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Publication Title | An advanced gas-solid UV LEDs photocatalytic reactor for organic syntheses and environmental applications

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An advanced gas-solid UV LEDs photocatalytic reactor for organic syntheses and environmental applications

Results and Discussion

Paolo Ciambelli*, Diana Sannino, Vincenzo Palma, Vincenzo Vaiano, Roberto S. Mazzei

This system allows to realize the photocatalytic deep oxidation of volatile organic compounds such as toluene, benzene and acetone on V2O5/TiO2 catalysts, with a contact time of 300 ms in a small reaction volume (0.1L). Selective photocatalytic oxidation of hydrocarbons can be achieved by selection and optimization of catalyst formulation, finely tuning of active species loading, polymolybate, and/ or polyvanadate and sulphate, on different supports like TiO2, Al2O3, TiO2/Al2O3, TiO2/SiO2. The photocatalytic oxidative dehydrogenation of cyclohexane to cyclohexene or benzene has been obtained with 100% selectivity and with a higher activity in comparison to previous photoreactor configurations [2, 4-5]. Photocatalytic tests feeding ethylbenzene showed the effectiveness in styrene production on sulphated MoOx/Al2O3 catalysts with 100% selectivity. In all the applications, no deactivation phenomena were detected. Finally, the designed photocatalytic reactor was tested in the selective oxidation of alcohols to the corresponding aldehydes in gas phase. Photooxidative dehydrogenation of ethanol was carried out on V2O5/TiO2 catalysts with high photoactivity and acetaldehyde selectivity (97%). The main results are reported in Table 1.

1University of Salerno, Department of Chemical and Food Engineering, 8408, Fisciano Salerno (Italy)

*pciambelli@unisa.it

Introduction

Photocatalysis is a “green” technology with potential applications in various disciplines, such as chemical synthesis and environmental technologies. For the industrial applications, photocatalytic reactors design mainly requires to overcome actual mass and photons transfer limitations. Fluidized bed reactors are well known in enhancing mass transfer. With respect to photon transfer, microscale illumination systems seem to be a promising solution [1]. Recently, we have developed a gas-solid photocatalytic fluidized bed reactor at high performances [2]. The device couples positive aspects such as wide exposition of catalyst to the radiation to the effective use of UV Leds which are long-lasting, robust, small in size and high in light efficiency. Illumination efficiency, defined in [1], appeared as key paramenter to compare different reactors configurations, and resulted higher than reported for slurry systems, spinning disc reactors, monolithic reactors and microreactors.

Table 1 List of the main reaction studied and their results

In this work different photocatalytic applications in the high efficiency gas-solid photocatalytic reactor are reported.

Benzene to CO2 Cyclohexane to benzene Cyclohexane to cyclohexene Ethylbenzene to styrene

V2O5/TiO2 27 100 80 MoO3/TiO2 33 99 120

Materials and Methods

MoO3/γ-Al2O3 28 100 120 MoO3/γ-Al2O3 27 100 120 V2O5/TiO2 100 97 100

Several catalysts were prepared by wet impregnation of titania and or alumina based supports with an aqueous solution of ammonium heptamolybdate or ammonium metavanadate, followed by calcination in air at 400°C. Sulphated photocatalysts were obtained according to [3].

Ethanol to acetaldehyde

The bidimensional fluidized bed reactor has 40 mm x 10 mm cross section, 2 mm thick, and 230 mm height pyrex-glass walls (2mm in thickness), supplied with an internal electrical heater to control the reaction temperature. A bronze filter (5 μm size) was used for gas feeding to provide uniform gas distribution. The reactor was illuminated by two or four UV-LEDs modules of 20 pieces each positioned in front of the pyrex windows. An electrical control system connected to the modules allows to control the light intensity incident to the external walls of the photoreactor The light intensity was regulated at 100 mW/cm2. Each UV- LED module consists of up to 20 pieces of UV-LEDs (Nichia Corporation) emitting at 365 nm. Moreover the fluidized bed reactor is equipped with Catalytic tests were carried out in the fluidized bed photoreactor feeding 830 (stp)cm3/min. The gas composition was continuously measured by an on-line quadrupole mass detector (TraceMS, ThermoElectron) and a continuous CO-CO2 NDIR analyser (Uras 10, Hartmann & Braun).

Significance

Photocatalytic tests started feeding the reaction gaseous mixture to the photoreactor at reaction temperature in dark. After the complete adsorption of hydrocarbon on the catalyst, UV-LEDs were switched on. In the absence of light, no reaction products were observed, either during hydrocarbon dark adsorption or after that hydrocarbon adsorption equilibrium on catalyst were completed.

Catal. Today, 128, 251 (2007).

4. P. Ciambelli, D. Sannino, V. Palma, V. Vaiano, Catal. Today, 99, 143 (2005).

5. P Ciambelli., D. Sannino, V. Palma, S. Vaccaro,V. Vaiano, Stud. Surf. Sci Catal., 172 ,

Reaction

Catalyst Hydrocarbon Selectivity Reaction conversion % temperature,°C

%

The UV-LEDs photocatalytic fluidized bed reactor was useful both for removing volatile organic compound and partial oxidation reactions under mild conditions with high selectivity, avoiding catalyst deactivation phenomena, resulting of high productivity and versatility.

References

1. T. Van Gerven, G. Mul, J. Moulijn A. Stankiewicz, Chem. Eng. Process, 46, 781 (2007). 2. P. Ciambelli, D. Sannino, V. Palma, V. Vaiano Italian patent pending SAA2008000012. 3. P. Ciambelli, D. Sannino, V. Palma, V. Vaiano, P. Eloy, F. Dury and E.M. Gaigneaux.,

453 (2007).

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