CeO<sub>2</sub> Aerogel-Induced Resilience of Catalytic Ni(OH)<sub>2</sub> under Oxidizing Conditions
Travis G. Novak, Paul A. DeSario, M. D. Johannes, Todd Brintlinger, Ryan H. DeBlock, Jeffrey W. Long, Christopher N. Chervin, R. M. Stroud, Debra R. Rolison
Abstract
Nickel-based heterogeneous catalysts are economical alternatives to traditional Pt or Au-based materials, but their specific activity and stability fall short of these precious metals. Many questions remain regarding the active Ni phase for CO oxidation and how the supporting oxide affects its activity and stability under operating conditions. We demonstrate that CeO2 aerogel-supported Ni(OH)2 nanoparticles (NPs) show superior activity compared to Ni(OH)2 NPs supported by commercial, nanometric CeO2 powder or TiO2 aerogels. Ex situ X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy reveal that intimate contact between Ni(OH)2 NPs and the bonded nanoparticulate CeO2 network prevents the conversion to NiO seen with larger aerogel-supported aggregates of Ni(OH)2 NPs and unsupported Ni(OH)2 NPs. The best stability and activity per mole of Ni is achieved at 2.5 wt % Ni(OH)2 on the CeO2 aerogel, which converts 95% of CO at 200 °C and maintains activity after 12 h of continuous reaction under dry or humid feedstreams. 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.