Comparative performance of copper and iron functionalized hydroxyapatite catalysts in NH3-SCR

Iron-functionalized hydroxyapatite (Fe/HAP, 2 < Fe wt% < 7) was prepared by ionic exchange and tested in the NOx reduction by ammonia (NH3-SCR). Iron dispersion, structure and acidity of the samples were investigated by UV-vis-DR spectroscopy, XRPD and ammonia titration. On Fe/HAP catalysts, NOx conversion started at higher temperatures and was always lower than on the reference Cu/HAP catalysts. Selectivity to N-2 was remarkable (> 95%) up to the attainment of maximum NOx conversion; for higher temperatures, selectivity declined due to the formation of N2O from NH3 over-oxidation. TPR-TPO cycles allowed to relate the redox properties of samples with their catalytic performances.