity

analyzer. Prior to the measurements the samples were degassed for 1hour at

90ºC followed by 200ºC overnight.

3.2.3. FT-IR Spectroscopy

Infrared spectroscopy is a very useful technique for characterization of

materials, providing information about the structure of molecules [10].

IR spectrum of a compound is the superposition of absorption bands of specific

functional groups. The advantages of infrared spectroscopy include wide


36 | P a g e

applicability, non-destructiveness, measurement under ambient atmosphere and

the capability of providing detailed structural information. Besides these

intrinsic advantages the more recent infrared spectroscopy by Fourier transform

(FT-IR) has additional merits such as higher sensitivity, higher precision

(improved frequency resolution and reproducibility), quickness of measurement

and extensive data processing capability. IR spectra originate in transitions

between two vibrational levels of a molecule in the electronic ground state and

are usually observed as absorption spectra in the infrared region. For a molecule

to present infrared absorption bands it is needed that it has a permanent dipole

moment. When a molecule with at least one permanent dipole vibrates, this

permanent dipole also vibrates and can interact with the oscillating electric field

of incident infrared.Thus, if the vibrational frequency of the molecule, as

determined by the force constant and reduced mass, equals the frequency of the

electromagnetic radiation, then adsorption can take place. As the frequency of

the electric field of the infrared radiation approaches the frequency of the

oscillating bond dipole and the two oscillate at the same frequency and phase,

the chemical bond can absorb the infrared photon and increase its vibrational

quantum number or increase its vibrational state to a higher level. As an

approximation, larger the strength of the bond higher will be the frequency of

the fundamental vibration. In the same way, the higher the masses of the atoms

attached to the bond, the lower will be the wavenumber of the fundamental

vibration. As a general guide, the greater the number of groups of a particular

type, more polar the bond, the more intense the band. The infrared spectrum can

be divided into two regions, one called the functional group region and the other

the fingerprint region. The functional groupregion is generally considered to

range from 4000 to 1500 cm-1 and all frequencies below 1500 cm-1 are

considered characteristic of the fingerprint region. The fingerprint region

involves molecular vibrations, usually bending motions that are characteristic of


37 | P a g e

the entire molecule or large fragments of the molecule and these are used for

identification. The functional group region tends to include motions, generally

stretching vibrations, which are more localized and characteristic of the typical

functional groups, found in organic molecules. While these bands are not very

useful in confirming identity, they doprovide some very useful information

about the nature of the components that make up the molecule. FT-IR

spectroscopy is one of the most widely used analytical techniques used for

material analysis. This characterization technique has a decisive role in

identifying the surface species of supported ceria catalysts. Dispersion of metal

species and their structure, support-metal interaction, metal-metal interaction,

surface acidity of catalysts, bulk catalyst structure etc. are some of the valuable

informations that can be attained from FT-IR spectroscopy. The intensities of

FT-IR absorption bands depend on the effects induced by the acid-base

interactions in the spectral features of the absorbed probe molecules. FT-IR

spectra of the prepared samples were measured by the KBrpellet procedure over

the range of 4000-500 cm-1 region using JASCO FTIR spectrometer. The entire

frequency range of the electromagnetic waves transmitted through the sample

was recorded simultaneously and the output was fed to a computer, which

reinforces the spectrum using Fourier transform.

3.2.4 Scanning Electron Microscopy (SEM)

The scanning electron microscope (SEM) is a type of electron microscope

capable of producing high-resolution images of a sample surface by analyzing

electrons emitted from a specimen. Scanning ElectronMicroscopy allows the

imaging of the topography of a solid surface by using back scattered or

secondary electrons with good resolution of about 5nm.In this technique, a fine

probe of electrons is scanned over the sample surface using deflection coils. The

interaction between the primary beam and specimen produces various signals,


38 | P a g e

which are detected, amplified and displayed on a cathode ray tube screened

synchronously with the beam. They can also be conveniently deflected and

focused by electronic or magnetic field so that magnified real-space images can

be formed. This makes the technique suitable for producing very impressive, in

focus images from a highly irregular structure, typical of catalyst specimens.

This technique is of great interest in catalysis particularly because of its high

spatial resolution [11]. In SEM analysis finely powdered sample was applied on

to a double sided carbon tape placed on a metal stub. The stub was then inverted

in such a manner that the free side of the carbon tapes gently picked up a small

amount of the sample, thereby creating a thin coating. It was then sputtered

witha thin layer of gold to obtain better contrast and provide improved cohesion

[12]. During SEM inspection, a beam of electrons is focused on a spot volume

of the specimen, resulting in the transfer of energy to the spot. These

bombarding electrons, also referred to as primary electrons, dislodge electrons

from the specimen itself. The dislodged electrons, also known as secondary

electrons, are attracted and collected by a positively biased grid or detector, and

then translated into a signal. To produce the SEM image, the electron beam is

swept across the area being inspected, producing many such signals. These

signals are then amplified, analysed, and translated into images of the

topography being inspected. Finally, the image is shown on a cathode ray tube.

SEM analysis of the samples was done using JEOL JSM-840 A (Oxford make)

model 16211 scanning electron microscope analyzer with a resolution of 13eV.

The sample was dusted on alumina and coated with a thin film of gold to

prevent surfacecharging and to protect the material from thermal damage by

electron beam. A uniform film thickness of about 0.1 mm was maintained for

all samples.


39 | P a g e

3.2.5 Thermo gravimetric analysis (TGA)

Thermo gravimetry (TG) in which the catalyst sample is subjected to a

controlled heating to higher temperatures at a specified heating rate is a well-

established technique in heterogeneous catalysis. It finds widest applications in

the determination of drying range, calcinations temperature,phase composition,

percentage weight loss and stability limits of the catalyst. Thermo gravimetric

analysis (TGA) is an analytical technique used to determine thermal stability of

a solid and its fraction of volatile components by monitoring the weight change

that occurs as the specimen is heated. The measurement is normally carried out

in air or in an inert atmosphere, such as Helium or Argon, and the weight is

recorded as a function of increasing temperature. As many weight loss curves

look similar, the weight loss curve may require transformation before results

may be interpreted. A derivative weight loss curve (DTG) can be used to tell the

point at which weight loss is most apparent. A sample of material (ranging from

1 to 100 mg) is placed on an arm of a recording microbalance, also called

thermo balance where that arm and the sample are placed in a furnace. The

furnace temperature is controlled in a pre-programmed temperature/time profile

(most commonly), or in the rate controlled mode, where the pre-programmed

value of the weight changes imposes the temperature change in the way

necessary to achieve andmaintain the desired weight-change rate. In addition to

weight changes, some instruments also record the temperature difference

between the specimen and one or more reference pans: (Differential thermal

analysis or DTA) or the heat flow into the specimen pan compared to that of the

reference pan (differential scanning calorimetry or DSC). The latter can be used

to monitor the energy released or absorbed via chemical reactions during the

heating process. Any transition that the sample undergoes results in liberation or

absorption of energy by the sample with a corresponding deviation of its

temperature from that of the reference. A plot of the differential temperature


40 | P a g e

(ΔT) versus the programmed temperature T indicates the transition temperatures

and whether the transition is exothermic or endothermic. When an endothermic

change occurs, the sample temperature lags behind the reference temperature

because of the heat in the sample.Exothermic behaviour is associated with the

decrease in enthalpy of a phase or a chemical system. DTA and thermo

gravimetric analysesare often run simultaneously on a single sample [13].

In TG, the weight loss of a sample is being continuously recorded over a period

of time under controlled heating rate. Changes in weight are due to the rupture

and /or formation of various physical and chemical bonds at elevated

temperatures, which lead to the evolution of volatile products or the formation

of heavier reaction products. From the thermo gram, where we plot weight

against temperature, information about dehydration, decomposition and various

forms or products at various temperatures can be obtained. The first derivative

of the thermogram (DTG) gives a better understanding of the weight loss and

can also be used to determine the thermal stability of the samples.

Perkin Elmer TG analyzer instrument was used for carrying out thermo

gravimetric studies. About 20mg of the sample was used at a heating rate of 20

ºC per min in nitrogen atmosphere. The TG data were computer processed to

get thermogram. Any decomposition of the sample is indicated by a dip in the

curve. These dips correspond to the weight loss due to decomposition and hence

provide an idea about the species lost during the heating step.

3.3.The doping process of the ZSM 5 by metal salts

Chemicals

1. ZSM 5 catalyst

2. Cobalt nitrate


41 | P a g e

3. Cadmium nitrate

4. Ferric chloride

5. Manganese nitrate

6. Distilled water

Equipment

1. Magnetic stirrer – heater

2. Muffle furnace

3. Hot air oven

4. Silica crucibles

Procedure

The dried and well powdered zsm 5 samples are used for this process.

Doping is done on samples of weight : 0.5 g. The weight of the metal salts that

is required to contribute : 5 %,10% and 15% by weight of the mixture is found

out using calculation. Using each metal salt, three mixtures with different mass

percentages (5%,10%,15%) are made. 0.5 g of the ZSM 5 is accurately weighed

out and mixed with minimum amount of distilled water (5 ml). The metal salt is

weighed out accurately according to the calculations, as required for preparing

the mixture with expected mass percentage of the metal. The metal is added to

the mixture of ZSM-5 in minimum water. The mixture in a beaker is stirred at

50 oC on a magnetic stirrer for one hour. The beaker is covered while the

stirring is in progress. The beaker is set aside for sometime after one hour of

stirring. Then it is put in the hot air over for an hour to evaporate the water

content and extract the dried sample. The dried sample is collected and heated

in the muffle furnace for 2 hours at 200oC, in order to yield a thoroughly dried

doped sample which is in very finely powdered form. This sample is analyzed


42 | P a g e

by the SEM analysis and XRD analysis, after noting the weight and physical

appearance.

Table : Dopping process

Sample Co Cd Fe

ZSM 5 (0.5 g)

5% 5% 5%

10% 10% 10%

15% 15% 15%

3.4. CHARECTERISATION TECHNIQUES

The prepared sample, commercial sample and the doped samples were

analyzed using the mentioned techniques and the results are included.

3.4.1. SEM (SCANNING ELECTRON MICROSCOPY)

The SEM imaging is utilized for analyzing the particle characteristics and

the size of the crystals obtained. The comparison is also done considering the

images generated by SEM analysis of the commercial ZSM 5, and the prepared

sample of ZSM 5. The technique is employed in the analysis and imaging of

the samples of ZSM 5 obtained by dopping with different transition metals as

given in the table.

3.4.2.X-RAY DIFFRACTION (XRD)

The x ray diffraction technique is used here for the analysis of the crystal

structure of the various samples of ZSM 5. The method is employed for ZSM 5

samples which are doped and pure. The comparison of characteristic peaks,

intensity and peak position are done among the various doped samples and the

pure samples prepared and obtained from commercial source. The results are


43 | P a g e

utilized to assess the purity and Crystallinity of the resultant samples compared

to the original ones after doping.

3.4.3.THERMOGRAVIMETRIC ANALYSIS

The TGA contributes highly to the studies on thermal stability and

temperature induced changes in the samples. The second order phase changes

are well indicated in the results.

The pure sample from commercial source is studied by the TGA in comparison

to the ZSM 5 prepared in the laboratory.


44 | P a g e

CHAPTER 4

THE RESULTS AND DISCUSSION

The Zeolite Socony Mobil 5(ZSM 5) was prepared by the gel seeding

technique in the laboratory. A silica based seeding gel of NaOH and TPABr is

made and used to induce the formation of ZSM 5 in a gel medium containing

NaOH and NaAlO2 .The gel was transferred into an autoclave and heated at

200 oC for 16 hours. Obtained product was strongly heated up to 300 oc in a

muffle furnace to get finer powder. The obtained white powder sample of ZSM

5 was comparable with the commercial sample in appearance.

After the successful preparation of the ZSM 5 samples, the doping of the

same with various transition metals was done. It was done by, continuous

stirring (with a magnetic stirrer) of the particular amount ie. 0.5 g of the ZSM 5

with various amounts of compounds of, metals such as: Co, Fe, Cd, Mn.

Doping was done on the 0.5 g samples of ZSM 5 by metals to 5 %, 10% and

15% by mass. The resultant samples after doping were analyzed by the

mentioned techniques of characterization after heating for 2 hours at about

200oc in muffle furnace to get good quality powder sample.


45 | P a g e

The data regarding the doping of ZSM 5

CHARECTERISATION

The described methods are used in characterizing the pure commercial,

prepared and doped samples of ZSM 5.

1. Thermo gravimetric analysis (TGA)

The TGA Diagrams obtained by analysis of the commercial and prepared

samples of ZSM 5 zeolite are compared.

1. Prepared sample


Metal Mass percentage of

metal in mixture

Weight of

zeolite(g)

Weight of

metal salt(g)

Cobalt (Co)

5%

10%

15%

0.5

0.5

0.5

0.0469

0.0938

0.1408

Cadmium(Cd)

5%

10%

15%

0.5

0.5

0.5

0.0418

0.0836

0.1254

Iron (Fe)

5%

10%

15%

0.5

0.5

0.5

0.0728

0.1456

0.2184

Manganese(Mn)

5%

10%

15%

0.5

0.5

0.5

0.08143

0.1628

0.2422

46 | P a g e

2. Pure commercial Sample

3.Doped sample (Fe 15 %)


47 | P a g e

The Thermo gravimetric analysis performed on the samples: pure

prepared, pure commercial and one sample doped with Iron( Fe 15% by wt). the

thermal stability of the materials are quite identical when the results of

commercial and prepared samples( pure) are compared. The prepared sample

shows a primary decrease in mass with temperature at 100O c, then the material

is seen stable in a wide rangwe of temperature ie, 100o C to 450 o C. After this

temperature, the sample is decomposed.

The commercial sample shows a similar TGA spectrum, At about 100o C

there occurs a decrease in mass with temperature, but not as steep as in the case

of prepared sample. This mass change most probably indicates the loss of

water , and this difference in steepness of TGA is explained by the presence of

lower amount of moisture in the commercial sample , compared to the

laboratory prepared sample. The Stability is not much altered here, till 450 o C

the sample is much stable, and after it, the decomposition occurs.

The TGA of a sample which is doped with Fe was also analyzed, the

results show much lower change in mass in lower temperatures, like 100o C

unlike the pure samples. This shows that the process of doping has eliminated a


48 | P a g e

considerable amount of moisture from the crystal structure so that the process of

evaporation of water is not seen in the TGA. The thermal stability of the

material is a little improved by the doping with Fe metal as shown by TGA. The

decomposition temperature is about 500 oC as shown by TGA, and is much

greater than that of pure ZSM 5. The Fe Doped sample are much more suitable

for higher temperature catalysis as required by some reactions. We can have the

assumption that the doping increases the thermal stability of ZSM 5 to an extent

making it a more applicable catalyst in high temperature reactions

4.2 Surface area and pore volume measurements

The mesoporous zeolites showed a high (BET) surface area of 164

m2g−1. In the literature, most of the publications report ZSM with specific

surface areas below 100 m2g−1 and only in a few cases was values around 200

m2g−1 were obtained [2].

Table 4.2 Surface area and pore volume of prepared ZSM - 5 and modified

systems

Catalyst SBET(m2 g-1)Pore volume

(cm3 g-1)

Pore

diameter(nm)

ZSM 152 0.26 3.9

ZSM – 5 Fe 158 0.29 4.1

ZSM-10 Fe 164 0.3 4.5

ZSM -15 Fe 212 0.37 5.1

* Pore volume measured at p/p0 of 0.997

There is a surface enhancement for ceria due to the metal dopping. The

surface areas increase with metal loading. It is due to the large amount of

deposited metal oxides.


49 | P a g e

Nitrogen adsorption isotherm

Fig. 4.1 shows adsorption isotherms of some representative samples of

ZSM modified with different % of Fe which resemble Type IV of IUPAC

classification [3] with a hysteresis loop which is characteristic of mesoporous

solids. This hysteresis loop is due to the capillary condensation, in the

mesopores. Adsorption at lower relative pressures (p/p0) is due to the formation

of monolayer of nitrogen molecules on the walls of mesoporous material

Fig. 4.1. Adsorption isotherms of ZSM and modified samples


50 | P a g e

4.3. Pore size distribution

Fig. 4.2. shows the pore size distribution of mesoporous ZSM 5. The

narrow pore size distribution shows uniformity of the pores.


51 | P a g e

Fig. 4.3.Pore size distribution of mesoporous zeolite

4.4 XRD (X-Ray Diffraction)

1. Pure ZSM 5 sample(commercial)

All the three metal doped samples(15%) were analyzed by X Ray

diffraction and the diffraction spectra are included. The standard XRD of pure

ZSM 5 consists of very sharp peaks all over the range of angles, in which the

spectrum is taken. This proves the high degree of crystalline nature of the

product ZSM 5. Clear and sharp peak with high intensity at about 2theta range

20 -30 is characteristic of the ZSM 5(pure).In the XRD spectra obtained from

the analysis of the doped samples, the clear sharp peaks are again seen similar


52 | P a g e

to the spectrum of pure ZSM 5. This indicates the high form of Crystallinity is

quite intact in ZSM 5 after the doping with transition metals. The metals are

well accommodated by probable replacement of certain existing ions with very

little alteration in the crystal structure of ZSM 5.

The XRD Spectrum of each doped sample contains, peaks clearly

corresponding to the metals present in them. The cobalt doped sample shows a

pair of peaks with same intensity in the 2 theta angle range of 45-50. The Iron is

characterized by the presence of clear peaks in the 2 theta range of 45-50, and

an intense peak at 2 theta 50.

Cadmium doped samples contains the peaks at 40-50 and 50-60 2 theta

range. These peaks indicate the presence of the corresponding metals without

the loss of the inherent properties of ZSM 5 as a Zeolite.

2.Co doped ZSM 5 (15%) XRD I

Operations: Smooth 0.150 | Background 1.202,1.000 | ImportFile: SAIFXR150713A-01 (XRD I).raw - Step: 0.020 ° - Step time: 32.8 s - WL1: 1.5406 - kA2 Ratio: 0.5 - Generator kV: 40 kV - Generator mA: 35 mA - Type: 2Th/Th locked

Lin

(Cou

nts)

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

2-Theta - Scale

3 10 20 30 40 50 60 70 80


53 | P a g e

3.Cd doped ZSM 5(15%)XRD II

Operations: Smooth 0.150 | Background 1.202,1.000 | ImportFile: SAIFXR150713A-02 (XRD II).raw - Step: 0.020 ° - Step time: 32.8 s - WL1: 1.5406 - kA2 Ratio: 0.5 - Generator kV: 40 kV - Generator mA: 35 mA - Type: 2Th/Th locked

Lin

(Cou

nts)

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

1700

1800

2-Theta - Scale

3 10 20 30 40 50 60 70 80

4.Fe Doped ZSM 5 (15%)XRD III

Operations: Smooth 0.150 | Background 1.202,1.000 | ImportFile: SAIFXR150713A-03 (XRD III).raw - Step: 0.020 ° - Step time: 32.8 s - WL1: 1.5406 - kA2 Ratio: 0.5 - Generator kV: 40 kV - Generator mA: 35 mA - Type: 2Th/Th locked

Lin

(Cou

nts)

0

100

200

300

400

500

600

700

800

900

1000

2-Theta - Scale

3 10 20 30 40 50 60 70 80


54 | P a g e

4.5 SEM

1.Co doped

1. 5%

2. 10%


55 | P a g e

3. 15%

Cd Doped

1. 5%


56 | P a g e

2. 10%

3. 15%


57 | P a g e

Fe Doped

1. 5 %

2. 10%


58 | P a g e

3. 15%

The SEM imaging of all the samples was done and the images are

studied. The SEM images invariantly have the highly homogeneous distribution

of crystals of considerable size and structure with order. The crystalline nature

of pure ZSM 5 is very well retained in the samples which are doped by three

different transition metals in three different mass percentages. No aggregation

of crystals is seen anywhere in the images studied, proving that the distribution

of the certain metals we used are homogeneously occupied in the crystal lattices

without any change in the micro porous and highly crystalline structure of ZSM

-5


59 | P a g e

Chapter 6

SUMMARY OF FINDINGS

Zeolite ZSM – 5 was prepared in laboratory conditions by gel seedling

technique successfully.The obtained product by the employed “gel seeding”

quite resembles the commercially available ZSM 5 in physical appearance. The

prepared ZSM 5 was dopped with different transition metals in different weight

ratios. After the doping is done as in the method described, the color of Co

doped and Fe doped samples changed to grey and brown respectively. The color

of the Cd and Zn doped samples was intact after doping.

The Thermo gravimetric analysis performed on the samples: pure

prepared, pure commercial and one sample doped with Iron( Fe 15% by wt).

The thermal stability of the materials are quite identical when the results of

commercial and prepared samples( pure) are compared. The prepared sample

shows a primary decrease in mass with temperature at 100O c, then the material

is seen stable in a wide range of temperature ie, 100o C to 450 o C. After this

temperature, the sample is decomposed.

The commercial sample shows a similar TGA spectrum, At about 100o C

there occurs a decrease in mass with temperature, but not as steep as in the case

of prepared sample. This mass change most probably indicates the loss of

water , and this difference in steepness of TGA is explained by the presence of

lower amount of moisture in the commercial sample , compared to the

laboratory prepared sample. The Stability is not much altered here, till 450 o C

the sample is much stable, and after it, the decomposition occurs.

The TGA of a sample which is doped with Fe was also analyzed, the

results show much lower change in mass in lower temperatures, like 100o C

unlike the pure samples. This shows that the process of doping has eliminated a

considerable amount of moisture from the crystal structure so that the process of


60 | P a g e

evaporation of water is not seen in the TGA. The thermal stability of the

material is a little improved by the doping with Fe metal as shown by TGA. The

decomposition temperature is about 500 oC as shown by TGA, and is much

greater than that of pure ZSM 5. The Fe Doped sample are much more suitable

for higher temperature catalysis as required by some reactions. We can have the

assumption that the doping increases the thermal stability of ZSM 5 to an extent

making it a more applicable catalyst in high temperature reactions.

All the metal doped samples(15%) were analyzed by X Ray

diffraction and the diffraction spectra are included. The standard XRD of pure

ZSM 5 consists of very sharp peaks all over the range of angles, in which the

spectrum is taken. This proves the high degree of crystalline nature of the

product ZSM 5. Clear and sharp peak with high intensity at about 2theta range

20 -30 is characteristic of the ZSM 5(pure).In the XRD spectra obtained from

the analysis of the doped samples, the clear sharp peaks are again seen similar

to the spectrum of pure ZSM 5. This indicates the high form of Crystallinity is

quite intact in ZSM 5 after the doping with transition metals. The metals are

well accommodated by probable replacement of certain existing ions with very

little alteration in the crystal structure of ZSM 5.The XRD Spectrum of each

doped sample contains, peaks clearly corresponding to the metals present in

them.The cobalt doped sample shows a pair of peaks with same intensity in the

2 theta angle range of 45-50.The Iron is characterized by the presence of clear

peaks in the 2 theta range of 45-50, and an intense peak at 2 theta 50.Cadmium

doped samples contains the peaks at 40-50 and 50-60 2 theta range.These peaks

indicate the presence of the corresponding metals without the loss of the

inherent properties of ZSM 5 as a Zeolite.

The SEM imaging of all the samples was done and the images are

studied. The SEM images invariantly have the highly homogeneous distribution

of crystals of considerable size and structure with order. The crystalline nature


61 | P a g e

of pure ZSM 5 is very well retained in the samples which are doped by three

different transition metals in three different mass percentages. No aggregation

of crystals is seen anywhere in the images studied, proving that the distribution

of the certain metals we used are homogeneously occupied in the crystal lattices

without any change in the micro porous and highly crystalline structure of ZSM

5.


62 | P a g e

REFERENCES

[1] Barrer, R.M. Hydrothermal Chemistry of Zeolites, Academic

Press, London, UK, 1982; pp 360.

[2] Breck, D. W. Zeolite Molecular Sieves: Structure, Chemistry and

Use; John Wiley and Sons, London, UK, 1974; pp 4.

[3] Bekkum, V. H.; Flanigen, E.M.; Jacobs, P.A.; Jansen, J.C.

Introduction to Zeolite Science and Practice; 2nd. Revised Edn., Elsevier,

Amsterdam, 1991; pp 13-34.

[4] Meier, W. M.; Olson, D. H., Atlas of Zeolites Structure Types; 2nd

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[5] L. B. McCUSKER, F. LIEBAU, D, G. ENGELHARDT,

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microporous and mesoporous materials with inorganic hosts, Pure Appl. Chem.,

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[6]Terres, E., 1996. Influence of the Synthesis Parameters on Textural

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Mesoporous Materials, 431, p.111-116

[7] Boukadir, D., Bettahar, N., Derriche, Z., 2002. Synthesis of

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[8] Ríos, C.A., Williams, C.D., Fullen, M.A., 2009. Nucleation and


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growth history of zeolite LTA synthesized from kaolinite by two different

methods, Applied Clay Science, 42, p.446-454

[9] D. Georgiev, B. Bogdanov, Y. Hristov, I. Markovska, Synthesis of

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[10] D. Georgiev, B.Bogdanov, Y. Hristov, I. Markovska, I.Petrov,

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[11] Georgiev D., B. Bogdanov, K. Angelova, I. Markovska, Y.

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[12] D. Georgiev, B. Bogdanov, Y. Hristov, I. Markovska, K.

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[13] M. Alkan, C. Hopa, Z. Yimaz, H. Guler, The effect of alkali

concentration and solid/liquid ratio on the hydrothermal synthesis of zeolite

NaA from natural kaolinite, Microporous and Mesoporous Materials, 86 (2005)

176–184.

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259–265.

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stpauls.ac.instpauls.ac.in/.../201612090401586619-20.docx · Web viewThis work concerns with the laboratory production of an industrially important catalyst material namely: ZSM 5