Abstract We report on XPS results that show an inhomogeneous charge effect, greater than 1.0 eV and far greater than the accuracy of the measurements (∼0.2 eV), exhibited by a natural mineral essentially composed of SiO 2 and Fe 2 O 3 . This mineral has proved to be an efficient catalyst in a Fischer–Tropsch reaction. We have corrected this differential charge effect by using two internal references in order to interpret satisfactorily our XPS data.
