Destruction of PAH and dioxin precursors using selective oxidation over zeolite catalysts. Influence of the presence of ammonia in the flue gas

This work reports the influence of ammonia during 1-methylnaphthalene (1-MN) and 1-methylnaphthalene/1,2-dichlorobenzene mixture oxidation over USHY zeolite and 0.8%PtUSHY catalyst. The USHY zeolite was able to transform 1-MN into carbon dioxide from 400 °C whatever the reaction conditions. However the presence of ammonia improves the transformation rate of 1-MN: 1-MN was totally transformed from 300 °C when the reaction was carried out in the presence of ammonia. Whatever the reaction temperature, only carbon dioxide was formed from 1-MN and no aromatic by-products were observed. Over the PtUSHY catalyst, the same phenomenon was observed in the 200–300 °C temperature range. Indeed, the 1-MN was totally transformed from 200 °C when the reaction was carried out with ammonia against 250 °C when 1-MN was alone. It was also shown that the presence of NH3 favoured the 1-MN transformation into adsorbed oxygenated polyaromatic compounds over the USHY zeolite. In the case of PtUSHY catalyst, the presence of NH3 improves the transformation rate of 1-MN into carbon dioxide by formation of NO2, which can participate in the oxidation reaction of 1-MN.The oxidation reaction of 1-methylnaphthalene/1,2-dichlorobenzene (1-MN/1,2PhCl2) mixture was also studied in the absence and presence of NH3 over PtUSHY catalyst. The presence of 1,2PhCl2 and 1,2PhCl2/NH3 had no influence over 1-MN transformation in the temperature range studied (250–400 °C). Indeed, 1-MN was completely converted into CO2 from 250 °C. 1,2PhCl2 appears as the most difficult compound to destroy. However, the presence of NH3 leads to a promoting effect over 1,2PhCl2 transformation rate. 1,2PhCl2 was totally transformed from 350 °C in the presence of NH3 against 400 °C in the absence of NH3. As for 1-MN this promoting effect can be explained by the NH3 oxidation over Pt atoms leading to NO2 formation. Some experiments carried out with NO confirm that NO2 formation (formed by the oxidation of NH3) participate in the oxidation reaction. However, for an initial concentration of NH3 up to 100 ppm, an inhibitory effect over the 1,2PhCl2 transformation rate was observed.