Catalytic removal of nitrogen- and sulfur-containing volatile organic compounds/Destruction catalytique des composés organiques volatils contenant de l'azote ou du soufre
(2003)
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- Authors
- Supervisors
- Grange, Paul
- Abstract
- This thesis investigates the catalytic oxidation of nitrogen- and sulfur-containing volatile organic compounds. Besides being very malodorous and present in many effluents, N- and S-VOCs may poison catalysts. Their removal through catalytic oxidation has thus been considered in view of the development of a flexible catalytic system. The first part of the thesis concerns the selection of a candidate for the removal of VOCs including hetero-atom of nitrogen or sulfur at low temperature. The preparation of gold catalysts (deposition-precipitation vs. ion-exchange) was first understood. Comparison of the catalytic activities of metal oxides (Co, Cu, Fe, Mn, Ni, V) and TiO2 supported noble metals (Ag, Pt, Pd, Rh, Ru, 'optimized' Au) led to the selection of gamma-MnO2 for the continuation of the study. In the second part of the thesis, an in-depth study of the activity and stability of gamma-MnO2 in the oxidation of N- and S-VOCs is undertaken. Identification of the active sites and mechanism of reaction is carried out mainly on basis of physico-chemical characterizations. The working state of the catalyst is different from the fresh gamma-MnO2. The total oxidation of n-hexane and trimethylamine over gamma-MnO2 was first investigated. A Mars and van Krevelen (MvK) mechanism is evidenced. The reoxidation of the reduced sites is the difficult step of the mechanism. In addition, gamma-MnO2 undergoes two phenomena during the reaction : adsorption of VOCs and reduction. The adsorption phenomena control the competition between VOCs. The reduction state of the solid at work is influenced by the nature of the organic molecule. The strength of the VOC adsorption influences the extent of bulk oxygen participation. The nature of the VOCs is thus assumed to tune the reduction state and the reaction rate at steady state. The modifications encountered by gamma-MnO2 during the oxidation of S-VOCs were then studied. Below 200°C, adsorbed sulfate species accumulate on the catalyst surface and poison the MvK mechanism. Around 280°C, the reduction and the formation of the bulk manganese sulfate phase modify the activity. MnSO4.H2O is highly active in the oxidation of CH3SH. The loss of the hydration water around 280°C causes a deactivation of the MnSO4.H2O phase.
- Affiliations
Citations
Cellier, C. (2003). Catalytic removal of nitrogen- and sulfur-containing volatile organic compounds/Destruction catalytique des composés organiques volatils contenant de l’azote ou du soufre. https://hdl.handle.net/2078.5/97431