CO elimination processes over promoter-free hydroxyapatite supported palladium catalysts

- Palladium supported on calcium-deficient hydroxyapatite catalysts are synthesised and characterised.
- 0.3 wt% Pd is incorporated into hydroxyapatite structure and deposited Pd with small particle size is favoured at low loading.
- Pd(0.5)/HAP catalyst exhibits the best catalytic performance in COTOX, COPROX and WGS reactions.
- The distribution of Pd species plays a decisive role in the oxygen mobility and the activity.

The catalytic performance of synthesised calcium-deficient hydroxyapatite supported Pd catalysts are examined for various CO elimination processes, namely CO total oxidation, CO preferential oxidation and water gas shift reactions. The prepared samples loaded with different amounts of palladium (0.5-2%) are thoroughly characterised by a wide number of analytical techniques including N2 physisorption, XRD, H2-TPR, TEM, CO-TPD, H2 chemisorption, OSCC and OSC techniques. The characterisation results show that, besides an incorporation of 0.3 wt% Pd into hydroxyapatite structure, on the Pd(0.5)/HAP sample, small Pd particle sizes (7.6 nm) are deposited on the HAP support surface presenting relatively high dispersion (19%). The OSCC and OSC studies show that the highly dispersed Pd species lying on the HAP surface present high reducibility and high oxygen mobility.In the three investigated CO elimination processes the Pd(0.5)/HAP catalyst proves to be highly active and exhibits higher stability compared to that of the Pd(1)/HAP and Pd(2)/HAP catalysts. The catalytic performance of the series of the catalysts demonstrates their structure-sensitivity in the investigated processes. The latter are remarkably enhanced in the presence of small Pd particle sizes which provide high reducibility and high oxygen storage capacity. Moreover, the performances of the Pd/HAP catalysts evidence the potential of HAP support as promising alternative to those reported in the available literature.

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