Application of metal-exchanged zeolites in removal of emissions from combustion of biofuels

The activity of the Pd, Pt, Pd-Pt/HZSM-5 and Pd/HZSM-35 catalysts was inves tigated at temperature ranges of 120-600 degrees C in the conversion of gas mixtures consisting of CH4, C2H4, CO, naphthalene (model polyaromatic hydr ocarbon), O-2, CO2, H2O and N-2. The prepared catalysts exhibited high acti vities in the complete removal of the model pollutants. Increase in the Pd- content of the catalyst was found mostly to affect the low temperature acti vity of the catalyst in methane oxidation. The effect of S-poisoning was st udied by subjecting the catalysts to 5 ppm SO2 in the feed gas mixture. Cat alyst de-activation due to catalyst ageing in the reactant flow was observe d. The ageing of the catalyst only affected the methane oxidation. Addition of Zr and La improved the low-temperature activities of the Pd and Pd-Pt/H ZSM-5 catalyst and stabilised the catalysts against de-activation. The XPS and O-2-TPD data indicated that on the freshly prepared catalyst, palladium is present as Pd+ and Pd2+ species. The ageing of the catalysts decreased the number of the Pd2+ sites in favour of the PdOx species. (C) 2000 Elsevi er Science B.V. All rights reserved.