Unravelling the structure and reactivity of supported Ni particles in Ni-CeZrO₂ catalysts

We report about the synthesis and characterisation of two NiCeZrO₂ catalysts prepared by one pot-co-precipitation method. The two samples are characterised by similar chemical composition (15wt% Ni, Ce/Zr=80/20 atomic ratio) and properties of the CeZrO₂ support, which is a cubic phase solid solution with nanometer sized (5-6nm) crystalline hexagonal/roundish particles. The main differences between the samples are in the NiO particles dispersion and surface area, which were found to be affected by the synthesis pH. Both samples were characterised about their surface properties by employing FTIR spectroscopy of adsorbed CO probe, and tested about their activity and stability in methane steam reforming (MSR) reaction at relatively low temperature (793K). The results show a good activity in MSR irrespective of the NiO size and morphology, with negligible CO formation, but a strong dependence of the catalysts stability upon these parameters. Only the catalyst with smaller (5-10nm) NiO particles was found stable for 250h in MSR at relatively high steam to carbon ratio (S/C=2). This performance could be related to a positive effect of the CeZrO₂ support, allowing fast and easy oxygen transfer to and from the NiO/Ni⁰ active phase, most likely thanks to the occurrence of a strong metal-support interaction.