Nickel migration in high performance water-gas shift Ni_xCe_1-xO ceria aerogels

We use scanning transmission electron microscopy (STEM) and spectroscopy to characterize stable, Ni-doped CeO₂ aerogels that exhibit near perfect efficiency for water-gas shift (WGS) reaction, thus avoiding standard Fe-Cr oxides that are expensive, inefficient, and known Cr⁶⁺ toxin emitters. Here, nickel dopants are typically atomically dispersed throughout the aerogel via their chemical synthesis. With STEM EDS and STEM EELS, three types of Ni configurations are identified depending on expected final Ni content directly impacting catalytic behavior: atomically dispersed, weakly-bound aggregates (~1nm), and strongly-bound oxides (>100nm). Further STEM EELS shows Ce oxidation state variations following electron beam exposure as has been observed for other CeO_x morphologies such as films and nanoparticles. We will present the interplay of overall catalytic performance as related to atomically dispersed Ni mobility into weakly-bound Ni at different Ni loadings, and how the composition and morphology of oxide support and metal nickel drive these reactions.

We acknowledge support from the Office of Navel Research through the Naval Research Laboratory Base Program.