Sythesize and investigate the catalytic activity of three-way catalysts based on mixed metal oxides for the treatment of exhaust gases from internal combustion engine

- MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY NGUYEN THE TIEN SYNTHESIZE AND INVESTIGATE THE CATALYTIC ACTIVITY OF THREE-WAY CATALYSTS BASED ON MIXED METAL OXIDES FOR THE TREATMENT OF EXHAUST GASES FROM INTERNAL COMBUSTION ENGINE CHEMICAL ENGINEERING DISSERTATION HANOI-2014 MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY NGUYEN THE TIEN SYNTHESIZE AND INVESTIGATE THE CATALYTIC ACTIVITY OF THREE-WAY CATALYSTS BASED ON MIXED METAL OXIDES FOR THE TREATMENT OF EXHAUST GASES FROM INTERNAL COMBUSTION ENGINE Speciality: Chemical Engineering Code: 62520301 CHEMICAL ENGINEERING DISSERTATION SUPERVISOR: ASSOCIATE PROFESSOR, DOCTOR LE MINH THANG HANOI-2014 Synthesize and investigate the catalytic activity of three-way catalysts based on mixed metal oxides for the treatment of exhaust gases from internal combustion engine Nguyen The Tien 1 ACKNOWLEDGEMENTS This PhD thesis has been carried out at the Laboratory of Environmental Friendly Material and Technologies, Advance Institute of Science and Technology, Department of Organic and Petrochemical Technology, Laboratory of the Petrochemical Refinering and Catalytic Materials, School of Chemical Engineering, Hanoi University of Science and Technology (Vietnam) and Department of Inorganic and Physical Chemistry, Ghent University (Belgium).
- She helped me a lot in the scientific work with her thorough guidance, her encouragement and kind help.
- Nguyen The Tien September 2013 Synthesize and investigate the catalytic activity of three-way catalysts based on mixed metal oxides for the treatment of exhaust gases from internal combustion engine Nguyen The Tien 2 COMMITMENT I assure that this is my own research.
- All the data and results in the thesis are completely true, was agreed to use in this paper by co-author.
- Le Minh Thang Nguyen The Tien Synthesize and investigate the catalytic activity of three-way catalysts based on mixed metal oxides for the treatment of exhaust gases from internal combustion engine Nguyen The Tien 3 CONTENT OF THESIS LIST OF TABLES 6 LIST OF FIGURES 7 INTRODUCTION 10 1 LITERATURE REVIEW 11 1.1 Air pollution and air pollutants 11 1.1.1 Air pollution from exhaust gases of internal combustion engine in Vietnam 11 1.1.2 Air pollutants Carbon monoxide (CO Volatile organic compounds (VOCs Nitrous oxides (NOx Some other pollutants 12 1.1.3 Composition of exhaust gas 13 1.2 Treatments of air pollution 14 1.2.1 Separated treatment of pollutants CO treatments VOCs treatments NOx treatments Soot treatment 15 1.2.2 Simultaneous treatments of three pollutants Two successive converters Three-way catalytic (TWC) systems 17 1.3 Catalyts for the exhaust gas treatment 19 1.3.1 Catalytic systems based on noble metals (NMs) 20 1.3.2 Catalytic systems based on perovskite 21 1.3.3 Catalytic systems based on metallic oxides Metallic oxides based on CeO Catalytic systems based on MnO Catalytic systems based on cobalt oxides Other metallic oxides 26 1.3.4 Other catalytic systems 27 1.4 Mechanism of the reactions 28 1.4.1 Mechanism of hydrocarbon oxidation over transition metal oxides 28 1.4.2 Mechanism of the oxidation reaction of carbon monoxide 29 1.4.3 Mechanism of the reduction of NOx 31 1.4.4 Reaction mechanism of three-way catalysts 33 1.5 Aims of the thesis 35 2 EXPERIMENTAL 37 2.1 Synthesis of the catalysts 37 2.1.1 Sol-gel synthesis of mixed catalysts 37 2.1.2 Catalysts supported on γ-Al2O3 37 2.1.3 Aging process 38 2.2 Physico-Chemistry Experiment Techniques 38 2.2.1 X-ray Diffraction 38 Synthesize and investigate the catalytic activity of three-way catalysts based on mixed metal oxides for the treatment of exhaust gases from internal combustion engine Nguyen The Tien 4 2.2.2 Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) 40 2.2.3 BET method for the determination of surface area 40 2.2.4 X-ray Photoelectron Spectroscopy (XPS) 40 2.2.5 Thermal Analysis 41 2.2.6 Infrared Spectroscopy 41 2.2.7 Temperature Programmed Techniques 42 2.3 Catalytic test 43 2.3.1 Micro reactor setup 43 2.3.2 The analysis of the reactants and products Hydrocarbon oxidation CO oxidation Soot treatment Three -pollutant treatment 47 3 RESULTS AND DISCUSSIONS 48 3.1 Selection of components for the three-way catalysts 48 3.1.1 Study the complete oxidation of hydrocarbon Single and bi-metallic oxide Triple metallic oxides 51 3.1.2 Study the complete oxidation of CO Catalysts based on single and bi-metallic oxide Triple oxide catalysts MnCoCe Influence of MnO2, Co3O4, CeO2 content on catalytic activity of MnCoCe catalyst 59 3.1.3 Study the oxidation of soot 62 3.2 MnO2-Co3O4-CeO2 based catalysts for the simultaneous treatment of pollutants 66 3.2.1 MnO2-Co3O4-CeO2 catalysts with MnO2/Co3O MnO2-Co3O4-CeO2 with the other MnO2/Co3O4 ratio 68 3.2.3 Influence of different reaction conditions on the activity of MnCoCe Activity for the treatment of soot and the influence of soot on activity of MnCoCe Influence of aging condition on activity of MnCoCe catalysts The influence of steam at high temperature The characterization and catalytic activity of MnCoCe 1-3-0.75 in different aging conditions 77 3.2.6 Activity of MnCoCe 1-3-0.75 at room temperature 80 3.3 Study on the improvement of NOx treatment of MnO2-Co3O4-CeO2 catalyst by addition of BaO and WO3 81 3.4 Study on the improvement of the activity of MnO2-Co3O4-CeO2 catalyst after aging by addition of ZrO2 84 3.5 Comparison between MnO2-Co3O4-CeO2 catalyst and noble catalyst 87 4 CONCLUSIONS 91 REFERENCES 92 LIST OF PUBLICATIONS 100 Synthesize and investigate the catalytic activity of three-way catalysts based on mixed metal oxides for the treatment of exhaust gases from internal combustion engine Nguyen The Tien 5 ABBREVIATION TWCs: Three-Way Catalysts NOx: Nitrous Oxides VOCs: Volatile Organic Compounds PM10: Particulate Matter less than 10 nm in diameter NMVOCs: Non-Methane Volatile Organic Compounds HC: hydrocarbon A/F ratio: Air/Fuel ratio λ: the theoretical stoichiometric value, defined as ratio of actual A/F to stoichiometric.
- λ = 1 at stoichiometry (A/F = 14.7) SOF: Soluble Organic Fraction DPM: Diesel Particulate Matter CRT: Continuously Regenerating Trap NM: Noble Metal Cpsi: Cell Per Inch Square In.: inch CZ (Ce-Zr): mixtures of CeO2 and ZrO2 CZALa: mixtures of CeO2, ZrO2, Al2O3, La2O3 NGVs: natural gas vehicles OSC: oxygen storage capacity WGS: water gas shift LNTs: Lean NOx traps NSR: NOx storage-reduction SCR: selective catalytic reduction SG: sol-gel MC: mechanical FTIR: Fourier-Transform Infrared Eq.: equation T100: the temperature that correspond to the pollutant was completely treatment Tmax: The maxium peak temperature was presented as reference temperature of the maximum reaction rate in TG-DTA (DSC) diagram Vol.: volume Wt.
- weight Cat: catalyst at: atomic min.: minutes h: hour ppm: part per milllion ppb: part per billion Synthesize and investigate the catalytic activity of three-way catalysts based on mixed metal oxides for the treatment of exhaust gases from internal combustion engine Nguyen The Tien 6 LIST OF TABLES Table 1.1 Example of exhaust conditions for two- and four-stroke, diesel and lean-four-stroke engines Table 1.2 Adsorption/desorption reactions on Pt catalyst Table 1.3 Surface reactions of propylene oxidation Table 1.4 Surface reactions of CO oxidation Table 1.5 Surface reactions of hydroxyl spices, NO and NO Table 2.1 Aging conditions of MnCoCe catalysts Table 2.2 Strong line of some metallic oxides Table 2.3 Binding energy of some atoms Table 2.4 Specific wave number of some function group or compounds Table 2.5 Composition of mixture gases at different reaction conditions for C3H6 oxidation Table 2.6 Composition of mixture gases at different reaction conditions for CO oxidation Table 2.7 Composition of mixture gases at different reaction conditions for treatment of CO, C3H6, NO Table 2.8 Temperature Program of analysis method for the detection of reactants and products...45 Table 2.9 Retention time of some chemicals Table 3.1 Quantity of hydrogen consumed volume (ml/g) at different reduction peaks in TPR-H2 profiles of pure CeO2, Co3O4, MnO2 and CeO2-Co3O4, MnO2-Co3O4 chemical mixtures Table 3.2 Consumed hydrogen volume (ml/g) of the mixture MnO2-Co3O4-CeO Table 3.3 Adsorbed oxygen volume (ml/g) of some pure single oxides (MnO2, Co3O4, CeO2) and chemical mixed oxides MnCoCe Table 3.4 Surface atomic composition of the sol-gel and mechanical sample Table 3.5 Tmax of mixture of single oxides and soot in TG-DTA (DSC) diagrams Table 3.6 Catalytic activity of single oxides for soot treatment Table 3.7 Tmax of mixture of multiple oxides and soot determined from TG-DTA diagrams Table 3.8 Catalytic activity of multiple oxides for soot treatment at 500oC Table 3.9 Soot conversion of some mixture of MnCoCe 1-3-0.75 and soot in the flow containing CO: 4.35%, O2: 7.06%, C3H6: 1.15%, NO: 1.77% at 500oC for 425 min Table 3.10 Specific surface area of MnCoCe catalysts before and after aging in the flow containing 57% vol.H2O at 800oC for 24h Table 3.11 Consumed hydrogen volume (ml/g) of the MnCoCe 1-3-0.75 fresh and aging at 800oC in flow containing 57% steam for 24h Table 3.12 Specific surface area of MnCoCe 1-3-0.75 fresh and after aging in different conditions Table 3.13 Specific surface area of catalysts containing MnO2, Co3O4, CeO2, BaO and WO Table 3.14 Specific surface area of some catalyst containing MnO2, Co3O4, CeO2, ZrO2 before and after aging at 800oC in flow containing 57% steam for 24h Table 3.15 Specific surface area of noble catalyst and metallic oxide catalysts supported on γ-Al2O Synthesize and investigate the catalytic activity of three-way catalysts based on mixed metal oxides for the treatment of exhaust gases from internal combustion engine Nguyen The Tien 7 LIST OF FIGURES Figure 1.1 Micrograph of diesel soot, showing particles consisting of clumps of spherules [110].13 Figure 1.2 A typical arrangement for abatement of NOx from a heavy-duty diesel engine using urea as reducing agent Figure 1.3 Principle of filter operation (1) and filter re-generation (2) for a soot removal system, using fuel powered burners Figure 1.4 The working principle of the continuously regenerating particulate trap Figure 1.5 Scheme of successive two-converter model Figure 1.6 Three- way catalyst performance determined by engine air to fuel ratio Figure 1.7 Diagram of a modern TWC/engine/oxygen sensor control loop for engine Figure 1.8 Wash-coats on automotive catalyst can have different surface structures as shown with SEM micrographs Figure 1.9 Improvement trend of catalytic converter Figure 1.10 Scheme of catalytic hydrocarbon oxidation.
- H-hydrocarbon, C-catalyst, R1 to R5-labile intermediate, probably of the peroxide type Figure 1.11 Reaction cycle and potential energy diagram for the catalytic oxidation of CO by O Figure 1.12 Reaction pathways of CO oxidation over the metallic oxides Figure 1.13 Chemical reaction pathways of selective catalytic reduction of NOx by propane [99] 32 Figure 1.14 Principle of operation of an NSR catalyst: NOx are stored under oxidising conditions (1) and then reduced on a TWC when the A/F is temporarily switched to rich conditions Figure 1.15 Schematic representation of the seven main steps involved in the conversion of the exhaust gas pollutants in a channel of a TWC Figure 2.1 Aging process of the catalyst (1: air pump.
- 2,6: tube furnace, 3: water tank, 4: heater, 5,7: screen controller, V1,V2: gas valve Figure 2.2 Micro reactor set up for measurement of catalytic activity Figure 2.3 The relationship between concentration of C3H6 and peak area Figure 2.4 The relationship between concentration of CO2 and peak area Figure 2.5 The relationship between concentration of CO and peak area Figure 3.1 Catalytic activity of some mixed oxide MnCo, CoCe and single metallic oxide in deficient oxygen condition Figure 3.2 Catalytic activity of MnCo 1-3 and CeCo 1-4 catalysts in excess oxygen condition......49 Figure 3.3 C3H6 conversion of CeCo1-4 in different reaction conditions (condition a: excess oxygen condition with the presence of CO: 0.9% C3H6, 0.3% CO, 5% O2, N2 balance, condition b: excess oxygen condition with the presence of CO and H2O: 0.9% C3H6, 0.3% CO, 2% H2O, 5% O2, N2 balance Figure 3.4 XRD patterns of CeCo=1-4, MnCo=1-3 chemical mixtures and some pure single oxides Figure 3.5 Conversion of C3H6, C3H8 and C6H6 on MnCoCe 1-3-0.75 catalyst under sufficient oxygen condition Figure 3.6 SEM images of MnCo 1-3 fresh (a),MnCoCe 1-3-0.75 before (a) and after (b) reaction under sufficient oxygen condition (O2/C3H Figure 3.7 XRD pattern of MnCoCe 1-3-0.75 and original oxides Figure 3.8 CO conversion of some catalysts in sufficient oxygen condition Figure 3.9 SEM images of MnCo=1-3 before (a) and after (b) reaction under sufficient oxygen condition Figure 3.10 CO conversion of original oxides (MnO2, Co3O4, CeO2) and mixtures of these oxides in excess oxygen condition (O2/CO Figure 3.11 TPR H2 profiles of the mixture MnCoCe 1-3-0.75, MnCo 1-3 and pure MnO2, Co3O4, CeO2 samples Figure 3.12 IR spectra of some catalyst ((1): CeO2.
- (5):MnCoCe 1-3-0.75 (MC).
- (6): MnCoCe 1-3-0.75 (SG Synthesize and investigate the catalytic activity of three-way catalysts based on mixed metal oxides for the treatment of exhaust gases from internal combustion engine Nguyen The Tien 8 Figure 3.13 XRD pattern of MnCoCe 1-3-0.75 synthesized by sol-gel and mechanical mixing method Figure 3.14 XPS measurement of Co 2p region (a), Ce 3d region (b), Mn 2p region (c) and O 1s region (d) of the mechanical mixture (1) and chemical MnCoCe 1-3-0.75 sample Figure 3.15 XRD patterns of MnO2-Co3O4-CeO2 samples with MnO2-Co3O4=1-3(MnCoCe 1-3-0.17 (a), MnCoCe 1-3-0.38 (b), MnCoCe 1-3-0.75 (c), MnCoCe 1-3-1.26 (d).
- MnCoCe 1-3-1.88 (e Figure 3.16 XRD patterns of MnO2-Co3O4-CeO2 samples with MnO2-Co3O4=7-3: MnCoCe 7-3-4.29 (a), MnCoCe 7-3-2.5 (b) and MnCo=7-3 (c Figure 3.17 Specific surface area of MnCoCe catalysts with different MnO2/Co3O4 ratios Figure 3.18 Temperature to reach 100% CO conversion (T100) of mixed MnO2-Co3O4-CeO2 samples with the molar ratio of MnO2-Co3O4 of 1-3 (a) and MnO2-Co3O4=7-3 (b) with different CeO2 contents Figure 3.19 TG-DSC and TG-DTA of soot (a), mixture of soot-Co3O4 (b), soot-MnO2 (c), soot-V2O5 (d) with the weight ratio of soot-catalyst of Figure 3.20 XRD patterns of MnCoCe MnCoCeV MnCoCeV Figure 3.21 TG-DTA of mixtures of soot and catalyst (a: MnCoCe 1-3-0.75, b: MnCoCeV c: MnCoCeV d: MnCoCeV Figure 3.22 Catalytic activity of MnCoCeV in the gas flow containing 4.35% CO, 7.06% O2, 1.15% C3H6 and 1.77% NO Figure 3.23 C3H6 and CO conversion of MnCoCe catalyst with MnO2/Co3O4=1-3 (flow containing 4.35% CO, 7.65% O2, 1.15% C3H6 and 0.59% NO Figure 3.24 Catalytic activity of MnCoCe catalyst with MnO2-Co3O4 =1-3 (flow containing 4.35% CO, 7.06% O2, 1.15% C3H6, 1.77% NO Figure 3.25 SEM images of MnCoCe 1-3-0.75 (a), MnCoCe 1-3-1.26 (b), MnCoCe 1-3-1.88 (c).68 Figure 3.26 Catalytic activity of MnCoCe catalysts with ratio MnO2-Co3O4=7-3(flow containing 4.35% CO, 7.06% O2, 1.15% C3H6 and 1.77% NO Figure 3.27 Catalytic activity of MnCoCe 1-3-0.75 with different lambda values Figure 3.28 CO and C3H6 conversion of MnCoCe 1-3-0.75 in different condition (non-CO2 and 6.2% CO Figure 3.29 Catalytic activity of MnCoCe 1-3-0.75 at high temperatures in 4.35% CO, 7.65% O2, 1.15% C3H6, 0.59 % NO Figure 3.30 Catalytic activity of MnCoCe 1-3-0.75 with the different mass ratio of catalytic/soot (a: C3H6 conversion, b: NO conversion, c: CO2 concentration in outlet flow.
- d: CO concentration in outlet flow) at 500 oC Figure 3.31 Catalytic activity of MnCoCe (MnO2-Co3O4 =1-3) catalysts before and after aging at 800oC in flow containing 57% steam for 24h Figure 3.32 XRD patterns of MnCoCe catalysts before and after aging in a flow containing 57% vol.H2O at 800oC for 24h (M1: MnCoCe 1-3-0.75 fresh, M2: MnCoCe 1-3-0.75 aging, M3: MnCoCe 1-3-1.88 fresh, M4: MnCoCe 1-3-1.88 aging), Ce: CeO2, Co:Co3O Figure 3.33 SEM images of MnCoCe catalysts before and after aging at 800oC in flow containing 57% steam for 24h (a,d: MnCoCe 1-3-0.75 fresh and aging, b,e: MnCoCe 1-3-.26 fresh and aging, c,f: MnCoCe 1-3-1.88 fresh and aging, respectively Figure 3.34 TPR-H2 pattern of MnCoCe 1-3-0.75 fresh and aging at 800oC in flow containing 57% steam for 24h Figure 3.35 Catalytic activity of MnCoCe 1-3-0.75 fresh and after aging in different conditions ..78 Figure 3.36 XRD pattern of MnCoCe 1-3-0.75 in different aging conditions Figure 3.37 SEM images of MnCoCe 1-3-0.75 fresh and after aging in different conditions Figure 3.38 Activity of MnCoCe 1-3-0.75 after activation Figure 3.39 CO and C3H6 conversion of MnCoCe 1-3-0.75 at room temperature after activation 2h in gas flow 4.35% CO, 7.65% O2, 1.15% C3H6, 0.59% NO with and without CO Figure 3.40 XRD pattern of catalysts based on MnO2, Co3O4, CeO2, BaO and WO Synthesize and investigate the catalytic activity of three-way catalysts based on mixed metal oxides for the treatment of exhaust gases from internal combustion engine Nguyen The Tien 9 Figure 3.41 Catalytic activity catalysts based on MnO2, Co3O4, CeO2, BaO and WO3 in the flow containing 4.35% CO, 7.06% O2, 1.15% C3H6 and 1.77 % NO Figure 3.42 SEM images of catalysts containing MnO2, Co3O4, CeO2, BaO and WO Figure 3.43 Catalytic activity of MnCoCe 1-3-0.75 added ZrO2 fresh (a, c, e) and aged (b, d, f) in flow containing 4.35% CO, 7.65% O2, 1.15% C3H6 and 0.59% NO Figure 3.44 XRD pattern of MnCoCe 1-3-0.75 added 2% and 5% ZrO2 before and after aging at 800oC in flow containing 57% steam for 24h Figure 3.45 SEM images of MnCoCe 1-3-0.75 added 5% ZrO2 before (a) and after (b) aging at 800oC in flow containing 57% steam for 24h Figure 3.46 SEM image of 0.1% Pd/γ-Al2O3 (a), 0.5% Pd/γ-Al2O3 (b) and 10% MnCoCe/γ-Al2O3 (c Figure 3.47 TEM images of 0.1% Pd/γ-Al2O3 with different magnifications (a), (b) and 10% MnCoCe1-3-0.75/γ-Al2O Figure 3.48 STEM and EDX results of crystal phase of 10% MnCoCe/γ-Al2O3 sample Figure 3.49 Catalytic activity of MnCoCe supported on γ-Al2O3 (flow containing 4.35% CO, 7.06% O2, 1.15% C3H6, 1.77% NO Figure 3.50 Catalytic activity of 0.5% wt Pd and 20%, 40% MnO2-Co3O4-CeO2 supported on γ-Al2O3( flow containing 4.35% CO, 7.06% O2, 1.15% C3H6, 1.77% NO Synthesize and investigate the catalytic activity of three-way catalysts based on mixed metal oxides for the treatment of exhaust gases from internal combustion engine Nguyen The Tien 10 INTRODUCTION Environmental pollution from engine in Vietnam was more and more serious since the number of motorcycles used in Vietnam is increasing significantly.
- The development of the automotive industry attracts more attention on the atmosphere pollution from exhaust gases, and three-way catalysts (TWC) are the best way to remove these pollutants.
- In the world, precious metallic catalysts such as Pt, Rh and Pd were focused for three-way catalyst application and represented the key component, as the catalytic activity occurs at the noble metal (NM) centre.
- In Vietnam, NM catalysts (from Emitec company-Germany) have been tested for the treatment of exhaust gases of some kinds of motorbikes.
- Therefore, the recent research trends is the partial or complete substitution of precious metals in the catalytic converter by a less expensive components.
- Meanwhile, metal oxides are an alternative to NMs as catalysts for pollutant treatment.
- The aim of the thesis is to study on a catalytic system that exhibit high activity, high thermal resistance, low cost and easy to apply in treatment of exhaust gases.
- The most active single metal oxides are the oxides of Cu, Co, Mn, and Ni.
- Among all metal oxides studied, manganese and cobalt containing catalysts are low cost, environmentally friendly and relatively highly active.
- The catalytic properties of MnOx-based catalysts are attributed to the ability of manganese to form oxides of different oxidation states and to their high oxygen storage capacity.
- Appropriate combinations of metal oxides may exhibit higher activity and thermal stability than the single oxides.
- Moreover, it is necessary to lower temperature of the maximum treatment of toxic components in exhaust gas to enhance the application ability of metallic oxides.
- Thus, this study focuses on optimization of composition of the catalyst in order to obtain the best catalyst.
- The influence of activation, aging process to catalytic activity of the samples were also studied.
- The first chapter, the literature review, summarizes problems on air pollution, pollutant in exhaust gas, treating methods, catalytic systems mechanism of exhaust treatment.
- The second chapter introduces basic principles of the physico-chemical methods used in the thesis, catalyst synthesis, aging processes and catalytic measurement.
- Furthermore, the influence of aging and activation processes to the activity of the catalysts was investigated in details in this chapter.
- The last chapter (4) summarizes conclusions of the thesis.
- Synthesize and investigate the catalytic activity of three-way catalysts based on mixed metal oxides for the treatment of exhaust gases from internal combustion engine Nguyen The Tien 11 1 LITERATURE REVIEW 1.1 Air pollution and air pollutants Now a day, air pollution from exhaust gases of internal combustion engine is one of serious problems in the world and immediate consequences are hazards such as: acid rain, the greenhouse effect, ozone hole, etc.
- 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 [126].
- 1.1.1 Air pollution from exhaust gases of internal combustion engine in Vietnam Vietnam is a developing country reaching the next stage of economical level.
- Motorbikes are the main way of transportation for the moment.
- 1.1.2 Air pollutants Pollutants for which health criteria define specific acceptable levels of ambient concentrations are known as "criteria pollutants." The major criteria pollutants are carbon monoxide (CO), nitrogen dioxide (NO2), volatile organic compounds (VOCs), ozone, PM10, sulfur dioxide (SO2), and lead (Pb).
- NOx and SO2 are important in the formation of acid precipitation, and NOx and VOCs can real react in the lower atmosphere to form ozone, which can cause damage to lungs as well as to property [42].
- HC and CO occur because the combustion efficiency is 1500 ◦C) of the combustion process resulting in thermal fixation of the nitrogen in the air which forms NOx [43].
- 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 process (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 [41].
- In this field they are often divided into the separate Synthesize and investigate the catalytic activity of three-way catalysts based on mixed metal oxides for the treatment of exhaust gases from internal combustion engine Nguyen The Tien 12 categories of methane (CH4) and non-methane (NMVOCs).
- Other hydrocarbon VOCs are also significant greenhouse gases via their role in creating ozone and in prolonging the life of methane in the atmosphere, although the effect varies depending on local air quality.
- VOCs react in the atmosphere in the presence of sunlight to form photochemical oxidants (including ozone) that are harmful to human health [41].
- It is one of the several nitrogen oxides.
- NO2 is one of the most prominent air pollutants.
- Nitrous oxides can be formed by some reactions: N2 + O22NO NO + ½ O2NO2 In engine combustion, NOx is created when the oxygen (O2) and nitrogen (N2) present in the air are exposed to the high temperatures of a flame, leading to a dissociation of O2 and N2 molecules and their recombination into NO.
- Further oxidation of SO2, usually in the presence of a catalyst such as NO2, forms H2SO4, and thus acid rain.
- This is one of the causes for concern over the environmental impact of the use of these fuels as power sources [1, 41].
- Increased levels of fine particles in the air are linked to health hazards such as heart diseases, altered lung function and lung cancer [1, 41].
- from a dilution tunnel, is found to be in the form of agglomerates which are around 100 mm in size.
- The fundamental unit of the soot agglomerates are the spherules with diameters of 10–50 nm.
- The surface of the spherules has adhering hydrocarbon material or soluble organic fraction (SOF) and inorganic material (mostly sulphates).
- The SOF and other adsorbed species such as sulphates and water are captured by the soot in the gas cooling phase e.g.
- in the exhaust pipe of a diesel engine.
- The nitrogen BET area of a soot was found to be only 40% of the external surface area calculated for spherules whose diameter was measured by electron microscopy as seen in Figure 1.1 [110].
- Synthesize and investigate the catalytic activity of three-way catalysts based on mixed metal oxides for the treatment of exhaust gases from internal combustion engine Nguyen The Tien 13 Figure 1.1 Micrograph of diesel soot, showing particles consisting of clumps of spherules Composition of exhaust gas As shown in Table 1.1, the exhaust contains principally three primary pollutants, unburned or partially burned HCs, CO and nitrogen oxides (NOx.
- Table 1.1 Example of exhaust conditions for two- and four-stroke, diesel and lean-four-stroke engines [67] Exhaust components and condition a Diesel engine Four-stroke spark ignited- engine Four-stroke lean-burn spark ignited- engine Two-stroke spark ignited- engine NOx 350-1000 ppm 100-4000 ppm ≈ 1200 ppm 100-200 ppm HC 50-330 ppmCf 500-5000 ppmCf ≈1300 ppmCf ppmCf CO 300-1200 ppm ppm 1-3% O H2O CO SOx 10-100 ppmb 15-60 ppm 20 ppm ≈ 20 ppm PM 65 mg/m3 Temperature (test cycle) Room temperature-650oC (420 oC) Room temperature-1100 oCc Room temperature-850 oC Room temperature-1100 oC GHSV (h λ (A/F)d ≈ 1.8 (26.
- Synthesize and investigate the catalytic activity of three-way catalysts based on mixed metal oxides for the treatment of exhaust gases from internal combustion engine Nguyen The Tien 14 c Close-coupled catalyst.
- e Part of the fuel is employed for scavenging of the exhaust, which does not allow to define a precise definition of the A/F.
- They were devided into two categories: treatments of single pollutant and simultaneous treatment of pollutants.
- 1.2.1 Separated treatment of pollutants 1.2.1.1 CO treatments Method 1: Carbon monoxide can be converted by oxidation: CO + O2 CO2 The catalysts were based on NMs .
- Moreover, some transition metal oxides (Co, Ce, Cu, Fe, W, and Mn) could be used for treating CO [48-52].
- Method 2: water gas shift process could convert CO with participation of steam: CO + H2O CO2 + H2 ΔH0298K= -41.1 kJ/mol This reaction was catalyzed by catalysts based on precious metal [53].
- 1.2.1.2 VOCs treatments Catalytic oxidizers used a catalyst to promote the reaction of the organic compounds with oxygen, thereby requiring lower operating temperatures and reducing the need for supplemental fuel.
- Periodic replacement of the catalyst is necessary, even with proper usage [41].
- Catalytic systems based on NM, perovskite or, metal and metallic oxide .
- There are several methods of applying these combustion modification NOx controls, ranging from reducing the overall excess air levels in the combustor to burners specifically designed for low NOx emissions [41]

Xem thử không khả dụng, vui lòng xem tại trang nguồn
hoặc xem Tóm tắt