Active Mn species well dispersed on Ca 2+ enriched apatite for total oxidation of toluene

Abstract Hydroxyapatite (Hap)-supported manganese oxide catalysts (10 wt% Mn based on MnO 2 ) were prepared by two different routes, from Mn nitrate (Nit) and Mn acetate (Ac) precursors. The catalyst precursors were calcined at 400 °C for 4 h to get the final MnNit-Hap and MnAc-Hap catalysts. Elemental analysis, XRD, SEM, HRTEM, N 2 adsorption experiments, FT-IR, temperature programmed reduction (H 2 -TPR), X-ray photoelectron spectroscopy (XPS) and ToF-SIMS characterization methods were used to identify the Mn species and their environment. The overall characterization studies indicated that the nature of the counter-ion played a significant role in the speciation and dispersion of manganese species in Hap although the Mn AOS in both cases is around 3. The nitrate Mn precursor allowed to get after calcination at 400 °C well dispersed and easily reduced active Mn n + ( n  + ≥3) oxidized species on a Ca 2+ enriched hydroxyapatite surface, likely in a polymeric form or/and in small Mn x O y crystallites, while part of Mn in the form of Mn 2+ ions incorporated into the Hap substituting Ca 2+ at the apatite surface. By opposition the acetate Mn precursor primarily results in large Mn 3 O 4 oxide nanocrystals along with an amorphous Mn 5 O 8 phase and Hap incorporated Mn 2+ ions. The total oxidation of toluene was investigated on these new catalysts and the catalytic performances were compared to those of a reference 10 wt%Mn on alumina (Mn–Al). It is found that the nature of the support plays a significant role. Indeed the different AOS of Mn (about 3 for supported Hap; ≈4 for supported alumina catalyst) showed that the Mn active phases are different. The best performances were achieved on the MnNit-Hap catalyst with the complete conversion of toluene at 220 °C. The Mn oxidized species well dispersed on Ca 2+ enriched apatite using a strong oxidizing counter-ion as NO 3 − in the Mn precursor were responsible for optimal toluene conversion. In that case it was found that the incorporation of part of NO 3 − in the hydroxyapatite promoted the surface Ca 2+ enrichment of Hap by the incorporation of Mn 2+ into the Hap support.