Effects of supports and combined process on hydrogen purification over nickel supported catalysts

Hydrogen purification must be done to meet the different purposes of hydrogen utilization. In the present work, it is confirmed that the catalyst Ni/CeO₂ has the highest activity for total methanation (Total MET) of CO and CO₂, and is thus most suitable for hydrogen purification for ammonia synthesis. While, the catalyst Ni/ZrO₂ appears the best one for selective methanation of CO (CO-SMET) in the H₂-rich gas to produce clean fuel for proton exchange membrane fuel cell (PEMFC). In spite of this, the catalyst Ni/ZrO₂ without adding chlorine ions as promoter is not yet capable of removing the CO in the reformate gas to below 10 ppm in a wide reaction temperature range by the way of CO-SMET. Adding chlorine ions as promoter is indeed not favorable for practical application due to its gradual loss in the catalytic reaction as proved in our previous work. Therefore, a step to decrease CO₂ concentration (called as de-CO₂ step) is suggested to be set prior to the CO-SMET step in this work. It is proved that such combination of de-CO₂ step and CO-SMET step is efficient to achieve a deep removal of CO to below 10 ppm with a high selectivity more than 50% in a wide reaction temperature range of 220–280 °C over the catalyst Ni/ZrO₂ without adding chlorine ions as promoter. The combined process has potential for practical application, at least in the large-scale power plant of PEMFC.