Highly efficient Ni-ZrO2 catalyst doped with Yb2O3 for co-methanation of CO and CO2 Original Research Article

A type of highly efficient Ni-ZrO2 catalysts doped with Yb2O3 for co-methanation of CO and CO2 was developed, and displayed excellent activity and thermal stability. Over the Ni6Zr2Yb2 catalyst under the reaction conditions of 0.1 MPa and 573 K, the observed total conversion of CO and CO2 (denoted as X(CO and CO2)) maintained continuously at a high level of ∼97.4% during 25–126 h after the reaction started, with the corresponding STY(CH4) reaching ∼9.11 g h−1 g−1. The results of heat-resisting test showed that, over the Ni6Zr2Yb2 catalyst after undergoing 24 h of the methanation operation at 1073 K followed by going down to 573 K, the X(CO and CO2) still maintained stable at the level of 89%; whereas X(CO and CO2) observed on the other two reference systems, Ni6Zr4 and Ni6Zr2Sm2, which both underwent the similar heat-resisting test at 923 K and 1023 K, respectively, fell to 2.8% and 2.4%, respectively. The results of the catalyst characterization demonstrated that the high activity, and especially the extremely high thermal stability, of the Ni6Zr2Yb2 catalyst for CO and CO2 methanation were associated with the formation of (Zr-Yb)Oy oxide with c-ZrO2 structure. The pronounced promoter action of Yb2O3 may be due to the high solubility of Yb2O3 in ZrO2 lattice as the ionic radius of Yb3+ (0.087 nm) is quite close to that of ZrIV (0.079 nm). Solution of a considerable amount of Yb3+ in the ZrO2 host resulted in the formation of (Zr-Yb)Oy oxide with simple c-ZrO2 structure. It is the major factor for the high activity and high thermal stability of the Ni6Zr2Yb2 catalyst.