Evaluating the effects of OH-groups on the Ni surface on low-temperature steam reforming in an electric field

Abstract

The effect of OH-groups on the surface of a Ni catalyst for low-temperature (473 K) steam reforming of methane in an electric field (EF) was investigated. Ni-doped YSZ (Zr_0.65Y_0.05Ni_0.3O₂) was chosen as a highly active catalyst for this purpose. The effects on catalyst activity of adding hydrogen and steam in the pre-treatment were assessed with and without EF. When an EF was applied, activity increased irrespective of the electronic state of Ni, whereas the metallic Ni state was necessary for activity without EF. Furthermore, the highest activity with EF was observed for the pre-treatment with a mixture of H₂ and H₂O. Investigation of the superiority using XPS measurements showed an increase in the amount of Ni(OH)₂, OH groups and H₂O near the surface after the activity test, which are regarded as the reaction sites with EF. This finding suggests that a pre-treatment with steam increases the surface OH groups and Ni(OH)₂ on the Ni catalyst, and enhances surface proton conduction, thereby improving the activity.