Impact of dopant X in zirconia on carbon deposition at the Nickel/X-stabilized zirconia(XSZ) surface in dry CH4 and CH4/H2O environments: First-principles density functional theory calculation and experimental study
Hirotatsu Watanabe, Seina Muto, Teppei Ogura
Abstract
The impact of a dopant (X; X = Y or Sc) in zirconia on carbon deposition in CH4 and CH4/H2O environments was studied experimentally and via first-principles calculations. In the CH4 environment, the apparent activation energy for the carbon deposition of Ni/ScSZ was lower than that of Ni/YSZ. SEM/EDS observation indicated the Ni/XSZ interface was key to elucidating the dopant-induced difference. To clarify the difference, the calculation presented two mechanisms: first, the vacancy in ScSZ rather than that in YSZ was readily moved to a neighboring site, thereby stabilizing the vacancy configuration after CH–CH bonding. Second, Ni was readily distorted in Ni/ScSZ at the specific vacancy configuration, thereby decreasing the forward activation energy. In CH4/H2O environment, the calculation showed larger dopant Y caused steric hindrance to prevent CH + O→CHO which was the sensitive reaction in the steam reforming. This explained lower reforming rate in Ni/YSZ than in Ni/ScSZ.