Skip to Main content Skip to Navigation
Theses

Dioxyde d'étain : Synthèse, Caractérisation et Etude des Interactions avec Différents Gaz Polluants - Application à la Catalyse DeNOx

Abstract : Two high specific surface area tin dioxides after calcination at 600°C under O2 have been synthesized : SnO2-HNO3 (24 m2 g-1) and SnO2-N2H4 (101 m2 g-1). The surface of the 600°C-calcined SnO2-N2H4 sample was found to be more hydroxylated than the 600°C-calcined SnO2-HNO3 one. The thermal treatment under O2 involves the formation of mono-ionized oxygen vacancies, leading to non-stoichiometric tin dioxides. A specific treatment like outgassing at temperatures above 300-400°C, was found to be necessary to extract surface oxygen atoms. The CO adsorption at liquid N2 temperature on the SnO2-N2H4 sample has shown the existence of two cationic Sn4+ sites, having different Lewis acidities. Concerning the surface OH groups, it has been observed: i) hydroxyls which are inaccessible to CO, ii) weakly acidic surface hydroxyls and iii) surface hydroxyls having a weak Brönsted acidity. Then, a study of the interactions between the 600°C-calcined SnO2-N2H4 sample and various pollutant gases has been carried out by transmission FTIR spectroscopy. Carbon dioxide interacts with SnO2 surface, leading to CO2 species adsorbed on cationic sites together with carbonates and bicarbonates ad-species. The absence of participation of free electrons in the surface reactions considered, could explain that SnO2-based sensors are not sensitive towards CO2. Carbon monoxide involves the partial reduction of SnO2 surface by reaction of CO with surface oxygens to form carbonate species and CO2. This reduction results in the release of free electrons to the solid together with the formation of surface oxygen vacancies. This leads to an important loss of transmission which represents the high sensibility of SnO2-based sensors towards CO. Interactions of SnO2 surface with NO2 have shown the formation of NO+, nitrite and nitrate ad-species. The surface reactions which involve these species have allowed to interpret the SnO2 conductivity variations in the presence of NO2. The NO adsorption on SnO2-N2H4 have shown the formation of electron donor species (nitrite and nitrate species) together with electron acceptor species (nitrosyl species). The presence of these species could explain the complex conductivity variations observed as a function of temperature. Finally, in the Selective Catalytic Reduction (SCR) of NOX by propene in oxygen excess, SnO2 was found to be active at high temperatures (> 350°C) and selective in N2. Nevertheless, active sites are blocked up by oxygenated polymer compounds of propene (coke). For SnO2-N2H4 sample, the presence of water inhibits the formation of coke, leading to a slight improvement in the catalytic activity, whereas for commercial SnO2, water has an inhibiting effect on the SCR of NOX. A higher surface acidity for the SnO2-N2H4 sample could explain this phenomenon.
Document type :
Theses
Complete list of metadata

https://tel.archives-ouvertes.fr/tel-00002302
Contributor : Nicolas Sergent <>
Submitted on : Tuesday, April 22, 2003 - 11:34:13 AM
Last modification on : Wednesday, June 24, 2020 - 4:18:17 PM
Long-term archiving on: : Wednesday, March 29, 2017 - 10:33:06 AM

Identifiers

  • HAL Id : tel-00002302, version 2

Citation

Nicolas Sergent. Dioxyde d'étain : Synthèse, Caractérisation et Etude des Interactions avec Différents Gaz Polluants - Application à la Catalyse DeNOx. Catalyse. Université Jean Monnet - Saint-Etienne, 2003. Français. ⟨tel-00002302v2⟩

Share

Metrics

Record views

1493

Files downloads

4656