Ceria morphology role on methane dry reforming over Ni/CeO2 with transient and isotopic techniques

What is it about?

The effect of ceria morphology, nanorods-NR and nanopolyhedra-NP on important kinetic parameters of the dry reforming of methane (DRM) over Ni/nano-ceria (dNi ∼20 nm) was investigated by transient and isotopic experiments. Transient isothermal reduction by hydrogen evidenced lower activation energy and higher reduction rates of lattice oxygen in the case of CeO2-NR compared to those of CeO2-NP. Transient 16O/18O isotopic exchange provided a lower Eapp of bulk oxygen diffusion (by ∼90 kJ mol−1) for CeO2-NR compared to CeO2-NP. 18O/16O isotopic exchange followed by DRM revealed higher carbon oxidation rates by lattice oxygen to C18O(g) in the case of CeO2-NR compared to those of CeO2-NP, in harmony with the lower amount of carbon accumulated in the former catalyst. The lower Eapp of DRM and carbon oxidation by lattice oxygen confirm the higher DRM activity on Ni/CeO2-NR compared to Ni/CeO2-NP. HAADF-STEM and Raman studies were linked to the observed transient kinetic results.

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Why is it important?

By synthesizing CeO2 in the form of nanorods (NR) and nanopolyhedra (NP), we uncovered compelling insights for the role of ceria morphology on critical kinetic parameters and aspects of the DRM reaction (e.g., resistance to carbon accumulation) in the 655–700 °C range. The essence of our findings lies in the profound impact of catalyst support morphology on the activation energy barriers associated with surface oxygen reduction and bulk oxygen diffusion of ceria, and their influence on the oxidation of carbon (formed mainly by CH4 decomposition) by ceria lattice oxygen to form CO(g).