Session 6: 1,2-dichloro-benzene oxidative conversion over V{sub 2}O{sub 5}-WO{sub 3}-TiO{sub 2} powder and monolith catalysts

In this study 1,2DCB catalytic destruction has been investigated in a laboratory reactor, in oxidizing conditions, and in the temperature range of 523-673 K, over both powder and monolithic shaped V{sub 2}O{sub 5}-WO{sub 3}-TiO{sub 2} catalysts . A supported Pt catalyst has also been tested for comparison. 1,2DCB has been fed as vapor at low partial pressure (500 ppm), in helium carrier and in the presence of large excess oxygen. C-containing reactants and products were analyzed through GC equipped with TCD and FID detectors and GC-Mass spectrometry. Catalysts has been loaded in the quartz tubular reactor in form of powders (0.5 g loaded) or in form of honeycomb modules (16 mm x 16 mm in cross section and 21 mm long, with channel shaped as equilateral triangles). Total flow rates were in the range 175-350 ml/min. The VWT1 catalyst powder has a typical composition for application to power plants deNO{sub x} reactors and allows almost complete conversion of 1,2DCB near 600 K, leading to the detection of CO{sub x}, but also to heavier products. In the same conditions the commercial VWT2 catalyst (used in incinerator plant) has been tested in the form of crushed powders and has proved to be quite effective for the oxidative destruction of 1,2DCB vapor, reaching a maximum of 70% conversion around 573 K. However irreversible deactivation occurs in catalytic tests at higher temperatures, probably due to the high contact times reached in these set of experiments. The formed VWT2 catalyst, tested at different flow rates, reaches lower 1,2DCB conversions (50% at 673 K), without the appearance of deactivation phenomena at the laboratory scale-time (20 h) and with high selectivity to CO{sub x} (around 60% selectivity to CO{sub 2}, 20% selectivity to CO). Molecular chlorine is not detected in the downstream gases. In the same conditions the Pt catalyst shows a good oxidation activity but not improved with respect to the vanadia-based one in the temperature range considered, allowing a 50% conversion of 1,2DCB at 653 K. Selectivity, however, is almost total to CO{sub 2}. The conversion values obtained in the considered temperature range should be in principle considered sufficient to abate chlorinated compounds below the required regulation limits in flue gases i.e. from incinerators. IR data on 1,2DCB adsorption and reaction in static conditions at the catalyst surface point out that the dechlorination step of the aromatic ring occurs through a nucleophilic substitution already at room temperature. This step has already been proved to occur in not very demanding conditions. The resulting phenate species are strongly adsorbed at the surface, where they evolve to more oxidized fragments (carboxylate species) at increasing reaction temperature. Thus it seems likely that the critical step is the burning of the aromatic ring. (authors)