Effect of anions on the structure and catalytic properties of a La-doped Cu-Mn catalyst in the water-gas shift reaction

Effects of the anion type on the structure, thermal stability, and catalytic performance of La-doped Cu-Mn catalysts prepared by co-precipitation were characterized by X-ray diffraction, Brunauer-Emmett-Teller, temperature-programmed reduction, temperature-programmed reduction of oxidized surfaces, and temperature-programmed desorption. The Cu-Mn catalyst was tested for the water-gas shift (WGS) reaction. The main crystalline phase of samples prepared with sulfate, acetate, chloride, and nitrate as the starting materials was a Cu1.5Mn1.5O4 spinel structure, following the WGS reaction, the main crystalline phases were transformed into Cu and MnO. The sample prepared with acetate as the starting material showed the most obvious MnCO3 characteristic diffraction peaks, with better synergistic effects of Cu and MnO, increased adsorption of CO2 and improved dispersion of Cu on the catalyst surface; also, the best thermal stability and the highest low temperature catalytic activity were observed. The sample prepared with nitrate as the starting material maintained high thermal stability and catalytic performance in the range of 400°C to 450°C, but CO conversion decreased below 350°C. Catalytic performance of the sample prepared with sulfate and chloride as the starting materials was poor, ranging from 200°C to 450°C.