Possible sites of copper located on hydroxyapatite structure and the identification of active sites for formaldehyde oxidation

•A small amount doping of Cu strongly improved the activity of HCHO oxidation for HAP.•Different synthesis methods were used to adjust Cu locations and species on HAP.•Five possible sites of Cu on HAP were proposed based on the experimental results.•Relationship of Cu species & location with HCHO oxidation activity was obtained.•Highly-dispersed Cu(II) clusters was mainly responsible for HCHO oxidation.

Different methods including ion exchange, co-precipitation and impregnation were used for the preparation of copper doped hydroxyapatite catalysts (CuHAP) to adjust the location of Cu on HAP and resulted in the difference of catalytic performance. Adjustments of synthesis conditions (ion exchange) were adopted for the further identification of active Cu sites for formaldehyde oxidation over CuHAP catalysts. Methods of characterization including XRD, H2-TPR, EPR and XPS were used for the identification of Cu species and its environment on the HAP. A hypothesis of five possible sites for Cu location was proposed based on the features of HAP structure and the experimental results. It has also been concluded that the highly-dispersed Cu(II) clusters was mainly responsible for HCHO oxidation. The best activity was achieved over CuHAP (1.4 wt.%) prepared by the ion exchange method with the complete conversion temperature of 180 °C.

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