The comparison of RAE surface content of the fresh samples with the surface RAE content of the activated samples under NAP alkane-rich conditions, denoted L M,9:;9<# OPQ in Fig. , shows that the surface RAE content increases for most materials and reactions. The difference between L M,9BC OPQ , measured by XPS, and L M,9:;9<# OPQ , measured by NAP-XPS, can be attributed on the one hand to the different depth of information. NAP-XPS examines the outer surface (inelastic mean free path R SPT OPQ = 0.53 -0.74 nm), while XPS includes the composition of the sub-surface (R :9\ OPQ = 1.19 -2.06 nm). On the other hand, the chemical potential in the gas phase has a significant influence on the surface composition, as can be seen from the comparison of the surface concentrations of almost all catalysts containing at least two metals in the dry, wet and alkane-rich feed determined by NAP-XPS (Fig. ). The increase in RAE during the in situ measurement (Fig. ) is significantly more pronounced than the changes observed between L M,$"