Wet air oxidation of a reactive dye solution using CoAlPO 4-5 and CeO 2 catalysts

Abstract

Wet air oxidation of a prepared reactive dye solution was performed to assess the efficacy of CoAlPO 4-5 and CeO 2 as catalysts in the reaction. Via adsorption and oxidation of dye, CoAlPO 4-5 effectively decreased American Dye Manufacturers Institute and chemical oxygen demand (COD) values in the dye solution. At a reaction temperature of 135 °C and an applied pressure of 1.0 MPa, color and COD removal were as high as 95% and 90%, respectively, after 2 h. Active sites on the outer surface of CoAlPO 4-5 are responsible for adsorption and decomposition of dye while active sites in the pores dominate further destruction and oxidation of intermediate products. Since the outer surface only represents a minor part of the total surface, the color removal does not increase appreciably with loading of CoAlPO 4-5. The CeO 2 catalyst, calcined from cerium chloride under high thermal impact (type A CeO 2) was very effective in removing color and COD from the solution. This catalyst demonstrated near 100% color removal at temperatures above 135 °C and the COD removal could be above 95% at 165 °C. With both CoAlPO 4-5 and CeO 2 catalysts, COD rose and then fell back during the reaction, a feature typical of a consecutive reaction. In contrast to prepared CeO 2, a commercial CeO 2 did not exhibit any catalytic ability for the removal of color and COD. The durability of both CoAlPO 4-5 and prepared CeO 2 is considered to be fair.