Vanadium and Manganese oxides in aromatic VOC catalytic combustion.

ELISSABETA FINOCCHIO; LUCAS BAGATTI; MIGUEL A PELUSO; M. VICTORIA CURIA; JORGE SAMBETH; LUIS GAMBARO; HORACIO THOMAS; GUIDO BUSCA

Pisa

Congreso; XV Congresso Nazionale di Catalisi; 2007

Dipartimento di Chimica e Chimica Industriale - Sociedad Italiana de Catalisis

We present here results on the oxidation of aromatics and chlorinated aromatic compounds in vapor phase over high Vanadium containing catalyst and on alternative Mn-based catalysts (table I). Mn-based structured catalysts (MnOx over FeCrAlloy and alumina foils), prepared at the CINDECA laboratories have also been tested. Catalytic tests were carried out over powders and monoliths in a flow reactor operating at atmospheric pressure (500-2000 ppmv VOC, O2 excess, He gas carrier, dry conditions). 1,2 dichlorobenzene (1,2DCB), toluene and benzene oxidation has been tested. 1,4 dichlorobenzene (1,4DCB), chlorobenzene, 1,2-chlorophenol reactivity has also been studied over 5VWT catalyst. All the samples have been fully characterized by XRD, FTIR and UV-Vis NIR spectroscopies. Table I. Catalysts (powders) powder catalyst composition support phase 5VWT* V2O5-WO3-TiO2 5% wt V2O5 WO3-TiO2 W/Ti 4.5% atom. anatase 7MWT* MnOx-WO3-TiO2 7% wt Mn WO3-TiO2 W/Ti 4.5% atom. anatase KMO# KMnOx KMnOx Al2O3 cryptomelane MVO° MnVO MnOx/VOx -- a-MnO2 *prepared by conventional wet impregnation, # prepared by washcoating °prepared by sol-gel method 5VWT catalyst is active in 12DCB, chlorobenzene, toluene and benzene conversion, reaching 90% conversion around 300-350°C, with almost complete selectivity to COx. Adding water vapor to the feed does not significantly change the conversion results. In our conditions, 1,4 DCB complete conversion occurs at higher temperatures, pointing out a strong isomer effect of the second chlorine atom. Manganese-based catalysts show good activity in aromatic compounds combustion, CO2 as the only C-containing reaction product. As for chlorinated compounds conversion, the best result reached is 23% conversion of 1,2DCB at 350°C over KMnOx catalyst, with high selectivity to CO2. These data are confirmed by the activity of monolith catalysts which are very active in converting toluene below 300°C to CO2, while converting around 10% of 1,2DCB at the same temperature. IR data reveal that over both 5VWT and 7MWT surfaces 1,2DCB adsorbs through one chlorine atom substitution by lattice oxygen, giving rise to adsorbed chlorophenate at room temperature. At increasing temperatures, however, the evolution of the surface species to carboxylate (total combustion recursors) differs over the two catalysts. Gas-phase oxygen is also involved in COx formation.