Hydroxyapatite-supported rhodium catalysts for N2O decomposition

Abstract

Several hydroxyapatite (HAP) supports were prepared by precipitation under different pH values (8.5, 9.5, or 10.5), and rhodium was loaded onto the supports by impregnation followed by calcination at 500°C. The pH value during the precipitation was found to play an important role in determining the catalytic activity of the resulting catalysts in N2O decomposition. The Rh/HAP catalyst prepared under optimal conditions (pH 10.5) showed superior catalytic activity than Rh/Al2O3, Rh/TiO2, and Rh/SiO2, due to the rich basic sites of the HAP support and the dispersion of ultra small rhodium particles on HAP. A pretreatment of Rh/HAP in 4% H2 at 400°C can further improve the activity owing to the partial reduction of the rhodium species. The catalysts/supports were characterized by X-ray diffraction (XRD), N2 adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), CO2 temperature-programmed desorption (CO2-TPD), and X-ray photoelectron spectroscopy (XPS).