Nickel is an attractive economical alternative to traditional Pt or Au-based catalysts for many industrially relevant reactions, but its activity and stability are still not competitive with the best precious metal catalysts. Recent research has demonstrated positive effects of supporting Ni on reducing oxides – such as TiO2 or CeO2 – but many questions remain regarding the nature of the active Ni phase and how its activity and stability are affected by the oxide support. Here, we use CeO2 aerogels as supports for photodeposited Ni(OH)2 nanoparticles (NPs) and demonstrate the effect of Ni/CeO2 morphology on Ni speciation. At 2.5 wt.%, Ni, NPs are uniformly dispersed within the aerogel structure, with excellent catalytic activity and stability towards CO oxidation achieved even under humid feedstreams. At higher weight loadings (5 or 10 wt.% Ni), larger aggregates form that lose interfacial intimacy with CeO2, resulting in lower specific activity and a continuous loss of activity under reaction conditions. Ex situ XPS and XANES reveal that while the well-dispersed Ni on CeO2 persists as Ni(OH)2, larger aggregates readily convert to the less catalytically active NiO phase, a phenomenon observed in unsupported Ni(OH)2 or Ni(OH)2 supported by commercial CeO2 nanoparticles under the same reaction conditions. Computational analysis indicates that CO has far lower adsorption energy on Ni(OH)2 compared to NiO, resulting in less poisoning of the active surface sites. Our results shed light on the influence of Ni speciation for CO-based catalytic reactions and demonstrate how Ni||CeO2 intimacy ensures a resilient active hydroxide phase.

Stabilization of catalytically active nickel hydroxide on CeO2 aerogels for CO oxidation

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