Performance of alumina-supported noble metal catalysts for the combustion of trichloroethene at dry and wet conditions

The performance of four different alumina-supported noble metal catalysts (0.5% of Pd, Pt, Rh and Ru, respectively) for the deep oxidation of trichloroethene (1000–2500 ppmV, WHSV = 55 h^?1) in air was studied in this work. Experiments were carried out at both dry and wet (20,000 ppm of H₂O) conditions. Catalysts were compared in terms of activity, selectivity for the different reaction products (CO₂, HCl, Cl₂, C₂Cl₄, CCl₄ and CHCl₃), and stability at reaction conditions.

As general trend, the activity of the catalysts decreases in the order Ru  Pd > Rh > Pt. Concerning to the effect of the water addition, no important effect on the catalyst activity was observed, except in the case of Pt, for which an increase of the catalytic activity was observed. Reaction mechanism (and hence product distribution) is very similar for Rh, Pd and Pt, being in these cases C₂Cl₄ the only organochlorinated by-product detected. In the case of Ru, the reaction mechanism seems to be quite different, CCl₄ and CHCl₃ being the main organic by-products.

Simple power-law kinetic expressions (first order on trichloroethene concentration for Pd, Rh and Ru, and zeroth order for Pt) provide fairly good fits for catalytic performance of the studied catalysts.

Finally, deactivation studies show that both formation of active metal chlorides (especially in the case of Rh) and fouling (especially for Pd and Pt) are the main deactivation causes.