Skip to Main content Skip to Navigation
Theses

Développement de catalyseurs métalliques et conducteurs ioniques pour la conversion catalytique du méthane

Abstract : The aim of this thesis is to develop catalysts for the abatement of residual methane the exhaust pipe of vehicles powered by natural gas engines. More precisely, this study was based on the concept of the association of two catalysts. Each of the two catalysts is devoted to specific task. The first one is dedicated to the production of active oxygen species to favour the methane activation which takes place on the second catalytic bed, to initiate the oxidation reaction through a Mars van Krevelen mechanism. The first part of this work is focused on the sol-gel synthesis optimisation of CaTi1-xFexO3-δ perovskites (denoted CTFx with x = 0; 10; 20; 30; 40, iron substitution percentage for titanium). Three chelating agents were investigated: ethylene glycol (EG), glycerol (Gly) and 1.6-hexanediol (HD). High specific surface area (SSA) were obtained (until 49 m²/g) using 1.6-hexanediol (CTF40-HD) and about 37 m²/g using glycerol (CTF40-Gly). 1.6-hexanediol as polymerizing agent induced bigger pore volume related to its longer carbon chain compared to ethylene glycol, while using glycerol induced smaller pore size related to its chelating properties by its three hydroxyls groups. Oxygen vacancies induced by iron substitution for titanium confers oxygen mobility to CTFx perovskites, with better exchange performances observed with the perovskites synthesized with glycerol and high iron loading. For selected CTFx-Gly samples, temperature programmed isotopic exchange (TPIE) experiments have shown an improvement in the oxygen activation with the increase in iron loading. This has been linked to their high SSA and the generation of undercoordinated Fe3+ (4CN and 5CN) detected by Mössbauer spectroscopy, favourable for oxygen mobility. Catalytic tests and TPIE experiments led to the selection of the CTF30-Gly perovskite for further investigation in the dual-bed system.The second part of this manuscript is focused on the selection of the second catalyst for the dual-bed concept. Two YSZ (yttria stabilized zirconia) supports with different SSA, TOSOH (15 m²/g) and SGRP (65 m²/g), were studied. TPIE experiments showed an oxygen activation at lower temperature over SGRP than TOSOH, which is enhanced by precious metal addition (Rh or Pd) at the surface of the support. However, Rh/SGRP catalyst showed a deactivation during methane combustion, associated with a poor stability of the SGRP support due to its low calcination temperature. Rh/TOSOH showed good stability in catalytic oxidation but it was less active than Pd/ TOSOH which was then selected to be implemented as the second part of the dual-bed. Adding palladium over YSZ enhanced the oxygen adsorption/desorption steps, which resulted in faster exchange rates than over the supports without palladium. Additionally, palladium based catalyst showed better activity in methane oxidation after 30 min at 600°C under CH4+O2, due to the generation of an active Pd0/PdOx phase.Catalytic tests on CTF30-Gly+Pd/TOSOH associations were the subject of the last part of this work. A synergetic effect has been observed between CTF30-Gly and Pd/TOSOH in mechanical mixture (50/50). Multiple contacts between catalysts’ grains favour the use of active oxygen from CTF30-Gly to promote the CH4 oxidation on Pd/TOSOH. This hypothesis is supported by the quasi-absence of this synergy when the catalysts are implemented in a different configuration, or when Pd/TOSOH is replaced by Pd/γ-Al2O3 which exhibits low oxygen mobility. Adding CO2 and/or H2O induced a strong deactivation in the methane conversion, attributed to the formation of carbonates and/or hydroxyl species.
Complete list of metadata

https://tel.archives-ouvertes.fr/tel-03699382
Contributor : ABES STAR :  Contact
Submitted on : Monday, June 20, 2022 - 11:19:11 AM
Last modification on : Tuesday, June 21, 2022 - 3:25:11 AM

File

2022-Delporte-Maxime-These.pdf
Version validated by the jury (STAR)

Identifiers

  • HAL Id : tel-03699382, version 1

Collections

Citation

Maxime Delporte. Développement de catalyseurs métalliques et conducteurs ioniques pour la conversion catalytique du méthane. Génie chimique. Université de Poitiers, 2022. Français. ⟨NNT : 2022POIT2260⟩. ⟨tel-03699382⟩

Share

Metrics

Record views

0

Files downloads

0