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Hindawi Publishing Corporation International Journal of Photoenergy Volume 2009, Article ID 709365, 7 pages doi:10.1155/2009/709365

Research Article

Improved Performances of a Fluidized Bed Photoreactor by a Microscale Illumination System

Paolo Ciambelli,1, 2 Diana Sannino,1, 2 Vincenzo Palma,1 Vincenzo Vaiano,1 and Roberto S. Mazzei1

1 Department of Chemical and Food Engineering, University of Salerno, Via Ponte Don Melillo, 84084 Fisciano (Salerno), Italy 2 NANO MATES, Research Centre for Nanomaterials and Nanotechnology at Salerno University, University of Salerno,

Via Ponte Don Melillo, 84084 Fisciano (Salerno), Italy

Correspondence should be addressed to Diana Sannino, Received 31 March 2009; Revised 17 July 2009; Accepted 2 September 2009 Recommended by Mohamed Sabry Abdel-Mottaleb

The performances of a gas-solid two-dimensional fluidized bed reactor in photocatalytic selective oxidation reactions, irradiated with traditional UV lamps or with a microscale illumination system based on UV emitting diodes (UVA-LEDs), have been compared. In the photocatalytic oxidative dehydrogenation of cyclohexane to benzene on MoOx/TiO2-A12O3 catalyst the use of UVA-LEDs modules allowed to achieve a cyclohexane conversion and benzene yield higher than those obtained with traditional UV lamps. The better performances with UVA-LEDs are due to the UVA-LEDs small dimensions and small-angle emittance, which allow photons beam be directed towards the photoreactor windows, reducing the dispersion outside of photoreactor or the optical path length. As a consequence, the effectively illuminated mass of catalyst is greater. We have found that this illumination system is efficient for photo-oxidative dehydrogenation of cyclohexane to cyclohexene on sulphated MoOx/γ-A12O3 and ethanol to acetaldehyde on VOx/TiO2.

Copyright © 2009 Paolo Ciambelli et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1. Introduction

Heterogeneous photocatalysis is the subject of an increasing interest during the last twenty years. A challenging research topic is the synthesis and production of chemicals by partial photo-oxidation reactions by molecular oxygen under mild conditions [1]. In this context photocatalysis can lead to more sustainable processes by increasing both reactivity and selectivity towards the desired products because of mild operating conditions, that are, low temperature and pressure [2]. However, a competitive full-scale photocatalytic oxida- tion process in industrial application requires overcoming photons and mass transfer limitations in the photocatalytic reactors [2]. With reference to mass transfer limitations a large number of novel solutions have been developed for the photoreactors, including spinning disc reactors [3, 4], monolith photoreactors [5], and microreactors [6]. Fluidized bed photoreactors are well known in enhancing mass transfer kinetics. Moreover, they provide easy temperature control

and good contacting between reactants and photocatalysts with respect to fixed bed photoreactors [7–11].

Regarding photons transfer, microscale illumination sys- tems are a promising solution [2]. This type of illumination is realized mainly by irradiating the photoreactor with UV emitting diodes (UVA-LEDs) device [12–14]. LEDs are replacing traditional UV lamps in many applications, owing to the much higher efficiency in light-electricity conversion, since the light emission by LEDs is induced by the recombi- nation of electrons and holes excess [15]. Further advantages of LEDs derive from the small dimensions, robustness, and the long lasting (hundred thousands of hours compared to thousands of hours in the case of classical lamps) [2].

The use of microscale illumination in photoreactors can provide both a large catalyst surface area per unit of reactor volume and high illumination efficiency, also profiting of the small angle of emittance of the LEDs [2].

In this work, the performances of a gas-solid two- dimensional fluidized bed reactor with traditional UV lamps

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