How hydroxyapatite governs surface Cu(II) and Fe(III) structuring: effects in the N2O decomposition under highly oxidant atmosphere

In this work, we present copper- or iron-loaded hydroxyapatite samples as active catalysts in the direct N2O decomposition reaction. Hydroxyapatite, functionalized with increasing amount of Cu(II) or Fe(III) species (from 3 to 9 wt%), were characterized by XRPD, DR UV-Vis, XPS, CO-adsorption followed by FT-IR, TEM-EDS, and tested in the N2O decomposition. Stability tests (550 °C, 72 h), reusability, resistance to sulfur (50 ppm) and to alkali (ca. 1 wt% of K or Ba) completed the study of the catalyst performances. Copper catalysts showed superior performances than iron counterparts. The structural evolution of the metal species with loading plays a critical role in the catalytic behavior. In the case of Fe-catalysts, a gradual Fe-coverage of HAP surface resulted in an increasing trend in the activity. Conversely, for Cu-catalysts high activity and selectivity were associated with a moderate structuration of Cu(II) in the form of nanoparticles with size of around 1.6 nm.