Water gas shift reaction over Cu–Mn mixed oxides catalysts: Effects of the third metal

Highly efficient Cu–Mn spinel catalysts for water gas shift (WGS) reaction were achieved by a single step urea-nitrate combustion method. A series of doped Cu–Mn-M catalysts (M = Ce, Zr, Zn, Fe, Al) were prepared by the same method. Effects of dopants on WGS activity and stability of doped Cu–Mn catalysts were investigated. The doped catalysts were characterized by BET, XRD and TPR. XRD results showed that non-doped samples and Zr-doped samples are mainly composed of Cu1.5Mn1.5O4 phase, while CuO, Cu2O and Cu1.5Mn1.5O4 for other doped samples. It was further found that WGS activities depend strongly on the natures of the dopant employed despite of their lower content, varying in the order of Zr > Fe > non-doped > Ce > Al > Zn. TPR profiles revealed that all dopants shift the reduction peaks to lower temperature region, indicating no direct correlation between WGS activity and the reducibility. In addition, Zr-doped Cu–Mn catalyst with 5 wt.% content showed the best catalytic performance and, optimal stability exposed to oxygen-stream and on-stream operation. It indicates that ZrO2 is an effective promoter for Cu–Mn catalyst, and the catalytic performances are related to the existence of a Cu1.5Mn1.5O4 phase and ease reducibility of the catalysts.