Analysis of the simultaneous catalytic combustion of chlorinated aliphatic pollutants and toluene over ceria-zirconia mixed oxides

In the present work the oxidation of representative VOCs, such as toluene, 1,2-dichloroethane and trichloroethylene, present in trace amounts in air streams over a series of CexZr1-xO2,02 oxides (CeO2, Ce0.8Zr0.2O2, Ce0.68Zr0.32O2, Ce0.5Zr0.5O2, Ce0.15Zr0.85O2, ZrO2) as catalysts was investigated with focus on the difference in catalytic performance in the oxidation of single and chlorinated VOC/toluene mixtures, and on the mixture effects on product selectivity. In general, the efficiency for the single VOC destruction decreased in the following order: toluene > 1,2-dichloroethane > trichloroethylene. For chlorinated compounds the best performance was observed for the mixed oxides with 50 and 85 mol% of zirconia content, while ceria exhibited the best behaviour for toluene oxidation. With regard to chlorinated compounds the combination of surface acidity and accessible lattice oxygen appeared to control the catalytic performance of the mixed oxides. On the contrary, the combustion of toluene was essentially controlled by surface oxygen species. Notable 'mixture effects' on both activity and selectivity were noticed when a given chlorinated feed was decomposed in the presence of toluene. On one hand, mutual inhibition took place but the conversion of trichloroethylene was retarded much more severely. On the other hand, the destruction of toluene was less affected by the presence of 1,2-dichloroethane. Competitive adsorption played an important role in the inhibition detected with CeO2-based catalysts. However, no one species was able to dominate the adsorption sites and thereby completely prevent the adsorption and reaction of other species. On the other hand, HCl selectivity was greatly enhanced by the presence of toluene in the feed stream. (c) 2006 Elsevier B.V. All rights reserved.