Light sensitivity of phenol hydroxylation with TS-1

Effect of light intensity on the phenol hydroxylation using hydrogen peroxide (H2O2) as an oxidant and titanium silicalite-1 (TS-1) as a catalyst was studied. Three different levels of light intensity were examined; without light, 18 and 500 W light intensity. At 60 degrees C under the 500 W light intensity, phenol conversion significantly increased and reached maximum conversion (50%) within 2 h. Higher light intensity provided more efficient formation of the hydroxyl radicals ((OH)-O-.) from H2O2 and titanium-hydroperoxide species. The effect of light intensity was less prominent as the temperature was further increased. The light intensity did not have a significant effect on the desired product selectivity. The intensity of light influenced benzoquinone product decomposition. Benzoquinone conversion under the 500 W light intensity was twice as high as that under the 18 W light and no reaction occurred under the absence of light. In addition, the light intensity affected the product selectivity from the benzoquinone reaction, enabling an alternative for product selection from phenol hydroxylation. (c) 2005 Elsevier B.V. All rights reserved.