Etude de l'interaction plasma/catalyseur pour le développement de systèmes de réduction des émissions de COV oxygénés résultants de la combustion de biocarburants – BioPac

The main objective of the project BioPAC (Biofuel Combustion Emission Pollutant Reduction by Plasma Assisted by Catalysis) for the 'ANR Jeunes Chercheurs 2007' concerns the interaction between a plasma, a catalytic material and its porous support. The approach we propose consists to perform fundamental studies on the interaction between an electrical discharge, a catalyst material or a porous medium, on the surface chemistry involved during the plasma process, on charge transport phenomena between the plasma and the catalyst material, …. This proposal is composed by two main points: the study of the interaction between a plasma and a catalyst surface, and the ignition and development of plasma in porous medium. The reaction of acetaldehyde (CH3CHO) abatement has been chosen as the reference reaction, as the concentration of this pollutant increases largely when using bioethanol as fuel in internal combustion engine. In the first part of this project, we propose to focus our attention on two aspects: the first one concerns the elaboration and optimisation of photo-catalytic (TiO2,..) and catalytic materials (as Pt/Al2O3, ZnO, SnO2…), analysed by classical structure and composition characterisation techniques (Raman, FTIR, …) and surface analysis (MEB, MET, BET, ..). This catalytic material will be deposited on spherical pellets made of SiO2, quartz, a-Al2O3, …, or on the internal walls of the reactor. The second one concerns the development of medium pressure pulsed or continuous micro-wave plasma processes (1-100 mbar, Ar/O2/CH4) and the interaction between a catalytic surface and a medium pressure plasma using analytic techniques (as ultra-violet, visible or InfraRed absorption spectroscopy, gas chromatography, or mass spectroscopy). Concentrations of active species (acetaldehyde and carbon containing species) and their spatial and temporal evolutions will be compared with those obtained by chemical and transport models developed in the group, aiming to a better understanding of the plasma / catalytic surface interaction key phenomena. Since most of the applications of plasma-catalyst system are considered at near atmospheric conditions, the interaction between a Surface Dielectric Barrier Discharge (SDBD) and a plane catalytic surface will be at the centre of the second part of the project. From a fundamental point of view, the influence of the porosity of the catalytic material (in terms of pore sizes and specific surface) and the ignition of the discharge in contact with the catalytic surface will represent a key point of the study. This point could be achieved by studying, for example, the influence of the porosity of the catalytic material and its porous support, of the waveform of the electrical excitation (through the use of a TREK generator), of the properties of the dielectric support and of the total pressure in the vessel, on the ignition and propagation of the electrical discharge by confronting results obtained through the electrical characterisation of the discharge, and local high speed imaging. In the last part of the project, based on the results obtained in the previous part, the optimisation of the abatement of acetaldehyde will be carried out in an atmospheric plasma reactor containing catalytic material, either deposited on spherical balls or on the internal walls of the reactor. Influence of waveform excitation, porosity and compacity of the catalytic bed, … will be studied. The optimisation of the atmospheric pressure discharges, in terms of by-products, will be carried out to validate the choice of a specific catalytic material (type and configuration) and a specific plasma process (pressure, excitation system, …). The studies proposed should enable us to come out with a clear qualitative, hopefully quantitative, picture of the mechanisms involved in the interactions between electrical discharges and porous catalytic materials as far as partial oxidation of methane is concerned. From discharge physics point of view, the investigation of electrical discharge formation in small spaces such as those encountered in porous materials is a central point of the proposal. From the application point of view the present proposal is also motivated by setting up a rational methodology to investigate these high potential, although complex, devices that combine the use of an electrical discharge and a catalyst. The different skills and expertises of the researches involved in this project will cover extensively the main objectives of the project, i.e.: plasma characterisation, development of new plasma reactors, catalytic materials synthesis and characterisation, plasma modelling, modelling of the catalytic activity of electro-catalytic materials, ... This young and newly formed research group will part of the Group 5 'Environmental and Energy Applied Processes' and received the support of the Laboratoire d'Ingénierie des Matériaux et des Hautes Pressions (LIMHP – CNRS UPR1311).