The effect of potassium addition to the Ni/Al 2 O 3 steam reforming catalyst has been investigated on several model systems, including K/Al 2 O 3 with various amounts of alkali promoters (1–4 wt% of K 2 O), a model catalyst 90%NiO-10%Al 2 O 3 promoted with potassium and a commercial catalyst. The potassium surface state and stability were investigated by means of the Species Resolved Thermal Alkali Desorption method (SR-TAD). The activity of the catalysts in the steam reforming of methane and their coking-resistance were also evaluated. The results reveal that the beneficial effect of potassium addition is strongly related to its location in the catalysts. The catalyst surface should be promoted with potassium in order to obtain high coking-resistant catalysts. Moreover, the catalyst preparation procedure should ensure a direct interaction of potassium with the Al 2 O 3 support surface. Due to the low stability of potassium on

-Al 2 O 3 this phase is undesirable during the preparation of a stable steam reforming catalyst.