Durability of catalytic performance of the chlorine-doped catalyst Ni(Clx)/ZrO₂ for selective methanation of CO in H₂-rich gas

Chlorine-doped catalysts Ni(Clx)/ZrO₂(x = 0.0–0.6) were prepared for selective methanation of CO in H₂-rich gas (CO-SMET). Effects of chlorine ions were studied by means of X-ray diffraction (XRD), temperature programmed reduction (TPR) and adsorption measurements. It is found that chlorine ions could promote Ni crystallite growth and suppress CO₂adsorption. As a result, a deep removal of CO to below 10 ppm was achieved with a high selectivity of more than 50% in a wide reaction temperature range. And, at the reaction temperature of 220 °C, the selectivity of CO methanation kept at 100% with CO outlet concentration below 10 ppm in the 100 h durability test over the catalyst Ni(Cl_0.1)/ZrO₂. However, the selectivity decreased with reaction time at the higher reaction temperatures of 240 °C and 280 °C. Both X-ray fluorescence spectroscopy (XRF) analysis and ion chromatography analysis proved that chlorine ions evolved in the catalytic reaction, which then allowed for more CO₂to be adsorbed on the catalyst and hydrogenated into methane. This finally resulted in the decrease of the selectivity of CO methanation.