This work studied the effect of reactant mixture on the performance of Pt/Al2O3 and Pt/CeO2/Al2O3 catalysts for the SR of toluene, methane and toluene/methane mixture. Both catalysts only slightly deactivated during SR of toluene or methane, separately. However, they underwent a strong deactivation when both reactants were present in the feed. The Raman spectra of the used catalysts after different reaction conditions revealed the formation of very few carbon deposits, which were more significant for the SR of the mixture. in situ X-ray absorption spectroscopy showed that oxygen vacancies were formed on Pt/CeO2/Al2O3 but they did not inhibit catalyst deactivation. Therefore, the main cause of deactivation of Pt/Al2O3 and Pt/CeO2/Al2O3 catalysts is likely due to the competitive adsorption of toluene and methane on the same active sites that leads to an accumulation of carbon on the surface.