Supercritical water gasification of phenol over Ni-Ru bimetallic catalysts

Incorporating Ru in a Ni catalyst for gasification of phenol in supercritical water at 450 °C and 30 min promoted formation of cyclohexanol via hydrogenation, which is a key step toward gasification. Both Ni and Ni-Ru catalysts were effective to reduce the formation of cyclohexanone and oligomerization products, compared with the case with no catalyst. H₂ and CH₄ yields increased as the Ru/Ni ratio increased, as did the carbon and hydrogen yields in the gas phase products. The Ni₈₀Ru₂₀/Al₂O₃ catalyst provided good gasification performance and it exhibits Ru (101), Ru (100) and Ni (111) facets and evidence of overlaid bimetallic particles. DFT calculations show that the presence of Ru (either as pure Ru or as a Ni-Ru alloy) reduces the energy barrier for phenol hydrogenation by close to 0.2 eV relative to pure Ni, and that the energy barrier is not as largely affected by the amount of Ru present, provided it is non-zero.