Catalytic performance of Cu/hydroxyapatite catalysts in CO preferential oxidation in H2-rich stream

A series of Cu/HAP catalysts was prepared by impregnation and characterised by TEM, BET, DRS, XPS, H-2-TPR, XRD, TEM and FTIR techniques. H-2-TPR and DRS data revealed that at low concentration (<1%) large fraction of Cu incorporated the HAP framework. The increase of the Cu loading significantly increased the density of the CuO particles spread over the carrier. Moreover, as shown by XPS, these species suffered from segregation when the Cu loading was close to that required for the formation of a theoretical monolayer. The structural characterisation of the reduced samples showed a significant increase in the lattice strain with increasing Cu content, indicating an increase in the concentration of Cu lattice imperfections. The activity of the reduced samples in COTOX and COPROX processes revealed remarkable differences when the Cu content was increased from 0.8 to 14.8%. For instance, analysing the TOF values calculated for the two processes and the characterisation data, it was concluded that the catalysts with low Cu loadings (0.8% and 3.6%) were the most active ones and their sites involved in the CO oxidation reaction were almost similar. The addition of CO2 and water seemed to affect the performances of the two catalysts via different pathways. Indeed, in contrast to the Cu(4)/HAP, the Cu(1)/HAP catalyst became more selective in the presence of CO2 and water. Moreover, under these realistic COPROX conditions, the latter was 6.6 times more active than the former. A correlation with the characterisation data showed that the most efficient species consisted of those presenting strong interaction with the HAP support. By contrast, the sites exhibiting high concentration of Cu lattice imperfections showed a relatively low activity. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.