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

The activity of the Pd, Pt, Pd–Pt/HZSM-5 and Pd/HZSM-35 catalysts was investigated at temperature ranges of 120–600°C in the conversion of gas mixtures consisting of CH4, C2H4, CO, naphthalene (model polyaromatic hydrocarbon), O2, CO2, H2O and N2. The prepared catalysts exhibited high activities in the complete removal of the model pollutants. Increase in the Pd-content of the catalyst was found mostly to affect the low temperature activity of the catalyst in methane oxidation. The effect of S-poisoning was studied by subjecting the catalysts to 5 ppm SO2 in the feed gas mixture. Catalyst de-activation due to catalyst ageing in the reactant flow was observed. 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/HZSM-5 catalyst and stabilised the catalysts against de-activation. The XPS and O2-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.