Abstract
The photo activities of some photo-catalysts including TiO<sub>2</sub>, Bi<sub>2</sub>WO<sub>6</sub> and Bi<sub>2</sub>WO<sub>6</sub>-TiO<sub>2</sub> (in various mixing ratios) were evaluated for photo-epoxidation of propylene. The photocatalytic epoxidation reaction was performed in gas-phase under atmospheric pressure. Typical reaction mixture of C<sub>3</sub>H<sub>6</sub>:O<sub>2</sub>:N<sub>2</sub> corresponding to the ratio 1:1:18, afforded PO (PO) in addition to other products such as acetone, acetaldehyde and propanal as observed by the FTIR-GCMS tandem analysis. It was established from the results that Bi<sub>2</sub>WO<sub>6</sub>-TiO<sub>2</sub> photo-catalysts were more preferable for selectivity of PO peaking at 49%. The highest formation rate of PO achieved was 111μmol g cat<sup>-1</sup> h<sup>-1</sup> over 12mol% Bi<sub>2</sub>WO<sub>6</sub>-TiO<sub>2</sub> ratio in a typical flow reaction for 1h at 345 K under UVA illumination. Under this condition the selectivity of products was also observed to be very stable. Further study on the effect of light intensity revealed that increasing the light intensity from 0.1 to 0.3mWcm<sup>-2</sup> significantly increased the selectivity of PO by 5%. Higher intensity depreciated the PO selectivity. In order to study the effect of temperature on the photocatalytic epoxidation reaction, a systematic approach was followed. As raising the reaction temperature influences the distribution of products significantly, a temperature range of 335-355 K was used in the optimised reaction condition. At 355 K, it was observed that the formation of propanal was favoured which was attributed to its inhibition to be transformed into propionic acid. However, raising the reaction temperature was observed to affect the rate of reaction in two ways: first, the adsorption of PR on to the photo-catalyst which causes a decrease in the reaction efficiency was reduced and secondly, the desorption of products of reaction which in turn reveals more active sites, was improved.
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