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

Abstract A type of highly efficient Ni-ZrO 2 catalysts doped with Yb 2 O 3 for co-methanation of CO and CO 2 was developed, and displayed excellent activity and thermal stability. Over the Ni 6 Zr 2 Yb 2 catalyst under the reaction conditions of 0.1 MPa and 573 K, the observed total conversion of CO and CO 2 (denoted as X (CO and CO 2 )) maintained continuously at a high level of ∼97.4% during 25–126 h after the reaction started, with the corresponding STY(CH 4 ) reaching ∼9.11 g h −1  g −1 . The results of heat-resisting test showed that, over the Ni 6 Zr 2 Yb 2 catalyst after undergoing 24 h of the methanation operation at 1073 K followed by going down to 573 K, the X (CO and CO 2 ) still maintained stable at the level of 89%; whereas X (CO and CO 2 ) observed on the other two reference systems, Ni 6 Zr 4 and Ni 6 Zr 2 Sm 2 , 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 Ni 6 Zr 2 Yb 2 catalyst for CO and CO 2 methanation were associated with the formation of (Zr-Yb)O y oxide with c -ZrO 2 structure. The pronounced promoter action of Yb 2 O 3 may be due to the high solubility of Yb 2 O 3 in ZrO 2 lattice as the ionic radius of Yb 3+ (0.087 nm) is quite close to that of Zr IV (0.079 nm). Solution of a considerable amount of Yb 3+ in the ZrO 2 host resulted in the formation of (Zr-Yb)O y oxide with simple c -ZrO 2 structure. It is the major factor for the high activity and high thermal stability of the Ni 6 Zr 2 Yb 2 catalyst.