Luận văn thạc sĩ synthesis and catalytic properties of catalyst system based on ceo2 zro2 for the complete oxidation of hydrocarbon to treat motorcycle's exhaust gases

Synthesis and catalytic properties of catalyst system based on CeO;— ZrO; for the coniplete oxidation of hydrocarbon fo treat motoreyele x exhaust gases MINISTRY OF EDUCATION AND TRAI

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Synthesis and catalytic properties of catalyst system based on CeO;— ZrO; for the

coniplete oxidation of hydrocarbon fo treat motoreyele x exhaust gases

MINISTRY OF EDUCATION AND TRAINING

HANOI UNIVERSITY OF TECHNOLOGY

NGUYEN THE TIEN:

SYNTHESIS AND CATALYTIC PROPERTIES OF CATALYST SYSTEM

BASED ON CeO,-Zr0, FOR TIE COMPLETE OXIDATION OF ITYDROCARBON TO TREAT MOTORCYCLE’S EXHAUST GASES

SPECIALITY: ORGANIC AND PETROCIIEMICAL TECIINOGLOGY

SCTENCE MASTER THESIS

ORGANIC AND PETROCHEMICAL TECHNOLOGY

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1.12 Air pollution problem in the world and in Vietnam 21

13 International and Vietnam researches on catalyst for exhaust gas 33

1.3.3 The imperative task, the aim and the research directian of the 39 thesis,

1.4 The catalysts based on Cerium and Zirconium oxide 41

a Oxygen storage capacity (OSC) of CeO,-ZrO, mixed oxides 45

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1 5.Completed hydrocarbon oxidatian af hydrocarbon 47

IL1.2 Synthesis of several single oxides, CeO0,-Zr0, and CeO,-Co,0, $2

catalysts by sol-gel method

11.1.4 Synthesis af Co,0./CeQ,-Z.r0, catalysts by impregnation %4

11.3.3 BET method for the determination of surface area a

TIT.1.2 02 volume concentration in the exhaust gas “ I11.1.3 Hydrocarbon concentrations im the exhaust gas analyzed by T0 GC-MS and GC- FID

H.2 Characterization of several single metallic oxides for the 73

hydrocarbon completed oxidation

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11.2.1 Surface properties of the investigated oxtdes Tã

IL2.3 Catal

IIL.3 Characterization of CeO.-8nO, mechanical mixtures 16 11.3.1 Catalytic activity of CcO,-SnO; mechanical mixtures for 77 complete oxidation reaction of propylene

11.3.2 Phase composition and surface propertics of CeO;§nO, 78 mechantcal mixtures

IIL41 Phase composition and surface properties of CeO,-7.rO, 81 mixtures

11.4.2 Catalytic activity of CcO,-ZrO, for complete oxidation 82 reaction of propylene

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ACKNOWLEDGEMENTS

This Master thesis has been carried oul al the Depariment of Organic and Petrochemical Technology and Laboratory of Petrachomistry and Calalysis Matcrial Faculty of Chemical Technology, Hanoi University of Technology during the petiod February 2010 to Angust 2010 The work has been completed under

supervision of Associate Prof Dr Le Minh Thang

Firstly, I would like to thank Associate Prof Dr Le Minh Thang She helped me a

lot in the scientific work with her thorough guidance her encouragement and kind help

T want to thank all teachers of Department of Organic and Petrochemical Technology and the technicians of Laboratory of Petrochemistry and Catalysis Matetial, Faculty of Chemical Technology for their guidanee, and their helps in my work

1 acknowledge to all members in my research group for their friendly attitude and their assistances

Finally, 1 want to thank my family for their love and encouragement during the whole period

Nguyen The Tien August 2010

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PROTESTATION IN THE THESIS

T assure that my scienlific resulls arc righteous They haven’! been published in

any scientific document I have responsibilitios for my protestation and mry roscarch,

results in the thesis

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SYMBOLS IN TIE TITESIS

TUT: Hanoi University of Technology

PMLO: particulate malicr less than 10 nm in diameter

NO,; oxides of nitrogen

YOCs; volatile organic compounds

PAHs: polycyclic aromatic hydrocarbons

ILAPs: hazardous air pollutants

CFCs: chloroflucrocarbons

TIC: hydrocarbon

SO, suifur oxides

COVNM: compound organic volatile not counting methane

PCBs; polychlorinated biphenyls

PCDDs: polychloinated dibenzodioxins

USA: United States of America

HCMC: Ho Chi Minh City

LEA: Low excess air

OFA: Overfire air

FRG: Flue gas recirculation

LNR: Low NO, burner

SNCR: Selective noncatalytic reduction

SCR: Selective catalytic reduction

AVF, ait/fuel ratio

TW: three-way catalyst

Cpsi: call per square inch

SULEY: super ultra low level vehicle

ULRV: nilira low level vehicle

CZ; mixtures of Cerium oxide and Zirconium oxide

CZS: mixtures of Cerium oxide, Zirconium oxide, Strontium oxide

4; the theoretical stoichiometric value

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Tee! temperature for 50% conversion

in: inch

OSC: oxygen slorage capacity

CZALa: mixtures of Cerium oxide, Zirconium oxide, Alumitum oxide, Lanthanum oxide

NGVs: Natural Gas Velucles

LPG: Liquefied Petroleum Gas

ECE R40: Economic Commission for Euro Regulation 40- Emission of gaseous pollutants of motorcycles)

HMDC: Hanoi Motoroycle Driving Cycle

GC-MS: Gas Chromatography — Mass Spectroscopy

GC-FID: Gas Chromatography- Flame Ionization Detector

XRD: Xuay diffraction

SEM: Scanning Electron Microscopy

BET equation: Branauer- Emmett-Teller

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TABLES IN THE THESIS

1 Anthropogenic Emissions of Selected Air Pollutants in USA 22

2 Annual Combustion-Gener ated Emissians of Selected Pollutants | 23

by Stationary Source Category in USA

3 Emission Reduction from Different NO, Control Technologies | 27

6 Classification of the phases in tha CeO,-ZrO, binary system 43

7 Chemicals used in the thesis 52

8 Characteristic of BCE R40 and IIMDC driving cycles 56

9 Measurement conditions using a GC-Thermo Electron with FID 38

10 Retention time of some organic compound detected by GC Thermo | 58

Electron with FID detector and the condition mentioned in table 9

12 Pollutant concentration of some molorcycle types 68

13 Pollutant concentrations analysed by BCE 1140 and TIMDC 69

14 Oxygen concentrations at different operating condition ø9

l5 Camposttion 0ƒ exhatst gas ín địƒorenf operating condiions 70

16 Hydrocarbon concentrations analyzed oy GC-MS 70

17 Composition of Organic compounds in the motoreyele’s exhaust | 7

gases with measurement tima up to 40 minutes

19 CO; selectivity of investigated metal oxides at different reaction | 76

temperatures

21 BET surface area of some Ce-Zr oxides depend on temperature | RA

22 CO; selectivity of CeOz-Co;0, catalysts at different reaction 89

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FIGURES IN THE THESIS

Zz Schematic drawing, causes and effects of air pollution: (1) 21

greenhouse effect, (2) particulate contamination, (3) increased LV

radiation, (4) acid rain, (5) increased ozone concentration, (6)

increased levels of nitrogen oxides

4 Diagram of a modern TWC/engine‘axygen sensor control loop for 29

engine exhaust control

3 Three way catalyst performance determined by engine air to fuel 30

6 Wash-coals on automotive catalyst can have different surface 31

structures as shown with SEM micrographs

9 Scheme of catalytic hydrocarbon oxidation; 1I-Laydrocarbon, C- 50

catalyst, R, io R-tabile intermediate, probably of the peroxide type

10 Scheme of CeO;ZrO; synthesis by sol-gel method 33

1 Seherne gƒ the sunthesis gƒ Co;O//CeO;-ZrO; cafalysts ñp %5

15 Tiustrates how diffraction of ray by erystal planes allows one 60

to derive lanice by using Bragg relation

16 The interaction between the primary electron beam and the sample in 61

an electron microscope leads to a number of detectable signal

17 Constitution and operating principle of SEM instrument 61

20 X-ray pattern of several single oxides synthesized using sol-gel 73

method

21 ‘Reaction rate of propylene conversion (r,w, CsH3 conv) of several T5

oxides at different reaction temperatures

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22 Reaction rate of propylene consumption (r,w, C2H; cons) of 7?

CeOQ,-SnO; mechanical mixtures

23 CO; selectivity of Ce0,SnO; mechanical mixtures (in low 78

temperatures, CO and CO; peaks were not detected)

24 X-ray patterns of pure CeO pure SnO>, mechanical mixture of 79

CeO;-SnG;

SAM images of CaO/SnO,=53.29/46 72 machanical mixture before 80

afier reaction

26 Kray pattern of CaO-2r(0- solid solution with different Cafir ‘82

atomic ratios before reaction

27 Reaction rate of propylene consumption of CeOx-zrO, solid 8

solutions (Ce, 27,02) at different reaction temperatures

28 CO; selectivity of CeO;-ZrO; solid solutions (Ce;.ZrQ:) at 84

different reaction temperatures (x: optional of Zr atom in solid

solution) (in low temperatures, CO and CO; peaks were not

detected)

29 Reaction rate of propylene conversion of CeO/ZrO;-2 prepared 85

by mechanical mixed and sol-gel synthesis at different reaction

temperatures

30 CO) selectivity of CeO./ZrO;=8'2 synthesised by mechanical 86

mixture and sol-gel method at different reaction temperatures (at

Jaw temperatures, CO or CO: peaks were not detected)

31 XRD patterns of mechanical sample before reaction (a), solgel 86

samples before and afier reaction (6) with molar ratio

CeO//2rO:—8/2

32 SEM images of CeO./7rQ,=8/2 sol-gel sample before and after 87

reaction

33 Reaction rate of propylene consumption of CeO,-Co;0, catalysts af 8B

different reaction temperatures

34 Reaction rate of propylene consumption af CeQ-7rO; support, 89

Co:0, active phase, CoO, supported on CeyeZ1'n0- samples

35 ‘Reaction vate of propylene consumption of CeO,-ErOs 90

supports, Co;O, active phase, CoO, supported on Cen sZt 02

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ABSTRACT

In Vietnam, a developing country, motorcycles are the main way of transportation for the momont The number of motoraycles is about 90% of all vehicles in Vieinam, Emission from fucl combustion contributes essentially in pollution, Hydrocarbons in exhaust gases enhance the greenhouse effect, plobal warming

‘The aun of this work is synthesis and determination of catalytic achvity of catalyst systems based on Ce, and ZrO» for the complete oxidation of hydrocarbon (propylene) to treat motoreycle's exhanst gases Furthermore, other metal oxides such as SnO., TiC,

ALO, VeO5, Coy, NiO, calalytic activity of some of their mixtures and impregnation

samples wore tested The physicochamical proporties of these investigated catalysis wore also characterized carefully

The following, main findings have been obtained from the results

- The main composition of the exhaust gases are 0.5+4,5 val.% hydrocarbon, 0,5+8 vol.%

CO, 4:12 vole CO:, 0.08 to 0.4 vol% NO, and 18+12 vol.% © Amongst Rydrocarbons in the exhaust gases, C;H, are one of the main components

- Amongst investigated catalysts (Co; CeO-, SnO›, TiO., NiO, ZrOs, V0, and AlOy)

C0;0 and CeO; exhibited the highest catalytic activity

Catalytic activily of mixtures of CeO, and SnQs, CeO, and ZrO, were investigated CøC+-SnO+ mixtnros exhibited rather high activity for the complete axidation of propylene but CoO.-Zr0, sample has even higher activity

- Catalytic activity of some cobalt oxide supported on CeO.-ZrO, catalysts was studied, It can be seen that the samples hos high activity at wide reaction temperature range since at low temperature due to the combination of Cobalt and Cerium active site acts The

impregnation limit should be 10%wt an Ce, 521g 0, and 5%wt on CeusZra:O;

- Amongst investigated catelysts, the sample with 5% wt CoO, impregnated on CeasZra-Oh exhibited highest conversion and selectivity at wide temperature range from

250°C to 500°C This catalyst was able to convert 33 % propylenc in the reaclant with the

CO, selectivity of 100%

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INTRODUCTION, AIMS AND OLTLINE OF THE TIIESIS Vieinam is a developing country reaching the next stage of ecanomical level Moloreycles are the main way of transportation for the moment The number of motorcycles is about 90% of all vchiclos in Victuam, Thus, the cavironmental pollution is very heavy by emission from exhaust gases of motorcycles Hydrocarbons in exhaust gases contritmte to enhance the greenhouse effect, global warming or hazard to human health

‘The most popular catalysts for the treatment of automobile exhaust gases are noble

metals such as Pi, Pd The studies altracied alientions of many international

rascarchers since 1980s [4-7] Seme other groups fecuscd on the preparation of perovskites catalysts [8, 9, 58] Recently, some authors paid attention on the usc of

enhanced stability against thermal sintering [11, 17] In Vietnam, there has been several research groups (Faculty of Chemistry, Hanoi National University of Science, Institute of Chemistry, Vietnamese Academy of Science and Technology) studied on designing new catalytic systems for the treatment of automobile exhaust

In this thesis, the composition of motorcycle exhaust gas was siudied in detail by different methods The aim of this work is synthesis and determination of catalylic activity of catalyst syslems bascd on CeO and Z1O-, Furthermore, catalytic activity

of other metal oxides such as $nO;, TÌO,, Al;O;, V:C,, C

mixtures and Co,O, supported on CeO,-Z10, catalysts were also tested The

1», NiO, some of their

properties of these investigated catalysts were also characterized

The main content of the thesis included three chapters The first chapter summarizes the aspects about air pollution problem, immediate consequences, main pollutants, pollutant treatments, rasearches in the world and in Vietnam, the catalyst based on Ceria-Zirconia and complete hydrocarbon oxidation using metal catalyst

in the literature

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The second chapter introduces methods to synthesize catalysts (sol-gel, impregnation), methods to determine the pollulant concentralions (ECE R40,

HMDC, GC- FID and GC-MS), physicochemical techniques (XRD, SEM and BET)

and catalytic test used in the thesis

The most important chapter of this thesis (chapter III) focused on results and discussions on composition of motorcycle exhaust gases, characterization and

catalytic activity of investigated catalysts

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Synthesis and catalytic properties oƒ catahst system based on CeO›— ZrO› for the

complete oxidation of hydrocarbon to treat motorcycle's exhaust gases

CHAPTER I: LITERATURE REVIEW

L1 Air pollution problem

An air pollutant is known as a substance in the air that can cause harm to humans and the environment Pollutants can be in the form of solid particles, liquid droplets,

or gases, In addition, they may be natural or man-made [18]

Now a day, air pollution is one of serious problems in the world and immediate consequences are hazards such as: acid rain, the greenhouse effect, ozone hole Emission from fuel combustion contributes essentially in pollution In Vietnam, environment, especially in big city, is so bad due to the rapid increase of automobile

[60]

Air pollution from World War II production Smog over Santiago

Fig 1 Images of air pollution over the world [18]

1.1.1 Air pollutants

Pollutants that are of primary concem are those that, in sufficient ambient

concentrations, adversely impact human health and/or the quality of the environment Those pollutants for which health criteria define specific acceptable

levels of ambient concentrations are known in the United States as "criteria

pollutants.” The major criteria pollutants are carbon monoxide (CO), nitrogen

dioxide (NO.), ozone, particulate matter less than 10 nm in diameter (PM10), sulfur dioxide (SO.), and lead (Pb) Ambient concentrations of NO; are usually controlled

by limiting emissions of both nitrogen oxide (NO) and NOs, which combined are

referred to as oxides of nitrogen (NO,) NO, and SO: are important in the formation

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of acid precipitation, and NO, and volatile organic compounds (VOCs) can real react in the lower atmosphere to form ozone, which can canse damage to lungs as well as to property [3]

Other compounds, such as benzene, polycyclic aromatic hydrocarbons (PAHs), other trace organics, and mercury and other metals, are emitted in much smaller quantities, but are more toxic and in some cases accumulate in biological tissue over time, These compounds have been grouped together as hazardous air pollutants (IAPs) or "air toxics, and have recently been the subject of increased regulatory conirol Aiso of increasing interest are emissions of compounds such as carbon dioxide (CO»), mothane (CH,), or nitrous oxide (N20) thal, have the potential io affect the global climate by incrcesing the level of solar radiation trapped in the Earth's atmosphere, and compounds such as chlorefluorocarbons (CFCs) that react with and destroy ozone in the stratosphere, reducing, the atinosphere's ability to screen out harmful ultraviolet radiation from the sun [40]

‘The year 2000 had seen over 500 mullion passenger cars in use worldwide with an annnal worldwide production of new cars approaching 60 million In addition, there are about 10% more passenger vehicles represented by trucks The majority of these vehicles (automobiles and trucks) use a spark ignited gasoline engine to provide power and this has become the mosl frequent form of transpartation Gasoline blend still remains a mixture of paraffins and aromatic hydrocarbons which combust in air

at avery high efficiency [14]

The simplified reaction is

Gasoline + Os {in air) + CO; + H,0 + heat Due to incomplete combustion in the engine, there are a number of incomplete combustion products Typical exhaust gas composition at the normal engine operating conditions is

+ Carbon monoxide (CO, 0.5 voi %6);

+ Unbumed hydrocarbons (HC, 330 vppin),

+ Nitrogen oxides (NO, , 900-vppm),

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* Llydrogen (11h, 0.17 vol %),

+ Water (ILO, 10 vol %Y,

* Carbon dioxide (COs, 10 vol %),

%)

HC, CO and NO, are the major exhaust pollutants HC and CO occur because the combustion efficiency is <100% due to mcomplete mixing of the gases and the wall

+ Oxygen (O», 0.5 vol

quenching effects of the colder cylinder walls The NO, is formed during the very high temperatures (>1500 °C) of the combustion process resulting in thermal fixation of the nitrogen in the air which forms NO, [66]

Because of the large vehicle population, significant ameunls of HC, CO and NO,

are cmitted to the atmosphere, The formation of ground level ozone occurs as a result of a chemival reaction between HC and NO, and sunlight When stagnant air masses linger over whan areas, the pollutants are held in place for long periods of time, Sunlight interacts with these pollutants, transforming them into ground level

ozone Ozone is a major component of smog Of course, CO is a direct poisan to

humans The benefits of catalytic controls have been documented and it 1s now estimated that by the year 2000, over 800 million tons of combined pollutants of

HC, CO and NO, will have been abated using aulo exhanst catalyst and prevented from cnicring the atmosphere [15]

* Particle matter (PM10): Particulates, alternatively referred to as particulate

matter (PM) or fine particles, are tiny particles of solid or liquid suspended in a.gas In contrast, acrosol refers (a particles and tha gas logether Sources af particulate matter can be man made or natural Some particulates occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray Human activities, such as the buming of fossil fuels in vehicles, power plants and various industrial processes also generate significant amounts of aerosols Averaged over the globe, anthropogeme aerosols—those made by human activities—currently account for about 10 percent of the total amcunt of aerosols in our atmosphere

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Increased levels of fine particles in the air are linked to health hazards such

as heart diseases, altered lung function and ling cancer [28, 60]

© Sulfur oxides: (SO,) - especially sulfur dioxide, a chemical compound with the formula 802, SQ) is produced by volcanoes and in various industrial processes, Sinev coal and peiraloum ofien contain sulfur compounds, thcir combustion generates sulfur dioxide, Further oxidation of $C, usually in the presence of a catalyst such ax NO», forms H,$Os, and thus acid rain This is one of the causes for concem over the environmental impact of the use of these fuels as power sources [18, 28, 60]

© Nilrous oxides: (NO,) - especially nilrogen dioxide are emitted from high temperature combustion Can be seen as the brown have deme above or plume downwind of cities Nitrogen dioxide is the chemical compound with the formula NO), [t is one of the several nitrogen oxides This reddish-brown toxic gas has a characteristic sharp, biting odor NO, is one of the most

prominent air pollutants, Nitrous oxides can be formed by some reactions:

Fucl NO, is duc to the presence of nitrogen in the fucl and is the greatest conttibulor lo total NO, cmissions in uncontrolled coal flames, By Limiting the

presence of ©» in the region where the nitrogen devolatilizes from the solid fuel, the

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formation of fel NOx, can be greatly diminished NO formation reactions depend upon the presence of hydrocarbon radicals and O,, and since the hydrocarbon- oxygen reactions are much faster than the nitrogen-oxygen reactions, a cmirollod introduction of air into the devolatilization zone leads to the oxygen preferentially reacting with the hydrocarbon radicals (rather than with the nitrogen) to form water

and CO Finally, the combustion of CO is completed, and since this reaction does

not promote NO production, the total rate of NO, production is reduced in comparison with uncontrolled flames This staged combustion can be designed to take place within a single bumer flame or within the entire furnace, depending on the type of controt applicd (sec below) Fucl NO, is important primarily in cool combustion systems, although it is important in systems that use heavy oils, since both fuels contain significant amounts of fuel nitrogen [40]

Prompt NO, forms at a rate faster than equilibrium would predict for thermal NOx formation Prompt NO, forms from nonequilibrium levels of oxide (O) and hydroxide (OH) radicals, through reactions initiated by hydrocarbon radicals with molecular nitrogen, and the reactions of © atems with N, to form N.O and finally the subsequent reaction of N;O with © to form NO Prompt NO, can account for more than 50% of NO, formed in

-tich hydrocarbon flames However, prompt

NO was not done typically account for a significant partion of the tolal NO omissions from combustion sources [40], Like $O,, nitrous oxides damage the respiratory system and they are causes of acid rain, photochemical smog [28]

+ Carbon monoxide (CO) is a colorless, odorless, non-imritating but very poisonous gas [18] Carbon monoxide emissions are typically the result of poor combustion, although there are several processes in which CO is formed as a natural byproduct of the provess (such as the refining of oil), In combustion processes, the most effective method of dealing with CO is to ensure that adequate combustion air is available in the combustion zone and that the air and fuel are well mixed at high temperatures Where large

amounts of CO are emitted in relatively high concentration streams

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dedicated CO boilers or thermal oxidation systems may be used to bum out

the CO to COs, CO bailers use [he wasle CO as the primary fuel and extract

useful heat from the combustion of the waste gas An auxiliary fuel, usually natural gas, is uscd to maintain combustion temperatures and as a start-up fuel [40]

Volatile organic compounds (VOCs) are an important outdoor air pollutant VOCs are emitted from a broad varicty of stationary sources, primarily manufacturing, processes, and are of concern for two primary reasons In this field they are often divided into the separate categories of methane (CH,) and non-methane (YMVOCs) Methane is an extremely efficient greenhouse gas which contributes to enhance global warming Other hydrocarban VOCs are also significant preenhouse gases via their role im creating ozone and mn prolonging the life of methane in the atmosphere, although the effect varies depending on local air qualily First, VOCs react in the atmosphere in the presence of sunlight to form photochemical oxidants (including ozone) that are harmful to human health Second, many of these compounds arc harmful

to human health at relatively low concentrations This second group of VOCs

is referred to as hazardous air pollutants (HAPs) and is included for potential regulation under Title II] of the Clean Air Act Amendments of 1990, Total VOC emissions in the U.S have been declining over the past 10 years, primarily due to significant improvements in vehicle emission levels During, the same period, VOC omissions from indusirial sources, solvent utilization, and chemical manufacturing have increased slightly, making these sources more important from a control perspective, In addition to VOCs, heavier organic compounds, such as polycyclic aromatic hydrocarbons (PAHs), nitrogenated PAHs, polychlorinated biphenyls (PCBs), and polychlorinated dibenzocioxins (PCDDs), are also important HAPs that may be emitted from

a vatiety of sources Combustion processes in general can form PAIIs:

however, proper equipment operation and maintenance typically results in

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PAH emissions from combustion sources on the order of parts per billion or less Within the NMVOCs, the aromatic compounds benzene, toluene and xylene are suspected carcinogens and may lead to leukemia through prolonged exposure, 1,3-butadiene is another dangerous compound which is often associated with industrial uses (18, 40]

1.1.2 Air pollution problem in the world and in Vietnam

Combustion processes are a major anthropogenic source of air pollution in the United States, responsible for 24% of the total emissions of CO, NO,, SOs, VOCs, and particulates In 1992, 146 million tonnes (161 million tons) of these pollutants were emitted in the United States Of these pollutants, stationary combustion processes emit 91% of the total U.S SO; emissions, and 50% of the total U.S NO,

emissions The major combustion-generated pollutants (not including CO.) by

tonnage are CO, NO,, PM, SOs, and VOCs [40]

Fig 2.Schematic drawing, causes and effects of air pollution: (1) greenhouse effect,

(2) particulate contamination, (3) increased UV radiation, (4) acid rain, (5)

increased ozone concentration, (6) increased levels of nitrogen oxides

Table 1 presents total estimated anthropogenic and combustion-generated emissions

of selected air pollutants in the United States Combustion-generated air pollution

can be viewed as originating through two major methods, although some overlap

occurs between the two The first of these methods is origination of pollution primarily from constituents in the fuel Examples of these "fuel-bome" pollutants are SO; and trace metals The second is the origination of pollutants through

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Vicinam is a developing country reaching the next stage of economical level Motorbikes are the main way of transportation for the moment The number af motorbikes is about 90% of all vchicles in Vietnam In 2006, there wore cightecn million operating, motorbikes, the average increase of motorbikes is 15-30% each year, Thus, the environmental pollution is very heavy, the emitted exhaust gases

each year are six million tons of CO;, sixty one thousand tons of CO, thirty five

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thousand tons of NO, , which excess the standard 1.5 — 5 times [63] In big cities,

the air pollution is becoming serious The air in Tanoi and Io Chi Minh City

contains dangerous levels of benzene and sulfur dioxide Levels of onc of Ihe most dangerous pollutants, microscopic dust known as PM10, are moderate compared with other developing Asian cities but could worsen if Vietnam chooses to build

coal-fired power plants to satiate demand for electricity, which is growing at double-digit annual rates [19] The most recent check of the level of dust and

other pollutants in the air shows that air pollution is increasing at an alarming rate

over many residential areas and main streets in IICMC, according to the (TICMC)

Environmental Protection Agency

Table 2 Annual Combustion-Generated Eimissions of Selected Pollutants by

Stationary Source Category in USA [401

Pollutant Stationary Fuc! Combustion Emissions

Utility Tndusirial Other % of total

Crossroads, Dinh Tien Hoang-Dien Bien Phu Intersection and areas along Hanoi Ilighway show the highest concentrations of air pollution in the city The agency’s

monitoring also showed that levels of lead, benzene, nitrogen dioxide and noise around the city have been increasing at a faster rals Compared to year 2009, load content has inercased by 2.2 times and benvana by 1.4 times

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Table 3 Percents of pollutants in Buro in 1994 %) [60]

*COVNM: compound organic volatile nol counting methane

Highway and on many city streets have contributed to the air pollution According

to the city’s Transport Department, the city has 3.8 million motorbikes, 300,000 cars and 30,000 industrial manufacturers discharging large amounts of smoke into

the air Some 60% of the motorbikes do not meet smog standards and some 80% of

the industrial smoke 1s still untreated [20]

Emission standards for passenger cars and light commercial vehicles are summarized in the following tahles

Table 4 EU emission standard for passenger car, g/km

1.2 Air pollution treatments

1.2.1 Original pollutant treatments

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co O:——— co,

The calalysis base on noble metals [10, 11] Moreover, some transition metal

oxides (Co, Co, Cu, Fe,W, Mn .) can be used for treating CO [12, 52, 53]

Method 2: watcr gas shift process can converted CO with participation of steam:

CO+H,O ————* CO.+H, AH»=-41.1kmdl This reaction was catalyzed by catalysts base on precious metal [35, 49]

Method 3: NO elsmination:

NO CO _, CO.) AN,

‘The most active catalyst is Rd [60] Resides, Pa calalysts were applied [23, 33]

b VOC treatments:

Volatile organic compounds (VOCs) arc emitted from a broad varicty of stationary sources, primarily manufactming processes, and are of concem for two primary reasons Firstly, VOCs react in the atmosphere in the presence of sunlight to form photochemical oxidants (including ozone) that are harmful to human health, Secondly, many of these compounds are harmful to human health at relatively low concentrations This second group of VOCs is referred to as hazardous air pollutants (IIAPs) and is included for potential regulation of the Clean Air Act

Amendments of 1990

See control technologies were uscd

Thermal oxidizers: destroy organic compounds by passing thom through high- temperature environments in the presence of oxygen In practicg, thenmal oxidizers

or incinerators typically operate by directing the pollutant stream into the combustion air stream, which is then mixed with a supplementary fuel (usually natural gas or fuel oil) and bumed,

Boilers or industrial furnaces that are already present on a plant site can also be used as thermal incincralion systems for appropriate streams of VOCs and organic HAPs,

Flares are a simple farm of thermal oxidation that does not use a confined combustion chamber As with other forms of thermal oxidation, flares often require

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supplemental fuel Flares are often used when the emission stream is intermittent or uncertain, such as the result ofa process upsel or emergency

Catalytic axidicers usc a calalyst {0 promote the Teaclion of the organic

compounds with oxygen, thercby requiring lower operating temperatures and reducing the need for supplemental fuel, Destruction efficiencies are typically near 95%, but can be increased by using additional catalyst or higher temperatures (and thus more supplemental fuel) The catalyst may be either ñxed or mobile (flud bed), Because catalysts may be poisoned by contacting improper compounds, catalytic oxidizers are neither as flexible nor as widely applied as [hermal oxidation systems Periodic replacernenl of Ihe catalyst is necessary, even with proper usage Adsorption systems rly on a packed bed containing an adsorbent material to capture the VOC or organic HAP compound(s) Activated carbon is the most common adsorbent material for these systems, but alumina, silica gel, and polymers are also used, Adsorbers can achieve removal efficiencies of up to 99 %, and in many cases allow for the recovery of the emitted compound Organic compounds such as benzene, methyl ethyl ketone, and toluene are examples of compounds that are effectively captured by carbon bed adsorption systems

Condensers are used to reduce the concentrations of VOCs and organic TIAPs by Iowering the lemperattro of the emission stream, thereby condensing those compounds Condensers arc most often uscd to reduce pollutant concentrations before the emission stream passes into other emission reduction systems such as thermal or catalytic oxidizers, adsorbers, or absorbers

Biofilters rely on microorganisms to feed on and thus destroy the VOCs and orgamc HAPs In these systems, the emission stream must come into direct contact with a filter containing the microorganism for sufficient time for the bioreaction to occur Although biofilters can have lower overall costs than ofher technologics, technical problems, such as proper matching of the emission stream and the microorganisins, long-term operational stability, and disposal of the resulting solid

wastes, may prevent their use in patticular situations [40]

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c, NO, treatments

NO, formed by the combustion of fuel in air is typically composed of grealer than

90% NO, with NO; making up the remainder Unfortunalcly, NO is not amenable to

fluc gas scrubbing, processus, as SO, is Au undetstanding of the chemistry of NO,

formation and destruction is helpful in understanding emission-control technologies for NO,

Becanse the rate of NO, formation is so highly dependent upon temperature as well

as local chemistry within the combustion environment, NO, is ideally suited to control by means of modifying the combustion condilions There are several meihods of applying these combustion modification NO, controls, ranging from

reducing the overall excess air levels in the combustor to burners specifically

designed for low NO, emissions [40]

Tuble 5 Emission Reduction from Different NO, Coniral Technologies [40]

Emission Reduction,

%

Overfire air (OFA) Pulverized —coal-fired- boilers 5-20

Stoker-fired coal boilers Flue gas recirculation (FRG) | Nalural- gas - fired boiler 20-50

Low NO, bumer (LNB) Natural- gas - fired boiler 40-60

Pulverized coal, tangentially fired [35-45 Pulverized coal, wall fired boiler 40-65

pulverized-coal main fuel Coal reburn fuel with pulverized 40-60 coal main facl

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L2.2 Treatments of simultaneous three pollutants — three-way catalysts

a Method 1: Il can be treated simultancous three pollutants (NO,, CO, 1IC) by designing successive oxidalion and reduction converters The main reactions

in treatment process are:

Reduction reaction: NO = 4 N, +4 O»

Oxidation reactions: CO + 40: CO;

CyHy ~ (x+y/4) + x COs + y/2 HO Steam formed in process reacts with CO to form CO, and H Thus, some Teactions occur:

COFHO + CO.+Hy NO+52H, >NH,+H.0 NH; + 5/4 ©, + NO ~ 3/2 HO

In this method, reduction converter only operates well in excess fuel condition Furthermore, NH; can be formed in reduction condition This pollutant will be converted into NO-another pollutant in oxidation media [28]

gas

HC + CO.+ H.0

Fig 3 Scheme of successive two converter made!

b Method 2: The basic reactions for CO and HC in the exhaust are oxidation with the desired product being CO-, while the NO, reaction is a reduction with the desired product being Nz and H.O, A catalyst promotes these reactions at lower temperatures than a thermal process giving the following

desired reactions for HC, CO and NO,:

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1.2.3 Three-way catalyst characteristic

There are some common components, which represent the state-of-art of the wash-

coating composition:

+ Alumina, which is employed as a high surface area support

+ CeO.-Z10: mixed oxides, principally added as oxygen storage promoters

+ Noble metals (NM = Rh, Pt and Pd) as active phases

+ Barium and/or lanthanum oxides as stabilizers of the alumina surface area [65]

Today the required conversion of pollutants is greater than 95%, which is attained

only when a precise control of the A/F (air to fuel ratio) is maintained, i.e within a narrow operating window Accordingly, a complex integrated system is employed for the control of the exhaust emissions, which is aimed at maintaining the A/F ratio

as close as possible to stoichiometry (Fig 4), To obtain an efficient control of the

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A/F ratio the amount of air is measured and the fuel injection is controlled by a computerized system which uses an oxygen sensor located at the inlet of the

catalytic converter The signal from this sensor is used as a feedback for the fuel

and air injection control loop A second sensor is mounted at the outlet of the

catalytic converter (Fig 4) [25]

Alll the above reactions required some heat or temperature on the catalyst surface for the reaction to occur When the automobile first starts, both the engine and catalyst are cold After startup, the heat of combustion is transferred from the engine and the exhaust piping begins to heat up Finally, a temperature is reached

within the catalyst that initiates the catalytic reactions This light-off temperature

and the concurrent reaction rate is kinetically controlled; i.e depends on the

chemistry of the catalyst since the transport reactions are fast Typically, the CO

reaction begins first followed by the HC and NO, reaction When all three reactions are occurring, the term three-way catalyst or TWC is used Upon further heating,

the chemical reaction rates become fast and the overall conversions are controlled

by pore diffusion and/or bulk mass transfer Figure 5 shows a typical response of a TWC catalyst as a function of the engine air to fuel ratio

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Synthesis and catalitic properties oƒ catalyst system basedl on CeO›:— ZrO: for the

complete oxidation of hydrocarbon to treat motorevele's exhaust gases

history of three-way catalyst [22] The monolith can be thought of as a series of parallel tubes with a cell density ranging from 300 to 1200 cpsi Advances in monolith technology, catalyst-mounting methods, flexibility in reactor design, low pressure drop and high heat and mass transfer rates, are the main reasons the

monolithic support dominates the entire market as the preferred catalyst support

Ceramic materials were chosen for the initial monolith and they still dominate the market The preferred material is called cordierite (synthetic cordierite has a composition approximating 2MgO, SSiO, and 2Al:O; and a softening point

>1300s€) [10] In preparing the catalyst, this desirable property has to be matched

by the thermal expansion properties of the catalyst carrier or wash-coat to prevent a mismatch in thermal properties Figure 6 shows the surface coating on a modem

TWC,

phate Top

Botton Coat Cede support

Honeyeomb' cordierite

Fig 6 Wash-coats on automotive catalyst can have different surface structures as

shown with SEM micrographs

Today, cordierite monoliths of 400 cpsi and 0.004 in wall thickness and 600 epsi and 0.004 in wall thickness are available [10] Monoliths of 900 and 1200 cpsi

have been made and tested in road-simulated aging and offer benefits for the super ultra low level vehicle (SULEV) type vehicles Recently, metallic monolith

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structures are being used in certain niche markets for exhaust control because they can be made with thinner walls and have opan (rontal areas close to 90%, allowing lower pressure drop Cell densities >400 opsi can be used which permits smaller catalyst volumes and smaller converters The base matcrial of construction is a feutitic stainless steel alloy having iron/chromefaluminunviare earths Typical

monoliths have 400 and 600 cpsi with 0.002 in wall thickness By the year 2000,

approximately 30 years of catalyst technology development have been devoted to

the automotive exhaust catalyst Fignre 6 shows a typical auto catalyst design

Along with Ihe advances in calalyst technology, the aulomotive engineers were developing new engine platforms and new scnsor and control iechnology This tas resulted in the full integration of the catalyst into the emission control system The catalyst has become integral in the design strategy for vehicle operation During this time period the auto catalyst has progressed through the following development

Oxidation catalyst ‘Three-way catalyst Thigh temperature

- Bend and monolil: -HC, C0 and NO, Three-way calalysl

-EC and CO pmiedone |_, -PURAtasedcatalyst |_,| - Stabilized Ce with Zr oaly + Ce onygen storage - PƯRh, PdfRh and

- Stabilized alumina

Ra lo emission “vehicles Low emission Vehicles sca Ve ‘All Palladium three - :

~ Hinh tempetamre close - High temperatnre way catalyst

‘i lose couple catalyst - Layeced coating

approaching 105 29pteding TC bilized Ca with #r

“Thetearing volume = Underfloor catalyst underfloor catalyst, high

precious meral loading

Fig 7 Improvement irend of catalytic converter

Additional background information on the olber Lechnology developments from

1970 to 1995 van be found in [16]

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1.3.International and Vietnam researches on catalyst for exhaust gas treatment 13.1 International researches

Three-way calalysl (TWC) is one of new methads for exhaust treating now Il can

be transformed polluted agents approximately 100% in large temporature range to

reach Euro III and IV standards Catalysts are classified to some groups beyond metal characteristic:

a Noble metallic catalyst: Noble metal catalysts have received considerable attention for more than 20 years for used in automotive emission control systems, [37] essentially base on Pt group ex: Pt, Pd, Rh on supports Supports can be CeO ZrOn, AlOs, mixtures of some oxides Catalyst based on noble melal exhibited high

catalytic activity in pollutant treatment and these catalysts were used oxtensively

Containing Pd catalyst was researched by Jiangiang Wang et al.[66] For fresh catalyst it can be observed that both Pd/CZ (Ce-Z1) and Pd¿CZ8 (Ce-Zr-§r) show the almost same oxidation activity for CO, the conversion of which can reach almost 100% under 2> 1 conditions, but descend as decreasing 4 -valule under A <1 conditions (A: the theoretical stoichiometric value and 2 can be calculated A= (20, INOY (10C3I I, CO)

Pd supported on Ce-Zir-La-AlsO3 was used for transforming COQ, CslTe, NO With these fresh calalytic systerns, the conversions are 100% af above 240, 300, 340°C far

CO, NO, CsH, respectively And opcraling temperatures for aged catalysts arc higher [34] Furthermore, Palladium catalysts were prepared by impregnation on CeO.-

Z1O-Al,O3 (CZA} and CeQ:-Z2O:-Al:Oi-La:O; (CZALa) for CH¡, CO and NOx treatment in the mixture gas simulated the exhaust from natural gas vehicles (NGVs) operated under stoichiometic condition was investigated by Xiaoyu Zhang [87]

In high temperature (above 300°C), Pd is suitable whereas Pt is better in low

temperature [60] F Dong and collcagucs rescarch investigalion of the OSC

performance of PYCeO,Z10.,¥20; catalysts by CO oxidation and %0/"0 isotopic exchange reaction and obtained good results They indicated that the development

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Sudhanshu Sharma showed thal catalytic activity of cordierite honeycomb by a completely new coating method for the oxidation of major hydrocarbons in cxhaust gas Weight of active catalyst can be varied from 0.02 wi% to 2 wt% which is sufficient but can be loaded even up to 12 wt% by repeating dip dry combustion Adhesion of catalyst to cordierite surface is via oxide growth, which is very strong

in coemparison with CeasZTa;O; TWC [22]

Ana Iglssias et al [23] showed that the behaviors of a seriss of Pá-M bímetallic calalysls for CO oxidation and NO reduction processes has been tested and comparcd with thal of monometallic Pd toferences The calalytic properties display a strong dependence on the degree of interaction which exisis between the metals in the calcinations state For CO oxidation with oxygen, the second metal

plays no significant role except im the case of PACuCZ, (Ce-Z)

Li-Ping Ma et al.[37] investigated “Kinetic study of three-way catalyst of

automotive exhaust gas: modeling and application” The results show the catalytic

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Daniela Meyer Fernandes and co-worker used the commercial Pd/Rh-based automotive calalyst, The catalysts were evaluated for CO and propane oxidation with a stoichiometric gas mixture similar to engine exhaust gas The catalytic activity results, reported as T,, (convert 50% amount of gas) values, were consistent with ageing temperature and time, In spite of the severe thermal impacts caused by ageing, evidenced by the characterization results, the commercial catalyst coud still convert 100% of CO at 450°C [7],

HU Chunmuing et al [4] showed that the Pt/Pd/Rh three-ways catalyst was prepared using a high-performance Ce ssZt03s¥0osL@o 050: solid solution and high surface area I_a-stabilized alumina (1.a/Al,Os) as a wash-coal layer The activity anid durability of the catalysts under simulated conditions and aclual vehicle test conditions were studied, The results revealed that CeossZinasYousLaaesCh solid solution maintains superior textual and oxygen storage properties, and LALO, has superior textual properties, The catalyst had high low-temperature activity, wide ait-to-fuel ratio windows, and good thermal stability, The results from the emission test of a motorcycle showed that the catalyst can meet Buro III emission requirements

Some added metals not only increase thennal resistant of supports but also inercase oxygen storage capacity, redox propertics and calalytic activity of calalyst The effect of Lav; on the physicochemical propertics of supports and catalysts was characterized by various techniques La:O; restrained effectively the sintering

of crystallite particles, maintained the crystallite particles in nanoscale and

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stabilized the crystal phase after calcinations at 1000:C La,0; improved the textural properties, reducibilily and OSC of composite supporis Activily testing resulls showed thal the calalysts exhibit excellent activities for the simullancous removal of methane, CO and NO, in the simulated exhaust gas The catalysts supported on CZALa showed remarkable thermal stability and catalytic activity for the three pollutants, especially for NO,, The prepared palladium catalysts have high ability to remove NO,, CH, and CO, and they can be used as excellent catalysts for the purification of exhaust from NGVs operated under stoichiometric condition The catalysis reporled in this work also have significant potential in industrial application bocanse of their high performance and low cosL

A Papavasiliou and his collcague idenfied that ccria-zirconia solid solution yields

an improvement in ceria’s oxygen storage capacity (OSC), redox properties, thermal resistance and catalytic activity at low temperatures, These improved

properties originate from the structural defects induced by Zr*' incorporation in

ceria lattice which enhances mobility of bulk oxygen ions Trivalent cations such as

: La, ¥*, Ga* favour phase homogeneity of the CeO-—ZrO, solid solution and

improve OSC even at low temperatures [50]

b Perovskite catalysts

D Fino and colleague realized thal the LaMing ;Fo, 0; catalyst was found ta provide the best performance of combustion of methane Further catalyst development allowed to maximize the catalytic activity of this compound by promoting, it with CeO, (1:1 molar ratio) and with 1 wt% Pd This promoted catalyst was lined on cordierite monoliths in a †-À1;O;-supported form [8]

Following L Forni’s investigation, series of La,,Ce,CoOn, perovskite-type

catalysts, with x ranging from 0 to 0.20, showed to be quite active for reduction of

NO by CO and for oxidation af CO by air oxygen al lemperalures ranging from 373

to 723 K [9]

Hirohisa Tanaka et al.[58] showed that one of the most important issues of

automotive catalysts is the endurance of fluctuations between reductive and

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oxidative (redox) atmospheres at high temperatures exceeding 1173 K The calalytic activity and structural slabilily of LagsCe,1Co1-,Fey O: peravskite catalysts (x - 0, 0.2, 6.4, 0.6, 0.8 and 1.0), both in powder and monolithic forms, were

investigated after aging treatments in real and simulated “model” automotive

exhaust gases

c, Base metallic catalysts

Some authors used base metals for exhaust gas treatment Sander Stegenga and colleague realized that containing Cu-Cr catalytic activity as well as noble catalyst for redox reaction The support is AlLOs (dp from 105 to 145 pm, surface area —

195mg) [56]

@ Metallic oxide catalysts

JIA Liwei showed that redox performances of ceria-based materials could be enhanced by synergetic effects between Mn-O and Ce-O Fresh and aged samples were characterized with the fluorite-rype cubic structure similar to CeO, and furthermore, the thermal stability of Mn, CeosO, materials was improved by the introduction of some Zr atoms [36]

Masakaini Ozawa [18] described as the examples of the high potential of rare earth modification in alumnina-based catalyst as well as support The surface modification using Tare earths lo alumina Icad betlor heal-stable calalytic supporl with nanometer

order particles The effect of the La pre-modification on the thermal stability of transition metal catalysts was evident Using this effect, the La-modified, transition

metals-promoted alumina catalyst, e.g CuO, La AlO; is developed as an inexpensive de-NO, catalyst with heat stability,

K.A Bethke and co-worker indicated that a number of metal oxides are effective lean NO, reduction catalysts Incorporation of reducible transition metal ions into the metal oxides, such thal the transifion metal ions arc highly dispersed, greatly

incrasod the activity of the catalysis such that lean NO, reduction ocours readily at

temperatures below 573 K Mixed metal oxide catalysts of ZrO; containing Cu, Co,

Fe, and Ni, which are as active as the corresponding ZSM-S-based catalysts [1]

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e, Other catalysts

Some researchers are interested in some kind catalysts like thai : Cu-Z8M-5,

complexes catalyst MAX (M: transition metals such as: Cu, Fe, Co, Ni, A: 80,7

SO." anion, X 3-amino-1,2,4 triazol) was condensed with formaldehyde on porous

supporter ( silica gel, Al,©,, bentonite, zeolite), Ag catalyst or Ag compound ( halogen, oxide, sulfate, phosphate} on Sr oxide; and may be added Al.Os, Tid: l0 55]

L Keiski showed that metal substrate ZSM-5 zeolites ion-exchanged with copper are effective calalysts in the elimination of nitrogen oxides fram lean automotive exhaust gascs when propene works as a reduclant Some co-calions improve the

catalytic activity of Cu-ZSMS [27]

1.3.2 Rescarches in Vietnam

In Vietnam, exhaust gas treatment was researched in recent years However, it was not studied as much as in the world Authors introduced essentially some catalysts for single pollutant treatment,

Le Thi Ioai Nam studied on Au-ZSMS catalysts for carbon monoxide oxidation to carbon dioxide The resull showed that catalytic aclivi

can be affected at very low temperahe Cataiylic activity increases when lemperalure increases and il is more preeminent than some systems (Awa-Fe-O; AwFe 1:19), Pở/ y-Al2O;) [44]

Tran Thi Nhu Mai and co-worker used of V-0,-TiO,/Me,0, (Me= Mo, Cu, Ce)

catalyst supported on honeycomb-texture veramic Catalysts properties were

estimated by LPG advanced oxidation reaction The reaction temperature range was

from 350 to 400°C to reach 100% conversion [39]

Author Neuyen Van Quy researched Ap-Co system for selective catalytic reduction

of NO, by propylene in the presence of excess oxygen At about 240°C, the oxidation

of propylene observed with the strong formation of COs, The consumption of NO, was nearly 100% below temperature range The strong formation of CO, shows that the catalyst is a good oxidation one [51]

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‘Tran Thi Minh Neuyet studied de©, properties of La; „8t,CoO; perovskiteicomplex oxides The results showed thal calalyst with molar ralios Taa:Sr:Co—0.4:0.6:1; a single phase peravskite exhibited only an oxidation function, while Ihe product with three

phases realized three functions of DeNO, reaction The conversion was 40% [46]

Author Le Minh Thang synthesized some catalysts such as: Ni/y-AlLO,/Cordierite (5% Ni, 10% y-Al:O;), Co-AlaOyCordierite (5% Co, 10% +-AlOj), Ni-Co#- AI.O;iCordierile (2.5% Ni, 2.5% Co, 10% +ALO;) for complete oxidation of hydrocarbon They have suitable operation temperature is from 350 to 400°C

Containing Co catalysts are beller (han Ni-catalysts in mhexane oxidation and cquivalont with noble calalyst, The maximum conversion was 80 % [60]

13.3 The imperative task, the aim and the rescarch direction of the thesis

The imperative task of the th

‘As mentioned previously, environmental pollution from motoreycle in Vietnam is significant since the number of motorcycle used in Vietnam is very high However, expensive and complex catalytic converters may not be welcome in a developing country like Vietnam Thus, the catalysts shotild not be noble catalysts (PL, Pd ) as normal used and studied in the world

The aim of the thesis

Therefore, the objective of this project is (o study and find oul optimal catalysts for treatment of motorcycle exhaust gases The expected catalysts should have better activity to treat exhaust gases, longer lifetime, low cost, be able to operate at low temperature and require very little modification of motorcycle’s design, which can help to apply it easier (even with being used motor bikes} in a developing country like Vietnam The catalysis should be fonnd from metal oxides like cerium, vanadium, titanium To make the converters mare simple, calalyals should work at low lomperalure, thus the heat of the cxhaust gas flow is cnough for the reaction, Catalysts should also work under the condition of lacking oxygen

The new direction of the research

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In the world, noble metallic catalysts such as Pt, Rh and Pd were used for treating gaseous emission fram fuel combustion, The catalytic activily is high but decrease rapidly al high temperature These systems are poisoned casily in harsh condition and very expensive They aren’t suitable in developing country like Vietnam,

Meanwhile, some catalysts base on metal such as Co, Ni, Fe may also have high activity (because these metals are in VIII and IB group as noble metals) but cheaper than noble metals

Our proposal is to synthesize catalysts from inexpensive components Since these metals are easier 1o be oxidized than well-known used noble metals, the oxide forms

of these components should be used instead of the melal forms Ta make the convertcrs more simple, catalysts should work at low temperatures, the temperature

of the exhaust gas flow The catalysts should also work under the condition of lacking, oxygen since the normal composition of exhaust gases in motor engines only contains a small amount of oxygen, Catalysts should accelerate many different reactions from complete oxidation to reduction; therefore a multi component system with multi functions is necessary Based on the desired properties described above, this project will focus on the synthesis and characterization of catalyst: CeO for its high capacity to store oxygen, ZrO» for ils high conductivity and possibility 10

converl NO,, SiO for its ability 10 break carbon-carbon bonds, V0; for ils ability

to brcak oxygen — oxygen bonds, Ni to conver! hydrocarbons

In these metallic oxides, CeO, and ZrO, were paid attention because of their advanced characteristics, CeO, has been widely used in automotive emission control because it can store or release oxygen under oxygenean or zich conditions and promoted the dispersion and catalytic activity of noble metal, However, CeO; will deactivate significantly at high temperature due to the loss of surface area and oxygen slorage capacity 1 has hoon shown thal the introduction of forcign cation with smaller ionic radius than Cc" can favorably modify the structure of ccria—

Zirconia so as to improve its properties [66]

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Tiêu đề	Synthesis and catalytic properties of catalyst system based on CeO2-ZrO2 for the complete oxidation of hydrocarbon to treat motorcycle's exhaust gases
Tác giả	Nguyen The Tien
Người hướng dẫn	Associate Professor, Doctor Le Minh Tuan
Trường học	Hanoi University of Technology
Chuyên ngành	Organic and Petrochemical Technology
Thể loại	Thesis
Năm xuất bản	2010
Thành phố	Hanoi

Định dạng
Số trang	101
Dung lượng	1,75 MB