Spherical Ni Nanoparticles Supported by Nanosheet-Assembled Al₂O₃ for Dry Reforming of CH₄: Elucidating the Induction Period and Its Excellent Resistance to Coking

The design and preparation of efficient coking-resistant catalysts for dry reforming of methane (DRM) is significant for industrial applications but a challenge for supported Ni catalysts. Nanosheet-assembled Al2O3 (NA-Al2O3) with hierarchical hollow microspheres was used to support Ni nanoparticles, which exhibits superior long-time stability and coking resistance for the DRM reaction from 700 to 800 °C without coke deposition. Active Ni species, exsolved from NiAl2O4 spinel, are aggregated into Ni nanoparticles and finally stabilize as spherical Ni nanoparticles of 18.0 nm due to the spatial confinement of hierarchical hollow microspheres of the NA-Al2O3 support after the DRM reaction for 60 h. The catalytic activity in the induction period of the Ni/(NA-Al2O3) catalyst increases because of the enhancement of the surface Ni0/(Ni0+Ni2+) ratio, that is, the increment of the amount of active Ni sites. The spherical Ni nanoparticles embedded in the NA-Al2O3 support, superior CO2 adsorption ability, and more surface hydroxyl groups on the Ni/(NA-Al2O3) catalyst are the determining factors for its long-time stability and excellent anti-coking for the DRM reaction.