(74a) Atomic Layer Deposited Nickel Nanoparticle Catalysts for Dry Reforming of Methane (Invited)

Highly dispersed nickel (Ni) nanoparticle catalysts were prepared by atomic layer deposition using bis(cyclopentadienyl)nickel and hydrogen as precursors at 300 °C. Both porous γ-Al₂O₃ particles and dense γ-Al₂O₃ nanoparticles were used as the substrates. For comparison, Ni nanoparticles supported on porous γ-Al₂O₃ particles were also prepared by the incipient wetness (IW) method using an aqueous solution of Ni(NO₃)₂·6H₂O. The Ni/alumina catalyst was employed to catalyze the reaction of dry reforming of methane (DRM). It was found that the ALD Ni nanoparticles were much more active than the Ni nanoparticles synthesized by the IW method; the porous γ-Al₂O₃ supported ALD Ni nanoparticle catalyst showed higher activity and greater stability, as compared to the dense alumina supported ALD Ni nanoparticle catalyst. The porous γ-Al₂O₃ supported ALD catalyst showed exceptionally high catalytic activity (a methane reforming rate of 1840 Lh^-1g_Ni^-1 at 850 °C) and excellent stability of DRM reaction in over 300 hours at temperatures that ranged from 700 °C to 850 °C. The greater stability could have been due to the porous structure of the support and the formation of NiAl₂O₄ spinel during the ALD coating process, which could limit the sintering of the Ni nanoparticles and, thus, inhibit coking during the reaction. The high catalytic activity was due to the high dispersion of Ni nanoparticles deposited by ALD and the reduction of NiAl₂O₄ spinel to Ni during the DRM reaction at 850 °C. It was verified that NiAl₂O₄ can be reduced to Ni in a reductive gas mixture (i.e., carbon monoxide and hydrogen) during the reaction at 850 °C, but not by H₂ alone.