The catalytic stability of TiO₂-shell/Ni-core catalysts for CO₂ reforming of CH₄

Bare and TiO₂-coated Ni particles were used as catalysts for the CO₂ reforming of CH₄ (CRM) reaction at 800 °C and TiO₂ layers with two different thicknesses were prepared by atomic layer deposition (ALD). We focused on the deactivation mechanism of Ni-based catalysts upon long-term operation. All of the catalysts showed a decrease in the catalytic activity as a function of the reaction time for 160 h, and the TiO₂-coated Ni showed a less pronounced decrease in the catalytic activity in comparison to that of the bare Ni catalyst. The graphitic carbon layers that have been formed on the Ni particles during the reaction are suggested to be responsible for the deactivation and the additional TiO₂ layer facilitated the formation of separate carbon filaments rather than the graphitic layer on the Ni, reducing the possibility of the deposited carbon layers to cover and poison the Ni active sites of catalysts. The fabrication of core-shell structures of metal and oxide by ALD can be a useful approach for the synthesis of heterogeneous catalysts, for which not only high activity, but also enhanced stability at an elevated temperature can be achieved.