Filtered air (relative humidity ) 9-10%) containing methanol was flown through a cold plasma reactor connected to a photocatalytic reactor. The results showed a synergetic effect between the two purifying technologies, which is principally attributed to plasma-generated O 3 benefiting the photocatalytic process.

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We have investigated the effects of the TiO 2 type and coating method, two important factors for TiO 2 -based photocatalytic purification/deodorization of air. First, two TiO 2 powders (PC500 and 105) designed by Millennium Chemicals for photocatalysis were compared with Degussa P25 TiO 2 , a common reference, for removing methanol or n-octane in a flowing dry mixture of O 2 (20 v/v %) and N 2 . Under the conditions used, the differences were very small. For methanol mineralization, PC500 (the highest surface area sample) was, however, more efficient, which is attributed to increased adsorption of methanal (main intermediate product). Second, PC500 and 105 coated on a fibrous tissue (Ahlstrom) using a silica binder were tested for removing methanol in the O 2 + N 2 mixture in a batch reactor. Increasing the SiO 2 wt % from 20 to 50, at equal mass of TiO 2 + SiO 2 , was detrimental but not markedly, and the interest of using PC500 preferentially to PC105 to mineralize methanol was confirmed. Third, experimental design was used to optimize the thickness and quality of P25 coatings on quartz (or similarly on aluminum), which were obtained by several dipping/drying steps followed by a final calcination. For the optimized coatings, methanol or n-octane disappearance (batch reactor) and mineralization reached a maximum for three dip-coating steps (ca. 0.6 µm coating thickness, likely corresponding to UV light maximum penetration depth).

Dielectric barrier discharges (DBD) are commonly used for gas effluent cleanup and ozone generation. For these applications, the energy efficiency of the discharge is a major concern. This paper reports on investigations carried out on the voltage shape applied to DBD reactor electrodes, aiming to evaluate a possible energy efficiency improvement for ozone production. Two DBD reactor geometries were used; pin-to-pin and cylinder-to-cylinder, both driven either by a bi-directional power supply (voltage rise rate 1 kV/µs) or a pulsed power supply (voltage rise rate 1 kV/ns). Ozone formed in dry air was measured at the reactor outlet. Special attention was paid to discharge input power evaluation using different methods including instantaneous current-voltage product and transferred charge-applied voltage figures. The charge transferred by the discharges was also correlated to the ozone production. It is shown that, in the case of the DBD reactors under investigation, the applied voltage shape has no influence on the ozone production efficiency. For the considered voltage rise rate, the charge deposit on the dielectric inserted inside the discharge gap is the important factor (as opposed to the voltage shape) governing the efficiency of the discharge -it does this by tailoring the duration of the current peak into the tens of nanoseconds range.