Oxidation of trichloroethene over metal oxide catalysts: Kinetic studies and correlation with adsorption properties

The performance of bulk chromium oxide is compared with that of a Mn commercial catalyst for the deep oxidation of trichloroethene (1000–2500 ppmv, 55 h−1 space velocity) in air, in dry and wet (20 000 ppm of H2O) conditions, in terms of activity, selectivity and stability.Chromium oxide was found to be more active (on a catalyst weight basis), however its activity decreases continuously with time on stream. The presence of water increases its stability, the Mn catalyst showing the opposite behaviour. The effect of water on the Cr catalyst can be explained according to the Deacon equilibrium, as the presence of water tends to decrease the Cl2 concentration, assumed to be responsible of the catalyst deactivation.Regarding to the selectivity, the Mn catalyst yields C2Cl4, CCl4 and CHCl3 as organochlorinated by-products, whereas chromium oxide produces only trace amounts of CCl4.Simple power-law kinetics expressions (first-order for Mn and zero-order for Cr) provide fairly good fits for the evolution of the conversion with the temperature. Furthermore, the kinetic behaviour of chromium oxide can be represented with a Langmuir–Hinshelwood model taking into account the chlorine inhibitory effect.