Deactivation of chromium oxide catalyst for the removal of perchloroethylene (PCE)

The effect of a wide range of feed concentration of PCE from 3 0 to 10,000 ppm on the stability of chromium oxide supported on TiO2 and Al2O3 for the removal of chlorinated volatile organic compounds (CVOCs) has been investigated over a fixed bed flow reactor. Both chromium oxide catalysts exhibited stable PCE removal activity up to 100 h of reaction time without any catalyst deactivation when 30 ppm was introduced into the reactor. However, the high concentrations of PCE from 1,000 to 10,000 ppm, significantly deactivated the catalyst, regardless of the support. The deactivation of chromium oxide catalyst was neither caused by the evaporation of chromium from the catalyst surface nor the reduction of surface area by coking which is the most suspicious deactivation mechanism in the present reaction system. It was mainly due to the phase transformation from Cr(VI), active reaction sites on the catalyst surface, to Cr(III). The phase transformation of Cr(VI) to Cr(III) is probably attributed to the relatively slow rate of re-oxidation step of Cr(III) compared to the lattice oxygen consumption step during the reaction at a high feed concentration of PCE. Although some of Cr on the catalyst surface evaporated, it was insignificant in reducing PCE removal activity of the catalyst.