1

CHAPTER 1

INTRODUCTION

1.1 AUTOMOBILE POLLUTION

Pollution is defined as the introduction of chemicals, particulate matter, or

biological materials to the atmosphere that cause harm or discomfort to the living

organisms.

Due to the advancement in science and technology there is an drastic

improvement in automobile production which results in more amount of harmful gas is

let into the atmosphere. Thus these gases react with the atmosphere and pollute it.

Generally, automobile plays an important role in contribution to the pollution.

Various exhaust product and its characteristics were listed below.

Table 1.1 Pollutants and its characteristics

Pollutant

Characteristics Nitrogen oxides It is an reddish-brown toxic gas emitted

from high temperature combustion Carbon monoxide Colourless, odorless, non-irritating but

very poisonous gas. Particulate matter These are tiny particles of solid or liquid

suspended in a gas which cause health hazards such as heart disease, altered lung function

Sulfur oxides Generally SO2 reacts with atmosphere to form H2SO4, and thus acid rain

Thus it is really necessary to incorporate a device which reduces the exhaust

pollution.

2

1.2 NANOTECHNOLOGY

Nanotechnology refers to a field of applied science and technology whose

theme is the control of matter on the atomic and molecular scale, generally 100

nanometers or smaller, and the fabrication of devices or materials that lie within that size

range.

As far as nanotechnology is concern, Nanoparticles may be defined as those

particles have dimensions in the range 1 to 100 nm. Nanoparticles possess unique hybrid

properties of neither the molecular nor the bulk solid-state limits. Materials reduced to the

nanoscale can suddenly show very different properties compared to what they exhibit on

a macroscale, enabling unique applications. For instance copper nanoparticles smaller

than 50 nm are considered super hard materials that do not exhibit the same malleability

and ductility such a huge improvement in properties is observed in case of nano

materials. Generally nanoparticles are classified as nanotubes, nanowire, nano crystals

etc. Table 1.2 summarizes the main categories of nanoparticle according to their

morphologies, material from which they may be composed and the type of application in

which they may be used.

Table 1.2 Nanoparticles-Categories and Applications

Nanostructure Example Material or Application

Nanotubes Carbon, (fullerenes)

Nanowires Metals, semiconductors, oxides

Nanocrystals, quantum dots Insulators, semiconductors, metals,

1.3 NANOMATERIALS

Nano materials widely used are metallic nanoparticle, germanium, ceramic

and aluminium oxide nanowires, carbon, silicon and germanium nanotubes, zinc oxide

nanocrystals, gold nanowafers and copper oxide nanotubes which can be synthesized by

3

various processes such as laser ablation, condensation from vapour, thermal

decomposition etc.

1.4 CATALYTIC CONVERTER

A catalytic converter is most effective after treatment process used to reduce

the toxicity of emissions from an internal combustion engine. A catalytic converter is a

device that converts the harmful toxic combustion products and its by-products into less-

toxic substances. Catalyst is not consumed during the reaction hence it is non-degradable.

Catalytic converter is generally used for reduction of HC, CO and NOx. It consists of

steel container of honeycomb structure through which the gas flows. It consists of small

embedded particles of catalytic materials such as platinum, palladium, rhodium that

promotes oxidation reaction in exhaust gas. Catalytic converter uses alumina as base

material because it can withstand high temperature, low thermal expansion etc.

Reaction that take place inside the catalytic converter as shown

2CO + O2 → 2CO2

2NOx → xO2 + N2

2CxHy + (2x+y/2)O2 → 2xCO2 + yH2O

1.5 APPLICATIONS OF CATALYTIC CONVERTER

Catalytic converter is widely used in various sectors such as

� Petrol engine emission control

� Diesel engine emission control

� Food processing industries.

� Chemical manufacturing industries

� Gas turbines

1.6 PRESENT WORK

Recent year’s catalytic converter has becoming an important device for

reducing the exhaust emission. Due to the advancement in technology there is a drastic

4

improvement in automobile production which results in more amount of pollution is fed

into the atmosphere. Thus focus should be made in the field of catalytic converter for the

reduction of exhaust emission must be done.

Thus this project deals with design and fabrication of catalytic converter by

replacing the expensive metals such as platinum, palladium etc with the nano iron oxide

powder which results in reduction of the exhaust pollution. Further the characterization of

nano iron oxide powder is made through scanning electron microscope, X-ray diffraction,

transmission electron microscope.

5

CHAPTER 2

LITERATURE SURVEY

Flytzani-Stephanopoulos et al (2008) have studied that SO2-introduction

increases stability of Ag-alumina catalysts for the selective catalytic reduction of NO

with methane. The reaction generally taken place above the temperature of 600oC at those

temperatures catalytic deactivate is more and measurable. By using Time-resolved TEM

analyses it is studied that deactivation is due to sintering of silver at that temperature

range. Thus presence of SO2 dramatically suppresses the sintering of silver. Further

structural stabilization is achieved by using SO2 thus accompanies stable catalyst activity

for reducing NO.

Shanks et al (2008) have illustrated that Potassium promoted iron oxide

catalysts are primarily used for producing styrene. In this process, a large amount of

steam is used and for economic reasons it is desirable to be able to operate at lower

steam/ethylbenzene molar ratios without creating severe short term deactivation. Thus in

this study, the stabilities of Fe2O3, K Fe2O3 (10 wt% K+), KFeO2 (30 wt% K+), and a

potassium polyferrite mixed phase (K2Fe10O16/K2Fe22O34) were investigated in different

gas phases including H2, CO2, and ethyl benzene. The effect of simultaneous steam

addition was also considered. Thermo gravimetric analysis and x-ray powder diffraction

were used to monitor sample weight variation and phase change, respectively. Fe2O3 and

K2Fe10O16/ K2Fe22O34 were stable in CO2 but not stable in H2KFeO2 was resistant to

H2but easily decomposed by CO2. K-Fe2O3 was adversely impacted by both H2and CO2

the results suggest that the reduction of the iron oxide in this system was mainly caused

by surface deposited carbon instead of H2. A transformation diagram is proposed for the

phase changes of potassium promoted iron oxide materials in the reaction-relevant gas

phase conditions

6

Koganei-shi et al (2006) have studied that anodic alumina supported silver

catalyst with a low Ag loading of about 1.68 wt.%is used to measure NOx adsorption and

NOx-temperature programmed decomposition (TPD)/temperature programmed surface-

reaction (TPSR) measurements in different gas streams (He, C3H6/He, C3H6//O2/He) for

investigating the formation, consumption and reactivity of surface adsorbed NOx species.

During NO adsorption, no noticeable uptake of NO was detected. Introducing oxygen

greatly improved adsoption of NOx species.Thus the result of TPSR indicates that the

surface nitrate species can be effectively reduced by propene when oxygen is introduces

into it. Thus selective reduction of NOx in the presence of excess oxygen is proposed to

pass through the selective reduction of the adsorbed nitrate species with the activated

propene.

Sipho C. Ndlela et al (2006) have illustrated that Potassium-promoted iron

oxide catalysts are used in large volume for the commercial ethylbenzene

dehydrogenation to styrene process. Short-term deactivation of these catalysts, which is

addressed by operating in excess steam, is thought to be caused due to reactive site loss

through coking and/or reduction. Further the relative importance of the two mechanisms

is not known. Thermo gravimetric experiments and X-ray diffraction analysis were used

to examine the reduction behavior of potassium-promoted iron oxide materials. The

reduction behavior was then compared with results from isothermal ethylbenzene

dehydrogenation reactor studies under low steam-to-ethylbenzene operation. Potassium

incorporation was found to stabilize the iron oxide against reduction apparently through

the formation of KFeO2. Chromium addition improved the reduction resistance has stated

in this paper.

Apostolescu et al (2005) has stated that new Fe2O3 based materials are

developed for the selective catalytic reduction (SCR) of NOx by NH3 in diesel exhaust.

As a result of the catalyst screening, ZrO2 is considered to be the most effective carrier

for Fe2O3. The modification of the Fe2O3ZrO2 system with tungsten leads to drastic

increase of SCR performance as well as pronounced thermal stability. These results show

that tungsten acts as bifunctional component. The highest catalytic activity is observed

7

for ZrO2 that is coated with 1.4 mol% Fe2O3 and 7.0 mol% WO3 (1.4Fe/7.0W/Zr) also

discussed in this paper.

Hizbullah et al (2004)have illustrated that with the preparation and

modification of iron oxide with different alkali metals which can be used as catalysts for

exhaust reduction. Among the prepared catalysts, Fe1.9K0.1O3 proved to be the most

promising catalyst which is suitable for the simultaneous removal of NOx and soot from

diesel engines exhaust. The study has shown that long-time treatment leads to a decline in

the activity, and remains constant after at least 20 sample experiments. This shows that

the catalysts can be used for particular long time. On the other hand long-time treatment

causes a significant enhancement of N2 selectivity, and the formation of by-product N2O

was not observed. This alteration of catalytic performance is likely due to addition of the

potassium as the promoter. This study confirms that Fe1.9K0.1O3 is a suitable catalyst for

simultaneous removal of soot and NOx between 350 and 480 ◦C.

Jan Kaspar et al (2003) have illustrated technology for importance of exhaust

emissions by analyzing the current understanding of three way catalytic converter, the

specific role of the various components, the achievements and the limitations. The

challenges in the development of new automotive catalysts, and the future pollution

nomes are also discussed.

Guido Ketteler et al (2002) have stated the details of the surface structure and

composition of potassium promoted iron oxide model catalyst films prepared on Ru are

investigated by scanning tunneling microscopy (STM), low energy electron diffraction

(LEED), and Auger electron spectroscopy (AES). At 700 K, polycrystalline KFeO2 films

are formed.On annealing, the potassium content in KFeO2 films decreases and a mixed

phase which consists of polycrystalline KFeO2 on top of partially uncovered

K2Fe22O34forms. At 970 K, the whole film transforms to K2Fe22O34

8

Kureti et al (2002) stated that simultaneous catalytic conversion of NOx and

soot into N2 and CO2 in diesel exhaust gas. Several iron containing oxide catalysts were

partially modified by the alkali metal potassium and were used for NOx–soot reaction in

a model exhaust gas. Fe1.9K.1O3 has shown highest catalytic performance for N2

formation in the so far investigated catalysts. Further studies have shown that Fe1.9K.1O3

was deactivated due to the agglomeration of the promoter potassium. Experiments carried

out over the aged Fe1.9K.1O3 catalyst have shown that NOx–soot reaction was suppressed

at higher O2 concentration. In contrast to that, the catalytic activity was increased in

presence of NO2 and H2O also explained in this paper.

Joseph et al (2001) have stated that Potassium promoted iron oxide model

catalyst films were prepared by deposition of potassium onto epitaxial Fe2O3 at 200 K,

followed by annealing in the range 200 to 970 K. Their formation and composition were

investigated by X-ray photoelectron spectroscopy (XPS) in combination with thermal

desorption spectroscopy (TDS) Already at 300 K a solid-state reaction occurred and the

iron oxide was partly reduced. For certain potassium content, this surface develops a well

ordered phase with a superstructure. The potassium containing phases are not stable in

water atmosphere:

Keshavaraja et al (1999) have studied that Silver-alumina catalysts prepared

by a single-step co-gelation technique is used for the selective catalytic reduction of NO

with methane. This type catalyst is active over a temperature range from 450 to 650oC,

and for a relatively wide range of Ag loading (1–7 wt.%) is used. Excess O2 in is fed for

better SCR reaction. This Catalysts having high conversions efficiency of NOx by CH4.

The structural stability of Ag was studied in by using UV–VIS diffuse reflectance

spectroscopy.

9

CHAPTER 3

NANOTECHNOLOGY

3.1 INTRODUCTION

Nanotechnology refers to a field of applied science and technology whose

theme is the control of matter on the atomic and molecular scale, generally 100

nanometers or smaller, and the fabrication of devices or materials that lie within that size

range.

Nanotechnology is a highly multidisciplinary field, drawing from fields such

as applied physics, materials science, interface and colloid science, device physics,

supramolecular chemistry( which refers to the area of chemistry that focuses on the non

covalent bonding interactions of molecules), self replicating machines and robotics,

chemical engineering, mechanical engineering, biological engineering and electrical

engineering. Grouping of the sciences under the umbrella of “nanotechnology” has been

questioned on the basis that there is little actual boundary-crossing between the sciences

that operate on the nanoscale. Instrumentation is the only area of technology common to

all disciplines; on the contrary, for example pharmaceutical and semiconductor industries

do not “talk with each other”.

Examples of nanotechnology are the manufacture of polymers based on

molecular structure, and the design of computer chip layouts based on surface science.

Despite the promise of nanotechnologies such as quantum dots and nanotubes, real

commercial application have mainly used the advantages of colloidal nanoparticle in bulk

form, such as suntan lotion, protective coatings, drug delivery and stain resistant clothing.

3.2 NANO PARTICLES

Nanoparticles possess unique hybrid properties of neither the molecular nor

the bulk solid-state limits. Nanoparticles processing offers a practical way to tailor the

10

properties at the atomic or molecular level, producing novel materials with a unique size-

dependent behavior such as quantum size effect and greater micro-structural uniformity.

The advancement of technology at different levels has improved the manufacturing of

materials with improved and definite characteristics. Hence the traditional materials are

facing high competition with the advanced materials. Ceramics, composites and

polymeric materials claim to provide lighter weight, greater strength and overall better

electrical, thermal and optical properties than the conventional materials. The recent

technology focuses mainly on the size of the particles in the order of nano meters.

Nanoparticles may be defined as those particles have dimensions in the range 1 to 100

nm.

It is realized that the nano particles have high surface to volume ratio, the

basic factor that has improved the material performance in general. The volume of an

object decreases as the third power of its linear dimensions, but the surface area only

decreases as its second power. This somewhat subtle and unavoidable principle has huge

ramifications. Materials scientist are challenged to identify, build, control and test the

structures whose dimensions are in the nanometer scale and to demonstrate the potentials

of these nanostructures in scientific, industrial or medical applications while keeping in

mind their potential impact on the society. In general, the nanoparticles are larger than

individual atoms and molecules but are smaller than bulk solid. Hence they obey neither

absolute quantum chemistry nor laws of classical physics and have properties that differ

markedly from those expected.

Nanoclusters have at least one dimension between 1 and 10 nanometers and a

narrow size distribution. Nanopowders are agglomerates of ultrafine particles,

nanoparticles, or nanoclusters. Nanometer sized single crystals, or single-domain

ultrafine particles, are often referred to as nanocrystals.

Nanoparticle research is currently an area of intense scientific research, due to

a wide variety of potential applications in biomedical, optical, and electronic fields.

11

3.3 PROPERTIES OF NANOPARTICLES

The properties of materials change as their size approaches the nano scale and

as the percentage of atoms at the surface of a material becomes significant. For bulk

materials larger than one micro meter the percentage of atoms at the surface is minuscule

relative to the total number of atoms of the material. The interesting and sometimes

unexpected properties of nanoparticles are not partly due to the aspects of the surface of

the material dominating the properties in lieu of the bulk properties

Materials reduced to the nanoscale can suddenly show very different

properties compared to what they exhibit on a macroscale, enabling unique applications.

For instance, opaque substances become transparent (copper); inert materials become

catalysts (platinum); stable materials turn combustible (aluminum); solids turn into

liquids at room temperature (gold); insulators become conductors (silicon). Materials

such as gold, which is chemically inert at normal scales, can serve as a potent chemical

catalyst at nanoscales the bending of bulk copper occurs with movement of copper

atoms/clusters at about the 50 nm scale. Copper nanoparticles smaller than 50 nm are

considered super hard materials that do not exhibit the same malleability and ductility as

bulk copper.

The change in properties is not always desirable. Ferroelectric materials

smaller than 10 nm can switch their magnetization direction using room temperature

thermal energy, thus making them useless for memory storage. Suspensions of nano

particles are possible because the interaction of the particle surface with the solvent is

strong enough to overcome differences in density, which usually result in a material

either sinking or floating in a liquid. Nanoparticles often have unexpected visible

properties because they are small enough to confine their electrons and produce quantum

effects. For example gold nanoparticles appear deep red to black in solution. Much of the

fascination with nanotechnology stems from these unique quantum and surface

phenomena that matter exhibits at the nanoscale. Generally nano particles are classified

as nano tubes, nano wires, nano crystals which are discussed below.

12

3.3.1 Nanotubes

Nanotubes are a particularly novel form of nanoparticles about which there is

great interest and excitement. Carbon Nanotubes (CNT) were first discovered by Iijima

(1991), and are a new form of carbon molecule. They are similar in structure to the

spherical molecule C60 (buckminsterfullerene or bucky balls) discovered in the 1980s

but are elongated to form tubular structures 1-2 nm in diameter. They can be produced

with very large aspect ratios and can be more than 1 mm in length. In their simplest form,

nanotubes comprise a single layer of carbon atoms arranged in a cylinder. These are

known as single-wall carbon nanotubes (SWCNTs). They can also be formed as multiple

concentric tubes (multi-wall carbon nanotubes, MWNTs) having diameters significantly

greater, up to 20 nm, and length greater than 1 mm.

CNTs have great tensile strength and are considered to be 100 times stronger

than steel whilst being only one sixth of its weight thus making them potentially the

strongest, smallest fibre known. They also exhibit high conductivity, high surface area,

unique electronic properties, and potentially high molecular adsorption capacity.

Applications which are currently being investigated include; polymer composites

(conductive and structural filler), electromagnetic shielding, electron field emitter, super

capacitors, batteries, hydrogen storage and structural composites.

Synthesis methods

• Laser ablation

• Arc discharge

• Chemical Vapour Deposition (CVD)

• Plasma-enhanced CVD

• Chemical precipitation

One major focus of current research on nanotubes is on scaling-up of

production rates to kilogram quantities. Nanotubes have also been produced from other

13

materials including silicon and germanium but the development of various forms and

applications for CNTs remains the main focus of activity.

3.3.2 Nanowires

Nanowires are small conducting or semi-conducting nanoparticles with a

single crystal structure and a typical diameter of a few 10s of nanometres and a large

aspect ratio. Various metals have been used to fabricate nanowires including cobalt, gold

and copper. Silicon nanowires have also been produced.

Most approaches to the fabrication of nanowires are derived from methods

currently used in the semi-conductor industry for the fabrication of microchips. Typically

they involve the manufacture of a template followed by the deposition of a vapour to fill

the template and grow the nanowire. Deposition processes include Electrochemical

Deposition and CVD. The template may be formed by various processes including

etching, or the use of other nanoparticles, in particular, nanotubes.

3.3.3 Quantum dots

Quantum dots of semiconductors, metals and metal oxides have been at the

forefront of research for the last five years due to their novel electronic, optical, magnetic

and catalytic properties. The number of atoms in a quantum dot, which range from 1000

to 100,000, makes it neither an extended solid structure nor a single molecular entity.

This has led to various names being attributed to such materials including nanocrystals

and artificial atoms. To date, chemistry, physics and material science have provided

methods for the production of quantum dots and allow tighter control of factors affecting,

for example, particle growth and size, solubility and emission properties.

The main objective of the present work is to produce nano iron oxide (Fe2O3)

powder by using the special technique and to characterize them to confirm the formation

of nanosized powder. Further introduction of nano iron particles into the catalytic

14

converter, comparison is made based on their properties To understand the basic

property of the produced nano iron powder, certain physico chemical diagnostic studies

were carried out using high resolution powder X-ray Diffraction (PXRD), The size and

shape of the powder were analyzed by carrying out through scanning electron microscope

(SCM) and Transmission Electron Microscope (TEM) studies.

15

CHAPTER 4

CHARACTERIZATION OF NANOCOMPOSITES

4.1 SCANNING ELECTRON MICROSCOPE (SEM)

4.1.1 Introduction

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

that images the sample surface by scanning it with a high-energy beam of electrons in a

raster scan pattern. The electrons interact with the atoms that make up the sample

producing signals that contain information about the sample's surface topography,

composition etc.

4.1.2 Principles of Operation

SEM operates by scanning an electron beam over the sample and measuring

the electrical interactions with the surface. When the electrons hit the surface, weakly

bound electrons will be ejected to produce secondary electrons. These secondary

electrons can then be measured by a detector, and used to calculate the color for each

pixel of an SEM image. Since these secondary electrons are of low energy their

trajectories can be easily influenced by electromagnetic fields. In order to avoid a charge

build-up on the surface of the sample must be conducting. However, by using shadowing

methods non-conductive samples is coated with conductive material with a thin layer of

metal so that SEM measurements can be done easily.

4.1.3 Sample preparation

The types of signals produced by an SEM include secondary electrons, back

scattered electrons (BSE), characteristic x-rays, transmitted electrons. These types of

16

signal require specialized detectors for their detection. SEM can produce very high-

resolution images of a sample surface, 1 to 5 nm in size.

For conventional imaging in the SEM, specimens must be electrically

conductive, at least at the surface, and electrically grounded to prevent the accumulation

of electrostatic charge at the surface. Metal objects require little special preparation for

SEM except for cleaning and mounting on a specimen stub. Nonconductive specimens

tend to charge when scanned by the electron beam, and especially in secondary electron

imaging mode, this causes scanning faults and other image artifacts. They are therefore

usually coated with an ultra thin coating of electrically-conducting material, commonly

gold, deposited on the sample either by low vacuum sputter coating or by high vacuum

evaporation. Conductive materials in current use for specimen coating include gold,

gold/palladium alloy, platinum etc. Two important reasons for coating, even when there

is more than enough specimen conductivity to prevent charging, are to maximize signal

and improve spatial resolution, especially with samples of low atomic number (Z).

Broadly, signal increases with atomic number, especially for backscattered electron

imaging. The improvement in resolution arises because in low-Z materials such as

carbon, the electron beam can penetrate several micrometres below the surface,

generating signals from an interaction volume much larger than the beam diameter and

reducing spatial resolution. Coating with a high-Z material such as gold maximises

secondary electron yield from within a surface layer a few nm thick, and suppresses

secondary electrons generated at greater depths, so that the signal is predominantly

derived from locations closer to the beam and closer to the specimen surface than would

be the case in an uncoated, low-Z material. These effects are particularly, but not

exclusively, relevant to biological samples.

4.1.4 Detection of secondary electrons

The most common imaging mode collects low-energy (<50 eV) secondary

electrons that are ejected from the k-orbital of the specimen atoms by inelastic scattering

interactions with beam electrons. Due to their low energy, these electrons originate within

17

a few nanometers from the sample surface. The electrons are detected by an Everhart-

Thornley detector which is a type of photo multiplier system. The secondary electrons are

first collected by attracting them towards an electrically-biased grid at about +400V, and

then further accelerated towards a phosphor or positively biased to about +2000V. The

accelerated secondary electrons are now sufficiently energetic to cause the scintillator to

emit flashes of light which are conducted to a photomultiplier outside the SEM column

via a light pipe and a window in the wall of the specimen chamber. The amplified

electrical signal output by the photomultiplier is displayed as a two-dimensional intensity

distribution that can be viewed and photographed on an analogue video display. Thus

image is obtained

Figure 4.1 Electron Beam Scanning

4.1.5 Detection of backscattered electrons

Backscattered electrons (BSE) consist of high-energy electrons originating in

the electron beam that are reflected or back-scattered out of the specimen interaction

volume by elastic scattering interactions with specimen atoms. Since heavy elements

18

backscatter electrons more strongly than light elements and thus appear brighter in the

image, BSE are used to detect contrast between areas with different chemical

compositions

The Everhart-Thornley detector, which is normally positioned to one side of the

specimen, is inefficient for the detection of backscattered electrons because few such

electrons are emitted in the solid angle subtended by the detector, and because the

positively biased detection grid has little ability to attract the higher energy BSE

electrons. Dedicated backscattered electron detectors are positioned above the sample in a

"doughnut" type arrangement, concentric with the electron beam, maximizing the solid

angle of collection. BSE detectors are usually either of when all parts of the detector are

used to collect electrons symmetrically about the beam, atomic number contrast is

produced. Thus advantages of scanning electron microscope are higher resolution, Faster

Scanning, provides surface image. .

4.2 TRANSMISSION ELECTRON MICROSCOPY (TEM )

4.2.1 Introduction

Transmission electron microscopy (TEM) is a microscopy technique whereby

a beam of electrons is transmitted through an ultra thin specimen, interacting with the

specimen as they pass through. Thus the image is formed from the interaction of the

electrons transmitted through the specimen, which is magnified and focused by an

objective lens and onto an imaging device, such as a fluorescent screen, thus the image of

the specimen is produced.

4.2.2 Sample preparation

The TEM is generally used in material science, metallurgy and the biological

sciences. In each case the specimens must be very thin and able to withstand the high

vacuum present inside the instrument.

19

Sample preparation in TEM can be a complex procedure. TEM specimens are

typically hundreds of nanometres thick, as the electron beam interacts readily with the

sample, High quality samples will have a thickness that is comparable to the mean free

path of the electrons that travel through the samples, which may be only a few tens of

nanometres. Preparation of TEM specimens is specific to the material under analysis and

the desired information to obtain from the specimen. As such, many generic techniques

have been used for the preparation of the required thin sections.

To withstand the instrument vacuum, biological specimens are typically held

at liquid nitrogen .Generally samples are prepared as a thin foil, or etched so some

portion of the specimen is thin enough for the beam to penetrate.

4.2.3 General properties of TEM

The transmission electron microscope (TEM) operation has same optical

principle as that of light microscope. The TEM has the added advantage of greater

resolution. This increased resolution allows us to study ultrastucture of viruses and

macromolecules etc. Specially prepared materials samples may also be viewed in the

TEM. The light microscope and TEM are commonly used in conjunction with each other

to complement a research project.

Since electrons are very small and easily deflected by hydrocarbons or gas

molecules, it is necessary to use the electron beam in a vacuum environment. A series of

pumps are used to accomplish an adequate vacuum for this purpose. Rotary Pumps are

the first in the series. They are also called the “roughing pumps” as they are used to

initially lower the pressure within the column through which the electron must travel to

10 -3 mm of Hg range. Diffusion Pumps is used to achieve higher vacuums of about 10-5

mm Hg range but must be backed by the rotary pump.

20

4.2.4 Working of TEM

� The electron gun which is at top, producing a stream of monochromatic electrons.

� This stream is focused to a small, thin, coherent beam by the use of condenser

lenses. The first lens largely determines the "spot size”. The second lens usually

controls the intensity or brightness of the image.

� The beam is restricted by the condenser aperture, knocking out high angle

electrons

� The beam strikes the specimen and parts of it are transmitted

� This transmitted portion is focused by the objective lens into an image

� The image is passed down the column through the intermediate and projector

lenses, being enlarged all the way

� The image strikes the phosphor image screen and light is generated, allowing the

user to see the image. The darker areas of the image represent those areas of the

sample that fewer electrons were transmitted and the lighter areas of the image

represent those areas of the sample that more electrons were transmitted through

the space which is useful to represent the size of the sample. Schematic diagram

of TEM as shown in Figure 3.2 and Figure 3.3

Figure 4.2 Transmission Electron Microscope (TEM) apparatus

21

Figure 4.3 Transmission Electron Microscope (TEM) setup

4.3 X-RAY DIFFRACTION

4.3.1 Introduction

X-rays are electromagnetic radiation of wavelength about 1 Å (10-10 m),

which is has the same size as an atom. They occur in that portion of the electromagnetic

spectrum between gamma-rays and the ultraviolet. Each crystalline solid has its unique

characteristic. Once the material has been identified, X-ray crystallography may be used

to determine its structure, i.e. how the atomic packing in the crystalline state and to find

the inter atomic distance and angle are etc. X-ray diffraction is one of the most important

characterization tools used in solid state chemistry and materials science

for determine the size and the shape of the unit cell for any compound

22

Figure 4.4 X-ray diffraction

4.3.2 Working principle

The X-ray radiation most commonly used is that emitted by copper, whose

characteristic wavelength for the K radiation is =1.5418Å. When the incident beam

strikes a powder sample, diffraction occurs in every possible orientation of 2θ. The

diffracted beam may be detected by using a moveable detector such as a Geiger counter,

which is connected to a chart recorder.

Figure 4.5 Schematic diagram of X-ray powder diffractometer

23

In normal use, the counter is set to scan over a range of 2θ values at a constant

angular velocity. Routinely, a 2 θ range of 5 to 70 degrees is sufficient to cover the most

useful part of the powder pattern. Minimum time of about 30 minutes is needed to obtain

a trace. Schematic diagram for X ray diffraction as shown in Figure 3.5

1. Place the sample onto the double-side tape which is then placed on an aluminum

sample holder.

2. Switch on the start knob and chart recorder (slow) simultaneously, run your

sample on constant speed.

3. Draw the graph by taking intensity on y axis and diffraction angle 2θ on X axis.

4. Locate all peaks on the chart and corresponding 2θ values and write their values

into the data chart below

4.4 FOURIER TRANSFORM INFRARED (FT-IR) SPECTROMETRY

4.4.1 Introduction

FT-IR stands for Fourier Transform Infrared, the preferred method of infrared

spectroscopy. In this process IR radiation is passed through a sample. Some of the

infrared radiation is absorbed by the sample and some of radiation transmitted through

the sample. Thus by analyzing the resulting spectrum molecular representation of

particular specimen can be found out.

Information obtained from FT-IR:

• It can be used to identify the unknown materials

• It can be used to determine the quality or consistency of a sample

• It can also determine the amount of components present in the mixture

4.4.2 Working Principle

Infrared spectroscopy is an unique technique for analysis the material in the

laboratory . In this method, absorption peaks represents the frequencies of vibrations

between the bonds of the atoms of the material. Since different material is a unique

combination of atoms, no two compounds produce the exact same infrared spectrum.

24

Therefore, infrared spectroscopy can be used for positive identification of every different

kind of material. Further the size of the peaks in the spectrum is a direct indication of the

amount of material present in the sample. Fourier Transform Infrared (FT-IR)

spectrometry was developed in order to overcome the limitations encountered in ordinary

infra red spectrometer. The main difficulty was the slow scanning process. FT-IR is the

method for measuring all the infrared frequencies simultaneously, rather than

individually. In this process a very simple optical device called an interferometer is

employed which produces unique type of signal which has all infrared frequencies

encoded into it. Thus the resultant signal can be measured easily and quickly. At the next

process the encoded frequency are decoded into indugual frequency through the process

Fourier transformation. This transformation is performed by means of computer represent

the desired spectral information for analysis.

4.4.3 Sample preparation

Gaseous samples require little preparation beyond purification, but a sample

cell with a long path length (typically 5-10 cm) is normally needed, as gases show

relatively weak absorbance.

Liquid samples can be sandwiched between two plates of a high purity salt.

The plates are transparent to the infrared light and will not introduce any lines onto the

spectra. Some salt plates are highly soluble in water, so the sample and washing reagents

must be without water

Solid samples can be prepared in three major ways. The first method is to

grind a quantity of the sample with a specially purified salt (usually potassium bromide) .

This powder mixture is then crushed in a mechanical die press to form a pellet through

which the beam of the infra red rays can travel through. The second technique is the Cast

Film technique, which is mainly used for polymeric materials. The sample is first

dissolved in a suitable, non hygroscopic solvent. A drop of this solution is deposited on

surface of KBr or NaCl cell. The solution is then evaporated to dryness and the film

formed on the cell and it is analyzed directly. Care is important to ensure that the film is

25

not too thick otherwise light cannot pass through. This technique is suitable for

qualitative analysis.

The final method is to obtain a thin (20-100 micrometer) film from a solid

sample. This is one of the most important ways of analyzing plastic products because the

integrity of the solid is preserved.

4.4.4 Experimental procedure

Infrared energy is emitted from a glowing black-body act as the source for

infrared spectrometer. This beam passes through an aperture which is used to controls the

amount of energy presented to the sample. Then the beam enters the interferometer where

the “spectral encoding” takes place. The resulting interferogram signal then exits the

interferometer. At next stage the beam enters the sample compartment where it is

transmitted through or reflected off of the surface of the sample, depending on the type of

analysis being accomplished. This is the region where adsorption of energy takes place.

Then the beam finally passes to the detector for final measurement. The detectors used

are specially designed to measure the special interferogram signal. Finally the measured

signal is digitized and sent to the computer where the Fourier transformation takes place.

The final infrared spectrum is then presented to the user for interpretation and

manipulation.

Figure4.6 Schematic Diagram of Infrared Spectroscopy

26

4.4.5 Advantages of FT-IR

• Speed

Since all of the frequencies are measured simultaneously, most of the

measurements made by FT-IR are made in a matter of seconds rather than several

minutes. This is called as the Felgett Advantage.

• Sensitivity

Sensitivity is dramatically improved by employing FT-IR . The detectors

employed are much more sensitive which results in reduction of the noise to any desired

level

• Mechanical Simplicity

The simple moving mirror is employed on to the interferometer for the

continuous monitoring of part in the instrument. Thus, there is very little possibility of

mechanical breakdown.

• Internally Calibrated

These instruments employs HeNe laser for internal wavelength calibration

standard. These instruments are self-calibrating and never need to be calibrated by the

user.

4.4.6 Application Of FT-IR

• Infrared spectroscopy is widely used in both research and industry as it is simple

and reliable technique for measurement, quality control and dynamic measurement.

It is of especial use in forensic analysis in both criminal and civil cases, enabling

identification of polymer degradation

• By measuring at a specific frequency over time, change in the character of a

particular bond can be measured. This is especially useful in measuring the degree

of polymerization in polymer manufacture.

27

• Techniques have been developed to assess the quality of tea-leaves using infrared

spectroscopy. This will mean that highly trained experts (also called 'noses') can be

used more sparingly, at a significant cost saving.

• Infrared spectroscopy has been highly successful for applications in both organic

and inorganic chemistry. Infrared spectroscopy has also been successfully utilized

in the field of semiconductor microelectronics for example, infrared spectroscopy

can be applied to semiconductors like silicon, gallium arsenide, gallium nitride,

amorphous silicon, silicon nitride, etc.

4.5 ENERGY DISPERSIVE X-RAY ANALYSIS 4.5.1 Introduction Energy dispersive X-ray Analysis (EXDA) is an analytical technique used

predominantly for the elemental analysis or chemical characterization of a specimen.

Being a type of spectroscopy, it relies on the investigation of a sample through

interactions between electromagnetic radiation and matter, analyzing X-rays emitted by

the matter in this particular case. Its characterization capabilities are due in large part to

the fundamental principle that each element of the periodic table has a unique atomic

structure allowing x-rays that are characteristic of an element’s atomic structure to be

uniquely distinguished from each other.

This technique is used in conjunction with SEM and is not a surface science

technique. An electron beam strikes the surface as a conducting sample. The energy of

the beam is typically in the range 10-20Ke. This causes X-rays to be emitted from the

point of material. The energy of the X-rays emitted depends on the material under

examination. The X-rays are generated in a region about 2 microns in depth, and thus

EDX is not a surface science technique. By moving the electron beam across the material

an image of each element in the sample can be acquired in a manner similar to SAM. Due

to low X-ray intensity, images usually take a number of hours to acquire. Elements of

low atomic number are difficult to detect by EDX. The SiLi detector is often protected by

a Beryllium window. The absorption of the X-rays by the Be precludes the detection of

elements below n atomic number of 11 (Na). In windowless systems, elements with as

28

low atomic number 4 (Be) have been detected, but the problems involved get

progressively worse as the atomic number is reduced. Spectroscopy data is often

portrayed as a graph plotting x-ray energy vs. count rate. The peaks correspond to

characteristic elemental emissions.

To stimulate the emission of characteristic x-rays from a specimen, a high

energy beam of charged particles such as electrons or protons, or a beam of x-rays, is

focused in to the sample to be characterized. At rest, an atom within the sample contains

ground state (or unexcited) electrons situated in discrete energy levels or electron shells

bound to the nucleus. The incident beam may excite an electron in an inner shell,

prompting its ejection and resulting in the formation of an electron hole within the atom’s

electronic structure. An electron from an outer, higher-energy shell then fills the hole, and

the difference in energy between the higher-energy shell and the lower energy shell is

released in the form of an X-ray. The x-ray released by the electron is then detected and

analyzed by the energy between the two shells, and of the atomic structure of the element

from which they are emitted.

4.6 THERMO GRAVIMETRIC ANALYSIS

4.6.1 Introduction

Thermo gravimetric Analysis or TGA is a type of testing that is performed on

samples to determine changes in weight in relation to change in temperature. Such

analysis relies on a high degree of precision. A derivative weight loss curve can be used

to tell the point at which weight loss is most apparent. TGA is commonly employed in

research and testing to determine characteristics of materials such as polymers, to

determine degradation temperatures, absorbed moisture content of materials, the level of

inorganic and organic components in materials, decomposition points of explosives, and

solvent residues. It is also often used to estimate the corrosion kinetics in high

temperature oxidation.

29

4.6.2 Working principle

DTA involves heating or cooling a test sample and an inert reference under

identical conditions, while recording any temperature difference between the sample and

reference. This differential temperature is then plotted against time, or against

temperature. Changes in the sample which lead to the absorption or evolution of heat can

be detected relative to the inert reference.

Differential temperatures can also arise between two inert samples when

response to the applied heat {treatment is not identical. DTA can therefore be used to

stuffy thermal properties and phase changes which do not lead to change in enthalpy. The

baseline of the DTA curve should then exhibit discontinues at the transition temperatures

and the slope of the curve at any point will depend on the micro structural constitution at

that temperature. A DTA curve can be used as a finger print for identification purposes,

for example, in the study of clays where the structural similarity of different forms

renders diffraction experiments difficult to interpret.

The area under a DTA peak can be the enthalpy change and is not affected by

the heat capacity of the sample. DTA may be defined formally as a technique for

recording the difference in temperature between a substance under reference material

against either time or temperature as two specimens are subjected to identical temperature

regimes in an environmental heated or cooled at a controlled rate.

4.6.3 Apparatus required

• Sample holder comprising thermocouples, sample containers and a

ceramic or metallic block.

• Furnace

• Temperature programmer

• Recording system.

30

The last three items come in a variety of commercially available forms are not

being discussed in any detail. A temperature programmer is essential in order to obtain

constant heating rates. The recording system must have a low inertia to faithfully

reproduce variations in the experimental set-up.

Figure 4.7 Schematic Diagram of TG-DAT

The sample holder assembly consists of a thermocouple each for the sample and

reference, surrounded by a block to ensure an even heat distribution. The sample is

contained in a small crucible designed with an indentation on the base to ensure a snug fit

over the thermocouple bead. The crucible may be made of materials such as Pyrex, silica,

nickel or platinum, depending on the temperature and the nature of the tees involved. The

thermocouples should not be placed in direct contact with the sample to avoid

contamination and degradation, although sensitivity may be compromised. On the other

hand, the high thermal conductivity leads to smaller DTA peaks. The sample assembly is

isolated against electrical interference from the furnace wiring with an earthed sheath,

often made of platinum coated ceramic material. The sheath can also be used to contain

the sample region with in a controlled atmosphere or a vacuum. During experiments a

temperature in the range of -200 to 500oC, problems are encountered in transferring heat

uniformly away from this spectrum. This may be migrated by using thermocouples in the

form of (degree) at discs to ensure optimum thermal contact with the flat bottomed

sample container, made of aluminum or platinum foil. To ensure reproducibility, it is then

necessary to ensure that the thermocouple and a container are consistently located with

respect to each other.

31

CHAPTER 5

CATALYTIC CONVERTER

5.1 INTRODUCTION

A catalytic converter is a device used to reduce the toxicity of emissions from

an internal combustion engine. A catalytic converter converts the harmful toxic

combustion products and its by-products into less-toxic substances.

• It is the most effective after treatment process for reducing engine emission.

• Catalyst do not consume during the reaction hence it is non-degradable.

• Catalytic converter is generally called as three way catalytic converter

because it promotes in reduction of HC, CO and NOx.

• It consists of steel container of honeycomb structure inside which contains

porous ceramic structure through which the gas flows.

• It consists of small embedded partials of catalytic materials that promotes

oxidation reaction in exhaust gas.

• Catalytic converter uses alumina as base material because it can withstand

high temperature, low thermal expansion etc.

• Catalyst generally used are platinum, palladium and rhodium.

• Materials such as platinum, palladium promotes oxidation of HC&CO while

rhodium promotes reaction of NOx

Reaction as shown below

2CO + O2 → 2CO2

2NOx → xO2 + N2

2CxHy + (2x+y/2)O2 → 2xCO2 + yH2O

32

5.2 CATALYSIS

Catalysis is the process in which the rate of a chemical reaction is increased by

means of a chemical substance known as a catalyst. Unlike other reagents a catalyst is not

consumed during the chemical reaction. Thus, the catalyst may participate in multiple

chemical transformations, although in practice catalysts are secondary processes

5.2.1 General principles of catalysis

Catalysts generally react with one or more reactants to form intermediate

substances that subsequently give the final reaction product, in the process regenerating

the catalyst. The following is a typical reaction, where C represents the catalyst, X and Y

are reactants, and Z is the product of the reaction of X and Y:

X + C → XC......................... (1)

Y + XC → XYC ...................(2)

XYC → CZ ...........................(3)

CZ → C + Z ..........................(4)

Although the catalyst is consumed by reaction 1, it is subsequently produced by reaction

4, thus the overall reaction is listed below:

X + Y → Z

As a catalyst is regenerated in a reaction, often only small amounts are needed to increase

the rate of the reaction. In practice, however, catalysts are sometimes consumed in

secondary processes.

33

5.2.2 Catalysis and reaction energetic

Catalyst is used serves for two purpose

1. Enhances the reaction rate

2. Direct the reactants to specified product.

General potential energy diagram showing the effect of a catalyst in the

chemical reaction of X + Y to give Z. Due to presence of the catalyst reaction occurs

in different pathway which results in lower activation energy. The final result and the

overall thermodynamics are the same. Potential energy diagram as shown in Figure 4.1

Fig 5.1 Potential Energy Diagram

Rate of reaction(R) is inversely proportional to exponential of the activation

energy. Let k be the reaction rate constant, Ca, Cb be the concentration at point of time

of reactant molecules and x, y be the reaction order. Thus rate of reaction is represented

as

Rate of reaction R =kCaxCby

34

Catalysts work by providing an (alternative) mechanism involving a different

transition state and lower activation energy. The effect is due to the molecular collisions

have the energy needed to reach the transition state. Catalysts do not change the

favorableness of a reaction: they have no effect on the chemical equilibrium of a reaction

because the rate of both the forward and the reverse reaction are both affected.

5.2.3 Mechanism of catalytic reaction

Mechanism of catalyst by chemisorption. Chemisorption is the type of

adsorption where the molecules adhere to the surface of catalyst through the formation of

chemical bond.

Strength of the adsorption in the order of O2>C2H2>CO>H2>CO>N2

variation of chemisorption among metals is represented as follows. Based on this it is

clearly represented that Au can readily react with metal and can act as efficient catalyst

for most of the reaction. At the same time Ti has low chemisorption thus it cannot be

used as catalyst.

Au>Cu>Pd>Pt>Rh>Co>Ni>Ag>Mn>Fe>Mo>W>Nb>Ta>Ti

5.2.4 Catalytic materials

Many types of material often used as catalyst in the recent years. Proton acids

are probably the most widely used catalysts, especially for the many reactions involving

water, including hydrolyses and its reverse. Multifunctional solids often are catalytically

active, e.g. zeolites, alumina, certain forms of graphitic carbon etc. Transition metals

such as platinum,paladium, rhodium, iron, silver are often used to catalyses redox

reactions

5.2.5 Types of catalyst

Generally catalyst can be classified into two types

1. Homogeneous catalyst

35

2. Heterogeneous catalyst

3. Electrocatalyst

Homogeneous catalyst

Homogeneous catalysts are those in which reactant and product are of same

phase. One example of homogeneous catalysis involves the influence of H+ on the

etherification of esters, e.g. methyl acetate from acetic acid and methanol.

Heterogeneous catalysts

Heterogeneous catalysts are those in which reactants and product are of

different phase. For example, in the Haber process, finely divided iron serves as a catalyst

for the synthesis of ammonia from nitrogen and hydrogen.

Electrocatalyst

In the context of electrochemistry, specifically in fuel cell engineering,

various metal-containing catalysts are used to enhance the rates of the half reactions that

comprise the fuel cell. One common type of fuel cell electrocatalyst is based upon

nanoparticles of platinum that are supported on slightly larger carbon particles. When this

platinum electrocatalyst is in contact with one of the electrodes in a fuel cell, it increases

the rate of oxygen reduction to water (or hydroxide or hydrogen peroxide).

5.2.6 Significance of catalyst

• Estimates are that 90% of all commercially produced chemical

products involve catalysts at some stage in the process of their

manufacture.

• Increases the reaction rate

36

5.2.7 Application of catalyst in various fields

Petroleum refining

Petroleum refining makes intensive use of catalysis for alkylation, catalytic

cracking naphtha reforming, steam reforming

Exhaust gas treatment

Exhaust gas which is obtained by burning the fossil fuels are treated through

Catalytic converters, typically composed of platinum and rhodium, break down some of

the more harmful byproducts of automobile exhaust.

2 CO + 2 NO → 2 CO2 + N2

Chemical manufacturing

Many other chemical products are generated by large-scale reduction, often

via hydrogenation. The largest-scale example is ammonia, which is prepared via the

Haber process from nitrogen. Methanol is prepared from carbon monoxide. Bulk

polymers derived from ethylene and propylene are often prepared via Ziegler-Natta

catalysis. Polyesters, polyamides, and isocyanates by acid-base catalysis. Many fine

chemicals are prepared by catalysis; methods include those of heavy industry as well as

more specialized processes that would be prohibitively expensive on a large scale.

Biology and biotechnology

In nature, enzymes are catalysts in metabolism and catabolism. Most

biocatalysts are protein-based, i.e. enzymes, but other classes of bimolecular also exhibit

catalytic properties including enzymes, ribozymes, and synthetic deoxyribozymes.

37

5.3 DISPERSED CATALYTIC CONVERTER MODEL

• Number of reacting molecules to product is directly proportional to

the number of catalytic sites available

• For increasing number of catalytic sites catalytic component are

dispersed on to the surface of the substrate.

• In normal practice dispersing the catalyst such as Pt, Rh, Pd, Fe, Ag in

powder form into the high surface charge carriers such as Al2O3, SiO2,

TiO2 etc

• Carriers are themselves catalytically active but pay a major role in

overall stability and durability.

• In general practice Pt,Pd,Rh practical are deposited by solution

impregnation.

• Alumina Al2O3 is bonded to monolithic honeycomb structure.

• The internal structure of Al2O3 is rich with OH-groups. These OH-

covers entire surface and parts of wall of each pores represents site on

which catalytic substances can bond physically or chemically.

• Thus physical surface of Al2O3 is the sum of internal areas of oxides

from all wall of the pores.

• Catalytic surface is the sum of all areas of the catalytic compounds

• Thus small size of the pores result in more catalytic reaction of the

species.

• Thus tiny catalytic particles are dispersed through porous Al2O3 thus

generate high Pt surface area.

5.4 GENERAL TYPES OF CATALYTIC CONVERTER

Catalytic converters are also used on generator sets, forklifts, mining

equipment, trucks, buses, trains, and other engine-equipped machines.

Generally there are two types of catalytic converter widely used. They are

38

1. Three-way catalytic converters

2. Two-way catalytic converters

5.4.1 Three-way catalytic converter

Three-way catalytic converter is widely used in the automobile

industries. The three-way catalytic converter is scheduled to perform three simultaneous

tasks

• Reduction of nitrogen oxides to nitrogen and oxygen

2NOx → xO2 + N2

• Oxidation of carbon monoxide to carbon dioxide

2CO + O2 → 2CO2

• Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water:

CxH2x + 2xO2 → xCO2 + 2xH2O

These three reactions occur most efficiently when the catalytic converter receives exhaust

from an engine running slightly above the stoichiometric point. This is between 14.6 and

14.8 parts air to 1 part fuel, by weight, for gasoline.

5.4.2 Two-way catalytic converters

These types of catalytic converter not widely used in the automobile sector. A

two-way catalytic converter is scheduled to perform two simultaneous tasks:

• Oxidation of carbon monoxide to carbon dioxide:

2CO + O2 → 2CO2

• Oxidation of unburnt hydrocarbons (unburnt and partially-burnt fuel)

to carbon dioxide and water:

CxH4x + 2xO2 → xCO2 + 2xH2O

This type of catalytic converter is widely used on diesel engines to reduce hydrocarbon

and carbon monoxide emissions.

39

5.4.3 Catalyst poisoning and deactivation

Catalytic poisons are the substances which retards the catalytic activity of the

other substances. Catalyst poisoning occurs when the catalytic converter is exposed to

exhaust containing substances that coat the working surfaces, encapsulating the catalyst

so that it cannot contact and treat the exhaust. Some of the catalytic poison that occurs in

exhaust system is listed below.

Lead, manganese silicon, phosphorus, zinc etc

5.5 PROPERTIES OF CATALYST

Surface area and pore size

High surface area results in maximum dispersion of catalytic compound.

Smaller pores size result in increase in catalytic activity.

Particle size distribution

Thus more number of particles dispersed result in increase in catalytic

activity. Thus huge number of particle distribution obviously increases the catalytic

action.

Wash coat thickness

Optical microscope study is often used to obtain washcoat thickness directly.

The space between washcoat and monolith gives the washcoat thickness measurement.

Thus wash coat formed must be as small as possible.

Adhesion

Common method for the measure of the adhesion between washcoat

monotyth is passing jet of air that simulates velocity used to measure adhesion between

substrate and catalyst. There must be sufficient adhesion between molecules for higher

catalytic activity.

40

5.6 STEPS FOR DISPERSION OF PARTICLES ON TO THE CATALYTIC

CONVERTER

� Capillary Impregnation

It is the process by which adsorption of nano particles on to the surface of

catalyst converter when the particles are dispersed in the liquid medium. The

adsorption of particles on to catalytic converter takes place unto saturation limit.

Further drying and calcinations at high temperature results in fixing of particles on to

catalytic converter.

� Drying

Drying process take place at 110oc for the matter of one hour in the closed

furnace.

� Calcinations

Calcinations process take place at 550oc for the matter of five hour in the

closed furnace. Thus results in fixing of particles on to the catalytic converter.

5.7 INTRODUCTION TO 4 STROKE DIESEL ENGINE

Intake Stroke

The piston is at top dead center at the beginning of the intake stroke, and, as the piston

moves downward, the intake valve opens. The downward movement of the piston draws

air into the cylinder, and, as the piston reaches bottom dead center, the intake valve

closes.

41

Compression Stroke

The piston is at bottom dead center at the beginning of the compression

stroke, and, as the piston moves upward, the air compresses. As the piston reaches top

dead center, the compression stroke ends.

Power Stroke

The piston begins the power stroke at top dead center. The air is compressed

to as much as 25 bar and at a compressed temperature of approximately 1400°C. At this

point, fuel is injected into the combustion chamber and is ignited by the heat of the

compression. This begins the power stroke. The expanding force of the burning gases

pushes the piston downward, providing power to the crankshaft. The diesel fuel will

continue to bum through the entire power stroke (a more complete burning of the fuel).

The gasoline engine has a power stroke with rapid combustion in the beginning, but little

to no combustion at the end.

Exhaust Stroke

As the piston reaches bottom dead center on the power stroke, the power

stroke ends and the exhaust stroke begins. The exhaust valve opens, and, as the piston

rises towards top dead center, the burnt gases are pushed out through the exhaust port. As

the piston reaches top dead center, the exhaust valve closes and the intake valve opens.

The engine is now ready to begin another operating cycle.

42

CHAPTER 6

PROCESS COMPARISON AND MATERIAL SELECTION

6.1 NANOPARTICLES PREPARATION METHODS AND ITS

CHARACTERISTICS

Various physical and chemical methods, their advantages and limitations are

tabulated in tables 3.1 and 3.2

Table 6.1 Physical methods for preparation of nanoparticles

Method Advantages Limitations

Evaporation condensation method

High purity powder The limitation of mass production

Plasma heating method High melting point and low vapour pressure materials (W, Al2O3, SiO2, C)

Very expensive equipment

CO2 laser method Low vapor pressure materials Difficult for the application of Metal nano powder

Mechanical alloy method Nano powder of metal alloy Agglomeration & introduction of impurity

Pulsed wire evaporation wire Metal wire source Low energy consumption & friendly environment

43

Table 6.2 Chemical method for preparation of nanoparticles

Method Advantages Limitations

Chemical Vapor Deposition (CVD) Liquid phase reduction method

Hydro-thermal synthesis

Sol-gel method

Mass production facility Impurity contamination & the danger of chemical materials

6.2 METALS AND ITS PROPERTIES

Generally material selection for catalytic activity is done through by

chemisorptions. Chemisorptions is the type of adsorption where the molecules adhere to

the surface of catalyst through the formation of chemical bond. Generally transition

metals have high catalytic activity.

Strength of the adsorption in case of gases is of order

O2>C2H2>CO>H2>CO>N2

Generally transition metals have high catalytic activity. variation of chemisorption among metals were listed below

Au>Pd>Pt>Rh>Co>Ni>Ag>Mn>Fe>Mo>W>Nb>Ta>Ti

Thus finally five materials are selected and their properties are compared. The materials are Pt,Pd,Rh,Ag,Fe. There properties are shown below.

44

Table 6.3 Properties of the metals based on its catalytic activity

Properties Platinum Palladium Rhodium Nano Silver Nano iron

Pore size Max 106 A Max 106 A Max 106 A 200-300nm 200-300nm

Specific

surface area

10-20m2/g 10-20m2/g 10-20m2/g 10-20m2/g 10-20m2/g

Particle

distribution

6% 6% 6% 6% 6%

Bulk density 1-1.5 g/cm3 1-1.5 g/cm3 1-1.5 g/cm3 0.3-0.6 g/cm3 0.1-

0.25g/cm3

chemisorption

Pt>Pd>Rh>Ag>Fe

6.3 MATERIAL SELECTION

From the material comparison and material study it is noted that iron oxide

supported by potassium can be effectively used in catalytic converter for the removal of

exhaust gas. Potassium being highly reactive metal it generally acts the promoter which

initiates the catalytic activity of iron oxide powder.

6.3.1 SAMPLE PREPARATION

General step for preparation of potassium supported ferric oxide powder involves

various processes such as mixing, drying, calcinations etc. First step of sample

preparation is to mix 17.7 wt% K2CO3 and 82.3 wt% Fe2O3 in the ball mill. At next step

the sample is allowed to dry in the oven at 90-105oC for the time duration of 1 hour.

Finally dried mixture was re-ground and followed by calcinations in air at 1100oC for the

45

time duration of about 7 hours. Thus EDX pattern of the sample clearly indicated a

mixture has potassium polyferrite phases.

Next step of preparation of nano composites through planetary ball milling

process. Ball mill is an efficient tool for grinding many materials into fine powder. A ball

mill is an cylindrical device used for grinding (or mixing) materials like ores, chemicals,

ceramic raw materials and paints. Ball mills rotate around a horizontal axis, partially

filled with the material to be ground plus the grinding medium. Different materials are

used as media, including ceramic balls, stainless steel balls. It is noted that loading the

ferric oxide composites on to the ball mill results in gradual reduction in size of the

particles which is represented through Figure-6.1

0

50

100

150

200

250

0 8 16 24

Milling time (hours)

Par

ticl

e si

ze (n

m)

Figure-6.1 Particle size reduction chart

46

CHAPTER 7

RESULT AND DISCUSSION

7.1 SCANNING ELECTRON MIROSCOPE

Powder morphology and its composition were observed with

SEM(JEOL(Japan)) model JSM-840A combined with energy dispersed analysis through

X-ray spectroscopy(EDAX).The scanning electron microscope (SEM) is a type of

electron microscope that images the sample surface by scanning it with a high-energy

beam of electrons in a raster scan pattern. The electrons interact with the atoms that make

up the sample producing signals that contain information about the sample's surface

topography, composition etc. SEM image of the ferric oxide nano composites as shown

in Figure-7.1 which indicates the microstructure of the sample and its size.

Figure-7.1 SEM image of nano-ferric oxide composites (a)Before milling (b) 8 hrs

image (c) 16 hrs image (d) 24 hrs image

47

Ferric oxide composites of size 225 nm are taken as the sample. Figure-7.1(a)

shows the size and structural orientation of ferric oxide composites which has been taken

for milling

The periodical analysis of ferric oxide nano composites is done by collecting

the samples after milling at an regular intervals of 8,16,24 hours.

Figure-7.1(b) illustrates the SEM image of samples after 8 hours of milling. It

is observed that the particles size varies from 163nm to 180 nm. The kinetic energy

transferred during the milling process leads to the production of array of dislocation. This

is accompanied by atomic level straining. At certain strain level, these dislocations

annihilate and recombine to form small angle grain boundaries separating the individual

grains. Thus sub grains are formed with reduced grain size. The stage conversion

efficiency was found to be 23%.

Figure-7.1(c) illustrates the SEM image of samples after 16 hours of milling.

After 16 hours there is some kind of agglomeration.The particles size varies from 106nm

to 124 nm. This is due to the delayed process and environmental factors. This revels that

the time period after each milling must be uniform and the temperature change have a

impact in the process.

Figure-7.1(d) illustrates the SEM image of samples after 24 hours of milling.

It is observed that the particles size varies from 80 nm to 104nm. During further milling,

the particles experience very high stress and the particle size decreases and reach

nanosize.

7.2 ENERGY DISPERSIVE X-RAY DIFFRACTION

Energy dispersive X-ray spectroscope is an analytical technique used for the

elemental analysis or chemical characterization of a sample. A high energy beam of

charged particles such as X-rays, is focused into the sample. The energy of the X-rays

emitted from a specimen indicates the elemental composition of the specimen. EDX

image of the ferric oxide composites as shown in the Figure-7.2.Further the composition

of various elements present in the sample are listed in Table-7.1. The EDAX pattern

48

clearly indicates that the composite contains 61.75wt% of iron, 18.26wt% of oxygen and

2.21wt% of potassium which together acts used for the production of nano ferric oxide

composites. Ferric oxide present in the composites acts as a base material and the

Potassium added in this process acts as a re-enforcement material. Oxygen present in the

significant amount (18.26 wt%) indicates the presence of oxide particles in the

composites.

Figure-7.2 EDAX pattern for nano-ferric oxide composites Table-7.1 Composition of elements present in nano-Ferric oxide composites

Elements Net count Weight% Atom% C 1076 6.69 18.92

O 11105 18.26 38.77 Fe 5248 61.75 37.57 K 1740 2.78 2.42 Al 556 .46 .58 Au 5768 10.06 1.74

Total 100 100

49

7.3 X- RAY DIFFRACTION

XRD measurement is done on nano ferric oxide composites with the scan rate

of 28/min at 2000 cycle using CuK radiation of wavelength 1.54 Ao was applied.

Figure7.3 shows the XRD spectrum of ferric oxide nano composites obtained using

planetary ball milling process. Thus by calculating using sheer formula the crystalline

size of the particles was found to be 90 nm. Further intense peak were observed below 20

degree. This is due to the presence of nano sized particles. The morphology of the

spectrum clearly indicates that the nano composites are amorphorous in nature. The small

peak observed during 21, 25, 31 degree indicates the presence of potassium crystal.

Figure-7.3 XRD pattern for nano-ferric oxide composites

50

7.4 TEM IMAGE

The TEM study was carried out on Phillips transmission electron microscope.

Fig7.4 shows the TEM structure of nano ferric oxide composites obtained by planetary

ball milling process. From the figure the particle size were found to be varying from 80

nm to 106 nm. Further it is observed that the particle sizes are found to be non-uniform

over the surface. Thus is due to the amorphorous nature of the particles.

Figure-7.4 TEM image for nano-ferric oxide composites

51

7.5 FOURIER TRANSFORM- INFRARED SPECTROSCOPY

Fourier transform infrared spectrum of potassium doped ferric oxide nano

composites as shown in figure 7.5. The intense band was found at 3444 cm inwards is

due to the overstretching vibration of water. The presence of water is once again

confirmed at bending vibration at 1630 inwards. The peek at 2853cm, 2923cm inwards

are due to the symmetric and asymmetric vibration of arsenic group(potassium). The

corresponding bending of arsenic group was found to be occurring at 1283 cm inwards.

The ferric oxide vibration was produced at the intense broad band between 720 cm and

500 cm inwards.

From this analysis it is concluded that ferric oxide nano composites are

prepared by doped potassium molecules with ferric oxide particles in the presence of

water molecules.

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 450.0

0.0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100.0

cm-1

%T

Fe2O3

3433

2923

2853

1630

15581384

1119

1021

857

791774

693

634 618

587

481

Figure7.5 FT-IR Spectrum

52

7.6 THERMO GRAVIMETRIC-DIFFERENTIAL THERMAL ANALYSI S

The TGA-DTA study was carried out with netzch STA 409PC equipment.

The experiment was performed in a nitrogen atmosphere in the range 25oC to 1400oC, at

a heating rate of 27oC/min, alumina is used as the standard catalyst.

In TG curve, an gradual reduction in weight loss of about 4.0-6.0% is

observed between 1000-1400oC. This is due to the phenomenon by which degradation of

arsenic and ferric oxide takes place at that temperature with the release of oxygen.

Figure 7.6 shows differential thermal analysis curve of nano- ferric oxide

composites prepared by planetary ball milling process. It has been seen from the

figure7.6 that sharp endothermic peak is observed at 316oC. This is due to the fact that

evaporation of water molecules which results in change of chemical composition. A

small endothermic peak is observed at 1271oC. This is due to the degradation of arsenic

and oxide particles. Finally at 1333oC an endothermic peak is observed due to the phase

change. No other exothermic peak is observed below this temperature.

Figure7.6 TG-DTA pattern

53

7.7 ENGINE ANALYSIS-PERFORMANCE PARAMETER 7.7.1 Specific Fuel Consumption

The variation of specific fuel consumption with different brake power value

and at different conditions as shown in the figure 7.7. The specific fuel consumption

value is found to be increasing on introduction of catalytic converter and finally reaches

the maximum value on using coated catalytic converter. Thus at no load condition there

is about 5 %increase in SFC value and at peak load condition there is about 5.56

%increase in SFC value. This is due to the fact that back pressure at the engine exhaust

increased on introduction of catalytic converter. Thus more fuel is consumed to overcome

the back pressure. Thus the SFC value steadily increases with the introduction of coated

catalytic converter.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 1.0697 2.1395 3.2093 4.279

bp(Kw)

SF

C(k

G/k

W-h

r)

WITHOUTCATALYTICCONVERTER

WITH UNCOATEDCATALYTICCONVERTER

WITH COATEDCATALYTICCONVETRE

Figure-7.7 Variation Of Specific Fuel Consumption With Brake Power

54

7.7.2 Brake Power Efficiency

The variation of brake power efficiency with brake power value and at

different conditions as shown in the figure 7.8. The brake efficiency percentage keeps on

decreasing on introduction of catalytic converter and finally reaches the minimum value

on using coated catalytic converter. Thus at no load condition there is about 5.7 %

decrease in BP value and at peak load condition there is about 8.2 % decrease in BP

value. This is due to the fact that more fuel is consumed on using coated catalytic

converter which results in decrease in brake power efficiency. Thus the brake power

efficiency steadily decreases with the introduction of the coated catalytic converter.

0

5

10

15

20

25

30

0 1.0697 2.1395 3.2093 4.28

BP(kW)

Bra

ke t

her

mal

eff

icie

ncy

(%)

WITHOUTCATALYTICCONVERTER

WITH UNCOATEDCATALYTICCONVERTER

WITH COATEDCATALYTICCONVETRE

Figure-7.8 Variation of brake efficiency with brake power

55

7.7.3 Nox Reduction

The variation of NOx value with brake power value and at different

conditions as shown in the figure 7.9. The NOx value keeps on decreasing on

introduction of catalytic converter and finally reaches the minimum value on using coated

catalytic converter. Thus at no load condition there is about 33.33% decrease in NOx

value and at peak load condition there is about 54.3 % decrease in NOx value. This is due

to the fact that NOx undergoes catalytic reaction with catalytic particles such as platinum,

palladium, rhodium, nano ferric oxide composites results in the production nitrogen and

oxygen as the end product. Thus there is steady decrease in NOx value with the

introduction of the coated catalytic converter.

0

100

200

300

400

500

600

700

800

0 1.0697 2.1395 3.2093 0.48

BP(kW)

NO

x V

alu

e(p

pm

)

WITHOUTCATALYTICCONVERTER

WITH UNCOATEDCATALYTICCONVERTER

WITH COATEDCATALYTICCONVETRE

Figure-7.9 Variation of NOX value with brake power

56

7.7.4 HC Reduction

The variation of HC value with brake power value and at different conditions

as shown in the figure 7.10. The HC value keeps on decreasing on introduction of

catalytic converter and finally reaches the minimum value on using coated catalytic

converter. Thus at no load condition there is about 72.1% decrease in HC value and at

peak load condition there is about 68.8 % decrease in HC value. This is due to the fact

that HC undergoes catalytic reaction with catalytic particles such as platinum, palladium,

rhodium, nano ferric oxide composites results in the production water and oxygen as the

end product. Thus there is steady decrease in HC value with the introduction of the

coated catalytic converter.

0

10

20

30

40

50

60

70

80

90

100

0 1.0697 3.2093 0.48

BP(kW)

HC

val

ue(

pp

m)

WITHOUTCATALYTICCONVERTER

WITH UNCOATEDCATALYTICCONVERTER

WITH COATEDCATALYTICCONVETRE

Figure-7.10 Variation of HC value with brake power

57

7.7.5 CO Reduction

The variation of CO value with brake power value and at different conditions

as shown in the figure 7.11. The CO value keeps on decreasing on introduction of

catalytic converter and finally reaches the minimum value on using coated catalytic

converter. Thus at no load condition there is about 60% decrease in CO value and at peak

load condition there is about 40 % decrease in CO value. This is due to the fact that CO

undergoes catalytic reaction with catalytic particles such as platinum, palladium,

rhodium, nano ferric oxide composites results in the production carbon di oxide and

oxygen as the end product. Thus there is steady decrease in CO value with the

introduction of the coated catalytic converter.

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0 1.0697 2.1395 3.2093 0.48

BP(kW)

CO

val

ue(

%)

WITHOUTCATALYTICCONVERTER

WITH UNCOATEDCATALYTICCONVERTER

WITH COATEDCATALYTICCONVETRE

Figure-7.11 Variation of co emission value with brake power

58

CHAPTER 8

CONCLUSION

A detailed work has been done on synthesis and characterization of nano

ferric oxide composites by using planetary ball mill. Preparation of ferric oxide nano

composite is found to be feasible.

It is concluded that the conversion efficiency of the particles is found to be

about 26% during 8 hrs and 16 hrs samples. Thus there is a great reduction in size of the

particles during 8 hrs and 16 hrs sample. The conversion efficiency of the particles is

found to be 16% during 24 hrs sample. Thus there is less reduction in size of the particles

observed during 24 hrs sample. The particles are found to be in dispersed state with the

particle size ranging from 90-95 nm. Further EDAX pattern obtained for ferric oxide

nano- composites shows the composite contains 61.75wt% of iron which acts as a base

metal and 2.21wt% of potassium which acts as a re-enforcement material. Presence of

oxygen in significant amount (18.16 wt %) indicates that there is an presence of oxide

particles in the composites. The XRD pattern shows the intense peak below 20 degree.

This confirms the presence of nano sized particles and by using sheer formula the

crystalline size of the particles was found to be 90 nm. The morphology of the spectrum

clearly indicates that the nano composites are amorphorous in nature. TEM image clearly

identifies that the particle size were found to be varying from 80 nm to 106 nm. Further

the particle is found to be non-uniform over the surface. The Fourier transform infrared

spectroscopy shows the intense band at 3444 cm inwards due to the overstretching

vibration of water. The presence of water is once again confirmed at bending vibration at

1630 inwards. The peek at 2853cm, 2923cm inwards are due to the symmetric and

asymmetric vibration of arsenic group (potassium). The corresponding bending of arsenic

group was found to be occurring at 1283 cm inwards. Finally the intense broad band

between 720 cm and 500 cm inwards are due to the vibration was produced by the ferric

oxide molecules.

59

The engine exhaust test has been carried out by using nano composites coated

catalytic converter Thus by using nano composite coated catalytic converter there is

about 33.33% decrease in NOx value at no load condition and about 54.3 % decrease in

NOx value at peak load condition. HC value is found to be decreasing 72.1% at no load

condition and at peak load condition. Finally at no load condition there is about 60%

decrease in CO value and at peak load condition there is about 40 % decrease in CO

value.

60

REFERENCES

1. Apostolescu , B. Geiger , K. Hizbullahb, M.T. Jan , S. Kureti , D. Reichert, F. Schott , W. Weisweiler, (2005),’ Selective catalytic reduction of nitrogen oxides by ammonia on iron oxide catalysts’, vol 62 pp 104–114

2. Guido Ketteler, Wolfgang Ranke, and Robert Schl, (2002), ‘Potassium-Promoted

Iron Oxide Model Catalyst Filmsfor the Dehydrogenation of ethylbenzene: An Example for Complex Model Systems’, vol 212, pp104–111

3. Hizbullah , S. Kureti , W. Weisweiler, (2004), ‘Potassium promoted iron oxide

catalysts for simultaneous catalytic removal of nitrogen oxides and soot from diesel exhaust gas’, vol93–95 pp-839–843

4. Joseph, G. Ketteler, C. Kuhrs, W. Ranke, W. Weiss and R. Schlo, (2005),

‘Preparation and composition of potassium promoted iron oxide model catalyst films’.

5. Kureti , W. Weisweiler , K. Hizbullah, (2003), ‘Simultaneous conversion of

nitrogen oxides and soot into nitrogen and carbon dioxide over iron containing oxide catalysts in diesel exhaust gas’, vol-43 pp 281–291

6. Li, B.H. Shanks, Stability, (2006), ‘Phase Transitions of Potassium Promoted Iron Oxide in Various Gas Phase Environments’, APCATA 11768

7. Ronald M.Heck and Robert J.Farrauto, (1997),‘Catalytic Air Pollution Control’, by Tata Mcgraw-Hill publication limited, New Delhi

8. She, M. Flytzani-Stephanopoulos, C. Wang, Y. Wang, C.H.F. Peden, (2008),

‘SO2-induced stability of Ag-alumina catalysts in the SCR of NO with methane’, APCATB-10478

9. Sipho C. Ndlela and Brent H. Shanks, (2006), ‘Reduction Behavior of Potassium-

Promoted Iron Oxide under Mixed Steam/ Hydrogen Atmospheres, vol-45 pp 22.

10. Yu Guo , Makoto Sakurai, Hideo Kameyama, (2008), ‘Temperature programmed desorption/surface-reaction study of an anodic alumina supported Ag catalyst for selective catalytic reduction of nitric oxide with propene’, vol-79 pp382–393.

61

PUBLICATION

National Conference

1. N.Harshavardhana, G.Sakthinathan (2009) ‘Synthesis and Characterization of

Ferric oxide nano composites’ RTMT conference 2009, Department of

Manufacturing Engineering, Anna University Chennai.

62

ANNEXURE-I

ENGINE SPECIFICATION

NAME Kirloskar

Bore 87.5mm

Stoke 110mm

CC 662 CC

No. of cylinders 1- vertical

Compression ratio 17.5:1

Cooling system Air

Peek pressure 76 bar

Rated speed 1500 rpm

Weight 163 Kgs

Specific fuel consumption 251 g/kW-hr

Injection pressure 200 bar

Brake power 4.4 kW