Catalytic combustion of polycyclic aromatic hydrocarbons (PAHs) over zeolite type catalysts: Effect of water and PAHs concentration

The catalytic combustion of 1-methylnaphthalene (1-MN), a PAH representative molecule, was carried out over USHY and 0.8%PtUSHY catalysts in presence of steam. These catalysts are able to transform low concentration of 1-MN into carbon dioxide at 300 °C over USHY catalyst and at 200 °C over PtUSHY, without by-products formation. The presence of platinum on the USHY increases the catalytic activity, hence the reaction rate. The influence of platinum content showed that 0.5% of platinum deposited on the zeolite was sufficient to oxidize 900 ppm of 1-MN at 300 °C.The influence of water content in the feed was investigated and several assumptions were put forth to explain our results. The carbon dioxide yield decreases in the 0–12% range of relative humidity (RH). When RH increases up to 12% the carbon dioxide yield increases. Over USHY catalyst and for low water content (RH < 12%), water could be adsorbed over strong hydrophylic sites of USHY zeolite or via H₂O dimer (neutral complex form) formation. Over PtUSHY catalysts, water adsorption over the PtO phase could be considered. For high water content (RH > 12%), water cluster formation via H₂O dimer (ion-pair complex form) is proposed on both catalysts. This form of H₂O dimer (ion-pair complex) could generate an acidity, which facilitates the formation of oxygenated compounds easily degradable into carbon dioxide.