Structure-reactivity study of model and Biodiesel soot in model DPF regeneration conditions

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X-Ray Diffraction (XRD)

The X-ray diffraction was performed on PANalytical-Empyrean diffractometer (Japan Science) with CuKα radiation (λ = 0.154056 nm) to obtain some information about internal lattice parameters of soot. The X-ray tube was operated at 40 kV and 40 mA.
The XRD patterns of samples were recorded in the range of 10° ≤ 2θ ≤ 90° with a scanning step size of 0.02°. The stacking thickness of crystallites (D) and the crystalline length (L) as crystallite dimensions of soot samples can be calculated by applying the Scherrer equation to the bands 002 and 100, respectively, where K and K’ are the shape factors and β002 and β100 are the full widths at half maximum of the bands.

Temperature-Programmed Reduction (TPR)

The hydrogen temperature-programmed reduction (H2-TPR) profiles were obtained using a BELCAT-M (BEL-Japan) apparatus, equipped with a TCD. The materials were outgassed and activated at 400 °C for 1 h in Ar, then cooled down to room temperature and reduced until 700 °C in 5 vol.% H2/Ar at a heating rate of 8 °C/min.
30 mg of soot–catalyst mixture in tight contact was used for soot catalyst mixture in tight contact was used for soot temperaturetemperature–programmed reduction (sootprogrammed reduction (soot–TPR). The sample was heated from 80 to TPR). The sample was heated from 80 to 650 650 °°C at a ramp rate of 5 C at a ramp rate of 5 °°C/min in a pure Ar flow (100 ml/min). The cC/min in a pure Ar flow (100 ml/min). The consumption onsumption signals (COsignals (COxx concentration) of soot were monitored by a MS (mass spectrometry) concentration) of soot were monitored by a MS (mass spectrometry) detector (Figure 3detector (Figure 3–2).2).

Temperature–Programmed Desorption (TPD)Programmed Desorption (TPD)

The catalyst (50 mg) was outgassed at 450 °C°C under Ounder O22/Ar flow fo/Ar flow for 30 min to clean r 30 min to clean the surface and then cooled down to 350 the surface and then cooled down to 350 °C°C. NO and NO. NO and NO22 adsorptions in the catalyst adsorptions in the catalyst were separately performed in a Uwere separately performed in a U–shaped quartz reactor by the exposure in 400 ppm shaped quartz reactor by the exposure in 400 ppm NO/9% ONO/9% O22/Ar and 400 ppm NO/Ar and 400 ppm NO22/9% O/9% O22/Ar for 1 h. After that, the sample was /Ar for 1 h. After that, the sample was kept at kept at 80 80 °C°C in pure Ar flow for 1 h for proper degassing. The desorption profiles of NOin pure Ar flow for 1 h for proper degassing. The desorption profiles of NOxx and Oand O22 were obtained by heating the sample from 80 to 550 were obtained by heating the sample from 80 to 550 °C°C at 10 at 10 °C°C/min in Ar /min in Ar flow (100 ml/min). The concentrations of desorption species were calculated by the flow (100 ml/min). The concentrations of desorption species were calculated by the m/m/z = 30 (NO), 32 (Oz = 30 (NO), 32 (O22) and 46 (NO) and 46 (NO22) on a mass spectrometer (MS) (Figure 3) on a mass spectrometer (MS) (Figure 3–2).2).

NOxx–TPD coupled to IRTPD coupled to IR The prepared MnO

The prepared MnOxx–CeOCeO22 mixed oxides were treated at 350 mixed oxides were treated at 350 °°C for 30 min in 600 ppm C for 30 min in 600 ppm NO/10% ONO/10% O22/N/N22, and then cooled down to 100 , and then cooled down to 100 °°C, the gas mixture was rC, the gas mixture was replaced by eplaced by pure Npure N22 and the sample was maintained for 1 h to remove the weakly adsorbed NOand the sample was maintained for 1 h to remove the weakly adsorbed NOxx species. The NOspecies. The NOxx (NO and NO(NO and NO22) temperature) temperature–programmed desorption (NOprogrammed desorption (NOxx–TPD) TPD) tests were carried out in a fixedtests were carried out in a fixed–bed reactor. 50 mg of pretreated sample was heated to bed reactor. 50 mg of pretreated sample was heated to 650650 °°C from 100 C from 100 °°C at a heating rate of 10 C at a heating rate of 10 °°C/min in NC/min in N22 or 10% Oor 10% O22/N/N22 flow with a flow with a flow rate of 500 ml/min. The concentration of NOflow rate of 500 ml/min. The concentration of NOxx desorbed from the catalyst was desorbed from the catalyst was recorded on an IR detector.

Thermal Gravimetric Analysis (TGA)

The SOFs content of soot samples was evaluated by means of thermogravimetric oxidation in a SDT Q600 apparatus (TA Instruments), under air flow, heating from ambient temperature to 800 °C at a rate of 10 °C/min.
The soot oxidation reactivity of the catalysts was also measured through means of thermogravimetric oxidation in a HCT-2 apparatus, in 10% O2/N2 flow (50 ml/min), heating from ambient temperature to 700 °C at a rate of 10 °C/min.

Transmission Electron Microscope (TEM)

High-resolution transmission electron microscopy (HR-TEM) (JEOL JEM 100CX) with a point resolution of 0.3 nm was utilized for an analysis of the internal structure of soot particles. The high-resolution images were acquired under 500,000 magnification. The carbon fringes lengths of different soot samples were also measured and analyzed by a software Image J in this work. The carbon fringe length distribution (f(x)) of soot was obtained by the following: 0 2 1 ( ) 2 2 2 ( )          , x f x e where μ is the mean value of fringe lengths, σ is the standard deviation and σ2 is the variance.

Raman Spectroscopy (Raman)

Raman spectra of soot were obtained on a micro-Raman system (Horiba Jobin Yvon HR 800 UV) with an exciting source of 532 nm. The output power of 0.1 mW was chosen in the scanning range of 800-2000 cm-1. The spectrometer includes a grating with 600 grooves mm–11 and a CCD detector with 50and a CCD detector with 50×× magnification objective lens.magnification objective lens.

Diffuse Reflectance Infrared Fourier Transform Spectra (DRIFTS)(DRIFTS)

Diffuse reflectance infrared Fourier transform spectra (DRIFTS) of soot were of soot were measured by using a Nicolet 6700 spectrometer with a DTGS detector and a high measured by using a Nicolet 6700 spectrometer with a DTGS detector and a high temperature cell. Soot sample was diluted by KBr at a soot/KBr ratio of 1/40, then the temperature cell. Soot sample was diluted by KBr at a soot/KBr ratio of 1/40, then the mixture was placed in a reaction cell and pretreated at 100 mixture was placed in a reaction cell and pretreated at 100 °°C in pure NC in pure N22 forfor 10 min. 10 min. After that,After that, the IR spectra were recorded.the IR spectra were recorded. The diffuse reflectance infrared Fourier transform spectra (DRIFTS) of catalyst were measured by using the same equipment. MnOmeasured by using the same equipment. MnOxx–CeOCeO22 powder sample was diluted by powder sample was diluted by KBr and placed in a reaction cell and thenKBr and placed in a reaction cell and then pretreated at 500 pretreated at 500 °°C in pure NC in pure N22, the , the background spectra were recorded at 250, 350 and 450 background spectra were recorded at 250, 350 and 450 °°C. The sample was finally C. The sample was finally exposed in 600 ppm NO/10% Oexposed in 600 ppm NO/10% O22/N/N22 at each temperature for 30 min for DRIFTS at each temperature for 30 min for DRIFTS measurements.measurements.
XPS measurement was conducted on an AXIS Ultra DLD spectrometer (Kratos, surement was conducted on an AXIS Ultra DLD spectrometer (Kratos, England) by using AlKEngland) by using AlKαα radiation as the excitation source (300 W). All binding radiation as the excitation source (300 W). All binding energies (B.E.) were referenced to carbon C 1s line at 284.6 eV.energies (B.E.) were referenced to carbon C 1s line at 284.6 eV.

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NO oxidation reactivity (NO-TPO)

The NO temperature-programmed oxidation (NO-TPO) tests were conducted in a fixed-bed reactor. The reaction gases including 600 ppm NO, 10% O2, N2 were fed to the fixed-bed reactor at a flow rate of 500 ml/min. 50 mg of MnOx-CeO2 sample was firstly mixed with 200 mg SiC powder and the mixture was then used in NO-TPO test.
In order to a comparison, the mixture of 50 mg catalyst and 5 mg soot was also used for NO–TPO under same conditions. The reactor temperature was heaTPO under same conditions. The reactor temperature was heated to 650 ted to 650 °°C at C at a heating rate of 10 a heating rate of 10 °°C/min. The effluent gases were detected on an infrared (IR) C/min. The effluent gases were detected on an infrared (IR) spectrometer (Thermo scientific).spectrometer (Thermo scientific).

Table of contents :

Remerciements
Sommaire
1. Introduction
1.1 Overview
1.2 Objectives of Ph.D. work
2. Literature review on soot emission control
2.1 Diesel exhaust emissions, environment pollution and health impact
2.2 Diesel Particulate filter (DPF)
2.2.1 DPF filtration
2.2.2 DPF regeneration
2.3 Soot structure
2.4 Catalyst materials
2.4.1 Precious metal catalysts
2.4.2 Ce-based mixed oxide catalyst
2.5 Soot oxidation reaction mechanism
3. Materials and experimental methods
3.1 List of materials
3.1.1 Materials for soot preparation
3.1.2 Materials for catalyst preparation
3.2 Physicochemical characterization
3.2.1 Brunauer-Emmett-Teller (BET)
3.2.2 Laser Granulometry
3.2.3 X-Ray Diffraction (XRD)
3.2.4 Temperature-Programmed Reduction (TPR)
3.2.4.1 H2-TPR
3.2.4.2 Soot-TPR
3.2.5 Temperature-Programmed Desorption (TPD)
3.2.5.1 NOx-TPD coupled to MS
3.2.5.2 NOx-TPD coupled to IR
3.2.6 Thermal Gravimetric Analysis (TGA)
3.2.7 Transmission Electron Microscope (TEM)
3.2.8 Raman Spectroscopy (Raman)
3.2.9 Diffuse Reflectance Infrared Fourier Transform Spectra (DRIFTS)
3.2.10 X-ray Photoelectron Spectra (XPS)
3.3 Reactivity evaluation by TPOs
3.2.1 Soot oxidation reactivity
3.3.2 NO oxidation reactivity (NO-TPO)
3.4 Isothermal experiment
4. MnOx-CeO2 mixed oxides as the catalyst for NO-assisted soot oxidation: The key role of NO adsorption/desorption on catalytic activity
4.1 Introduction
4.2 Materials preparation
4.3 Physicochemical properties
4.3.1 DRIFTS tests
4.3.2 XPS analysis
4.3.3 Raman analysis
4.3.4 TPD analysis with IR and MS
4.3.4 Soot-TPR tests coupled to MS
4.4 Soot oxidation activity
4.4.1 Soot-TPO
4.4.2 Isothermal reaction at 400 °C
4.5 Summary
5. Structure-reactivity study of model and Biodiesel soot in model DPF regeneration conditions
5.1 Introduction
5.2 Materials preparation
5.2.1 Soot samples preparation
5.2.2 Catalyst preparation
5.3 Physicochemical properties of soot
5.3.1 Laser granulometry
5.3.2 HRTEM analysis
5.3.3 XRD analysis
5.3.4 Raman spectra analysis
5.4 Soot oxidation activity analysis by TPOs
5.4.1 Non-catalytic soot oxidation
5.4.1.1 TPOs in 9% b.v. O2/Ar
5.4.1.2 TPOs in 400 ppmv NO2 + 9% b.v. O2 in Ar
5.4.2 Catalytic soot oxidation
5.4.2.1 TPOs in 9% b.v. O2/Ar
5.4.1.2 TPOs in 400 ppmv NO/NO2 + 9% b.v. O2 in Ar
5.4.3 Effect of soot-catalyst contact
5.5 Structure and reactivity correlation
5.6 Summary
6. Structure, surface and reactivity of activated carbon: From model soot to Bio Diesel soot
6.1 Introduction
6.2 Materials preparation
6.2.1 Soot samples preparation
6.2.1 Catalyst preparation
6.3 Reactivity analysis
6.3.1 TPO tests in O2
6.3.2 TPO tests in NO + O2
6.3.3 Isothermal reaction rate at 350 °C
6.4 Physicochemical properties of soot
6.4.1 Laser granulometry
6.4.2 BET analysis
6.4.3 Raman analysis
6.4.4 HRTEM analysis
6.4.5 XPS analysis
6.4.6 DRIFTS analysis
6.5 Correlation of structural and surface properties to reactivity
6.6 Summary
7. Effect of Biodiesel impurities (K, Na, P) on noncatalytic and catalytic activities of soot in model DPF regeneration conditions
7.1 Introduction
7.2 Materials preparation
7.2.1 Soot samples preparation
7.2.2 Catalyst preparation
7.3 Reactivity tests by TPOs
7.3.1 Soot oxidation under noncatalytic regeneration conditions
7.3.1.1 Soot-TPOs in 9% b.v. O2/Ar + 5% H2O
7.3.1.2 Soot-TPOs in 400 ppm NO2 + 9% b.v. O2/Ar + 5% H2O
7.3.2 Soot oxidation under catalytic regeneration conditions
7.3.2.1 Soot-TPOs in 9% b.v. O2/Ar + 5% H2O
7.3.2.2 Soot-TPOs in 400 ppm NO + 9% b.v. O2/Ar + 5% H2O
7.3.2.2 Soot-TPOs in 400 ppm NO2 + 9% b.v. O2/Ar + 5% H2O
7.4 Physicochemical properties
7.4.1 Raman analysis
7.4.2 BET analysis
7.4.3 HRTEM analysis
7.4.4 XPS analysis
7.5 Summary
8. Conclusion
Reference

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