The effect of a cerium additive on the catalytic activity of a 2 wt % Ni/SiO 2 catalyst is studied. It found that under both flow and static conditions the activity of (2 wt % Ni + 0.2 wt % Ce)/SiO 2 catalyst is higher than that of the original sample; the increase in activity results from a sharp increase in the number of active sites. A change in the composition of the surface layer of the catalysts is analyzed by X-ray photoelectron spectroscopy. It was found that the fraction of nickel decreases and the fraction of carbon increases in cerium-containing catalyst. An explanation of the change in the elemental composition of the catalytic active sites of a nickel catalyst in the presence of cerium is proposed on the basis of XPS data and previous quantum chemical calculations. © Pleiades Publishing, Ltd., 2012.