Water-gas shift reaction over a novel Cu-ZnO/HAP formulation: Enhanced catalytic performance in mobile fuel cell applications

Abstract

CuO-ZnO/HAP catalysts were prepared by co-impregnation and tested in the water-gas shift reaction. The prepared samples were thoroughly characterised by a wide number of analytical techniques including N2 physisorption, XRD, DRS, XPS, H2-TPR, N2O chemisorption, CO-TPD, H2-TPD, CO2-TPD, OSCC and OSC techniques. The properties of the synthesised materials were compared with those of a CuO-ZnO/Al2O3 sample. In contrast to the alumina support, the hydroxyapatite seems to favour the deposition of the CuO and ZnO phases exhibiting an intimate contact. Owing to this suitable distribution and the rich surface chemistry of the support, the CO-TPD, H2-TPD and CO2-TPD data point out that, with independence of the adsorbed molecule, the Cu-ZnO/HAP surface results as the most reactive and provide the largest density of the adsorption sites compared to the Cu-ZnO/Al2O3. The OSCC and OSC data, moreover, show that the former provides relatively high reducibility and larger amounts of reactive oxygen atoms. In realistic WGS reaction conditions the Cu-ZnO/HAP system proves to be highly active and exhibits an excellent stability at 250 °C. The reported data also suggest that the sample with the intermediate copper loading (12 wt.%) represents an optimum chemical composition (Cu/Zn = 3) providing the best catalytic performance. Furthermore, while previous research findings consider the Cu-ZnO as less practical for mobile applications, the current study sheds light on its great potential when supported on hydroxyapatite materials. Indeed, besides its higher activity the CuZn(3)/HAP catalyst successfully withstand the shut-down/start-up conditions exhibiting only 14% activity loss after six cycles. This excellent performance is linked to suitable textural, structural and chemical properties, provided by the HAP support, which make the active sites highly sintering-resistant.