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

The oxide sample NiO/CeO2 with feed atomic ratio of Ni/Ce at 40%, prepared by co-precipitation method and calcination at 500 degrees C for 2 h, was impregnated by aqueous solution of NH4Cl to dope chlorine ions. After the impregnated samples were dried and calcined at 400 degrees C for 2 h, the calcined samples NiO(Cl-x)/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 CO2 and CO on the reduced sample Ni(Cl-0.3)/CeO2. The reduced samples Ni(Cl-x)/CeO2 (x = 0.0-0.5) were used as catalysts for selective methanation of CO in H-2-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 H-2-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 degrees C. However, the selectivity of CO methanation decreased with reaction time in the durability tests over the catalyst Ni(Cl-0.3)/CeO2 at the reaction temperature of 260 degrees C and even at 220 degrees C. The lowering of the selectivity was found to be related with the surface composition change of the catalyst in the catalytic reaction.