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Highly Active Noble‐Metal‐Free Copper Hydroxyapatite Catalysts for the Total Oxidation of Toluene

Hydroxyapatite (Hap) supported Cu materials prepared by the wet impregnation method were designed as noble‐metal‐free catalysts for the total oxidation of toluene. Cu/Hap materials with different Cu loadings (2.5–20 wt %) calcined at 400 °C were characterized by using inductively coupled plasma optical emission spectroscopy, N2 physisorption, XRD, Raman spectroscopy, IR spectroscopy, X‐ray photoelectron spectroscopy, and time‐of‐flight secondary ion MS. The tenorite CuO phase was detected in all materials, and the libethenite Cu2(PO4)OH phase was observed for the sample with 20 wt % Cu. The presence of libethenite was accompanied by the formation of Ca2CO3H+ ions at the Hap surface. Residual NO3− species that interact with Cu and Ca were also found, and their amount increased with the increase of the Cu content in the sample. Interestingly, the specific activity in the total oxidation of toluene increased with the decrease of the Cu content in the catalyst. The rate per mole of Cu was increased by 10 times if the Cu content was decreased by four times. This noticeable result could be related to the presence of acid sites with a moderate strength as well as finely dispersed CuO species on the Hap, which allow the activation of toluene molecules and their oxidation through a redox mechanism. Moreover, Cu2.5 wt %/Hap showed a remarkably stable catalytic performance for 45 h time‐on‐stream, which evidences that this material has a high potential for applications in the removal of volatile organic compounds.