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The influence of water vapour on the photocatalytic oxidation of cyclohexane in an internally illuminated monolith reactor

Dijk, Vic van (2011) The influence of water vapour on the photocatalytic oxidation of cyclohexane in an internally illuminated monolith reactor.

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Abstract:Titania (anatase, Hombikat uv100) photocatalyst was coated onto a cordierite monolith and used in an internally illuminated monolith reactor (iimr) for photocatalytic oxidation of cyclohexane. Reactor temperature was kept constant at 25 °C, irradiance amounted 0.19 mol h−1 m−2 (wavelength range 230–388 nm) and irradiance limited bulk cyclohexanone production. The dry gas flow was in total 200 mLmin−1 and consisted of equal parts nitrogen and air. Bulk production rates around 6 · 10−6 mol h−1 cyclohexanone were achieved for at least 7 hours under humid conditions. No mass transfer limitations were detected. All production rates were corrected for evaporation of cyclohexane. The illuminated monolith produced cyclohexanone under dry conditions, no significant cyclohexanol production was observed. After 80 minutes of illumination under dry gas flow, the monolith deactivated, likely due to irreversible adsorption of carboxylates and carbonates. Water vapour content of the air/nitrogen gas flow was varied. Water vapour enhanced product desorption from the monolith surface, likely by competitive adsorption. Cyclohexanone bulk production rate depended linearly on relative humidity. For relative humidity > 20 %, a deactivated monolith produced bulk cyclohexanone and cyclohexanol; water vapour decreased selectivity towards cyclohexanone. Hydroxyl radicals formed due to water vapour played a minor role in maintaining activity: cyclohexanol bulk production rate dependency on humidity was nonlinear. We think that hydroxyl radicals were not able to remove carboxylates and carbonates from the monolith surface significantly: once the monolith deactivated under dry gas flow, water vapour was not able to restore activity under dry conditions to any extent.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:35 chemistry
Programme:Chemical Engineering MSc (60437)
Link to this item:http://purl.utwente.nl/essays/61198
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