Functionalized Iron Hydroxyapatite as Eco‐friendly Catalyst for NH 3 ‐SCR Reaction: Activity and Role of Iron Speciation on the Surface

Eco‐friendly catalysts have been obtained by functionalizing hydroxyapatite (HAP) with iron (Fe/HAP), according to three preparative methods ( flash ionic exchange, deposition‐precipitation, and impregnation). Fe/HAP samples ( ca . 2–7 wt.% Fe) have been tested in the reaction of NO x reduction by ammonia (NH 3 ‐SCR) in the 120–500 °C interval with different NH 3 /NO ratios (0.6–2) at fixed contact time (0.12 s). All Fe/HAP samples were active and selective in the NH 3 ‐SCR reaction starting from ca . 350 °C. Better performances have been observed on catalysts prepared by deposition‐precipitation and impregnation (about 70 % of NO x conversion and selectivity to N 2 higher than 95 % at 350 °C), where α‐Fe 2 O 3 and 3D ‐Fe 2 O 3 nanoclusters were present, as indicated by Mössbauer and UV‐Vis‐DR spectroscopies. On the opposite, paramagnetic Fe 3+ centres were the predominant species on samples prepared by flash ionic exchange. Further characterization techniques (XRPD, N 2 ‐physisorption, acidity by NH 3 adsorption, and H 2 ‐TPR) have concurred to elucidate Fe‐sitting HAP and structure‐activity relationships.