Co/Hydroxyapatite catalysts for N2O catalytic decomposition: Design of well-defined active sites with geometrical and spacing effects

Abstract Different methods including ion exchange, impregnation and hydrothermal method were used to prepare Co/hydroxyapatite catalysts with various Co species. The catalytic activities for N2O decomposition were studied. It was concluded that Co2+ⅡOh existed in Co(1.2)-IE prepared by ion exchange is more active than Co2+Td, Co3+Oh and Co2+Ⅰ obtained by impregnation and hydrothermal methods, respectively. Meanwhile, Co(1.2)-IE shows better stability and stronger resistance against 2.0 vol.% O2 or 2.3 vol.% H2O in the feed gas. The higher catalytic activity of Co2+ⅡOh is attributed to its octahedral coordination geometrical structure, which make Co2+ⅡOh tend to donate electrons to activate N2O. Furthermore, the closer spacing distance between two Co2+ⅡOh sites can facilitate the combination and desorption of oxygen species. The above mentioned reasons ultimately lead to the increased catalytic activity. Finally, the results of density functional theory calculations indicate that the Co2+ⅡOh possesses the highest d-band center, which means the excellent catalytic activity.