State of Supported Nickel Nanoparticles during Catalysis in Aqueous Media

The state of Ni supported on HZSM-5 zeolite, silica, and sulfonated carbon was studied during aqueous-phase catalysis of phenol hydrodeoxygenation using in situ extended X-ray absorption fine structure spectroscopy. On sulfonated carbon and HZSM-5 supports, NiO and Ni(OH)₂ were readily reduced to Ni⁰ under reaction conditions (≈35 bar H₂ in aqueous phenol solutions containing up to 0.5 wt. % phosphoric acid at 473 K). In contrast, Ni supported on SiO₂ was not stable in a fully reduced Ni⁰ state. Water enables the formation of Ni^II phyllosilicate, which is more stable, that is, difficult to reduce, than either α-Ni(OH)₂ or NiO. Leaching of Ni from the supports was not observed over a broad range of reaction conditions. Ni⁰ particles on HZSM-5 were stable even in presence of 15 wt. % acetic acid at 473 K and 35 bar H₂.