Surface composition change of chlorine-doped catalyst Ni(Clx)/CeO2 in methanation reaction

The oxide sample NiO/CeO2with feed atomic ratio of Ni/Ce at 40%, prepared by co-precipitation method and calcination at 500 oC for 2 h, was impregnated by aqueous solution of NH4Cl to dope chlorine ions. After the impregnated samples were dried and calcined at 400 oC for 2 h, the calcined samples NiO(Clx)/CeO2(x=0.1–0.5) were characterized by means of X-ray diffraction(XRD) and temperature programmed reduction(TPR) techniques. It was comfirmed that the doped chlorine ions hindered reduction of Ni2+ions in the calcined samples, and suppressed adsorption of CO2and CO on the reduced sample Ni(Cl0.3)/CeO2. The reduced samples Ni(Clx)/CeO2(x=0.0–0.5) were used as catalysts for selective methanation of CO in H2-rich gas. When chlorine ions were doped at the feed atomic ratio of Cl/Ce(x) equal to 0.3–0.5, CO in the H2-rich gas could be removed to below 10 ppm with a high selectivity more than 50% in a wide reaction temperature range of 220–280 oC. However, the selectivity of CO methanation decreased with reaction time in the durability tests over the catalyst Ni(Cl0.3)/CeO2at the reaction temperature of 260 oC and even at 220 oC. The lowering of the selectivity was found to be related with the surface composition change of the catalyst in the catalytic reaction.